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Large clusters and postmortem of yesterday's flight 1 month 1 week ago #3272

I somehow got sidetracked into this area (some was seeing Jay's Hydra 7 lift on 7 Quest B6-6's). Here is postmortem of my flight yesterday.\

On the PS, sorry about being exhausted - only got three hours of sleep Saturday so was ready to go to sleep by 1100.

USR Warp7  with 4 x C6-7 and 3 x C6-0 - modded the motor mount so tubes with "0's" were closed.
4/7 motors ignited, 3 C6-7's and 1 C6-0
All 7 of my Pro-Cast dipped AT First-Fire micro igniters lit - checked at pad post-launch. These have long leads and were twisted into two leads.
One C6-0 popped out at burnout in spite of internal and external tape installed to hold motors in place. Audible pop.
Putting the  JL Altimeter 2 onboard with open-cell foam wrapped around it was a good idea for postmortem and the 'landing'
Even with off-axis thrust, kit was stable and didn't go unsafe - explains the large fins.
Parachute ejected and didn't unwind - haven't checked yet but I think I know what caused that.

JL Altimeter 2 recorded max accel of 5.9G's, to ground observer (me) the whole flight was sloppy and slow. I did a sim of the flight and Rocksim predicted near 12g acceleration with 4 motors lit. Appears either two of the motors that lit were slow up to thrust or some motors didn't perform up to specs, or both. Since BP motors light instantly, the "slow up to thrust" seems strange to me.

Checking motor date codes:
C6-0: I191219 - packages have a 2013-2018 copyright on them
C6-7: J200121 - packages have a 2013-2020 copyright on them
I'm pretty sure the date code is now "as read" instead of a letter sequence with these motors being 12/2019 and 01/2021. However, the C6-7 packages have a copyright of 2013-2020 on them while the C6-0 packages have a 2013-2018 copyright on them.

Old motors can perform oddly or be difficult to light if not stored properly. Possible since the zero's failed more.

Some launch issues
1.) Possible - the souped igniters create some pressure and popped out before completing ignition. Solution - tape or hold them in gently with pieces of launch lug or similar. Allows burn to complete w/o popping out.
2.) Longer leads - make leads long enough they don't pull out of rocket until near top of launch rod.
3.) Gang the igniters with multiple long leads. If some get popped out, fail, or fall out, others won't.

Suggestions are greatly appreciated. I'll post pics of the motor install if requested to Google drive.

Cheers / Robert

 
Cheers / Robert

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Large clusters and postmortem of yesterday's flight 1 month 1 week ago #3273

Hi Robert, did you have the igniters wired in series or parallel?

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Large clusters and postmortem of yesterday's flight 1 month 1 week ago #3274

All 7 in parallel - the FF micros supplied by Quest are lower current than the Estes starters. No issue with launching system based on 100% starter ignition.

Watching the movie I made in slo-mo, I discovered some issues. Wind was VERY light at launch but it caused the blast deflector to "rock" slightly. Since the launcher leads were clothes-pinned to the deflector....OOPS! The igniter leads were being slightly pulled by this. Maybe an issue, maybe not, but variable to remove.

Secondly, the movie clearly shows 1 or 2 motors lighting first and the model starting up the rod before more fire up. Explains the 2.1 second thrust time measured by the JL2 vis 1.6 for a standard C6. There is a requirement for longer leads. I have the motors and will try this again with one of our wood posts for roping off the launch area next to the pad for anchoring the starter leads. Leads will be clipped at a point where they'll make it nearly to the top of the rod before they pull out.

Third - not sure this was the problem, but...will figure a way to hold the starters inside the motors without allowing pressure buildup. I don't think this was p/o the problem but it is a variable. Put 'em in, bend 'em 90 degrees, and tape (or something like it).

Video record of unusual prep or launches is a great way to post-mortem, especially on a large cluster launch. Warp 7 is already fixed up if looking a little worse for the wear, and will fly at next meet with the same load. Due to slightly compromised structure, it will NOT fly on 7 Quest D20W-8's. When I get to 100% with it, then I'll look at the 12 x 18mm model.

Also a plug for the glue prime, glue rivet, and paper hinge method of surface mounting. It is painful to do but even as hard as it hit the ground, no fin completely came off the rocket. If you have to do a surface mount on a high performance model, it is the way to go.

Cheers / Robert
Cheers / Robert

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