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Four "E" Engines in a BT80 Rocket?

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Fore Check

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Ok, I'm looking at building a rocket that is BT80 based with four 24mm motor mounts, set up to accomodate the longer E engines.

Today I came across this review that someone put together for a scratch upscale Astron Ranger with a 4 x 24mm "E" engine mount. It's basically an overbuilt Super Big Bertha (BT 80 Based).

http://www.rocketreviews.com/reviews/scratch/super_ranger.html

Anyway, scroll down to the bottom of his review/report. You will notice that he indicates after his 1st 4 x E launch "you can clearly see the heavily charred motors and mounts. In hind site, it might have been very wise to coat the inside of the rocket and all around the mounts with epoxy or some other fire inhibiting substance! As it is, the inside areas of the mounts below the centering ring were completely burned away and the areas all around the mounts were badly charred. This was all cleaned away as well as possible and the area coated with epoxy. It will fly again!"

What does he mean by "the inside areas of the mounts below the centering ring" that were completely burned away? Is he simply talking about any portions of engine mount tube that extended beyond the aft-most centering ring? Will a "Tulanko tail" solve this issue? I have a couple of launches on a 2 x 24 mm motor mount where the aft most centering ring looks pretty charred, but the damage seems entirely cosmetic and the rocket is still quite flyable with no repairs necessary. It has the "Tulanko tail."

Further, if you coat the inside of an engine mount tube with epoxy, aren't you going to have to sand most (if not all) of it back off just to get the motor to fit?

Will using heavy walled (non-foil-lined) BT50 solve the problem?




Truth be told, I just recieved my Super Big Bertha kit off eBay today, and it's the rocket I was considering installing this motor mount in. Strange that I came across this article on EMRR today too.
 

Johnnie

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Fins that hang that far back behind the rocket, with 4 times the amount of intended flame front, are bound to get charred a little. If they must hang that far back so as to be an upscale something, then an extended boat tail might be in order. I would also try a slight modification to the high "charr" prone areas of the fin.

I bet that flight was a good one, as it was a blurrrrr on the photo. I would love to have seen a clear photo to see exactly how the flame front was interacting with the fins.

good luck
 
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