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  #11  
Old 01-12-2012, 03:33 PM
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Quote:
Originally Posted by maricopasem
My suggestion is to leave the thrust ring out of the rocket entirely. Instead, use masking tape to create a thrust ring at the end of the motor. That way you can use any length 24mm motors (Estes D-12 or E-9, for example) without worrying about spacers, etc.
A-MEN!

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  #12  
Old 01-12-2012, 06:49 PM
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Quote:
Originally Posted by Doug Sams
A-MEN!

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(feeling dim...) I am not following. How will masking tape hold a 24mm engine in a 24mm tube under thrust and/or at ejection? Anyone got a picture for me?
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  #13  
Old 01-12-2012, 07:02 PM
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Quote:
Originally Posted by Scott21
(feeling dim...) I am not following. How will masking tape hold a 24mm engine in a 24mm tube under thrust and/or at ejection? Anyone got a picture for me?

The tape is wrapped around the nozzle end, making a thrust ring that pushes against the aft of the motor mount tube. In order to keep it from ejecting, you can friction fit the motor or you can tape the end of the motor and motor mount tube with a few rounds of tape. I'll find a quick pic.

The green part is the tape thrust ring.

This is how you keep it from kicking out the motor. It's usually a better way than friction fitting because the tape doesn't get hot and melt and stick the motor in the motor mount.

(these photos are from Apogee's website)
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Old 01-12-2012, 07:06 PM
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Quote:
Originally Posted by Scott21
(feeling dim...) I am not following. How will masking tape hold a 24mm engine in a 24mm tube under thrust and/or at ejection? Anyone got a picture for me?
Instead of a forward "motor block", we are advocating an aft "thrust ring". These are built into most reloadable motor cases. The benefit is that it doesn't matter how long the motor is, no plugs or length adapters are required.

In the pic below, there are three wraps of ¼" wide masking tape forming the thrust ring on this motor. It works perfectly. I've used it all the way up to I motors, and I'm sure others have used it beyond that.



Motor retention - eg, a hook - is still needed, but there's no need to lug around various plugs to extend motors up to the motor block. For example, with 24mm motors, there's not only the 70 and 95mm long Estes motors, but there are (were) even longer F32 and G55 SU motors from Aerotech which were also 24mm in diameter. A rocket built to use all these would require three different adapter plugs, a PITA to maintain.

Doug

[Edit] Here's an even better pic: An estes 24mm motor inserted into a 24-29mm adapter. The tape ring keeps the motor from shooting forward thru the adapter, and the hook holds the motor in at ejection. The wood ring keeps the adapter from shooting thru the rocket. (Additional retention is needed to hold the adapter into the rocket.) DS.



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Old 01-12-2012, 07:17 PM
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You will sometimes run into problems with the tape thrust ring - no spacer method. After many flights with shorter motors, the motor mount tube gets charred and sometimes deforms to the point that it can be hard to get a longer motor in there. A spacer will protect the motor mount tube from that.

There are only two negatives for an internal thrust ring. You have to keep up with the spacer, and you are limited in motor length. If you are only flying with 24mm motors, it's not an issue because right now there are only the D12 (70mm) and E9 (95mm) lengths being manufactured. Aerotech's 24mm motors are also 70mm. If you are doing a 29mm or larger mount, there are several lengths and going without an internal ring is the only way to go.
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Old 01-12-2012, 07:46 PM
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Got it. So how do you secure a retention hook if only the aft end has a 90* bend? Obviously when using an adapter, I can see epoxy in use. In this case the bottom tube of the disruptor is a 24mm tube.

Should I just epoxy the retention hook's "bar" to the body and paint over?
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Old 01-12-2012, 08:11 PM
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Quote:
Originally Posted by Scott21
Got it. So how do you secure a retention hook if only the aft end has a 90* bend? Obviously when using an adapter, I can see epoxy in use. In this case the bottom tube of the disruptor is a 24mm tube.

Should I just epoxy the retention hook's "bar" to the body and paint over?

Doug makes a zig zag bend and lays it flat on the motor tube and lays down some gauze and epoxy. I think I can find the illustration on his website.......here it is. Click here for the description.
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  #18  
Old 01-13-2012, 12:25 PM
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Quote:
Originally Posted by tbzep
Doug makes a zig zag bend and lays it flat on the motor tube and lays down some gauze and epoxy. I think I can find the illustration on his website.......here it is. Click here for the description.
Ooh, I'm flattered

BTW, I've gotten away from the S-bends - they're unnecessarily tedious. I've gone to C-bends instead. They seem to attach just as strongly but are easier to form.

For bonding, the one above is nylon mesh (from the fabric store) with yellow glue. The one below is glass cloth and epoxy. I've gotten away from the gauze which was inspired by the old Estes Scout. It stretches out of shape too easily during application, and is harder to get a finish over it (in the case of an externally mounted hook). HTH. Doug .






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  #19  
Old 01-13-2012, 12:37 PM
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Quote:
Originally Posted by Doug Sams
Ooh, I'm flattered
BTW, I've gotten away from the S-bends - they're unnecessarily tedious. I've gone to C-bends instead. They seem to attach just as strongly but are easier to form.

I would have waited for you to answer, but I saw where you went offline and didn't want him to lose his building buzz.

I initially typed "Z-bend" but amended it when I hunted up your images. I've got some z-bend pliers used for R/C so it popped into my head.
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  #20  
Old 01-13-2012, 01:02 PM
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Quote:
Originally Posted by tbzep
I would have waited for you to answer, but I saw where you went offline and didn't want him to lose his building buzz.

I initially typed "Z-bend" but amended it when I hunted up your images. I've got some z-bend pliers used for R/C so it popped into my head.
Z- bend, S-bend, zig-zag - they're all the same...unless you're rolling cigarettes

Doug

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