Carbon Prepreg Airframe build for the Loki 54/4000 - Fins Attached

Bob,
The aluminum plates are Alcoa Mic 6, good to 800 degrees warp free and specifically intended for applications such as this. And it is a convection oven with a digital thermostat. There was a vacuum bag in between the plates. The ramp up to temperature took over 2 hours. Both plates were within a few degrees of each other the entire cure cycle measured by thermocouples. You can see the thermometer laying beside the oven in the rocks.

I would say that from a strictly physics perspective, the contraction of the matrix with the carbon fibers trying to keep the plate a ruled surface would tend to form a hyperbolic paraboloid:



I do say that in my experience making carbon plate (not with uni, for what it's worth), I have put the forming plates inside the vacuum bag (protected by release film) instead of outside, so that the vacuum will pull the layup flat against the plate. Some c-clamps could provide as much pressure as vacuum bagging, but it'll never be as even.

Carvac, that's the shape, just not as severe.

The layup was in a vac bag between the plates. The clamps were there to add even more pressure. Which looking back was not needed and indeed could have led to problems. Great care was taken to ensure that the clamps were all exerting the same pressure, using an in/lb torque wrench and then measuring the plates along their length. The stack was al equal thickness all the way across to a great degree of accuracy.

But I also believe like Flyinfrog, Bob and Carvac have pointed out that the clamps may have been part of the problem. But I fear it's not that simple of a problem based on the reading I've been doing. I sincerely hope removing the clamps and putting the caul plates in the bag solves the issue. But institutions with much larger budgets and autoclaves have had the same issue we are having. Ponderous tomes have been written on the internal stresses of composite layups.

have you tried trimming the edges yet? you might be pleasantly surprised

A new plate was made yesterday and it came out perfectly flat. Based on the research, the layup schedule was changed to eliminate warping and the clamps were abandoned. The layup was also bagged directly onto the bottom caul plate, and Teflon tape was used to eliminate friction between the plate and the layup. Bingo. At least one of those things worked. Flyinfrog was pretty dead-on.


Flat.

After a full day of making the plate, we spent a full day cutting out the fins. Lots of care was taken in Solidworks and printing the patterns, so it felt a little funny cutting them out with a hacksaw. But once all was said and done, I had four identical fins. Next weekend the leading and trailing edges get beveled.


The hack job.



Finishing an edge.


Nice cross-section, no voids.


Four fins, cut one by one, all identical.


They all weigh identical as well.


Bevels next week.

nice work

flynfrog said:

nice work

Click to expand...

Thanks

Bevels.

That is gorgeous.

Has access to mills uses hacksaw to cut out fins

Bevels look really nice.

flynfrog said:

Has access to mills uses hacksaw to cut out fins

Bevels look really nice.

Click to expand...

It was a carefully calibrated hacksaw!

Thanks guys. The more I look at them the more enamored with them I become. I feel like Gollum with his ring...

watheyak said:

It was a carefully calibrated hacksaw!

Thanks guys. The more I look at them the more enamored with them I become. I feel like Gollum with his ring...

Click to expand...

The more I look at them, the more I want them. I feel like Sauron without his ring...

Just got news that the reload for this has bee certified! Here's what Scott from Loki has to say about it-

"It will soon be announced by TMT that Loki Research has certified 2 new 54mm reloads. These two reloads are by far the most impressive performance wise and are guaranteed to enable anyone break their own personal best records, and perhaps the TRA “L” altitude record. They are also the two largest 54mm motors to ever be certified for use by the hobby organizations.
The first is the L-2050 Loki White, designed for the 54/4000 hardware. It delivers an astounding 4,802.4 Ns, burns for almost 2.5 seconds and has a peak thrust of over 700 pounds. In a minimum diameter rocket, it is capable of breaking mach 3 and is unlike anything previously available to the hobby flier in 54mm."

Here's a picture of the reload-


The sheer size and power of this motor makes me a little nervous, as it probably should.

Heisenberg?



Even flooded with water and dustless, I still needed a mask. Either that or I'm getting sick. Or wimpy.

what mill is that? Im looking to get something similar for my robot kids

I believe it's this one-

https://www.harborfreight.com/1-1-2-half-horsepower-heavy-duty-milling-drilling-machine-33686.html

Or something very similar.

