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CTI C-Star 5800 AKA "Shredder" with a composite airframe

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mpitfield

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So I have aspirations to build a composite carbon fiber 4" MD, stick a CTI C-Star 5800 in it, and have a successful flight and recovery. The project is at a very early discovery, and feasibility, stage. Ideally I would like to use off the shelf carbon fiber tubing, the product formerly from Rocketry Warehouse which is now Madcow Rocketry, however this is new territory for me and I have read, talked to, and watched videos, where it is suggested that a composite airframe for this particular motor needs to be at the higher end.

My question is, are the carbon fiber 4" tubes from Madcow up to the task for this motor or am I looking at a roll your own scenario?

https://www.madcowrocketry.com/4-carbon-fiber-airframe/
 
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markkoelsch

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You should take a look at the new carbon fiber tubes Wildman has.

The N5800 is a serious beast though. You fin attachment, and fin design need to be on the money. I would lean towards 1/4" or 3/8" carbon plate.
 

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So I have aspirations to build a composite carbon fiber 4" MD, stick a CTI C-Star 5800 in it, and have a successful flight and recovery. The project is at a very early discovery, and feasibility, stage. Ideally I would like to use off the shelf carbon fiber tubing, the product formerly from Rocketry Warehouse which is now Madcow Rocketry, however this is new territory for me and I have read, talked to, and watched videos, where it is suggested that a composite airframe for this particular motor needs to be at the higher end.

My question is, are the carbon fiber 4" tubes from Madcow up to the task for this motor or am I looking at a roll your own scenario?

https://www.madcowrocketry.com/4-carbon-fiber-airframe/
Whether it is roll your own or filament wound, it should hold up to the task. The only reason they get destroyed is due to after the shred.

Like mark stated, the part where you should be most concerned is your fins.


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bobkrech

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....The N5800 is a serious beast though. You fin attachment, and fin design need to be on the money. I would lean towards 1/4" or 3/8" carbon plate.
Virtually all failures using this motor have occurred because the builders undersized their fins and the rocket coned, went unstable and shredded when it went sideways at Mach 2+. Don't make the same mistake.

1.) Use 4 fins each with a span of 5" (1.5 X AF diameter). This insures sufficient projection into clean air to provide sufficient corrective reaction to prevent the rocket from going sideways.

2.) Make sure your CG/CP ratio is >2 for all flight regimes. Use RAS Aero 2 to check is.

3.) Use commercial carbon plate for the fins so the edges will not delaminate. ACP composites is a good source and they can cut them for you.

4.) Surface mounting is fine as long as you use 3 to 4 layers of uni-fabric within the fillet to stiffen the joint.

https://www.sollercomposites.com/composites/carbon fiber uni-fabric.html 4.1 oz, T700, 12" wide x 0.006" thick. 10 linear feet is $19.10.

Each side of fin would have 3 or 4 ~1" x fin length strips embedded in the fillet on each side of fin. It's just like putting an L-bracket to attach the fins to the airframe but much lighter and more aerodynamic. The strips should be cut so the fibers are ~1" long (0.5" on airframe and fin).

5.) You should not break of a fin under any know circumstances short of a motor cato using this attachment method.
 

SpaceManMat

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Whether it is roll your own or filament wound, it should hold up to the task. The only reason they get destroyed is due to after the shred.

Like mark stated, the part where you should be most concerned is your fins.


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Can you give us an example of a MD flight that was successful without a protected leading edge and Nose cone point? If so how fast and high did it go?

Pretty sure you need to protect your LE and nose cone from erosion going Mack 3+

Taking on the N5800 in a MD is going to take you to the limits of ameture rockery, best place to start is by reading about those who have done it before.

https://www.ausrocketry.com/forum/viewtopic.php?f=10&t=3659&hilit=Mad+max
 

REK

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Can you give us an example of a MD flight that was successful without a protected leading edge and Nose cone point? If so how fast and high did it go?

Pretty sure you need to protect your LE and nose cone from erosion going Mack 3+

Taking on the N5800 in a MD is going to take you to the limits of ameture rockery, best place to start is by reading about those who have done it before.

https://www.ausrocketry.com/forum/viewtopic.php?f=10&t=3659&hilit=Mad+max
Im talking about tubes not nose cones and fins. There has not been one tube that did not hold up to mach 3+ until either the fins shredded off or the rocket coned due to unstable conditions.


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markkoelsch

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There is no info on the website about them other than 60" long - got any details?
They are not filament wound- they are cloth. I have held them in my hands, and they are likely the nicest/best tubes I have seen.

I do not have dimensions and weights though.
 

crossfire

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I agree with Mark the WM carbon tubes are very nice.
 

GRIFFIN

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Virtually all failures using this motor have occurred because the builders undersized their fins and the rocket coned, went unstable and shredded when it went sideways
WHAAAAAAT????

The failures I've seen have never made it past motor burn out and the fins get ripped off at max-q

Kinda a blanket statement to say "virtually all failures are from coning"
 

JimJarvis50

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......just say'n
I had an N5800 ready to fly at Balls a few years ago. Yes, that's the motor sticking out of the bottom. The launch was delayed due to clouds, and after they cleared, I was unable to fly due to a gps problem. At least, that's my story.

Jim

Tower.jpg
 

mpitfield

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Thank you to everyone for your input, I appreciate all of it.

