Build Thread: High Performance M Motor

[Graham Orr]

Hi peoples,
I'm working on an M motor with a friend. We are shooting for 10kNs and maximum Isp. The MEOP of the motor is 1000psi and we wish to use composite construction...which is a bit extraordinary.

M-2600 green. (We really don't care about the flame color...)
4 second burn.
Cf=1.66
0.531 inch diameter throat
11.17 expansion ratio
Calculated Isp: 264.5 (Same method calculated SSME performance to within 0.27%)

The propellant formulation is pretty standard APCP with a twist: 1.5-2% boron powder added to the mix. We wish to use this, along with careful CD nozzle design and fabrication (carbon/ceramic) to boost Isp up to about 262sec. Yeah.

The motor is 3 inches ID and about 27 inches long. There are four grains, each being a pseudo-finocyl and the aft grain a modified version for decreased erosive burning effects. Each grain is 2.875inch OD and 6.0 inch long. The grain burn characteristics were modeled using Matlab (see burnsim thread)

The closures are interesting...all "aerotech-type" screw on. Because we cannot do the inside threading on a piece this large, adapter ends are going to be machined and bonded to the main tube. The load axial load will be distributed through a special epoxy bond and the external carbon fiber.

The hoop stress in the carbon fiber will be about 8000psi while the hoop stress in the aluminum will be about 3800psi. Nice and low...The CF is being used for manufacturing reasons... it's a long story but it has to due with the end adapter's mechanical stability. We've done most of the preliminary design and will start with some FEM analysis of a few possible problematic parts.

I'm really excited. I hope to get this thing finished early Summer and do some ground-based test firings (5-6) to see if it performs to our expectations.

Below is a picture of the aluminum part of the casing (Not finished).

 

[Graham Orr]

And here is a drawing of the motor (with some parts clear):

 

[SpartaChris]

Very cool, Graham!

Where will you be static firing this bad boy?

 

[Graham Orr]

Very cool, Graham!

Where will you be static firing this bad boy?

Thanks Chris!
Yeah, we are planning on firing it in the desert or our newly acquired launch site several times. We really want to get this thing down and learn as much from it as possible. We are planning about six test-firings this Summer. We may do LDRS and/or Balls.

Sadly, the big propellant cost for us it the initial purchase of the boron powder...that runs at $200+/pound. This, however, is well worth the performance boost. (Noted to be 15-20 sec in research)

 

[afterburner]

Sweet.

You seem to have developped a propellant that is very energetic, yet that has a pretty slow burn rate. Is it what the Boron does in this recipe?

 

[loopy]

Ooooh...shiney! Nice looking case, and the motor sounds awesome! Can't wait to see pics of the burn!

 

[Anthony Cesaroni]

Hi peoples,
I'm working on an M motor with a friend. We are shooting for 10kNs and maximum Isp. The MEOP of the motor is 1000psi and we wish to use composite construction...which is a bit extraordinary.

M-2600 green. (We really don't care about the flame color...)
4 second burn.
Cf=1.66
0.531 inch diameter throat
11.17 expansion ratio
Calculated Isp: 264.5 (Same method calculated SSME performance to within 0.27%)

The propellant formulation is pretty standard APCP with a twist: 1.5-2% boron powder added to the mix. We wish to use this, along with careful CD nozzle design and fabrication (carbon/ceramic) to boost Isp up to about 262sec. Yeah.

The motor is 3 inches ID and about 27 inches long. There are four grains, each being a pseudo-finocyl and the aft grain a modified version for decreased erosive burning effects. Each grain is 2.875inch OD and 6.0 inch long. The grain burn characteristics were modeled using Matlab (see burnsim thread)

The closures are interesting...all "aerotech-type" screw on. Because we cannot do the inside threading on a piece this large, adapter ends are going to be machined and bonded to the main tube. The load axial load will be distributed through a special epoxy bond and the external carbon fiber.

The hoop stress in the carbon fiber will be about 8000psi while the hoop stress in the aluminum will be about 3800psi. Nice and low...The CF is being used for manufacturing reasons... it's a long story but it has to due with the end adapter's mechanical stability. We've done most of the preliminary design and will start with some FEM analysis of a few possible problematic parts.

I'm really excited. I hope to get this thing finished early Summer and do some ground-based test firings (5-6) to see if it performs to our expectations.

