Scratch No Fins Required Original Design / Scratch Built

Scratch - No Fins Required {Scratch}

Contributed by Mark Schrader

Manufacturer: Scratch

(Scratch) No FinsBrief:
Spin stabilized finless rocket.

Construction:
This is an unusual rocket that uses two 13mm canted motors to induce a spin. Clay ballast is packed around the lower portion of the nose cone to improve gyro stability.

It is a four engine cluster consisting of two 18mm motor mounts and two canted 13 mm motor mounts. The 13mm motor mounts are capped so at ejection the motors themselves are ejected. Since angular momentum is conservative, this actually increases the spin of the rocket! The two 18mm engines vent into the body tube and blow the nose cone.

(Scratch) No Fins The two 18mm engine mounts are assembled like a conventional rocket and use thin, corrugated cardboard centering rings. The canted motor mounts are glued to 3/32" basswood that's glued inside the body tube. I had to cut notches out of the BT-80 body tube to allow the exhaust from these motors to vent.

The launch lug actually runs through the center of the rocket and consists of Apogee 10.5 mm body tube. In order to seal the launch lug and prevent ejection gas from escaping, I used a BT-5 tube coupler at the end of the 10.5 mm tube to join the "launch lug". The top half of the lug runs through a corrugated cardboard centering ring in the nose cone and can slide to facilitate prepping the rocket. In other words, you can pull the launch lug out to fit it into the body tube lug then slide the nose cone into the body tube.

(Scratch) No Fins (Scratch) No Fins For recovery, the nose cone and body recover on separate streamers. A conventional shock cord tangles too much what with all the spinning.


(Scratch) No Fins Finishing:
The finish is gray primer. I masked off a white stripe around the middle and use Monokote stripes to make a test pattern.

Flight:
I've flow this rocket four times and have to say the best combination is 2 C6-3 and 2 A10-3 motors. A typical flight is straight and stable up to about 150-200 feet at which point it becomes unstable and briefly tumbles harmlessly after motor burnout prior to ejection. This is a real crowd pleaser!

Recovery:
Recovery is a breeze since there are no fins to break.

comment Post a Comment