Extreme Velocity

[HyperSonic]

Has anybody ever heard of a case where the nosecone became glued on to the CF airframe and not let it separate
because of extreme velocity (Mach 3+) heating up the epoxy used to laminate the CF airframe? If so, what can be
done to minimize this aeroheating of the airframe joint besides just slowing down?

 

[markkoelsch]

High temperature epoxy to start with. Something like Cotronics epoxy that takes a 250 f post cure with controlled ramping.

Then I would think a high temperature paint over that.

 

[HyperSonic]

High temperature epoxy to start with. Something like Cotronics epoxy that takes a 250 f post cure with controlled ramping.

Then I would think a high temperature paint over that.

I was going to use some cotronics with some high heat BBQ paint but I was wondering about the epoxy that was used when the tube was rolled.
Don't know what they used but I'm sure it wasn't high temp stuff. If I just coat the outside with cotronics would that help shield the inner epoxy?
I typed in Mach 3 at 8000 feet with a 10 foot long rocket on this websight (don't remember the address) and it said the heat generated at that
velocity would be between 1100 and 1200 degrees F. If that is true, my cotronics will have a hard time staying cool. Tip of cone might see the worst of it, but what would the temp be at the nosecone airframe joint? It is critical that the nosecone separates or else its a lawn dart!

 

[markkoelsch]

Cotronics Duralco 4460. Post cured as recommended.

While the air temp might be what those predictions are, they will not be that for long. So, they will not warm the laminate to those temperatures that fast. It is sort of the idea that you can quickly put your hand through a candle flame without getting burned.

You could also investigate a ceramic ablative coating instead of paint. I think they did that on an x15.

 

[NateLowrie]

You could also just put the break further back on the rocket. At that point the flow should be smooth enough where the heating is not as much of an issue.

I second the ceramic ablative. You were talking about using Contronics 904 earlier. Any reason why you wouldn't just apply it in a thin coat?

 

[dhbarr]

Intentionally undersizing the aft portion a bit and/or oversizing the fore portion; or a similar method of intentionally trading/relocating heat for a turbulence cost.

 

[Kip_Daugirdas]

I was going to use some cotronics with some high heat BBQ paint but I was wondering about the epoxy that was used when the tube was rolled.
Don't know what they used but I'm sure it wasn't high temp stuff. If I just coat the outside with cotronics would that help shield the inner epoxy?
I typed in Mach 3 at 8000 feet with a 10 foot long rocket on this websight (don't remember the address) and it said the heat generated at that
velocity would be between 1100 and 1200 degrees F. If that is true, my cotronics will have a hard time staying cool. Tip of cone might see the worst of it, but what would the temp be at the nosecone airframe joint? It is critical that the nosecone separates or else its a lawn dart!

Depending on where the shock wave sets up and reattaches to the rocket will dictate the conditions that your components will be exposed to. On a Von Karman cone you will likely see very little damage but behind the shock wave will be a different story - temp and pressure increase instantaneously.

On a different shape nosecone - conic or ogive the shock wave will behave differently.

On my 144k flight, I spent a good amount of time above Mach 3 but at a high altitude >30k ft. I used BBQ paint on the airframe and cotronics on the leading edges of the fins. The BBQ paint looked bubbled but survived intact - the entire airframe took on this look. The fins didn't break a sweat- no damage. Just in front of the shockwave there was no damage to the paint. The entire VK cone was unscathed but the paint behind camera lens openings, countersunk screw holes was bubbled in the shape of the shockwave that setup behind the features. The polycarbonate lens covering on one of the GoPro viewing holes in the airframe partially melted.

I have no experience flying rockets fast at low altitudes so take my experience with a grain of salt. For your flight I'd look into coatings that ablate and carry the heat away with them. Good threads on this forum that used ablative coatings are "honey badger" and "honey badger 2"

 

[G_T]

Perhaps a paint like Cerakote is worth considering. IIRC, the version that does not use a post cure has a higher temp rating but is not as tough.

