[RocketsNW] Fins on a Minimum Diameter

[Greg Clark]

Jeff's method results in an extremely strong fin mounting system, and
probably lets him put the biggest motor he can in it with out fear
(Mike -- got a motor?)  But this surely  sacrifices some altitude.

I flew a min diameter on a K250 to 17K AGL using more traditional
techniques (plywood fins tacked to outside of airframe, kevlar
fillets, 2 x carbon fiber overlay) , and the fins held fine during the
mach+ flight.

http://bigredbee.com/images/k250big.jpg

on the other hand, I flew a K850 a couple of years ago that just had
one layer of carbon, and no fin fillets.  The first few seconds looked
good, but then all heck broke loose, and it came fluttering down in
pieces.

My opinion?  A good reinforced fillet, and 2 layers of carbon "tip to
tip" on the fin can should do well for most flights.

-- Greg



On Wed, Feb 3, 2010 at 7:14 PM, Jeff Moore <tnetcenter at gmail.com> wrote:
> The rocket did 10,750 ft on a K550 on it's maiden voyage.  The motor section
> separated from the tether between the two sections and came in on a flat
> spin and landed about 25 ft away from the rest of the rocket w/o a scratch
> on it.  The airframe is carbon fiber aerosleeve over phenolic tubing.  The
> rocket is over 7 ft long as it was designed for  hybrid motors as well as
> solids.  The motor section is approx. 50 inchs long by itself.  It's pretty
> stout.
>
> Jeff Moore
> BORG
>
> p.s. The rocket is actually not finished yet, it still needs a final coat of
> epoxy to fill the weave of the carbon fiber and fiberglass sections.  This
> is the lowest level of performance I expect from it.
>
> ----- Original Message ----- From: "Julian Picard" <jman13 at gmail.com>
> [snip]
>
> Thanks for all your help!
> Julian
>
> Also, to Jeff Moore, how did the flight go on your minimum 54"? The
> wire/kevlar thread idea around the fin can sounds robust, and you didn't
> have any problems with cracking around the holes you drilled?
> J
>
>
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