Shear pins on main only, or main and drogue?

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TBSSJoe

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Shear pins on main prevent deployment at apogee due to shock from the drogue charge firing, yes?

Shear pins on fincan (drogue) prevent drag separation, yes?

So do most dual deploy setups use them on both?
 
I only put them on the payload section for the main. You should have a friction fit on your coupler enough so if you turn the rocket upside down it would keep together, but it is still easy enough to separate that it can deploy easily.

I've seen some RSOs turn rockets upside down before signing off on them.

The point is, shear pins shouldn't be necessary on the drogue side. That is, unless you have a more complex arrangement such as with air starts or multiple stages.

That being said, shear pins aren't going to hurt anything if it makes you feel better about it. As long as you ground test to make sure your charge is enough to break the pins.

If I could give one tip for shear pins, it would be to invest in a #2 tap. Makes it much easier to get them in w/o making the hole too big.
 
You are correct about the use of the pins.

I don't know what "most" DD setups are. I can tell you that I didn't use shear pins at all until I started flying large fiberglass rockets.

For the 4" and smaller cardboard tubes I just used tape and friction fit, and still do. In 50+ DD flight with the cardboard I've only had one flight that deployed the main at apogee and I attribute that to "go fever" We had a perfect day with no wind above 300ft. I bought a Pro54 6G motor and got my 4" rocket to +7000 ft. It was using a new payload tube and I didn't retape the nose cone joint for the new tube and the main deployed at apogee. According to the Alt data it was 350 seconds from apogee to landing and it landed less then 200 yards from the pad. It was a perfect day and "No harm No foul" on that one.:facepalm:

I can't say if you would have the same success with friction fitting as I have. The drogue charge size, length of shock cords, rocket design, etc. all play into how well the recovery system works.
 
Perhaps my experience is with somewhat bigger, heavier, and faster than average rockets. But I always shear pin everything. I've seen a friend's 70# rocket on an N drag separate at burnout. At least it was under mach. I never did get my Rocketman drogue back that I'd loaned for the flight. It ripped the tubular Kevlar and was never seen again. Etc. But the rocket was built solidly. It lived to fly another day.

Gerald
 
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