[AR] Re: BFR Noise
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Fri, 30 Sep 2016 18:56:36 -0400 (EDT)
On Fri, 30 Sep 2016, Nels Anderson wrote:
As a first approximation, I would think acoustic power would scale as
jet power.
Maybe, kinda, more or less, with the caveat that certain details of the
engines can matter quite a bit.
Are there any mitigating factors? Might the gas-on-gas Raptor be
fundamentally quieter than the liquid-on-liquid F-1? I recall a claim
by Firestar that mixing affects noise.
My understanding (never had the chance to hear a Saturn V launch in
person, SIGH) is that the F-1 was infamous for being loud, at least partly
because of very unsteady afterburning -- possibly including actual
detonations! -- as the outer layer of slow-moving very-fuel-rich turbine
exhaust gas mixed with the surrounding air.
(The F-1 dumped its turbopump exhaust into its nozzle partway down, partly
just as a convenient way of getting rid of it, partly because it kept the
really hot stuff away from the lower nozzle wall -- which therefore didn't
need regen cooling. This is why there's a sort of shimmering black
curtain around the first little bit of F-1 exhaust plume: the turbine
exhaust is full of soot.)
A staged-combustion engine likely wouldn't be as bad. Certainly the noise
from the one shuttle launch I saw (from one of the old 3-mile-away viewing
sites -- this was before KSC started pushing spectators out farther and
farther) didn't measure up to the apocalyptic descriptions of what Saturn
V launches were like.
Henry
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