[Kosh]

The point of this is that we can't continue to rely on fossil fuels for our transportation. For airplanes, other than kerosene, what else is there? Answer: At the moment nothing, because nothing has enough energy density, except nuclear which isn't used for other reasons.

So does anyone have other ideas for what can be used instead of fossil fuels?

[SypheDMar]

The benefits are great, but the only problem I have would be when a group of people decides to pull a 9/11. It may be safe for the passengers, but how much damage would it do to the ground? Several square miles seems a lot on the ground.

[NGTM-1R]

The classic answer to sustained thrust with a nuclear powersource has been something like a ramjet, only substitute "air piped through a nuclear reactor" for "bleeding ignited fuel into the jet." It's a fairly elegant solution, if you can make it work, as the limit on the system is how long until it builds up a dangerous amount of heat instead of any real need for an external fuel source. The problem is that reactors are safe because they are more or less closed systems. This system would be emitting god-knows-what into the environment.

[Mars]

It's like I said, Hydrogen is the only way to go, really, if you're looking for something remotely sustainable and safe. IIRC it has twice the energy density / mass of most fuels (assuming wiki isn't lying), but 1/16 the energy per volume. The obvious solution is a larger airframe, but then mass goes up. It seems like a problem that can be solved, and eventually, will need to be.

Nuclear powered plane = more stupid than nuclear powered truck.

[IceFire]

The point of this is that we can't continue to rely on fossil fuels for our transportation. For airplanes, other than kerosene, what else is there? Answer: At the moment nothing, because nothing has enough energy density, except nuclear which isn't used for other reasons.

So does anyone have other ideas for what can be used instead of fossil fuels?

Helium airships with charged batteries plus the latest in solar panels along the top to charge the batteries.  Its slow but the environmental impact is very small from what I know.

[NGTM-1R]

Nuclear powered plane = more stupid than nuclear powered truck.

Perhaps. But the unlimited range and possibly operating time sound pretty good, yes? If a way can be found to render it radiation-safe, then this is an incredibly appealing system. Unfortunately, that's probably going to mean waiting until viable small-scale fusion.

[Spicious]

Fusion tends to release dangerous particles too.

[Scuddie]

I say they need to bring prop planes back into circulation.  They are many times more efficient than jet fuel injection.

Either that, or have the turbine system should be driven by electric motors...  Though the kind of electric motor of that size is suspect to issues regarding power, stability, and reliability.  However, in conjunction with solar plates and a supplemental natural gas based generator, it would make for a MUCH cleaner and cheaper solution.

But then again, I don't know how well (or even if) heavy electronic components would hold up to the stresses of an airliner.

[Kosh]

The point of this is that we can't continue to rely on fossil fuels for our transportation. For airplanes, other than kerosene, what else is there? Answer: At the moment nothing, because nothing has enough energy density, except nuclear which isn't used for other reasons.

So does anyone have other ideas for what can be used instead of fossil fuels?

Helium airships with charged batteries plus the latest in solar panels along the top to charge the batteries.  Its slow but the environmental impact is very small from what I know.

We don't want it to take a week to go from one side of the pacific to the other.

I say they need to bring prop planes back into circulation.  They are many times more efficient than jet fuel injection.

But also have their own problems such as needing highly refined (read: expensive) fuel, and they are nowhere near as fast as a jet.

Either that, or have the turbine system should be driven by electric motors...  Though the kind of electric motor of that size is suspect to issues regarding power, stability, and reliability

The motor wouldn't be the problem, it would be the batteries. Their energy density just isn't enough and, to make matters worse, they wear out relatively quickly.

[Mika]

Regarding travelling times, what is your hurry? You would see a lot more on that single trip than nowadays!

Batteries then, take a look at the proposed hybrid cars and the weight of their batteries. Normal gasoline tank contains about 60 litres of fuel, it probably weighs something like 40 kgs (Stealth?), so that the fuel storage of average car weighs about 100 kgs. With this, it is possible to travel ~ 700 kms at the speed of 100 km/h. The electric or hybrid cars are quite a far away from that. Why is this relevant? Because the power demand in aircraft is actually higher, and more than ever, every kg counts!

Again, anything that has "nuclear" in it means radiation in many forms. And when photon energies get high, you need something dense to stop and absorb them (+ their residuals!). Unfortunately, anything dense is also heavy. Traditionally, that something dense has been lead, graphite and reinforced concrete. And since you cannot use open air reactors due to the pollution effects, reactor has to be a closed system, from which the power is then collected via heated water and turbines and is transformed to electricity. This will also require a lot of space, but also weight. Maybe the only alternative would be a nuclear battery if they happen to work. Even then you would have to fight hard with the weight and radiation protection.

