Yes, air for combustion is pre-heated by the bow shock

Space/Science » in reply to You wrote: "You'll find that the detonation velocity for hydrogen-air at STP is 1968 m/sec"

Yes, air for combustion is pre-heated by the bow shock

Gary — 6/2/2004 4:25:13 PM (archived)

Yes, air pre-heated by the bow shock has a higher local speed-of-sound but it doesn't make the scramjet run better. Scramjets crap out at Mach 10. In a former life, I studied scramjets for a living. I was part of an experimental team that conducted development work on scramjets using a shock tunnel. The scramjets that we investigated worked fine at Mach 6 but produced diminishing thrust with greater Mach number. Beyond Mach 10 they were producing no thrust.

One can cook up science fiction concepts to get beyond Mach 10 but the problem is always added mass. Scramjets were supposed to be beneficial because the vehicle doesn't need to carry oxidizer. Unfortunately a scramjet powered vehicle does need to carry lots of extra hardware to support the scramjet's operation. After the smoke clears and the dust settles, dumb old rockets require less mass than scramjets and can get you from Mach zero to orbital velocity.

Gary

The whole thread (31 posts)

Airships to orbit - Tom Brosz - 5/27/2004 3:07:34 AM
- re: I don't understand why anyone would build all that hardware if they didn't do the numbers - Success_Machine - 5/31/2004 4:10:21 PM
  - There's no way you'll get an L/D of 50 - Gary - 5/31/2004 8:27:13 PM
    - re: I believe it does get an L/D of 50, when forced to go hypersonic speed - Success_Machine - 6/1/2004 11:06:48 AM
- There are exactly TWO practical ways of launching a payload into orbit. - David F Mayer - 5/30/2004 5:22:24 AM
  - Actually...... - Gary - 5/31/2004 8:31:49 PM
    - A scramjet won't get you into orbit (they flame out at Mach 10). - David F Mayer - 6/1/2004 1:03:18 AM
      - Scramjet 101 - Gary - 6/1/2004 4:35:26 AM
        
        re: Scramjet 101 - David F Mayer - 6/2/2004 12:32:24 AM
        
        Use a detonation wave analogy to understand this - Gary - 6/2/2004 3:27:55 AM
        
        You wrote: "You'll find that the detonation velocity for hydrogen-air at STP is 1968 m/sec" - David F Mayer - 6/2/2004 7:06:04 AM
        
        Yes, air for combustion is pre-heated by the bow shock - Gary - 6/2/2004 4:25:13 PM
        
        re: The only design for a scramjet that works in theory - Success_Machine - 6/2/2004 1:09:56 PM
        
        re: Controlled Flame Speed Limited to Mach 5 - Success_Machine - 6/2/2004 2:34:40 AM
- Do the numbers, Tom. Then forget it. - David F Mayer - 5/30/2004 5:09:45 AM
  - re: Do the numbers - Tom Brosz - 5/30/2004 6:22:58 AM
    - Look at the VOLUME of a balloon of ANY type required to lift a reasonable spacecraft to 30,000 meters. - David F Mayer - 5/30/2004 1:35:00 PM
  - I was only referring to using a balloon to lift a rocket here. (n/t) - DFM - 5/30/2004 5:19:50 AM
- re: Airships to orbit - Nathan Koren - 5/28/2004 3:12:12 AM
- It was me... - Adam - 5/27/2004 11:33:12 AM
- Low thrust to orbit for an airship has got to be bogus - Gary - 5/27/2004 5:52:06 AM
  - "Something is not right here." You are correct. The concept is bullshit! (n/t) - David F Mayer - 5/30/2004 5:17:07 AM
  - Color me skeptical - Larry J - 5/27/2004 6:12:43 PM
    - power sources... - Adam - 6/1/2004 11:19:27 PM
      - Still very skeptical - Larry J - 6/2/2004 2:33:32 PM
    - re: Skipping Over the Atmosphere on a Surfboard - Success_Machine - 5/27/2004 9:04:04 PM
  - re: Low thrust to orbit for an airship has got to be bogus - Adam - 5/27/2004 11:31:06 AM
    - Use VASIMR - phil - 5/27/2004 12:42:19 PM
      - For a large balloon, at any altitude, the air resistance even at low speed is comparable to its weight. I STILL say the idea is bullshit. (n/t) - David F Mayer - 5/30/2004 1:37:21 PM
- re: Airships to orbit - Raoul - 5/27/2004 5:35:39 AM
  - Visible Horizon... - Adam - 5/27/2004 11:30:18 AM

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