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External combustion aircraft engine

not quite a rocket
  (+8, -7)
(+8, -7)
  [vote for,

Conventional aircraft could be made more exciting.

If there was a sufficiently large surface area on the back of an airplane fuel could be pumped and dispersed into the air and there ignited into a continuous fireball, pushing the craft along.
I'm not proposing a rocket engine as a rocket engine works to shape the expanding exhaust. This craft would simply squirt fuel into a fine constant mist behind it.
Voice, Oct 25 2010

"Zippo" http://www.strangem...es/content/8831.jpg
[DIYMatt, Oct 25 2010]

Cool video of the above process http://www.youtube....IHs&feature=related
[doctorremulac3, Oct 25 2010]

Project Orion film http://www.youtube....watch?v=E3Lxx2VAYi8
[coprocephalous, Oct 27 2010]

Ayaks http://en.wikipedia.org/wiki/Ayaks
As nutty as this seems, apparently a prototype was "demonstrated" in 2001 [BunsenHoneydew, Oct 31 2010]


       Well, yea. I guess if you call slowly rolling along the runway being incinerated by that fireball roaring away behind you exciting. To get any movement at all, you'd have to get that uncontained fireball really big and at that point you've got another cooked passenger scenario. Exciting for the people on the ground maybe, not so much for the people in the plane.   

       So it's not quite a rocket so much as a slowly rolling fire blasting death machine.
doctorremulac3, Oct 25 2010

       Is this idea in sarcasm? Because it's baked. Afterburners [they're called that for a reason] work by spraying a mist of fuel directly behind the engine creating a continuous fireball. Also look what the F111 can do in that link!
DIYMatt, Oct 25 2010

       Well, an afterburner or "reheater" as the British call it actually sprays additional fuel in downstream of the turbine behind the initial fuel ignition point but it's still contained within the pipe of the engine. Otherwise, you wouldn't be able to tap the reaction to the fast escaping gas to provide additional thrust.   

       I think the jet in the picture is dumping fuel into it's exhaust stream where it's burning but not providing any additional thrust. This might be done to minimize the amount of fuel onboard that could add to the hazard of landing a plane damaged in combat for instance, but many jets, including passenger jets have this capability. Passenger jets don't burn it as they dump it though.   

       Cool shot anyway. (see link of the video version)
doctorremulac3, Oct 25 2010

       You could put a big flat back side on an airplane, and make fuel-air explosions/combustion in the air behind it, and maybe even get a boost from doing so. But you'd still be shoving the front side of the big, flat back side through the air, and wasting most of the oomph of your fuel.   

       Pretty it might be, but efficient, not hardly.   

       The idea is not a radical departure from current practices, it is just off at the wrong end of a well-known efficiency spectrum. Generally, compressing the incoming air as much as possible is done. Extracting the maximum energy from the combustion involves controlled expansion, the very opposite of this idea.   

       This idea is sort of like jet afterburners, which are incredibly wasteful, but it is worse in wastefulness and in thrust. It is also a bit like the nuclear Orion spaceship drive, which is done in a vacuum and is also wasteful. It is also a little like the aerospike rocket engines, which are slightly wasteful and only really start working at supersonic speeds.
baconbrain, Oct 25 2010

       In the case of the Orion concept, which is where you blow up a series of nuclear bombs behind a shock absorbing plate, this would work because of the massive energy you've got to play with and the impossibility of containing the nuclear explosion in a contained area.   

       Wouldn't be welcomed at most airports though.
doctorremulac3, Oct 25 2010

       // slowly rolling fire blasting death machine. //   


       // Wouldn't be welcomed at most airports //   

       Baghdad ?
8th of 7, Oct 25 2010

       I worry about troubles steering a plane powered in this way. One could do a mockup using a remote controlled car and a series of M80s or other explosives. That sounds like a concept for Mythbusters if ever there was one.   

       After the success of the prototype it will be a car in neutral, steered with Adam's remote control, a huge flat plate behind it, powered by successive blasts of dynamite.
bungston, Oct 25 2010

       "Can you make a car powered by dynamite?"   

       Ratings gold. I'll put the letter together.   

