'DMD2' D minimum diameter 2 stage

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RodRocket

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So to not take over 808rocketmans thread I am starting a build of a 2 stage D to D rocket I'm calling DMD2.

The concept is bare minimum build, try a different, to me, coupling technique, small thin fins, minimal parts count and see what happens.

So far have the body tubes cut, sustainer is 370mm, booster is 92mm white 24mm ID paper tubing wall thickness is maybe 1/2 mm.

Glued booster thrust ring at aft of tube, while that was drying I notched the other thrust ring to tie a kevlar cord to. I guessed at the kevlar length, maybe 6 ft total.

Then I took a spent D case and slipped it into the booster followed with another D case. Ran the cord through the ring and both cases and out the bottom to keep out of the way and stacked the thrust ring on top. Took a quick skewer measurement to locate the glue area for the thrust ring and applied the glue inside body tube, then slid the stack into the tube and pushing the ring into the glue. Then quickly but carefully pulled the cases out and left to dry.

Pulled the cord back through the body tube and tied on the cone and a couple inches below the cone tied a simple loop for recovery attachment.

Now I need to visit hobby store to pick up wood for the fins. Think I may try thin aircraft ply this time. And then get to finishing. Hope to have this rocket ready for Kloudburst in April at Kloudbusters pasture in Argonia, Ks.

Going to do tweaks to Openrocket sim file below. Going with a nose cone I already have, and changing position of fins on booster. May even change their shape a bit, worried that the tapered fins will let the booster stabilize and not tumble during decent. Will be sure to let everyone know of that possibility before launch. Really only one way to find out what will happen. Build it and stick in a spent case and give it a toss in the yard.

Not a difficult build at all. And with minimal parts will be really light. Minimal standard left over Estes launch lugs, 1/4 inch long at body and tapered ends.

This rocket is gonna scoot on D's! See no reason why it wouldn't fly well with adapters to fly 2 C's or a D boost to a C for smaller fields. Will have to sim those to see what happens.

I'm gonna John Force it with D's for the first launch. Win the race or blow it up trying!

See ya,
Rod

View attachment DMD2 min dia 2 stage D engines.ork
 
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Here is the openrocket file for the booster stage with a mt motor case.

I copied and pasted the booster section to a new file and then added the motor case. I had to figure out the weight of the clay nozzle so I made the bulkhead in the sim weigh zero and removed the fins from the file. That gave me a sim parts weight and then I put the actual parts, mt case and body tube with motor block, on my scale and subtracted the two. Got about 7g for the clay nozzle. Did a mass override for the bulkhead and added it to the file.

This is what I have, a booster section after staging. Openrocket shows the CG and CP.

So now where should those two be in order for the booster to tumble? Should they be on top of one another? I can move the fins back and the CG and CP get closer together. The fins are the only part I can adjust. Maybe make them a bit larger? And adjust location?

View attachment DMD2 booster with case.ork
 
It's Go For Launch.

Just have to tie on a streamer and load engines. Probably use a crepe paper streamer, slide booster engine into booster, tape friction fit sustainer engine, tape fit the booster to sustainer engine case so it will separate at booster burn out.

This will launch at next Kloudbusters launch. Winds permitting of course. I no longer launch 2 stage if winds are not favorable. Just too risky.

But I plan to give it a shot. These may be the last photos, unless I can capture it on the pad. May try and capture the booster separation. Will see, may be too busy watching where rocket goes to push the camera button.

DMD2-3.jpg

DMD2-2.jpg

DMD2-1.jpg
 
The launch day was breezy but there were times when the wind would slow, so I prepped the rocket.

Friction fit taped the main engine and had a slip fit for the booster. Few bits of wadding, fold and stuff the small chute, starter and plug into the booster engine, filled out card and headed to LCO.

Got to pad double checked the rod angles, slid rocket down into position, hooked up leads to starter wires, pressed check button and got the green light.

I was the first launch of the event, got the five count, button was pushed and up it goes on booster engine, quickly it gained speed and altitude and at about 500 feet it staged, and really started moving, and after a second or two I lost visual on it. Never saw it again. And didn't watch where the booster fell, but I know it was headed for some very tall grass, so there was no way it was going to be found. I made an effort to look at fields down wind, hoping the orange chute would blow but the wheat is tall enough to hide larger rockets, so I would have had to darn near step on it to find it. But next launch should be easier to find rockets in the fields.

But it did work and staged properly. That was the intent of the build. And actually with the breeze it behaved well, I was worried it might wind vane into the wind, but it went about as straight up as it could have.

So I will build another and hope for a better recovery next time. It was funny, I was watching it go and hopping it would work, and when it did and was going so fast, I thought 'oh no!' as it went out of sight.

Version two will get upgrades, epoxy for fin joints instead of wood glue, little bit more nose weight, and a different recovery.

Our launches are done until July for farmers wheat harvest, so I have plenty of time to build a couple of these for the next events.

See ya,
Rod
 
For your consideration: you might build the next one with room to install an E sustainer; D12-0 and E9-(choose after simulating) should get you very impressive altitude. Also, for a rocket like that I'd use a metalized mylar streamer to give a chance of catching the sun on the way down and thus being spotted. You could even cover the tube with metal leaf (and clear coat) instead of paint. If not that, consider painting it in high contrast, obnoxiously contrasting colors like neon green and flaming pink. Looks like puke, but it's easy (well, easier) to spot. (My avatar is the exact color scheme I intend for my L2 cert flight.)
 
Yep the next ones might get emergency blanket streamers. It was plenty high enough with the D's. It jumped off the rod and when it staged, it was at full speed on the booster engine and it didn't waste any time going out of sight. Might have been easier to watch it if there weren't high clouds, making it impossible to follow the smoke.

Might even make the next one break in the middle and tumble recovery. Working on that now with tubing and other bits.

This is such a great performer, I will try and have one or two at every launch now.
 
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