Tip to tip, leading edge question

Trying to wrap my mind around the leading edges of a tip to tip layup.

I've watched every video and searched for a while. Example situation would be, 2x2 carbon fiber tip to tip with surface s-glass, wet lay, vacuum bagged. After curing, trim the excess. It kinda stops there for me.

Im drawing a blank on the leading edges, actually, all the edges. In my mind this is a uncapped or un unprotected area of the fin that will delaminate or split. How are people continuing the fabric with the weave wrapped over the leading edge. Is it cut a certain pattern to lay over? If not, are you just joining the seams and sealing with laminating epoxy over the joint and make it pretty?

Is capping the best way by means of 1/4 inch perimeter of black higher temp/hardness epoxy where its recessed a bit into the edges and layup, but level across the surface as the edge?

I think Jim Jarvis has done leading edges with Cotrinics high temp epoxy.

Others have capped the edge with aluminum.

I thought about just using aluminum tape.


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I end my tip to tip just below the fin's bevel. I've not had any issue up to mach 2.6.

I've used aluminum tape in the past with no apparent issues.

Tony

Any pictures of your fins?

I've done a lot of experimenting surrounding edge protection with composite layups over the years. Used different techniques, epoxies, ablatives.

Long story short, a good composite layup will withstand speeds up to about M2.5 without too much additional care as evidenced by Mr. A above. In my experience, around M2.7 or 2.8 things start to get wild. Yes, there are many variables, and I'm generalizing, but basically: mach 2 isn't that tough, mach 3+ is a bigger challenge.

Going off memory without checking the notebook...

Things that have worked well:
-"capping" the leading edge with a ~1" wide lightweight (.3-.5oz) glass laminated in place with high temp resin (1/2" on each side so it covers the exposed edges beneath).
-painting the leading edge bevels with hard-curing ablative mixture.
-layering the lay-up. IE: the layer of fabrics are successively 1/4" smaller around all edges....widest piece on top (protects layers underneath)
-Cotronics epoxies in general
-Omitting the layup where unnecessary. IE: if your base materials and fillet epoxies are stout by themselves, skip the extra layers!
-Heat curing epoxies. The better epoxies will perform better when subjected to a cure cycle in an appropriate oven. Taking the time to actually do this helps!!!

Things that didn't work as well:
-coating the leading edge in high temp epoxy (Jim Jarvis method). I still had delamination....
-Painting the leading edge with soft curing ablatives (like that smelly silicone based Nasa surplus Dow-Corning stuff)
-West System and Aeropoxy epoxies near the leading edge. Not surprising...
-Going really fast close to the ground. IE: higher speeds in thinner air equates to gentler on the lamination.
-High temp paint: don't waist your time/money IMO.
-"Hobby grade" epoxies. They work fantastic for 95% of our hobby. Fast movers aren't the place to use them.

Rob702Martinez said:

Any pictures of your fins?

Click to expand...

Even better than that, Tony (tfish38 on YouTube) has a video that shows how.
https://youtu.be/PtYYsX3VEmc



Steve Shannon

On my latest build I'm laying up one ply over the leading edge and forming the cutting edge with high temp thickened epoxy, with the expectation that this could be sacrificial- but would prevent delamination. I'll let you know how it goes this summer...

Thanks Steve. Seen that video a few times and it didnt cover much of my question, unless I missed it.

Time has taught me to ditch G10 T-T & just go with carbon plate for fins. Over all cost is less than sum of needed material to do carbon T-T.
That and good aero-space quality glue [I'm partial to Hysol, there are many others]

Simply glue them on with good size filets & done.
Good to M-2.8 for me & M-3.6 with others I associate with.

Phenolic beads and high temp [750] glue will do a good job of coating leading edge of T-T if you insist on doing that.
Phenolic [strips with a groove] cover thins G-10 fins [1/16] then lay in carbon flush with phenolic caps.
Stainless shim stock can be bent into cuffs covering your layup also, then glued in place with high temp.


