[AR] Re: dynamic stability
- From: "Tony" <hypergolic2@xxxxxxx>
- To: <arocket@xxxxxxxxxxxxx>
- Date: Thu, 21 Aug 2014 17:53:37 -0700
Hi guys-
Been following the discussion on dynamic stability, mass properties, fuel
slosh and canted fins for a liquid rocket.
1) Few amatuer rocket types do a mass properties analysis on the vehicles.
When done, it's ususlly weight and c.g. A complete mass properties analysis
includes the vehicles moments of inertia and products of inertia. The
products
of inertia are what will cause you trouble when your vehicle spins (not to
mention what the fluid geometry inside the tanks will do to your c.g. and
hence
to your products of inertia). A two plane dynamic balance is required if it
spins
and a detailed mass properties analysis should get you reasonably close to a
balanced condition. The caveat here is that propellant consumption and fuel
slosh/spinning propellant geometry will make it difficult to calculate a
proper
c.g. Suggest don't spin a liquid. Install slosh baffles. And get into the
habit
of doing a detailed mass properties analysis as part of the design effort.
2) How to do a real mass properties analysis and dynamic balance is beyond
the scope of this forum. Keep in mind that it is doable with hand
calculations
(yes, very labor intensive, but that's how we did it for spinning spacecraft
in
the "old days").
Tony
----- Original Message -----
From: "Carl Tedesco" <ctedesco@xxxxxxxxxxxxxx>
To: <arocket@xxxxxxxxxxxxx>
Sent: Wednesday, August 20, 2014 2:45 PM
Subject: [AR] dynamic stability
I am starting the process for getting a class 3 waiver for a rocket launch.
Most of the FAA required documentation looks straight forward. One piece of
information they require is "The dynamic stability characteristics for the
entire flight profile." A static stability analysis is straight-forward,
but I have never done a dynamic stability analysis.
How have folks on this list addressed this requirement? Is this software
driven analysis or just hand-calculations? Does anyone have an analysis
they could share? If software analysis is the norm, can anyone point me to
affordable software?
--- Carl
--
Carl Tedesco
Flometrics, Inc.
5900 Sea Lion Place, Suite 150
Carlsbad, CA 92010
tel: 760-476-2770 ext. 515
fax: 760-476-2763
ctedesco@xxxxxxxxxxxxxx
www.flometrics.com
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