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Crazy Space Plane Idea I have

  1. Aug 18, 2005 #1
    I don't know if this would work or not.

    What if you used one engine bay of an F-15 for a scramjet, the other for an SR-71 engine. That takes you to mach 10 and the edge of space. If you strapped PAM rockets to the missle racks on the wings and belly, could you make it to orbit velocity?

    Obviously I haven't thought the heat shield through yet, but I am just wondering over the possibilites it opens up.

    And obviously there is no possibility for Star Wars fighters, but the maneuvering would be done by maneuver rockets on all control surfaces.
     
  2. jcsd
  3. Aug 18, 2005 #2

    FredGarvin

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    Three things immediately come to mind:

    1. The F-15's fuselage would have to be greatly modified to go to those speeds and altitudes. Also would you be able to carry enough fuel to get that far?

    2. The wing structure and missile mounting scheme would have to be modified to withstand that kind of thrust load.

    3. How the heck would you control the thing at hypersonic speeds? The normal control surfaces would probably be non existant after Mach 3 or 4.

    Just some initial thoughts. I guess if you strap a large enough engine on anything you can get to where you need to go.
     
  4. Aug 18, 2005 #3

    Pengwuino

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    Probably with enough motifications.... but why the hell would you want to do that?
     
  5. Aug 18, 2005 #4
    It's a neat idea but (this question goes to Fred) wouldn't the plane have to be so heavily modified that at some point you'd end up spending as much as if you'd just built an original airframe?
     
  6. Aug 18, 2005 #5

    FredGarvin

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    I agree with you 100% on that thought. There would probably be a list as long as my arm as to why you couldn't use that airframe. I am not a structures type of guy though.
     
  7. Aug 18, 2005 #6
    I figured that the structure needed to be modified, I was just wondering if the propulsion scheme would work out for it. As far as fuel goes, you would need to carry only the fuel needed by the two engines. The PAM's carry their own fuel. And I think that airframe could carry enough to do it, but I am not sure.

    But thanks for your input!!!
     
  8. Aug 18, 2005 #7

    DaveC426913

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    "If you strapped PAM rockets to the missle racks on the wings and belly, could you make it to orbit velocity?"

    The SR-71 and scramjet speeds would require a very streamlined veseel. As soon as you strap on an external set of rockets, you immediately screw up any aerodynamics.
     
  9. Aug 18, 2005 #8

    russ_watters

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    Well, an F-15 would utterly disintegrate before it got to mach 5 (flip a coin between aerodynamic forces and heating), but the general idea of having two engines for two different flight envelopes is valid.

    One of the more difficult problems with supersonic/hypersonic wind tunnel testing is making models that won't melt too fast (a steel model melts in a matter of seconds at mach 4), but still aren't too expensive (steel is cheaper than, say, titanium). I've seen better, but HERE are some videos of such research.
     
  10. Aug 18, 2005 #9

    Danger

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    Even if all of the other problems that folks have pointed out were adequately addressed, I'd be very uncomfortable with the asymmetrical thrust aspect of having incompatible engines side-by-side. One above the other would be okay, but I think that having your centre of thrust offset from the midpoint of the plane would cause trim problems at extremely high speed. I'm not sure, but that's my impression from a pilot's perspective.
     
  11. Aug 18, 2005 #10
    That is an interesting point, Danger.

    I do know that military aircraft with two engines can fly with one, but the extreme speeds are not known.

    It sounds like there is just not a lot of research into control over mach 3/top speed of the SR-71. That would have to be the first thing addressed in order to make a true space plane work.
     
  12. Aug 19, 2005 #11

    FredGarvin

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    I was going to mention adverse yaw but I figured if they could get by the airframe problems and control issues, they could work that into the scheme as well. Good call Danger.

    I can't imagine what they would have to do to counteract that yaw at mach 5+ when the scramjet kicks in and the conventional engine cuts out.
     
  13. Aug 19, 2005 #12

    Pengwuino

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    I think one huge problem there is that, like commercial jets, once you lose an engine, you either start to roll or you start to yaw to one side.
     
  14. Aug 19, 2005 #13

    russ_watters

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    You may note that the engines of the F-18 are significantly closer together than those of the F-14. The reason is that the F-14 is not a lot of fun to fly on one engine due to the asymetric thrust.
     
  15. Sep 23, 2005 #14
    hey Cu i think you will be better off getting plans for a scram jet or something like that.
    Plus what r u going to use as a oxidizer and a fuel?
    There is a lot of planing but if u got the money and the parts(and guts)do it!
     
  16. Sep 24, 2005 #15
    I think taking advantage of (Specific Gravity) is the best option to get into space with less effort. (Specific Gravity Ballast), (like Submarines) but with lighter than Air ballast tanks. Everyone is looking for speed to get into space but you don't need to go fast, Just float up, It would take a pretty good material and design effort to accomplish it, Maybe NASA could afford it. It seems to also be the better way to come back to Earth by ballasting Specific Gravity, You could put Scram jets or even the latest Black light Ion engines on it. Just a thought.
     
  17. Sep 24, 2005 #16

    Danger

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    That's fine for getting something to an altitude where it can be launched with less power and fuel consumption, and it's been done, but a balloon can't get into space by 'floating'. It will inevitably reach a point where the trapped gas inside is of equal density to the atmosphere and quit rising.
     
  18. Sep 24, 2005 #17

    russ_watters

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    Actually speed is by far the more important consideration (the goal for getting to space is orbit, which for low-earth orbit of 100 miles or so, is 17,500mph), which is why balloons such as what Danger describes are not used. The idea has been kicked around before, but it just doesn't help much to lift a rocket to 100,000 feet, then light it.
     
  19. Sep 24, 2005 #18
    Think of the Space Shuttle. Consider the huge fuel tanks it takes up and then drops off when they are used up. Consider the shuttle returning using up all it's remaining fuel slowing down to re-enter the atmosphere and coast to the landing site dry of fuel. Consider the shuttle being carried from awest coast landing to Florida on the back of a 747, reminds me of a monkey on an elephants back; it's not much bigger than an F-15.

    The moral of this is that you must find a fuel with a lot more energy per pound than what is now available. Now, most of the fuel is spent getting the fuel up to speed!
     
  20. Sep 24, 2005 #19
    ??? Have you ever stood next to a shuttle orbiter? that thing is MUCH BIGGER than an F-15. Its nearly 4-5 stories tall at the tail fin. Its monsterous.
     
  21. Sep 25, 2005 #20
    whoa. very original idea. plausible but not practical though. your taking pieces of aircraft that had to be engineered from the ground up to be unique/groundbreaking and meshing them together.

    u know how much fuel it takes for an SR-71 to operate? sr 71 is HUGE compared to an F-15. it makes an F-22 look like a midget. your taking a SCRAM jet and a RAM jet and putting them in the engine bays of an F-15.

    Even if the engines fit and the fuel works, an F-15 isn't aerodynamically designed to go anywhere near mach 3-5 let alone 10. you'd have to redesign the nose, wings, air intake, stabilizer fin, and heat/friction management systems from the ground up
     
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