18mm machbuster 3.0 Design

[ScrapDaddy]

what do you guys think of this design for a machbuster i am pretty sure about the general idea (minimizing everything) I think its close to the bear minimum of what can be called a "rocket" it even utilizes featherweight recovery There are however a few things i have for questioning

1) the fins They are swept back and are a little tall and i am worried about fluttering at mach 1.31 :jaw: i plan on making them out of 3/32 hard balsa, coating them with CyA and paper skins and on MarkII suggestion laminating epoxy is there anything else i can do for this without compromising weight?

2) The phelenic body tube will it need reinforcing? i now know thanks again to MarkII (well i kinda also used common sense)that low power components are not normally designed for this stress.

3) Anything else you may find a problem

4) i have had thoughts about covering the body tube with mylar, any thoughts?
Please let me know thanks!:caffeine: I really owe The rocketeers on TRF alot

 

[UPscaler]

what do you guys think of this design for a machbuster i am pretty sure about the general idea (minimizing everything) I think its close to the bear minimum of what can be called a "rocket" it even utilizes featherweight recovery There are however a few things i have for questioning

1) the fins They are swept back and are a little tall and i am worried about fluttering at mach 1.31 :jaw: i plan on making them out of 3/32 hard balsa, coating them with CyA and paper skins and on MarkII suggestion laminating epoxy is there anything else i can do for this without compromising weight?

2) The phelenic body tube will it need reinforcing? i now know thanks again to MarkII (well i kinda also used common sense)that low power components are not normally designed for this stress.

3) Anything else you may find a problem

4) i have had thoughts about covering the body tube with mylar, any thoughts?
Please let me know thanks!:caffeine: I really owe The rocketeers on TRF alot

If you do not want to reinforce your tubing, i suggest you use blue tube. It is available from apogee among other vendors. I plan on using it in my competition rocket for XPRS ( If I ever get around to actually building it) and they say it goes mach unmodified :bangbang:

I also might suggest you use plywood fins instead of balsa.

 

[The EGE]

Neither Blue Tube nor phenolic are available in 18mm size. The only game in town is plain old 18mm Estes-type tubing, which prolly is strong enough for a rocket this tiny.

 

[rstaff3]

You may bot be able to prove you broke mach, but you probably will be able to tell that you exceeded the speed of balsa.

Uncle Mike has BT20 'tough tubes' https://www.unclemikesrocketshack.com/Parts/Body_Tubes/Body_Tubes.html

 

[ScrapDaddy]

Out of curiousity what are these tough tubes made of?

 

[Rocketjunkie]

I've got a few old Aerotech E45's and F55's around here somewhere... I just glue 1/32" thick plywood fins to the motor. Works well, don't have to find them

 

[ScrapDaddy]

Go ask Layne from pem tech he friction fitted the cr and the mmt in his king kraken!

 

[Initiator001]

My Mach 1 breaking D21 model used standard Estes BT-20 and plastic nose cone with G10 fiberglass fins.

No paint but I did seal the spiral on the BT-20.

Tower launched.

 

[ScrapDaddy]

What was the fin shape? Swept back? Delta? Square?

 

[rocket999]

I have made a few of these (Although I have yet to find one...). First off, I used a normal Estes body tube. In these small rockets they are strong enough. For fins, I used 1/16 inch plywood from the local hobby store I attached them using hobby grade epoxy. These fins were plenty strong, and in my opinion, overkill. I used nose blow recovery on this one (I think, it may have been a streamer..).

Here is a picture of my rocket. (This was two years ago.)
https://www.epickett.net/jmrc2008-9-6/pages/101_7498.html

Look at how small the fins are. They don't need to be much bigger than that. For speed you want the smallest fins possible (and keep the measurement from the root of the fin to the tip 1.5 times the diameter of the BT). If you sweep them back the fins may need more reinforcement.

If I were to do this one again I would use the same fin design, but I would make them out of really thin balsa wood (3/64 maybe) covered in lightweight fiberglass. This would make the fin set really thin and light weight. Just glue them to the body tube with epoxy and give them some small fillets.

What program are you using to simulate the rocket? Mach 1.3 sounds really optomistic. But if you keep it light you may hit mach 1 (transsonic).

Picture:
https://www.epickett.net/jmrc2008-9-6/pages/101_7531.html

Youtube: (skip to 5:00)

[YOUTUBE]ZKUC3s_L8sM[/YOUTUBE]
https://www.youtube.com/watch?v=ZKUC3s_L8sM

I hope this helps.

Sam

 

[ScrapDaddy]

Rocksim has been known to make rocketeers feel better about themselves but it does have better supersonic support than open rocket

 

[ScrapDaddy]

That mach buster looks just like my first! Except mine had tiny double delta fins

 

[ScrapDaddy]

Mine should come in 3 grams stock condition