Question on Staging

OK, here goes...I am looking for some input on High Power Staging design. I have a 45% Scale Standard ARM AGM-78 designed and construction has begun. The model will be build using G12 6" fiberglass tube, 1/8" G10 fins, dual deployment and stands 81" tall (there is that "strong" rule of thumb showing through again). I am using a 75mm Motor Mount with a custom 54mm adapter and according to RockSim, it will be able to handle a range of motors from a J415W to possibly a baby M, M1315W. What I want to do is incorporate some form of mount for staging so it could be used as a sustainer as I wish to build the RIM-67 version booster down the road.

I opted for the 75mm motor mount so a 3" coupler along with a custom recessed 54mm motor adapter could be used as part of the coupling for alignment. Under normal single stage flight, I have designed a 54mm adapter and plate that fit inside the 75mm motor mount for single stage flight and will bolt to the bottom centering ring. I would like to use steel rod on the booster section as I have seen this used before, but am looking for the experiences and suggestions from those that have done this as I'm not sure how alignment rods and such would work. This is a new area of rocketry for me, so any help would be appreciated.

I am all ears guys....

Thanks in advance,

Carl

Carl,

While I have not used this method, I have seen it done before with good results. John Cato posted some on it on rec.models.rockets and suggested using heavier carbon arrow shafts for alignment. Mating with either more carbon shafts or brass tubing. I found the post and will post it below

https://groups.google.com/groups?q=...7&[email protected]

Your design would incorporate appropriate sized holes drilled into your centering rings.


Hope that helps.

ACS,

Thanks for the reply, the information was indeed helpful. I did want to get some info on shaft sizes before the centering rings are installed so I could tap them and install sleeves. Speaking of which, what is normally used for sleeve in the sustainer? Any takers? Also, it appears that this is a free separation, or did I read it wrong? How safe will it be to push a large sustainer on a free seperation system?

It does appear that I will need to use 1/2" carbon fiber shafts, but how brittle are they and will they handle stresses froma 15+lb sustainer? this is a 6" rocket with a 7 1/2" booster stage. Also, what methods are used for fastening the rod inside the booster?

Thanks again for the info, yea, I know...questions, questions

Carl

Hey Carl,

You asked:
"Thanks for the reply, the information was indeed helpful. I did want to get some info on shaft sizes before the centering rings are installed so I could tap them and install sleeves. Speaking of which, what is normally used for sleeve in the sustainer? Any takers? Also, it appears that this is a free separation, or did I read it wrong? How safe will it be to push a large sustainer on a free seperation system?"

What I've seen used mostly is brass tubing for sleeves/guides. I presume that CF might be available at the kite shops but not sure how large they come. Certainly much more expensive than brass. Doubt you need CF for the sleeves. As far as safety goes, I would stick to the measurements used by John in the post. He's an engineer and has probably stayed up late at night calculating them. This method provides a lot of strength if mounted correctly. It is a loose fit and insures stage separation at boosted burnout. The 4 protruding shafts seems a little scary if the booster comes in ballistic, but it's done a lot, and proper launch angle can help with appeasing both yourself and an RSO for safety concerns.

You asked:
"It does appear that I will need to use 1/2" carbon fiber shafts, but how brittle are they and will they handle stresses froma 15+lb sustainer? this is a 6" rocket with a 7 1/2" booster stage. Also, what methods are used for fastening the rod inside the booster? "

I would say that they are very strong. Possible that they may shatter on impact if you prang the booster, but that could be a good thing. They have been used extensively, so I would say that they are worthy of the job. For fastening, it would help a lot to have at least two contact points at the CR's for adhesive. As, well as some fillets along the motor mount. If the shafts aren't in contact with the motormount or body tube, you can get creative with a different method. Perhaps, add another CR for more contact area.

As I said, I've never done this, but have read up a little on it. I do have an old issue of High Power Rocketry that has a good article on it written by Ed Holland. I can scan it or fax it to you if you would like to read it.

HTH,

Hello Karl.

The best way to attain perfect alignment of your rods and sleeves, whichever type you decide upon, is to drill the holes through all appropriate centering rings at the same time while stacked together on a drill press. However, that may be a little difficult if you have already assembled your sustainer!

Brian

Hi Carl-
Your rocket sounds like you might have some weight to it if ever used as a sustainer.
Several guys in AERO-PAC have had great sucess in staging by extending from the rear of the sustainer a coupler (minimum 1 caliber length), with the motor and retention system at the rear of the coupler. This makes a super strong component as the coupler , motor, and motor tube are all adding strength. Not to mention the centering rings in that area. I often line the inside of the coupler with 4 layers of carbon so no failures result there.
The staging coupler must be strong!

The booster can then have the airframe strengthened with fiberglass and/or carbon laminations around the outside to make it beefcake. The coupler extending below the sustainer with the motor will slide in to the booster airframe perfect and the booster airframe can be made as strong as you wish.
This also makes it easy to fine tune the friction fit between the booster and sustainer so if you wish, you can accomplish a smoth drag seperation at booster burnout.
Another nice result of the extended coupler on staging is that you get little base drag motor caused damage to the fins and other items at the bottom of the rocket.
AND it makes the CG and CP calcs better by having the fins forward 1 caliber too!

Tom

As I said, I've never done this, but have read up a little on it. I do have an old issue of High Power Rocketry that has a good article on it written by Ed Holland. I can scan it or fax it to you if you would like to read it.

Ned,

Do you still have that article laying around? I would like a copy if you can spare the time.

Thanks,

Shane

mshaner - I doubt if you'll get a reply from ACS (aka Ned). The post just before yours on this topic was back in August of 2001. ACS hasn't posted on the forum since then. I doubt if he is still browsing the forum.

You could try going to his profile and sending him an e-mail message and see if he answers that.

I noticed the date, but thought I might get lucky. Oh well, I'll try him via email.

Thanks,

Shane