[AR] Re: airbreathing engines (was Re: Re: to the stars, soon)
- From: Ian Woollard <ian.woollard@xxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Tue, 5 Apr 2016 23:26:58 +0100
On 5 April 2016 at 20:49, Henry Spencer <hspencer@xxxxxxxxxxxxx> wrote:
Sorry, wrong, fundamental misconception (although a common one).
Nope, that's exactly why that curve goes as an inverse law.
In practice, particularly at ramjet speeds and above, to keep airframe
loads and heating tolerable, you must increase altitude so air density
drops *faster* than the speed increases. (Remember that dynamic pressure
scales with the square of speed, and heating roughly with the cube.) Which
means that unless the intake can somehow get larger and larger, it will
deliver less mass flow, not more.
Doing that certainly means less mass flow, lower pressure and hence lower
thermal loading. But lower pressure means reducing thrust, NOT efficiency.
It's exactly the same as throttling back a rocket; the actual exhaust
velocity of the flamy bits coming out of a rocket is independent of
throttling, because the exhaust velocity of jet engines and rockets is set
by the *expansion ratio* (provided you maintain the mixture ratio, and
match the exit pressure) not the chamber *pressure*!
Henry
--
-Ian Woollard
Sent from my Turing machine
- References:
- [AR] Re: to the stars, soon
- [AR] Re: to the stars, soon
- [AR] Re: to the stars, soon
- [AR] Re: to the stars, soon
- [AR] Re: to the stars, soon
- [AR] Re: to the stars, soon
- [AR] airbreathing engines (was Re: Re: to the stars, soon)
- [AR] Re: airbreathing engines (was Re: Re: to the stars, soon)
- [AR] Re: airbreathing engines (was Re: Re: to the stars, soon)
- [AR] Re: airbreathing engines (was Re: Re: to the stars, soon)
- [AR] Re: airbreathing engines (was Re: Re: to the stars, soon)
- [AR] Re: airbreathing engines (was Re: Re: to the stars, soon)
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