By the time the exhaust gases have reached ambient pressure, they've
cooled considerably from the combustion chamber temperature. You'd
probably be fine with many stainless steel (look at the AISI 300 series
- you can get a 36" by 2" strip of 304 from McMaster-Carr for under 14$
OR you can go the innovative route and use an aluminum alloy. If the
vanes have enough thermal capacity, they can stay well below their
melting point. If you know the maximum burn duration of your engine,
you can make some harsh thermal assumptions and figure out how thick
the vanes need to be to prevent thermal compromise.
No tungsten needed (it's expensive anyway).
Let's say 20% of the exhast flow is intercepted by the vanes (in
reality, it's probably alot less). Worst-case scenario, the total
available blast force can only be equal in magnitude to the total
thrust... so for 4 vanes intercepting 20% of a 100 lb thrust, that'd be
5 lbs of "blast force" per vane. That's also assuming the vanes are 90
degrees with respect to the thrust (blocking as much of the flow as
possible). Angle the vane 30 degrees from the thrust direction (more
realistic), and you've decreased the blast force per vane to 2.5 lbs.
Are you SERIOUS?
Are either of you under the impression that an estimate using HIGH
SCHOOL physics is providing information that someone couldn't estimate
for themselves without a calculator? What I posted is useless for
someone that would thinking about making something dangerous... If you
disagree, then perhaps you need to report NASA to Homeland Security.
Their technical reports server is loaded with far more technical
reports regarding control vanes and guidance.
Seriously, this is an unmoderated newsgroup and you can post just
I can't speak for Jerry, but your impression of HIGH SCHOOL physics is
clearly different from mine. Your assumption of "someone's"
capability, with or without a calculator, is interesting.
I understand and I do not disagree with the sharing of your opinions.
However, it would be more helpful to the originator of this thread if
you would share URLs to those tech reports. And yes, your post seemed
to help Roy Green's understanding.
Using conservation of momentum, trig, and elementary multiplication and
division is all I needed to derive this equation:
20% x 100lb x sin(30) /4 vanes = 2.5 lbs
Do you see anything that's above high-school level? And the only
reason you'd need a calculator is if you don't remember that
Thank you. But do you really think a newsgroup *estimate* would be
used to create something like a guided missle? A guided missle is
extremely sophisticated, and you need to analyze thousands of things.
Anyone using estimates from a newsgroup CERTAINLY will not be able to
And the whole point of my original post was to show that blast force is
a non-issue, in the same way that flying through clouds made from
orange juice is a non-issue. ("Hey Ahmer, forget about the orange
juice cloud analysis... some guy on usenet said it was a non-issue").
Also, to enlighten you on the wealth of data out there, please see the
"Preliminary Investigation of a Fin-Actuated Jet-Vane Control System
for Stabilization of Rocket-Powered Models":
I don't know why you are going on about guided missiles, orange juice
I do agree that it is a non-issue in the sense that using spin vanes
in the flow of a BP G motor is not a very good idea, regardless of the
loads on the vanes. And while nobody has yet given the temperature
that was requested, you did suggest some alternative vane materials.
He is most likely into AR so a better solution would be to use
multiple canted nozzles rather than put spin vanes in the flow of a
single nozzle. Of course he could also use Micromaxx or A10-P motors
as spin motors, and develop his own spin buck program. Further, it
was pointless of me to suggest that your estimate of vane loads should
have been better, especially when the purpose of my reply to Jerry was
that you COULD make such a reply.
Thanks for sharing. Although this may not be the best report to refer
to, it does provide a link to the NASA (and old NACA) reports, and he
may be able to find a more helpful report.
It is also one that I had not read, and one of greater interest to
sport rocketry. Perhaps it will inspire a reader to do a similar R&D
I was under the impression that you thought my reply was immoral or
unethical in the sense that I was providing information that could be
used to make something harmful. Jerry asked if I was allowed to post
"this stuff", which I took to mean he thought it was wrong to provide
information that could be used to make something harmful. Your
response to Jerry's post ("but that does not make it correct") gave me
impression that you both thought my reply was immoral or unethical in
that sense. I guess you were questioning the actual numbers... I think
I picked the wrong week to kick coffee.
It was a rhetorical question and I should invent an emoticon for how I
felt, after seeing many such replies from others on rmr over the years.
I have only very rarely seen non-public information posted to rmr and
mostly from first hand experiences of ex-military persons on items of
There are plenty of websites that go farther into actual guided missile
technology and WMD manufacture and delivery.
rmr is tame by camparison.
But mindlessly attacking nonetheless.
Jerry Irvine, Box 1242, Claremont, California 91711 USA
Opinion, the whole thing. <mail to: email@example.com>
I mean, once a rifle bullet leaves the barrel, there's nothing that
continutes to physically impart a spin, but the bullet keeps spinning,
Interesting thread for a switch...
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