24mm engine in place of 18mm?

[Scott21]

Can I do this with a rocket whose lower body tube is 24mm and I just skip inserting the 18mm motor mount? This is for an Estes Photon Disruptor assembled with CA glued fins and body tubes with some sanded wood filler all around (extra strength?) The upper body tube (33mm) is being extended ~ 4 inches as I didn't get the ejection baffle installed low enough. :(

[Bazookadale]

Watch the CG but this should flt well on a D motor

[tbzep]

You will need to use one of those green centering rings that were intended for the 18mm mount as a thrust ring for the 24mm motor. Forget about the motor hook and use friction fit for motor retention.

[Scott21]

I have an expended E motor. I'll saw off a 1/4" and use that in the 24mm tube for the motor block. An I'll cut off a 1/2" piece to use as a spacer and start with a D12-3. I have some Kevlar strings being glued to the top of the baffle to form a 3-string anti-zipper shock cord attachment point.

Unfortunately, I already glued the green ring to the 18mm mount. I 'll work things out so I can slide in the 18mm mount...for windy days. ;)

Thanks all

[ghrocketman]

Sounds good.
Go BIG or go HOME !

[jharding58]

I have an expended E motor. I'll saw off a 1/4" and use that in the 24mm tube for the motor block. An I'll cut off a 1/2" piece to use as a spacer and start with a D12-3. I have some Kevlar strings being glued to the top of the baffle to form a 3-string anti-zipper shock cord attachment point.

Unfortunately, I already glued the green ring to the 18mm mount. I 'll work things out so I can slide in the 18mm mount...for windy days. ;)

Thanks all

Buy a rings 'o' plenty from Apogee or get a ring assortment from Semroc (or whomsoever your favourite vendor may be). You can always find a use for rings...

If you are going to use an 18mm adapter your going to have to find a way to engage the adapter in the main tube. Otherwsie it will spit the 18mm on ejection charge.

[CPMcGraw]

Not a warning about the conversion, but an observation about using CA...

They don't hold fins well. In my experience, CA is a bit too brittle for the stresses of launch and landing, so for the fin-to-BT attachment, I'd strongly recommend using something like Titebond (I, II, or the new Translucent formula) instead. A balsa-to-balsa joint may be OK if the glue is fresh enough; but if it has any age on it, go get a new bottle. Use the medium-viscosity, too, not the thin.

Been there, done that, had to un-done it, too... :D

[jharding58]

I would endorse with only one qualification. If the joint is tight already, then use a thin formula first. The mechanism of CA is to penetrate and then form rigid chains; hence the bond. If the surfaces are gappy, then the adhesive simply bonds on the surfaces. The counter is that no amount of glue is as strong as a solid, tight joint with a good penetrating adhesive. The thinned Aliphatic branded as Super Phatic is IMHO the best of both worlds. It will wick straight from the bottle and penetrates extremely well. Once cured, there is a higher level of flexibility in the joint that you would achieve with a CA.

[jamjammer53150]

always , always go one size bigger on a motor mount , you can always sleeve down.
I know this guy who spent nealy 100 hrs on a project , that in the end nothing in 24mm could fly it ( perhaps with a cti Imax it MAY fly ) , so always over build

[maricopasem]

You will need to use one of those green centering rings that were intended for the 18mm mount as a thrust ring for the 24mm motor. Forget about the motor hook and use friction fit for motor retention.
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.

[Doug Sams]

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!

Doug

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[Scott21]

A-MEN!

Doug



(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?

[tbzep]

(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.
http://www.apogeerockets.com/images/Motors/Motor_insertion.jpg
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.
http://www.apogeerockets.com/images/tape_motor.jpg
(these photos are from Apogee's website)

[Doug Sams]

(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.

http://www.doug79.com/mma10-13/mma10-13-3p.jpg

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.

http://www.doug79.com/mma24-29/mma24-29-5p.jpg

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[tbzep]

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.

[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?

[tbzep]

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. (http://www.doug79.com/stuff/tailconehook.html)
http://www.doug79.com/stuff/hook-top.jpg

[Doug Sams]

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. (http://www.doug79.com/stuff/tailconehook.html)
http://www.doug79.com/stuff/hook-top.jpgOoh, 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 .



http://www.doug79.com/motor-retention/s1-1-2p.jpg


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[tbzep]

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. :p

[Doug Sams]

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. :pZ- bend, S-bend, zig-zag - they're all the same...unless you're rolling cigarettes :D:D:D

Doug

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