Betty-Sprint - Quasi Sprint upscale bashed from Quest Big Betty

Betty-Sprint
Quasi Sprint upscale bashed from a Quest Big Betty

I have this F32-10 that's been ripening in my rocket cabinet for about two years. I built a Quest Big Betty to use it, but lost the rocket before I ever got around to using that motor. So I picked up another Big Betty at a Hobby Lobby half-off sale and bashed it into this Sprint-like rocket. It should be able to handle the F32. The key will be flying it at a club launch where the chances of recovery will be much better.

Below is a close-up of the boat tail. I wanted something other than friction-fit for motor retention, so I put a slot in the tail and added a piano wire hook. It should work like a charm.

April 20, 2004

Update: 12-31-2008

The finished product has flown several times, all successfully. Like the original Sprint, its boattail is very low drag. The rocket flies surprisingly high on common C motors, and rocks on D's. I have an F32 and a G55 in my stash, but I may never muster the chutzpah to use either of them in this rocket, even though they were in mind while I was building it.

The base of the nosecone was opened to allow access for anchoring a 6-32 screw-eye which in turn attaches the noseweight, here comprised of fender washers.

Having the noseweight adjustable allows for more motor choices. For small motors, I can really lighten it up without loss of stability.

My current shock cord technique combines kevlar cord and nylon ribbon. Inside the rocket, kevlar connects from the motor mount to the 1" wide nylon just below the opening. The kevlar handles well the heat of the ejection charge.

Outside the rocket, kevlar is resumed and connects to the nosecone. Previously, I would use nylon all the way to the nosecone. But the only place it is really needed is at the opening where it guards against zippers by spreading any jerk loads over a wide area.

Furthermore, the ribbon can be bulky and hard to pack whereas kevlar cord or string takes up much less space in the airframe.

The Tango Papa decal is for a stock Sprint, but it works pretty good on the Betty-Sprint, too.

The boat tail was engineered to include a motor hook. While I'm quite proficient at friction fitting, positive motor retention is much preferred - it's so much easier.

The hook is made with piano wire.

The two pictures below show the walls of the channel for the hook. Small balsa triangles were cut and glued in place astride the hook, then the tail cone wrap was applied.

Sanding the edges with the hook in place was tricky, and as a result, I didn't do a perfect job. If I had anticipated such a revealing look, I might have done a little better job

At left, the Betty-Sprint starts its liftoff on a flight in Plano, Texas, at Bob Woodruff park. In the center is a somewhat blurry shot from a flight in McGregor, Texas. And at right is another flight from McGregor.

12-31-2008