Are practical aircrafts dependent on carbon-based fuels?

[Gonzolo]

Is it concievable to build passenger, cargo and military aircrafts that run on something other than petroleum? I suspect electricity is out of the question because of the weight of batteries, but what about hydrogen? How does the the weight/energy ratio of hydrogen systems compare to that of common gas-kerosene engines?

What will aerospace engineers be working on when the world oil supply runs low?

 

[russ_watters]

Hydrogen/oxygen fuel has the best energy/weight ratio of just about any fuel (with the possible exception of aluminum/magnesium, but I'm not sure...). The problem is the density. Liquid hydrogen and oxygen are not very dense and as a reasult, require large fuel tanks. As first proposed, the SR-71 was going to be hydrogen fueled...and 300 feet long.

But there may be ways around this.

 

[Gonzolo]

I just checked that a 747 is about 150 feet long. The challenge to find alternative long distance travel systems seems quite interesting.

 

[Astronuc]

Fuels for aerospace; Fischer-Tropsch Synthesis

Are practical aircrafts dependent on carbon-based fuels?

Simple answer - yes. Primarily based on specific energy (i.e. heat of combustion per unit mass) and properties such as low vapor pressure, high flash point (safety issue), low viscosity (can be transferred easily), freezing/boiling point (won't freeze), etc at the ambient (operating environment) conditions.

Liquid hydrogen would require a cryogenic system and size could be large since the density is low (as already indicated). Then if there was a leak or accident (crash) - *BOOM* - remember the Hindenburg - and that was gas.

Diborane (B2H6) would be an interesting fuel, but it's flammability/explosivity is worse than LH2. Also CO2 is much better than borates in the environment.

What will aerospace engineers be working on when the world oil supply runs low?

Well before that starts to happen, the fuel suppliers will presumably have developed synthetic fuel processes - which may be expensive - but then fuel will become 'very' expensive when supplies become limited (Economic principle of 'supply and demand').

There are already chemical processes using Fischer-Tropsch sythesis (using FTS catalysts) which are used to produce aliphatic (light to moderate alkanes) using H2 and CO/CO2. FTS was first developed by two German chemists (Franz Fischer and Hans Tropsch) in the early 1920's.

see - http://www.encyclopedia.com/html/F/FischerT1.asp

http://themerckindex.cambridgesoft.com/TheMerckIndex/NameReactions/ONR139.htm

http://encyclopedia.thefreedictionary.com/Fischer-Tropsch synthesis

http://www.ecn.nl/biomassa/research/poly/fischertropsch.en.html

 

[ceptimus]

The Russians flew a nuclear fission powered bomber a few times. It had conventional jet engines as well for take off, but could cruise on nuclear power alone.

The problems were the pollution of the environment, and the difficulty of engineering sufficiently lightweight radiation shielding to protect the crew. The Russians 'solved' both problems by not caring too much about them.

 

[gschjetne]

Another thing: How would they cool the thing? I don't know much about nuclear reactors, but according to what I do know is that they use the heat to evaporate a liquid (H2O) and pipe it through a turbine. But where would they get enough water from? A huge air cooling system for liquid recycling would've generated extreme amounts of drag! Am I missing a different way of turning power from a reactor into torque or thrust?

And an irrelevant aviator remark: I'd rather stick with my carbureted reciprocating Lycoming, even if you threw a gas turbine at me. AVGAS100LL is a safe, reliable fuel, and recip engines are very agile, yet economical for light aircraft.

 

[LURCH]

The Russians flew a nuclear fission powered bomber a few times. It had conventional jet engines as well for take off, but could cruise on nuclear power alone.

The problems were the pollution of the environment, and the difficulty of engineering sufficiently lightweight radiation shielding to protect the crew. The Russians 'solved' both problems by not caring too much about them.

Do you have a link to that? I knew the US flew a bomber with a nuclear power plant inside, but the plane was never powered by the reactor. It just flew around on its regular jet engines with a reactor in the back reactoring away. This was to prove that we could, in preperation for a nuke-powered aircraft.

I didn't know someone had actually flown on reactor power. However, I do know of a small private plane flown on battery power (the batteries from a Prius, I believe). The next step the inventors plan is a feul cell.

 

[Gonzolo]

However, I do know of a small private plane flown on battery power (the batteries from a Prius, I believe). The next step the inventors plan is a feul cell.

Do you have a link to that?

 

[ceptimus]

Do you have a link to that? I knew the US flew a bomber with a nuclear power plant inside, but the plane was never powered by the reactor. It just flew around on its regular jet engines with a reactor in the back reactoring away. This was to prove that we could, in preperation for a nuke-powered aircraft.

I can't find much on line about this, but I saw a documentary on Discovery about it.

The documentary focused on the history of the B-36 (the American nuclear testbed that you described). At the end of the program was the 'shock news' bit - Russia had actually flown about 50 nuclear powered flights - not just tests with airborne reactors - back in the 70s. They saved weight from the planes by fitting only minimal radiation shielding. The crews had been selected from older air force members - they had all been badly irradiated, and only one member (I think) from all the crews was still surviving.

Maybe Discovery were hoaxing, or had been hoaxed themselves? Perhaps I have misremembered this - though it seems a pretty clear memory to me. Does anyone else remember seeing this program?

 

[russ_watters]

Batteries would provide a horrible power to weight ratio and poor endurance. A fuel cell, on the other hand, would probably be far superior to a conventional engine on a small plane. But it isn't without its problems.