4" Der V-3 Upscale

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EXPjawa

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I've finally pulled together most of the parts needed to start a project that I've been thinking about for a while now. This will be a 4" upscale of an Estes Der V-3, built from LOC tubing. I built a clone of the original Der V-3, and I almost always fly that first at every launch I've been to since. It seems natural to want to take that design and go bigger. If it works well, then I plan to also use this for a Level-1 flight.

However, one issue I'm going to put to bed right away is that this design is going to be 29 mm. I know that some (many?) might argue that it should be 38 mm from the start, given that it might be a L1 rocket and technically high-power. I still think of this as a heavy mid-power rocket (like the Mega Red Max), which is why this thread is located here. What's more is that most of the flying I (currently) intend to do with this is squarely mid-power range, and my preferred way to fly this is in a low-and-slow fashion. There are a lot good motor choices for this design that fall into the 29 mm range, including a number of single-use options to get started. At this time, I don't want to get into the expense and complexity that comes with larger motors and higher flights, that's not the fun part for me. My reasons for getting an L1-certification isn't to go higher and fast, at least not at this time. Rather, its more about opening up options for engine combinations, especially in larger clusters. If this build is to be used for L1-certification, I want it to be rugged, simple, and fairly low flying. KISS pretty much sums up the approach I want to take, and staying with 29 mm keeps with that. If I ever do want to go higher and faster, I'll build a bigger one.

Anyway, now that's out of the way, this will use 4" LOC tube, 1/4" light ply fins, a 36" or 45" Top Flight chute (depending on engine choice). Several of the minor parts came out of a box of parts I got from TopRamen on trade (thanks!). The parts:

IMG_4436.jpg


  • 22.25" length of LOC 4" tube
  • 4" ogive nose cone from Apogee
  • 11" section of 29mm mmt tubing from TR
  • 45" red Top Flight chute
  • 3/16" ply centering rings from Rocketarium
  • 29mm Estes plastic retainer
  • 1010 die cast guide buttons from TR
  • 1/2" elastic shock chord from TR
  • coil of kevlar chord (300#, I think) from TR
  • a couple of sections of 1/4" light ply and a fin pattern

This is the design, per Rocksim:
der_v3 4in.jpgder_v3 4in side.jpg

It should be pretty close to scale, the nose cone is just about the right size/shape. Overall size & weight is expected to be roughly similar to the Mega Red Max, which I see as a sort of cousin. Length will be just short of 36", with a 15.25" finspan. Its built heavy enough to keep it slow & rugged, as desired, and expect performance to be pretty similar to the original. It'll be finished as per the original as well; I've already spoken to Gord about upscaled decals.

I drew up a tube marking guide using UG at work, so I can plot that full scale and have accurate marking to cut the fins slots. One area I am deficient is that my fin jig is too small for the 4" tube, so I'll have to align the fins the old fashioned way (which I do more often than not anyway). I expect to start on this in the next few days as time allows...
 
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A little progress - last night, I started marking out the parts. Lengths of tubing has already been cut, so that's done. But I cut out the fin pattern, transferred it to cardstock, then laid out the fins on the plywood. Unfortunately, I could only get 3 of them onto a 12"x12" piece, so I'll have to cut the 4th from another sheet:
WP_003310.jpg

Then I started the motor mount. I predrilled one of the centering rings for the recovery harness, cut a section of the kevlar shock cord and tied the end off in a small loop. Then, after marking the positions on the motor tube, I slid the rings and the cord loop on and epoxied in place:
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For the moment, the epoxy fillets are just on the bottom side of the rings. Tonight, I'll turn it over and do the tops. The kevlar loop was epoxied into the fillet on the top ring. After that, I set about marking the body tube. My fancy CAD-based marking guide didn't pan as planned; apparently, my software and plotter don't quite seem able to print 1:1, so there was a myriad of scaling issues before I reverted to measuring and marking by hand. It appears to have worked out just fine though.
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Then, I decided that I had time before going to bed to actually start cutting the slots out:
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I started out trying to use a straight edge, but on the comparatively large diameter, that proved more trouble that it was worth. I wound up doing most of them by hand/eye, but they came out pretty well and straight. Next up will be to cut out the fins from the ply sheet. I'll have to do that over the weekend using my father's band saw; I don't really think its practical to cut them with a razor...
 
