This style of standoff goes back to when Estes sold it's "C Rail". The dowel standoff fits the C Rail launch rod.
I'm tired of BT-20 and BT-50 models crimping and buckling right above the fins. That's a weak point when the model touches down.
This coupler should strengthen that weak area that's prone to bending.
After the strengthening coupler was pushed into place the engine mount was quickly removed.
Another line of glue was applied with a dowel end and the mount slid into place. The rear centering ring is even with the back end of the main air frame tube.
To be sure the ring is flush, the last 1/2" was pressed in place with the flat side of my sanding block.
The rear ring was "sealed" with some medium thickness CA applied with a Q-tip.
This hardens the outside surface and can be smooth sanded with 400 grit.
Good tip on adding the internal reinforcement of the body tube. The first time I'd seen the crimping was on the Astron X-ray (the second model rocket that I'd built), Once a crimp develops, it goes downhill from there (as it tends to worsen with each successive flight).
ReplyDeleteHi Naoto,
DeleteI've hated BT-20s and BT50s ever since I tried to remove a friction fit motor after an early Wac Corporal flight. I ordered a Centuri Javelin (ST-7 tube) and thought: "That's how body tubes should be made!"
Ah yes, the struggles in removing friction-fit motors... Was one of the contributing factors in the shortened lifespan of my Astron X-ray (i.e. added stresses imparted on the airframe tube during motor extraction).
DeleteNeither the kit instructions nor the "Alpha Book of Rocketry" booklet (included with the starter set) gave much guidance with regards to application of tape for friction fit (aside from "enough masking tape around the engine for a tight fit"). Didn't find out (until I tried extracting the spent motor) that:
* motor casing will swell a bit upon use -- so a tight fit is apt to become even tighter.
* wrapping masking tape at middle of motor probably wasn't a good idea (as that's the part of the motor most apt to swell).
* masking tape adhesive "melts" from heat and oozes out the edges of the tape -- potentially gluing the motor to the motor mount tube.
* the direction you twist the motor while extracting and the direction you wrapped the tape around the motor makes a difference.
After mulling over the problem, it did eventually occur to me that I could use a rod inserted into the front of the rocket to push the motor out the rear -- and this method would be least stressful on the rocket.
DeleteOften wondered what happened to the old 'C Rails".
ReplyDeleteHi Bill,
DeleteI read the C-Rails original purpose was for fabric curtain "slides" in older RVs. I don't believe anybody makes the 3/8" square aluminum tracks anymore.