Gerald

 

[markkoelsch]

Perhaps a paint like Cerakote is worth considering. IIRC, the version that does not use a post cure has a higher temp rating but is not as tough.

Gerald

Gerald, I thought about that a while back, and forgot about it until reading your post. I think this idea might be a winner.

 

[HyperSonic]

Cotronics Duralco 4460. Post cured as recommended.

While the air temp might be what those predictions are, they will not be that for long. So, they will not warm the laminate to those temperatures that fast. It is sort of the idea that you can quickly put your hand through a candle flame without getting burned.

You could also investigate a ceramic ablative coating instead of paint. I think they did that on an x15.

In the sim, (this rocket is only in the sim for now) it will be at or above Mach 2 for 5.2 seconds. Its starts at 2000 feet and finally drops below Mach 2 at 19000.
This is my theory, tell me if you agree or not with it. If I can build an upper stage 4 inch MD that can survive (may not look pretty) Mach 3 in the lower dense
air, then that same upper stage will handle Mach 4+ at altitude, say above 30K. One day I might stack 2 N5800 on top of one another. But that is for another
day. Maybe some day I'll live up to my name Hypersonic!!

 

[HyperSonic]

You could also just put the break further back on the rocket. At that point the flow should be smooth enough where the heating is not as much of an issue.

I second the ceramic ablative. You were talking about using Contronics 904 earlier. Any reason why you wouldn't just apply it in a thin coat?

I never thought of moving it back to a less heated area. Thanks Nate. I'll keep that in mind during the build. Yes, my 904 and thinner came yesterday. That stuff
is heavy!! A pint jar of it weighs 3 pounds. If you ever need nose weight, just put a layer of this 904 ceramic stuff on your nosecone and it will add 1/4 pound!
I have more than $400 in cotronics epoxy and ceramic stuff. 4461SS, 4460, 904 and thinner. Anybody need some. I need to build a bigger oven that can handle
60 inch lengths of airframe while rotating.

 

[HyperSonic]

Intentionally undersizing the aft portion a bit and/or oversizing the fore portion; or a similar method of intentionally trading/relocating heat for a turbulence cost.

If I were to do something like that, do you think that it would add more drag and possibly slow me down more than if the airframe stayed the same diameter?
To me ,it's all about the speed. Anything that will slow me down is not wanted unless it is necessary for survival. My heart will be beating 160 times a second
just before they push that launch button. Pure adrenaline rush!!!!! Nothing like it anywhere!!!! Unless I was on board my self.

 

[HyperSonic]

Depending on where the shock wave sets up and reattaches to the rocket will dictate the conditions that your components will be exposed to. On a Von Karman cone you will likely see very little damage but behind the shock wave will be a different story - temp and pressure increase instantaneously.

On a different shape nosecone - conic or ogive the shock wave will behave differently.

On my 144k flight, I spent a good amount of time above Mach 3 but at a high altitude >30k ft. I used BBQ paint on the airframe and cotronics on the leading edges of the fins. The BBQ paint looked bubbled but survived intact - the entire airframe took on this look. The fins didn't break a sweat- no damage. Just in front of the shockwave there was no damage to the paint. The entire VK cone was unscathed but the paint behind camera lens openings, countersunk screw holes was bubbled in the shape of the shockwave that setup behind the features. The polycarbonate lens covering on one of the GoPro viewing holes in the airframe partially melted.

I have no experience flying rockets fast at low altitudes so take my experience with a grain of salt. For your flight I'd look into coatings that ablate and carry the heat away with them. Good threads on this forum that used ablative coatings are "honey badger" and "honey badger 2"

Haven't made up my mind yet on which type of nosecone to use. From what I've read (on this forum) the Von Karman is the best shape for extreme velocity
flights. Between you and Jim Jarvis and a handful of others (don't mean to leave all the others out) your flights in the past are truly incredible. I've tried to read
everything you have ever written about those flights and the results. I want to thank you personally for posting the information about how you did it, why and what happened. It's people like you that inspire people like me and make me want to push my builds to their limit and beyond! How did you attach your fins to the airframe? Were your fins highly swept back? How much more than airframe diameter do you need for the span? Everything I'm asking is for extreme speeds. Every
rocket I build will be leaner, meaner, and faster than the one before. I want to stay with composites like CF airframe, dragon plate fins, and be RF capable with the nosecone. I have many questions for you but don't want to bombard you with them now. This build is for Airfest 2018. I will be at Airfest 2017 getting my L3 and playing around with Mach 2. I'm taking things slow, one Mach at a time!