Heat cure whatever you do at 185 for at least 4-6 hrs

ECayemberg said:

I've done a lot of experimenting surrounding edge protection with composite layups over the years. Used different techniques, epoxies, ablatives.

Long story short, a good composite layup will withstand speeds up to about M2.5 without too much additional care as evidenced by Mr. A above. In my experience, around M2.7 or 2.8 things start to get wild. Yes, there are many variables, and I'm generalizing, but basically: mach 2 isn't that tough, mach 3+ is a bigger challenge.

Going off memory without checking the notebook...

Things that have worked well:
-"capping" the leading edge with a ~1" wide lightweight (.3-.5oz) glass laminated in place with high temp resin (1/2" on each side so it covers the exposed edges beneath).
-painting the leading edge bevels with hard-curing ablative mixture.
-layering the lay-up. IE: the layer of fabrics are successively 1/4" smaller around all edges....widest piece on top (protects layers underneath)
-Cotronics epoxies in general
-Omitting the layup where unnecessary. IE: if your base materials and fillet epoxies are stout by themselves, skip the extra layers!
-Heat curing epoxies. The better epoxies will perform better when subjected to a cure cycle in an appropriate oven. Taking the time to actually do this helps!!!

Things that didn't work as well:
-coating the leading edge in high temp epoxy (Jim Jarvis method). I still had delamination....
-Painting the leading edge with soft curing ablatives (like that smelly silicone based Nasa surplus Dow-Corning stuff)
-West System and Aeropoxy epoxies near the leading edge. Not surprising...
-Going really fast close to the ground. IE: higher speeds in thinner air equates to gentler on the lamination.
-High temp paint: don't waist your time/money IMO.
-"Hobby grade" epoxies. They work fantastic for 95% of our hobby. Fast movers aren't the place to use them.

Click to expand...

My experience is more inline with tfish as far as my max velocity of m2.5. Based on that I would agree with Eric's viewpoint that m2.5 is pretty easy and forgiving as compared to the extreme side of this hobby.

I have played with my setup, but generally it is a carbon plate fin with a single 2x2 3k twill T2T, under vacuum. The result is a very well bonded layup.

I am starting to try more things as my velocity moves up, but so far I have done either a Proline 4500 painted leading edge or tried to roll it, or done nothing. My reasoning for doing the leading edges is not because I believe it is necessary for these m2.5 or less velocities, as it seems to be fine without it.

I have goals to well surpass m2.5 so it is more about experimenting and gaining some practical hands on to better my techniques at this stage. So I would say do what you feel you need to do that is inline with your goals.

Tony

tfish said:

Tony

Click to expand...

Tony, does that fincan fly on that rocket with just a friction fit? If not, how?

I see people using the motor case as a coupler, separate fin cans, etc, can you please explain a little of how this works?

Yes, The fin cans are friction fitted to the motor case with masking tape.

The upper ends are a bit tricky. The motor case swell with heat. You need to account for that. But they can't just be a loose fit either.

I'm working on a project now that is truly sub min dia.

Tony

Thank you.

In that photo with the case, the fin can, and the nose cone, is there a break in that upper section?

ECayemberg said:

-coating the leading edge in high temp epoxy (Jim Jarvis method). I still had delamination....

Click to expand...

You probably just put on one layer...confess! I've had good luck with the method with numerous flights to around Mach 2.7. I haven't seen any indication of delamination at all. I don't have many flights above that (I do what I can to keep velocity low and/or the altitude high). My one venture into the mid Mach 3's probably delaminated, but I never found a fin.

Jim

Chris, That rocket was some parts from another project that was designed around the AT M650. The parts where then used to do some reefed parachute tests...2009ish.. IIRC the upper end Body was bolted to the FC. It was a rocket mostly testing reefed parachutes.

Tony

On this subject of fast flights and aero-heating, what are the limits of a standard thickness FWFG nosecone of the type that is commonly available?

Does someone make similar nosecones with high temperature epoxy, for sale?

Is it best to make your own?