The reason why I'm thinking more traditional engineered airliners is that even though USAF has proven the flying wing concept, nobody else uses it. The reason? I don't know, but I suspect it is a pretty good one.

Mika

[Mars]

Could the prop plane design be modified using existing technologies, making it slightly faster / more efficent?

[FreeSpaceFreak]

The reason why I'm thinking more traditional engineered airliners is that even though USAF has proven the flying wing concept, nobody else uses it. The reason? I don't know, but I suspect it is a pretty good one.

Some of the bigger airliner firms are working on a Blended Wing Body. (I haven't got time now to find a link, sorry). So it's likely that there will be 'flying wing' airliners in the (distant) future.

Could the prop plane design be modified using existing technologies, making it slightly faster / more efficent?

Yes, it can. It's called a propfan, but it's fairly new and unproven yet.

[IceFire]

Certainly with complex computer calculations you can make the propeller based engine better than anything they had during WWII ...but really there are limits to what a propeller can do. During WWII propeller design went incredible steps to the point of making some very efficient designs that from what I understand haven't changed too much since then.  We can do things with more precision now...but even back then they were really far along on this stuff.

Propeller based aircraft are still going to be nosier, with more vibration, and they simply won't be able to go as fast.

And yes an airship might take a long time but if it comes down to it and were desperate...we may have to "take several steps back".  The airships might be a very good way to do long distance cargo hauls.  I've read a bit saying that might be a possibility.  Travel time wouldn't be too much different than a ship.

[TrashMan]

I can see that used only for a NASA shuttle.

anywhere else - no.

[Kosh]

Regarding travelling times, what is your hurry? You would see a lot more on that single trip than nowadays!

On a modern 747 it takes 13 hours to go from San Francisco to Shanghai (or more if you have a head wind). What is there to see except endless amounts of ocean?

The airships might be a very good way to do long distance cargo hauls.  I've read a bit saying that might be a possibility.  Travel time wouldn't be too much different than a ship

In which case it would be more cost effective to simply send it on a ship. The reason people would send freight via an airplane is because even though it is much faster, and often time = $$$$$$$. So if the speeds are similar, why bother?

And since you cannot use open air reactors due to the pollution effects, reactor has to be a closed system, from which the power is then collected via heated water and turbines and is transformed to electricity.

Part of this is finding better radiation shields and part of it is smaller reactor designs. Right now the worlds smallest closed loop reactor system that I know of (made by Toshiba) is 20 feet by 6 feet.


EDIT: Whoa, just recently discovered this gem describing the Air Force's attempt to build a nuclear power bomber. Evidently they had some success and it looks pretty promising. Check it out.

[Mika]

On a modern 747 it takes 13 hours to go from San Francisco to Shanghai (or more if you have a head wind). What is there to see except endless amounts of ocean?

[Sales pitch]
Tired of growing risk of heart attack due to bad lower body blood circulation? Annoyed about the jetlag in the destination country? Cannot get sleep in the aircraft? Why risk your health in a long non-stop flight? Spend a couple of days in the beautiful tropical islands of the Pacific Ocean! Bask in the glory of the sunshine, experience interesting people and local delicacies! Order your tickets today!
[/Sales pitch]

{Man, I'm getting good at this. I almost don't feel dirty anymore. Anyone note the obvious deficiency of this approach, by the way?}

Part of this is finding better radiation shields and part of it is smaller reactor designs. Right now the worlds smallest closed loop reactor system that I know of (made by Toshiba) is 20 feet by 6 feet.

Isn't this similar to the nuclear battery by Los Alamos research groups? What is the weight of that system?

Regarding the nuclear powered bomber, there are a couple of things to note: the aircraft where the reactor was fitted is large even by today's standard. But, it took away a lot of payload of the aircraft, and required quite a bit of shielding around the crew compartment. According to my understanding, the crew was restricted pretty much in the cockpit of the aircraft. This means that in order to use the reactor in current airliners, one would need to add a lot more of the shielding since the passengers must be protected also = more weight.

I'm not that hopeful on finding new materials to block radiation. Asking for a dense but light weight material sounds like a physical impossibility. Even if that could be done, the next question is price. These aircrafts should be commercially viable, after all.

