Anyway, I wanted to take that nose cone and build a 3" rocket along the lines of the Lance Delta, one of my favorite designs from North Coast Rocketry, with those long, ultra swept fins, and cool canards.

The first thing I did is rough in a basic design in OpenRocket, adding my recovery gear, an ejection baffle, an altimeter and a motor retainer. Once I had a preliminary design in place, I ordered parts from BMS—nose cone, body and motor tubes, couplers, bulkheads, and centering rings. I picked up two sheets of .125" basswood from Hobby Lobby, a 29mm Aero Pack retainer from Apogee Components, and eye bolts from Lowes.

With parts in hand, I went back into OR and entered exact weights and measures of all components. I added a mass object to account for adhesives and paint, then set that at 2 oz. and placed it about a third of the way up from the aft end of the rocket.

Once I had the total weight of the rocket, I started tweaking fin shape and canard placement until I got the stability factor where I wanted it with a G80 loaded—a shade over 1 caliber.

Then I started running sims with the G80, and five other single-use motors, adjusting the weight of the rocket until I came up with three motors—G74-6, G78-7 and G80-7—that gave me deployment velocities well below 10 mph.

With the design pretty much nailed down, I ran a fin flutter analysis using a trick I learned from John Cipollla for calculating flutter with swept fins—measuring semispan from the center of the root chord, to the center of the tip chord. I set the fin thickness to .158, which is the thickness of .125" wood, papered and painted.

Flutter threshold is 386 fps—263 mph. That's 28 mph over VMAX on a G80, which is not the 25 percent margin Cipolla recommends, but close enough for me.

Finally, a calculation of ejection pressure to make sure the parachute ejects. The body tube ID is 2.93", length of area to pressurize is 13.5", and the BP charge is .7 grams, which gives me 15 psi, with a force of 101 lbs on the bulkhead.