Is coating a standard nosecone in the Cotronics epoxy sufficient? (Polishing it up after)

Also, I thin some epoxies and polyesters with acetone, and have for years with no adverse affects. Can the Cotronics epoxy be thinned with acetone to enhance it's flow, without causing issues? Only in relatively thin coats, of course, no heavy build ups that would trap the acetone from gassing off.

5% thinning of epoxy with alcohol (except for isobutyl alcohol) -> 50% loss of strength. That was the old numbers at least. DO NOT THIN EPOXY with your usual alcohol! Use a thinner epoxy instead, or change application methods or temperature. 0.02c

Now, you said Acetone. Acetone is better, but still not good. https://epoxyworks.com/wp-content/uploads/2014/08/thinning4.jpg - an example for one epoxy. Results may depend on epoxy formulation.

Gerald

G_T said:

5% thinning of epoxy with alcohol (except for isobutyl alcohol) -> 50% loss of strength. That was the old numbers at least. DO NOT THIN EPOXY with your usual alcohol! Use a thinner epoxy instead, or change application methods or temperature. 0.02c

Now, you said Acetone. Acetone is better, but still not good. https://epoxyworks.com/wp-content/uploads/2014/08/thinning4.jpg - an example for one epoxy. Results may depend on epoxy formulation.

Gerald

Click to expand...

For something structural, I would never thin it. For surface coatings and finishes, that is where I thin it. Mainly with polyesters, and also with System 3 Clear Coat epoxy for using as a penetrating stabilizer/ initial coat filler over Smiths CPE.

I don't see the point of thinning. Get a good laminating epoxy that's fit for purpose and you're good.

JimJarvis50 said:

You probably just put on one layer...confess! I've had good luck with the method with numerous flights to around Mach 2.7. I haven't seen any indication of delamination at all. I don't have many flights above that (I do what I can to keep velocity low and/or the altitude high). My one venture into the mid Mach 3's probably delaminated, but I never found a fin.

Jim

Click to expand...

You're right Jim...probably went with too thin of a layer. Think it was Cotronics 4525 that I tried.

I have had better results with lower viscosity high temp resins filled with desirable solids. My rockets never look nearly as nice as yours though!!!!

Barkley said:

I don't see the point of thinning. Get a good laminating epoxy that's fit for purpose and you're good.

Click to expand...

Expand your use of epoxy, and you might. If it were for laminating, I would not have ask the question. Finishes are almost always reduced. I was specifically asking about increasing the flow of the cotronics to increase its flow, as a finish, for after an initial shape was formed on the leading edge, unthinned. Not for laminating, not for structural work, and not for filets.

You know any good laminating epoxies with the same heat characteristics as the Cotronics?

Chris_H said:

Expand your use of epoxy, and you might. If it were for laminating, I would not have ask the question. Finishes are almost always reduced. I was specifically asking about increasing the flow of the cotronics to increase its flow, as a finish, for after an initial shape was formed on the leading edge, unthinned. Not for laminating, not for structural work, and not for filets.

You know any good laminating epoxies with the same heat characteristics as the Cotronics?

Click to expand...

Chris_H said:

Expand your use of epoxy, and you might. If it were for laminating, I would not have ask the question. Finishes are almost always reduced. I was specifically asking about increasing the flow of the cotronics to increase its flow, as a finish, for after an initial shape was formed on the leading edge, unthinned. Not for laminating, not for structural work, and not for filets.

You know any good laminating epoxies with the same heat characteristics as the Cotronics?

Click to expand...

Does Cotronics require heat to finish curing? Seems like you could thin with something pretty volatile (lookin' at you, acetone!) and let the thinner offgas for a while before going in to final cure. Maybe that still leaves voids, though.

Thank you for the reference. I just called PTM&W, they said that epoxy you show in the photos above has a max working temp of 250f. They do sell a high temperature laminating resin, I think it is 2876, that is good to 350f. The Cotronics is good to 600f, which is way different.

