Batman,

I have been in the same spot, but with a slightly larger BT. I measured the BP included with the J350 and it was approx 1.5 grams (somewhere between 1.3 and 1.6)

Sorry, I can't remember the exact amount - I wish I wrote it down.

I ended up adding more BP to fill the well completely. I am currently looking at using a paper tube to extend the forward well for motor based ejection on a 6" diameter tube.

There is an excellent site at ROL http://info-central.org/recovery_powder.shtml that discusses black powder charges and how to calculate them. My gut instinct is that the 1.5 grams with the motor will be fine. For my 6", 24" chute compartment and using a piston I use 3 grams.

Doug

For that rocket, you should be fine. My dad uses the full charge (and no more) with his PML endeavour, and it works fine (4" with no piston, loose fit).

There is an excellent site at ROL http://info-central.org/recovery_powder.shtml that discusses black powder charges and how to calculate them.

Doug,

I use this calculator, too. I'm using 6-32's for my nose cone holding the main... the calculator goes only to 4-40's, so I'm taking a shot for 6-32's doubling what blasts (4) 4-40's. Does that sound right?

Also, because I couldn't get the materials from PR, I'm not using pistons for my L3. Gonna blast and pray (after ground testing). 🙂

8) Bruce, stand back from the fence!! 🙂 8)

I use this calculator, too. I'm using 6-32's for my nose cone holding the main... the calculator goes only to 4-40's, so I'm taking a shot for 6-32's doubling what blasts (4) 4-40's. Does that sound right?

My experience with the calculator is that it errors on the consertative side. I too need to go to 6-32 screws and although it had been said here many times before, do the ground test. I would recommend doing a ground test with the charge the calculator recommends for four 4-40's on the four 6-32's. My guess would be that it will shear the 6-32's no problem. Then fly with 1.5 times that amount to make you feel better.

Doug

P.S. I tested with half the powder it recommend to shear four 4-40's and it still sheared them. But there are too many factors to take into account so please do the ground testing.

I would recommend doing a ground test with the charge the calculator recommends for four 4-40's on the four 6-32's. My guess would be that it will shear the 6-32's no problem. Then fly with 1.5 times that amount to make you feel better.

Thanks, Doug. That's good advice. And, I'm using a dummy chute until I find the working amount, THEN I'll do a last test with the correct chute.

Why 6-32's Bruce? I have 3 x 4-40 nylon screws and they hold things together just fine and surely shear when I do a deployment test.

Warren

Why 6-32's Bruce?

Why? Paranoia! My nosecone has weight in it, and like the dart, it should be loaded with inertia/momentum. I just don't want to take any chances. 4-40's probably would have worked just fine. That's what I originally had and what I'm using on the booster apogee separation. Conway used 6-32's on his nosecone, and I think that's the way to go in my case. The ground test will show a lot.

Its all about mass and speed and better to be prepared then not. What if when the apogee charge opens things up and it tosses out a little hard and yanks the cone off? or what about if you ever or even if this flight has enough momentum going and as it hits burn out negative g's happen it separates at the nose (as well as body). it can happen. And you don't want it to. Each "6 is worth about 30lbs force. Those G forces multiply the weight of pressure on the cone area of contact. Its amazing how fast things get heavier under those circumstances. Besides I had several people like JW and James and Jim Amos and others recommend me the same advice, So I paid heed to experience. My charge for my rocket was 10 Grams on the apogee. Very very important to get that out or its lawn dart city. If you are flying higer altitude I recommend a bit more BP. My calculations for my apogee was 6 to 7 grams only and it wouldnt seperate the apogee with 4 X #4's but its also got alot of space inside. Now my mains ended up right on at 6 grams on the ground with 4 number 6's. But for safety factor I added to it. I went from 9 grams to 10 on the apogee charge for the primary altimeter. My secondary/Backup Altimeter fired a 12 gram charge. So I recommend not just redundant but make the next one a gram to two larger. Just in case it needs more. Same on my mains a main of 7 grams with a back up of 8grams. You can see where it got me I hope. Also here is a video of one of my ground test.

http://s13.photobucket.com/albums/a255/1n5an3o/?action=view&current=rockets.flv

You can see where it got me I hope. Also here is a video of one of my ground test.

And, I want mine to have that clean separation. I have (12) 12 gram Quickburst canisters--and as far as I know, still can't buy 'em, and I need four for the flight. Best case, I'll have some left over. If not, I'll make my own. Can't wait until the L3 is over and successful... so I can get a good night's sleep. 🙂

You're using dual charges? I would stick with a single charge, but dual matches and dual altimeters....but that's just me....and I'm probably worse than Wilke when it comes to oversized charges. I don't advertise this much, but I had one rocket look like Elmer Fudd's proverbial shotgun after Buggs stuck his finger in the end due to a charge that was a "tad" oversized. I've had several others succumb to charges that were a might too big. My 38mm J570 bird flew beautifully, but the apogee charge was so oversized that it ballooned the apogee piston, not only wedging it in the airframe, but spiral fracturing the airframe besides... When the main went off, it was going probably 600 mph and it just completely stripped. I was lucky to find most of the bird (minus nose cone, main chute and one fin) a bit over a mile E-SE of the launch area...

Warren

I don't advertise this much, but I had one rocket look like Elmer Fudd's proverbial shotgun after Buggs stuck his finger in the end due to a charge that was a "tad" oversized.

I blew up the top of my VA's booster section (and drogue) at Oktoberfest with an ambituous charge--which Ray LaPanze and his camera caught in great detail. Chute happens! 😯 🙂

You're using dual charges? I would stick with a single charge, but dual matches and dual altimeters....but that's just me....and I'm probably worse than Wilke when it comes to oversized charges. I don't advertise this much, but I had one rocket look like Elmer Fudd's proverbial shotgun after Buggs stuck his finger in the end due to a charge that was a "tad" oversized. I've had several others succumb to charges that were a might too big. My 38mm J570 bird flew beautifully, but the apogee charge was so oversized that it ballooned the apogee piston, not only wedging it in the airframe, but spiral fracturing the airframe besides... When the main went off, it was going probably 600 mph and it just completely stripped. I was lucky to find most of the bird (minus nose cone, main chute and one fin) a bit over a mile E-SE of the launch area...

Warren

TRUE redundancy is having 2 charges. If the charges are done correctly you will see all the 2nd charge is doing is make a chuff. Thats because the primary worked fine. Oh yea and my charges have 2 matches per charge as well as the 2 charges per event and 2 altimeters. So here is a question. what happens if under flight or at any point in time something happens to your BP. Moisture when making the charge or just bogus BP? maybe gets busted loose while assembling or in flight? Who knows what. 2 matches there aren't gonna save you. How about if you calculated wrong and even with testing on the ground but due to a different altitude and Temperature it fails? (things do shrink when cold and BP is less effective at higher Altitudes) its best to have a 2nd charge with more umpf. Ask James Russell as a TAP and L3CC as well as the west Coat L3cc Chair for NAR what he thinks. I can tell you. He thinks that larger rockets that are of the magnitude that L3 projects are should have as much redundancy as possible. Did you know that even in some of the rules I belive NAR specifically it ask for redundant charges?

I just prefer to error on the safer side when it comes to the hard part of flying a rocket and that of course being recovery.