High Performance High-Temperature Fin Material-thoughts?

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CCotner

CCotner

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Semi-affordable RCC Panels for hobbyist users!

https://www.dragonplate.com/ecart/product.asp?pID=5687&cID=191

My concerns would be machineability, and the quality of a machined surface-the faces look rough and porous. Also, I'd be worried about it's brittleness. I'm imagining this as a material for fins for minimum-diameter 75mm and up flights. What do y'all speed junkies and industry veterans think?
 
Cstsales.com, look at the Rohacell panels. I believe Rohacell is a high-temp tolerant core material


Sent from my iPhone using Rocketry Forum
 
I used to work for Goodrich. One division made wheels and brake for airplanes. One of the engineers from that division gave us a test coupon from a run of brake discs. It is rough on t he surface but perhaps it could be sanded. It is really strong, it rings like steel.
The panels are heat resistant but for fins the attachment needs to be up to the same task
The Brake factory made other parts for reentry vehicles and other secret stuff. They are made to near net shape and finished ground to final.
IIRC it takes forever to make the parts and are priced accordingly. A nice fincan would cost about the same as Nebraska.

M
 
Here's the key sentence I quoted from their site........"Reinforced carbon-carbon sheets are an ideal solution where high stiffness and low weight are required under extreme temperatures, but the working load remains relatively low."
 
Binder Design said:
Here's the key sentence I quoted from their site........"Reinforced carbon-carbon sheets are an ideal solution where high stiffness and low weight are required under extreme temperatures, but the working load remains relatively low."
Click to expand...

Fair enough. Maybe it could be used as a leading-edge insert for a regular carbon fin, then? That would solve the problem with metal leading-edge caps or inserts of drastically different thermal expansion coefficients.
 
This something I thought of, bit I am not sure it would work. A carbon fiber fin made with a high temp epoxy. Then the leading edge made of a ceramic.


Mark Koelsch
Sent from my iPhone using Rocketry Forum
 
CCotner said:
Fair enough. Maybe it could be used as a leading-edge insert for a regular carbon fin, then? That would solve the problem with metal leading-edge caps or inserts of drastically different thermal expansion coefficients.
Click to expand...

I actually thought of using the Dragonplate RCC for my upcoming L3 flight. I arrived at the same conclusion to not use it as a replacement for the fin material due to the brittleness and lower load handling abilities. I instead have gotten into contact with dragon plate (Allred) to try and have a custom RCC "cap," made to replace the metal cap that will go on my leading edges of the fins. Well after speaking with 4 different people there and exchanging emails I am not very impressed with their company. They did tell me that other than RCC all their other plates are rated for 150F, I have not verified that though. Nonetheless I thought that an RCC cap on the leading edge would be great… expensive maybe… but worth it.

I have since thought about using the RCC as the fin core and then layer it up with say 5 layers of CF on each side and then bond it to the airframe. The layered CF on the RCC would have to be at the right distance from the leading edge to prevent it from delamination. But I think with the right paint and construction technique it could work. Just FYI I will not be doing that for my L3; I am sticking with the metal caps. I would like to try an play with RCC though...

markkoelsch said:
This something I thought of, bit I am not sure it would work. A carbon fiber fin made with a high temp epoxy. Then the leading edge made of a ceramic.


Mark Koelsch
Sent from my iPhone using Rocketry Forum
Click to expand...

I also have thought of this, and think it would work. I was thinking of using some of the Cotronic ceramic adhesives, they have some that can withstand very hot temperatures.
 
A5tr0 An0n said:
I actually thought of using the Dragonplate RCC for my upcoming L3 flight. I arrived at the same conclusion to not use it as a replacement for the fin material due to the brittleness and lower load handling abilities. I instead have gotten into contact with dragon plate (Allred) to try and have a custom RCC "cap," made to replace the metal cap that will go on my leading edges of the fins. Well after speaking with 4 different people there and exchanging emails I am not very impressed with their company. They did tell me that other than RCC all their other plates are rated for 150F, I have not verified that though. Nonetheless I thought that an RCC cap on the leading edge would be great… expensive maybe… but worth it.
Click to expand...

