# ACP Composites

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#### markkoelsch

##### Well-Known Member
I thought they were just a materials supplier.

#### dixontj93060

##### Well-Known Member
I have been ordering from them for 5+ years. Yes, give them a call, I believe they do custom work, but my impression it is for higher volume production.

#### markkoelsch

##### Well-Known Member
I am sure you can buy it. Whether they will cut part for you I cannot answer. I assume this is for the 1mm thick fins you want? If I understand you correctly you want these fully air foiled, correct? That will take much machining per fin. You might want to start with slightly thicker material.

#### TRFfan

##### Well-Known Member
A one-off custom boattail might be pretty expensive. A few years ago I made a run of 1.5"-24mm fiberglass boattails. The making of a plug, then mold, then getting the layup right is very time consuming. You'd be looking at a \$250 boattail regardless of size due to labor alone.
What about making a 3D printed mold? That would be alot cheaper.

#### dhbarr

##### Amateur Professional
That takes care of the plug & mold, maybe. But there's a lot of labor there in finishing the mold, creating the part, and finishing the part.

Of course you can jump straight to a 3d printed boattail or NC, or turn one out of basswood, or whatever.

Wherever you do it yourself, plan for extra materials dollars. Wherever you have it done, plan for extra labor dollars.

#### watheyak

##### Barnstormer
TRF Supporter
What about making a 3D printed mold? That would be alot cheaper.
Perhaps. Not sure about successfully polishing a 3D printed part to a mirror finish, though. Otherwise the part won't release. I'm sure it's been done, though.

#### TRFfan

##### Well-Known Member
It would basically be like making a NC and then cutting a little bit off, right?

#### TRFfan

##### Well-Known Member
That takes care of the plug & mold, maybe. But there's a lot of labor there in finishing the mold, creating the part, and finishing the part.

Of course you can jump straight to a 3d printed boattail or NC, or turn one out of basswood, or whatever.

Wherever you do it yourself, plan for extra materials dollars. Wherever you have it done, plan for extra labor dollars.
The boatail is going to be pretty close to the nozzle and so I want it made out of a lightweight, strong material. CF is too expensive but Fiberglass is fine.

#### watheyak

##### Barnstormer
TRF Supporter
It would basically be like making a NC and then cutting a little bit off, right?
Exactly. But it still needs to be polished or the part won't release from the mold. What diameter airframe is the boat tail for?

#### TRFfan

##### Well-Known Member
Exactly. But it still needs to be polished or the part won't release from the mold. What diameter airframe is the boat tail for?
A fiberglass BT-50 (24.8 mm).

#### watheyak

##### Barnstormer
TRF Supporter
A fiberglass BT-50 (24.8 mm).
I'm confused then. Isn't this for a 24mm motor? What diameter would the boattail reduce to?

#### dhbarr

##### Amateur Professional
I'm confused then. Isn't this for a 24mm motor? What diameter would the boattail reduce to?
Topload a disposable 24mm APCP that has the nozzle protruding aft? I have that in mind for my 18mm D's.

#### TRFfan

##### Well-Known Member
I'm confused then. Isn't this for a 24mm motor? What diameter would the boattail reduce to?
The boatail's aft diameter is around 19 mm, length is 17mm, and fwd diameter is 24.8 mm. It is connected to a 24.8 mm diameter body tube.

#### watheyak

##### Barnstormer
TRF Supporter
The boatail's aft diameter is around 19 mm, length is 17mm, and fwd diameter is 24.8 mm. It is connected to a 24.8 mm diameter body tube.
Sounds like it would extend past the nozzle quite a bit, reducing your thrust a bunch. Not to mention the thrust ring from the aft closure that would prevent you from attaching ithe boattail to the airframe. The diameter of that thrust ring is ~28mm.

Carolina Composites makes a tapered aft closure for the CTI 24mm hardware that might be exactly what you're looking for. Not sure if that part would be legal for a CAR record attempt, though.

#### TRFfan

##### Well-Known Member
Sounds like it would extend past the nozzle quite a bit, reducing your thrust a bunch. Not to mention the thrust ring from the aft closure that would prevent you from attaching ithe boattail to the airframe. The diameter of that thrust ring is ~28mm.

Carolina Composites makes a tapered aft closure for the CTI 24mm hardware that might be exactly what you're looking for. Not sure if that part would be legal for a CAR record attempt, though.
I am confused. Why would it reduce the thrust? It's not like the boatail is going to be in contact with the flame.

I am using a custom closure that is attached with the boatail and so the nozzle will not exactly be flush with the top of the boatail. Rather, it will be a couple mm ahead so that the flame will not come near to the boatail. And I think the closure itself will be legal, since I am not exactly modifying it in any way.

#### TRFfan

##### Well-Known Member
Exactly. But it still needs to be polished or the part won't release from the mold. What diameter airframe is the boat tail for?
What about making the boatail and then dissolving the mold?

#### watheyak

##### Barnstormer
TRF Supporter
I am confused. Why would it reduce the thrust? It's not like the boatail is going to be in contact with the flame.

I am using a custom closure that is attached with the boatail and so the nozzle will not exactly be flush with the top of the boatail. Rather, it will be a couple mm ahead so that the flame will not come near to the boatail. And I think the closure itself will be legal, since I am not exactly modifying it in any way.
If the nozzle is up inside the boattail it will reduce thrust because of something called Krushnic Effect. Even if it's not in contact with the flame.

And the closure is "custom" but not modified? Anything other than the exact part from CTI would not be legal for a record. And that part can't be modified in any way, otherwise it's an EX motor, and not legal for records.

What about making the boatail and then dissolving the mold?
Many people make male molds from styrofoam and dissolve it with gasoline.