Building with an Aeropack tailcone

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BDB

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I'm building a 3" Punisher-ish rocket out of parts that I have collected over the past year. I want to use a 54 mm Aeropack tailcone retainer, but I'm nervous about getting everything flush and aligned. I, of course, will measure twice (or more) before epoxying the MMT, but does anyone have any advice about a method to ensure that the tailcone joins flush with the airframe?

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Red Phenix

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Hi BDB,

Fwiw, I have glues the retainer to the mmt. Then, when dried, insert assembly (with the unglued centering rings on the mmt) into the airframe. Put a wrap of tape around the junction between the tail one retainer and the airframe. That sucker won't go anywhere now.

Insert a long skinny object into the fin slots and jiggle the centering rings so they are moved to the end of the fin slots. Repeat until everything is square. Small drop of ca will set them where they need to be. Extract mmt assembly from airframe. You can either fillet on the nosecone end of the upper centering ring and the business end of the lower centering ring. That way, no fillets to interfere with the attachment of the fins to the mmt. Or- my preference - mark where the centering rings are located on the mmt - using a writing instrument. Glue the c/r at the marked location. When dry, test fit fins and then epoxy in place. Then, Bob's your uncle. 😄🚀

CJ did a great thread on his 3" dark star and discussed this and his way of internal filleting the fins to the mmt. It is a sticky at the start of this section. Check that out, it is the rocketry bible of f/g rocketry.

With that in mind, clear skies and still winds!

Good luck.
 

crossfire

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A guy in our club flew is P3 yesterday with a tail cone. The tail cone really adds to the kit. Looks nice.
 

BDB

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JohnCoker

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I recently used one of these on a Sky Scraper kit:



With these sorts of things, I find it easier to dry fit and then mark locations rather than measuring and planning.
 

mpitfield

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I recently used one of these on a Sky Scraper kit:



With these sorts of things, I find it easier to dry fit and then mark locations rather than measuring and planning.
I use John's method. Dry fit, mark off, mask, and install last (after painting).
 

blackwing94

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I just did this yesterday on a Madcow Adventurer 3...

I epoxy the top centering ring in place on the motor tube at least 1/4 inch from the top of the motor mount. (remember to install the eye bolt and shock cord if you're using one). Less than 1/4 of an inch from the top and you might get epoxy into your motor tube. (see below)

Then I dry fit the aft centering ring and the part of the retainer that fits on the motor tube. I want the retainer part to be pretty snug on the motor tube.

I get a good idea where the top centering ring will end up in the booster tube, then with a dowel I ring the inside of the booster tube with epoxy about 1 inch below where the top centering ring will end up.

Then I insert the motor tube into the booster tube until the top centering ring it's almost at the epoxy,

Then I slide~wiggle~push the aft centering into the booster tube so the motor tube will be aligned,

I point the booster tube upright and slowly push the motor mount in until it's almost to it's correct location.

NOTE: tilt the booster tube upright and push the motor tube in slowly so the epoxy being pushed up by the top centering ring will level out on top of the centering ring and not spill over into your motor tube. Remember it's only 1/4 inch from the top? ..... live and learn...

Then I screw on the retainer cone and slowly push everything into place so that the cone is where I want it to end up against the booster tube. Done!!!

Set the whole thing upright to cure.

NOTE: do not unscrew the cone yet. Leave it on until everything is cured. Then unscrew the cone, pull off the retainer on the motor tube, remove the aft centering ring and it's time to do fins and rail buttons.

NOTE2: I usually put two small screws into the aft centering ring to make it easy to put it in or pull out as needed.
 

BDB

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I just did this yesterday on a Madcow Adventurer 3...

I epoxy the top centering ring in place on the motor tube at least 1/4 inch from the top of the motor mount. (remember to install the eye bolt and shock cord if you're using one). Less than 1/4 of an inch from the top and you might get epoxy into your motor tube. (see below)

Then I dry fit the aft centering ring and the part of the retainer that fits on the motor tube. I want the retainer part to be pretty snug on the motor tube.

