time to try 29mm? help please...

stevem · Mar 16, 2004

Hey Guys,
it looks like my latest scratchbuild is going to require something more powerful than what 24mm motors can provide. The rocket is a 40" long BT-80 based cigar-shape built out of styrofoam and coated with galss cloth and epoxy.
The thing already weighs in at 17oz and that's just the airframe.
I am pretty certain I need to move into the 29mm realm to power this one.
Are there any differences in the way a 29mm MMT is built? other than the obvious need for 29mm tubing, what can you guys tell me about getting into 29mm stuff? Are there 29mm MMT kits available? Does 29mm use engine hooks for motor retention?
I know nothing about 29mm so any info will be helpful.

Thanks,
Steve

Rocketmaniac · Mar 16, 2004

Originally posted by stevem

Are there any differences in the way a 29mm MMT is built? other than the obvious need for 29mm tubing, what can you guys tell me about getting into 29mm stuff? Are there 29mm MMT kits available? Does 29mm use engine hooks for motor retention?

Steve,

Moving up to 29mm is a jump, but nothing you can't handle....... I don't see any major differences in building a 29mm MMT, except a little stronger bond to the centering rings and body tube.... You might move up to using epoxy........ I don't know of any 29mm MMT kit, you just buy the tube and centering rings (or make them yourself)....... And as far as engine hooks, I think you leave them for 24mm and below........ Choices for motor retention range from friction fit all the way to devices like the "aeropack" kits.......

Aeropack kits can be found here, they are a little expensive but work great......

https://www.magnumrockets.com/mmr.html

Larry · Mar 16, 2004

Steve,
With the 29mm you don't need an engine block if your using RMS. As for motor retention, it depends on rocket dia. In small dia. rockets an engine hook, or friction fit is simple. If its 3" or bigger in Dia. I've used the PML type retention, which is a ring with ears. Screws go through the ears into nuts mounted on the back side of your aft CR to hold the motor in place. For engine hooks I have used the aerotech hooks on a couple of occasions and they work real well.

This is a photo of the PML retainer used on my 4" AMRAAM. The one on the floor is one I made for a 3" rocket. The one on the 29mm motor tube I made for the PML Quasar. Its 2-1/2" in Dia. The nylon collars are used to space between the retention and the CR so you don't bend the heck out of the retainer....Larry

BlueNinja · Mar 16, 2004

Aerotech has 29mm kits, with CRS but I think the 2.6in will fit bt80(?).

Ryan S. · Mar 16, 2004

Dont use an engine block as this will restrict what motors you can put in and it is unneeded. With AT motors, which I imagine you will be using, the aft closure works as an engine block, for single use just use tape. to keep the motor in when the ejection charge goes off you could agian use tape, or take 2 engins hooks and file off one side then glue them to the side of the MMT. These will hook over the motors and keep them in (use some tape to hold them down)

umm also make sure you use plywood centering rings and epoxy. Thats all I cant think of

Missileman · Mar 16, 2004

I agree with all above posts.
Ply center rings recommended.
I like slimline retainers, they glue onto end of motor tube and use a C clip to hold motor in, but kind of expensive 20 something bucks.
PML retainers are around $15.
A much cheaper alternative that is widely used is to install blind nuts inside your aft center ring (put 2 180 degrees apart)epoxy them in place but be careful not to get epoxy on threads.
Use caphead bolts and screen door clips to hold engine in place.(all available at most hardware stores)
I get my engine tubes and center rings (until I started cutting my own) from Publicmissiles.com
A good place to start is right here. Look through some of the build photos in mid power and scratch build sections.
I hope this helps and good luck.