 

[HyperSonic]

Perhaps a paint like Cerakote is worth considering. IIRC, the version that does not use a post cure has a higher temp rating but is not as tough.

Gerald

I bought some rustolium high heat BBQ paint from Lowes because I was there for something else and happened to see it. I will check out the Cerakote that you
are talking about. I might have to post cure my cotronics stuff anyway, so even if it needs post cured, I'll be able to do it as long as its not at a to high a temp.

 

[dhbarr]

If I were to do something like that, do you think that it would add more drag and possibly slow me down more than if the airframe stayed the same diameter?
To me ,it's all about the speed. Anything that will slow me down is not wanted unless it is necessary for survival. My heart will be beating 160 times a second
just before they push that launch button. Pure adrenaline rush!!!!! Nothing like it anywhere!!!! Unless I was on board my self.

Yes, these would all slow you down.

 

[Kip_Daugirdas]

Haven't made up my mind yet on which type of nosecone to use. From what I've read (on this forum) the Von Karman is the best shape for extreme velocity
flights. Between you and Jim Jarvis and a handful of others (don't mean to leave all the others out) your flights in the past are truly incredible. I've tried to read
everything you have ever written about those flights and the results. I want to thank you personally for posting the information about how you did it, why and what happened. It's people like you that inspire people like me and make me want to push my builds to their limit and beyond! How did you attach your fins to the airframe? Were your fins highly swept back? How much more than airframe diameter do you need for the span? Everything I'm asking is for extreme speeds. Every
rocket I build will be leaner, meaner, and faster than the one before. I want to stay with composites like CF airframe, dragon plate fins, and be RF capable with the nosecone. I have many questions for you but don't want to bombard you with them now. This build is for Airfest 2018. I will be at Airfest 2017 getting my L3 and playing around with Mach 2. I'm taking things slow, one Mach at a time!

In terms of sweep, I'm guessing you mean how far back behind the the fin (trailing edge sweep)? In that case, I had none. The fins are a clipped delta shape with the trailing edge canted slightly forward. I did this so shock cords don't get snagged or wrapped around the fins (as they could if you swept the trailing edge backward). And to minimize flutter because the fins on Workbench 2.0 are really thin.
A swept back fin will be more efficient but then you have to contend with flutter- which means a thicker fin, which means more drag.....In the end it's all a trade off and there is no right answer. It's really dependent on what works for each specific rocket.

The span was 3" on the sustainer and 4" on the booster - so ~1 caliber. I would recommend building the entire rocket minus the fins first. See where your CG falls and then design a fin shape that best suits your rocket/motor combo. This way you can really optimize your design.

In terms of how I did the fins you can read about that in my thread. I would stay away from dragon plate- the resin they use has a low Tg. Unless they changed resins since I looked last...

The VK cone shape is more efficient over a wider range of speeds that most hobbyists fly than ogive or conic (M1-3?). That's why it's so popular. There's a chart out there somewhere that shows this.

Hope this helps! Good luck on your projects!

-Kip

 

[HyperSonic]

Yes, these would all slow you down.

Maybe I'm creating a problem that doesn't really exist. According to Mark, he doesn't think the heat will transfer into the laminate long enough to cause a problem. I guess I was just curious if anybody ever heard that happening to anybody else.

 

[Dwatkins]

West system epoxy, Mach 3.5 at 8200' above Black Rock or about 12,000' ASL!

 

[HyperSonic]

View attachment 315329
West system epoxy, Mach 3.5 at 8200' above Black Rock or about 12,000' ASL!

