I have built an Aerotech G-Force to use for Mid Power. This is my first venture into Mid Power so I have read and asked questions about it.
I decided to upgrade a little so I replaced the coupler with a longer and thicker (8") one from GLR using the existing one to beef up the rear tube aft of the motor. I also swapped out the composite forward bulkhead and screw eye for a 3/32 ply and u-bolt. I went with 12' of 1/4" Tublar kevlar,5' of 9/16 Tubular nylon and a small piece of the original 5/8" elastic attached to a 48" Sperachute with a kevlar chute protector. All of this was connected with quick links. I also added removable rivets to the coupler/lower body tube and to the nosecone to upper body tube to be able to remove them later when I add a camera.

In doing this I figured that I should ground test the ejection charge to see if the upper section and the laundry will deploy properly.

That's where I found a problem. I tried the test by loading the charge for a "G" motor into the fwd closure of my 29mm case along with an ignitor.
When the ejection charge fired the upper section it only moved up the coupler about 2-3 inches. See video here:


I tried packing things inside tighter to make them more loose (even though they were already loose enough I thought)and tried again with same result.
The upper section is not too tight on the coupler in my estimation. When I pick up the rocket by the upper section the bottom slides easy off and when I turn it nose down it stays put.

Maybe I'm missing something so I'm asking here. I am glad that I did this first because they way it seems that if I had loaded the motor and just flew it probably would not have ended well.

I have searched but could not find any reference to mid power ground test's only high power. Not that they aren't there I just could find any. Probably the same and seems that adding more BP to the ejection does the trick. I could try that but what about the SU motors? You can't change them.

In looking at the video I noticed a lot of ejection and flame thru the aft closure. Could the lack of back pressure (Empty casing) be the problem?

Thanks for any help.

I'm pretty sure that's the problem. I flew my G Force a dozen times and the parachute never failed to deploy using the standard ejection charges in the Aerotech motors.

-- Roger

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-Fred Shecter NAR 20117 (L2)
Southern California Rocket Association, NAR Section 430