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Aviation and Oil Depletion
Posted by Euan Mearns on December 19, 2006 - 12:38pm in The Oil Drum: Europe
This is a guest post by Christopher Smith who is a Captain with the airline BA Connect. The post is based on a presentation (pdf) made to the oil depletion conference held in London last month.
Aviation is one of the fastest growing industry sectors in the world, growing at 2.4 times the rate of world GDP. The industry consumes over 5 million barrels of oil per day worldwide, almost one tenth of all the oil used for transportation. In the UK, according to the Department for Transport, the UK aviation industry is growing at approximately 5% per year while its fuel consumption is growing at 3% per year.
Carbon dioxide emissions from aviation vary directly with kerosene consumption. The resulting CO2 from UK aviation accounted for 5% of the national total in 2003. The UK Environmental Audit Committee forecasts the value will be 10 to 12% in 2020 and could rise to 40% by 2050 if not checked. The unconstrained growth of aviation CO2 emissions is incompatible with the UK government's target to reduce national CO2 levels to 40% of the 1990 level by 2050.
In this discussion we will look at issues specific to jet aircraft fuel. Jet fuel has several unique requirements that complicate the search for a replacement. Next we will examine the possible alternatives and weigh their pros and cons. Finally we will look at what the airline industry is doing today with the fuel it has available.
Key properties of aviation fuel
Aviation fuel should have several key properties:
High Energy Content
There are two parameters by which we can measure the energy content of fuel. Specific energy is the energy content per unit mass (Joules / Kg) and energy density is the energy per volume (Joules / Litre).
By law, jet aircraft carry at least enough fuel to reach overhead their planned destination, thereafter fly to their planned alternative landing aerodrome, fly an approach to land at that aerodrome and still have enough fuel to hold for 30 minutes. There is always the possibility that some unforeseen difficulty will arise which causes a delay or necessitates a diversion to an alternate aerodrome. Airlines add a bit more to allow for these unexpected delays.
The more fuel an aircraft has on board at takeoff, the heavier it will be. From a design point of view, the more fuel the aircraft needs to carry, in mass or volume, the larger the aircraft and engines would need to be and the more fuel needed to perform the flight. Operationally, the heavier the aircraft is at takeoff, the more fuel that will need to be carried to lift it into the air and carry it to its destination. As fuel is consumed in flight, the aircraft becomes lighter and more efficient.
A fuel with high specific energy would have two benefits. Firstly, the higher the specific energy of the fuel, the lighter the fuel load for a particular range. This in turn means that less fuel would be consumed over the duration of the flight. All fuel on board an aircraft in flight that is not being used at that moment is little more than payload and requires additional fuel to carry it. Secondly, an aircraft designed to achieve its maximum range with a smaller mass of fuel would be built lighter and with smaller engines.
The argument for high energy density is similar. Energy density is the amount of energy per unit volume. For a given flight distance, an aircraft using a fuel with a low energy density would need a larger volume of fuel. Even if the total mass of fuel was the same (or even less), the higher volume would require a larger fuel tank, likely resulting in a larger aircraft. Jenkinson, Simkin and Rhodes, in their book "Civil Jet Aircraft Design", state that for every kilogram of unnecessary structure mass, the maximum takeoff mass will increase by about 3 kilograms. They also state that there is direct relationship between operational empty weight and both purchase price and operating costs. The best jet fuel would be one with a very high specific energy and energy density.
Safety over a wide temperature range
Fuel used in commercial aircraft must meet stringent safety requirements. Aircraft operate for long periods in the heat of the desert and in the freezing cold of the stratosphere, and from the high atmospheric pressure at sea level to the extremely low pressure at high altitudes. Aircraft are subjected to turbulence and, occasionally, lightning. The Jet A-1 kerosene used in Europe has a flash point of not lower than 40° Celsius. This high flash point minimizes the flammability and explosion hazard within the fuel tank and in aircraft accidents. The air temperature at jet aircraft operating altitudes is extremely cold. It is critical that the fuel does not freeze or thicken at temperatures as low as -47°C. It is equally important that the fuel does not contain or absorb water. In these cold temperatures ice crystals will form which will block fuel filters and lead to fuel starvation.
Environmentally clean and energy efficient
The consumption of kerosene in jet aircraft generates 3.2 tonnes of CO2 for every 1 tonne of kerosene consumed. While there is currently no restriction on the production of CO2 from aviation sources it is only a matter of time. Domestic aviation sources of CO2 are included in national greenhouse gas emissions inventories and are likely to be subject to emissions limits in the next couple of years. International aviation emissions are more problematic but there is increasing pressure on the International Civil Aviation Organization (ICAO) and national governments to develop a workable solution. There is increasing likelihood that aviation will be included in the EU Emissions Trading Scheme as early as 2011.
In 1999, the Intergovernmental Panel on Climate Change (IPCC) produced a report titled "Aviation and the Global Atmosphere". The report was the first comprehensive assessment of the climate change effects of air transport. One of the most significant results of the study was the determination that the current focus on CO2 and Global Warming Potential was unsuitable for aviation. The report states that Radiative Forcing is a better indicator because it takes into account CO2, water vapour, soot, particulates and ozone. Due to the high altitudes at which jet aircraft operate, these other products of combustion play an increased role. The contrails formed by jet aircraft in some environmental conditions may also have a significant radiative forcing value. The IPCC determined that the overall climate change effects of aviation are approximately 2.7 times greater than the effect of the CO2 alone.
The aircraft and engine manufacturers have made great strides in improving the energy efficiency of their products. The problem for the aviation industry is that its growth is outstripping the efficiency improvements in technology. As other industries strive to reduce their overall CO2 emissions, the aviation industry percentage of the total will increase. This is bringing the industry under increasing scrutiny from all quarters. The aviation industry needs a fuel with less environmental impact if it is to continue to grow.
Availability and Cost
The greatest advantage of kerosene over other fuels today is that it is available everywhere. Aircraft are expensive and highly mobile assets but they are of no value if they cannot be refuelled. Wherever they go on the planet there will usually be a supply of aviation kerosene. Kerosene is portable, storable and available. For many years it has also been relatively inexpensive. Even so, for most airlines, fuel is their single greatest expense at somewhere between 10% and 35% of total operating costs. The price of fuel is frequently cited in airline profit and loss statements.
Other useful characteristics
Jet aircraft fuel performs other useful functions which have a bearing on the suitability of alternatives:
- Aircraft in flight operate within a narrow centre of gravity range. The consumption of fuel during the flight alters the aircraft's centre of gravity and, on larger aircraft, fuel may be pumped forward or aft to maintain trim. This may not be possible with solid or gaseous fuels.
- The heat absorption qualities of the fuel are used to cool engine oil and sometimes cool the airframe. These qualities also allow it to be pre-heated before use to improve combustion efficiency without compromising safety.
- Kerosene provides lubrication to fuel pump and fuel metering components.
Current aircraft technology is optimised around the use of kerosene. Changes in aircraft fuel will require changes in both aircraft and engine design. Aircraft being manufactured today are expected to be in service for 30 years or more. Airlines will be unwilling to turn their backs on these major financial investments mid way through their amortized life. We can expect these assets will still be flying and will still be using kerosene at that time. In the long term there will have to be an alternate to petroleum aviation fuels. One major uncertainty is whether technology will change to accommodate the future fuel or whether the fuel will be selected to match the available technology. The ideal jet aircraft fuel will have a high energy content, wide operating temperature range, safe, clean, inexpensive and widely available. Lets take a look at some of the alternatives.
Alternative fuels
Hydrogen
The most commonly discussed alternative aviation fuel is hydrogen. At first glance, hydrogen is a good choice. It has a specific energy 2.5 times greater than kerosene and generates no CO2. Hydrogen does have some disadvantages however. Hydrogen requires a cryogenic storage system. The pressures involved will require cylindrical or spherical tanks and even with this high pressure storage system, hydrogen's energy density would be only 40% of kerosene. That means that for the same design range, the fuel tanks will need to be 2.5 times larger and significantly heavier. Hydrogen power will therefore require a radical change in aircraft and engine design. The combustion of hydrogen generates 2.6 times as much water vapour as the equivalent quantity of kerosene. At high altitudes, water vapour is a potent greenhouse gas. Notwithstanding this, the IPCC forecast that a hydrogen powered aircraft would be more environmentally friendly than the kerosene version at all altitudes.
The greatest single problem with hydrogen will be its availability and possibly cost. Before manufacturers will invest in the design of a hydrogen aircraft for commercial service and before airlines would consider adding them to their fleets, there would have to be universal availability of hydrogen at every airport the aircraft is intended to serve, as well as every conceivable alternate aerodrome that might be selected due to weather or technical difficulty. There is currently no worldwide infrastructure and hydrogen will not be a practical jet aircraft fuel until there is.
Ethanol / Methanol
Alcohols are another potential fuel but they too have their complications. Alcohol fuels have between 50% and 75% of the specific energy of kerosene. An alcohol fuelled aircraft might be 25% larger than an equivalent kerosene powered aircraft due to the increased volume of fuel. The engines may be 50% larger due to the combined increase in fuel and aircraft weight. Another significant argument against alcohol is its affinity for water. Alcohol readily absorbs water vapour which, in the extreme cold of the stratosphere, would turn to ice crystals and block fuel filters. Alcohol evaporates at significantly lower temperatures than kerosene and it has a flash point of at most 18°C. Alcohols are worse for Volatile Organic Compounds which are bad for the ozone layer and when operating at low power settings alcohol fuelled engines generate some hazardous by-products, including formaldehyde.
Biodiesel
Biodiesel is another potential aircraft fuel. On its own, biodiesel is unsuitable for jet aircraft due to its very high flash point, very low volatility and because it thickens and crystallizes at the temperatures found at jet cruising levels. Biofuels generate less than half the greenhouse gas emissions of kerosene. For this reason, the International Airline Transportation Association (IATA) has committed to using 10% biofuel across the industry within ten years. Biodiesel is currently approved as a "Kerosene Extender" at concentrations up to 10%. It may eventually be approved for use at concentrations up to 20%.
