Fuelish Question


New Member
I think that most of us would agree that oil is a big problem. It is a security issue because most of the world's oil is found in politically unstable areas. Oil is related not only to our economy's stability, and many of our jobs and job prospects through the cost of jet fuel, but also our ecology, because oil-based fuels are not clean burning.

The question is what to do about it.

In the short term, we can explore and harvest oil in more secure areas of the world. But eventually, we are going to need something else.

Hydrogen fuel cells have been touted as the possible powerplants for future cars. They are currently used in submarines, so they can move some heavy equipment.

My big question is would fuel cells be able to efficiently power an airliner? Can they possess the thrust to weight needed for safely moving an airplane the size of a 777 from one continent to another? If not, what can we look forward to?

I have read in the past that some research was done in 60s on a nuclear powered airplane. This research ended before the plane ever flew. This was probably a good thing. Nuclear power is one thing when we are talking about a stationary plant or a slow moving ship, but an airplane cruising at 800 mph is something altogether different.

I know that some of you have scientific and engineering backgrounds, so fire away!
I read somewhere that the answer to the worlds energy problems could be "cold water fusion". I'm not Einstien or anything but supposedly the physics involved appear sound. However, no one has yet to figure out the engineering side. (I think some egg heads claimed to a few years ago but later recanted).

If it does work, unlimited energy with the only by-product being water...(Wasn't the Delorian in Back to the Future powered by a "Mr. Fusion" engine?)
how about ionized propulsion?
i saw the end of a discovery show of a satalite thats supposed to intercept a meteor. think the show was called deep space one
Ion engines for now don't create nearly enough thrust to power a large jet (or even a small aircraft).

Did anyone see 'The Saint'? That was a sweet movie; it had something do do with cold fusion too.

If anything's for sure, we will someday see a change in the kinds of fuel used by aircraft, though aviation is usually the last to take advantage of such advancements (especially GA). With all the aircraft currently in use and still in production (with no end in sight), any major change in fuel types is still a loooooong way off. My perdiciton is that cars will be the first to switch types (some are already gas electric hybrids).

I THINK I remember reading that hydrogen fuel cells don't have the power to volume ratio that Jet-A does, which would mean that more space would need to be devoted to the fuel to get the same output.
The main problem is energy density. The amount of energy a certain volume/weight of fuel has. Electric cars are a joke because of the weight of the batteries and the low amount of energy they carry. It is also true that it is still necessary to generate electricity (often with fossil fuels), force it through wires at a loss, charge the batteries at a loss (often for hours) and then lug the batteries around. Just heating an electric car takes lots of power and really eats into range. Of course you can always use a combustion heater....

The reason cars are a likely candidate for fuel cells is becuase it doesn't take much power to make a car go. Even if you have a 200 hp engine it takes a small fraction of this to make it go 60-70 mph. Just look at your tach when cruising. My car goes 80 mph at 2300 rpm and redlines about 5500. Cars need big engines to get going in a hurry, once there not much power required. This is why the new hybrids are efficient. Use a 60 hp engine to charge the batteries and make the car go. The batteries are used to store excess power for acceleration and so regenerative braking can salvage the wasted energy normally lost when stopping (the electric drive motors revert to generators when stopping). The best mpg would be with a small turbo diesel since this is the most efficient type of recip. engine.

This will not work with aircraft engines. Most aircraft cruise at 75% power or more. This is why car engines blow up when used as aircraft engines. You do not see people putting many Corvette engines in their homebuilt aircraft for a reason. They can't handle the continous high power required. Jets run in the 90% range for best efficiency. So the short answer is you will not see anything replacing fossil fuels in the near future in aircraft due to the high power required and low weight needed.

There are continous improvements made to efficiency and pollution for internal combustion engines. Few realize how clean a current car is. This is why auto makers do not jump on the bandwagon everytime someone wants to pass a law to reduce emissions "by 50%" etc. Engines are about 98% cleaner today than their 1960's counterparts. Going for a 50% improvement in the last 2% of pollution is not always feasable. Huge cost for dininishing returns. It is also true that the current Toyota and Honda hybrids are sold at a loss. Even then most are unwilling to pay the higher cost for these cars. Improvements will come, but with oil so available at a cheap price there is not a huge incentive.

For recip aircraft I see diesel engines replacing most in the future. This gets rid of the nasty lead and gives better efficiency. It also allows us to use Jet-A, which is cheaper. We are already seeing this with the Diamond twin using two 135 hp diesels and performing like a seminole with 180 hp gas engines. SMA has also gained approval for its 235 hp diesel that will replace gas engines in the 230-300 hp range. It will be used on the 182 and Cirrus SR22 in the future.

