PDA

View Full Version : Disaster for Semroc Space Shuttle and Estes Goblin (clone)


space_bus
11-12-2007, 10:19 PM
We had some pretty nice weather for November in Maryland yesterday, so it seemed a good day to launch some rockets. Unfortunately, disaster struck for the first launch of my recently completed Semroc Space Shuttle, and for the first D-powered flight of my Estes Goblin clone.

Pre-launch Semroc Space Shuttle pics:

http://i226.photobucket.com/albums/dd258/gjc90/153_5367.jpg
http://i226.photobucket.com/albums/dd258/gjc90/153_5368.jpg

Fleet pics:

http://i226.photobucket.com/albums/dd258/gjc90/153_5369.jpg
http://i226.photobucket.com/albums/dd258/gjc90/153_5375.jpg

Space Shuttle on the pad:

http://i226.photobucket.com/albums/dd258/gjc90/153_5377.jpg

space_bus
11-12-2007, 10:25 PM
The Space Shuttle took off (C6-3) and got up about 30 feet as she arced to the left and powered sideways into the ground shearing fins and causing extensive damage to the larger glider.

I suppose I built too heavy (only one coat of sealer, one coat of primer, and one topcoat) or maybe just had something misaligned. This was my first attempt at this kit (Centuri or Semroc).

Aftermath:

http://i226.photobucket.com/albums/dd258/gjc90/153_5378.jpg
http://i226.photobucket.com/albums/dd258/gjc90/153_5384.jpg

space_bus
11-12-2007, 10:33 PM
The Goblin also fell victim on this day. With the winds fairly low, I decided it was time to go for its first D-powerd flight (and my first D-powered launch as a BAR).

I used an old D12-7 (engine code 26Q5 (May 26, 1986, I believe)), and suppose I saw my first ever CATO. (I have used at least half a dozen leftover old engines as old as this one, but no problems with them.) It didn't explode so much as incinerate the inside of the rocket. The thing went up kind of slow and with a whooshing sound. It had an odd glow about it.

Aftermath:

http://i226.photobucket.com/albums/dd258/gjc90/153_5383.jpg
http://i226.photobucket.com/albums/dd258/gjc90/153_5385.jpg
http://i226.photobucket.com/albums/dd258/gjc90/153_5386.jpg

dwmzmm
11-12-2007, 10:36 PM
Ouch!! That really hurts! Been there and done that. Looks to me like it should be
repairable. It's not all that bad as it could have been. Spend plenty of time analysing
it before you embark on a plan to repair/rebuild. You'll be surprised at how such models,
after sustaining damage similar to this, can be rebuilt to look as good as new. Keep us
posted.

space_bus
11-12-2007, 10:38 PM
Here's a blur of the only rocket that survived the day completely unscathed, the Mini Bertha, as she streaks off the pad on a 1/2A3:

http://i226.photobucket.com/albums/dd258/gjc90/153_5381.jpg

dwmzmm
11-12-2007, 10:43 PM
What happened to your Goblin is the very same that happened to my vintage FSI OSO kit
not too long ago (tried launching with the F7-6 for the NAR OOP motor testing program).
Suffered a cato just like yours and burned the body tube into two sections (since fully
repaired)....

K.M.Knox
11-12-2007, 11:07 PM
Those are some sweet looking rockets, real bummer about the casualties. Your pics of the birds prior to their demise give them some justice, that shuttle looks awesome. Good luck with the repairs...

space_bus
11-12-2007, 11:08 PM
Ouch!! That really hurts! Been there and done that. Looks to me like it should be
repairable. It's not all that bad as it could have been. Spend plenty of time analysing
it before you embark on a plan to repair/rebuild. You'll be surprised at how such models,
after sustaining damage similar to this, can be rebuilt to look as good as new. Keep us
posted.
Thanks for the encouragement. :)

The yellow orbiter should be a relatively easy fix, and the pod is intact, but I was thinking more along the lines of a total rebuild on the big white shuttle glider. As I understand it, the Space Shuttle is a pretty touchy kit to get to fly and glide correctly. The thing didn't fly right the first time, so I was thinking adding more glue and paint would just make it more out of balance. I'm not sure what went wrong. There was a light breeze, so I had the rod pointed a bit towards the wind. Maybe that is a no-no with this rocket. Also, one of the paper elevation flaps is a little warped so perhaps that's a factor. Maybe the flaps weren't set equally and caused the rocket to arc...

dwmzmm
11-12-2007, 11:14 PM
Thanks for the encouragement. :)

The yellow orbiter should be a relatively easy fix, and the pod is intact, but I was thinking more along the lines of a total rebuild on the big white shuttle glider. As I understand it, the Space Shuttle is a pretty touchy kit to get to fly and glide correctly. The thing didn't fly right the first time, so I was thinking adding more glue and paint would just make it more out of balance. I'm not sure what went wrong. There was a light breeze, so I had the rod pointed a bit towards the wind. Maybe that is a no-no with this rocket. Also, one of the paper elevation flaps is a little warped so perhaps that's a factor. Maybe the flaps weren't set equally and caused the rocket to arc...


What you're describing is similar to what I've seen of the flight characteristics of the Estes
SR-71 kit. I built my daughter's, and we've launched it twice (to date). The first time, in
a good breeze and using the C6-5, flew perfectly. The second time, it went about 15 feet
before it powered back into the ground. My only guess is the way I had the wings aligned
with the wind direction during launch, so that should give a possible hint....

Rocket Doctor
11-13-2007, 05:30 AM
Great photos and a great fleet of rockets. Sorry to hear about your losses. I'm sure you will be able to repair the shuttle and fly it again.