I get a good idea where the top centering ring will end up in the booster tube, then with a dowel I ring the inside of the booster tube with epoxy about 1 inch below where the top centering ring will end up.

Then I insert the motor tube into the booster tube until the top centering ring it's almost at the epoxy,

Then I slide~wiggle~push the aft centering into the booster tube so the motor tube will be aligned,

I point the booster tube upright and slowly push the motor mount in until it's almost to it's correct location.

NOTE: tilt the booster tube upright and push the motor tube in slowly so the epoxy being pushed up by the top centering ring will level out on top of the centering ring and not spill over into your motor tube. Remember it's only 1/4 inch from the top? ..... live and learn...

Then I screw on the retainer cone and slowly push everything into place so that the cone is where I want it to end up against the booster tube. Done!!!

Set the whole thing upright to cure.

NOTE: do not unscrew the cone yet. Leave it on until everything is cured. Then unscrew the cone, pull off the retainer on the motor tube, remove the aft centering ring and it's time to do fins and rail buttons.

NOTE2: I usually put two small screws into the aft centering ring to make it easy to put it in or pull out as needed.
I like the idea of letting the epoxy on the forward CR cure with the tailcone on. That gets everything aligned, but how about internal fillets? I'm concerned that your forward centering ring may not be in contact the TTW fin tabs, weakening the motor mount and letting your internal fillets run everywhere.
 

pyrobob

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I recently used one of these on a Sky Scraper kit:



With these sorts of things, I find it easier to dry fit and then mark locations rather than measuring and planning.
Yeah, this works well for me, too.
 

blackwing94

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BDB, you are correct. The forward centering ring is about 3 inches above the forward edge of the TTW fin tabs. Long 54mm motor tube, short fins, 2 centering rings.

For the fin install I use the triple dip method. Dip the root edge of the fin in epoxy, then slide it in place against the motor tube. Pull it out and do that again. Three times. You will end up with a small fillet on either side of the root edge of the fin and the motor mount. Internal fillet done. (I think I got that tip from MAC Performance)

Add external fillets and foam the can.

There are a dozen ways to do all this. This is just my way.
 

Normzilla

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I just did this yesterday on a Madcow Adventurer 3...

I epoxy the top centering ring in place on the motor tube at least 1/4 inch from the top of the motor mount. (remember to install the eye bolt and shock cord if you're using one). Less than 1/4 of an inch from the top and you might get epoxy into your motor tube. (see below)

Then I dry fit the aft centering ring and the part of the retainer that fits on the motor tube. I want the retainer part to be pretty snug on the motor tube.

I get a good idea where the top centering ring will end up in the booster tube, then with a dowel I ring the inside of the booster tube with epoxy about 1 inch below where the top centering ring will end up.

Then I insert the motor tube into the booster tube until the top centering ring it's almost at the epoxy,

Then I slide~wiggle~push the aft centering into the booster tube so the motor tube will be aligned,

I point the booster tube upright and slowly push the motor mount in until it's almost to it's correct location.

NOTE: tilt the booster tube upright and push the motor tube in slowly so the epoxy being pushed up by the top centering ring will level out on top of the centering ring and not spill over into your motor tube. Remember it's only 1/4 inch from the top? ..... live and learn...

Then I screw on the retainer cone and slowly push everything into place so that the cone is where I want it to end up against the booster tube. Done!!!

Set the whole thing upright to cure.

NOTE: do not unscrew the cone yet. Leave it on until everything is cured. Then unscrew the cone, pull off the retainer on the motor tube, remove the aft centering ring and it's time to do fins and rail buttons.

NOTE2: I usually put two small screws into the aft centering ring to make it easy to put it in or pull out as needed.
This needs to be a YouTube vid.

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DavidMcCann

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I stupidly installed mine with an aero tech motor. Now I fly loki and gorilla cases and there’s a gap. D’oh
 

markkoelsch

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David, contact Aeropack- might be able to buy one. The other option might be to get a short piece of coupler, and cut it to the length you need.


