I've got a similar size (though much lower and slower than yours). 4" LOC paper tube (based on Fantom EXL).

Drogue:
24" drogue
about 12" space (very loosely packed)
no shear pins
1.1g charge

Main:
78" main
about 10" space
3x 2-56 nylon shear pins
1.5g charge

Both charges extend the 15-20' kevlar to full length with authority. Both charge holders are 1/2" pvc caps attached to the bulkheads of the ebay (yes, that means the drogue charge is above the chute, but it has worked 100% with the loose packing).

With 4 38mm motors, I haven't even broken 3k yet!

-Ken

I tend towards beefy charges... in my similar 4" bird I use 1.5g for the drogue (4"x12") and 2 or 2.5g for the main (4" x 24"). With composite birds, I rarely worry about overpowering things so long as the bearing surfaces are clean and smooth.

Of all people, Art Hoag told me that he never ground tests, he overbuilds - a philosophy I've long followed. Just compute the amount of BP your volume requires and make your charges at least 1.5 times larger. I personally go double. My successful L3 cert was done that way.

W

With that particular rocket, I would personally use 1.5-2g, and I would tend to ground test. It will almost definitely separate with less, but I like to be sure. On a paper or phenolic rocket, I would be a little more conservative, since an excessive charge is more likely to damage the tube, but with glass, I go fairly heavy.

The only tube I ever blew up in ground testing was a 3" phenolic tube using a little over 2 grams, which is why I converted to convolute fiberglass soley. I've yet to blow that up. With the PR fiberglass, you're pretty safe regardles of charge. There is a fine line between not having enough charge to separate and having too much. Pack the chute well and protected and blow that sucker apart. If your chute shreds, at least you've broken the stability of the rocket, and it will land much safer than if it DOESN'T shoot the laundry out. Make sense?

Flat spins w/o chute are repairable. I've even had one rather large rocket remain undamaged from this.

Ballistic recoveries usually involve a trash bag...

My 4" bird with carbon/glass on a phenolic tube and 3 layers of tip to tip has impacted from over 8K via a flat spin and flown multiple times since then.

I know there is lots of response that seems to favor "blow it up, or blow it apart", but I tend to be a bit cautious of over pressurising when using pistons. I have had a couple failures that I attribute to beefing up a charge too much when using a piston. I think if the charge is too strong then the piston just expands and binds in the BT. This seems to be particularly prone to phenolic.

Most powder calculators are not calibrated for our launch platform altitudes so an extra little helps assure deployment. In my humble opinion, it is still best or wisest to GROUND TEST flight configurations as much as possible for deployment with authority. When the rocket is still vertically travelling upward, in coast or at motor burn out, there are extra forces at work keeping the nose on. Too big of a charge for drogue deployment may also cause main deployment as the shock or force of the charge may not be properly directed internally. Bulk heads might take on the burnt of the charge force but that push travels the length of the bird.

And, I agree with both of the previous posts. I AM NOT a piston guy, Warren is and JW is; we have all had different experiences. There are SO MANY VARIABLES at work. Do, as JW says, “Dance with the girl who brought ya.” In other words, whatever has worked for you in the past, will for you in the future. I made all my mistakes, embarrassingly, achieving my L1. My successes are based on the minds and experiences and friendships of this club. Trust us, but go on calculations and instincts, my friend.

combined with a bit of science.

Having over charged my Little Dog Dual Deploy, I got so much velocity from the apogee deployment charge on my booster section that it sped away from the rest of the rocket with enough energy to cut the shear pins on the fore section, straighten out my eye hook, and cause separation of the booster from the fore section. This resulted in a four mile jaunt to retrieve the fore section, which was only found due to my DC-30.

The booster was eventually found (Thanks Bryan Schmidt in another forum).

Tribal knowledge from the club also helped me understand what had occurred (thanks Ken Riley).

It just proves that I am still learning and thus the creation of this thread.

This is fun. Thanks to all.

LS, you may have over-estimated our going above the calculated charge, four miles? Dude, even JW who set off car alarms for miles may even frown on that. Scale that puppy back! 🙂

separated at apogee and the chute came out at 10,500 feet (or so) the unlimbered chute carried it 2+ miles directly over the windmill to the northeast.

Deployment of the main at apogee was bad. Separation of booster from fore section was bad. Straightening out the eye hook hurt too.

Without the DC-30, I would have lost the entire thing.

Another learning experience. I've since launched it but with half the drogue deployment charge and larger shear pins in the fore section containing the main chute.

You can over charge with bad results other than blowing the tube. The fiberglass held up well. I also will used forged eye bolts or weld/braze them shut. A learning experience to say the least.

I'm a fan of pistons for the getting the main laundry out. Here's a great article on piston design.

http://deltavrocketry.com/piston.htm

I employ the "inverted" piston, bulkhead on the bottom with the coupler tube above it. Prevents binding due to expansion of the coupler or from wobble. I also am a fan of "big" charges, especially at apogee, I went a little "too" big at balls this year and blew a poorly glued bulkhead a little bit with the charge, which ended up kicking out my motor casing, which we luckily found.

This is what is absolutely amazing about this hobby, there is no ONE answer. Each of us has different experiences; each rocket is different, as is each motor.... isn't this fun?