Hi Jeff,
I didn't notice that but if that rocket had been inherently stable I believe it wouldn't have done that initial curving flight path off the rail. I could see where the asymmetric thrust from two of the three fin motors would result in that corkscrewing that was seen later on in the boost in that unstable flight.
If the rocket was stable right off and there was an early ignition of one of the fin motors, I would have expected a little bit of a curve in the boost phase and not the erratic spiral flight seen in the later portion of the video.
There was a lot of motor weight in the butt end of that rocket. If there was adequate noseweight, I wouldn't have expected that type of flight.
Yeah that full sized Phoenix was quite the ship. I spent a lot of time in the flier's shop mixing motors in 25kg batches in a commercial mixer.
The rocket group helped make the N and O motors. We generally had great success with our research motors and the motor on the Phoenix crash performed nominally.
Later on, it was used in three more projects. On one flight, the two altimeters were dorked by Rf from the 2 watt Garmin GPS dog tracker and the rocket core sampled. Only the engine retainer was sticking out of the ground. That was like a 12 foot long rocket. Took a backhoe to get it out.
Next flight in a shorter rocket, the ebay wasn't sturdy enough and the main chute deployment tore apart the ebay and that rocket died.
Last flight was in a 12 foot tall 16 inch diameter rocket and that was it for the 6 inch diameter motor casing. Upon ignition, the aft end of the motor casing blew out. The rocket worked itself off the rail, with flaming grains falling out by gravity, tipped over and the motor grains consumed the rocket and the launch trailer. Fortunately the launch trailer was from our Peoria group and no QCRS hardware was destroyed!
The flier, Pat Hibbs, gave up on large diameter motors after that.
What I believe is the recurrent heat flux on the aft end of the motor caused the aluminum to lose strength and it eventually gave way. The end of the motor fractured. It had a threaded and pinned aft closure. That did not give way. The case fractured well above the the aft closure. The motor had a big full diameter graphite nozzle and I've notice in the research groups that fliers in the large diameter range many times use a phenolic carrier for the graphite nozzle. Phenolic is a better insulator than graphite.
Heat stress doomed the motor after like 6 firings.
Sorry to drift a bit OT on this thread but butt heavy rockets can do screwy things. Kurt
