2.6” 38mm Crossfire ISX Upscale

[xXHeliMechXx]

I started a scratch build Crossfire ISX. I scaled it using open rocket to a 2.6” airframe tube and I am going to be using a 38mm motor tube. I spent yesterday drawing up vectors and cutting out my centering rings and fins using 1/4” birch. I found a motor retainer on thingverse im going to try out. It’s a bolt on type but the flange was over 3” in diameter so I did some modeling on that too so it will fit my body tube. I plan on building the fin can outside of the airframe so I can get strong epoxy joints against the motor tube.

More to come!

 

[Hobie1dog]

Thanks for the pictures.

 

[xXHeliMechXx]

Got my filets done and printed a motor retainer. I still haven’t decided on the motor tube length yet.

 

[xXHeliMechXx]

Got my nose cone printed and epoxied together and I began prepping my airframe tube for carbon fiber. I decided to cut my motor tube long enough so I have room for some bigger motors later on if I feel so inclined!

 

[xXHeliMechXx]

I epoxied my airframe tube using ADtech 820 using the 824 slow hardener. Then wrapped it with 0.003” Duralar sprayed with smooth-on universal mold release. After it was wrapped I used a thick piece of card stock to work out all the bubbles starting from the center working towards the outer edges.

After about 8-10 hours I peeled the Duralar off. The mold release made it much easier to remove. My first attempt using this epoxy and Duralar on another tube was much more difficult to remove so I highly recommend the mold release!
The finish came out perfect! This method always leaves a fine ridge along the tube where the plastic was first applied.
I originally put a coat of medium CA over the surface of my nose cone to fill in the layer lines from printing. I sanded it smooth and saw it still had low spots so I decided to use some of my excess epoxy from the airframe tube and coat the nose cone.
I’m overall happy with the result. It needs some sanding to blend the surface a little more smooth. I’m not sure if the CA had some sort of reaction with the nose plastic or if the CA reacted with the epoxy but one of those reactions caused the color to get dark in places. It still feel structurally sound so I’m not worried about it. It will be painted anyway. The spots that didn’t turn black are where I had used epoxy to adhere the printed parts together before the CA coat.
I got the airframe tube trimmed and slotted getting ready for final assembly. I have to cut a forward centering ring for the motor tube assembly and install an eye bolt and shock cord still.
It’s coming along nicely!

 

[xXHeliMechXx]

New updates! I took a piece of all thread and put 2 nuts on it and then cut a quick link and welded it to the nuts to make a thread on U bolt.

After epoxying everything in place, I hung the nose cone and finished the paint on it.

I finished doing my fin filets and attached the strakes.

Next was off to paint for the airframe!


I cut out my graphics with the vinyl plotter to match the original decorations.

I packed it and checked my CG!

I’m overall pretty happy with how this turned out! I’m excited to see how it flies! It’s pretty light.

 

[cwbullet]

Interesting attachment point with the welded all thread. That is fairly unique.

 

[xXHeliMechXx]

Interesting attachment point with the welded all thread. That is fairly unique.

I was a bit limited on options due to how I modeled the nose cone. The all thread sits in a thicker section of the print for strength and the nuts welded to the quick link section allowed me to rotate the threads to get the link centered before epoxying the ends. The jam nuts keep it all tight. I used the quick link because it’s more narrow than any of the u bolts I could find locally.

 

[xXHeliMechXx]

Got to shoot the Crossfire upscale today! I used an Aerotech I175 DMS motor with a jolly logic chute release and altimeter two. The launch went perfect! The altimeter 2 logged 3291 feet and 452mph! I’m very happy with how this project turned out!