As far as the D motor goes, it could have been cause by a "cycled" motor, whre there was tempeerature variations, the outer casing expands and contracts, leaving a space inbetween the inside of the casing and the propellant, when the motors ignites, , instead of burning from the bottom, the burn is along the entire surface along the propellant, up the sides creating higher heat and pressure causing the motor to CATO.

Motors are funny things at times, you just never know. Been there done that, and had some really great rockets destroyed beyond repair.

Send the casing into Estes customer service dept as see what happens.

Leo
11-13-2007, 06:34 AM
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.

space_bus
11-13-2007, 08:39 AM
Great photos and a great fleet of rockets. Sorry to hear about your losses. I'm sure you will be able to repair the shuttle and fly it again.

As far as the D motor goes, it could have been cause by a "cycled" motor, whre there was tempeerature variations, the outer casing expands and contracts, leaving a space inbetween the inside of the casing and the propellant, when the motors ignites, , instead of burning from the bottom, the burn is along the entire surface along the propellant, up the sides creating higher heat and pressure causing the motor to CATO.

Motors are funny things at times, you just never know. Been there done that, and had some really great rockets destroyed beyond repair.

Send the casing into Estes customer service dept as see what happens.
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.)

space_bus
11-13-2007, 08:45 AM
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.
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.

Shreadvector
11-13-2007, 09:29 AM
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).

cas2047
11-13-2007, 09:45 AM
Great fleet and beautiful Shuttle!

I hope you can rebuild.

space_bus
11-13-2007, 09:49 AM
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.

Shreadvector
11-13-2007, 10:06 AM
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.

barone
11-13-2007, 12:02 PM
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.

space_bus
11-14-2007, 08:01 AM
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.

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.

space_bus
11-14-2007, 08:04 AM
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).
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.

K.M.Knox
11-14-2007, 08:56 AM
Here is a shot of two A10-3T casings one flew perfect, the other had a blow through... Can you tell which one? Not sure if you still have the casing and maybe your nozzle looks similar... The other pic is the results of my little engine failure. She cleaned up nice though and was back on the pad for a couple of nice flights that same day.

space_bus
11-14-2007, 09:32 AM
Here is a shot of two A10-3T casings one flew perfect, the other had a blow through... Can you tell which one? Not sure if you still have the casing and maybe your nozzle looks similar... The other pic is the results of my little engine failure. She cleaned up nice though and was back on the pad for a couple of nice flights that same day.
I'm gonna say the casing on the right had the blow through. My problem D12-7 has a couple of those little scorch marks on the front edge like the one that A10-3T has (which would seem to indicate that some of the blow through came out the front edge).

Looks like the biggest damage to yours was that the nose cone came apart. Glad to hear you were able to get it cleaned up and back together again. Of course, it is the 'Lucky' Seven after all. ;) :rolleyes:

CPMcGraw
11-14-2007, 09:36 AM
Here is a shot of two A10-3T casings one flew perfect, the other had a blow through... Can you tell which one? Not sure if you still have the casing and maybe your nozzle looks similar... The other pic is the results of my little engine failure. She cleaned up nice though and was back on the pad for a couple of nice flights that same day.

The one on the right. The nozzle has not been eroded the way the one on the left has, indicating an abruptly-ended thrust flow.

K.M.Knox
11-14-2007, 10:50 AM
I tried to get a shot of the ejection end to show the difference but nothing turned out. The burn through had a very black and sooty inner casing to the end while the other has a very clean inner surface from clay cap to end along with some remnants of clay, the burn through engine is completely cleaned out from nozzle to end.

The black scorch mark on the casing edge is from the engine hook I believe. I think what happens with some of the 13mm engines is the hook actually catches some of the thrust burn/heat and redirects onto the casing under the hook. The mark is extremely uniform and shaped just like the hook.

moonzero2
11-15-2007, 05:06 PM
You have great building skills. Those models look awesome! Don't get discouraged. Re-build them! Even the pro’s loose some. That’s what makes this hobby so much fun is the challenge and learning experience. When a flight does go well, the satisfaction is tremendous!

mrhemi1971
11-16-2007, 06:16 AM
I know how bad it is when CATOs happen, lord knows I've seen enough. It's even worse when its an original kit that you cant get anymore or clone too easy. Those pre-launch photo's look really nice! Now I want one of the shuttle kits. Hope the repairs go well.

space_bus
11-17-2007, 09:12 PM
I really appreciate all the compliments and encouragement.

Now it is just a matter of when I get around to either repairing or rebuilding the shuttle ... I'm still not sure whether I should bother trying to do a repair on the white glider. The body tube has more creasing than shows up in the photos (mostly in the area of the mount for the orbiter). I'm not real sure there is a good way to repair BT dents/creases, especially on a glider, so I suppose it's either make the most of it and live with it or rebuild the whole glider.

On a positive note, I did finish another project recently with a better result from its first flight:

http://rocketryforum.com/showthread.php?t=41175

sandman
11-17-2007, 09:33 PM
Here is an example of a cycled motor having a blow through.

This was JimZ's original Goblin flown on I believe an old D11-9 at Naram 45 in Evansville.

Everyone just gasped and fell silent when this happend. :eek:

The picture is of the model about 8 feet above the launch rod.
The casing is about 2 feet below the model and the balsa nose cone is way above the model completely out of the picture.

Remarkably the only damage was a scorched crepe paper streamer. No other damage!

It flew again later in the day and dissapeared until I found it the next day.

tbzep
11-17-2007, 09:57 PM
Those are some really beautiful birds. I hope you have better luck with the rebuilds/replacements.