After browsing through some introductory articles of the blending wing, I'm starting to see why it is taking long. First is flight control, indeed the blended wing design functions more like a fighter aircraft, being unstabile and all. Judging by some of the reports, turbulence has proved to be pretty difficult in these cases, and sometimes the test models have experienced great accelerations (in non-intended directions) in these conditions. Though I'm curious to see a large aircraft in a deep stall.

Second thing is the pressurization of the compartments. Current airliners use cylindrical hull to equalize the pressure differences around the passenger cabin, but in blended wing the cabin is not cylindrical, which will stress the airframe differently in different places. Some researchers are placing hope for computer aided design to find the difficult places in the cabin, some are working with new materials. Though I'm a little sceptical about the new materials. Of course it is possible to find them, but at commercially viable price?

Mika

[ssmit132]

No. The one thing that counts in radiation shielding, is mass. AFAIK. The one thing that counts in airplane design, is also mass. The Soviets did it, yes, but they had so little shielding that after a couple of years, most of the crews that flew it were dead.

The Americans converted a B-36 to carry a nuclear reactor, and it had all the shielding required. Of course, that meant that it needed a crapload of engines (It had a combination of jets and props, IIRC). (My bad, all B-36 had jets and props.)

In May 1946, the Air Force began the Nuclear Energy for the Propulsion of Aircraft (NEPA) project which was followed in May 1951 by the Aircraft Nuclear Propulsion (ANP) program. The ANP program required that Convair modify two B-36s under the MX-1589 project. One of the modified B-36s studied shielding requirements for an airborne reactor to determine whether a nuclear aircraft was feasible. The Nuclear Test Aircraft (NTA) was a B-36H-20-CF (Serial Number 51-5712) that had been damaged in a tornado at Carswell AFB on 1 September 1952. This plane, designated the NB-36H, was modified to carry a 1 MW, air-cooled nuclear reactor in the aft bomb bay, with a four ton lead shield between the reactor and the cockpit. The cockpit was encased in lead and rubber, with a 6-inch (15 cm)–thick acrylic glass windshield. The reactor was operational but did not power the plane; its sole purpose was to investigate the effect of radiation on aircraft systems. Between 1955 and 1957, the NB-36H completed 47 test flights and 215 hours of flight time, during 89 of which the reactor was critical.

[Kosh]

Regarding the nuclear powered bomber, there are a couple of things to note: the aircraft where the reactor was fitted is large even by today's standard.

True, but then again the reactor was also designed and built with late 1950's technology, surely we have progressed at least a little in that regard.

I'm not that hopeful on finding new materials to block radiation. Asking for a dense but light weight material sounds like a physical impossibility. Even if that could be done, the next question is price. These aircrafts should be commercially viable, after all.

Radiation can also be reflected, right? So maybe it's not a question of piling on more lead but rather using some kind of crazy nanoscale engineering on what we've already got to reflect it.

[Slasher]

And yes an airship might take a long time but if it comes down to it and were desperate...we may have to "take several steps back".  The airships might be a very good way to do long distance cargo hauls.  I've read a bit saying that might be a possibility.  Travel time wouldn't be too much different than a ship.

Issues like the one raised above make me uneasy about the complications fossil fuel scarcity presents.  If things do get that desperate, I fear air travel may be more dispensable than we thought.  Intercontinental trade is heavily dependent on ships, more so than airplanes in terms of both monetary value and tonnage, and they too thrive on the readily available hydrocarbons found in petroleum.  At the end of the day, goods such as grain, shipped in bulk via freighters, demonstrate how keeping these ships running is essential to feeding countries that rely on imports for their food.  Even if the worldwide merchant fleet is able to replicate the U.S. Navy's record on nuclear safety, we still have the issue of distributing product once it reaches land.  Trains can go electric, and that electricity can be provided by nuclear reactors too, or renewable power sources where applicable.  But trucks are another problem.  As mentioned before, current battery technology is not yet up to the task of hauling around 40 tons of trailer.  Having observed what ethanol production entails, we should hope that a more environmentally and economically sound solution is developed.

It will be interesting to see how we answer the question of air travel in the coming decades.  Personally I wonder if synthetic fuels are the answer, or if we can reduce the chances of miniature Chernobyls happening such that nuclear powered planes are viable.  I like the blimp idea.

[Kosh]

or if we can reduce the chances of miniature Chernobyls happening such that nuclear powered planes are viable.

If we could make a black box survive almost any wreck, surely we could with a reactor, add to that an automatic shutdown routine when the plane gets to a certain distance from the ground.