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Up until the 1930's lighter than air aircraft were the preferred method of long range air travel. This was due to the relatively low power to weight ratio's of contemporary aircraft engines, and their poor fuel economy. A lighter than air airship (blimp, Zeppelin or other LTA craft) displaces the air and is therefore not dependent on the power of the engine for lift. A relatively low powered engine (or engines) will do for most flight regimes.

However, since engine technology isn't advancing very rapidly in this timeline, the various world military forces have concluded that long range bombing missions will have to be done by airships. Of course, a long range airship bomber will need to go very fast in order to reach targets in an acceptable timeframe and to evade enemy fighters. Looking at the situation, the problem seems insurmountable, or is it?

Reaching targets quickly and evading enemy fighters will require the airship bomber to move far faster than any existing aircraft, and also fast enough to evade detection by air observers and anti aircraft cannon on the ground as well. Some advanced thinkers believe the airships need to travel at over 1236 KPH, the speed of sound in the atmosphere! While no engine or combination of engines and airscrews seems capable of performing these feats, advanced thinkers in a few nations think otherwise:

In the United States, the US Navy is aware of Robert Hutchings Goddard and his experiments with liquid fuelled rockets. The new Chancellor of Germany has been briefed on the activities of the VfR (Verein für Raumschiffahrt), and in the Soviet Union, rocket research is being carried out by GRID (Group for the Study of Reactive Motion). Rocket research isn't as advanced in the British Empire, but there is this Frank Whittle chap working on what he calls a "jet" engine.

While flying the entire profile at supersonic speed is perhaps a bit ambitious, how can our various military forces achieve at least supersonic dash speed over the target with a lighter than air long range bomber? Assume generally 1930 era technology for the airship, propulsion systems and bombs and bombsights, but some handwaves are acceptable.

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    $\begingroup$ Try running with a helium balloon trailing behind and you will soon see the problems with making such a vehicle economically viable. $\endgroup$ – Zxyrra Dec 19 '16 at 5:33
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    $\begingroup$ With supersonic speed you no longer need neither wings nor buoyancy. nasa.gov/topics/history/M2_F1.html $\endgroup$ – Mołot Dec 19 '16 at 6:36
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    $\begingroup$ @Mołot more to the point; "supersonic buoyancy"? That isn't a thing. Supersonic air flows as a compressible fluid, for which density is non-constant. $\endgroup$ – Aron Dec 19 '16 at 8:00
  • $\begingroup$ Ben Bova got there first with his short story "The Great Supersonic zepplein Race". Originally published in THE FAR SIDE OF TIME (1974) and reprinted in his collection MAXWELL'S DEMONS (1978). Bova said the idea began with a lunch where two aerodynamicists tried to pull his leg about a SSZ & ended up convincing themselves the idea was solid. As a bonus a SSZ won't generate a sonic boom. $\endgroup$ – a4android Dec 19 '16 at 8:40
  • $\begingroup$ Do you have a description of how this would have worked? $\endgroup$ – Thucydides Dec 19 '16 at 15:26
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Aside from the fact that it's basically impossible even with modern-day technology to build a supersonic lighter-than-air bomber, if your military forces did have that sort of technology, they would be far better served by using that technology to build a conventional, heavier-than-air bomber that was far more capable, far simpler, far less vulnerable, and far more reliable, or just build a ballistic missile that could get the job done instead.

There's a reason the Germans stopped using Zeppelins for military purposes, and it wasn't because of restricted access to helium. Airships are slow and have low service ceilings, and even as early as WWI, they were incredibly vulnerable to ground fire or air interception. With 1930s-era or early WWII technology, fighters would have flown circles around them, and anti-aircraft gunners on the ground would have destroyed them handily. Plus with the development of radar in that that era, Zeppelins would have been visible from extremely far out, giving defenders plenty of warning and guaranteeing that their targets would be ready and waiting.

What might be feasible would be to have your airships act as "carriers" or "motherships", making the long-distance journey at much slower speeds (the Zeppelin bombers used in WWI had a cruising speed of ~40 mph), and then deploying long-range rockets like the V-1 or "parasite" bombers that would then attack the target at high speed. However, this could be countered by screening targets with long-range patrol craft and radar screens, allowing for interception before the Zeppelins get into launch range.

