[AR] Re: Precooled engine
- From: Norman Yarvin <yarvin@xxxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Thu, 9 Jun 2016 14:57:42 -0400
On Thu, Jun 09, 2016 at 04:21:29PM +0100, Ian Woollard wrote:
In the SABRE design the precooler isn't inline with the inlet; the air goes
into the inlet, where it slows and then it goes through a 90 degree turn
into the engine core. Presumably this is done specifically to avoid or
minimise the issues of debris intake. Debris will have a relatively high
ballistic coefficient and will tend to go straight through outside burners,
due to momentum and avoid the precooler entirely.
Well, the engine's planned arrangement is vaguely like that, but there
are still plenty of paths for debris to come in and strike the
precooler. The video on this page
http://www.reactionengines.co.uk/sabre_howworks.html
is the best depiction I found of the arrangement; it's pretty clear to
me from watching it how debris could smash into the precooler, though
I suppose if you put your wishful-thinking engine into full throttle
you could still deny it. Even if it's a glancing blow, thin tubing
doesn't do well against glancing blows; things catch and rip and tear.
Another figure of note, from this paper:
http://www.reactionengines.co.uk/tech_docs/JBIS_v57_22-32.pdf
The takeoff roll is planned to be 155 m/s, nearly half the speed of
sound. Skylon wouldn't just be flying low and slow through the bug
and goose zone; it'd be flying low and rather fast.
(By the way, the plans seem to have changed since that 1993 article
that Henry referred to: now the excess hydrogen is not simply to be
dumped overboard but to be burned in the bypass flow, yielding a bit
of thrust, or at least not as much drag as would otherwise be incurred
by taking extra air in through the engine.)
--
Norman Yarvin
http://yarchive.net/blog
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