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Date: Fri, 19 Nov 1999 20:04:26 -0800
From: Doug Jones <>
Subject: Re: seattle space enterprise symposium

Ian Stirling wrote:
> wrote:
> >Small correction. Jeff doesn't expect the X-1 replica to get up to
> >those speeds. However, the X-1 airframe was a fairly conservative
> >design, and higher speeds are possible with improved airframes using
> >the same engine. Also, his version of the XLR-11 would be significantly
> >more efficient than the original because, in his words, he doesn't know
> >*how* to design an engine with Isp that low. (The injector on the
> >original was "little better than a shower head.")
> Anyone know offhand what the ISP was?

From the operations manual for the XLR-11-RM-13, section 1-71,

"...Specific impulse: 190 pounds minimum thrust per pound of propellants
consumed per second."

Calculating the ideal Isp from the chamber conditions, I get 228 for a
perfect nozzle and combustion.  Since the injector really was pretty sad-
thirty oil burner swirl elements for the LOX with annular gaps supplying
the fuel- and the nozzle was a simple 15 degree cone that was
_underexpanded_ at sea level, it's not surprising that it had such low

For our new design XR-1 engine, an excellent injector, a far better nozzle,
higher O/F, and better materials allowing 99% alcohol will make large

Doug Jones
Rocket Plumber, XCOR Aerospace

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