Synthetic Fuels
The fuel that holds the greatest promise in the immediate future is synthetic kerosene (synfuel). Synthetic kerosene can be made from coal, natural gas or biomass. It is currently approved for use in commercial aircraft in a 50/50 mix with petroleum kerosene and aerospace manufacturers plan to have a fully synthetic fuel approved in 2006. The biggest advantages of synfuel are that it frees the aviation industry from dependence on petroleum resources and that it can be used in existing aircraft. Synthetic kerosene is slightly cleaner than petroleum kerosene but this does not take into account the large amount of CO2 generated during production. The relative merits of synfuel will depend on the raw material used to produce it and the CO2 mitigation strategy employed.
Fuel saving strategies
Aircraft engines have been using kerosene for decades and engine technology has been fine tuned around this fuel. Every year, incremental improvements increase the overall efficiency of aircraft but no large technical advances are forecast. Operational efficiency improvements are now offering the greatest rewards. Technical improvements generally apply to new aircraft but operational improvements apply to all aircraft, new and old. In fact, the less efficient the aircraft, the greater the benefit. Aircraft consume large amounts of fuel during their lifetime and even small reductions can have a large cumulative effect. As emissions are directly related to fuel consumption, any reduction in consumption will also mean a reduction in environmental impact. Manufacturers and airlines are putting significant effort into fuel efficiency.
There are several strategies being pursued by the aviation industry to reduce fuel consumption:
Minimum fuel
In the past, determining the required fuel load for a flight was an inexact science and included a healthy contingency factor. There are significant savings to be had by reducing the total amount of fuel on board the aircraft at departure to the minimum safe amount. The key is being able to accurately determine the fuel required based on aircraft weight, expected routing and accurate forecasts of winds and temperatures aloft. Modern sophisticated flight planning computer programs allow an accurate determination of the minimum fuel needed to carry out the flight. The calculations will even vary with individual aircraft. For large aircraft on long flights the savings can be measured in tonnes. Further improvements will be realized when air traffic control forecasts of traffic density can be factored in at the flight planning stage, rerouting flights to minimize delays and therefore fuel consumption. Modern onboard navigation systems and satellite positioning systems allow aircraft to navigate the forecast routing to a high degree of accuracy. Computer generated flight plans can be accurate to within one minute and several kilograms of total fuel requirements.
Air Traffic Control efficiency improvements
The longer the routing from departure to destination, the greater the fuel consumption. Many new routes take advantage of the improved navigational accuracy of modern aircraft allowing more routes and greater use of shortcuts between enroute waypoints. The new Y1 and Y2 air routes over central China are a good example. IATA forecasts that these new air routes will save 30 minutes on flights between China and Europe, resulting in a combined saving of 27,000 tonnes of fuel per year. Similar improvements are realized by new air routes across the North Pole. The IPCC predicts a 6 to 12% improvement in aircraft fuel efficiency by 2020 through more efficient air routes.
These savings are modest compared to the predicted savings from the next generation of air traffic control. The Future Air Navigation System (FANS) or Free Flight allows aircraft to fly the most efficient direct routing between airports and eventually from gate to gate. FANS relies on accurate flight navigation computers on board the aircraft, sophisticated air traffic control computers on the ground and satellite positioning and communications systems. FANS is currently being tested on selected aircraft and routes. Other potential fuel saving:
- The move towards larger, integrated air traffic control centres which provide a seamless service across a larger area.
- Continuous Descent Approaches which minimize the time aircraft spend at lower, less fuel efficient altitudes.
Aircraft and Engine Improvements
Aircraft technologies are continually improving. Aircraft coming off the assembly line are significantly more efficient than earlier models. They are also more efficient than the same model of last year. This continual improvement results in a year on year improvement in efficiency of at least 1%. Aircraft currently in service will become less efficient over time as they accumulate minor surface damage, coats of paint and dirt. In this respect, the general improvement in safety is reducing even minor incidents that result in repairs and the resulting increased weight and reduced efficiency. The company "Gas Turbine Efficiency" claims that their engine turbine cleaning service can win back a 1% improvement in fuel efficiency. While these individual strategies each produce only small improvements, together they add up to major savings. The International Airline Transport Association (IATA) claims that member airlines have improved their fuel efficiency by nearly 20% over the last ten years and 5% in the last two years.
Competition
Load factor is a measure of airline efficiency. It is the percentage of the total number of seats that are occupied by passengers on a particular flight. The load factor of a flight will vary from day to day but will follow a normal distribution around a mean. There is a limit to the mean load factor an airline can expect to achieve without losing customer goodwill and losing passengers, perhaps to the competition. A situation known as spill. Improved revenue management and direct sales channels allow airlines to increase average load factor while minimizing spill. Sometimes this improved revenue and capacity management allows an airline to operate fewer services on routes on which load factors were too low. Across airlines and the industry this trend has led to a reduction in overcapacity and is one of the reasons that airline fuel consumption has been growing at a slower rate than total passenger growth.
Coming up
Large fuel savings will be realized when passenger perception of airline quality is de-linked from energy wasting activities. Many airlines will start engines and join the queue at the runway knowing that there will be significant delays on departure. This improves the airline's on time departure and arrival statistics but is extremely wasteful. Similarly, aircraft will aim to get airborne on time knowing that favourable winds will bring them to their destination well ahead of schedule, sometimes before the airport even opens. For years, the aviation industry has been playing on passenger perception that jets are better than propeller aircraft. After a period of time in which the turboprop aircraft was almost completely wiped out of the market they are starting to make a comeback. The turboprop engine is simply a jet engine driving a propeller. Modern turboprop aircraft are able to match the speed and comfort of regional jets on flights up to 500 miles. These aircraft use the same fuel and have the same reliability as jets while delivering outstanding reductions in fuel consumption, greenhouse gas emissions and noise. If airlines fail to achieve emissions reduction targets on their own we could see a return to increased government intervention in which restrictions are placed on aircraft size and frequencies on each route. This is effectively the system in place at the moment on most international routes. While the current move is towards a more liberal system called Open Skies, government climate change objectives may force a reversal of the trend.
The Aviation Energy Trend
There is currently no alternative to the use of kerosene in aircraft engines. The hydrogen economy is still decades away and it will be decades after that before the majority of long haul transport aircraft are hydrogen powered. By that time there is likely to be serious supply problems with petroleum kerosene and fuel efficiency and fuel conservation strategies will continue to dominate airline fuel policy. These efficiency strategies are currently driven by high fuel costs but in the very near future these costs will be compounded by the cost of the fuel's associated greenhouse gas emissions. The switch from petroleum to synthetic kerosene will be driven by availability and price. The lower switching costs in other industries may help aviation avoid a kerosene supply crisis but is unlikely to mitigate the rising cost. The increasing cost of fuel and associated emissions may mean some of today's flying will no longer be viable. A lot of short haul point to point flying could be pushed onto alternative transport systems that are better able to switch to cleaner fuels
Hydrogen powered aircraft in particular offer little hope until there is a world wide supply in a mature hydrogen economy. Global warming emissions will continue to be a problem whichever fuel is being used. Even ultra clean hydrogen has global warming issues and we can expect that aviation will eventually be called upon to account for all its climate change effects, not just carbon dioxide. The cost of switching to non kerosene fuels is extremely high. The aviation industry is likely to accept very high fuel costs before any wholesale switch to an alternative.
Christopher Smith is a Captain with BA Connect flying the 50 seat Embraer-145. He has 11,000 hours as Pilot-in-Command of commercial aircraft and holds a Master of Science degree in Air Transport Management.
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I'd love to see some figures justifying that statement. It is common wisdom, but I just don't see it. I know someone who flys Dash-8s (now "Bombardier Q Series") for a living, and have looked at actual flight plans. For example, a DHC-8-300 on a 406 nm route, 2:02 gate-gate, fuel burn 2457 pounds. At 6.84 pounds per US gallon that's 359.2 US gallons, or 1.130 nm/USgallon or, finally, 1.284 statute miles per US gallon, commonly referred to as "mpg". Even a plane with all 50 seats filled will thus have an efficiency of 64.22 mpg (or, as stated on my page 59.3 mpg gasoline-energy equivalent for comparison with gasoline-powered cars).
This compares to a figure for JetBlue's A320 fleet as a whole of 69.7 passenger-mpg and Southwest's 737 fleet as a whole of 59.8 passenger-mpg.
Yes, the -400 is supposed to be more efficient, but really - how much more? ANA operates DHC-8-400s as well as A320 and ranks them at roughly equivalent efficiency.
http://www.ana.co.jp/eng/aboutana/corporate/csr/report/pdf/e2004.pdf
I'm not trying to be difficult, just trying to get to the truth of the matter. I'm prepared to believe that turboprops are more efficient over very short routes, as jets are particularly inefficient at lower altitudes, but there is little scope for improvement here as there are very few short routes in the world served by large jets.
I'd also like to see some proof of this as well. I thought so too, but I have yet to find any confirmation of the fact. The only ocean going ship providing passenger service (as opposed to "cruises") that I've found the numbers for is the Queen Mary 2. Amusingly, its fuel consumption works out to almost exactly 10 yards per gallon. With 3090 people on board that's 17.3 passenger-mpg, which is barely better than the Concorde managed.
In some ways it makes sense to me that trans-oceanic travel may actually be more efficient by air than by sea, as the space (and thus mass) per passenger must necessarily be much larger on a ship. If you could get people to sit in commercial aircraft density seating in a ship that is at sea for weeks then no doubt you would find it is vastly more energy efficient.
http://en.wikipedia.org/wiki/Fuel_efficiency#Fuel_efficiency_in_transportation
I certainly believe that bulk transport is far more efficient by ship, but the original topic had to do with transportation of people. Unless I'm mistaken it seems that ships are efficient for cargo and not for people, at least not on voyages long enough to require a lot of volume per person.
