Catostrophic loss of Der Big Green Max on Cluster

[Marc_G]

Hi everyone,

I'm trying to piece together what happened with my Der Big Green Max this morning on its final flight. It has flown and been recovered via a large streamer more than half a dozen times including some cluster launches.

Today I launched it on a trio of C6-5s. PRevious cluster launches were C6-3-based, and ejection happened while it was still climbing. So I went to the 5 second delay for today.

It was a beautiful ride up with just a bit of weathercocking early on.

Here's the video. Note the ejection puff about 21 seconds in.

[YOUTUBE]r-4u3hDYdbo[/YOUTUBE]

I was looking for the big green streamer to have deployed, but didn't see it. This thing usually takes a while to get down. But quickly enough I heard my son saying it had crashed about 100 feet away.

Went and recovered it. Pictures below. The nosecone was blunted as though the thing had nose-darted. The nosecone's attachment point for shock cord had ripped off. the Body tube was basically scrap. Surprisingly the fins survived, but uselessly attatched to scraps of body tube. Streamer was quite melted and was mostly still inside the remains.

Here's the pictures:



And another angle:



I'm guessing I screwed up packing the streamer in somehow and its shroud lines snagged on something during ejection (there's a scrap of wood holding the kevlar, since the original kevlar died a while ago. I think that got caught. Nosecone couldn't pop, thing nosedarted and shattered.

That's my guess anyway. Any other thoughts appreciated.

Marc

 

[kenobi65]

What a shame!

 

[Scode68]

That is harsh!

I like that color choice

 

[Marc_G]

The color is rustoleum fluorescent green on top of white primer, clearcoated before and after decals with Rustoleum Crystal Clear Enamel. It was a beauty. Fins were 3/32cnd inch basswood. She had less than 10 flights; I hardly knew her.

The saddest thing is that it's basically a complete loss.

Body tube of course, it's mostly in pieces. Fin area: not enough to graft new body tube onto even though the fins are in fine shape.

Nosecone: blunted, broken, bent, and useless.

Motor mount (it was made to be removable because I interchange several motor types in this bird): it cracked up at the top and basically only the three motor retainer clips will be salvaged. The tubes themselves are a bit burned and not worth salvaging.

I may reuse some of the kevlar rigging.

I really wish the nose cone had survived; those REd Max nosecones are somewhat hard to come by unless you buy a kit.

I have plenty of fin stock, plenty of BT-60, and I have a Red Max (non-decaled) that is a bit shorter than spec due to having to remove an inch of the body tube that crumpled. I may retire it, steal it's nose cone, and rebuild Der Green Max. But I'll probably get a set of Excelsior decals that properly proclaim it as Der Green Max instead of Red (people asked me about that all the time).

Marc

Marc

 

[Marc_G]

Oh, one last thing. I grabbed a frame from the launch. PRetty cool multiple thrusting engine plumes:

 

[KurtH]

Sorry to hear of the Loss of the Big Green Max. It sure was a neat rocket.

 

[gpoehlein]

There is one other rocket that contains the same plastic nose cone as the Der Red Max - the Mean Machine. I've picked up several for kit bashing (yeah for the 40% off web coupon at Hobby Lobby). Currently, I'm about to start on a BT-60 upscale of the old Centuri Groove Tube using that nose cone. Main body tube is 23.5" long and the tube fins are 5.5" long. I'm going to try using your universal motor mount system - I plan to make a full set of motor mounts (18mm, 24mm long for E motors, 20mm for Quest D5 and 3x18mm cluster. I also figure to build several different BT-60 models with the system so I can use that set in any of them.

 

[DAllen]

I wonder if the nose cone was on too tight. With the 3 motors that's a lot of ejection gas. That would explain why the body tube was shredded like that and why you never saw the streamer since it probably came down in a wadded up mass of rocket guts.

-Dave

 

[Marc_G]

I had thought the NC was nice and loose, but I had my kids with me and might have goofed and pinched a piece of elastic or something between NC and BT. Sigh. Time to start over.

I've got a couple Screamin' Mimi kits (same nose cone) and always on the lookout for BLue Nina's on clearance (also same NC).

Marc

 

[DAllen]

Yeah, I've had trouble with the elastic when you tie it off to the nose cone and are left with a little ear flopping around. Every once in a while getting that caught between the NC and BT. Lately, I've been trimming those off. I had the same sort of thing happen to one of my Big Daddy's once.

 

[Marc_G]

Yeah, I've had trouble with the elastic when you tie it off to the nose cone and are left with a little ear flopping around. Every once in a while getting that caught between the NC and BT. Lately, I've been trimming those off. I had the same sort of thing happen to one of my Big Daddy's once.

Yeah, I'm going to go around and either trim those off or just use a bit of tape to stick the excess to the main length.

Marc

 

[plano-doug]

I had thought the NC was nice and loose, but I had my kids with me and might have goofed and pinched a piece of elastic or something between NC and BT. Sigh. Time to start over.

You have a BT-60 rocket with three motors. All lit, right? So there were three chances to pop the nosecone off. I doubt it was stuck - you would have noticed it being extra tight when you inserted it. I suspect you have too much leakage out the back end of your interchangeable motor mount system.

With the BT-60 airframe, if the motors all popped sequentially rather than simultaneously, you may have not gotten enough pressure to blow the nosecone off. Rockets this size are marginal on a single ejection charge from a B or C motor. (My old Big Bertha wrecked multiple times because the nosecone barely came off without enough momentum to pull the chute with it.)

It may not have been jammed on by a stray bit of elastic, but, since it has a few flights on it, there may be enough ejection charge crud accumulated in the tube to make the cone a little snug.

Regardless of the actual cause, if you want to rule out leakage aft, trying inserting a set of motors into the mount, then blowing into the airframe from the forward end to see if it seals up well or not. (Obviously, you can't do it with this particular rocket...)

Anyway, that's my thinking. I can't see the nosecone being so tight without you noticing it.

Doug

.

 

[Marc_G]

Plano Doug,

Good thoughts all. This rocket has flown several times on a single C and never had ejection troubles, and the single 18 mm mount was "leakier" than the triple mount (which was actually pretty tight, almost hermetically so). I can rule out ejection gas leakage based on the fit.

The more I think about it, the more I remember my kids doing something as U pushed the streamer in. It was rolled up nicely and the bottom of it folded over a section of thin dowel, with two leads connecting to the swivel clip. I got distracted as I put it in, and I think I would up pushing it in farther than usual, which would likely have made the lead get caught on the wood piece I had attatched the kevlar cord mount to. This would have prevented proper ejection and caused the mess I saw.

Sigh.

Marc