CF Fin attachment

Reinhard said:

Perpendicular is ok. Depending on the sweep and the flutter behavior of the fin, it might be advantageous to sweep the fiber direction back a bit too, but a better answer here requires an understanding of the oscillation modes of your particular design.

Reinhard

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I would like to learn more about the oscillation of different shapes of fins, but for now I will just make an educated guess on the fabric orientation. Let me ask you this, isn't fin flutter just a harmonic of the frequency at which the fin in question resonates at? (the frequency you hear when you tap it with your knuckle) Take the resonate frequency and multiply it times 100, maybe 1000, and now you have fin flutter. Does that make sense? Or is my mind wandering around again. It does that from time to time. I try to keep it on a short leash.

Zebedee said:

nice plate - can I commission some from you?

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I have some scrap pieces if that is what you mean. If you want an entire plate made, I guess I could if you supply everything it takes to make it, the CF, the epoxy, all vac bagging materials. It would be cheaper if you just made it yourself. Find something flat and vac bag all the layers in the right order shown above. This is my first CF plate I ever made, so I am far from knowing what I am doing here.

Wait a minute, I've done this once so that makes me a professional. LOL

OverTheTop said:

If, as you say, you want to put a couple of layers of UNI on each side, why not put them orthogonal to each other and end up with mostly isotropic behaviour?

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I think I'm going to make an X with the two layers. One at 315 degrees, and the other at 45 degrees. That puts them orthogonal to each other as you say, and adds more stiffness and width. I'm shooting for around .21 thickness. This will put me at .18 after the UNI is added. The final layers will come from the T2T. I have more IM7 Hexcel 6k 6.13oz .013 thick Plain weave fabric for that. I used all IM7 fabric as the strength numbers were slightly higher than the regular stuff.

Here is a pic of the cores before adding the UNI, cut to size.

HyperSonic said:

Let me ask you this, isn't fin flutter just a harmonic of the frequency at which the fin in question resonates at? (the frequency you hear when you tap it with your knuckle) Take the resonate frequency and multiply it times 100, maybe 1000, and now you have fin flutter. Does that make sense?

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Conceptually, you're on the right track, but it is more complex, because flutter is not a simple one-dimensional problem. This video illustrates this:
[video=youtube;hP72aMeqLj0]https://www.youtube.com/watch?v=hP72aMeqLj0[/video]

Reinhard

HyperSonic said:

View attachment 338587Here is a pic of the cores before adding the UNI, cut to size.

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Wow those look great!

Reinhard said:

Conceptually, you're on the right track, but it is more complex, because flutter is not a simple one-dimensional problem. This video illustrates this:
[video=youtube;hP72aMeqLj0]https://www.youtube.com/watch?v=hP72aMeqLj0[/video]

Reinhard

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Thanks for the lesson on flutter. I understand why people use a quasi-isotropic layup on their fins because you
just don't know what mode or modes of flutter your fin design will experience in flight. So you try and guard
against every direction the best you can.

I know my homemade plate (HyperPlate) will not have the strength of the plate that is made by the pros (Dragon
Plate) but I'm hoping that by mixing different weaves of fabric, rotating the tows every layer, put some strong UNI
fabric in there and keep it all symmetrical, that these fins will handle the 5800 and Mach 3 at around 6000 feet.


One thing that has me concerned is i'm relying alot on FinSim and the thickness number. If I did anything wrong in
my FinSim adventure, anything, than the thickness number of .21 would not be accurate. And if I'm using data thats
not accurate, I will get into trouble. While I want to know everything about Mr. Flutter, I never want to meet him
in person. I'll just wave at him as I go by at Mach 3!

watheyak said:

Wow those look great!

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Thank you. Not bad for a rookie!

This is after adding the UNI. They are .160 inches thick right now.

Here are 2 of the four fins with airframe. Each fin has 16 layers of CF. 8 layers of 2x2 twill, 6 layers of UNI, and 2 layers of plain weave on the outside. They are at .185 inches. Time to stop adding CF and save the rest for the T2T. I could not be happier on how the fins turned out so far. They are beautiful.

Very nice work up to this point, HyperSonic. I look forward to watching this thread and the flight.

Nytrunner said:

There was a guy doing a build thread of his successful L3 flight which was essentially an N5800 flying case with composite Fin band at the back. I was looking forward to the fin part of the write-up, but he quit writing for some reason. (perhaps he didn't like his "Anonymous" handle linked to his name via Tripoli lol)

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Lol. The anonymous handle is not because I want to remain anon, but rather I just think sometimes people focus more on the person doing something than the action done. You can go and see the fincan now btw.