Below is a picture of the aluminum part of the casing (Not finished).

We make a lot of composite motor cases. Aluminum and carbon bonding is not trivial. You’ll have to inhibit the carbon/aluminum interface in the hardware or you’ll likely have bond line problems although they may not be apparent initially. There is a significant anodic potential (galvanic corrosion). An etchant and primer will also be required on the Al. If you’re not winding the carbon on (and you should be), then a bond line of .007”~.014” must be maintained. A high peel/shear, single part epoxy is your best bet and “pinning” should strongly be considered depending on the closeout design.

You may also want to consider doing some research regarding boron in propellants before you spend the money. That’s a very small motor with low combustion residence. Theoretical and demonstrated Isp are two different things.

Good luck.

Anthony J. Cesaroni
President/CEO
Cesaroni Technology/Cesaroni Aerospace
https://www.cesaronitech.com/
(941) 360-3100 x101 Sarasota
(905) 887-2370 x222 Toronto

 

[retro]

Graham,

I have experienced similar aluminum/CF corrosive reactions in composite layup joints. Anthony's has a raise a viable concern. The heat from the motor burn could accelerate this process. I utilize an insulating layer of S-glass and epoxy between the two substrates. Basalt may be an option as well. I'm just now getting acquainted with basalt not sure how it interacts with alloys however it does have excellent hi-temp qualities.

 

[Graham Orr]

Thanks for the reply guys!
Yeah, the bondline is definitely going to be tricky as Anthony pointed out (BTW, you guys make some great motors! But I'm sure you already know that!)

We are planning on using an aluminum surface-treating agent (I believe a product of West Systems) that is designed to aid in the aluminum-epoxy bonding on the surface of the motor. Also, at a few places on the motor, we plan to do a special knurl-type process that creates very sharp peaks of aluminum on the surface, which will aid in the mechanical capture of the CF (between the fibers). What do you think, Mr. Cesaroni?

Yeah, we are running into a bit of a problem with the burn-rate for this propellant. We are shooting for a target of 0.25 in/sec at 1000psi which is reasonable for standard APCP. The boron, as I suspect will increase this and particularly its temperature sensitivity throughout the burn. To help suppress some of the effects we may use a small amount of oxamide as a burn inhibitor...which shouldn't effect the Isp more than 1-2 sec.

 

[Graham Orr]

Graham,

I have experienced similar aluminum/CF corrosive reactions in composite layup joints. Anthony's has a raise a viable concern. The heat from the motor burn could accelerate this process. I utilize an insulating layer of S-glass and epoxy between the two substrates. Basalt may be an option as well. I'm just now getting acquainted with basalt not sure how it interacts with alloys however it does have excellent hi-temp qualities.

Thanks for this info. I'll definitely pass this thought on to my buddy. Would ultrafine 1.7 oz S-glass work? I'm not terribly concerned about the composite temperature stuff...though we are planning for 350 deg F on the casing... we've found some good epoxy.

 

[Graham Orr]

Machining pic below...

 

[Anthony Cesaroni]

Thanks for the reply guys!
Yeah, the bondline is definitely going to be tricky as Anthony pointed out (BTW, you guys make some great motors! But I'm sure you already know that!)

We are planning on using an aluminum surface-treating agent (I believe a product of West Systems) that is designed to aid in the aluminum-epoxy bonding on the surface of the motor. Also, at a few places on the motor, we plan to do a special knurl-type process that creates very sharp peaks of aluminum on the surface, which will aid in the mechanical capture of the CF (between the fibers). What do you think, Mr. Cesaroni?

Yeah, we are running into a bit of a problem with the burn-rate for this propellant. We are shooting for a target of 0.25 in/sec at 1000psi which is reasonable for standard APCP. The boron, as I suspect will increase this and particularly its temperature sensitivity throughout the burn. To help suppress some of the effects we may use a small amount of oxamide as a burn inhibitor...which shouldn't effect the Isp more than 1-2 sec.

