interstage coupler

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War Bird

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I am currently building a 2 stage 5.5" Nike Hercules. This rocket build has been a real challenge. I am a little concerned about my interstage coupling design. The two stages will connect with 4 - 5/16" carbon fiber rods mounted to the booster that will be inserted into aluminum tubing in the upper stage. The 4 carbon tubes have a bit of flex to them. My question is: Just how solid does this connection have to be. I am thinking it should be rock solid as to not allow any flex between the booster and sustainer.

Thanks Guys

Kevin Trueblood
 
Kevin,

I would want it to be a very solid connection...the last thing you want on a 5 1/2" bird is wobble on boost. On my smaller two stage, I used a double walled coupler for a 4 to 3" transition and that works fine for that style rocket.

However, you are getting into a bit larger airframe, so I can tell you what I have seen. One of our Prefects at Tripoli Mid Ohio, Kreig Williams, flies a 6" two stage monster on a L/M to a K/L. He uses rods as you described and he also has about a 1" high coupler at the joint. The coupler plugs into the base of the upper stage and adds the extra stiffness for the flight. He has been flying this rocket since LDRS19 and has many flights on it...all successful. You may want to consider that as an option.

Good luck,

Carl
 
Tight fitting shear pins may also be an option, but that totally eliminates the option of drag seperation, but its not like active seperation is terribly hard to do...

on my two stager, i use a coupler that extends about 2.5" into the sustainer, but its only a 54mm tube, but you get the idea... right?

Scott McNeely
 
I used Rods on my Terrier SH, and also a short peice of coupler as Carl describes, it holds it well, but has yet to be tested in flight.

As far as shear pins go, that isnt a bad idea, and you can seperate pre-sustainer ignition with a small Bp charge. Although, if a rocket this size wobbles, I dont know if they will hold it in place
 
Tubes are far stronger than rods...... carbon fiber tubing may help prevent this.....
 
Thanks for the input guys

Shears pins would be a great idea. However, the upper stage of the Nike has a boat tail making that difficult. I epoxied 1/4" threaded rod inside of the carbon fiber rods to stiffen them up. This helped but still has more flex than I would like. I should have used 3/8" solid stainless steel rods. Anyway, I installed a 1" tall centering ring into the bottom of the transition section. This did stiffen up the connection quite a bit. However, it fits tighter and probably will not drag seperate now. I'm thinking the use of a BP charge to do the separation duties is the way to go. I'm thinking of using the same timer and time interval to ignite the upper stage motor since the motor will take a little time to come up to pressure. Hopefully the booster will have time to get away from the sustainer before the motor scorches the booster transition. Pics attached of the progess so far.

Thanks again fella's

Kevin Trueblood
 
Here is a pic of the booster transition with the 1" tall coupler centering ring. The black stuff at the epoxy joints is chopped carbon. (Great stuff, I just cannot stop using it!)
 
A picture says a thousands words, right guys?

Here is one of the booster business end. The central motor mount is 54mm with the 2 outboards being 29mm. The other two compartments are for duel rear chutes. The kevlar cords are seen inside. I used kevlar here because there is no way to get into the 2.5" tubes to afix new ones. Also shown is the custom fiberglass 2 part nose cone w/ drouge e-charge holders on the bottom of the shoulder. The electronic bay will reside in the sholder and main chute in the nose itself. I'm a little concerned about the location of the static ports for the altimeter. With this configuration they will less than one caliper away from possible turbulance from the nose cone??? The altimeter here will be a Perfect Flight miniAlt/WD.
 
This picture shows the 2-part nose cone again and the booster transition access panel. The nylon fitting in the transition is for one of two e-charges to screw into. The opening is for access to the booster altimeter (another miniAltWD). You can see the JB weld holding the carbon fiber rods to the lower transition bulk plate. Holes through this bulk plate and ones lower in the outboard booster tubes will serve as venting ports. I think I'll just wrap the altmeter in foam and stuff it in here rather than securing it to a mounting board.
 
One more picture of the 5.25" Nike Hercules to date. The red/orange stuff on the sustainer is automotive body filler. Now comes the part of rocket building we all HATE! Sanding and priming, sanding and priming, sanding and priming, etc.......... :eek:
 
looks cool although, if you are sing rear chutes, you are going to bring the rocket right down on those interstage rods. You better hope you dont land on any firm ground or you may have problems.

why not eject the interstage off the central 54mm tube?
 
Sweet:D
I have a 6" on the drawing board myself.
I am building a smaller mid power one right now for testing.
For some great tips visit the king of Hercs at :
https://www.nikeproject.com/
I have sent him a few emails with questions on my build and he was more than happy to help.
 
Looks great to me, I doubt you'll have any problems at all with that interstage coupler. Andy Woerner built a Nike/Herc a while back with four 38mm I motors in the booster, and he just had the tailcone of the second stage fit into a matching "cup" at the top of the booster. No rods or anything else, and it worked fine.
 
War Bird,

You beat me on the 5.5" Nike, and you have done an excellent job. I have my booster done a little different, as I have it set up with (4) 38mm mounts that are massed towards the center of thrust...paid a nice penny for those special order rings as well.

kudos man! I likes it alot.
 
Hi,

I'm very new to this site so forgive me for any breach in etiquette. I'm currently working on a project and am tasked with designing (or purchasing) an interstage coupler. Do you know of any tutorials on designing a transition stage? Our rocket will have three stages total (6", 4", and 3" diameters) so I'm going to have to design two interstages, but I have zero experience in this particular area. Any advice you can give would be greatly appreciated!

Thanks,

Emma
 
Hi,

I'm very new to this site so forgive me for any breach in etiquette. I'm currently working on a project and am tasked with designing (or purchasing) an interstage coupler. Do you know of any tutorials on designing a transition stage? Our rocket will have three stages total (6", 4", and 3" diameters) so I'm going to have to design two interstages, but I have zero experience in this particular area. Any advice you can give would be greatly appreciated!

Thanks,

Emma

With progressively smaller stages, the easiest way to do interstage couplers is to use the motor itself as the coupler. Essentially, you design a motor adapter into the top of the stage below. Very strong. Lots of details to consider obviously, but that's the concept.

As it turns out, I'm planning a three-stage flight of my own in a couple of weeks. I have a thread (below) that documents much of the design and the techniques that I am using. The rocket has been recycled and re-purposed many times, so it is certainly not how you would build a three-stage from scratch. But, you might get a few useful ideas.

https://www.rocketryforum.com/showthread.php?66850-So-maybe-I-ll-try-a-three-stager&highlight=stager

Jim
 
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