WoW! Maybe CF isn't the best choice for extreme speeds. Do you think FG would of held together? Have you ever attempted another Mach 3+ flight with changes made from lessons learned, or just back off the speed? Certainly makes me wonder.

 

[Dwatkins]

WoW! Maybe CF isn't the best choice for extreme speeds. Do you think FG would of held together? Have you ever attempted another Mach 3+ flight with changes made from lessons learned, or just back off the speed? Certainly makes me wonder.

No! The epoxy is the issue. Did not tolerate those temp. Had Carolina Composite make tubes for me. The 54 mm did a little over Mach 3, and the 75mm did Mach 3.6. Both held up fine. This is the 75 mm.

 

[HyperSonic]

In terms of sweep, I'm guessing you mean how far back behind the the fin (trailing edge sweep)? In that case, I had none. The fins are a clipped delta shape with the trailing edge canted slightly forward. I did this so shock cords don't get snagged or wrapped around the fins (as they could if you swept the trailing edge backward). And to minimize flutter because the fins on Workbench 2.0 are really thin.
A swept back fin will be more efficient but then you have to contend with flutter- which means a thicker fin, which means more drag.....In the end it's all a trade off and there is no right answer. It's really dependent on what works for each specific rocket.

The span was 3" on the sustainer and 4" on the booster - so ~1 caliber. I would recommend building the entire rocket minus the fins first. See where your CG falls and then design a fin shape that best suits your rocket/motor combo. This way you can really optimize your design.

In terms of how I did the fins you can read about that in my thread. I would stay away from dragon plate- the resin they use has a low Tg. Unless they changed resins since I looked last...

The VK cone shape is more efficient over a wider range of speeds that most hobbyists fly than ogive or conic (M1-3?). That's why it's so popular. There's a chart out there somewhere that shows this.

Hope this helps! Good luck on your projects!

-Kip

I've read so many threads over the past couple of years that I forget who wrote them. I went back and reread your Workbench 2.0 thread and now I remember your rocket. Everybody was complimenting you on how beautiful your fin can was! The entire rocket was beautiful!

Thanks for the tip on fin optimization. (not sure if thats even a word) Everything is open to change right now. I was going to make my own dragon plate with some 6K IM7 CF at 45 degree angles laminated with cotronics. It's .015 thick, so I was going to start with 7 layers, then after two or three layers of T2T, I should be ready for Extreme Velocity. I seen Jim Jarvis C clamp his fins between two flat plates one time to generate more pressure and squeeze the layers together instead of vacuum bagging to keep everything as thin as possible. I was thinking about trying that.

 

[HyperSonic]

No! The epoxy is the issue. Did not tolerate those temp. Had Carolina Composite make tubes for me. The 54 mm did a little over Mach 3, and the 75mm did Mach 3.6. Both held up fine. This is the 75 mm.View attachment 315334

OK, I get it now. I feel better about CF as my choice for Extreme Velocity. Not many people visit the land of Mach 3. I've allready bought my ticket and can't wait to go! I'm just planning the safest way to get there. Do you know what type of resin was used on your successful flights?

 

[markkoelsch]

View attachment 315329
West system epoxy, Mach 3.5 at 8200' above Black Rock or about 12,000' ASL!

What is the underlying red tube made of? G10/12?

How was the surface of the tube prepped before application of carbon/epoxy? Was it either vacuum bagged or compressed with heat shrink tape? Was it post cured?

I see it was West, which has a pretty low Tg. I typically build with Aeropoxy, but even that may well be to low a Tg for this Flight regime. It will get warm, hence the Duralco/Cotronics high temp epoxy, or something similar.

 

[Dwatkins]

Tube was shrink wrapped no post cure. The red is high temp caliper paint.

 

[JimJarvis50]

I seen Jim Jarvis C clamp his fins between two flat plates one time to generate more pressure and squeeze the layers together instead of vacuum bagging to keep everything as thin as possible. I was thinking about trying that.