If you are doing a helical wind, the fibers will bridge the knurl pattern for the most part and you will be depending mostly on resin matrix for engagement. That won’t work well. There are other fiber orientation and inter-lamina stress issues as well that I won’t get into here, not to mention that the interface on a knurl will most likely have insufficient shear strength. Using a S-2 glass cloth as an inhibitor will make matters worse. 1.7 ounce S-2 cloth is not ultra-light BTW, you want to use .5~.75 ounce or non dimensional scrim and generally on planar geometries as a peel ply foundation. Under cut features in these types of applications are generally much more aggressive than knurling in amplitude but tend to have generous radiuses to prevent fiber slip during winding. Sharp features can cause problems as well. Regardless of the design, pinning is used more often than not for redundancy. Keep in mind that you will have about 3 ½ tons of force trying to push your closure out. That plus a safety factor will drive your shear requirements. You need to engineer everything to the nines or it won’t work. Make up some sample sections and use a press to test your design and material selections.

You also may want to consider a full length of aluminum tube, reducing the wall between the closure sections and recovering the hoop with a circumferential wind of carbon instead. You won’t get the same mass fraction but it will reduce the critical issues and gain you some experience. Be careful of material selection as well. West epoxy is down pack designed for boats, not rocket motors.

Don’t get too excited about boron either. Combustion efficiency is not one of its better characteristics.

Have fun and don’t forget the hydrostatic test before you put the propellant in.

Anthony J. Cesaroni
President/CEO
Cesaroni Technology/Cesaroni Aerospace
https://www.cesaronitech.com/
(941) 360-3100 x101 Sarasota
(905) 887-2370 x222 Toronto

 

[Graham Orr]

Anthony-
I'm loving it. *Ronald McDonald knocks down door*

What about a CF sleeve? I did my calcs with the assumption of an average tensile strength of CFRP as 75ksi. I will also look into those other types of glass buffers...

In terms of hydrostatic testing... this is what I am planning:

Finish the casing as expected for firing.
Use the standard forward closure.
Use the standard nozzle carrier.
Machine an aluminum NPT pipe adapter in place of the nozzle.
Manually fill the motor full of water (not under pressure).
Attach the high pressure water supply hose lines.
Remotely start pumping it up to MEOP.
Use strain gauges and hydraulic pressure to get strain vs pressure curve (for later use)
Remotely release pressure (should be minimum energy in this, right? I mean E=P∆V so water is only slightly compressible...)
Analyze data and determine whether we wish to push to 1.2 MEOP. etc.

sound good?

 

[bobkrech]

Graham

The galvanic potential of the graphite/aluminum couple is ~1.2 volts which is the same voltage supplied by a NiMH battery! If they are in intimate contact with each other in a humid environment you get rapid corrosion so you shouldn't join aluminum to a graphite composite in a structural situation without passivating/electrically isolating the aluminum first.

Before you bond Aluminum to a CF composite, you need to passivate the aluminum completely and I suggest you get the all the aluminum parts Type 3 (hard) anodized. This surrounds the aluminum with 0.002"-0.008" of aluminium oxide which is non-conductive and corrosion proof. (You must account for this surface growth when you machine your parts or they won't screw into each other after anodization. I usually allow an additional 0.0015" material per surface for hard anodization.) Furthermore the aluminum oxide surface is rougher than the bare aluminum surface so it should bond much better as well. Degreasing is necessary and using a surface primer is also a good thing to do before you filament wind around the aluminum.

Another point is why spend a lot of time and money on a fancy ceramic nozzle. Graphite is more robust and can be readily machined. A fancy contoured nozzle makes sense if you are looking for the lightest, shortest nozzle for a flight vehicle, but for a thrust stand motor a simple straight conical nozzle has less than a 2% loss if the cone half-angle is less than 15% is much simplier and cheaper to make.

Bob

 

[bobkrech]

Graham

I've atttached a picture of a CF tube I made and my hydrostatic testing rig constructed from standard ASA pipe flanges and Grade 7/8 threaded rods and bolts with a tube installed. It's designed to accommodate 38mm, 54mm and 75mm tubes. Not seen are the dual o-ringed plugs inside the CF tube and the external aluminum centering disks to position the tube within the flanges. I have a 6000 psi hydraulic hand pump to internally pressurize the tube to perform proof and burst tests.

The tubes shown are a nominal 54 mm tube with a 1/16" wall thickness made from 2 layers of heavy 2.5" 19 oz. 640 KPSI CF biaxial sleeve with a bisphenol-F resin cured at 121 C. A poor man's analog to a filament wound pipe. Once my strain gauges come in, I get break a few and get some material properties.