You may be correct about passenger transport, as long as it is deemed necessary to have the speed of air transport. However, in the future, I suspect that the age-old practice of freight ships taking on paying passengers will become the only practical way of travelling overseas for all but the very wealthy.
Thanks!
eg. If the ticket price rose to twice its current level, volumes would more than halve. That in turn would push up prices even further as economies of scale work in reverse. Its not long before liabilities meant it was best to liquidate the airline than attempt to battle on. Look at the US airlines following 911.
It would be interesting to see a financial structure of an airline with fuel prices 2-3 times the current level. Can a valid business model be found and is it possible to reach there from here with the current crop of aircraft?
It might be that the coming of the post peak world is heralded by an effective severing of the transport bonds that connect the global economy - as airlines go to the wall one by one.
My take on this, is that, during the 1970's ticket prices for aiviation were at least twice (in real terms) what they are now.
The airlines were financially viable then, why not now. After all, much airline business is corporate, and they would accept a price increase as the cost of doing business overseas.
The tourist market may suffer, but I'm not convinced that the internal domestic market would suffer too much. See my other post below.
Andy
For domestic flights, which would include flights to and in the US, both business and leasure travel have median elasticity just slightly greater than 1, with leasure just slightly more elastic.
However, for international business travel elasticity is .265.
"In the short run, much of the burden of adjustment will likely be borne by decreases in consumption from discretionary decisions, since 67 percent of personal automobile travel and nearly 50 percent of airplane travel are discretionary."
Of course what that really means is interesting. What proportion of eating and drinking is discretionary? If flying is cut down by 90% does that mean we perish?
One measure is their pax-miles/gallon of fuel. Since 2001 (from memory), they have increased from 48.x pax-miles/gallon to 56.3 pax-miles/gallon. Retrofitting winglets is part of the gain. Better operations and a mix of a/c that has eliminated the 737-200 and added more 737-700s (balance 737-300 & 737-500). As Boeing's best customer thay have significant influence.
The "word" is that if new engines are ready a 737 replacement a/c based on the 787 (0nce more, but smaller) will enter service in 2012 and be 20% to 25% more fuel efficient than the 737-700.
IMHO, The number of commercial airline seats will likely decline, the amount of fuel used will decline even more, but post-Peak Oil, airline travel is such high value that it will get a higher % (much higher ?) of available fuel.
There is little doubt that the Southwest business model will "work" in a high cost environment. Reduced a/c transfers at "hubs", more point to point travel with high load factors. Slow down to save fuel is likely (add a few minutes). Perhaps turboprops.
Alan
"A lot of short haul point to point flying could be pushed onto alternative transport systems that are better able to switch to cleaner fuels"
Interesting comment.
Currently in the UK short haul airlines are Massacring the railways.
The reason, amongst other things, is cost.
I can fly between Bristol and Glasgow (400 miles apart) for about £40 return. Flight time 1 hour. Door to door (including driving to airport, waiting in departure lounge, flying, landing, luggage collection, and driving to parents house) takes about 3 hours
The train will cost at least £90 return (if I book in advance) and takes 7 hours northbound and 15 hours southbound.
The airlines get almost no internal subsidy whilst the trains are awarded generous subsidy through Network Rail to upgrade large sections of the railway network.
And despite this aircraft are cheaper.
I have my suspicions that even with a doubling of fuel prices to cover the cost of pure CO2 neutral BTL fuels internal domesestic flights will still be cheaper and more pleasant than taking the train. After all if fuel is 30% of operating cost then on my £40 ticket (approx only £30 goes to the airline) then doubling 1/3 of that gives you a airline price of £40 + £10 tax = £50 airline ticket price.
Still cheaper and better than the trains.
Andy
I am not sure that the absence of a tax is a subsidy per se.
Alan
There is a small excise duty payable on railway gasoil, similar to that levied on home heating oil. It is nowhere near the duty levied on road vehicle fuel in the UK, but the railways pay directly for their right of way, whereas road vehicles do not.
sf
I know that in Canada the cost of ATC services alone was over $400 million per year about 15 years ago. That's a pretty damn hefty direct government subsidy - $13 for every man, woman and child in Canada, just for ATC, whether they set foot on a plane or not. The service is now run by NAV Canada, a "non-share capital, private corporation" which recovers costs from aircraft operators. i.e. the government subsidy is now gone. The cost of flying has, not surprisingly, increased substantially. Canadian registered aircraft in the range 2 to 3 metric tonne maximum takeoff weight (4400-6600 pounds) pay $236/year. The daily charge for a DHC-8-400 (as an example, as it cropped up above) is $2441.
http://navcanada.ca/ContentDefinitionFiles/Services/ChargesAndAdmin/guidetocharges/Customer_Guide_Ne w_en.pdf
Pretty much the same as any other large industry.
I have read that the British railways are carrying more passengers than they have carried in decades, and that problems include lack of capacity and overcrowding.
I recently took the train from London to Exeter and found it fast, comfortable and very reasonable - with advance purchased tickets. Twenty Five Pounds or $50 - first class - for a trip of about 200 miles, in less than three hours. I don't see how airlines can "massacre" the railways on medium distance trips like that.
Its the longer range North-South routes, especially the London-Edinburgh, London-Aberdeen, London-Manchester routes that the train companies are suffering.
Andy
A clairvoyant analysis in what comes to alternatives to jet fuel, with very important numbers on Specific Energy and Energy Density. Jet fuel is clearly the best compromise between the two, indicating that a shift to another energy vector will mean less efficient air travel.
Something that is missing from this post is a net energy analysis, because all of the alternative vectors to jet fuel originate from energy capture/extraction processes with lower EROEI than that of oil. Even for synthetic kerosene there's the Fischer-Tropsch process eating the net energy from the original source.
In my view Hydrogen powered aircraft in particular offer little hope (period). Earth is too small a planet to capture Hydrogen, thus using it as vector will imply even more degradation of the net energy yield for the entire process.
Then it is also worth stressing that right now none of the alternatives have any chance of getting close the today's jet fuel availability. Coal and biomass can eventually achieve it in the future, but only if competition from other sectors is restrained.
The sun is setting for the Aerospace Age.
If I want to go from the US to Europe there is absolutely no practical alternative to flying. Which means that you and I will go to Europe on an aircraft... no matter at what price.
Not sure why you want to capture hydrogen with a planet... even if you could do that... what would you burn it with?
Earth has plenty of hydrogen. There are two hydrogen atoms in every water molecule. They can be easily reduced to molecular hydrogen. It simply takes a little bit of energy. That energy can come from the sun. Please read up on how to do it economically with e.g. the ZnO-Zn process:
http://www.solarpaces.org/ZnOZn.HTM
There is a lot of interest in this and other thermochemical methods of hydrogen production since they are a lot more efficient than either biofuels or PV/electrolysis chains.
Of course, planes will probably never fly on hydrogen because the engineering problems with hydrogen as fuel are just too severe. And why should they? Jet fuel is fine and always will be. If the carbon in it comes from Earth's atmosphere and not from hydrocarbons, the net greenhouse gas from CO2 effect is zero... water vapor is a different animal, of course, but then... that would be much worse with hydrogen!
"You can't always get what you want.
But if you try sometimes
You just might find
You get what you need."
Given the power of marketing, wants are nearly insatiable. Actual needs are quite modest.
If we push too hard to get our wants, we just might find we can't even get what we need.
Not that there is much prospect of aviation getting too expensive for me. Poor idiots who bought a semi-truck penis enlargement will have to start cutting back on their fuel consumption long before I will ever start to feel real pain in international air travel.
You need to understand that the most PO does is to enhance already existing class differences in the US. That is problem far worse than the prospect of having to book your tickets far in advance or having to pay double for them.
PO does enhance existing class differences significantly - but it also changes the decisions people make.
Please note that I did not claim to be a person of average income. I am (just a little) above average. In the future I will stay (just a little) above average because the social dividing line that is moved higher by PO will still be far below my level of income.
Now... the forces that are moving that social dividing line in the US have much more to do with Neocon politics than economic fundamentals. You want to change things on the ground in the US, better make sure the political system changes. Voting democrats might help a little.
The researching is great, I'm glad they're doing it, I'm glad you're following it, but don't get confused between what we're trying to develop and what we have already successfully demonstrated working on a broad scale. Yesterday, you said there's "No Problem", that there's enough Sun and Wind, 'if only' we had started the changover 30 years ago. That's the problem.. it's a problem that we may well not have enough time, remaining energy or specific materials available to quickly enough transition over to the functioning alternatives, no matter how clear it is that they actually do work, and that a simple journey of a thousand miles would allow us to use them and be fine. But Infinite, it really does matter that a very few people have only been able to make a couple steps forward on that trek..
That's the substance I'm looking for..
"There's no food in your food"
Joan Cusack, Say Anything
"Yesterday, you said there's "No Problem", that there's enough Sun and Wind, 'if only' we had started the changover 30 years ago."
There is still enough sun and wind and always will be. We could have started researching and conserving thirty years ago and overall we could have saved a lot of money. We didn't, so the conversion will happen later. It does not mean the conversion will not happen. Of course it will. It will simply cost more.
I think I keep emphasizing in my statements that all of this will cost a lot of money. We got it... we just spent $450 billion on Christmas presents and something like that on a useless war. Next time we'll spend it on energy infrastructure and the kids will get their own solar panels instead of another gaming console and a "Global Hawk" with "Hellfire" missiles.
It will cost a lot of money, yes. At the same time as we're spending loads extra due to energy and environmental costs, we'll need that stretched energy and money supplies to replace the infrastructure the world currently runs on. So there's the cost of shortage AND the cost of upgrade/replacement.
And no, you - the US, I presume - do not have lots of money. 'You' are broke and the dollar is effectively worthless... Here are a few of the numerous and growing reasons why:
http://drmss.com/wordpress?p=17
http://bigpicture.typepad.com/comments/2006/11/the_return_of_m.html
http://news.bbc.co.uk/2/hi/business/6211513.stm
Globalisation, ultra-capitalism and mismanagement have gutted the US economy. The next 10 years will be hard for the average American; You won't be spending your 'disposable' income on air travel.
