Wednesday, May 20, 2009

Enhanced Motor Retention for Semroc Brighton

The Semroc SLS Brighton is a a very nice versatile kit. It has a motor mount system that can take a wide variety of single motor and cluster configurations. You can fly it on a cluster of four C motors (18mm), a cluster of three D-E motors (24mm), or single 29mm motor for flights up through H size motors. You can also fligh on a single 24mm motor using and included 24mm-29mm adaptor for the single 29mm motor mount.

The only major drawback to the stock design is the small engine hook (One typically used with 18mm motors) that is used to keep the motor mounts from ejecting. You have an overall very strong design of though-the-wall basswood fins and very strong tubes that when glued with epoxy make for a robust rocket that can be flown on motors up to high powered range. But then you haveonly the tiny little hook to hold in the removable motor mount. In the picture above you can see the small hook on the left side of th picture.

To compensate for this, I used Aves Fix-It epoxy putty to mount two threaded rods between the sustainer tube and the internal mount for holding the interchangeable motor mounts. I used one 3" 6/32 threaded rod cut in half. That made each rod 1.5" in length.

Shown above are the 3/16" One Hole Midget Cable Straps and wing nuts I used for the retainers. I was going to use these wing nuts as a "tool-less" design for ease out in the field. However, I will replace those with regular nuts to fly to cut down on the drag of the "wings" on the nuts. As you can see from the picture above, I also used the Fix-It epoxy putty for the fillets on the launch lugs and fins. I plan on fiberglassing the fins and lower body tube for added strength for high powered flights.

Hope this helps out some of you building this model. I had read several stories of high powereed motors being ejected and lost because of relying on the supplied hook. I would actually just have left it off to save on weight, if I had known I was going to add this modified retainer system.