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With speed you do not need buoyancy

The one advantage that airships offer over winged aircraft is that airships do not require speed to fly while airfoils do. And for a short while in history, this meant that airships could lift more than aircraft because engines were not powerful enough to propel an aircraft that could lift as much as an airship at the speed required to lift it.

But from the time there were engines that could propel aircraft that could carry 10 tons or more, airships offered no advantage over fixed wing aircraft(*). To haul 10 tons, why spend a crew of 40, flying at 10 000 ft and 130 kph, when you can carry the same cargo with a crew of 11, at 30 000 ft, at a speed of 570 kph?

Static lift has its uses. But once you can attain an airspeed of 200 kph or more, airfoils will beat aerostats every time.

(*) ...with the one exception of immense passenger comfort and luxury

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  • $\begingroup$ So dynamic lift would be the key to higher speed flight, then. Assuming there are no engines capable of the performance you set (the reason for this in the first place), how would you rearrange the envelope to provide both static (at low speed) and dynamic (at high speed) lift? $\endgroup$ – Thucydides Dec 19 '16 at 15:33
  • $\begingroup$ "So dynamic lift would be the key to higher speed flight, then" I am sorry... what?! No, the other way around: speed is they key to dynamic lift, and dynamic lift is vastly more efficient than static lift. This is why you do not see many helium- or hydrogen-birds but instead only the plain old flappety-flap variety. Once you have enough speed to do dynamic lift, static lift is just a waste of effort, and since the premise of the question was that you wanted a super-sonic craft... then the answer is: no... no super-sonic zeppelins. There is nothing you can do to make it worth the effort. $\endgroup$ – MichaelK Dec 19 '16 at 22:21
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Airships fly using lighter-than-air gas, mostly hydrogen or helium. The difference in weight is large in relative terms, but small in absolute terms. They need a lot of gas for their weight.

A large volume means a large surface area. A large surface area means a lot of drag. Shapes and materials can mitigate this effect, but they cannot solve it.

To overcome that drag, the airship needs powerful engines. The F-104, the F-15, and the F-22 have roughly half as much afterburning thrust as their loaded weight. Airships would need no drag-producing wings and they would benefit from the square-cube effect, but that probably won't be enough.

If there are supersonic airships, they are big.

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  • $\begingroup$ +1 from me. So basically you're saying that OP got this backwards and he needs more advanced engines, not less advanced ones? $\endgroup$ – Mołot Dec 19 '16 at 7:09
  • $\begingroup$ @Mołot, I believe that airships over 200 mph are unnatural, whatever the tech. There is a reason why everybody went to heavier-than-air. $\endgroup$ – o.m. Dec 19 '16 at 7:10
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I'm no expert in aviation, but based on the first supersonic flight (The Bell X-1) try something like this (as far as I can tell you will however need some handwave to preventing the thing form either exploding or tearing apart as soon as acceleration starts):

  • The ship would have a solid frame and a hard outer shell. The gas bags contained within.
  • To reduce drag, the gondola should either retract into the superstructure, or be internal in the first place.
  • The superstructure must not only be as aerodynamic as possible, but also capable of withstanding the g-force inflicted during acceleration. The gas bags must also be strong enough not to burst.
  • Stabilizing wings and a tail (So that the ship doesn't corkscrew as soon as the jet/rocket starts).
  • Rear mounted rockets/jet engines for mach-1 bursts, and retractable props/screws for standard flight.

You could make it a teensy bit more believable by having these ships take massive damage when performing a mach-1 burst, only using it in dire emergencies or to deliver their payload before going down*.

*In fact using smaller suicide airships of this design (manned or unmanned) would make an interesting anti-bomber defense.

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I don't think supersonic airships are viable, but with bad engine technology flying really high up is a good way to protect yourselfes.

Airships can reach high altitudes with quite small and weak engines, if they have a lot (really big) of space for gas and have good presure resistance. The relevant formula for the size is (p*V)/T = const. As an extreme example the Explorer-II.

Having such a big size will make them quite visible though so long range armament might be a threat.

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