HyperSonic said:

I ended up using Aeropoxy 2032 with the 3665 hardener. Cotronics website told me the viscosity of Duralco 4461SS was 600 cps, only to find out later that isn't true. Its really 3600cps, so I decided to use the epoxy that was made for layups. The core doesn't need to be high temp anyway, but the outer coats will be 4461SS.

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I have used both 4460 and 4461 for layups many many times. Worked flawlessly for me everytime. I almost use it exclusivley now.
Btw (think I saw mention of oven in above posts) 4461 is a room temp. cure epoxy - so you don't have to use a oven if you do not want too. Optimum properties at elevated temperatures. But the epoxy is plenty strong without the heat cure.

HyperSonic said:

I remember reading a thread a while back about whether or not slotting a MD airframe would be beneficial or not. Half the guys thought so, but the other half not so much. Some thought it wasn't necessary. To me personally, I think that slotting the airframe like you did in your builds will make a stronger joint than just epoxying to outside of airframe. Is it necessary, I don't know. My flight will be pushin it to Mach 3 at low altitude, and it very well might need everything I can do to hang on to my fins. I'm definitely going to consider it.

I would have to send my airframe out to someone who can do it right, as I don't have the mill (or whatever they use to do it accurately) to do it myself. Also, I like duralco 4525 instead of JB Weld because of the tensile strength difference. Beautiful builds by the way!

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I am not going to go into slotted vs unslotted - sure you can find many posts on here about that. I would not worry about slotting your airframe for this flight. If you beleive that it is beneficial - then you don't need the benefit in this case, imo. I don't think the marginal benefit is greater than the marginal cost. So I wouldn't let that worry you as a failure mode on this type of flight.

HyperSonic said:

I'm hoping that by mixing different weaves of fabric, rotating the tows every layer, put some strong UNI
fabric in there and keep it all symmetrical, that these fins will handle the 5800 and Mach 3 at around 6000 feet.


One thing that has me concerned is i'm relying alot on FinSim and the thickness number. If I did anything wrong in
my FinSim adventure, anything, than the thickness number of .21 would not be accurate. And if I'm using data thats
not accurate, I will get into trouble. While I want to know everything about Mr. Flutter, I never want to meet him
in person. I'll just wave at him as I go by at Mach 3!

Click to expand...

I would not stress it (see what I did there?). Personally your fins a pretty thick and you should be fine. I would be more worried about your attachment mode failing than the fin fluttering.

Yeah, I can see why you could think that way. I saw a recent post on FB where personalities with some prior history blew up over what I saw as implied tone. Maybe if they had been talking face to face it wouldn't have happened. Familiarity breeds contempt.

A5tr0 An0n said:

Lol. The anonymous handle is not because I want to remain anon, but rather I just think sometimes people focus more on the person doing something than the action done. You can go and see the fincan now btw.

Click to expand...

A5tr0 An0n said:

I have used both 4460 and 4461 for layups many many times. Worked flawlessly for me everytime. I almost use it exclusivley now.
Btw (think I saw mention of oven in above posts) 4461 is a room temp. cure epoxy - so you don't have to use a oven if you do not want too. Optimum properties at elevated temperatures. But the epoxy is plenty strong without the heat cure.

I am not going to go into slotted vs unslotted - sure you can find many posts on here about that. I would not worry about slotting your airframe for this flight. If you beleive that it is beneficial - then you don't need the benefit in this case, imo. I don't think the marginal benefit is greater than the marginal cost. So I wouldn't let that worry you as a failure mode on this type of flight.

I would not stress it (see what I did there?). Personally your fins a pretty thick and you should be fine. I would be more worried about your attachment mode failing than the fin fluttering.

Click to expand...

Thank you for your input. My 4461SS is over its six month life span but I hate to throw it away! I think I'm going to try the 4460 on my T2T with some spread tow fabric with a twill weave I seen at Composite Envisions. I got the idea from reading your thread. I like the look of light and dark checker board with the twill weave to it. Yes the 4461 does cure at room temp which is nice sometimes, but I still bake it at 150 F for 6 hours to come closer to those optimum properties. After curing for 24 hours at room temp, the 4461SS has a slight sticky feeling to the touch. Then bake it at 150 for 6 hours and that sticky feeling is gone.

Do you think this epoxy on the leading edges of my fins would work as an ablative? What makes a good ablative?

