What's the full name of that book?
Thanks,
Lars Osborne
On Wed, Dec 30, 2015 at 5:38 PM, Richard Garcia <GalaxyNGC1672@xxxxxxxxxxx>
wrote:
Allowing the inner wall to expand may ameliorate the problem but does not
eliminate it. What really matters is the temperature gradient across the
wall itself. The inner portion of the wall grows more that the outer
portion of the wall will let it. The inner wall of a dual wall chamber
would eventually crack even if it never touched the outer wall and could
support itself. What would really help is reducing the thermal gradient
across the wall. The best way to do that would be to make it out of
something very thermally conductive (i.e. copper) and to make it as thin as
possible. That thinness is where you start to run into trouble. Making the
thrust chamber walls thinner than some copper milled wall chambers already
are (less that 0.075") will limit what chamber pressure you can run at,
sacrificing performance. I was under the impression that most XCOR engines
ran at low or modest pressures, like 350 psi or so.
Also what XCOR is doing is here nothing new. A look in the ol' history
books will show many engines made in this way. Even amateur engines like in
the attached picture from the RRI. (now defunct offshoot of the RRS) It
happens to be one of the easiest way to build a regenerative thrust
chamber. Although to XCOR's credit I've never heard of anyone else choosing
this form of engine for the express purpose of increasing fatigue life.
State of the art, high performance, milled channel , nickle backed thrust
chambers can usually get around 100 runs before cracks start showing up
from thermal cycling induced fatigue. (Take a look at "Some Effects of
Thermal-Cycle-Induced Deformation in Rocket Thrust Chambers" by Hannum and
Price on NASA's NTRS) Put a margin on that number and only run 25 times.
Lets say about 10 runs for tests through the lifespan of the engine. That
leaves 15 flights. Replacing a thrust chamber every 10th or 15th flight is
a heck of a lot cheaper than replacing it every flight. Thats major savings
on reusability without having to advance the state of the art.
-Richard
________________________________________
From: arocket-bounce@xxxxxxxxxxxxx <arocket-bounce@xxxxxxxxxxxxx> on
behalf of Henry Spencer <hspencer@xxxxxxxxxxxxx>
Sent: Wednesday, December 30, 2015 4:23 PM
To: Arocket List
Subject: [AR] Re: fatigue life (was Re: Re: SpaceX F9 Launch/Update...)
On Wed, 30 Dec 2015, Brian Feeney wrote:
Does the Saddle / Jacket engine design alleviate much of the inner to
outer differential thermal wall stress by way of the inner wall (chamber
/ nozzle) sliding relative to the outer wall.
XCOR's patented (US# 7854395 B1) design lets the inner wall expand both
axially (by sliding within the jacket) and radially (by building the
jacket as a loose fit at room temperature, so it's only a snug fit -- not
a crushing constraint -- with the inner wall hot). In principle this
could avoid much of the problem. In practice the details probably matter
a lot...
Henry