The nuclear airplane was actually a highly modified B-36 which carried an air cooled reactor. It was not used to power the aircraft. They just wanted to see if they could put one in the airplane. The crew was in a removable pod that was heavily sheilded with lead and had windows over 1 foot thick made of special radiation resistant glass. When it flew a cargo plane with several platoons of soldiers went with it in case it had to land somewhere.
weird, my friend and I had this conversation a few days ago before I read this post....anyway...we decided that the economy will be a hydrogen economy, and most things will be powered by fuel cells. Problem is airplanes, jet airplanes....
Fuel cells could power prop planes (if the power to weight ratio is there)...but what to do about jets?
The thing most people don't realize is how little most engines pollute. Gas car engines are very clean. We keep spending more and more on technology to clean up exhaust gas at little gain. A better way is to get old cars off the road. One car that burns oil and leaves a stinking cloud in its wake will pollute as much as 30 normal cars.

There is also a limit to how efficient a gas engine can be. They require a certain fuel air mix to be able to run. Some engines use a 'stratified charge' that has a richer mixture near the spark plug and gets leaner as you go out. Honda did this in some of it's cars. The only problem is if you go lean, the engine makes more oxides of nitrogen and there is not a catalalist that can burn these up. Automakers have spent lots of money to develop a catalitic converter (sp?) that will rid the exhaust of NOx with no success. So the Honda that got the best MPG was not available in California, since it didn't meet emissions requirements.

These engines can also be made to burn alcohol and other renewable fuels (including hydrogen). There are already cars that run quite will on natural gas. Carrying high pressure gas cylinders in a car is not the safest system however.
Thanks for the information. I guess it confirms my suspicion that even if fuel cells become common in autos, airplanes will still be breathing Jet A.

I had heard about the B36, but also there were plans on the drawing board for a nuclear powered aircraft that never flew. I think I read this in Air and Space a while back.

Personally, I think that fission/fusion is ok for powerplants on tthe ground, but an accident waiting to happen in an airplane. Until, that is, the development of the Mr. Fusion machines that run off garbage.
There's some talk about a Sterling engine but even that still requires some kind of energy source to creat the teperature difference required for the engine to run. The key thing with the sterling is it would becomre more powerful the higher it climbed due to the larger temperature difference. A sweedish firm uses a Sterling engine for a sub but that's about the only "practical" use out there right now. Interesting but I thikn Diesel/Jet-A will get here well before Hydrogen and most certainly Sterling.
Speaking of engines I saw something on "wings" about a new "unducted turbo fan". Was a basic turbo fan engine without the cowling around it, kind of neat.
About 4-5 years ago there was alot of talk about Fan-jet engines that were a hybrid of turbofan/turboprop engines. They had 2 rings of 10-12 counter rotating blades that were larger overall than a regular turbofan, but smaller than a prop. It sort of bridged the efficiency gap between a prop and a turbofan. So not quite as high or fast as a turbofan, but faster than a prop plane and still quite efficient. I am not sure what became of them.
Unducted Fan (Ultra High Bypass)

Not so new.

GE proposed it in the 1980s or maybe even earlier. I don't know how far they went with development. Boeing proposed an airliner using the technology. (If you don't live in Seattle, Long Beach, or Tolouse you never hear about these stillborn ideas that appear about once a year.)

The upside: Supposed to be much more efficient than a ducted fan.

The deal-killer: Much noisier.
Re: Unducted Fan (Ultra High Bypass)

The upside: Supposed to be much more efficient than a ducted fan.

The deal-killer: Much noisier.

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The other downside is that passengers generally don't like to fly on a plane with props. Even though not technically a turboprop, thats what many passengers will see.
Re: Unducted Fan (Ultra High Bypass)

I heard that those things were not as efficient as the designers had originally hoped. Like things looked promising at first, but then after some testing they found that the efficiency gain was not worth it.

Only what I thought I heard somewhere, though. Anyone has specific numbers on how efficient it is?


John Herreshoff
Re: Unducted Fan (Ultra High Bypass)

The other downside is that passengers generally don't like to fly on a plane with props. Even though not technically a turboprop, thats what many passengers will see.

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As a turboprop pilot, I'm not sure that I agree with that statement. We do get the occasional prima donna who will complain about the size of the airplane, but these people also consider the CRJ to be a little airplane. The majority of passengers seem more concerned with:

(a) ticket price, and

(b) schedule

Most passengers, unless they travel frequently over the same route, don't even know what type of airplane they will be flying on.

I think that turboprops have two main disadvantages. They are noisy and, in many cases, uncomfortable. A cost efficient turboprop (or propellered) airplane with improved sound-proofing and passenger comfort items might be a huge success.

CRJs are nice, but on many regional routes they are just not efficient. It remains to be seen how popular they will be if operating a sexy airplane causes the airlines to make fewer flights to some destinations and be constantly oversold at others.