I am having trouble because my ground tests and actual flights are reacting very differently. I thought i understood ground testing: set up everything as you would for the actual flight then work your way up in the quantity of BP that gives you the desired results for ejection. Maybe there is something i am not understanding because I am getting totally different results with the flight.
The rocket:
- 38 mm with a 29 mm motor tube
- 29 mm G-79 motor
- 41 inches long
- 1.6 lbs.
- dual deploy, altimeter based ejection
- ejection charge in motor removed
- 12" drogue chute
- 24" main chute
- 100 # test Kevlar shock cord
- 15 feet of cord for the drogue and main chutes
- shock cord z-folded with tape at both ends of fold
- one 2-56 nylon shear screw for each parachute bay
I consulted a online charge calculator and started testing with .20 grams of 4-F black powder The charges just made a chuff sound and the rocket didn't separate at all. I eventually worked my way up to .5 grams for the drogue bay and .8 grams for the main. This seemed to get the parachutes out and about 1/2 of the z- folds broke. When I flew this rocket the shock cord for the main broke and it came down in two pieces. I thought this must be a fluke so I flew it again and this time the drogue shock cord broke. I went through the ground testing again and came up with the same results. I flew the rocket again ( I'm stubborn) this time both the drogue and main shock cords broke and the rocket came down in 3 pieces with the AV-bay free falling. The obvious thing to do is go to a heavier shock cord but this rocket is so tight I don't know if there is room. My main question is how can the ground tests and actual flight have such different results.
The rocket:
- 38 mm with a 29 mm motor tube
- 29 mm G-79 motor
- 41 inches long
- 1.6 lbs.
- dual deploy, altimeter based ejection
- ejection charge in motor removed
- 12" drogue chute
- 24" main chute
- 100 # test Kevlar shock cord
- 15 feet of cord for the drogue and main chutes
- shock cord z-folded with tape at both ends of fold
- one 2-56 nylon shear screw for each parachute bay
I consulted a online charge calculator and started testing with .20 grams of 4-F black powder The charges just made a chuff sound and the rocket didn't separate at all. I eventually worked my way up to .5 grams for the drogue bay and .8 grams for the main. This seemed to get the parachutes out and about 1/2 of the z- folds broke. When I flew this rocket the shock cord for the main broke and it came down in two pieces. I thought this must be a fluke so I flew it again and this time the drogue shock cord broke. I went through the ground testing again and came up with the same results. I flew the rocket again ( I'm stubborn) this time both the drogue and main shock cords broke and the rocket came down in 3 pieces with the AV-bay free falling. The obvious thing to do is go to a heavier shock cord but this rocket is so tight I don't know if there is room. My main question is how can the ground tests and actual flight have such different results.