Time for a rocketry update. I’ve been building quite a few rockets, each intended to be used in my Level 1 or 2 certification attempts. I built a LOC/Precision Vulcanite first but, on an H motor it looked like it would fly at least 2000′ – a bit high for single deploy at our site. I then built a Performance Rocketry Lil’ Rascal. For various reasons, I was still looking for another design, one that could be used for both Level 1 and 2. Two weeks before my planned Level 1 attempt, I saw an article for a BDR 4.0 and decided to build one. The article indicated a very high CD, 2.4, that would result in very low flights on both H and J motors.
I flew the BDR 4.0 on an H90 on November 6, 2010 at our Boy Scout Rocket-Ree event. NAR president Trip Barber was present and I asked him to be my Level 1 certification official. The flight went perfectly but there were indications that the rocket went much higher than expected. Unfortunately, I did not remember to turn on the altimeter and had no flight data. During the following week, there was extensive discussion among club members as to what the CD should be for a rocket like the BDR 4.0. There was a wide range of opinion, simulation results, and a void of published work on the CD of tube-finned rockets.
With great uncertainty as to what the CD actually was, I decided to go for my Level 2 certification two weeks later, November 20, 2010. I passed the written portion of the test with a perfect score and was antsy to fly before the winds were predicted to become unfavorable. I had selected a J285 motor and had run many sims. My expectations were for an apogee of between 2000′ and 2500′ with a modest range of optimal delays. I split the difference and went with a delay in the middle of the predicted range, 8 seconds. I should have known something was amiss when the igniter did not go very far into the motor but, I guess I was fairly nervous. With a puff of smoke, the rocket failed to come to life and sat on the pad. Jeff Goldstein, my certification official, offered me a spare and I made certain the igniter went all the way in the second time. This time the motor started and the rocket roared off of the pad. Once again, it seemed to go much higher then expected. The parachute deployed near apogee in a strong wind. I watched the rocket descend slowly and drift far off behind a row of trees. We jumped in the back of a pickup and headed off to the NE corner of the field. After a brief search, we located the rocket in a field of winter wheat and in perfect condition. The successful flight meant I had passed on to Level 2. I did remember to turn on the altimeter for this flight. The BDR 4.0 flew to 3010′! Follow up simulations could replicate this performance only if the CD was a rather low 0.67.