Nymphail

I overlooked something when I checked the Nymph for damage. Do you see it?IMG_0371

The rear stop for the motor pod — it’s gone!

I have a theory of what happened. The Nymph has no thrust ring. The idea is you’re supposed to trim the model by adjusting the position of the motor, then friction fit it at that position. Tightly!

The motor obviously wasn’t tight enough. The ejection charge spat it out. But before that happened… could the propulsion charge have driven it forward until it smacked up against the nose cone? That might have knocked the rear stop off. It also would have prematurely broken the burn string, obviously, in which case the pod would have been pulled back (or rather, the glider would have been pulled forward).

There seems to be only a little soot inside the pod, less than I would expect if the still-burning motor had pushed itself all the way up, but maybe that happened just an instant before burnout.

Or maybe the motor didn’t move up the pod at all. But the rear stop is what transmits the thrust to the pod holder which transmits it to the glider, and perhaps that was sufficient without any nose cone smacking to cause a weak glue joint to fail. And then the whole pod would have been pushed forward, breaking the string.

Either way, the loss of the rear stop had to be accompanied by breaking of the burn string, and then motion of the pod relative to the glider, bringing the center of gravity too far back and destabilizing the rocket. I find that a much more plausible cause for the crash than wind or clay.

Why would the joint fail? It was the same yellow glue I always rely on for thrust rings and fins. I don’t know. Maybe just not a tight enough fit for the glue to hold?

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