G-Force Build Question

[homebrew_58]

Just started building an AT G-Force. I left the thrust ring and motor hook out to give me more motor options. This had led me down a path of doing a couple of things I've never done before... fiberglassing and using Kaplow Klip style motor retention.
First question... do you think I need to fiberglass the fins if I may be using motors larger than G? And is this a skill I should be trying out on a rocket like this or should I practice elswhere first?
Second... the rear centering ring is about three inches into the rocket body. If I install the Kaplow Klips there, will it be a hassle getting to them? Or should I install another centering ring closer to the end of the mmt?

Thanks in advance,
Kevin

 

[rstaff3]

I have used 2 methods to connect motor retention clips.

The first is the more normal approach using either T-Nuts or inset bolts. (I don't know the real name of the latter but they are a female threaded tubes with teeth around the circumference.) This approach usually requires a CR near the end of the rocket, but you can also use long bolts with some sort of stanadoff that is sized to fit between the CR and a point that is flush with the end of the motor. This will keep the Kaplow Klip or equivalent in position. A piece of brass or aluminium tubing works well as a standoff.

The other method is to glue bolts into the CR itself, and use wing nuts to connnect the clips. If the ring is inset like yours, it would be best to use standoffs with this approach, although I have done without them. If standoffs aren't used the clip will not end up flush with the engine, but will end up at an angle as the wing nut is tightened below the plane of the engine. This will work with most clips but may not work with all shapes.

(Geesh, that sounds confusing...but it really isn't)

 

[KenParker]

I think rstaff has pretty much addressed the motor retention issues. I will add my .02 worth though and say that I would add a CR at the bottom of the rocket - it will make any scheme of engine retention much easier to implement.

As far as fiberglassing.... if you haven't done it before, my recommendation is that you practice on something before you try it on your rocket. If you go right into trying it the first time on your rocket and mess it up..... well, it could be a real pain to correct. If you want tips on fibeglassing, do a search here on the forum for "fiberglass" and I think you will find more than you ever needed to know about the process.

 

[PGerringer]

Guys...

n soapbox:

I am shocked and appauled that you are not suggesting the AeroPack solution for motor retention. https://www.aeropack.net/motor_retainers.html Ever since I tried my first one (29mm on the Aerotech Mirage) I have used nothing else which includes, 29, 38, 54, and soon 98 and 75mm. I strongly suggest you at least try one.

ff soapbox:

disclaimer: I neither work or get paid by AeroPack. If I did, I would give you one for free. But I don't so, tough luck.

 

[rstaff3]

I agree and disagree. The Aeropack is my favorite retainer and it was definitly an omission on my part, but they are a bit expensive.

Phil, have you used the 29mm variety with SU motors? I have one on a 38mm rocket that I usually fly on 29mm SU motors with an adapter. To make the Aeropack work, I cut a circular piece of thin metal that fits in the end of the retainer. I then cut a smaller circle that the nozzle will fit thru. This keeps the motor from blowing out the back.

Giant leap now sells something called the Slimline, which uses a snap ring that is removed with only a screwdriver. I haven't used one yet but plan to shortly. They also make boattail retainers that look pretty cool. They aren't cheap either, but are a little cheaper than the Aeropack ones. Here's the URL:

https://www.giantleaprocketry.com/

Oh, Phil, I suggest you start distributing these products so you can provide samples To TRF members only of course!

 

[PGerringer]

LOL... Sure they are expensive, only when you don't know where to get them from. I have found it is relatively inexpensive to buy only one cap with multiple bases. That saves about half the cost.

I've used SU in an AeroPack before. I just wrapped a ton of tape around the aft end of the motor and it became the thrust ring. I then sandwiched it in with the retainer ring.

Now, about Giant Leap and Slim Lines. They are also great. However, the snap ring can't be removed with a screwdriver. (Course, I could be wrong) A friend of mine (chime in here Mark) has one and it takes "pin" (???) plyers to pull out the ring. I found it difficult to remove and insert the ring. So, I'm sticking with the screw in cap style.

 

[rstaff3]

Ack! They have been advertising a snap ring that can be removed easily with a scredriver. I'll be sure to call Ed about the screwdriver vs. snap ring pliers issue BEFORE I buy. Maybe the screwdriver style ring didn't work out??? Thanks for the heads-up.

 

[MarkABrown]

Originally posted by PGerringer
A friend of mine (chime in here Mark) has one and it takes "pin" (???) plyers to pull out the ring. I found it difficult to remove and insert the ring. So, I'm sticking with the screw in cap style.

Dick is right. The slimlines that are sold by Giant Leap have a snap ring that can be removed by a screwdriver. What Phil is talking about is my brother built a 29mm retainer for me machined out of aluminum. The snap rings that he found for his version require Circlip pliers to insert and remove. The Circlip pliers aren't that big of a hassle. It just requires a bit more practice to become comfortable with it. BTW, my brother has also made a few retainers for me that are very similar to the Aeropack retainers. The threads are different and the knurling on the caps is better in my opinion.

 

[rstaff3]

Mark, thanks for the clarification. Man am I jealous of anyone who knows how to do machining, has a friend or relative who knows machining, works in a machine shop, has neat custom built toys.........just kidding, kinda

 

[EMRR]

Another thought and idea gone OOP was Budget Rocketry's retaininers. REVIEW .

I like these and actually have a few extra packets that I will install on a couple other kits coming up, but, Budget Rocketry seemed to shut down!

My two cents of OOP information. Maybe someone can figure out how to produce these again.

Nick

 

[Lee Reep]

Originally posted by MarkABrown
BTW, my brother has also made a few retainers for me that are very similar to the Aeropack retainers. The threads are different and the knurling on the caps is better in my opinion.

I think you and your brother should go into business selling these. And of course the deep discount offered to all your brethren on TRF would be greatly appreciated ...



BTW -- I haven't used one of the "quick change" retainers, but after going to the 100K In A Day launch, I'm sold. Took seconds to get the motors in and out. I find that when I use "Kaplow Klips", I always have the wrong straps on hand, or the wrong sized bolts (OK, I didn't standardize sizes and spacing over the years!).

 

[kgholloway]

IMHO the retainers from Budget Rocketry were the perfect solution for a high performance / low cost motor retainer. They work just like the Aeropack retainers but were injection molded instead of machined so they only cost 1/5 as much. I have a hard time justifying spending $25-30 dollars for a motor retention device when Kaplow clips are so cheap. The $5 cost for one of the Budget Rocketry retainers made it a lot easier decision.

I built a 'beefed up" NCR "Big Brute" last year to certify on and used one of these retainers. So far I've flown it 6 times on motors from a G64 to an H180 without a single problem with motor retention. The motor retainer is so strong, in fact, that except for a little soot on the surface it still appears brand new. I was really sorry to see Budget Rocketry shut down due to family problems.

Ken