RCC would be an excellent idea for protection of another fin material.

I have since thought about using the RCC as the fin core and then layer it up with say 5 layers of CF on each side and then bond it to the airframe. The layered CF on the RCC would have to be at the right distance from the leading edge to prevent it from delamination. But I think with the right paint and construction technique it could work. Just FYI I will not be doing that for my L3; I am sticking with the metal caps. I would like to try an play with RCC though...
Click to expand...

RCC isn't what you want for the interior of the fin. There's no point in putting it on the inside where it wouldn't get very hot anyway.
 
CarVac said:
RCC would be an excellent idea for protection of another fin material.



RCC isn't what you want for the interior of the fin. There's no point in putting it on the inside where it wouldn't get very hot anyway.
Click to expand...

Let me see if I can explain it a little better. The core would be RCC and it would be layered with CF up to say an inch (or whatever) away from the edges of the fin. So the whole leading edge/trailing edge of the fin would be RCC.

The main reason I thought to have it as the core is for ease of construction and not to mention it will probably allow good heat transfer. Meaning it could spread the heat throughout the RCC plate and dissipate it quickly away, carbon is good at getting rid of heat quickly. Just speculating here. Not shown in the picture is a bevel… just fyi.


14314158744_08dd8880ac_b.jpg


Here you can see what I was talking about. The RCC is exposed to the areas that receive the most heating and the CF is layed to "reinforce," the RCC plate. Now I am not sure how the strength properties of RCC compare to CF.
 
Last edited:
A5tr0 An0n said:
Let me see if I can explain it a little better. The core would be RCC and it would be layered with CF up to say an inch (or whatever) away from the edges of the fin. So the whole leading edge/trailing edge of the fin would be RCC.

The main reason I thought to have it as the core is for ease of construction and not to mention it will probably allow good heat transfer. Meaning it could spread the heat throughout the RCC plate and dissipate it quickly away, carbon is good at getting rid of heat quickly. Just speculating here. Not shown in the picture is a bevel… just fyi.


14314158744_08dd8880ac_b.jpg


Here you can see what I was talking about. The RCC is exposed to the areas that receive the most heating and the CF is layed to "reinforce," the RCC plate. Now I am not sure how the strength properties of RCC compare to CF.
Click to expand...

My hat's off to one who's not only trying to do an L3 cert flight but trying to push the envelope too. Others might exclaim it better to cert on a less
exasperating project and save the wild stuff for later. Best of luck to you. Kurt
 
Feckless Counsel said:
CCotner,

What peak temperatures are you expecting? Is that based on expereince (data) or calculation?

Feckless
Click to expand...

This isn't for a specific project; I was just throwing down the link to see people's thoughts on how they'd use it.

CarVac and my N was predicted to reach speeds that imply boundary layer air temperatures in the 2000C range, iirc; that doesn't mean the underlying material will get anywhere near that hot. I don't remember our estimates anymore, off the top of my head.
 
CCotner,

I believe aircraft aluminum melts at 1250'F. Inconel alloy, used in gas turbine vanes, melts at 2500'F. How fast are you flying?

Feckless
 
You are forgetting one very technical point, just because the boundary layer gas temperature is several thousand degrees, it doesn't mean the surface is at that temperature. You have to do the correct heat transfer calculations to determine what the energy transfer rate is, and then you have to determine what the thermal conductivity of the fins are which will determine the fins ability to transfer energy from the surface into the structure.

If you do not understand this, you are wasting your money on RCC as it has to transfer the energy somewhere, and in a fin, it is likely to debond from an inferior internal fin structure that most hobbyists use. Properly built CF fins have survived just fine in hobby rocketry applications at M 3.5+. You have to make them properly.

Unlike an aircraft which may have to fly at high mach in horizontal flight where the heat loading is continuous, a typical vertical rocket flight rarely experiences high heat loads for more than 10 seconds. With a properly planned ascent profile with a peak velocity of Mach 5 @ 40 kft your total heat load can be around 400 J/cm2 on the ram surfaces being deposited over 10 seconds. This is not a great amount of heat to dissipate if you know what you are doing, at least in my world. :cool:

Bob
 
bobkrech said:
Properly built CF fins have survived just fine in hobby rocketry applications at M 3.5+.
Click to expand...

