Re: F1D partial motor blast shield

From: Yuan Kang Lee <ykleetx_at_gmail.com>
Date: Fri, 20 Jul 2012 16:12:38 -0000

I'm wrong saying that it would be impossible to replicate the same CG. It is actually straightforward.

If the partial motor shield weighs 50 mg, take another 50 mg of ballast and put it opposite of the CG of the dummy motor. Take 100 mg out of the normal weight of the dummy motor. Now, the shield, ballast, and new dummy motor have the exact same weight and center of gravity as the normal dummy motor.

-Kang

--- In Indoor_Construction_at_yahoogroups.com, "Yuan Kang Lee" <ykleetx@...> wrote:
>
> Assuming that you place the extra balsa where the partial motor is, it will be impossible to replicate the same CG as the full motor. It would be 50 mg of weight placed well in front of the CG. Perhaps the effect is small.
>
> The other question I have is how much protection does the extra balsa provide. If the protection is adequate, does this mean that extra balsa over the full length of the motor stick (100 mg of balsa) could protect the whole motor stick? It would be nice if this is the case, but it would be difficult to find a spare 100 mg. If you could spare 50 mg and protect part of the stick from an exploding full motor, where would you place the protection?
>
>
>
> --- In Indoor_Construction_at_yahoogroups.com, Jake Palmer <82.jake@> wrote:
> >
> > I had the fortune to spend some time talking to Larry Coslick at the Kibbie
> > Dome this year. I lost 2 motor tubes to motors that broke during or after
> > loading them onto the model (one broke just seconds after launch). He
> > mentioned something he's done in the past and I think it's a brilliant idea.
> >
> > While he was doing partial motor testing he covered the first 4-5" of his
> > motor tube with a leftover piece of another motor tube. He cut open the
> > seam wide enough so it could slip over his motor tube, but narrow enough so
> > it stayed in place. The idea is that it's a semi-permanent blast shield
> > that stays on the plane during quarter and half motor testing. Even if the
> > motor breaks after launch it will protect the motor tube. It's about a
> > 40-50mg weight penalty, although you can use a lighter partial motor stick
> > to offset the weight (just make sure you get your CG right). When he
> > switched to a full motor he removed the sleeve. I plan to use this idea
> > for all my future partial motor tests and I thought I'd share it with
> > anyone else that might find it useful.
> >
>
Received on Fri Jul 20 2012 - 09:12:40 CEST