The plane lifted off from Edwards Air Force Base, Calif., with a 50/50 blend of FT and traditional JP-8 jet fuel which was burned in two of the eight engines on the plane. This marks the first time that FT jet fuel has been tested in a military flight demo, and is the first of several planned test flights..."
http://www.greencarcongress.com/2006/09/air_force_fligh.html
"...let`s face it, modern man is just ancient man...with better electronics..." - Mr. Jack
A TOD reader called Mr Snow emailed me this and asked me to post it.
15 years ago at the Royal Aerospace Establishment (as it then was). It
was technically possible then, and we had a working, flying aircraft, with full
computer controlled flight planning, and direct communication between
air traffic control route planning computers and the aircraft giving automated
redirection and updated meteo information. The met office could provide
accurate short range wind forcasts for busy aviation routes, using data
collected by the aircraft themselves. The whole system could have been
rolled out ten years ago, but I have never met such a bunch of hide bound,
technophobic beaurocrats as air traffic controllers. It is understandable,
they are responsible for thousands of lives, day in and day out, and will
not trust one of them to a computer system that does not have a fully
manual, human controlled fallback and override.
I quit the job because I couldn't see the system being implemented in my
working lifetime.
Wonder how the contrail haze will affect PV output on the rooftops below.
How would contrails over France effect PV output of concentrator systems operating in Saudi Arabia?
Just asking... or does anyone really believe the Sauis will never tap into their most valuable resource, solar energy?
Here is a little back of the envelope calculation:
Saudi Arabia has a land area of 1.96 million km^2. They can easily use 1% of that for solar power generation. That would be roughly 20.000km^2. The practically available power from every m^2 of that area is around 40W with current technology, that is 40MW per km^2.
20,000km^2*40MW/km^2 = 800GW.
800GW*3600s/h*24h/day = 6.912*10^16J/day.
1 barrel of oil is 6119MJ, so the KSA solar energy equivalent would be
6.912*10^16J/day/6119MJ/barrel = 11.2 million barrels a day.
Current KSA production happens to be... hold on to your hats... 11 million barrels a day.
So that was with current technology and at 1% land use. Guess what... future technologies can double this and what should stop the KSA from using 5% of their land area?
Just wondering...
However, that is peak output of these cells, assuming they're maintained pointed at the sun and in standard conditions. Standard conditions means 25C and kept clean. According to Wikipedia's references, cell efficiency drops off substantially at higher temperatures and when the solar cells are covered with blowing sand. How do you propose to keep these solar cells cooled to 25C and free of sand?
How do you propose Saudi Arabia export the electricity? How much would it cost to cover Saudi Arabia with solar cells at your proposed efficiency (and what efficiency are your numbers based on)?
"The second map shows the average global irradiance calculated from satellite data collected from 1991 to 1993. For example, in North America the average insolation at ground level over an entire year (including nights and periods of cloudy weather) lies between 125 and 375 W/m² (3 to 9 kWh/m²/day). [4] This represents the available power, and not the delivered power. At present, photovoltaic panels typically convert about 15% of incident sunlight into electricity; therefore, a solar panel in the contiguous United States on average delivers 19 to 56 W/m² or .45 - 1.35 kWh/m²/day."
I usually use 20W/m^2 for residential US and 40W/m^2 for commercial, concentrating solar which can be 30% efficient.
"However, that is peak output of these cells, assuming they're maintained pointed at the sun and in standard conditions. "
Not peak output. These are the 24/365 averages. Of course you have to keep your cells maitained. Commercial plants are all pointing concentrators. For residential solar the losses do to fixed angle are relatively small because of the cos(angle) law. It is simply not worth the mechanical complexity to adjust the angle, except maybe seasonally.
"Standard conditions means 25C and kept clean."
Commerical installations wash their cells regularly. So do residential owners who care. Do you wash your car? Do you clean the gutter? What stops you from cleaning your solar panels?
The temperature dependence leads to losses but they are in the range of a few percent. Concentrator cells actually work quite well at controlled high temperature and for residential you don't care about the additional losses. You care about the energy you get from the cheapest technology... if it costs a few m^2 more in area, you cover a few m^2 more of roof area. So far most homes have 0m^2 covered... so there is plenty of space left.
"How do you propose Saudi Arabia export the electricity?"
It is called a power line. Piece of copper cable on a mast. Quite easy to build and very high efficiency if done right.
"How much would it cost to cover Saudi Arabia with solar cells at your proposed efficiency (and what efficiency are your numbers based on)?"
How much does it cost to drill for oil? How much does the nuclear power plant or the hydroelectric dam you get your electricity from cost? Do you care? I bet you don't as long as you can buy the kWh for 10 cents. Europeans who need it won't care either that the kWh from KSA will cost 15 cents. They will pay whatever it is. Right now the German government is paying 45 Eurocents (55 cents) for every solar kWh from residential solar. That is enough to pay for the cost of the system. Germany is probably half as good as KSA for solar and commercial plants are far better than resdiential in terms of cost. I would guess that KSA could export at 30 cents a kWh today and will export at 10-20cents by the time they need the revenue. There will be plenty of customers.
- How will the Saudis keep your proposed photovoltaic array cool (25C)?
- How will the Saudis keep your proposed photovoltaic array clean?
- How much will your proposed photovoltaic array for Saudi Arabia cost?
You proposed it. Are you backing off your assertion?They won't because it is not necessary. Please read up on the physics of semiconductors.
"How will the Saudis keep your proposed photovoltaic array clean?"
Probably with water like everyone else. You do know how to clean windows, don't you?
"How much will your proposed photovoltaic array for Saudi Arabia cost?"
The same as for everyone else. Thus, they will be just as profitable as everyone else... Oh, no! They will be more profitable because they have way more sunlight than their customers!
You are a funny guy. Somehow you remind me of creationists. They, too, like to be ignorant, ask trivial questions and take the absence of their own knowledge as the indicator that they are right about whatever nonsense they propose. Are you a creationist, by any chance?
Let me start again. I think it's very interesting that photovoltaic cells have progressed to the extent that they have. I wasn't aware until you brought it up that active solar was becoming a cost-effective option. My neighbor, who I respect, put up a solar array on about a quarter of the south-facing part of his roof, but doesn't expect to break even on his investment for over 20 years. I still have my doubts that a solar-powered bicycle commute would be as efficient as a human-powered bike commute, but I completely agree that I need to look into it in more depth.
I'm a card-carrying Democrat who most certainly had no time for creationism. Why do you feel the need to be so caustic? You could be extremely valuable here, but you seem to enjoy being rude to people instead. Eventually you may end up having most people ignore you, and TOD will be poorer if you were to leave. Wouldn't it be better to be more polite, more patient, and just walk through the math with people without all the snide insults?
As a small child, in the 1950's, I was taken on several transcontinental flights. Later, in the 1960's, I remember passing through Heathrow's Terminal One with my younger brother and being recognized and greeted by Customs Officers - on our way to or from boarding school. I also remember how pretty the stewardesses used to be - sigh.
It would be nice to think that things will simply slip back to the way they were. However, that is most unlikely to happen. The rich will try to maintain their way of life but it will not be easy. A great number of the dispossessed will do their best to stop it.
At the moment, no politcian who wishes to keep his job will make a serious attempt to raise fuel duty on aircraft to the same level as that for cars. In the future, when few will be able to travel much, politicians will be competing with one another to make it even more difficult to travel by plane - because most of their constituents will consider it an unatainable luxury.
Not all jet fuel is the same. While kerosene is the largest fraction in all jet fuels the fractions of gasoline and lubricants vary. The ratios in Jet A are different than those in the JP-8 used in B-52s. Its these components that keep 747s from filling up at the corner Exxon and saving $1.57/gal.
I've been meaning to post this question for a while and today seems as good a day as any to do so.
Chris Smith sees hydrogen as the best long term alternative to kerosene as aviation fuel. Taking oil and gas depletion and climate factors into account, it seems that electrolysis of water would be the most likely source of that hydrogen.
This hydrogen may be produced by nuclear or renewable electricity. So here's my question / challenge. Setting economics to one side for the time being:
How many wind turbines would be required to produce the hydrogen by electrolysis to fuel a daily service from London to New York - One 747 sized jet flying each way each day (i.e. two planes in service)? Assume 5 MW turbines with 30% load capacity factor.
I really have no clue what the answer might be - 100, 1000, 10,000? IMO it would be a very interesting ball park statistic to have.
5 MW x 24 hours = 120 MWh
Load factor (x 0.3) = 36 MWh
After loss in conversion to the grid (x 0.6) = 21.5 MWh
After loss in conversion from electricity to hydrogen (x 0.7) = 15 MWh
After loss in hydrogen storage (x 0.97) = 14.5 MWh
14.5 MWh equals something between 8.5 and 9 boe.
A packed A380 spends 0.03 liters/passengers/km
Distance London - New York = 5575 km
Total distance = 11150 km
11150 km x 800 passengers x 0.03 = 267600 liters of jet fuel
Liters per barrel = 157 liters
Assuming 100% efficiency in refining, fuel spent = 1700 boe
Grand total with 9 boe/d/turbine = 190 turbines.
The differences between our accounting are the aircraft and the efficiency in the process of producing hydrogen.
200 is the number, now Euan what's prize for such speed and soundness in calculus? :-)
As mentioned in email to you, to do this using 2MW onshore turbines, the load capacity factor would drop and you probably need more than 600 windmills.
As for a prize - how do I know who's right? I'll wait till we hopefully get some more input from our US cousins. Prize for being first - I'll buy you all the Guiness you can drink at the ASPO conference in Ireland next year.
I'll be glad with the Guiness prize!
A 747-400 has a range of 13,450km and a fuel capacity of 216,840 litres.
http://en.wikipedia.org/wiki/Boeing_747
London to New York is 5572 km
http://www.geobytes.com/CityDistanceTool.htm
Therefore 89,831 litres needed for one trip. One trip each way each day means 179,662 litres per day or 65.5 million litres per year.
