TwoFin

Background

When I first started attending CMASS’s meetings, one of the recurring topics of discussion was the possibility of building rockets with only two fins. Many ideas were tossed around, but it was a fairly one sided debate with all parties reaching the conclusion that you did, in fact, need to have fins in at least three planes.

Being the troublemaker that I am, I couldn’t leave well enough alone. I decided to take on the challenge. Granted, the arguments all centered on having two standard, axial mounted fins, but I decided to take a slight departure from that design.

After several evenings of rough cutting, shaping, and sanding, I created a spin stabilized rocket with two canted fins. Since I had no way to predict the rocket’s stability, I decided to start with a small design to minimize any damage due to unexpected flight paths.

My first launches with A8-3’s and B6-4’s turned out to be absolutely wonderful. The rocket flew perfectly straight and you could easily see the spin on both ascent and, to my surprise, on descent.

Competition

Last summer I was fortunate enough to attend NARAM-41 in Pittsburgh. After several days of humiliating defeats on the competition range, I decided to give up and just stick to sport flying. I had just prepped my TwoFin and was proudly displaying it to some other fliers, when I was jokingly asked if I was going to fly it in the A-Streamer Duration event.

As I mentioned before I have a tendency to be a troublemaker, and I knew that the TwoFin flew well on A motors.

I rushed over to one of the vendor’s tents and purchased a handful of streamer material.

Needless to say, I did not win the event. In fact, the only reason I didn’t come in last was that I actually completed all three flights.

There is, however, an important lesson to be learned from this experience. If you can’t win with skill, you can at least lose with style.

Therefore, the TwoFin is now a competition veteran. Not a good one, but a veteran nonetheless.

Parts List

• 1 Body Tube, BT-50, 10 inches
• 1 Nose Cone (50Y or similar)
• 1 Motor Mount Tube, BT-20, 2 ¾ inches
• 1 Engine Hook
• 2 Centering Rings (BT-20 inside of BT-50)
• 1 Engine Block (18mm)
• 1 Launch Lug (1/8” x 1”)
• 1 Fin stock (3/32” balsa)
• 1 Kevlar®™ shock cord (12”)
• 1 Elastic shock cord (12”)
• 1 Swivel (not a snap swivel)
• 1 12” parachute or 30” streamer
• ½ Ounce of clay