Who are you referencing here? It would be nice to be able to see the rocket/fin design (size) and the methods they used.
 
A5tr0 An0n said:
Who are you referencing here? It would be nice to be able to see the rocket/fin design (size) and the methods they used.
Click to expand...
Jim Jarvis. I don't remember the reference for the report I mentioned but Jim's been on TRF after his big flights, and he knows how to build CF rockets.

https://docs.google.com/file/d/0B-aG1Nud-PDVVU1zb3ViOFpGZlU/edit?pli=1 is an example of what he does and how he does it. (Beware it's 80+ Mb and 263 pages.)

He also mentions the N4000 to M1450 Black Rock launch discussed in the High Power section of TRF. https://www.rocketryforum.com/showthread.php?58733-Balls-2013-Personnal-launch-report-Jarvis

Bob
 
Unlike the other whippersnappers on this thread, I try to fly as slow as I can, all things considered. This flight reached 3000 ft/s, but it was at 50K feet. I think this is the fastest I've ever had a rocket go.

https://youtu.be/mWOicBydGzc

The construction techniques for this rocket were documented in a companion article to the one you linked to, Bob.

https://www.raketenmodellbau.org/repository/archive/167793?view=true

The leading edges for the rocket were built-up Cotronics 4525. It's not easy to do, but it seems to work for me.

Jim
 
JimJarvis50 said:
Unlike the other whippersnappers on this thread, I try to fly as slow as I can, all things considered. This flight reached 3000 ft/s, but it was at 50K feet. I think this is the fastest I've ever had a rocket go.

https://youtu.be/mWOicBydGzc

The construction techniques for this rocket were documented in a companion article to the one you linked to, Bob.

https://www.raketenmodellbau.org/repository/archive/167793?view=true

The leading edges for the rocket were built-up Cotronics 4525. It's not easy to do, but it seems to work for me.

Jim
Click to expand...
Thanks for replying Jim. Your carbon fiber rockets are awesome.

The Cotronics 4525 datasheet is here. It is stable at high temperatures with a room temperature curve which makes it easy to work with. If you add silica microspheres to the resin you can reduce the weight, thermal conductivity and make sanding easier.

The Apollo heat shield which has withstood the highest reentry heating of any spacecraft used AVCOAT as the heat shield material, which is made with a specific brand and formulation of a phenolic epoxy resin.

"Avcoat 5026-39/HC-G is an epoxy novolac resin with special additives in a fiberglass honeycomb matrix. In fabrication, the empty honeycomb is bonded to the primary structure and the resin is gunned into each cell individually. ... The overall density of the material is 32 lb/ft3 (512 kg/m3). The char of the material is composed mainly of silica and carbon. It is necessary to know the amounts of each in the char because in the ablation analysis the silica is considered to be inert, but the carbon is considered to enter into exothermic reactions with oxygen. ... At 2160O R (12000 K), 54 percent by weight of the virgin material has volatilized and 46 percent has remained as char. ... In the virgin material, 25 percent by weight is silica, and since the silica is considered to be inert the char-layer composition becomes 6.7 lb/ft3 (107.4 kg/m3) of carbon and 8 lb/ft3 (128.1 kg/m3) of silica."

In simple language, AVCOAT is simply a epoxy Novolac resin with special additives (Silica microspheres and phenolic microspheres) in a fiberglass (or Nomex) honeycomb matrix. The initial density is half that of water...... 4.4x less than graphite, 5.4 x less than aluminum, 8x less than titanium, and 16x less than steel. The hexagonal carbon functional groups pyrolize and carry away heat. The silica melts and wets the surface preventing carbon oxidation. The remain carbon char is an excellent high temperature radiator and provides radiative cooling. As the material pyrolizes, the density and thus the thermal conductivity drops and the char become a pretty good thermal insulator.

That's how ablative shields work.

Bob
 
bobkrech said:
Thanks for replying Jim. Your carbon fiber rockets are awesome.