The energy density of kerosene is 36.8 MJ per litre so the annual energy requirement is 38.8 MJ x 65.5 million litres = 2.5x10^15 J
http://astro.berkeley.edu/~wright/fuel_energy.html
Annual energy output from wind turbine: 5MW x 8760 hrs x 0.3 = 13 GWh = 4.68x10^13 J.
Assume electrolysis is 25% efficient so only 1.17x10^13 J of hydrogen is produced.
Assume a joule of hydrogen is equivalent to a joule of kerosene.
Number of wind turbines needed = 2.5x10^15 J / 1.17x10^13 J = 214 turbines.
1GW of installed capacity. If nuclear was used with more than twice the load capacity then less than 500MW power station could fuel the two aircraft.
Another point to note is that the 65.5 million litres of kerosene per year costs around $40 million. If we equate $40m to 214x13 = 2782 GWh of electricity it works out at 1.4 cent per KWh which is around 10% the current cost of electricity. So the conclusion is that just in energy terms (ignoring technology and capital issues) running a 747 on electricity is ~10 times as expensive as oil.
Did I make a mistake anywhere?
I've been thinking about the issue of cost. 10 times more expensive sounds a lot - but as Captain Chris points out fuel accounts for 10 to 35% of operating costs - so the actual impact on the cost of flying may be significantly lower.
I often think about my skiing holdiays in France where the flight only accounts for around 20% of the total cost. So lets say the flight is 20% more expensive - then this only adds 4% to the cost of my holiday.
So far so good - but then I think about the need for a wind farm to power each route - or some equivalent form of power production and the feasibility falls away.
Now think about the other impacts of $600 oil. I think "demand destruction" will occur long before that $600 barrel. So whilst you may today, in a $60 oil world, be able to afford your holiday even with a 10-fold aviation energy price rise I doubt many people at all will be taking skiing holidays in the wreck of a $600 oil economy.
On a more serious note - what you are describing is an energy barrier that is so high it will never be crossed in a "oner". Substitution wil have to take place in stages following a cost hierarchy (either economic or EROEI).
I guess that's why I think all / most jets will still be flying on kerosene in 2050 - and the availability of kerosene will be secured by substitution in other areas - i.e. electric cars.
By 2050, oil will be $300 - 400 / bbl? And I'll be 93 - running on a stem cell replaced body - just waiting for $600 - and my oil stocks to take off.
Dang... wrong! Again!
http://www.solarpaces.org/ZnOZn.HTM
And this is just one example of one implementation of one possible process. Scientists all over the world are working on a lot of other methods that are far more efficient than electrolysis.
Same problem as posed in Challenge MK 1 (above) but using any means tried and tested to produce the hydrogen.
Present results in a format understandable to the layman or laywoman. If the process uses fossil fuel, or produces green house gasses then an energy accountable way of eliminating the climate impact has to be presented.
In other words, I understand what 200 5WM offshore turbines will look like and have a rough idea what they may cost - so fractional percents of this power plant will do.
If the hydrogen is produced by solar energy - then transportation costs and transportation losses need also to be accounted for.
Ideally, the EROEI of the technology needs also to be considered. I chose wind and water electrolysis as a base case example because where I live we have ample quantities of both - but virtually no sunshine for large periods of the year. EROEI for wind is believed to be roughly 18.
http://www.theoildrum.com/story/2006/10/17/18478/085
Wind energy is great... to offset natural gas burning power plants and some coal fired plants, too. In the short run that is what it should do. In the long run, we will see. But I would not bet on hydrogen for the next ten years.
Thxs for this post. I am not a pilot, so I may be entirely wrong here in my proposals. The military uses aerial tanker refueling--is this applicable to commercial aircraft, and can it result in fuel savings?
Or could a remote-piloted 'flying fuel tank' aerially meetup with a plane, then mechanically attach, allowing the other empty tank/engine to mechanically dis-attach, then glide back down by remote control? This would keep the aerodynamic profile consistent, but right-sized for the flight leg ahead. The main idea is to keep the payload airborne and moving, but shed those motive-resources as they empty to minimize weight, wingspan, and aero-drag.
For example: if a payload needing fuel has to fly a long 2500 mile leg, then the flying fuel tank will be scaled up appropriately. Alternatively, if it only needs to refuel for a short 250 mile leg, the replacement may have a 50ft shorter wingspan because the payload needs much less fuel. The smaller, lighter wingspan's dimensions will save additional fuel.
Short hop payloads thus can optimize fuel & wingspan dimensions to the projected route and weight. Long oversea routes won't require huge wingspan & fuel loads if the much smaller replacement fuel loads fly up to meet them at the appropriate aerial junctions.
Bob Shaw in Phx,Az Are Humans Smarter than Yeast?
I can imagine going to America from the UK one way round the world on the trade winds and going the same way back.
Here's an example of a new airship being developed for freight: http://www.aerospace-technology.com/projects/cargolifter/
:-)
I think I keep flying. The 777 is a nice plane. Can't wait to see the 787...
http://www.aps.org/policy/reports/popa-reports/helium.cfm
:-)
I love your unconstrained tech notions! Don't stop! However, I wonder if the Al Quaeda IT department would have any interest in a pilotless Fuel Tank program in the US..?
This morning, I'm remembering and scaling up a Savonius-sailboat concept model I was building and revising a few years ago to see if I couldn't make a Rotor-Sail to Prop or Paddlewheel combo that would "Use windpower to make a craft sail directly UPWIND" I had some marginal success with some very unrefined craft, so I know it's possible, but then moved away from NYC and the fine little boat pond where Tesla floated the first RadioControlled boats over a century ago, in Central Park, near the 'Inventor's Gate' at 72nd st.
Regards,
Bob Fiske
Thxs for the compliments, but the engineering hurdles may be impossible to overcome--I don't know. It basically is the
baton race concept applied to aircraft where the baton is the airborne fuselage payload.Aerial mating maybe just too dangerous, but if it can be accomplished: the aircraft flys in mated biplane mode while all the connections are made and systems started and checked, then the nearly empty tankwing detaches.I think it is much more likely that aircraft travel will contract to a very, very, small group of super-rich few.
Bob Shaw in Phx,Az Are Humans Smarter than Yeast?
Related to that project (and to the topics in this post) Dryden spent a number of years developing the Autonomous Formation Flight project. Just as birds fly in a "V" to conserve energy, their algorithms hold aircraft in very tight V-formation -- another very complex control problem. You can get as much as a 15% reduction in drag with the right geometry.
- Electric tugs to move planes around on the ground.
- Electric launch assist, maybe like what aircraft carriers use, or a linear motor to help a plane get up to takeoff speed.
- Speed arrester cables during landing, to let the plane slow down without reversing thrust.
- Flying tugs. A small piggy-back plane that's almost all fuel and engine that gives the plane additional power during takeoff and climb. This might even be electric.
- There are more wing/skin efficiences to be had as well. Things like perforated skins and small amounts of air suction/exhaust to improve airflow across the wing surface.
Other things we can do:- Charge passengers by weight as well as seat.
- Allow more choice in flight paths.
- Let people buy and sell seat futures. Sounds kooky, but it would allow airlines to better plan for future flights while allowing them to spread out the risks of flying without a full plane.
Of course, the best option is to encourage rail instead of short flights and leave longer journeys to aircraft.2,3,4 Sound all like technologies leading to massive deaths.
Charge passengers by weight? Yep. That will fly until the ACLU takes aim at it. After that it will fall like a lead eagle.
Allow people to trade seat futures? You mean allow profiteers to take control over a monopoly market and extract a toll? How would anyone but the traders profit from that? I guess the one airlane which would not put up their seats for sale would flourish... I would always fly with them.
:-)
Encourage rail? Good idea! Where do I get on the train to Europe in North America? Which railway station, which platform?
Charge passengers by weight - there is nothing unconstitutional about that. Which amendment to the constitution do you suggest that violates?
Having reading difficulties today? I don't consider a flight across the Atlantic to be a "short flight." I would call that a "longer journey" which should still be taken by air, as I said above. Getting a little testy when someone questions your "Infinite possibilities with expensive solar" cult?
I'd also like to be able to travel all the way from Aberdeen to France on a comfortable high speed electric train.
I'm not an environmentalist but am developing a very healthy dislike for many of our politicians who claim they are whilst piling all transport expenditure into roads and airports.
A 747 has a max takeoff weight of 800,000 lbs. 400 passengers weigh about 60,000 lbs which is only 4.75% of the total weight and 9.5% of empty weight. Considering how much less fuel an empty plane would need it comes to maybe a 15% difference between empty and full on a trans-Atlantic flight. So the weight surcharge would come to about 15% more.
LOL... I was asking for a railway across the Atlantic. Sorry you didn't get that JOKE. But let me know when engineers will have found a way to build rails on water.
What do we need solar energy for aviation for? Aviation is 5% of the problem! Solve the remaining 95% first and then we start talking about aviation.
Look... just because you seem to be having difficulties with numbers does not mean everyone else does, too.
It's an interesting idea, but I think the answer is "no" and "no".
Lifting the fuel into the air is going to cost energy, whether it is done by each plane that needs it or by a tanker. I can't see how you could possibly gain any efficiency using tankers, and I can see many ways in which you will lose efficiency. The tanker, after all, has to loiter about. There is also the question of trying to coordinate tanker sizes and locations to match a complex of air traffic - either that or the tankers act more like hubs and many aircraft must go out of their way. It is far less costly to have tanks that are "more than big enough" sitting on the ground, rather than trying to defy
gravity.
See http://archive.gao.gov/t2pbat5/150241.pdf for an interesting discussion of "efficiency" of tanker operations. Note in particular: "tankers often returned to base with a large amount of unused fuel, some of which had to be dumped in order for the tanker to land."
Or perhaps you're thinking of more efficient ways of lifting the fuel, such as airships? The problem there is that aircraft cannot fly slow enough to be able to take fuel from an airship. Also, the payload ability of airships is nowhere near great enough to serve as fuel tankers.