Last night, I epoxied the motor mount into the body tube, sans rear centering ring.
WP_003341.jpg
Today, I cut out the fins on the band saw. Stacking them together and sanding them on the belt sander gave pretty good results, though I expect I'll finish sand them by hand yet. I rounded the leading edges a bit, but intend to leave the others square.
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The fins were then numbered and fitted to the matching slots. A little filing and dremel work got them where they need to be - the blanks were pretty close off the bat, so it didn't take too much fussing to get the inner and outer mounting surfaces to have good fits. Rough approximation:
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And of course, it would only be fitting at this point to put the nose cone on and get an early basic fit up of everything together and see what it looks like:
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Fins are on. Shown with my normal Der V-3:

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Next step: internal filleting and installation of the rear centering ring.
 
Not according to Rocksim, though that might be in part to the use of a 29mm mount. I'd imagine that if I had used a larger motor it would be a different story. Also, the way its laid out, I am limited to the length of the motor case I can put into it, since the motor tube is 11" long. Anything long would stick up into the parachute & wadding. But within the range of the cases that I can fit, the worst case stability is a caliber around 1.2 or so, +/- a small amount. Its 1.29 on a G80. Obviously, we'll see how it really balances once everything is in place...
 
Yeah, I think so. Of course, I'll pay attention to how it actually balances, though the sim actually is built with a 36" thin-mil parachute (which I intend to use with smaller SU motors). When flying with heavier motors, I plan to use a 45" Top Flight chute that I bought specifically for this (at least for the L1 cert flight), so that'll bring the CG forward some as well. The bigger chute on the L1 flight is to slow the decent a little bit more to reduce the risk of landing damage. I don't mind walking farther on that occasion. On an F engine and the 36" chute, calculated decent is about 20 ft/s, which isn't bad considering the soft field. With an H180W, the rate is about 21 ft/s, but with the 45" chute is slows to about 16.6 ft/s. It probably won't make much of a difference at the end of the day, but I'll be less concerned about the flight if I know its coming in softer...
 
Yeah, depending on the field and rocket, I usually shoot for 16-18 fps.
 
More progress:

Internal epoxy fillets applied and the rear centering ring glued in place. Estes motor retainer in place.
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Der lugsfer launchin:
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And the outer fin fillets finished:
WP_003361.jpg

I've had good luck using JBWeld clear 5 minute epoxy for this, as long as you mix it as required. It applies readily and the stuff seems to self-level better than other products I tried. For the internal fillets, I used Loctite 5-minute epoxy in the small diameter syringe that has the long mixing applicator. It was long enough - and precise enough - to let me reach into the mount and apply an epoxy bead everywhere I wanted one. I also used it for drawing an epoxy fillet around the back of the rear centering ring. I used up the entire tube doing this, which was pretty small. But, with the exception of attaching the recovery system, this thing is fully functional, ready to go. I'll probably attache the harness and chute after painting, unless I attempt a flight first...
 
Thanks. I primed this thing over the weekend, did some more filling & sanding, and shot with an initial coat of red:
WP_003382.jpgWP_003381.jpg

Keep in mind that its only painted on the upper surfaces, I'll have to roll it over and paint the other side once this is dry enough to be set downward. I also got the decals from Sandman over the weekend - he went ahead and added it to his repertoire on his site, so anyone else wanting to build a 4" Der V-3 can. I expect now to make the first flight this weekend at some point at LDRS.
 
More likely Friday, and maybe Saturday. I finished painting last night, but I'd like to give it a day or two for the enamel to offgas before putting the decals on. At this point, the only think I have left to do is tie up the recovery harness and attach the chute. Shouldn't take long...
 
I flew this rocket twice so far at LDRS, Thursday on an F50-4 and again on Friday on a G80-7. Both flights were good, clean, landing relatively near the pad, upright on its fins the first time.

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I also put the decals on last night, and a coat of Future today. Should be ready for a third flight tomorrow, in full colors.
 
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Rustoleum spray can, baby! I've also been using a pistol-grip handle for spray cans, and I've found that it goes a long way to help control the paint. HD sells them, I'd imagine that Lowes, etc do too.
 
Great Job the Der V-3 has always been one of my favorites Mine is one of the originals still has the rubber shock-cord after seeing this I need to fly mine some more
 
Oh, man, I love the Der V3 and yours looks fantastic! And it stuck the landing...so cool.
 
Yes, beautiful rocket and with a 10 for landing, was a cool flight to see, nice job
 
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