Bob

View attachment P3050021_edited_600X800.JPG

 

[Anthony Cesaroni]

Graham

The galvanic potential of the graphite/aluminum couple is ~1.2 volts which is the same voltage supplied by a NiMH battery! If they are in intimate contact with each other in a humid environment you get rapid corrosion so you shouldn't join aluminum to a graphite composite in a structural situation without passivating/electrically isolating the aluminum first.

Before you bond Aluminum to a CF composite, you need to passivate the aluminum completely and I suggest you get the all the aluminum parts Type 3 (hard) anodized. This surrounds the aluminum with 0.002"-0.008" of aluminium oxide which is non-conductive and corrosion proof. (You must account for this surface growth when you machine your parts or they won't screw into each other after anodization. I usually allow an additional 0.0015" material per surface for hard anodization.) Furthermore the aluminum oxide surface is rougher than the bare aluminum surface so it should bond much better as well. Degreasing is necessary and using a surface primer is also a good thing to do before you filament wind around the aluminum.

Another point is why spend a lot of time and money on a fancy ceramic nozzle. Graphite is more robust and can be readily machined. A fancy contoured nozzle makes sense if you are looking for the lightest, shortest nozzle for a flight vehicle, but for a thrust stand motor a simple straight conical nozzle has less than a 2% loss if the cone half-angle is less than 15% is much simplier and cheaper to make.

Bob

Hi Bob,

Aluminum oxide is a low surface energy ceramic and its surface roughness can be measured in micro inches. Although its insulative properties make it attractive from an galvanic corrosion inhibiter standpoint, the low surface energy will reduce the adhesive performance dramatically. CF/AL bonding interfaces utilizing anodizing are not used in any commercial or military rocket motor or major structural application that I’m aware of for that reason. Specifically formulated primer/inhibitor/insulator coatings and application processes are generally used.

Your comment regarding fancy ceramics is spot on. Graphite is a ceramic as you are aware and one that is ideally suited for rocket nozzles in most regards.

As far as CF in general is concerned, it’s a ceramic as well. What type and properties is what most people at the consumer level don’t know. Is it PAN or pitched based? What modulus strength, weave type or fiber count etc.? The range is huge. Slapping carbon on something doesn’t necessarily make it better. Carbon sleeve is used a lot in HPR but it’s probably best suited to making cardboard tubes stiffer. Using it in a pressure vessel or structural design is far less than optimum. The orientation, filament angles and tension cannot be well controlled and are traded considerably in these regards.

Your mileage may vary of course.

Regards,


Anthony J. Cesaroni
President/CEO
Cesaroni Technology/Cesaroni Aerospace
https://www.cesaronitech.com/
(941) 360-3100 x101 Sarasota
(905) 887-2370 x222 Toronto

 

[Anthony Cesaroni]

Graham

I've atttached a picture of a CF tube I made and my hydrostatic testing rig constructed from standard ASA pipe flanges and Grade 7/8 threaded rods and bolts with a tube installed. It's designed to accommodate 38mm, 54mm and 75mm tubes. Not seen are the dual o-ringed plugs inside the CF tube and the external aluminum centering disks to position the tube within the flanges. I have a 6000 psi hydraulic hand pump to internally pressurize the tube to perform proof and burst tests.

The tubes shown are a nominal 54 mm tube with a 1/16" wall thickness made from 2 layers of heavy 2.5" 19 oz. 640 KPSI CF biaxial sleeve with a bisphenol-F resin cured at 121 C. A poor man's analog to a filament wound pipe. Once my strain gauges come in, I get break a few and get some material properties.

Bob

Neat.

Lose the tie rods and plates and do some free standing close outs then compare the data. ;-)

Anthony J. Cesaroni
President/CEO
Cesaroni Technology/Cesaroni Aerospace
https://www.cesaronitech.com/
(941) 360-3100 x101 Sarasota
(905) 887-2370 x222 Toronto

 

[retro]

Quick question.... why not titanium motor casing? Aluminum solid fuel casings were used way back in forties for the Deacon motors. What makes aluminum such a universal, durable and lasting choice for case material?

 

[bobkrech]

Quick question.... why not titanium motor casing? Aluminum solid fuel casings were used way back in forties for the Deacon motors. What makes aluminum such a universal, durable and lasting choice for case material?

$$$$$$$$
Titanium is very expensive and the machinability is poor.