One thing I had wondered about with hydrogen jet fuel was the economics and on the basis of calculations done by Luis and Chris up the thread a bit I guess I'm still sceptical that hydrogen will ever take off if electrolysis of water is the source.
You did a pretty good job of all but eliminating other alternative jet fuels and I'm left wondering where that leaves the aviation industry other than facing contraction and crisis.
You are probably aware that Richard Branson proposes to spend £3billion over the next 10 years researching new, green jet fuels. Maybe I lack imagination or am just too constrained by my limited understadning of the laws of physics and the Universe. But what on Earth is he going to spend his £3billion on? Have you any ideas on that front?
An alternative approach might be to start doing everything humanly possible to conserve liquid petroleum fuel for applications where it is indispensible - like aviation, and to move more rapidly to electrifying cars and trains - which is much easier and more economically feasible to do.
So perhaps Richard Branson should be focussing on designing electric cars and using the fuel saved to power his fleet of 747s? (Sir Richard please make the £1billion cheque payable to The Oil Drum - we'll find a way of sharing it out.)
Great post. One of the best benefits of reading TOD is the education that you recieve.
Thank you very much for your time.
I would agree with you in principle with regard to the potential of airships for intercontinental travel.
However, the practical difficulties of navigating a craft with such vast windage were such that,
in the heyday of their use,
it was not uncommon for craft to go wildly astray, for instance making landfall in S Italy
while trying to get to Berlin . . .
A modern service wouldn't tolerate such eccentricity, so further refinements seems necessary.
Adding sufficiently powerful propulsion to counteract the windage is a possibility,
but this has self-defeating costs in terms of structural weights
& additional fuel-stock weights or solar-powered-battery weights.
Which brings me to perhaps the world's greatest under-utilized rapid-transport resource,
namely the Jet Stream.
Circling the planet at > 700mph, its precise route varies somewhat
but is amply predictable for a few days hence.
So, rather than routinely attempting to bring very large LTA craft to land,
would they not be better riding the Gulf Stream semi-permanently,
with turbo-prop shuttle aircraft delivering passengers & frieght to them for onward transport,
and collecting the same from them for return to the ground ?
Those shuttles would of course need only a fraction of the present fuel/passenger
since they are neither travelling the long haul route
nor burning the fuel to raise that long-haul fuel requirement to 35,000ft.
In theory, they could in addition be fueled by synfuel-production plants on the LTA craft
that could be powered by very large solar arrays.
These ideas are sheer speculation of course,
but then if PO+GW are not to put an end to substantial air travel,
we need to think beyond the confines of past practice.
Regards,
Backstop
Just asking...
Noticing empty shelves, sky high prices in the produce section on a weekly basis is another story altogether.
Watch your local produce section. It's a canary in the coal mine in a lot of respects.
The canary is alive and well in Portland, OR. I was surprised to see fresh cherries in the market yesterday. Upon closer inspection, they turned out to be organic, no less. They were from either Chile or Argentina - can't quite recall. Tried one, they were fairly good but not great.
I recall being surprised, reading the inflight mag. on a recent flight, at the tonnage of commercial goods carried on 'passenger' flights. The airline even mentioned that this helps carries them through lean (passenger) times.
As long as wealthy folks can afford such things (to the detriment of many others) the planes will fly. They may even kick out the people and just fly fruit and fish. They sure don't get $10/lb for me when I fly.
Another of the little-realized problems stemming from extreme wealth inequality.
I think it may be too early to write off aviation. I am sure it will always be part of the transportation mix. I believe that it will be increasingly difficult for aviation to compete over short distances but over long distance or where there is a natural barrier it will be indispensable.
It is also important to remember that aviation is a derived demand. We rarely decide that we would like to go flying today, where shall we go? We fly to get somewhere that we want or need to be. As long is there are business meetings, overseas markets, must see tourist destinations, family overseas and students going to university, there will be an air transport industry.
One comment refered to the elasticity of air transport demand. It is true that in general that pleasure travel demand is elastic. A percentage increase in price results in a greater percentage decrease in demand. Business travel is inelastic. A discussion of the elasticity of demand assumes that the demand curve remains the same. In fact the demand curve changes when either the product or the market changes. We cannot assume that higher fuel prices in the future, if passed on to the consumer, will necessarily result in reduced demand because the demand curve will be different.
I am not a big fan of hydrogen. I see it as simply a means of storing and carrying energy. The same idea as synthetic kerosene or biofuel. The value of any of these energy transfer mechanisms will depend on the source material, the efficiency of the process and the environmental issues such as land use, resource depletion and global warming emissions. My money is on an artificial liquid hydrocarbon produced specifically for aircraft.
I would agree with your last comment that synthetic fuels will be produced. Hydrogen could never be used because it is a gas at normal temperatures and pressure, it's leakage risk, fire risk and absence of flame when burning are big drawbacks as well as the very big increase in fuel tank size and weight.
It's manufacture and distribution are technically improbable,especially for aircraft. A 40 tonne fuel tanker to a normal gas station using 26 tonnnes of fuel per day would need to be replaced by 22 Tube Trailer Tankers or 4 large liquid fuel carriers to deliver the same amount of fuel in energy equivalent. See Bossel and Eliasson' hydregen report:
http://www.methanol.org/pdfFrame.cfm?pdf=HydrogenEconomyReport2003.pdf
I don't agree with your point on propjets versus jets up to 500 miles. Below 200 yes but not over. A jet has a far better climb performance and speed and higher operating ceiling. The prop jet has a higher drag profile and inefficiences above 25,000'compared to a jet. A typical jet sector of 55 minutes takes 85 minutes for a prop jet - here I am comparing a B737 and a 400 series Dash 8
Another point regarding Jet Kerosene is that only a certain proportion of the barrel can be produced in refining so as crude production falls the corresponding amount of kerosene will fall. I am afraid that other points raised here by responses to your article such as airships and mid air refueling and electric tugs etc. etc are not realistic and indicate a lack of aviation knowledge.
You touched on fuel with weight and balance. Most people would not know that on the 400 series B747 on longer stage lengths fuel has to pumped from the tail or horizontal stabilizer early in flight to keep it with balance limits later in flight. For those who think new wing surfaces and materials will change things this is unlikely. The speed of the airflow over the wing is the important element because you can not exceed the critical Mach number ( which is Mach 1) over the wing without high speed buffet and that is why sub sonic aircraft will always cruise around the Mach .85/86 range. Modern aircraft designers get to this maximum figure by using the best angle of wing sweepback.
A good post Chris with lots of good information
I should have added that of course better materials to reduce weight will give better fuel performance but the operating speed is unlikely to change
and I agree..
So here's how I see things:
Hydrogen
Without going into details of the cost / eroei of various hydrogen sources, I think that cost and the lack of infrastructure that you discuss will mean that H will not be used in my life time - if ever.
Biofuels
In addition to the physical limitations that you discuss, most biofuels grown in temperate latitudes have low eroei and once that point gets hammered home I think biofuels will be banned. Furthermore, once politicians are confronted with starving 10s of millions worldwide, the morality of using food for transport fuel will come into sharp focus.
Demand
I've made about 6 flights this year - 2 skiing holidays, 1 fishing holiday, 1 family holiday, 2 conferences - none of this was actually necessary. I've grown to hate flying / travelling and would be content to do a lot less. There is a big difference between doing less and not doing it at all - so I'd be quite happy with some form of rationing / transferable quota.
But here in lies a critical problem. With less future air travel the whole airline, airport, aircraft and service businesses will really struggle. Some may still make a profit, but year on year lower profits is not how our growth orientated economy works.
Future fuel
My guess is that kerosene will continue to be used for the foreseeable future. All the fuel efficiency measures you describe will I believe become increasingly important. So less air miles will be travelled using more efficient aircraft and operational practices - so CO2 per capita will drop.
Fuel savings in ground transport willensure liquid fuel availablity for the foreseeable future - 2050? A comment to DownUnder (who is also a pilot) - I believe that refining heavy crude using crackers that this process may be tuned to optimise kerosene production.
UK transport policy
Expanding airports at this time is IMO utter madness. Aberdeen just got the go ahead for a massive expansion this week. Environmental and fuel availability constraints must mean less flying in future - but less flying is not necessarily bad - it is working out how to achieve this in a profitable business sustainable way that is the main challenge. Much higher prices i think.
I will grant that 50% of air travel is non discretionary, i.e., business travel. Should air ticket prices double or treble, very obviously the price driven discretionary traveller is no longer a function of the bottom line of any travel firm. At the same time that air ticket prices rise astronomically, we will see a concurrent rise in the cost of hotels, car rentals, food and all other peripherals surrounding travel (WTO estimates that world travel receipts including peripherals are about 70% business travel driven). Given that every calorie of food requires 10 calories of (largely) fossil fuel, restaurants will suffer dramatically.
Perhaps the greatest factor to reduce 'people' travel will be a psychological one. As a posting above noted, it will be seen to be a rude thing to do to board an aircraft...particularly if one is politically inclined for a future favourable election result.
As firms realize that increasing fuel costs increase the cost (and price in the market) of their products, the bean counters and IT people will step in. Business travel IS dropping (according to a recent edition of Canadian Travel Press). Sales calls can be accomplished, granted with more difficulty, by telephone and teleconference video.
The hassle factor of present airline travel is now a significant function of the travel decision. Will I spend 6 hours by air from Toronto (door to door) via Air Canada or 5 by VIA Rail to get to downtown Montreal? Obvious.
I suspect that there are others like me, with discretionary income and looking for a nice warm holiday who simply REFUSE outright to travel into the USA. Do I want to be kidnapped by thugs and shipped off somewhere after 3 days at JFK without food and water? NOT!
Were I to HAVE to travel on business, I would insist (as many business people are doing who have the finance available) on charter private aircraft out of civil aviation airports. I suspect, since many of these airports are small, relatively private (but close to major cities...Teterboro instead of JFK) that the intrepid traveller could quietly board aircraft without press or public opprobrium. Even general aviation out of major airports is like travel was in the 70s.
