Here's some pics of a scratchbuilt Soviet SS-17 ICBM and US Minuteman III ICBM that I built about 15-20 years ago. I found them upstairs at Grandma's house when I was hauling my old stuff out of her attic after she passed away year before last. I built them out of Christmas wrapping paper tubes. The SS-17 is about 3 inches in diameter or so, and the Minuteman is about 2 inches on the lower stage. They are 'roughly' the same scale; I have the data somewhere in my old notebooks The nosecones are hand-turned balsa, the transitions are posterboard. The decals are hand-drawn on real thin drafting paper and then painted with Testors model paints and cut out with an X-acto, and glued on with white glue.

They used a removeable 'fin can' (on the SS-17) for stability. The fin can had a tube that fitted snugly over the motor mount tube with the clear Plexi fins glued to it, and then another outer tube glued over the fins, which fit just inside the main body tube. The engine mount centering ring was recessed about 3-4 inches inside the model to make room for this fin can, which extended the fins out the back (the fins were L shaped). Unfortunately this fin can ended up under some stuff and didn't survive and I tossed it. The Minuteman uses an insertable 'fin/motor can' that slides into the base of the missile and sticks out the back about 2-3 inches, including the Plexiglass fins. It was in good shape, and still had a D11-9 installed in it, so I have it ready to go.

Enjoy! OL JR

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That's nice. Those two are starting to encourage me to make a finless rocket similar to what you have. I'm thinking of using spin stabilization. I know, I've heard of stories about people failing, but, if I do make one, I'm going to make sure it leaves the rod/tower at a relatively high RPM. I have some ideas of making it spin fast...I may just add some small fins for extra stabilization.

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Josh
NAR #87993

Weeelllll... These ain't exactly finless But prototypes like ballistic missiles and Gemini-Titan II's sure make you want to build one that way...

Spinning creates it's own set of problems though, and really robs altitude. Spinning with fins canted might work.

I wanted to keep these as 'finless' as possible for display and also for more scale appearance in flight, which is why I went with the fin can method. It's sorta like Dr. Zooch's (www.drzoochrockets.com) flame fins, only using clear fins while minimizing anything sticking out below the rocket. Painting what DOES stick out in a flame color/pattern (like flame fins) should pretty well minimize it's visual impact. Not having to worry about the clear fins should help a lot too

It's not a perfect solution but not bad for a kid of 18 or 19 and it probably predates flame fins by at least a decade (I guess)

Yall have a good one and good luck with your project OL JR

Well, I'd put small fins on as a last resort kind of thing. For this, I don't really mind altitude as it is purely experimental.

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Josh
NAR #87993

If you have RockSim you could play around in there quite a bit and maybe come up with some solutions... be sure to use plenty of nose weight Also anything with a 'flared out' transition at the base, like a Minuteman I, that also has smaller upper stages and nose cone and plenty of length, would be easier to make finless... kinda like pyramid rockets or those conical lifting bodies Quest makes... cones have their own 'natural' stability because of the cross section. I bet a Soviet N-1 Moon Rocket could be made stable without fins for precisely the same reason, with sufficient noseweight. Combining some pre-launch spin might help too, or using a 2 motor cluster with the motors just slightly and oppositely canted parallel to the centerline to create thrust-induced spin might help and be easier to do than spinning it up on the pad (sure would make for some interesting igniter connections!-- Maybe slip rings or something like an alternator??)

The conical bottom and plenty of noseweight are your friend I've seen a thread over on TRF about a finless Soviet Proton Booster rocket that was stable, probably for the same reason... so it CAN be done...

Good luck and be sure to post your results! OL JR

Yeah, I've seen the thread on TRF. That rocket was pretty impressive. I want to try to sim it in Rocksim, but I don't know how to compensate for the spin. Increasing the Cd won't help because it still won't be considered as stable in Rocksim. A CG override may not work because I don't know the differences in altitude/flight profile that can occur between a rocket that is stable from its CG being ahead of the CP and a rocket that is stable from spin.

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Josh
NAR #87993

Hmmm... I'm not sure either... I don't know if there is a way to 'trick' Rocksim into correcting for spin stabilization in a rocket or not... email Tim Van Milligan at Apogee and ask him... I know I read that his first launch of the Saturn Ib was marginally stable and he had some problems with it, and didn't want to make oversize fins... So he canted the fins on the next prototype model to induce some spin off the launch rod and it flew perfectly, so he incorporated that into the kit... I think I read that in the Peak of Flight newsletter somewhere.

Would be interesting to find out though... Have a good one! OL JR