|Launch & Static Tests|
Providing the PIRM2 functions as intended, the rocket was built to include a digital palm-corder for recording flight video. Although I think I'll wait with loading the camera until the rocket has been flown a time or two. The rocket is the again rebuilt fiberglass rocket. Reusing parts from the last rocket lost in Launch Test 61. On a positive note, the fin section survived making the rebuild a little less painful.
One problem I'm still running into using a PIRM, is the lack of room in the upper body tube for both parachutes and the shock cords. I was going to replace my 1" nylon webbing with 9/16" tubular nylon, that should help some, but after a month the rocketry supplier still hasn't delivered. So I decided to go with 1/4" braided nylon rope. It's not my first choice, but it should hold providing the flight is nominal. Even with using rope, it's a snug fit. I really think the PIRM2 would fit better in a 4" or larger diameter airframe. Part of the problem is my parachutes, I think they are a little bulkier than they could be. Of course I make them myself, and never having used a purchased parachute I'm speculating a little on the bulkiness.
Propellant Weight: 1.7674 Pounds
Propellant Length: 12.0"
Kn: 166 initial, 177 max
Launch Weight: 10.8 Pounds
Update: The rocket was launched today, but I need to back up a little. The 9/16" tubular nylon came in, so I replaced the rope with the tubular nylon. It is nice stuff, strong, lightweight and compact. I was still in a bit of a dilemma as to how to pack the parachute. The electronics module has an aluminum tube to extend the apogee deployment charge above the main parachute. The charge needs to be above the main parachute to keep from ejecting it. The problem is how to keep the drogue chute near the nose cone so it is ejected when the apogee charge goes off. I shortened up the length of shock cord between the nose cone and the apogee parachute, hoping when the nose cone blew off at apogee the nose cone would pull the apogee chute out.
Now, on to the launch.
It was a pretty good day, a little windy but not bad. I had Bill on hand to help with set up, it went quickly as I had the rocket ready to go before we left. The launch tower and controller were set up, and the rocket loaded on the tower. The electronics module used two magnetic reed switches for launch detection, so I taped a magnet to a light cord, and tied the cord to a heavy piece of iron near the launch pad. The magnet holds itself to the rocket while on the pad, and is simply pulled off the rocket at launch by the cord. An igniter was installed in the motor, then the electronics module was turned on.
All was set. 5, 4, 3, 2, 1 and ignition! The motor came to pressure quickly and the rocket soared into the sky.
Cleared the tower and on it's way.
Here's the rocket just prior to motor burn out.
I started a stop watch, glancing at the stop watch as I watched the rocket climb to apogee. At 15 seconds the apogee charge fired just as it should, leaving a nice cloud of smoke.
Click Here for a short video of the launch.
Then, nothing. We both lost sight of the rocket. After about 10 seconds of searching for a parachute, the distinctive sound of a rocket coming in ballistic was heard. I reacquired visual contact shortly before the rocket impacted. Bill and I walked into the field to assess the damage.
The damage wasn't too bad. Body tube broken in a couple of places, one timer was damaged when the apogee charge aluminum extension tube racked across it. The nose cone was fine, as is the tail section. The electronics module will need some minor repairs, but all in all it could have been a lot worse. A couple of hours in the shop and she should be ready to fly again.
Here's the rocket the way it was found.
So, what went wrong? The rocket was found with the nose cone off, and the parachute shroud lines outside the rocket. But the splice where the shroud lines attach to the shock cord was inside the body tube. It appears the splice got caught, and kept the parachute inside the body tube. My best guess is that the rocket had enough speed so that when the deployment charge went off, the nose cone ejected but was then blown by the air along side the rocket, the 180 degree bend in the shock cord caused the parachute attachment point to get caught. I'm also pretty certain the parachute was actually below the deployment charge when it went off. The parachute tends to slump due to the high gee forces at lift off. I had considered it as a potential problem, but I thought the nose cone would have enough energy on it's own to pull out the apogee parachute. In hind sight, I may have had an equal and opposing force. In that the parachute had the deployment charge force acting on it from one end of the shock cord, and the nose cone with an equal force at the other end. The nose cone could then have simply snapped back to it's position beside the rocket air frame.
So how do I prevent this? Well I've given this a lot of thought, even before the launch and failed recovery.
If the air frame was larger in diameter, I could make two separate compartments, one for each parachute. That would really simplify things, but I don't have the diameter to do that.
I could make a pouch to keep the main chute in place until released, that may be a good option and I'll explore it more.
I could retain the apogee parachute to the nose cone some how, to keep it in place until it exits the rocket. Another good option I'll think on some more.
I could also make a bulkhead that would only go out with the nose cone, and keep this floating bulkhead between the two parachutes. It could work, but I think there may be problems there with potential jamming or shock cord entanglement.