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Old 03-03-2018, 09:07 PM
MarkB.'s Avatar
MarkB. MarkB. is offline
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Join Date: Feb 2008
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Default Using Semroc baffles in BT-55/56 with 24mm power


The title sorta says it all; I am wondering if anyone else has had success or failures using the Semroc heavy card stock cone ejection baffles in BT-55/56 (1.3") size rockets when using Estes 24mm (D-E) size motors.

Why? Several weeks ago I launched a Rescue Sandhawk on a D12-5. As part of the repair process, I added a Semroc ejection baffle with a Kevlar leader. On it's first return-to-flight, at ejection, the plastic fin unit blew off and recovered ballistically. Luckily, it landed in a newly-plowed area and the plastic portions were undamaged. However, the motor tube, which extends about 4 inches into the body tube was split along the seam from the end to the paper ring just above the plastic unit itself. The upper ring completely vanished.

So my theory is that the small BT-55 + the force of a D ejection charge + the back pressure generated by the baffle was too much for the fin unit glue joint and the kraft paper engine tube. The glue joint appears to have been some kind of yellow glue. In my mind, yellow glue paper-to-paper probably should not have failed. And the motor tube should not have failed either.

I have used these baffles in all tube sizes larger than 1.3" with 24mm motors without any problems. So, if someone is using the Semroc baffle in a BT-55 and a D or E motor without problems, I'd like to hear about it. Then, I could likely blame the glue joint.

I'm gathering materials for repair and this Sandhawk will fly again . . . but maybe without the baffle.

Identifying a problem without proposing a solution is just whining.

NAR 79743
NARTrek Silver
SAM 062

Awaiting First Launch: micro V-2; Blossom V-2
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Old 03-03-2018, 09:53 PM
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BEC BEC is offline
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I have had mixed results using those baffles in models with 24mm motor mounts. I think I've blown the baffle out of my Eliminator and my Estes SLV. But I haven't had anything happen quite as dramatic as you did.
Bernard Cawley
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