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DavidMcCann

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I could misunderstand this, but the ring would need to be used on the aero tech motors. With the loki and gorilla motors I have a gap, meaning they are too long for the tailcone to seat. The loki almost hits flush, and the gorilla there’s a gap between the tailcone and the BT. The motors are solidly locked in place, that’s not the issue.
 

Steve Shannon

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I could misunderstand this, but the ring would need to be used on the aero tech motors. With the loki and gorilla motors I have a gap, meaning they are too long for the tailcone to seat. The loki almost hits flush, and the gorilla there’s a gap between the tailcone and the BT. The motors are solidly locked in place, that’s not the issue.
So I think you’re saying the thrust rings on the Loki and Gorilla cases are too large in outside diameter to fit down into the Aeropack retainer body.
Newer retainers and Loki thrust rings do fit together and the additional ring fills the gap in the retainer above the thinner thrust rings.
I am not sure whether the OD of the thrust rings were reduced or the ID of the retainer body was increased. Maybe you can just install a new thrust ring.
 

DavidMcCann

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So I think you’re saying the thrust rings on the Loki and Gorilla cases are too large in outside diameter to fit down into the Aeropack retainer body.
Newer retainers and Loki thrust rings do fit together and the additional ring fills the gap in the retainer above the thinner thrust rings.
I am not sure whether the OD of the thrust rings were reduced or the ID of the retainer body was increased. Maybe you can just install a new thrust ring.
nope.

On my gotilla case, the thrust ring is cut higher on the case, than the thickness of the aero tech cloursured thrust ring.

The loki and gorilla thrust tings fit on the retainer just fine. The rear of the casing sticks out, preventing screwing the tailcone flush with the BT. Photos tonight.
 

Steve Shannon

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Okay, maybe I understand better now. The opening in the cap/tailcone isn’t large enough to allow the case to pass through. Can the tailcone opening be opened up enough?
 

rharshberger

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Okay, maybe I understand better now. The opening in the cap/tailcone isn’t large enough to allow the case to pass through. Can the tailcone opening be opened up enough?
Sounds to me that the tailcone doesn't screw on completely ( but enough to secure the motors) with the other cases allowing a non-aerodynamic gap between the tailcone and the airframe, and David is searching for a source of a gap filling ring.
 

timbucktoo

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Okay, maybe I understand better now. The opening in the cap/tailcone isn’t large enough to allow the case to pass through. Can the tailcone opening be opened up enough?
Nope. What he’s saying is the motors fit fine but the axial location of thrust ring prevents the tailcone closure from seating (screwing) all the way to airframe. Hence a gap between airframe & tailcone.
 

DavidMcCann

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I think everyone gets it now ;)

a BT sized ring is my solution soon. But I posted to let others know it could happen if they planned to use multiple brand cases.
 

markkoelsch

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I see. You set it up with the AT motor without the spacer ring in place. So, the tail cone seats correctly for the AT, but you have a gap when using snap ring hardware as the thrust ring is farther from the motor base.

I am not sure how to fix that. Maybe ditch the tail cone and just use an Aeropack retainer cap.


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DavidMcCann

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I stupidly installed mine with an aero tech motor. Now I fly loki and gorilla cases and there’s a gap. D’oh
I see. You set it up with the AT motor without the spacer ring in place. So, the tail cone seats correctly for the AT, but you have a gap when using snap ring hardware as the thrust ring is farther from the motor base.
Yea he said it better.

I'm not terribly concerned. If/when I do fly the combo, I'll just use a regular cap.
 

Rob702Martinez

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Same here. Use flashlight to mark cr locations through tube if possible. Assemble it and test fit it to try it out.

Tack cr to mmt.
tape retainer threaded side to mmt end.
Screw on the tail cone.
Move it around, mark it.
I make a secondary set of marks 1mm forward of the exact measurement, to ensure a positive thread lock and tighten properly.
 
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