Mark

HyperSonic said:

Thank you for your input. My 4461SS is over its six month life span but I hate to throw it away! I think I'm going to try the 4460 on my T2T with some spread tow fabric with a twill weave I seen at Composite Envisions. I got the idea from reading your thread. I like the look of light and dark checker board with the twill weave to it. Yes the 4461 does cure at room temp which is nice sometimes, but I still bake it at 150 F for 6 hours to come closer to those optimum properties. After curing for 24 hours at room temp, the 4461SS has a slight sticky feeling to the touch. Then bake it at 150 for 6 hours and that sticky feeling is gone.

Do you think this epoxy on the leading edges of my fins would work as an ablative? What makes a good ablative?

Mark

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I've used some past the expiration before - but it was not too far gone. You can really see the hardner go first. As you past the expiration date the proprieties of the epoxy will degrade. I've never use their slow setting version; I've thought about trying it but have always been turned of by the 2 hour (or whatever it is) set time. Just too long for me - I usually have the fincan in the bag within 30 mins of starting.

I chose not to go with the twill weave because I was concerned that it would have larger crimps and therefore have a greater amount of excess resin. So it seemed to take away from what I was going for - a lighter and stronger product.

I've done the 4525 on the leading edges to protect the underlying carbon thing. I have since moved away from it. What makes a good ablative? Probably the ones in those NASA PDFs. As far as what I've settled on? Epoxy resin & hardner, milled glass, titanium dioxide, and phenolic microballoons. After some testing with quite a few different formulas I've settled on those constituents.

A5tr0 An0n said:

I've done the 4525 on the leading edges to protect the underlying carbon thing. I have sensed moved away from it. What makes a good ablative? Probably the ones in those NASA PDFs. As far as what I've settled on? Epoxy resin & hardner, milled glass, titanium dioxide, and phenolic microballoons. After some testing with quite a few different formulas I've settled on those constituents.

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Take a look at this thread and tell me what you think?

https://www.rocketryforum.com/showt...ramic-Adhesive&highlight=904+Ceramic+Adhesive

Here are some pics of my fins after beveling. They are ready to install on the airframe when epoxy arrives. They are almost "Bedazzling"

I finally talked Santa into bringing me some epoxy for Christmas, so I can get my fins put on. If anybody wants to know more details about the fin layup, just let me know. I want to wish everybody here at TRF a Very Merry Christmas and a Happy New Year! Hopefully you will have lots of rocket related gifts under your Christmas Tree. 2019 sounds like a good year to get my M3. Once again, I wish you all a Merry Christmas, and to all a good flight!

My epoxy finally showed up. Sure took long enough. lol I have decided not to slot the airframe. I want everyone to
know that any thing I do to this rocket(PePe), I do not claim that it is right or wrong. It is simply what I choose
to do to survive high mach(M3+)down low. Some of you like to call it "stupid fast". Well being stupid is something
that I have been good at in the past, so this flight is right up my ally. lol I will tell you what i did, why I
did it, and of course what happened during the flight. I'll leave it up to you all to determine whether it is
something you might try someday. Just remember that extreme speeds can be very expensive and your rocket can have a
very short life span! And of course I very much want any feedback that anybody has whether its good or bad.
According to the sims, if I can keep the weight down to 14 pounds or less minus the motor, PePe will touch mach 3.
PePe is all carbon fiber except for the nosecone. The airframe is a PML extreme carbon tube around .070 wall
thickness. The coupling/AV bay also came from PML about 12 inches long all CF. It is really 2 couplings one slid
inside the other. I cut a slot about .250 wide the length of the coupling and epoxyed it into the other one to make
a double wall around .100 thick. The AV bay lids are made from my home made Hyperplate, just like the fins. All
threaded rod will be grade 2 titanium to save on weight. The nosecone is a madcow VG fiberglass with an aluminum
tip. All the trackers(3 seperate systems,2 GPS and one RDF)will be housed in the nose along with a gopro. I DO NOT
want to lose PePe! I have a technicians licence and will try to seperate the frequencies into the 2 meter band for
one GPS, and the 70 cm band for the other. Not sure yet on the exact numbers. The RDF runs on 220.something MHz (I
forget). This will be a DD recovery with everything coming out the top. Right now my plan is to use the rattworks
ARRD for the main, but this might change because of its weight. A 24 inch drouge with a 72 inch main in a
deployment bag is the plan right now. Everything is likely to change as my imagination grows and suggestions from
all of you come in. I cannot change what I have allready done up to this point, but I can change things from this
point forward, so please talk to me. Just dont tell me to slow down. PePe will fly some low and slow flights at
first to tweek in the electronics and recovery system. After that its time to chase some mach numbers! Maybe a
M2245 to start with, and then what PePe was built for, to take on the N5800! Below are some pics of the fins being
tacked on with 4525. The L brackets were made from some IM 12K 4.3oz aerospace grade uni fabric I got from
Fibreglast.com. Item #2596-A. The epoxy used to lay up the L brackets is 4461SS. All epoxy used on this bird will
be high temp. The fillets will be done with 4525 on top of the L brackets. These 2 epoxys do not need to be baked
in the oven to cure, but they will get about 150F for 6 hours or so to get a little closer to those optimum
properties. The airframe will be around 85 inches long. That might change as I will use the length as a variable to
a certain extent when its time to fly the 5800, as I want a stability margin of at least 3. You will lose 1 cal
very quickly upon acceleration and that leaves me with a comfortable cal of 2. Because PePe is so light, he can fly
on anything from an I to an O.(will hold the CTI 98 6xl case) I will make a thrust plate/adapter out of hyperplate
(my homemade CF plate like the fins) to adapt down to whatever motor I choose to fly. RASAero 2 puts a 48 pound
(fully loaded)PePe with a 5800 at around 42K. Same rocket with RS or OR puts me at around 60K, so something is not
right somewhere. I tend to trust RASAero 2 in a flight like this, but I will have to look a little deeper into
this. When I am sure that all the numbers are correct in all the sims, I will post the files for you guys to look
at. I am a product of this forum, as alot of my ideas came from all of you. I think that there is very little, if
anything you can do to a rocket that somebody else has'nt already tried many times in the past. I also plan on 2
layers of tip to tip with some TeXtreme Spread Tow from Composite Envisions. Beautiful stuff!

