Protecting fin leading edges on a mach 3+ flight?

I'm looking for some first hand experiences on techniques to protect the leading edge of fins from heat during a mach 3+ flight. The sim shows me hitting a max speed of around mach 3.3. The fins are 1/4" machined solid carbon fiber plate.

I've read about Jim Jarvis' method of coating them with a high temp epoxy like Hysol. I've also heard people mention placing a folded metal foil tape over the edge.

I'm most curious about the metal tape method. Is the tape affixed permanently with epoxy? At mach 3.3, isn't there a high chance of air getting under the tape and it being ripped off? Or simply being pulled off of the leading edge by drag?

If I go the hysol route, does anyone know of a distributor that sells it in quantities less than $100?

Any thoughts on this would be appreciated... Thanks

SoCalChris said:

I'm looking for some first hand experiences on techniques to protect the leading edge of fins from heat during a mach 3+ flight. The sim shows me hitting a max speed of around mach 3.3. The fins are 1/4" machined solid carbon fiber plate.

I've read about Jim Jarvis' method of coating them with a high temp epoxy like Hysol.

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I use Cotronics 4525, but I wouldn't do it for Mach 3.3 from the ground.

Jim

If you’ve not seen the build for Mad Max, suggest you take a look https://forum.ausrocketry.com/viewtopic.php?f=10&t=3659&hilit=Mad+max#p43205

SpaceManMat said:

If you’ve not seen the build for Mad Max, suggest you take a look https://forum.ausrocketry.com/viewtopic.php?f=10&t=3659&hilit=Mad+max#p43205

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Very impressive how did they hold up? Kurt

JimJarvis50 said:

I use Cotronics 4525, but I wouldn't do it for Mach 3.3 from the ground.

Jim

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Thanks for the advice.

SpaceManMat said:

If you’ve not seen the build for Mad Max, suggest you take a look https://forum.ausrocketry.com/viewtopic.php?f=10&t=3659&hilit=Mad+max#p43205

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I haven't seen that thread, I will read through it this evening. Thanks

ksaves2 said:

Very impressive how did they hold up? Kurt

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He flew it on an N5800 at Balls in 2013 and held the N class motor record until Balls last year. So pretty good all considered.

SoCalChris said:

I haven't seen that thread, I will read through it this evening. Thanks

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While you're there you might also want to look at Mad Max II, which is to my knowledge the highest speed and altitude ever reached on a single stage commercially available motor.

https://forum.ausrocketry.com/viewtopic.php?f=10&t=4666

Here's a few stats from that flight.

Motor: CTI O3400
Max Speed: 2594 MPH or Mach 3.52 @ 6,750’ AMSL (where the speed of sound was 735mph on the day)
Altitude: 66,594’ AMSL (65,769’ AGL) as per GPS

A double wow. I bet the rocket is still flyable? The metal Leading Edge caps are probably the best remedy that can be had for that type of speed down low outside of a completely metal fin. Anything one chooses to paint on like 4525 IP or what-have-you will ablate off the Leading Edge no matter what. Delamination is free to occur. The only other option is a completely metal fin. Kurt

The metal cap is likely the easiest and most cost effective solution.

I have thought once or twice if making the leading edge out of a high temperature ceramic might work. Could be molded or possible machined to shape.

You could always try carbon carbon- joking with this last bit.


Sent from my iPhone using Rocketry Forum

ksaves2 said:

A double wow. I bet the rocket is still flyable?

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Doubtful. From my conversations with Nic he views most rockets that approach or exceed Mach 3 as effectively single use vehicles.

ksaves2 said:

The metal Leading Edge caps are probably the best remedy that can be had for that type of speed down low outside of a completely metal fin. Anything one chooses to paint on like 4525 IP or what-have-you will ablate off the Leading Edge no matter what. Delamination is free to occur. The only other option is a completely metal fin. Kurt

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Completely metal fins are fine in theory, in practice the bolt on metal fin cans with cantilevered fins appear to fold up like cardboard once you start to exceed Mach 2.5+ speeds, as can be seen here.