 

[bobkrech]

Hi Bob,

Aluminum oxide is a low surface energy ceramic and its surface roughness can be measured in micro inches. Although its insulative properties make it attractive from an galvanic corrosion inhibiter standpoint, the low surface energy will reduce the adhesive performance dramatically. CF/AL bonding interfaces utilizing anodizing are not used in any commercial or military rocket motor or major structural application that I’m aware of for that reason. Specifically formulated primer/inhibitor/insulator coatings and application processes are generally used.

As the surface of aluminum is actually thin aluminum oxide anyway, I wouldn't believe that anodizing changes the chemical surface properties for bonding very much however it's usually several orders of magnitude more porous on a microscopic scale, that's why you can color it after you anodize. I still would recommend coating the aluminum with a primer/inhibitor/insulator to enhance bonding, but I feel that the anodizing is useful if you're going to reload the motor casing many times. I'm pretty sure the military and commercial stuff are one use applications.

As far as CF in general is concerned, it’s a ceramic as well. What type and properties is what most people at the consumer level don’t know. Is it PAN or pitched based? What modulus strength, weave type or fiber count etc.? The range is huge. Slapping carbon on something doesn’t necessarily make it better. Carbon sleeve is used a lot in HPR but it’s probably best suited to making cardboard tubes stiffer. Using it in a pressure vessel or structural design is far less than optimum. The orientation, filament angles and tension cannot be well controlled and are traded considerably in these regards.

A filament wound tube is probably the minimal mass solution, but a properly designed sleeved tube should not be too far behind if you ignore the ends. You can control the ratio of axial to longitudonal strength by selecting the mandrel diameter and the braid diameter. If I can figure out where I filed the downloaded paper with the analysis, I'll e-mail it to you.

Neat.

Lose the tie rods and plates and do some free standing close outs then compare the data. ;-).

It's actually free standing within the frame. The inner plug seals the tube and the outer rings prevent any expansion at the ends which wouldn't be possible in a filament wound tube.

Bob

 

[retro]

I am mainly referring to extruded Ti 3-2.5 tubing. Yes I agree cost is a factor. Looks like there would be a weight savings advantage in using Ti. And ounces count at the tail end. Anyway Graham I am interested in finding out how much you’re finished motor tube ends up weighing. What are the limitations of phenolic tubing as to diameter and motor size?

 

[Graham Orr]

A filament wound tube is probably the minimal mass solution, but a properly designed sleeved tube should not be too far behind if you ignore the ends. You can control the ratio of axial to longitudonal strength by selecting the mandrel diameter and the braid diameter. If I can figure out where I filed the downloaded paper with the analysis, I'll e-mail it to you.

Bob

Bob, could you forward me this too? I'd really appreciate it!

I'm getting a lot of good ideas rolling around here! Thanks guys! At one point I found an aluminum priming kit for epoxy composites. By the looks of it, it appeared to be a multi-step process. I know that filament winding gets the best results but I simply do not have access to said machine. Because of this, I wish to do the sleeve thing and shoot for a fiber angle of about 54 degrees. However, I may be a bit shallow (52 degrees).

In terms of the nozzle:
I would really like to contour the nozzle. I know it sounds obsessive but I would really like to utilized the method of characteristics and do something really well... I guess I should start learning how to program for the CNC lathe...

And yeah, I recently realized that graphite should be just fine for what we're doing. You guys are spot on.

 

[Graham Orr]

I am mainly referring to extruded Ti 3-2.5 tubing. Yes I agree cost is a factor. Looks like there would be a weight savings advantage in using Ti. And ounces count at the tail end. Anyway Graham I am interested in finding out how much you’re finished motor tube ends up weighing. What are the limitations of phenolic tubing as to diameter and motor size?

If you can find relatively cheap titanium, hell, I'd be down to building a motor with you, Retro! (But for that thick of a wall, you aren't gonna have any weights savings unless you turn it down a bunch...which is a pain and a waste of all that Ti.

I still have a lot of material-removal to do but I think the finished casing will weigh in about 2.5 lbs (with the end adapters) and about 3.75 lbs with the closures and nozzle. When loaded, it will weigh about 12.5 lbs (with the tracking smoke mini-grain in the forward closure. Volumetric packing efficiency will be about 0.85 in the motor...which we can attribute to the finocyl.

