Re: [F-FT] More zipperless piston commentary

On Sun, 31 Jul 2005 19:43:54 -0700, David Erbas-White
<derbas@xxxxxxxxxxxxxxxx> wrote:

>Well, I had a chance to launch with the folks from MDARS yesterday
>(thanks to Kevin and the gang). I did several more launches of my
>'zipperless piston' design before a had a failure that will require some
>rework...
>
>I did several launches (3-4) on H-I motors with intentionally short
>delays. In every case, the design worked 'well', but in 1 case the
>piston went farther than intended because the tie wrap was a bit loose.
>I should add the for my first couple of launches (previous to this date)
>I had pulled the tie-wrap as tight as I could with a pair of pliers. I
>recently obtained a real 'tie wrap tool' from Fry's, and had the tension
>set a bit too loose, so the tie wrap ended up not as tight.
>
>For my final launch with the design, I used an I435T, but the piston
>shattered at ejection due to the bending forces. The good news is that
>the body tube is undamaged, so I simply have to replace the
>coupler/bulkhead assembly, so (overall) I'm ahead of the game, but it
>means I still have some improvements to make. On the other hand, for
>'nominal' flights this is probably a good design, as I doubt if I will
>be intentionally launching with short delays too often <G>.
>
>Somebody at MDARS suggested using the bulkhead plate with vertical
>'spars', such that looking at the end of the assembly would be like
>looking at an 'X' or an '*'. This way, there is maximum area for the
>exhaust gases to disperse, plus the stress force is distributed a bit
>better than on a slotted coupler. I'm going to take a look and see how
>difficult that would be to do.
>
>I'm a bit concerned about the smoothness of such a configuration as a
>'piston', but I'll have to experiment to find out.
>
>Any additional comments on this would be appreciated.
>
>David Erbas-White

Cut backon the BP. Glass the inside of the piston & review whatever
else I said in my previous post on the subject.

When you put a tie wrap on a wire, if it is to tight, it can cut
through the wire or insulation or cause the wire to break later. As a
result, most tie wrap guns don't make them REAL tight.
.

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