Insanity Plea: A sub minimum diameter M2245 project.

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ChrisAttebery

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I've been working on this project in the background for quite a while. I learned a lot from my M685 flight to 37,789' in September(Wildman Blackhawk 75). This project is will build on the foundation of that project.

My number one goal is for the rocket to survive the flight. The secondary goal is to attempt to break the Tripoli M motor record(45,554' AGL).

M2245 Profile.jpg

This rocket will be built around the CTI 75mm 6XL motor.

I'll be using the same basic nose cone altimeter bay design I used on the Blackhawk project. I've purchased the same high temperature FWFG nose cone and CF coupler that the Blackhawk comes with. The nose cone will be cut down to same OD as the coupler and attached the NC to the coupler with a machined aluminum adapter.

A turned aluminum adapter will be attached directly to the forward closure of the motor. The adapter will slide into the coupler.

The fins are the same basic design as the fins I machined for the Blackhawk. This time around I'll be machining them from 6061 T6 aluminum. I've already completed the design of the fin and the fixtures necessary to machine them. I have an 18" section of the CF tubing leftover from the Blackhawk to use as a fin can.

M2245 Fin Model.png
 
Prepping the fin stock and fixture:

I cut the I-beam to length. Then the flanges were machined down to leave the rough T shape for the fin stock. I'm not pushing my machine and it's only 1.5 hp so it took about 13 minutes for each side. My machine can be run unattended so I load the stock, push the big green button, set my timer and head back inside the house.

IMG_5479.jpg

The fixture plate was drilled and tapped in several places. The two holes in the center were drilled for hardened steel dowel pins. The dowel pins allow the parts to be flipped and maintain a precise location so that the two sides will line up perfectly. The fixture plate will be held in the vertical position with a pair of angle plates to machine the base of the fins first.

IMG_5480.jpg
 
Machining the prototype fin.

I machined the first prototype fin today. This involved generating all of the machining operations in Fusion 360, machining one side of one fin, debugging the CAM files and then machining the second side. Overall it went pretty well but I did snap a 5/32" end mill when I was slotting the fin from the stock. That also explains the rough edge you can see in the pictures. There were also a couple areas where the tools didn't overlap enough and left a burr. I sanded the burrs off with 220 grit and then decided to wet sand all of the faces while I was at it. I figured out the overlap issue so I shouldn't have to do this to the production fins.

IMG_5531.jpg

IMG_5532.jpg

IMG_5533.jpg
 
Fins machined:

I pulled the last fin off the mill today. Each fin took about 3 hours of machine time. They weigh about 100g each. They are very stiff and have a nice ring to them.

I dry sanded the first two fins with 220 and then wet sanded them with 320. I plan to wet sand all of them up to 600 grit.

IMG_5538.jpg
 
Since you are going for altitude, where do you think this will stand with respect to optimal mass?
 
1. Aluminum fins should hold up to heat of the M3+ flight and not be one time use.
2. They shouldn't suffer any increase in aerodynamic drag from delamination.
3. I have a small CNC mill and I like to machine aluminum.

The fins will have a 1" wide mounting surface roughly 9" long. I plan to use a reasonably high temperature epoxy to attach them to the tubing.


The fins are aluminum- why that versus a g10 or carbon? How will they attach to the carbon fin can tube?



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I think we need to get comfortable with single use in this hobby. Not everything is a 29/40-120.


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I think we need to get comfortable with single use in this hobby

I embraced this a few years back.....really a game changer on how you approach some problems....
 
Chris,

Nice project!

Did you happen to see a thread or post here on TRF awhile back. It might have been by Jerry O'Sullivan. He obtained some "Structural Aluminum I beam" and was making fins from it. It was a very cool idea/concept.

I'd post a link but unable to find it..

Maybe some one has that thread saved. I'd like to find it. My oldest son just picked up a Bridgeport torq cut 22.

Tony
 
You told me about it at XPRS. Yarde Metals. I have a 5' length sitting in my garage. [emoji6]
 
1. Aluminum fins should hold up to heat of the M3+ flight and not be one time use.
2. They shouldn't suffer any increase in aerodynamic drag from delamination.
3. I have a small CNC mill and I like to machine aluminum.

The fins will have a 1" wide mounting surface roughly 9" long. I plan to use a reasonably high temperature epoxy to attach them to the tubing.

Is an aluminum leading edge cuff on a composite fin a possibility? It could cut down on weight.
 
Let's call that plan B.

I have all of the materials for the fins and the fixtures sitting in my garage. If for some reason they don't work out I'll switch gears and do a full composite fin can.

Is an aluminum leading edge cuff on a composite fin a possibility? It could cut down on weight.
 
If you want to save some weight and make some really spiffy fins, check out Randy Steck's "airfoil fins" article in the latest issue of Rockets Magazine.

I'm the unnamed other flier the broke the first set of molds....
But I ended with a set of magnificent airfoil fins that weighed in at 43 grams each.
They were on my 3-inch MD "Thin Mint" rocket at Balls (flying an N-1850) that had it's fins removed by a fly-away that didn't....but that's another thread....

I was Randy's TAP, so as you know from reading, he has wanted to do this for a long time.
Hat's off to Randy for developing and publishing this technique!
 
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Sure, but why make it one time use if you don't have to. Jim Jarvis' and Curt von Delius' rockets aren't one time use and they are pushing the boundaries.

I think we need to get comfortable with single use in this hobby. Not everything is a 29/40-120.


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Yes, I saw Randy's article. It's a cool project.

This project is something that *I* have wanted to do for a long time. It combines two of my favorite hobbies: rocketry and CNC. The end result may not be the ultimate in light weight or even break the record.

If you want to save some weight and make some really spiffy fins, check out Randy Steck's "airfoil fins" article in the latest issue of Rockets Magazine.
...
I was Randy's TAP, so as you know from reading, he has wanted to do this for a long time.
 
Sure, but why make it one time use if you don't have to. Jim Jarvis' and Curt von Delius' rockets aren't one time use and they are pushing the boundaries.

From what I see, hitting composite rockets down low with high impulse is a stress test trying to turn the rocket into elemental carbon. The paint is stripped off, fin leading edges burn away and whatever is
laminated with "whatever" delaminates in various areas. Doesn't take into account fin flutter either. That's where a metal nosecone tip is "actually" needed whereas most of us use 'em cause they take
the landing loads of hitting the ground without dinging the paint! :wink:

Your idea of Aluminum is a sound one as others have pointed out. Besides, you got the skills and you got the tools to have at it. Best of luck for success! Kurt
 
I finished machining the root of the fins today. They came out pretty well.

I added pictures to post #3 in this thread: Fin Roots Finished

I'll move on to the fin faces this weekend if I have time.
 
I machined the prototype fin today. I had a few minor problems but overall it came out pretty well. I've cleaned up the problems with the CAM files so the production fins should come out cleaner.

I added pictures to post #4: Machining the prototype fin.
 
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