The projected outer diameter is 3.188 inches. It is non-standard. We were seriously considering a 75mm standard-type motor before but we were just not happy with the burn simulations with that slightly smaller diameter. I know, it sounds crazy...but I'm happy with it Plus, with the given diameter, a standard PML coupler can be used as a thermal liner. I know it isn't convolute but we plan to treat it with something to help it hold up a bit more.

 

[darkhelmet]

I vote for this thread as the "Best Thread Ever" on TRF! So, why hasn't it been deleted for Amateur Motor content?

Graham... it looks like your lathe could do the internal threading. What is the limiting factor?

Have you also considered a bolt-on nozzle adapter, or pins, and skip the CF layup?

Regarding the boron... as has been pointed out, you are unlikely to see any effect due to the limited combustion residence time. This is the same situation as pushing a theoretically optimal aluminum percentage.

 

[Graham Orr]

I vote for this thread as the "Best Thread Ever" on TRF! So, why hasn't it been deleted for Amateur Motor content?

Graham... it looks like your lathe could do the internal threading. What is the limiting factor?

Have you also considered a bolt-on nozzle adapter, or pins, and skip the CF layup?

Regarding the boron... as has been pointed out, you are unlikely to see any effect due to the limited combustion residence time. This is the same situation as pushing a theoretically optimal aluminum percentage.

Heh, thanks..I guess! (I read the "propulsion forum" intent thing and I thought the line is drawn when you start talking about specific propellant formulations and stuff. Am I wrong? I tried to steer clear of that, besides the mention of boron)

But yeah, that is definitely a possibility that the boron will not do anything. From the literature I've read, it appears it has to be ultrafine...and that is going to be a challenge..and perhaps is a contributing factor to the price? It may be worth a shot though...

With regards to the adapters and pins and stuff... I thought about it but I find threads oh so sexy Our lathe only allows for a feed-through of 1.75 inches...anything larger you have to have a live center...which kinda doesn't allow you to get in there with a threading bar... It is so sad.

 

[darkhelmet]

With regards to the adapters and pins and stuff... I thought about it but I find threads oh so sexy Our lathe only allows for a feed-through of 1.75 inches...anything larger you have to have a live center...which kinda doesn't allow you to get in there with a threading bar... It is so sad.

You do not have a large enough steady-rest, I assume?

There are also methods of cutting a retaining ring groove without using a lathe. There are pipe-end key cutters, or something similar could be fabricated to run off a drill motor. I have seen this done before but I haven't tried it myself.

 

[Graham Orr]

You do not have a large enough steady-rest, I assume?
There are also methods of cutting a retaining ring groove without using a lathe. There are pipe-end key cutters, or something similar could be fabricated to run off a drill motor. I have seen this done before but I haven't tried it myself.

You know, you are absolutely correct! I thought I saw a steady-rest in our shop but when I looked at it I didn't see wheels on it or anything. I didn't even consider trying to find one with wheels. You know, maybe I'll ask our machinist if he has something I can borrow....

Thanks!

 

[darkhelmet]

You know, you are absolutely correct! I thought I saw a steady-rest in our shop but when I looked at it I didn't see wheels on it or anything. I didn't even consider trying to find one with wheels. You know, maybe I'll ask our machinist if he has something I can borrow....

If you're going to turn down the outside anyhow, you don't need the wheels. Just use the brass inserts. Your machines should have some suggestions, too.

 

[daveyfire]

We've had good luck bonding carbon fiber to aluminum with a high-shear adhesive (e.g. Hysol) and a calibrated bondline thickness. The adhesive bears the load and separates the carbon fiber from the aluminum, thus mitigating the "battery" problem. Granted, we are using this method to bond an aluminum bulkhead into a carbon tube, while your design is the inverse. However, it's definitely possible to get the bond to hold up. We've hydrotested the joints to over 1000 psi in a 4" diameter with success, though we've been having some trouble keeping the carbon fiber cases from leaking. That's a whole 'nother ball of wax...

Looking forward to seeing the results. Where are you planning to static test?

 

[retro]

We've hydrotested the joints to over 1000 psi in a 4" diameter with success

4" composite motor case tubes? If so you have got my attention. What type of case did your "O" motor utilize? If composite are you using CF/epoxy or a hybrid
composite? If composite tube how does it compare weight wise to 6061 alloy?
Phenolic liner?