The Cotronics 4525 datasheet is here. It is stable at high temperatures with a room temperature curve which makes it easy to work with. If you add silica microspheres to the resin you can reduce the weight, thermal conductivity and make sanding easier.

The Apollo heat shield which has withstood the highest reentry heating of any spacecraft used AVCOAT as the heat shield material, which is made with a specific brand and formulation of a phenolic epoxy resin.

"Avcoat 5026-39/HC-G is an epoxy novolac resin with special additives in a fiberglass honeycomb matrix. In fabrication, the empty honeycomb is bonded to the primary structure and the resin is gunned into each cell individually. ... The overall density of the material is 32 lb/ft3 (512 kg/m3). The char of the material is composed mainly of silica and carbon. It is necessary to know the amounts of each in the char because in the ablation analysis the silica is considered to be inert, but the carbon is considered to enter into exothermic reactions with oxygen. ... At 2160O R (12000 K), 54 percent by weight of the virgin material has volatilized and 46 percent has remained as char. ... In the virgin material, 25 percent by weight is silica, and since the silica is considered to be inert the char-layer composition becomes 6.7 lb/ft3 (107.4 kg/m3) of carbon and 8 lb/ft3 (128.1 kg/m3) of silica."

In simple language, AVCOAT is simply a epoxy Novolac resin with special additives (Silica microspheres and phenolic microspheres) in a fiberglass (or Nomex) honeycomb matrix. The initial density is half that of water...... 4.4x less than graphite, 5.4 x less than aluminum, 8x less than titanium, and 16x less than steel. The hexagonal carbon functional groups pyrolize and carry away heat. The silica melts and wets the surface preventing carbon oxidation. The remain carbon char is an excellent high temperature radiator and provides radiative cooling. As the material pyrolizes, the density and thus the thermal conductivity drops and the char become a pretty good thermal insulator.

That's how ablative shields work.

Bob
Click to expand...

Great info here!
 
bobkrech said:
The Apollo heat shield which has withstood the highest reentry heating of any spacecraft used AVCOAT as the heat shield material, which is made with a specific brand and formulation of a phenolic epoxy resin.

"Avcoat 5026-39/HC-G is an epoxy novolac resin with special additives in a fiberglass honeycomb matrix. In fabrication, the empty honeycomb is bonded to the primary structure and the resin is gunned into each cell individually. ... The overall density of the material is 32 lb/ft3 (512 kg/m3). The char of the material is composed mainly of silica and carbon. It is necessary to know the amounts of each in the char because in the ablation analysis the silica is considered to be inert, but the carbon is considered to enter into exothermic reactions with oxygen. ... At 2160O R (12000 K), 54 percent by weight of the virgin material has volatilized and 46 percent has remained as char. ... In the virgin material, 25 percent by weight is silica, and since the silica is considered to be inert the char-layer composition becomes 6.7 lb/ft3 (107.4 kg/m3) of carbon and 8 lb/ft3 (128.1 kg/m3) of silica."

In simple language, AVCOAT is simply a epoxy Novolac resin with special additives (Silica microspheres and phenolic microspheres) in a fiberglass (or Nomex) honeycomb matrix. The initial density is half that of water...... 4.4x less than graphite, 5.4 x less than aluminum, 8x less than titanium, and 16x less than steel. The hexagonal carbon functional groups pyrolize and carry away heat. The silica melts and wets the surface preventing carbon oxidation. The remain carbon char is an excellent high temperature radiator and provides radiative cooling. As the material pyrolizes, the density and thus the thermal conductivity drops and the char become a pretty good thermal insulator.

That's how ablative shields work.

Bob
Click to expand...

How thin can AVCOAT be made? You keep bringing it up, Bob, but I have the feeling that it is less relevant for HPR fins. Nosecones, sure, but not ~3/16" thick fins like I would put on a revised Bare Necessities.
 
bobkrech said:
Thanks for replying Jim. Your carbon fiber rockets are awesome.

The Cotronics 4525 datasheet is here. It is stable at high temperatures with a room temperature curve which makes it easy to work with. If you add silica microspheres to the resin you can reduce the weight, thermal conductivity and make sanding easier.