       Dear Mythbusters,   

       I'm writing on behalf of a small group of science aficionados who frequent a online forum where we propose and discuss various ideas and inventions ranging from practical to absurd. In one thread we were talking about the Orion project which was a spaceship concept that proposed using a series of nuclear explosions detonating against a shock absorbing plate to propel it through space.   

       I had the totally original idea without any help from Bungston whatsoever to have you guys see if a smallish remote control car could be powered by a series of explosions from dynamite or other explosive being dispursed from the car and detonated against a shock absorbing back plate to provide forward movment.   

       One approach would be to simply have a few dozen sticks of dynamite in some metal grid or honeycomb arrangement so they're seperated from one another such that they might be detonated in sequence without causing the whole thing to blow. But if it didn't work, hey, big explosion, ratings gold, everybody wins.   

       If the remote control gear proved to be too expensive, perhaps an ancillary character on the show like a cameraman or sound technician could drive the car so nobody important would get hurt.   

       Signed, Doctorremulac3 on behalf of the fun folks at halfbakery.com.   

       P.S. Please don't publish our web site name. We don't cotton to outlanders.   

       Any suggested edits? Once approved I'll send it in. I'm super cereal about this.   

       (Just kidding about the credit Bungston, but it would be funny to leave it in.)
doctorremulac3, Oct 25 2010

       I think Buster is the ancillary character usually charged with such matters. Suggest he wear a helmet. Otherwise exactly as is.
bungston, Oct 25 2010

       You got it B. I haven't logged on to that site in years but if necesssary I'll re-register to send it in.   

       I'll keep you posted. Cross your fingers.
doctorremulac3, Oct 25 2010

       As [baconbrain] said, this is like Project Orion, with smaller explosions. Why would anyone want *smaller* explosions in a thing like that?
mouseposture, Oct 26 2010

       // I'm not proposing a rocket engine //   

       Well, yes, you are, just a very badly designed one. [-]
BunsenHoneydew, Oct 26 2010

       Rather than burn fuel out of the back of the plane, how about doing it out of the front? Would it be feasible to burn away the atmosphere in front of the plane and create a vacuum that would suck it along rather than going for the boring old propulsion model? If it was possible (unlikely I suspect) then you would have the additional coolness factor of constantly flying through a Star Wars-type explosion.
DrBob, Oct 26 2010

       "burning away the atmosphere", if it were possible (which it isn't) would create high pressure, not vacuum.
DIYMatt, Oct 26 2010

If it were possible to super-heat air at a constant distance in front of the aircraft, say using fucused microwaves, then that hot air pocket would be less dense than the surrounding air for a short time and cause less drag no?
So a continuously collapsing advance fireball should have the same effect if its distance scales up according to the crafts speed I would think.

       Too close, you get push. At the right distance you should get sucked along in the wake of the collapse.   

       [-2fries] - what you've (re)invented is called "supercavitation" (q.G.); it's doable in water, but might (given lack of a phase-change) be more problematic in air.
lurch, Oct 26 2010

       I was thinking about that at work yesterday. Supercavitaion would be difficult in air because of how less dense fluid air is than water right? So in the vacuum of space it would not be possible at all without expanding space itself, but if we could create non-sustaining singularities which dissipate on their own at a set distance from a space craft, would it be possible to surf the wake of this series of contractions of space?   

       ps. what does (q.G.) stand for? The closest thing I could find that might fit is Quantum Geometry.   

       Back in olden times, you'd see the abbreviation "q.v.", for the latin "quod vide" ("which see") as an invitation to look something up. I assume a more modern version of that should be "quod Google", hence the usage.
lurch, Oct 27 2010

       I am overwhelmed with mixed emotions related to the q.G. concept and lurch's invention and use of it without antecedent explanation. I think "marvel" sums them up. Thank you, 2 fries, for calling it out or it might have passed unnoticed.
bungston, Oct 27 2010

       If you google the term "quod Google" there's quite a number of hits. It's on Urban Dictionary with a 2006 date. Quite a few people have come up with it independently. However <buffs fingernails on shirt> my first use of it here on the HB was in 2003, so I was likely an early adopter.
lurch, Oct 27 2010

