The real problems with debris in jet engines tends to be in turbojets where
the vulnerable compressor blades are directly inline with the inlet. With
turbofans, the fan tends to chop up the debris and then send the pieces
around the outside and reject the pieces, sparing the compressor blades in
the centre of the engine.
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.
On 9 June 2016 at 05:30, Norman Yarvin <yarvin@xxxxxxxxxxxx> wrote:
On Wed, Jun 08, 2016 at 08:55:17PM +0100, Ian Woollard wrote:
On 5 June 2016 at 19:26, Henry Spencer <hspencer@xxxxxxxxxxxxx> wrote:simplicity
... But the complexity of the pre-cooler seems to outweigh the
of a second tank of oxygen.
Well, yeah, in the end it probably does. Honest comparisons of
airbreathers against rockets often reach such conclusions.
But not this one.
And honest comparison of pure rocket approaches such as SpaceX's give the
same performance that SpaceX get; and no better.
A truly honest comparison has to take into account that Skylon is a
paper rocket, while SpaceX's rockets have flown. For instance, just
what size bird (or bug) impact does it take to do lethal damage to
that ultra-lightweight precooler? This is a "fine pipework heat
exchanger" about which it is boasted that it exceeds the
performance-to-weight ratio of all other heat exchangers by a factor
of ten. A section was built and successfully tested... but somehow I
doubt that those tests involved wheeling out the "chicken cannon" used
to test airliner engines and giving it a shot. Even an insect might
be an overmatch for it. And Skylon isn't a rocket that lifts off
vertically; it's supposed to take off and land like an airplane,
giving it plenty of exposure to the bug and goose region of the
atmosphere.
--
Norman Yarvin http://yarchive.net/blog
