Then it would appear we’ll have to switch to airships sooner or later, for all air-travel needs but those where speed is of utmost importance. Unless somebody can figure out a way to fly a jumbo jet on propane, coal, hydrogen or plutonium.
A full 747 delivers something like 40 passenger-miles per gallon. I doubt any current airship can match that.
The airship may make a comeback in a very unexpected way - as a spaceship. JP Aerospace is working on a design for a large V-shaped blimp called the ‘Ascender’ that will use bouyant lift to get it up very high (140,000 ft ). One proposal is to have a suborbital inflatable ‘space station’ at that altitude - above 99% of the atmosphere, out of the weather, and permanently stationed.
From there, an even larger airship (like, a mile long so that its density is low enough to be bouyant even in the hyper-thin air on the way to orbit) with electric engines would transition to orbit. The engines will begin to accelerate it through the thin atmosphere. The vehicle has a lifting body shape, so the combination of bouyant lift and aerodynamic lift takes it higher and higher, while it goes faster and faster, until eventually it’s completely out of the atmosphere and in orbit.
To come back, it does the opposite. Very, very gradual deceleration (I think it takes days to get to orbit and days to get back), with a slow transition back to atmospheric flight. Since the transition happens very gradually, no heat shields are required, and the whole process is very safe. And it can haul a LOT of cargo.
It’s a very cool idea, and I think they’re already flying a prototype (non-space going). These guys are serious, and have big time funding from the U.S. Navy and private funds.
I’ve done some digging and found some info on rigid airship fuel consumption.
May 17-20 1937 the Hindenburg flew from Frankfurt Germany to Lakehurst, New Jersey. Total flight time was 78.5 hours and 4500 miles (7238 kilometers). They used a total of 41,110 kilograms (90632 pounds) of diesel fuel, which is about 12765 US gallons.
There were 41 passengers, so that works out to 14.45 passenger/miles per gallon. With a full load of 72 passengers, that would be about 25.4 passenger/miles per gallon.
The USS Macon was a US Navy airship, so it didn’t carry passengers, but it was close to the same size (6,850,000 cubic feet to the Hindenburg’s 7,062,000 cf). On the Macon’s 110,000 pounds of fuel (15,500 US gallons), it’s range was:
Speed in Knots…Hours…Range in Nautical Miles
…70…68…4760
…65…75…4855
…55…108…5940
…46…158…7268
So at it’s cruise speed of 55 knots (63.3 mph), the range was 5940 Nautical miles (6819 miles).
These figures are for seventy year old aircraft. Presumably a modern airship built with 21st century technology could be a lot more efficient, but I don’t know if it would equal the 747 numbers or not.
Figures are from the Airships Akron and Macon by Richard K. Smith and Graf Zeppelin & Hindenburg by Harold G. Dick and Douglas H. Robinson.
Aeschines: I was talking about a cruise experience, which I, based on the numbers I gave, think will never work.
Depends on the scale you’re talking about: what is a balloon ride but a short, local, cheap airship cruise?
See, now here is a case where a Hindenburg-type disaster might actually have been a positive boon. I can’t imagine that Lowell Thomas would have cried out, “Oh, the slickly produced glossy catalogs! Oh, the Valpaks and Pennysavers!”
Short - yes. Local - usually. Cheap - not very: typical cost of a balloon flight lasting 30-45 minutes is something like $150 - $200 / person.
BTW – does anybody know – is it possible to design a jet airplane to run on some non-petroleum-derived fuel? Propane? Hydrogen? Coal?
Quite a few hobbyists run their homebuilt jet engines on propane.
They do? I thought those little propane-powered model planes were all prop engines – I’ve never seen a jet!
I can see no reason why it should be difficult to get a jet engine to run on any easily atomized fuel, so propane and hydrogen should be no problem. Coal would require some sort of gasification.
A thornier problem might be carrying suitable quantities of these fuels. Safe pressure vessels tend to be heavy, expensive or both.
(And is propane not petroleum-derived?)
I’m not familiar with the model jet engines. I was referring to these turbocharger based engines that people like to build. It’s a great deal easier to run one on propane than to properly inject diesel or gasoline.
Do these engines propel airplane? Or what?
Just out of curiosity, were they making an attempt for the X-Prize?
None that I’ve seen. Most are mounted on runup stands and go-carts.
A **jet-**powered go-cart? What’s the point?
Never mind – is there any way one of these miniature propane-powered jet engines could be scaled up to propel an airliner?
Because if it can’t be – and if neither can an airliner be propelled by hydrogen, coal, plutonium, or anything else that we’re not going to run out of within the next 50 years – then, as I said above, sooner or later we are going to have to switch to airships (most likely powered by electric motors charged by propane-burning generators, as Bosda described) for all air-travel needs but those for which speed is of overriding importance.
Wouldn’t that be sumpin’!
A jet engine can burn all sorts of stuff. Jet fuel is kerosene, similar to diesel fuel. In a pinch, different fuels can be used. The difficult part will be getting the fuels to work with the delivery system. Don’t want to gum up the pipes. Some engines, like the GE CF6 are designed to be fed standard gasoline if necessary.
But you want to use a fuel that delivers lots of energy per unit weight, since this is an aircraft we’re talking about.
Asterion asks:
Nope. Their technology is not suitable for suborbital flight at all. Their smaller ‘ascender’ balloon can get up to about 140,000 feet, which is not quite halfway to space. From there, to get a balloon higher it needs to have ultra-low density and secondary propulsion. Such a balloon would have to be built in place, since it would never survive a trip through the atmosphere (it will be very light, and very large - a mile long). So they’re not talking about doing this in a year, or even five.
I think the company’s plan right now is to sell their permanent platforms at 140,000 feet which can be used for military purposes, weather reporting, communications relays, etc. But once they have such permanent floating platforms they can work on building the giant balloon that would float/fly to orbit.
I doubt if you’d see one within ten years. But it sounds like it’s at least possible, and if it is, it would lower the cost to low earth orbit by a couple of orders of magnitude.
Does that rule out coal? Or hydrogen? Or propane?
I think coal would be ruled out for lots of reasons, unless you processed it into something else before you left the ground. I don’t know about propane and hydrogen.