I wouldn't really recommend that. I believe when I posted that approach years ago that I also said I wished I had an alternative. One problem with that approach is that the clamping method doesn't provide even pressure, so you actually end up with a fin with varying thickness. That can be an issue if you then try to bevel the fins (several approaches that I use to bevel fins are affected when the fin isn't uniform). Further, C-clamps don't really provide all that much compression.

I've had the best luck laminating fins when I use two flat tiles and then bag the whole thing. I use bagging material that isn't too stretchy because the stretchy stuff gets sucked in between the tiles and messes things up. I also learned that you want tiles that are about the same size as the fin or fins (if you laminate a pair at a time). I tried over-sized tiles once, and the vacuum pressure easily broke them.

I have also tried one-sided bagging (i.e., tile, carbon, fin,bag) using a single tile, and then turning over the fin to laminate the other side. For reasons I don't quite understand, the result of this is usually just a curved fin.

Jim

 

[Kip_Daugirdas]

I have also tried one-sided bagging (i.e., tile, carbon, fin,bag) using a single tile, and then turning over the fin to laminate the other side. For reasons I don't quite understand, the result of this is usually just a curved fin.

Jim

I bought a 1" thick 6061 aluminum plate from a junkyard and milled it flat. I layup my fins on it (both sides at once and then vacuum bag the fins to the plate. Fins come out perfect.

Layers go:
-aluminum plate
-layer of Mylar .010 thick
-breather
-perforated film
-peel ply
-fin with carbon
-peel ply
-perforated film
-breather
-vacuum bag

Like Jim I tried doing one side at a time and I got warped fins. Doing both sides at the same time is a must. Composites love symmetry.

 

[watheyak]

I bought a 1" thick 6061 aluminum plate from a junkyard and milled it flat. I layup my fins on it (both sides at once and then vacuum bag the fins to the plate. Fins come out perfect.

Layers go:
-aluminum plate
-layer of Mylar .010 thick
-breather
-perforated film
-peel ply
-fin with carbon
-peel ply
-perforated film
-breather
-vacuum bag

Like Jim I tried doing one side at a time and I got warped fins. Doing both sides at the same time is a must. Composites love symmetry.

I've had great luck making plate with this exact method, as well. Just make sure all the carbon layers are symmetrical with regards to the 0,90 and 45 layers.

 

[AeroAggie]

For reasons I don't quite understand, the result of this is usually just a curved fin.

Jim

Because of the highly directional nature of composite fibers and internal stresses that build up as it cures, you want a balanced and symmetric laminate or it will warp as it cures.

Balanced = equal number of (-) and (+) angled plies as measured from your 0 direction (usually the long direction of a part). Typically with fabric, these are +/- 45 but could be 60/120 or something like that if you're using tape.
Symmetric = stacking sequence is mirrored about the midplane.

In the absence of very good knowledge of the external loads and probably a good finite element model, just aim for a quasi-isotropic laminate. That is, equal percentages of 0, +45, -45, and 90 degree plies.

You could laminate a fin in 2 steps without warping so long as each half of the laminate is also balanced and symmetric about its own midplane.

 

[Kip_Daugirdas]

You could laminate a fin in 2 steps without warping so long as each half of the laminate is also balanced and symmetric about its own midplane.

In theory yes but it's much harder in practice.

The initial warp from the first layup is pretty much impossible to correct when you layup the opposite side. I've attempted it a half dozen times with poor results.

 

[AeroAggie]

In theory yes but it's much harder in practice.

The initial warp from the first layup is pretty much impossible to correct when you layup the opposite side. I've attempted it a half dozen times with poor results.

What initial warp? Lay up a balanced, symmetric laminate and cure it. Flip it over, layup another balanced symmetric laminate on top of it.

Edit - I see now what I missed. You're talking about using an existing G10 (or other core) fin and laminating carbon on top of that. In that case, I agree you could get some warping with mismatched properties. I didn't read carefully enough and assumed you were talking about using the plate as a tool surface then flipping it to tool the other face of an all-carbon laminate.