Is the fin mounted on an angle plate?

watheyak said:

Bevels.

View attachment 253652

Click to expand...

ChrisAttebery said:

Is the fin mounted on an angle plate?

Click to expand...

It is. Half angles were figured in Solidworks.

I need to pull my head out if my rump. I could easily make one in my CNC mill, it just never occurred to me. Too many years of owning a manual just like the one you are using.

Just so you know. I spent $36 on aluminum this morning thanks to your thread. I have a fin beveling jig/angle plate designed and ready to cut on the mill this weekend.

CarVac said:

The more I look at them, the more I want them. I feel like Sauron without his ring...

Click to expand...

Carvac I felt the same way about most of Bare Necessities...

ChrisAttebery said:

Just so you know. I spent $36 on aluminum this morning thanks to your thread. I have a fin beveling jig/angle plate designed and ready to cut on the mill this weekend.

Click to expand...

Cool! Share pics.

We also made some test coupons of the material we're considering for the fin reinforcements. This is intermediate modulus bi-directional prepreg in toughened epoxy. Not sure how crazy I am about the stuff just yet. Nothing is quite as cool as the uni...

After life getting in the way for about a year, I am resurrecting this project.

The fins have been glued onto the airframe tube. I finally settled on 3M Scotch-Weld DP460 for the adhesive, and much care was taken on surface prep and alignment. I'm about to start adding to the fillets slightly for better aerodynamics and aesthetics. Then I'm not sure. there wont be tip to tip exactly, maybe even less than what I was thinking. Or, no additional reinforcement at all. That sounds completely insane, but based on who's suggestion that was and the points he made, it's a possibility.

Awesome I have been waiting patiently. That is going to go fast.

I got a cool addition to this project in the mail yesterday.



I had Charles Ogino from Carolina Composites turn a nosecone plug for me. It's a Von Karman profile and the diameter of the motor case. Charles turned it from hardwood then sealed and polished it. It looks great, super fast service and high quality work.

Next up is the mold, as well as an adapter between the Loki forward closure and the nosecone.

watheyak said:

Then I'm not sure. there wont be tip to tip exactly, maybe even less than what I was thinking. Or, no additional reinforcement at all. That sounds completely insane, but based on who's suggestion that was and the points he made, it's a possibility.

Click to expand...

Well..... I was at Carolina Composites over the weekend, gluing the uni-fins on my carbon uni pre-preg tube. 75mm minimum. Guess I'm insane also, no plans for any further reinforcement either. Used Hysol on mine. First flight will be M-1450.



This will make you sleep better, based on G-10, we're both using Carbon, even more leeway!



Good luck with your project!:smile:

blackjack2564 said:

Well..... I was at Carolina Composites over the weekend, gluing the uni-fins on my carbon uni pre-preg tube. 75mm minimum. Guess I'm insane also, no plans for any further reinforcement either. Used Hysol on mine. First flight will be M-1450.

View attachment 297354

This will make you sleep better, based on G-10, we're both using Carbon, even more leeway!

View attachment 297355

Good luck with your project!:smile:

Click to expand...

Hey that looks familiar! Just bigger. Lookin' really good, Jim. Any idea when the first flight will be?

Here's mine with the finished fillets.


They're a bunch smaller than yours. I may enlarge them a little or go with just one layer of the prepreg for a bit of tip to tip. Or both. Or neither. Lots to think about.

That's good info on the fins, thanks. I've been thinking I could have gone thinner, but oh well.

If I can finish it in time....Airfest

Well it's 75mm ...fins are 3/16th. I would expect yours to be smaller for a 54. LOl

I was lazy & just bought the plate. You have WAY more patience than I!

Just finished the coupler that adapts the Loki extended forward closure to the nosecone. Being that the OD of the closure is 1.5" and the ID of the nosecone is 1.875", it made for a burly thick little coupler. It'll survive a nuclear explosion with all the cockroaches and Volvos.



I used some heat shrink tube from Soller Composites that I had left over from way back. The part still needs a finish coat of epoxy and then a polish. A bulkhead will be attached to the forward end of this part.