Always hurts to see great built models get damaged like that.

I'd certainly repair the Shuttle and fly it again. Getting spare decals from Semroc shouldn't be a problem.

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Leo

My rocket fleet and more @ Leo's Leisure Site and on YouTube - My latest project: ALTDuino

Thanks. I think what you describe is exactly what happened to this engine (burning along the sides of the propellant). This engine had been stored the same as other old engines I've used (mostly in basements for the past 20+ years). Are the 24mm engines more susceptible to this condition than smaller engines? (I still have another D12-7 that was from the same pack as the failed one ... probably won't be using it.)

Carl and Sheryl at Semroc have been great to deal with. I already have a set of decals I could use for a repaired or rebuilt white shuttle. The kit had originally come with all white-backed decals (an error), but Semroc sent a clear-backed set once I contacted them. While the white-backed decals wouldn't look right on the yellow orbiter, they would be fine on the white shuttle glider.

I saw a Semroc X-Ray clone go unstable, with no problem or anomoly with the motor (i.e. not "Poopy Clay"), so I suspect the balsa used is lighter than the original kits used so the c.g. may not be as far forward as we would like for reliably stable flights. Contact Semroc and discuss this with them.

As for the motor failure, 24mm motors are more susceptable.

The whooshing sound is unusual. usually if there is a blow through, there is a fireball shotting completely through and out of the rocket top like a Roman Candle. If there was whooshing, perhaps the motor mount or motor casing flew up and into the rocket body? If the nozzle blew out during boost, but the propellant stayed intact, there would be a huge momentary thrust increase as the mass of the nozzle was ejected, followed by very reduced thrust and a slightly longer burn time since there is no back pressure to make the propellant burn at it's normal rate.

Was the casing blown upward into the rocket? What did the ends of the casing look like? one very rare scenario is to retain the propellant but have a tunnel burrow through one side of the propellant or along the casing wall. This allows blow-torch like effect blowing upward while retaining the nozzle below (and resulting in lower thrust).

Attached Files

CatoExplanation.pdf (11.4 KB, 61 views)

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-Fred Shecter NAR 20117 (L2)
Southern California Rocket Association, NAR Section 430

Great fleet and beautiful Shuttle!

I hope you can rebuild.

Shreadvector -- The motor and motor mount stayed put. The casing and clay nozzle is intact, but the casing is clearly scorched on the inside (but no burn through). What RD described sounds like what happened. However, the top didn't blow off the rocket. The rocket went up, but I'd say less than 100 feet, and it had an unusual sound. I called it whooshing ... it was sort of like that or a roar ... I'd say it sounded a bit like flames in a strong wind ... and not as loud as an engine normally sounds. The rocket sort of hung in the air and shimmered (I guess this was heat or fire coming out the sides). As it fell to the ground, the body tube above the engine mount shriveled and came apart. The streamer was only slightly singed and the nose cone has a a small burn mark on a portion of its base.

The rocket weighs next to nothing compared to the normal thrust of this motor. If the nozzle was intact, there would have had to be an almost complete loss of pressure/thrust through the nozzle to stop acceleration AND to stop the rocket in mid air it would require a force acting downward. A normal blow through would blow off the nose cone (see previouos Roman Candle comment). Of course, if your nose cone was extremely tight (paint on the shoulder or a bit of shock cord jammed between the tube and shoulder), it could have remained in place and the large fireball coming out the top of the motor could have incinerated the body tube and quickly burned an exit path - stopping the rocket in mid air.

The Wooshing Sound is a hint that you actually did not have a full "Blow Though" (Roman Candle), but that you had a burrowed tunnel of flame upward along the casing wall. Look inside with a flashlight and see if you can see a groove or grooves (they look like termite paths in wood, but are burned).

Casing glue quality control was a problem in the past but they really try to maintain high quality now.

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-Fred Shecter NAR 20117 (L2)
Southern California Rocket Association, NAR Section 430

Just a word of caution about flying large fin area rockets in a breeze. Most people will aim into the wind with the rocket to decrease distance to walk to get the rocket back. On large fin area rockets, you want to aim with the wind. The wind will act on the fins to make it weather cock into the wind...so if you aim downwind, it should get a staighter boost.

Nice fleet. Before pictures are great. After kinda makes the stomach sink.

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Don
NAR 53455
"Carpe Diem"

Thanks for the tip.

As I noted, I did point towards the wind a bit... Maybe this is the simple explanation for my shuttle's poor flight.

I think you are right on here, Fred. I took a quick look at the problem D12-7 and noted one obvious groove on the inside of the casing.