Re: XCOR engines

Henry Vanderbilt wrote: 
Henry Spencer wrote:

In article <MnB7f.867$Hj2.830@xxxxxxxxxxxxxxxxxxxxxxxxxx>,
Pete Lynn <pete@xxxxxxxxxxxxxxxxxx> wrote:

I was only wondering if someone could suggest whether their engines are
in the low, medium or high performance ranges with regard to T/W and
ISP.


"Medium" is a reasonable guess, given that XCOR tends to emphasize safety
and reliability over absolute maximum performance.



For what it's worth, back when the EZ-Rocket was first flying,
I took published figures on the 400 pound thrust LOX-alcohol
engines propellant load, working pressure, and burn duration,
and rough-approximated the Isp to be a bit better than 90% of
the
theoretical max for that combination.  Then when I asked their
chief engineer about these figures, he wouldn't give specific
numbers, but seemed bemused that anyone would think he'd settle
for merely a bit better than 90%.  For what it's worth.



It's the old 90/10 rule. You get 90% of the performance at 10% of the
cost. The remaining 10% of the performance gets the remaining 90%
of the cost.

In this case, The should be able to inch that up incrementally. They
are operating at nowhere near the materials limit. For a first
generation design, 90% theoretical is a good pretty target number.


.

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