I frankly see no great future for the travel industry. It won't go with a bang; I suspect it will whimper for a while.
Thermocatalytic splitting of water using high temperature output from a nuclear reactor will probably be a more effective method of preparing hydrogen.
a 1 GW (electric) nuke at 50% efficiency produces 2 GW of thermal output.
At approx 25% efficiency for the thermocatalytic means that at 37.4 kWh per Kg of hydrogen a 2 Gw thermal plant would produce approx 13,368 kg per hour of H2. Assuming a load factor of 85% for a nuke means that each year you could produce approx 98 million kg of H2.
1 kg of H2 is approx = to 3.8 litres of jet fuel.
So your nuclear plant will produce about 378 million litres per year equivelant.
Or to put it another way, approx 2.3 million barrels a year.
ok, so liqufaction might be a challenge, but it beats being grounded.
One thing that always makes me wonder, is that aircraft already have a large space on board that would easily accomodate huge cylindrical cryotanks. The cargo hold.
After all, if its a choice between flying with only hand luggage and not flying at all, I'll take the hand luggage option.
Andy
Here is a hint: there is a nuclear reactor that produces the right temperatures without any radiation, at all. It is fully operational for four billion years and completely maintenance free... and here are a few ideas how it can make hydrogen:
http://www.hydrogen.energy.gov/pdfs/progress06/ii_i_1_perret.pdf
All the high temps you could ever want and the yanks have already built and proven one.
Did you know the US experimentally tested nuclear jet engines? The radiation levels were actually lower than anticipated. Still high enough to kill the population the aicraft was flying over, though.
:-)
All this nuclear crap belongs into "engineering curios". And that is where it will stay.
It was scrapped as ICBM's were invented so the US had no further need for an aircraft that could fly massive ranges.
The then head of the AEA pushed for a programme to develop the Molten Salt Reactor into a civillian power generation reactor but as the reactor doesn't produce plutonium the military concluded there was no point. By this time the inefficient solid core boiling water reactors were already in widespread use, thus crowding out any new type of reactors.
And yes, the corrosion problem has been solved.
Indeed, the MSR may yet be resurected. It is efficient in its use of Uranium and produces no long lived nuclear waste. Its fissile products have a half life of just 50 years.
<sarcasm>However for a technophobe luddite like yourself that just wouldn't be an acceptable soloution</sarcasm>
For the rest of us, it'll do just fine.
Andy
These are all well within the range of proven gas cooled reactors.
You can do exactly the same easily with solar. No nukes needed. But nobody does as far as I know. Which kind of tells me that it is a non-starter.
First off, learn to spell (b)lose(b) dammit. Its not that hard.
second, thermo catalytic production of hydrogen doesn't use any electricity.
It simply uses the heat produced from the nuclear reactor.
Say we have a reactor that produces 2,000,000 kW. Its output comes in the form of hot coolant of some description.
We have two choices of what we can do with this energy.
We can either turn it into electricity, with an efficiency of approx 40%. In this instance we'd get about 800 Mw of power.
Or we could utilise a chemical process, running of the heat of the reactor output, to produce hydrogen at approx 25% efficiency. In this instance we'd get approx 13.3 tonnes per hour of hydrogen.
This hydrogen can then be piped to the end user who can do with it what he/she chooses. This could be the upgrading of crude oil to produce more light fractions, the production of nitrate fertiliser using the Haber process, or it could be the fuelling of airliners, etc etc.
Andy
It depends on the process. The more energy you have in the delta T the less you have to pull from a heat engine. When you arent using steam electrolysis you have massive exergy losses... it heats the water up! Think about it for just a second.
Not even close. The more heat you have to turn into electrcity before turning into hydrogen, the more you're just throwing down the crapper. If you're running the entire reactor as a heat engine... a _steam_ heat engine, you get maybe 33% efficiency from the generator and then you multiply that by the efficiency of the electrolysizer, which is generally awful. If you're doing a direct thermochemical process you're getting the carnot efficiency, and if you're doing high temp steam electrolysis you dont have any excergy losses, but you still want as much energy coming from the heat as possible.
This is one hell of an ignorant sentance. First, solar is far more expensive than nuclear, no matter how people try to diddle with the economics of solar power towers and thermal storage and other whatzits that still have no market share. Why would you think that solar would be more desirable in the near term? Someday perhaps...
But second, natural gas (and coal) is still cheap and plentiful, relative to the price of synthetic nuclear hydrogen infrastructure. Now when the price of natural gas and coal really rises because of synthetic fuel demand and depletion among other things, we might very well see nuclear synthetic hydrogen plants.
Cargo is what makes the money for major carriers, which is why American Airlines (AAL not generic US carriers) is still hanging on to the A300 Airbus, lots of cargo space.
I don't think that the cargo space provides sufficient volume. One of the real techies here answer this one..
I wouldn't want to ride over the fuel tank, maybe below or have it out under the wings outboard of the engines.
The space in the overhead of the cabin might give considerable volume for hydrogen tanks, not all required but half?
Changing gears a little: how about flying slower; deflecting more traffic to rails? I fly from Tulsa to NYC, and it is at least a 10 hour day door to door. Plus getting up early at both ends, to make the airport, security etc.
Sleeper compartment on train running 120 mph and Tulsa to NYC shouldn't be an unreasonable time with sleep included.
Not any hope if we continue business as usual. Absent pie in the sky approaches to fixing the problem, we just need to cut way back on aviation. Ok, let's say some of these approaches would make a dent in the problem. I say we limit carbon and other ghg emissions by cap and trade or other means. If one can come up with a way to meet these emission levels with efficiency or hydrogen or whatever, fine. But let us not wait twenty years assuming all these supply oriented approaches come on line.
According to Monbiot, aviation could eat up almost the entire British quota on greenhouse emissions in the future.
We can speculate all day, but let us not put all or even most of our chickens in the supply basket.
In my experience, airlines nowadays tend to suggest carrying minimum fuel while the captain is the party opting to carry more...
I see this every day. I know that with flight plan fuel I always land with more than an hour of fuel remaining in the tanks. Europe is full of suitable diversion airfields and yet I cannot convince pilots that they just don't need that extra 100, 200 or 400 kilogrammes (3-10%). Regardless of the extra fuel on board, when we reach the minimum diversion fuel quantity we divert. The extra fuel is usually wasted avoiding the decision. When there is a high probability of holding due to low but manageable weather then it makes sense to carry a bit more for delays.
The comment about aircraft equipment for low visibility approaches is bang on. Aircraft with the ability to land in zero visibility (Category 3) will save money, fuel and emmisions resulting from diversions. For the system to work the aircraft, both pilots and the airport must be at the required standard. (Just yesterday I replaced a first officer who was not Cat 2 qualified because of the likelyhood that we would need to do a Cat 2 approach to get home). Individual airlines will balance the extra cost of the equipment, maintainance and crew training on the likely cost saving from having it (Think large airliner that has travelled half way around the world or operators in places that are frequently fogged in.). There is an intermediate option (Category 2) that may be more cost effective for some operators. While many of the aircraft sitting on the ground all day yesterday at one UK airport are Cat 3, it didn't do them much good. Arriving aircraft were turned away because there was limited parking left available.
The comparison of turbprops versus jets on short sectors really does depend on the route. The issue is how much time is spent on the ground, how much time is spent below 10,000 feet and is the 250 knot speed limit enforced, and how much time is spent in the approach sequence at a busy airport. Jets are always faster but sometimes the difference is just a couple of minutes. I have seen articles about jet aircraft specifically designed for these 500+ distances that have a straight wing and lower cruise speed.
I think that this article was wonderful - a work of love. I also think that many of the comments are articulated by people who have a really keen technical sense. I know, because I am a professional engineer. I also worked for numerous airlines as a consultant in a previous existence.
Nevertheless, I believe that we are not heading for a technical nirvana - that is not how things really work. For example, the motor car could have come into being 100 years earlier - before the French Revolution. There was no significant technical restriction that did not exist 100 years later. But it did not.
The airline industry is one of the most conservative and politicized creatures of the 20th century. What Ryanair and Easyjet did could have been done 30 years earlier by people even before Freddy Laker?
As soon as fuel becomes seriously expensive, people will firstly have to work out how to get to work - if they are lucky enough to have a job. Long-distance air-travel will revert to being a luxury. The government will bring in something equivalent to the £50 travel allowance introduced by the Labour government of the 1960's. Only a minority of readers of TOD will have heard of it so let me explain. People, from the UK, had to have stamped into their passports how much foreign currency they used - with a maximum of £50 per year. If you bought a package tour, almost all your allowance would be used up and you might be left with £10 of spending money. Even adjusting for the intervening inflation (multiply above figure by a factor of 11), one ends up with really dismal figures.
It would not make any commercial sense in that environment to come up with entirely new technical solutions - the current investments must be repaid somehow. I would suspect that fuel would be rationed first (not just by price) in order to maintain necessary air-travel. Further into the "long emergency", substitutes such as butanol would be manufactured since they most closely resemble aviation fuel.
If you are in any doubt that the boot is on the other foot, just read the papers of the last 2 weeks:
Instead of trying to reach as close as possible to Mach 1.0, typically 0.85 as mentioned above, why not fly at, e.g., Mach 0.75, saving about one quarter of the energy? Or even slower. I know passengers like to "get there" as quick as possible, but if the ride is otherwise unaffordable... With some attention to winds aloft, the actual travel time when going downwind would not change very much, but upwind would be a lot worse, so altering flight paths and altitudes, and even the schedule, to dodge the worst headwinds may be worthwhile.
What's the big hurry? It used to take months on the Oregon Trail, and one had a 50% chance of not surviving the trip! We've gotten so spoiled since...
With long straight wings an aircraft can cruise at moderate speeds on little energy - as gliders (sailplanes, without engines altogether) do. Lift generated by wings can be low-energy. Drag generated by very wide bodies (airships) is a much bigger energy hog, except at very low speeds. Those who propose airships instead of airplanes do not grasp this.
