am i insane?

[Elapid]

i'm building my 38mm honest john with balsa fins...now, it's not 1/16" balsa, i'm using 3/16 soaked with thin CA.

i will probably glass the whole thing...when i ca'd the fins, i accidentally glued the body tube to the mmt, so i have one centering ring that i can't get glue to without making a hole...ooohhh.. how about a series of pinholes around the bt centered on the centering ring, then apply drops of thin ca! that should work to secure it...

i'm building it with the idea that the MMT is the rocket and the rest is just along for the ride.

what's the biggest rocket you guys have heard of with balsa fins?
ummm...successful rocket.

failures would also be of interest, especially if there is any failure analysis data.

i really should have used the nomex honeycomb/carbon fiber to make some super-fins...wwit?

 

[Elapid]

the proper response was, "Yes, Rob, you are quite insane, but what does that have to do with your rocket?"

ok, here's the synopsis of the build so far, i really need input.

i overbuilt the MMT, i think. it has 4 centering rings (2 in the boattail to brace the fins, two in the body tube for structural support) from 5/32 5-ply aircraft plywood. i used JB Weld to bond the rings and fins to the MMT. the TTW fins and also glued to the boattail with jb weld. i drilled a 1/8" hole in each resulting compartment and injected expanding foam.

fins are 3/16 balsa with thin CA skin

i used a section of coupler tube to strengthen the body tube. i tried aliphatic resin glue to put it ni to give me some time to position it, but that's not how it worked; as soon as i stopped pushing for an instant (when the coupler was flush with the end of the body tube) the glue set up. i had to tear out the top inch of coupler to allow the nose cone to fit. now i know... put the coupler in place, then glue with thin ca. d'oh!

it would have looked sweet on the inside too...


now my question; should i glass the body tube and fins?

i read in an apogee newsletter that said that balsa can easily withstand mach speeds...is the coupler/foam combination enough?

thanks for any input!

 

[BlueNinja]

Yes, glass. 3/32 balsa can be put through mach (DPatell?) and to do that it needs to be glassed.

 

[shrox]

Basswood is great, especially when CAed.

shrox

 

[edwardw]

About going through Mach, what can take it unglassed and what can't? Has anyone tried it unglassed and glassed? I know I put my L2 rocket to .96 mach on 1/8" 3 ply fins and had no problems.

After reading TVM's newest newsletter I am starting to wonder how much 'overbuilding' we do and what is the proper amount for "Allowable Stress Design (ASD)" for you structural engineers out there.


Edward

 

[firemanup]

Edward,

Elaborate on that L2 flight a little more would you or point me to the thread about it if there already is one..

Thanks

 

[edwardw]

Here you go!

https://www.rocketryforum.com/showthread.php?s=&threadid=8244

Edward

 

[DPatell]

lol, yea, my 24mm mach buster had 3/32" balsa fins, glassed tip to tip with 4oz. glass. Make sure the grain is perpendicular with the body tube, or parallel with the leading edge and you should be fine.

I would suggest glassing the crap out of it.

 

[firemanup]

Thanks Ed,

What's the specs on the rocket..?? If you can recall components too..?

I've got a launch next weekend and i keep changing my mind on whether or not i want to put the THOR up on a K445, what has me worried is that it will be doing .85 of mach, at least according to sims.

I'm just not too sure how the thing will hold up, built stock, plywood fins, paper body tube..etc....

 

[eugenefl]

I think the reason we overbuild is because of the non-flight damages rockets are succeptible to. ie - storage and transport, failed recovery phase, and dreaded fin damage upon hard landings. I suppose overbuilding is a paranoia. It doesn't hurt though.

Good luck with that 38mm HJ. Should be crazy.

 

[edwardw]

Fireman,

Fins were 1/8 3 ply. CR's were 1/8 3 ply. Rear cr was 3/8 5 ply (for motor rentention (but I didn't use it cause I used a slimline)). Bulkhead is 3/8 ply with two 1/8 ply baffles.

I used West System, LOC 2.14 tubing and TTW fins.

Edward

 

[DynaSoar]

Originally posted by edwardw
After reading TVM's newest newsletter I am starting to wonder how much 'overbuilding' we do and what is the proper amount for "Allowable Stress Design (ASD)" for you structural engineers out there.

I'm very interested in this topic. What's TVM and where can I find one?

 

[edwardw]

TVM is Tim Van Milligan (spelling). He own Apogee and he wrote in his latest newsletter about high power centering rings. He was using foamboard. Got to Apogee's website and sign up for their e-zine.

Edward