Threaded rod reinforcement

[Neil]

I was working on a 4" diameter mailing tube rocket (in rocksim), and I was just wondering what the purpose/use of threaded metal rods is. I have seen pictures of them on many motor mount assemblies on really big rockets, and I didnt know exactly what they did. Do they just go through all the CRs for reinforcement, or what? i dont really get it.....

And would a 4" rocket really need them, or would it be overkill? And which size do I use?

So really I justneed to know everything about threaded rod reinforcement (and maybe some other reinforcement techniques I might want to look into). Thanks guys! -Neil


BTW. Heres the rocsim model for it. I like the name.... (get the "LOTR" Balrog connection? )

 

[daveyfire]

Neil -- ya don't need allthread in a 4" rocket in my experience. Even in my biggest bird, No Sniveling, I only used 4 pieces of 1/4" allthread. The main purpose is to transfer the recovery forces directly aft and the thrust forces directly forwards into the airframe without relying on the body tube to transmit the forces. For rockets with big diameter (read: weak) or thin walled airframe tubes, it's a good idea. However, it's not really necessary in birds this size (smaller tubes are stronger -- like that 54mm cardboard rocket that I fly through Mach ). I have a 4" glass rocket that I fly on fast Ks and Ls, and expect it to handle an L1500B easily, without allthread. Just use plenty of epoxy on the motor mount and you'll be fine

 

[Neil]

Thanks.... Thats what I needed to know. Would it make sense to fiberglass the fins to the MMT?

 

[Ryan S.]

I wouldnt glass the MMT. the CR's provide plenty of support and the cardboard itself is probably strong enough tow ithstand the biggest motor you will endup putting in there

 

[Neil]

Not glass the MMT... use fiberglass on the MMT/fin root joint along with the fillet.

And should I put a layer of glass on the sides of the fins, or is 1/4" 5 or 7 ply plywood enough to take... Say... I dunno... A K670GG.. Thats the max motor I will ever want to fly this thing on, and even though I proabably wont actually fly it on that motor, I would like it to be capable of doing it, just to be sure. The rocket in question has a 54MM motor mount, and if I change the plans to 75MM, yell at me. I dont want any crazy ideas invlolving M1315s.... :kill:

 

[Ryan S.]

I would build this the simple way fiirst and fly some Is and stuff. Then build another one for a K. You could glass the point but I dont really think you need it. If you are worried, use some mashed up FG in your fillet. If you are gonna use FG it would work but its gonna add weight and strength you wont really need

ITs really up to you man

 

[Neil]

(slaps forhead with hand) WHOOPS. I musta accidentally deleted the part that said that I would fly it on Is and Js for a year or two and then try a K.... DOH!:kill:

So I can just cut up glass and stick it in the epoxy? is that fiberglass tape stuff any good?

 

[Ryan S.]

I am saying fly this one on Is and Js then build another one for Ks

 

[Chuck Rudy]

I posted this pic elsewhere. Is this whay you're talking of? If so this MMT is removed from the rocket every flight and, depending on the choice of motor(s) and sizes the centering rings can be changed to suit. This particular setup was for three M impulse motors which are sitting behind the MMT on the table. If you want a rocket which can switch from 3" to 54mm to three clustered 38mm this is the setup.

 

[Neil]

Why make two different rockets for different impulses? Why not just use one all around one?


Why am I arguing agains making more rockets? OK. Im makin 2 rockets. Not at once, but one as soon as my workshop is warm, the other a month before LDRS or something. Gotta run... Dogs barkin.

 

[Ryan S.]

because as you build more you will gain techniques you can implement iin your bigger rocket, therefoer it will be of optimal design and you ddont need to go into any grey areas while building.

 

[Neil]

That too.


Yeah, thats more than enough reasons for me to build two or three extra rockets.

Ya know, just for safetys sake..... Do you think I should make one with a few outboards just to refine my modelling techniques? I wouldent complain too much if I HAD to....

 

[Ryan S.]

if you can fit them.....it is never a bad idea to put outboards in

 

[Neil]

Well, in that case....

Heres my modded Shadow and Flame. I took out the tailcone and put in 4 29MM outboards, which seem to fit. If you look at the back view it shows the electronics bay, and it makes it look like it doesent fit, but actually it does. Just barely, though, It may take some sanding.

 

[Neil]

Shoot. Try this again....

 

[Airdale]

Chuck Rudy has finally design & implemented the proper use of thread all for a motor mount assy.

Every other implementation I have ever seen is where thread all was used to strengthen a motor mount when the centering rings are glued in-place to the airframe and motor mount tube or tubes.

which makes no sence at all because the over all assembly will be strong enough to transfer the loads to the rest of the airframe imposed by the flight of the rocket. IMHO

 

[jetra2]

In the attached picture, you can see where and how I used all thread for alignment and added structure in this cluster MMT. It was a heckuva puzzle trying to get all the nuts and washers on correctly, but as you can see, I did it!

Jason