I think you have a few misconceptions here about aircraft design. Having an aircraft with long straight wings and flying slower would use more fuel not less. If you look at the advances in design from the propellor driven aircraft to jets you will notice how the wings have bcome swept back. It give less of a drag profile through the air and there are lots of structural and aerodynamical reasons to have the wing root wider and thicker versus the wing tips - to carry fuel and the undercarriage structure just to name a couple.
Jet engines operate far more efficiently at higher altitudes and there is less resistance to the aircraft through the air. You will burn more fuel in a jet going lower and slower than higher and faster. Wing sweep back which is about 32 degrees on the B747 gives a smoother ride and better handling characteristics through most phases of flight.
Aeronautical engineers design the wing for optimum speeds and below those speeds the centre of lift will move position over the wing and you would in fact create increased drag and higher fuel burn( I am talking about on cruise here). Another consideration is the higher the altitude the better chance to avoid weather, especially storms fronts if necessary and low speed flight at altitude can sometimes be in fact quite dangerous in turbulence or turns.
The fuel burn is very significant lower down and to give an example, on a Sydney to Los Angeles flight a fully laden B747 cannot get above 31,000' until past Hawaii because it is too heavy, but once the aircraft is light enough it is necessary to climb higher to decrease the fuel flow, weather considerations aside. Hope this is some sort of explanation
I suggested lower speeds, not lower altitudes. Of course drag increases if the speed is very low, but over a range of "cruising" speeds drag increases with speed AFAIK. If indeed the design of current airliners is thus that the typical cruise speed is the most efficient one, my point was that new designs could be optimised for somewhat lower speeds and thus save fuel. High cruising speed used to be a selling point, perhaps in the future fuel economy would be more important. One possible change in design that I alluded to was somewhat less sweep-back of the wings. (Of course I did not mean a constant chord from root to tip...) My main points were:
* lift from an airfoil is not necessarily energy intensive, and
* high speed has an energy cost
Basically a considerable amount of fuel can be saved by the airlines simply by slowing down. Some years ago I worked for Continental Airlines. They had a program that asked for employee input about saving money. The pilots came up with the idea of cruising the aircraft at a lower speed. All aircraft have several different speeds that allow either for best time, or best fuel inefficiency. Continental was able to save money simply by flying slower. A turboprop aircraft of the same passenger capacity as a jet will always be more fuel efficient.
When the first generation of commercial jets appeared on the scene, like the Comet, their fuel range did not allow them to go nonstop London to New York. They were required to stop in Iceland for a refueling. During that time some British aircraft manufacturers came up with the design of an aircraft that would be able to fly nonstop London to New York. It would be powered by a Niaper Nomad engine. It was a 12 cylinder opposed diesel engine. It had a turbo compound supercharger it was geared to the engine by a variable speed drive. The concept was that this would burned so little fuel it would easily be able to make the London New York route. The ultimate king of low fuel consumption was the Douglas DC seven, and the Lockheed constellation 1049. These aircraft used an 18 cylinder 3350 cubic inch radial engine. It was a turbo compound engine that used an exhaust turbine to help drive the crankshaft through a fluid coupling.
In parts of the world aviation gasoline is almost impossible to get. I worked with a linguistic missionary organization that operated in Indonesia and the Philippines. During that time in the late 1970s aviation gasoline was almost seven dollars a gallon. And in some areas impossible to get. This organization was pushing several companies that were developing a diesel engine for light aircraft. As of today almost 20 years later these diesel engines have not come to market. However they are much more economically feasible in those parts of the world where jet fuel is the only thing available.
In the 1980s both Pratt & Whitney and General Electric developed what was called the prop fan engine, it was basically a large direct drive fan driven from the turban section of a jet engine. Today's high bypass turbine engines approach the fuel economy of the prop fan engines of that era. If aviation fuel costs become high enough I believe you'll see the introduction of the high-speed turboprop aircraft. It would be much easier to design to design a fuel-efficient aircraft from the low-speed up.
A jet aircraft, flying at its normal cruise speed, uses only 10% of its power to provide lift. The other 90% is to overcome drag; anything the aircraft manufacturers can do to cut drag will improve efficiency.
It may interest you to know that there is an Austrian firm - Diamond Aircraft Industries - that has an amazing twin-engined four-seater that is is diesel powered. This plane the DA42 Twin Star is the first diesel-engined twin to cross the North Atlantic. It has remarkable fuel economy and here is an article about it.
As for 747's and suchlike, I can confirm that in the 1970's, when airlines were desperate to save on fuel and to survive financially, the planes were flown at a lower cruising-speed. As a passenger, this became noticeable as the service-trolleys tended to need their brakes badly and stewardesses had to often work in pairs so as to push them uphill.
I believe that the following generation of planes flew at slightly slower speeds and that the problem with the trolleys went away as the design was altered. In fact, I believe that one of the fastest non-supersonic planes was the Hawker-Siddeley HS121 Trident - a lot earlier than the 737 and DC8. However, it was a very thirsty plane and the extra few minutes saved by travelling on it were almost an irrelevance to the passengers.
Wing design is, of course, the key to the economical speeds at which an aircraft can be operated. If we substantially slow down an aircraft designed to operate at Mach 0.83, for example, we increase drag and wind up wasting fuel instead of saving it.
Aircraft require a lot of maintenance and most of the maintainance is dirctly related to the time the aircraft spends in the air. Flying slower means the more maintanance cost atributed to that flight. The tradeoff would be different for each aircraft type and route.
Aircraft need to operate as many flights as possible, usually with quick turn arounds to get back in the air quickly. The fewer flights per day the greater the portion of fixed costs that need to be attributed to each flight (meaning higher fares, meaning fewer passengers, affecting profitablity).
Tailwinds help and we can reduce speed to take advantage of them. If we are being followed by another aircraft this would have a knock on effect to someone who may already be behind schedule and wants to go faster. Aircraft are not allowed to get too close to each other and are frequently assigned a speed in busy airspace.
Headwinds are more complicated and sometimes going faster saves fuel.
With respect to staight versus swept wings. Swept wings are designed to go fast. That's why they need all the other stuff ( slats, slots, flaps and more) when they slow down to land. A long straight wing like that found on gliders and most turboprops is better for slow speed, high lift applications.
When you look at a turboprop engine you see 4 or 6 blades attached to a turbine engine. When you look at a high bypass jet engine (the type found on almost all modern jets) what you don't see is the dozens of blades attached to a turbine engine. You don't see it because the blades are contained within a cowling. The cowling is there because it is the only way to keep all those blades attached to the engine. If manufacturers could do away with the cowling they would. The engine would be more efficient.
Turboprops are not restricted to 25,000 feet because they have to be. The altitude restriction is due to the requirement for a drop down oxygen system above that level. There is no technical reason why turboprops can't fly higher.
I am sorry but I have to disagree with some of your comments above because they are misleading. The cowling has nothing to do with holding the blades in place. On modern jet engines the compressor blades are arranged in radial form attached to the central engine shafts of which there are normally two. Depending on the type of engine, you have many stages of compressor blades and they are housed inside the engine casing.
This has to be to compress the air as it passes through each stage before it reachs the burners and on to the turbines. Outside the engine shroud or casing there are many take off pipes for engine sensing, air conditioning and anti ice air bleed valves which have to be taken off at specific compressor stages,and other attached ancillary equipment such as starters, generators etc. If there were no cowl around the engine the drag implications and ice protection problems would be immense.
The propellor blades you refer to on the propjet should not really be compared to compressor blades inside the engine because, as you know, they are entirely different and may confuse people reading this.
It is a simplification intended to show that there is little difference between turboprop engines and high bypass turbofan engines. They use the same concept, technology and fuel.
You are confusing the fan stage of the jet engine with the compressor stage(s) of its high pressure core(s). The turboprop propeller does the same job as the fan while the high pressure core (aka gas generator) may be identical in the two engines.
The long thin props are better at low speed and the short wide fan blades are better at high speed. An unducted fan (no cowling) may be good somewhere in between and could give up to 25% improvement in propulsive efficiency.
Check out:
Understanding Flight (ISBN 0-07-136377-7)
pages 140-143 The Turbofan, The Turboprop
Flying Jets (ISBN 0-070049296-4)
page 105 Turbofan engines
Aviation and the Global Atmosphere (ISBN 0-521-66404-7)section 7.4.3 Future Development Paths for Aircraft Engines (for more on unducted fans)
I am not confusing the fan part of the engine. I am simply saying that the cowling is not what holds the blades in the engine. You stated that "the cowling was the only way to keep all the blades attached to the engine".In all the aircraft I have ever flown in the blades were attached to the engine drive shaft. You also stated that if engine manufacturers could do away with cowls they would. As far as I know they haven't,as I see no sign of unducted fan jet engines coming without cowling.
Both the new GE and Rolls Royce Trent engines for the B787 have cowls,the newest commercial aircraft to fly. You are welcome to stand by your statement, however all I am saying is those comments could be misleading to anyone not familiar with jet engines.
with the ashes....
http://www.grida.no/climate/ipcc/aviation/index.htm
Section 7.3.3 Nacelle Efficiency
'As engine bypass ratios have risen over the past 2 decades, so too have the drag and weight of the nacelle.'
Section 7.4 Engine Performance and Technology
'The relatively larger reduction in aircraft weight derives from concomitant reductions in requirements for supporting structure. The benefits are further magnified by the fact that the reduction in fuel burn attributable to engine weight savings is proportional to increasing aircraft range.'
Section 7.4.3 Future Development Paths for Aircraft Engines
'Studies of aircraft with ductless propulsors show that aircraft performance tends to optimize at flight speeds 5-10% below that of current transports as a result of aerodynamic efficiency considerations.'
Section 7.2.1 Aircraft Historical and Future Developements
'For domestic travel, however, shorter range designs with a larger payload can provide benefits in fuel efficiency.'
Also Figure 7-12 Evolution of aircraft gas turbine efficiency