[SS-VehDev] Re: fins

[Lakestake Rocketry]

Hi Bill,

I had always heard 1 caliber was stable, that .8 or less was marginal.
Then again most of my designs are marginal for one reason or another.... ;)

What about aluminum sheeting over a honeycomb interior? That would
be very light while offering better flutter resistance and a good high-temp,
heat conductive outside presentation. There would be more drag due
to a thicker fin.

Matt C

On 10/11/05, william colburn <space1space at sbcglobal.net> wrote:
>
> By greatly sacrificing the resistance to flutter, I
> redesigned for a fin with greater span.
>
> A fin with a 12 inch root, 6 inch tip, 10 inch span
> and with a thickness of .188 inch is 5 lbm.
>
> However the resistance to flutter is about half that
> of the narrower fin. It still exceeds that calculated
> for the Super LOKI fin, though. It offers a Barrowman
> stability value of 1.5 calibers.
>
> The stability is such an important factor in the
> flight that I think we should continue to be
> conservative. In the hobby rocket field, 2 calibers is
> said to be the limit for a stable flight.
>
> BC
>
>
> --- Richard Nakka <richard.nakka at aero.bombardier.com>
> wrote:
>
> > Gents,
> > Basically the report looks good. I do have one major
> > concern though.
> > I calculated the mass of the fins assuming 1/4" (6.4
> > mm) uniform
> > thickness aluminum, and for 3 fins it is 17.2 lbs.
> > The mass target is 5
> > lbs (2.3 kg) for the set of fins:
> >
> > http://sugarshot.org/downloads/config_dph47.gif
> >
> >
> > Assuming the fins are milled such that the outboard
> > half is tapered down
> > to nearly zero, the mass would be reduced to 13 lbs.
> > Still awfully high.
> >
> > Solutions? I'd suggest looking at carbon composite,
> > reconsidering the
> > shape (it's currently very conservative design, as
> > Bill noted in the
> > report), or revising the mass target upward.
> >
> > Richard> begin:vcard
> > n:Nakka;Richard
> > x-mozilla-html:FALSE
> > org:Bombardier Aerospace, Toronto;Ph. (416) 375 7636
> > adr:;;;;;;
> > version:2.1
> > email;internet:Richard.Nakka at aero.Bombardier.com
> > title:Stress Engr/DAD
> > x-mozilla-cpt:;-23456
> > fn:Richard Nakka, P.Eng.
> > end:vcard
> >
>
>
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