REALLY digging this build! I am a huge fan of composites and really like what you have done with the fins. I aim to try something similar this year and then scale up in the future.

Wishing you the best on this one. Looks like you’re killing it so far

Theory said:

REALLY digging this build! I am a huge fan of composites and really like what you have done with the fins. I aim to try something similar this year and then scale up in the future.

Wishing you the best on this one. Looks like you’re killing it so far

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Thank you Theory. I too am a fan of composites. I love the way it looks when finished with a see thru type shine. Jim J (The King of Carbon) has done some beautiful CF builds and I hope PePe turns out half as good as his Too Carb Yen.

You know at my house, it is against the law to paint or cover up in any way CF! lol

Oh yes, I have read Jim’s carbon ‘how too’ several times. I even have it saved on my work computer for when things are a little “slow”

This type of joint applies the highest stress riser to the weakest orientation of the material, which is peel. It might be strong enough, but this is not the strongest way to build the thing. In fact it is probably one of the weakest ways to use the material.

+1

atypicalguy said:

This type of joint applies the highest stress riser to the weakest orientation of the material, which is peel. It might be strong enough, but this is not the strongest way to build the thing. In fact it is probably one of the weakest ways to use the material.

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Do explain further, I like to know more about things

Nytrunner said:

Do explain further, I like to know more about things

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Standard TOW has all the strands running in one direction. Like glueing balsa fins on tube with grain running wrong way, they will break with grain very easily. No strength unless oriented correctly. When using TOW or UNI you run it in layers at various directions for strength.

Say 0 then 45 then 90 again 0 etc..etc. Tow is also used for filament winding tubes...again various angles as seen in the tube.
I could be mistaken he may have TOW cloth which has 2 layers sewn together at different angles.

If it's running parallel to tube it does nothing or very little. If running across the fin [90 to tube] it functions. I can't really tell by pics. Hopefully I am wrong about the orientation.

But judging by the cut strips laying on table, they all look to be running lengthwise. [bad]

blackjack2564 said:

But judging by the cut strips laying on table, they all look to be running lengthwise. [bad]

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When I first saw the pic I did a double-take on the uni as well. But I think what we're seeing that looks wrong is actually the binder that holds the fibers together and runs perpendicular to the fibers.

I'm interested to see/hear more about the build!

I might have misunderstood atypicalguy's comment. I though he was referring to something to do with the mechanics of the joint layout, not the fiber orientation (fiber orientation I'm familiar with, but great explanation regardless )

Who makes the 4461SS and 4520 resins?

That's cotronics slowset and duralco

These strips are 1 inch by 12 inches long. The polyester fill thread that holds the fibers together run the 12" long direction. The tows run the 1" direction. Im at work right now but I will take a better pic of the strips for you to look at.