Aviation Fuels

[GTX]

Hi folks,

It is a common enough discussion point today, but rarely one that is discussed in relation to combat aircaft:  What would be the result if there was a major Oil crunch (ie the use of oil based fuels needed to be severly curtailed).  Specifically, what sort of design changes could we expect to see if the major combat aircraft of the world needed to change over to something like Hydrogen/Methane or something similar (ie something probably requiring more volume)?

Some of the possabilities I can see are:

• Large external tanks or conformal tanks (like the F-16E/F)
• Large bulges like some of the cyrogenically fueled airliner derivatives - think A-4 hump but for fuel;
• Increased use of UCAV thereby avoiding many training flights;
• Increased use of missiles - only to be fired in case of war;

What others do you see?

Regards,

Greg

[Madoc]

Greg,

Hydrogen offers the best bang for the buck, at least in terms of pounds of fuel required for pounds of thrust achieved.  However, Hydrogen is about the worst fuel from a volume perspective.  You need absolutely huge tanks for the equivalent fuel load of a JP4 fueled machine.  Back in the 70's I saw some provisional studies drawn up for switching jetliners over to hydrogen fuels.  These were illustrated in an issue of Aviation Leak & Space Mythology.  The planes looked for all the world like winged dirigibles.  Or perhaps passenger carrying Super Guppies.  The tanks were that huge.

I dunno about methane as far as its volume goes.  I do know that both hydrogen and methane tend to have some pretty undesirable materials effects.  Methane, if I recall correctly, as used in air racers has to be flushed out of the plane's engine and fuel system at the end of each flight lest it corrode everything through.

Hydrogen is different.  As Hydrogen is so atomicly small it will seep through _anything_ it's place in.  Aside from being bad from a tankage perspective, this seeping also changes the material properties of the containment medium.  In metals this makes them very weak.  "Hydrogen embrittlement" is the term and it can lead to metal tanks shattering or fracturing even after they'd been drained and come up to room tempurature.  Thus, Hydrogen is a pretty exotic fuel in and of itself.  Just imagine trying to maintain the fuel gaskets over time on any jet engine using the stuff!

Madoc

[Leigh]

Ethanol?
and some people are running cars on corn oil now too.

[GTX]

Madoc,

I agree with what your saying re hydrogen - its volume and other features make it difficult (though not impossible) to easily accomodate in aircraft.  Here are some pictures of Russian experiments/concepts for hydrogen/other cyrogenically fuelled airliners to give an example of what results:








In the extreme, the aircraft could end up carrying vast external tanks like these from Myasishchev (though in these cases the tanks are just cargo):


Perhaps the best compromise if something such as Hydrogen were to be used would be something akin to these BWB tanker concepts from Boeing:




However, whilst these may be acceptable for tankers/transport and derived aircraft would it be acceptable for combat aircraft?  Could we see a resurgence in interest for designs such as the A-12 that offer large internal volumes:



More ideas to follow.

Regards,

Greg

[GTX]

or perhaps a system where large transport aircraft (able to offer the volume to carry  the necessary fuel) carry fleets of smaller, short range UCAVs that do the actual bombing/shooting - somewhat akin to the FICON concept or some of the FOAS concepts:





or maybe combat aircaft will develop into something more akin to the Boeing ABL:



As for Ethanol and other bio-fuels, the requirement for vast aggricultural support systems is a major hurdle, though again not a necessarily insumountable one.  Either way, the design and use of combat aircraft would need to be carefully considered - hence my interset in starting this discussion (I am considering some what-f models in relation to it).

Regards,

Greg

[GTX]

Another option would be to use electric motors (perhaps powerd by solar boosted fuel-cells) driving propellors or ducted fans.  This could see a resurgence of retro-prop designs of the late 1940's/50's (Thunderscreech anyone?) or perhaps something more advanced like a military version of the Pond Racer:




Other ideas?

Regards,

Greg

[GTX]

Madoc,

I dunno about methane as far as its volume goes.

Whilst not necessarily exact, this picture from Bill Sweetman's "Aurora" book gives an impression of the volume requirements for JP-4, Methane and Hydrogen:



Regards,

Greg

[GTX]

Another option (though unlikely) could be a return of the nucleared powered aircraft concept - though again, probably only for larger aircraft.

Regards,

Greg

[Son of Damian]

Another option would be to use electric motors (perhaps powerd by solar boosted fuel-cells) driving propellors or ducted fans.

Hydrogen fuel cell technology could also be used for propellor or ducted fan powered aircraft, I think. And if the price of the technology becomes more affordable in a year or so and the price of oil doesn't drop you could see a significant return to propellor driven passenger aircraft.  

[overscan]

Just think how big flight refuelling tankers will need to be!

Of course, there is always nuclear power as well....

What about a fleet of giant dirigible tankers with nuclear engines, that take in water from the atmosphere and turn it into hydrogen?

Like a set of 24 hour gas stations in the sky...

Your hydrogen planes then take on board the hydrogen from the dirigible, reducing the amount of tankage required.

[Hobbes]

Methanol in itself isn't that corrosive, IIRC the problem is that methanol always contains some water.

I think methanol, ethanol and biodiesel are better choices than hydrogen, because they have a higher power density and are easier to store. Aircraft using these fuels wouln't look different from current designs.


If all else fails, we can always go back to the coal-fired designs the Germans dreamed up in WW2.

[MartG]

Jules Verne rules !  

[BlackOps]

Are we still technologically too far away from orbiting satellites than can pop terrestrial targets?

How sucky would it be to get zapped from space for jaywalking?  


Jeff G.

[GTX]

Are we still technologically too far away from orbiting satellites than can pop terrestrial targets?

As in the "Rods of God" concept:




or the Space Based Laser:



Possible - but does that mean you would forsee all combat aircraft becoming obsolete in the csase of a need to move away from oil based fuels?  I guess in this discussion, I was trying to consider the combat aircraft changes if oil based fuels weren't available - I hope to incorporate these possabilities into some what-if models I am thinking of.

Regards,

Greg

[GTX]

What about a fleet of giant dirigible tankers with nuclear engines, that take in water from the atmosphere and turn it into hydrogen?

I like it - I may incorporate this into my idea for a modern aircraft carrying airship using UCAVs and UAVs.  These would use a version of the Skyhook that British Aerospace experimented with the Harrier. My idea is to have the UCAVs having some sort of VTOL or at least hover capability and being captured by the Skyhook. If manned aircraft were carried, they would also need to utilise this approach. As for small UAVs, they could be captured using a net or such. These approaches avoid the problem of speed differential between the airship and the aircraft.

The airship would also fitted with inverted vertical launch tubes with long range air-to-air and air-to-surface missiles (kind of like a flying Arsenal Ship) and maybe even a version of the Airborne Laser Weapons System.  Last but not least the airship could carry a large compliment of sensors.

Regards,

Greg