Jon:
I'd find a supplier of silica phenolic prepreg, and see if you can get a roll of
tape long enough to build your engine (which is not a trivial size) at a
reasonable price. When you wrap it, you stand the tape on its edge on the
mandrel, albeit at a slight angle (angled toward the front of the engine, i.e.
>90 degrees measured in a counterclockwise sense from the engine inner wall).
If the burn time is very long, use a high density silica phenolic for the throat
to keep it dimensionally stable. Add a flat wrap of at least two layers on top,
then machine the whole thing to fit in a metal housing beefy enough to hold the
chamber pressure you plan. Downstream of the throat, the pressure will drop
dramatically. Thus, the exit cone can be overwrapped with any handy composite
cloth/resin of sufficient strength.
I cut my teeth on an engine built just this way. It was about two and a half
times the thrust of the engine you are planning. It could fire for a total of
195 seconds, either in a number of burns, or a single long burn. IIRC, the
ablative thickness was about an inch in the chamber, two inches at the throat,
and then tapered down to about half an inch at the exit.
We static fired and flew scores of these, without a single failure.
Good luck!
Mike
On April 12, 2021 at 11:13 PM, Carl Tedesco <ctedesco@xxxxxxxxxxxxxx> wrote:
Jon,
A long time ago I got some advice from an RRS member to make an ablative liner
for a LOX/alcohol motor (~660 lbf) using fiberglass and this resin. The
combustion chamber liner was made by soaking fiberglass sheets in this DAP
resin glue and wrapping it around a carboard tube to close to net size. To get
an exact fit to the metal motor tube, the wrapped liner was coated with bondo
and lathed to the diameter of the motor case. For this motor the throat and
nozzle were graphite. It worked with no noticeable erosion for 10 seconds.
--- Carl
From: arocket-bounce@xxxxxxxxxxxxx <arocket-bounce@xxxxxxxxxxxxx> On Behalf Of
Jonathan Adams
Sent: Friday, April 9, 2021 5:47 AM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Ablative engine composite layup
Hello everyone,
I'm getting to the construction stage of a 4.5kN ablative liquid propellant
engine, and I was wondering if anyone had any good resources for composite
layup for the ablative wall. Possibly even resources specific to composite
layup for small rocket engines.
I haven't been able to find many good resources out there for how to do this,
and I wanted to know if anyone could point me in the right direction for how to
go about this. Even personal experience for how to do this right (and
cost-effectively!) would be greatly appreciated.
Thanks,
Jon.