I think a lot of people do not understand the reduction of finishes well. The best example I can think of, is with paints, and more so, specifically with oil paints and varnishes. Latex paint very often benefits from reduction, also. With a slightly reduced viscosity, often the flow increases the workability, which can directly affrect the quality of the film in a positive way. Take unthinned oil paint, as the example, with a brush, it pulls, does not 'wet out' as well, and does not penetrate as well. With even a little reduction, the brushing becomes much easier, faster, and the finish wets the surface much better, and possibly, penetration is a benefit, also, with more porous surfaces. Often it is possible to end up with a thicker overall dry film thickness by reucing the finish slightly to change the handling behavior. Oil paints and varnishes should always be reduced for this reason, in 95% of cases, even though on the can it usually says either 'thinning not necessary', or 'do not thin'. This is all gleaned from more than 20 years of high end professional finishing experience.
In reading Jim Jarvis' articles, I believe that I recall a comment about the Cotronics requiring some effort to sand. From what I have seen of people working with materials like epoxy, you have some that can barely get a smooth fillet with 2 applications, and hours of sanding, and then you have some that can get excellent fillets with a minimum of sanding. And you have Jim who gets excellent results with the methods he describes, and then Eric, who did not se the same results, using the same materials and a similar process. It is the details that matter. Using a low viscosity resin for building up a protective surface near a sharp (ish) edge, like the edge of a fin, may not give the desired results without numerous coats. The Cotronics has been said to give sufficient build in 3 applications, to protect a fin's leading edge. Perhaps the Cotronics is fine without reduction. I know very well that I am not the only one who reduces epoxy for some applications.

My personal experience with thinning epoxies, has been as a surface stabilizer and initial filler coat, where a very small amount of acetone has given better wetting and spraying characteristics. It cures hard, as it does un-reduced, however, in the mixing containers where there are greater amounts of the epoxy, the thinned epoxy has moe of a rubbery feel to it after sufficient cure time, I am guessing, due to trapped acetone. These were applications where the viscosity of a laminating resin was greater than I wanted.

Chris_H said:

Thank you for the reference. I just called PTM&W, they said that epoxy you show in the photos above has a max working temp of 250f. They do sell a high temperature laminating resin, I think it is 2876, that is good to 350f. The Cotronics is good to 600f, which is way different.

Click to expand...

It's good to "over 425F". I grant you Cotronics has a higher Tg, but you asked me for a good high temp laminating epoxy, and I gave it to you. Dollars to doughnuts you aren't getting 600F with Cotronics when you cut it, but I have no idea how much degradation occurs. My $0.02.

https://www.ptm-w.com/technical-lib...terials Bulletins/PT2846 Bulletin 28Dec10.pdf

Barkley said:

It's good to "over 425F". I grant you Cotronics has a higher Tg, but you asked me for a good high temp laminating epoxy, and I gave it to you. Dollars to doughnuts you aren't getting 600F with Cotronics when you cut it, but I have no idea how much degradation occurs. My $0.02.

https://www.ptm-w.com/technical-lib...terials Bulletins/PT2846 Bulletin 28Dec10.pdf

Click to expand...

Cool. Thank you for posting that. The guy I just spoke with at PTM&W told me different, he said 250f, 350f for a different laminating resin. I think I trust that link more the phone call.

so, stupid question, but what is the typically-used cotronics product for high-speed applications? Durapot 862 is what I'm thinking, but am only basing that on the fact that it's low viscosity, so useful for layups, and is good to 600f, which was previously cited. How much does this cost? Their website has technical specs, and an ordering form, but no pricing.
Additionally, does anyone have any experience with Duralco 6150 SP? https://www.cotronics.com/vo/cotr/pdf/6105sp.pdf Am not thinking for rocketry, but for my homebrewery...

I've heard Cotronics 4525 is awesome. Room temp cure & good to 500F. https://www.cotronics.com/catalog/05 4525 4525IP.pdf

It's very expensive though. I called an got a quote for their smallest pre-measured kit and it was more than I was willing to pay for a Mach 2 rocket. Mach 2's easy though - things get real serious in the Mach 3+ range.