[AR] Re: dynamic stability
- From: Norman Yarvin <yarvin@xxxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Thu, 21 Aug 2014 11:28:40 -0400
On Wed, Aug 20, 2014 at 05:24:32PM -0700, Carl Tedesco wrote:
>That is what I wondered. From an aerospace engineering point of view, dynamic
>stability looks to see how a rocket will respond when a disturbance is
>imparted on it. CP/CG rules determine static stability, albeit still
>important. So, the Tripoli example you mention suggests that they just want
>to know how the CP and CG change throughout the entire flight?
Probably. I don't know what the distinction between 'static' and
'dynamic' stability would be. I'm not claiming to be expert on the
terminology of rocketry regulation, but in terms of physics, there's
just one kind of stability here; it relates to how the rocket responds
to a disturbance; and it can be computed from the positions of CP and
CG. The quoted rule text mentions 'dynamic stability':
> The information shall include [...]
>(3) The dynamic stability characteristics for the entire flight profile,
but it doesn't seem to be drawing any distinction between that and
anything that might be called 'static stability'; rather, the word
'dynamic' seems to be there just to clarify that it is talking about
stability in flight, as opposed to some other sort of stability that a
creative reader might misinterpret it into. (Chemical stability of
propellant? One never knows what someone might think a rule means.)
If you have liquid propellant rockets, with propellant sloshing
around, computing stability gets more complicated (it's not just CP
and CG), but there's still basically only one sort of stability, as
regards the dynamics of flight. It's not like balancing a wheel (or a
rocket) where there's static balance and dynamic balance.
--
Norman Yarvin http://yarchive.net/blog
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