       Please click on the link coprocephalous put up about the Orion project. It's extremely good.
doctorremulac3, Oct 27 2010

       //could be difficult in air because of how less dense fluid air is than water right//

Hmm! So if we can come up with a method of making the air around the body of the aircraft more dense then would that give it a bit more incentive to zoom through the explosions occurring at the front?
DrBob, Oct 27 2010

       Precisely. And when we spot the physics flaw in that hypothesis, we'll get back to you.
8th of 7, Oct 27 2010

       //So if we can come up with a method of making the air around the body of the aircraft more dense then would that give it a bit more incentive to zoom through the explosions occurring at the front?//   

       I'm confused by that. When I run the simulation in my head I see the craft taking the brunt of the initial shockwave. The shockwave of each subsequent explosion will be at least partially cancelled when encountering the preceding shockwave but the collapse would remain just as powerful. Is this thinking wrong?   

       Isn't this how some of the more experimental ram/scram-jets work?
zen_tom, Oct 28 2010

       Could you not use a shaped charge, so that none of the force of the explosion goes towards the craft? It would have to be an annular force, because we want the explosion to be symmetrical otherwise the charge would be propelled towards the craft. I am imagining the explosion spewing out a kind of annular mushroom cloud, which would suck everything in towards the centre along the axis - on which is our craft.
pocmloc, Oct 28 2010

       If a jet engine simply compresses air, adds fuel, before igniting it and then squirting it out the back (which they do) and if pulse-engines work (and they do) then it should be possible to form the fuselage into a kind of funnel (it doesn't need to be a closed shell) that does the same job at high speeds. You might even be able to set up a compressing vortex that creates a region of air with all of these qualities without any 'touching' surfaces at all. You can add the fireball thing as well if you want, but it's really not necessary [+]
zen_tom, Oct 28 2010

       This idea is top. Though window seats in the rear compartment might be a little toasty! [+]
saedi, Oct 28 2010

       [zen-tom] that's essentially how a scramjet works, when it does.   

       // burn away the atmosphere in front of the plane and create a vacuum // [DrBob]
// super-heat air / in front of the aircraft, say using fucused microwaves // [2 fries shy of a happy meal]

       Have a look at the splendidly halfbaked Russian Ayaks concept plane [link]   

       // the Ayaks can be equipped with a Soviet plasma anti-friction generator / which uses lasers and high-frequency radiation to create plasmoids. This generator doubles the Ayaks's speed by considerably reducing air resistance. // [wikipedia]
BunsenHoneydew, Oct 31 2010

       Ooh, fab, Bunsen! It seems that even an ignoramus like me can occasionally find himself in tune with the cutting edge of technology.
DrBob, Nov 04 2010

       The problem with "the cutting edge" is that if you get too close, you end up in severe pain, covered in blood, and possibly in need of reconstructive surgery.
8th of 7, Nov 04 2010

       So is that a good thing or a bad thing? Or just a thing?
DrBob, Nov 05 2010

       Kind of depends what you like ...
8th of 7, Nov 05 2010


       //frequent a online forum where//   

       *an* online forum.   

       Woo hoo! That felt pedantastic!
MikeD, Nov 05 2010

       This is basically an aerospike engine, no?
MaxwellBuchanan, Mar 30 2012


       A "plug nozzle" (of which the "aerospike" is a derivative) doesn't have a large surface area , and the combustion is typically annular, or at least peripheral.   

       This design is better characterised as a "spectacularly inefficient and dangerous nozzle".
8th of 7, Mar 30 2012

       // the combustion is typically annular//   

       Yes, we've all been a little too brave with the chillies at one time or another.
MaxwellBuchanan, Mar 30 2012

       [marked-for-deletion] afterburners (a tube on a jet engine), Project Orion (nuclear explosions behind a spacecraft propel it).
FlyingToaster, Mar 30 2012

       //Baghdad ?// Especially not Baghdad. That airport requires a corkscrew approach.
mouseposture, Mar 30 2012

       [Bunsen], where are you getting that Ayaks was demonstrated in 2001? I don't see that in the Wikipedia article, and don't remember seeing a mention of a demonstration there in the past either.
notexactly, Nov 08 2018


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