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  #11  
Old 10-03-2019, 05:44 PM
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tbzep tbzep is offline
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Clarification/rebuttal (however you want to look at it).

You can easily fly BP motors without a thrust ring. It is handy to have one, but not necessary. If you go without them, you will need to use tape to create a thrust ring at the rear of the motor and do a light friction fit into the motor tubes. A wrap or two of tape around the motor abd tube and you are good to go. I've done it dozens of times with BP motors. It does eventually char up the upper end of the motor tube, so I wouldn't do it this way if you plan to fly the thing a lot with shorter motors then fly with a longer one.

That said, if you know you will never go over a certain length motor, go ahead and put in a thrust ring and use spacers to protect the motor tube when you use shorter motors.

It is fine to mix ejection charges. A D12-3 will not eject at the exact same time as a C6-3, so it won't matter if they are "matched". As an example the D12-3 has a burn time of 1.65s and delay of 2.39s giving a total ignition to ejection time of 4.04s. A C6-3 has a burn time of 1.86s and delay of 2.47, with a total time of 4.33s. That's 0.29s difference, which doesn't sound like much, but the D12 has already kicked the laundry out before the C6 fires. These are the average NAR test times, so it's possible or even probably to get them even farther apart.

What you must do is make sure the extra ejections do not burn your shock cord because there won't be any wadding left to prevent direct contact of the charge. My son and I have often flown the Semroc Saturn 1B with two B6-2's and two B6-4's to make sure we did not have too strong of an ejection with all four going at once. It works great.

Once you decide on motor combination, make sure your core, or a couple of the outboards have the right ejection time. The rest can have longer ejection times so that you won't end up with a shotgun ejection.
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Last edited by tbzep : 10-03-2019 at 05:59 PM.
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  #12  
Old 10-04-2019, 10:14 AM
KILTED COWBOY KILTED COWBOY is offline
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The center 24mm motors ejection charge will go up through the Estes kit supplied motor tube.
It will have 2 centering rings/bulkheads.
The outer 4 18mm just go up into the bottom BT101 body tube . I do not think they will get to the recovery devices.
Some gave me the advice to use booster motors with 0 delay and stuff wadding into the rear of the motor and tape in to protect inside of rocket. What do y'all think?
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  #13  
Old 10-04-2019, 01:57 PM
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Rocket Babe Rocket Babe is offline
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Quote:
Originally Posted by KILTED COWBOY
The center 24mm motors ejection charge will go up through the Estes kit supplied motor tube.
It will have 2 centering rings/bulkheads.
The outer 4 18mm just go up into the bottom BT101 body tube . I do not think they will get to the recovery devices.
Some gave me the advice to use booster motors with 0 delay and stuff wadding into the rear of the motor and tape in to protect inside of rocket. What do y'all think?






You can't allow the burn through gases of 4 boosters or the ejections of 4 engines to "dump" into the bottom of the BT. That would cause A LOT of problems! So just don't.

I suggest extending the tubes of the outboards and using the same delay time ejections on all 5. Using all 5 will greatly increase the chance of survival if the core engine doesn't light. However, if all 5 will kick the chutes you CAN NOT use boosters because when they burn through, the rocket will separate while still climbing at a good clip and well ahead of the core ejection.

If you seal the 4 outboards off completely at the end of the engine mounts so that nothing can enter the lower BT, use boosters only, and do not clip or tape them on; let them kick out.

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  #14  
Old 10-05-2019, 08:19 AM
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I modified a 2157 for a 5 motor cluster, and added 2 18mm stuffer tubes to double up on the ejection charge. The other 2 18mm motor tubes are plugged, and I use epoxy plugged C6-0 motors. To get the balance to where Verna recommends, the total weight w/o engines is about 19oz. The nose weight is in 3 different locations in the upper section, so it comes down horizontal as designed.

Flies great on D12 + 4x C6 combo, I've flown it probably a half-dozen times this summer. It's getting pretty beat up from hard landings, the fairings are very fragile. Next time I'll extend the motor tubes so it can be flown with nozzles.
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