Minimum Diameter tube fin rocket

My 9 yo son wants to build a scratch MPR, and he wants it to go high and fast...

I put together a tube fin design using a MPR motor tube. But, now I have real concerns about the speed it can handle. A G80 is models at 0.9 Mach using OR. That seems absolutely crazy. If I use an epoxy construction, do you all believe it would hold up? Or, do I just stay away from those larger engine sizes (F40 is .45 Mach and 2400 feet apogee)? Possibly this is just a really bad design and should be avoided...




Minimum Diameter tube fin rocket?

Not quite a Kraken, more of a standard tube fin.

You can beef up the tube fins a lot by glueing couplers inside them, this will mean a little more nose weight or length of body to balance. Also, you could beef up the whole rocket by using BlueTube.

If you are building out of paper based tubing, then wood glue would be the best bet. Epoxy is heavy, and I believe that the wood glue does a better joint paper to paper. Remember to glue each fin to each other as well.

Bottom line? Build it and fly it. Tube fins do not like going over 500mph, but, they create a ton of drag and always end up flying slower than the sims state.

I am currently creating a Kraken like this, I will post a picture for you. This 6 fin version is stronger than the standard Kraken due to the fact that the fins are bonded together.

You can see how I joined my fins
https://www.rocketryforum.com/showthread.php?66053-Winter-rebuilds-Krakens-etc&highlight=squid

My little boy turned his second nose cone today. He is improving.

It turned out not to be a Kraken. But, he is excited since it simulates out to extreme height and speed with some F & G motors.


Willie

Why a MD tube fin they don't like speed ? If you like building it that is all it matters

Yup... I tried overpowering my Kraken "Polly". Ripped two fins off, which were opposite each other. Flew pretty well for the rest of the flight with just two! The overfilled ejection charge then burnt through the lower shock cord right at the connection to the motor mount. The top section came in on chute, the lower body tube section with the two fins then glided in very nicely!

chris m said:

Why a MD tube fin they don't like speed ? If you like building it that is all it matters

Click to expand...

The Tube design is simply for the ease of building it with a 9yo. If the tubes rip off, and we get it back, maybe my boy will try some fins with epoxy fillets..

The tube design also allowed me a place to epoxy a threaded rod to the outside of the tube for motor retention. I'm not sure how that would work with fins.

All for fun! It can rip apart, so long as we don't hurt anyone or anything. My boy would be happy to build another..

I understand what your saying . That would be my kids first scratch build . It will teach the basics and there easy to build . I'm doing a 36" 4.25" tube fin now . The foam nose cone I built and glass is another story . It didn't lay down very well . Have it baged right now

chris m said:

I understand what your saying . That would be my kids first scratch build . It will teach the basics and there easy to build . I'm doing a 36" 4.25" tube fin now . The foam nose cone I built and glass is another story . It didn't lay down very well . Have it baged right now

Click to expand...

I've done a handful of MPR scratch builds, and even more LPR scratch. Builds. One of MPR, crosses over enough for HPR flights. But, I've never glassed any of them. All my FG birds are full FG tube kits (Wildman Rocketry Kits). Glassing seems difficult. Is it?


Willie - using Rocketry Forum

Maiden Flight today at DARS.. F20-7 was a beautiful flight that made it possible to recovery. The flight was extremely stable.

My son wanted to fly a G-motor, but cloud cover prevent us from making that flight.

My boy got his wish. G80-10 in a 6oz minimum diameter rocket. OR sims it at 3562 apogee, and 1014 ft/sec velocity. It was a really long recovery walk. But, it was quality time walking with my boy to pick it up. It was a good thing we painted it fluorescent orange.

I wonder what he will ask to do next.


Willie