The wreck of the Der V-3

Perhaps 13 is unlucky. Friday the 13th, Apollo 13, etc. Yesterday, I made my 13th flight of my Estes Der V-3 clone. Up to this point, I've always flown it on C11 or D12 motors, but yesterday, due to fairly low winds and having a shiny new Chute Release on hand, I decided to kick it up a notch and fly it on an E12-6. The up part was great. It scooted off the pad and got really small in a hurry. Rocksim says it should've hit about 950', but I didn't put the altimeter on it, since the model has (had) no vent holes.

Anyway, it arcs over, starts heading back and I made a mental note that maybe 6 seconds was too long. But it just kept coming down ballistic; the nose cone never separated. As Arthur Dent once said, "it isn't a question of who's habit it is, its a question of how hard you hit it". It hit it hard enough to do this:



The nose cone split into a few pieces, the forward tube unwound and split open. OTOH, the lower 50% and fin can are fairly intact. I may be able to cut off the upper tube and graft on new piece with a coupler. I'll have to muck about with the motor mount to do it, as the upper ring in above the blow-out line. Maybe I ought to kit bash it together with my old Phoenix, which had the rear tube & fin can fail.

Anyway, here's what I'm wondering: if the cone wasn't tight (it rotated/slid readily after packing), what would prevent separation? The only thing I did different this time was add the CR. If the delay was too long, is possible that the ejection charge wasn't strong enough and aerodynamic forces kept the cone on? My understanding is that Estes ejection charges are pretty damn strong. I pulled the motor afterward, and it does appear that the charge worked, it didn't fail. Could the burst tube be from the charge and not the crash? I'll have to get a picture of the other side of it, this (obviously) shows the rocket as I found it. But at least I didn't have to walk far...

If the cone was very loose, then it is possible that enough ejection gas escaped to keep the tube from pressurizing enough to pop the cone. If the charge blew, then that's about the only viable explanation.

It wasn't very loose. It was tape-sized to a nice slip fit, and, as I said, had a dozen previous flights with good deployment. The only other thought I had was that it got bound somehow, and the charge blew the tube instead. But I'm not sure how that would've occurred either. I performed a puff test before installing the motor. It slid out as expected.

Remove the entire body tube and replace with a full section. Pretty simple to do.

That's a bummer.
As a kid, my DER V-3 was one of my most frequently flown rockets, and I even remember a few times when I ran out of wadding and used grass in it's place, wreaking havoc on the chutes, which I would then have to replace of course.
It finally succumbed to the tube rot caused by the BP ejecta build up on the inner walls.

DanP said:

Remove the entire body tube and replace with a full section. Pretty simple to do.

Click to expand...

Sad story. 8( Dan's got a good idea. And you could put in an ejection charge baffle instead of just a plain coupler...

I think I can get everything I need to repair it out of a V-2 kit, save for the coupler (which I have). I'll have to check the tube length from that kit compared to what I'll have to trim off to be sure. And Sandman still has decals for it, so that's a plus.

It's essentially a smaller version of my dad's North Coast Big Brute that he used for his L1 cert. That rocket has had multiple crashes, including on an F22J on its first flight 12 years ago. We got smarter after that.

After that crash, he cut the entire body tube off, cleaned off the fillet remnants, and slipped a new slotted tube over the fins/MMT and re-glued it all.

Dude, That SUCKS!!! :sad:

The the JLCR survive the unexpected ballistic return?

Yes, the CR survived and was used later that day - though one subsequent flight did have an apogee release of the parachute. I expect that's a coincidence that tied to prel-launch prep.

Dan, I get what you're saying, but in this case, the rocket has surface mount fins. Basically, I'd be assembling a whole new rocket (with a pre-built motor mount & used fins) rather than replacing one aspect of it. I'm actually planning on doing exactly that with my old Estes Phoenix (referring to in original post), because the tube failed in the fin can area. I cut all of the fin glue joints and removed them intact. But with the DV3, its just the upper half of the tube that's damaged. So, I should be able to simply graft on a coupler and tube segment. That makes for a lot less work. And I only have repaint and replace the decals on the upper part.

oh man, I liked that one! there were a lot of great chute release flights last weekend!