The Apollo heat shield which has withstood the highest reentry heating of any spacecraft used AVCOAT as the heat shield material, which is made with a specific brand and formulation of a phenolic epoxy resin.

"Avcoat 5026-39/HC-G is an epoxy novolac resin with special additives in a fiberglass honeycomb matrix. In fabrication, the empty honeycomb is bonded to the primary structure and the resin is gunned into each cell individually. ... The overall density of the material is 32 lb/ft3 (512 kg/m3). The char of the material is composed mainly of silica and carbon. It is necessary to know the amounts of each in the char because in the ablation analysis the silica is considered to be inert, but the carbon is considered to enter into exothermic reactions with oxygen. ... At 2160O R (12000 K), 54 percent by weight of the virgin material has volatilized and 46 percent has remained as char. ... In the virgin material, 25 percent by weight is silica, and since the silica is considered to be inert the char-layer composition becomes 6.7 lb/ft3 (107.4 kg/m3) of carbon and 8 lb/ft3 (128.1 kg/m3) of silica."

In simple language, AVCOAT is simply a epoxy Novolac resin with special additives (Silica microspheres and phenolic microspheres) in a fiberglass (or Nomex) honeycomb matrix. The initial density is half that of water...... 4.4x less than graphite, 5.4 x less than aluminum, 8x less than titanium, and 16x less than steel. The hexagonal carbon functional groups pyrolize and carry away heat. The silica melts and wets the surface preventing carbon oxidation. The remain carbon char is an excellent high temperature radiator and provides radiative cooling. As the material pyrolizes, the density and thus the thermal conductivity drops and the char become a pretty good thermal insulator.

That's how ablative shields work.

Bob
Click to expand...

Thanks Bob. Ditto the great information.

I had a conversation with an engineer at Cotronics a few years back. We went through the application and all of the various high-temp products they had, and his recommendation was the 4525. Obviously not an ablative, but pretty tough and impossible to sand. I have a number of rockets where this material is just painted on the leading edge. I've observed some degradation of the underlying Aeropoxy (the relatively high thermal conductivity of the 4525 probably doesn't help there), but the 4525 has never shown any evidence of damage. I suspect that at some point, plus or minus Mach 3, an alternative would be needed. So, I'm listening here.

Jim
 
JimJarvis50 said:
Thanks Bob. Ditto the great information.

I had a conversation with an engineer at Cotronics a few years back. We went through the application and all of the various high-temp products they had, and his recommendation was the 4525. Obviously not an ablative, but pretty tough and impossible to sand. I have a number of rockets where this material is just painted on the leading edge. I've observed some degradation of the underlying Aeropoxy (the relatively high thermal conductivity of the 4525 probably doesn't help there), but the 4525 has never shown any evidence of damage. I suspect that at some point, plus or minus Mach 3, an alternative would be needed. So, I'm listening here.

Jim
Click to expand...
I'd be surprised if 4525 is not an ablative (non-melting) (phenolic) epoxy. Phenolic epoxies do not melt as they have a graphitic (hexagonal) carbon backbone (so do aramids like Nomex). Since they can't flow when they get hot, they lose function groups (pyrolize) like -H, -CH3, -OH and sometimes -CO or -CO2, leaving behind a porous hexagonal graphitic structure with low density and low thermal conductivity.

You can add microballoons (silica or phenolic) to any epoxy to thicken it so it won't sag. The addition of the microballoons also lowers the density, reduces the thermal conductivity and heat capacity, and also makes the epoxy sandable, all of which are good. After sanding, you simply paint on a little more of the same epoxy, thinned if necessary, to seal the surface and make it look nice.

There are plenty of low viscosity phenolic epoxies that can be used for laminating so as simple change from the Aeropoxy you used to a laminating phenolic epoxy will mitigate in depth degradations as will the use of microballoons to reduce the thermal conductivity.

This is from NASA and DoD technology developed and published in the '60s that apparently and unfortunately is not taught in aerospace engineering schools today. It's also easy to find on-line now that the majority of NASA and DoD reports have been cataloged and digitized.

Bob
 

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