Shear Pins With Cardboard

[Rschub]

25 feet on the drogue heh heh. The plan is to add a tennis ball or something next time.

 

[b.wieting]

I also use a Y-yoke harness that joins the shock cord well outside the booster... maybe that helps too.

 

[Handeman]

Maybe kevlar, tho I've used it without incident on the Maggs. How about drogue shock cord length?

Couldn't figure out why Wildman Blackhawk38, with two 2-56 on the 38mm airframe, popped the main in addition to the drogue (streamer) at or shortly after apogee, two flights in a row.
I discovered that I'd accidentally swapped the (shorter) main and (longer) drogue shock cords, so apparently the abrupt forces when the short shock cord stretched out sheared the pins.
After swapping the cords to the correct (main-short, drogue-long), had a picture perfect flight, streamer at apogee, main at 300'.

Check your drogue deployment charges! Most problems like that occur because the charge is too big, not because the cord is short. You only have to get the rocket to open enough to get the drogue chute or streamer into the air stream. The drag of the chute or streamer can pull he rest of the cord out and get things stabilized on the way down. Adding length to the drogue shock cord is adding weight and compensating for a too large apogee charge, not fixing the root cause of the problem.

 

[b.wieting]

Check your drogue deployment charges! Most problems like that occur because the charge is too big, not because the cord is short. You only have to get the rocket to open enough to get the drogue chute or streamer into the air stream. The drag of the chute or streamer can pull he rest of the cord out and get things stabilized on the way down. Adding length to the drogue shock cord is adding weight and compensating for a too large apogee charge, not fixing the root cause of the problem.

Good suggestion, it's plausible. I did however use same charge (0.7g 4F) on all three flights, in which only the last flight with the swapped longer drogue cord deployed as designed (yes, thinnest of statistics). I had ground tested three different drogue charge levels; since even 0.60g gave brisk separation, tearing most the tape on the Z-folded cord, I'll fly with a smaller drogue charge next time.

Curiously, altimetry (fall rate) implies that on the first "failed" flight, the main deployed fully only about 7sec after apogee; on the second, the main deployed fully at apogee.