Well, to be clear, this was the smaller Estes-sized Der V-3, not the 4" version that I used for my L1. That one was flown (with the CR) immediately afterward and had a near-perfect flight, and is even now sitting on the back corner of my work area/desk at work. But still, this rocket was one of my favorites and flew at nearly every event...

In the grand scheme of things, since I started flying rockets again a year and a half ago, I've lost five. Three were wrecked on landing, one remains in a tree over the launch parking area, and one disappeared into the carrot field. That's out of 128 launches, if my records are correct. That's about 4%. I wonder what the normal statistics on that are...

This story has a happy ending. After a bit of surgery, the patient has been restored to flight status. The picture above in the first post shows the rocket as I recovered it. You can see that the tube is damaged, but not the extent:


As you can see, it was ruptured open down past the motor mount centering ring. So, the first order of business was to trim off the damaged portion of the tube. Given the circumstances, the normal tube cutter wouldn't work. So, I wrapped the tube with a few layers of masking tape (pulling tape around a tube straight is a skill I've developed thanks to rocketry) and used that as a cutting guide. Granted, it wasn't ideal, but it worked better than freehanding the cut:


Not bad. Now to do this repair, I need a replacement nose cone, a section of tube, a BT50-80 centering ring, a BT80 coupler, a segment of 3/16 launch lug (Der Lugsferlaunchen!) and given how charred the shock chord is, I'm going to replace that too. The coupler I have, but I needed everything else. Estes V-2 to the rescue! I picked up a V-2 for about $18 to repair my V-3.



Not only does it have the correct nose cone, but the included body tube is almost exactly the length I cut off:


So, I trimmed off the mashed upper centering ring. I tied a loop in the end of a segment of kevlar chord and slipped that over the MM tube. Then I installed a 4" coupler section and then glued a new centering ring above it. I thought I took a photo at that step, but apparently didn't. Then, I glued on the new body tube section:



Then, it was a matter of tying on the nose cone and gluing on the upper launch lug. I wound up cutting the part included in the V-2 kit in half to match what was on the model and putting the other half in my LL bag (which seems to contain only 1/8" and 1/4" lugs). And, because it amused me to do so, I used a Sharpie to fill in the now missing decals:


I suppose I may repaint it all at some point, but somehow it seems fitting (given the Patchwerk and Der Fin Wiggler) for the rest to look patched up too... Anyway, since coming back to the hobby, this rocket has been with me at every club launch. This weekend is the next one, so it won't have missed any.

Looks good! Using a sharpie to draw in the missing decals is a nice touch. It certainly is nice seeing a destroyed rocket come back to life.

Any other theories as to what happened?

Thanks!

Hard to say. It never separated, but it does appear the the motor burned through to the ejection charge. I can't complain to Uncle Vern about one his motors failing. But it didn't separate. The cone moved/rotated ok when setting it up (I turned it after the fact so the decal on the cone aligned with the "DER V-3" script). Maybe it got bound after, maybe the hull was breached by the charge going off and not having an outlet. Who knows? I can't think of a good reason for the cone to not come off it if it moves freely and and the charge fired. There's either another variable or that set of assumptions didn't hold once it was on the pad... :confused2:

EXPjawa said:

In the grand scheme of things, since I started flying rockets again a year and a half ago, I've lost five. Three were wrecked on landing, one remains in a tree over the launch parking area, and one disappeared into the carrot field. That's out of 128 launches, if my records are correct. That's about 4%. I wonder what the normal statistics on that are...

Click to expand...

This may be cold comfort after damage to a favorite rocket, but most of the major space programs seem to have failure rates around 5%. So you're just as good as SpaceX and ESA and the Space Shuttle and...

Glad to see it getting back into flying condition again!

Back on the pad again!