Fincan
https://forum.ausrocketry.com/viewtopic.php?f=10&t=4253&start=90#p51061

Result
https://forum.ausrocketry.com/viewtopic.php?f=4&t=4591&start=30#p54893

Anybody tried stainless steel tape like McMaster-Carr carries (iirc it was McMaster-Carr)?

I've used Cotronics 4700. It was the highest temp and tensile strength I've found recommended by BALLS flyers for a student launch. I told the aeropoxy sales guy lives were on the line and he recommended it. Apparently real rockets use it. Granted I have no Mach 3+ experience. I was horrified of M2.4 with no experience last year first multistage scratch. That particular epoxy was a slight headache to work with as in you need to consistently heat the epoxy while you mix then apply for oven cure, it shrinks in the oven cure meaning many fillets. Open windows, wear N-95 respirators, get an IR Food laser or you'll ruin it, and you'll still get migraines. Many applications for any realistic fillet size. Everyone argues 4525IP is the easier one to work with. They are totally right. If you need that extra hundred degrees F and 1,100 psi more tensile then go 4700. It's bullet proof practically at 11,100 psi and 600F. Very few epoxies touch that. It'll do carbon fiber joints fine with dissimilar materials. I've failed tubes by shearing before that epoxy failed. You may have to ablative coat fins before epoxing fins to a rocket tube. We learned all kinds of thermal horrors of don't cotronics oven cure shock cords because certain cords cinge or melt etc, lol. So think about what needs to bond. You have to hit the min. activation temp by the instruction book for hours at a time or it won't harden. It works on casing closures to permanently plug certified AT reloads. Oddly certain materials won't melt at activation temp so if you have datasheets on what your doing its fine, but the issue is materials that don't have datasheets may have unwanted results for curing.
Your not going to have perfect temp control with a household oven either. It is a industrial epoxy, lid open, you better have windows open respirator on, or you will be gagging and scrambling for an exit. That 4700 epoxy did all I ever wanted it to do, exceeded expectations for supersonic airfoil testing.


I really wonder if TRA would allow SS304 Tape by cotronics. Certain tapes and other products have ridiculous thermal ratings. We see more "Steel" hardware in recovery bolts and D-links. Maybe a BOD form would work. You can bond a L-1 I casing to a rocket with 4700, and thermally it won't fail.
I preferred overkill than not enough thermal protection.

markkoelsch said:

I have thought once or twice if making the leading edge out of a high temperature ceramic might work. Could be molded or possible machined to shape.

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Look up services with ultrasonic machining apparently that's doable. IDK the costs, it's a very slow machining process. Apparently nuclear industry likes it on certain bits. Germany has a bunch of tooling now being exported to US for wacky one offs. I found it interesting topic.

Andrew_ASC said:

I really wonder if TRA would allow SS304 Tape by cotronics. Certain tapes and other products have ridiculous thermal ratings. We see more "Steel" hardware in recovery bolts and D-links. Maybe a BOD form would work.

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Does TRA bar SS304 Tape specifically? If people are able to fly all metal fin cans (which to my knowledge they are) why wouldn't they be allowed to use metal tape?

plugger said:

Does TRA bar SS304 Tape specifically? If people are able to fly all metal fin cans (which to my knowledge they are) why wouldn't they be allowed to use metal tape?

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No. There’s no problem with the tape, but fin cans may not be made of steel. Aluminum is fine.


Steve Shannon

markkoelsch said:

The metal cap is likely the easiest and most cost effective solution.

I have thought once or twice if making the leading edge out of a high temperature ceramic might work. Could be molded or possible machined to shape.

You could always try carbon carbon- joking with this last bit.


Sent from my iPhone using Rocketry Forum

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The only problem with Ceramics is if isn't Bonded to the Leading Edge, vibration could cause it to fracture and fall away.
Kurt

Andrew_ASC said:

Look up services with ultrasonic machining apparently that's doable. IDK the costs, it's a very slow machining process. Apparently nuclear industry likes it on certain bits. Germany has a bunch of tooling now being exported to US for wacky one offs. I found it interesting topic.

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Hey yall from the other side of the world (China again, 6 out of the last 7 months) - Just for info - MACOR is a machinable ceramic I have a little experience with. Not on rocketry "stuff" but......anyway there you have it for your research!