I should have known that this topic could easily expand into other concerns, so I should have been a bit more specific in order to limit the discussion to the tubing. The project is actually my L3 and the reason I wanted to keep it at a casual level is because I respect my TAPs input and my personal preference is to get their input before it goes out to the public forum. Having said that I am not experienced or smart enough to go to them with a well enough thought out plan. Essentially I want to present a plan that will stand up to scrutiny and evolve as the discussion evolves. This is not just because it is an L3, but because it is a relatively ambitious and risky L3 that may raise eyebrows, so I want to ensure that I can support my ideas and ultimately get buy-in.

So here are a few details. It is a scratch 4" MD, 4 fin, conical nosecone design with carbon plate fins (thickness TBT) and a 1/3, 2/3, full T2T planned (layup method TBT), with a high temp epoxy (TBT) on the leading edge of the fins. I have purchased some of the basics, the first being 60" and 30" CF tubes and a 12" coupler from Rocketry Warehouse which was not his heavy gauge tubing, just regular. I also grabbed a conical nosecone, as a matter of design preference, and all of which were all originally meant for a different project. When I decided what I wanted to achieve for my L3, I thought I would try to use the tubing I had. Since then I have picked up 1 of the 2 Altimeters (Marsa54LHD 100G version) have not decided on the backup, and the CTI 98mm 6XL case with tailcone. I have also decided that Kate will be on-board for real-time telemetry/tracking, a camera will be in the airframe facing out. and I will use CO2 for primary and a traditional BP backup charge for both main and apogee.

Beyond the choices above I have a preliminary design which has been simmed in both OR and RASAero to ensure it stays within the waiver, and maintains 2 Calibers of stability, etc. I have also downloaded AeroFinSim but have yet to get into it, which will help me with the final fin design, plate thickness and layup decisions. I just picked up a copy of SolidWorks to learn and use to design my AV bays, recovery components as well as any other components that will benefit from CAD, and if required to perform some analyses on any component where there may be a concern. Other choices I am leaning towards are that this is not likely to take place until 2019 at Airfest.

I have reviewed every possible N5800 launch on this forum, as well as anything I could find on the web and YouTube, all in an attempt to get as much of a feel for this motor as I can...and it deserves a lot of respect. In doing so I am happy with my preliminary choices, 4 fins, the fin size the realization that the fins ripping off is a contributing factor for failure, etc. However I am starting to question using the tubing that I originally purchased for a much less extreme purpose and less extreme motor choices. I have no issue saving that tubing for another project at this stage if it is not up to this task.

So the purpose of this thread for me was not to make this about my L3, not to get into the nuts and bolts about leading edge and aero heating and erosion, 3 fins vs. 4 fins, etc., I will save those for future threads as well as possibly a build thread. I was looking to make this thread a sole subject thread in order to get a feeling if I am being short-sighted on using the tubing, just because I already own it, or should I roll my own, or look for another off the shelf solution such as the Wildman tubing mentioned. Not to ignore the obvious, which is in order to make a proper evaluation numbers would help, but so would anecdotal experiences from those who have survived this motor. Unfortunately I don't have any specs on the existing tubing except that it was purchased from Rocketry Warehouse so I am assuming that it is the same stuff that Madcow is now offering. If anyone has any specifications on the tubing then great, and no I have not tried to reach out to Curtis, or Mike but I may if this does not yield and results.
 
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watermelonman

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As in purchase it without an L3, yes if the purpose is for my L3.
I mean can you physically find one. It will be a while before vendors have M3700/M2245/N5800/O3400 with any regularity. Heck even some of the less popular big Cesaronis I have been buying second hand.
 

mpitfield

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I mean can you physically find one. It will be a while before vendors have M3700/M2245/N5800/O3400 with any regularity. Heck even some of the less popular big Cesaronis I have been buying second hand.
This flight is likely two seasons away from reality as I am targeting Airfest 2019. Whether I am around, Algoma is still a launch site, or the motor is available is not something I can guarantee but I hope so, especially the first one.

I did have the option to pick one up a couple of months ago in the for sale thread, and to be honest I kind of regret not jumping on it, but I am pretty confident CTI will have fully recovered, and some, by that point. Having said that if I see one in the for sale section again I will likely jump on it, or ask one of my TAPs to grab it if the seller is concerned about selling it to an L2.
 

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Thank you to everyone for your input, I appreciate all of it.

I should have known that this topic could easily expand into other concerns, so I should have been a bit more specific in order to limit the discussion to the tubing. The project is actually my L3 and the reason I wanted to keep it at a casual level is because I respect my TAPs input and my personal preference is to get their input before it goes out to the public forum. Having said that I am not experienced or smart enough to go to them with a well enough thought out plan. Essentially I want to present a plan that will stand up to scrutiny and evolve as the discussion evolves. This is not just because it is an L3, but because it is a relatively ambitious and risky L3 that may raise eyebrows, so I want to ensure that I can support my ideas and ultimately get buy-in.

So here are a few details. It is a scratch 4" MD, 4 fin, conical nosecone design with carbon plate fins (thickness TBT) and a 1/3, 2/3, full T2T planned (layup method TBT), with a high temp epoxy (TBT) on the leading edge of the fins. I have purchased some of the basics, the first being 60" and 30" CF tubes and a 12" coupler from Rocketry Warehouse which was not his heavy gauge tubing, just regular. I also grabbed a conical nosecone, as a matter of design preference, and all of which were all originally meant for a different project. When I decided what I wanted to achieve for my L3, I thought I would try to use the tubing I had. Since then I have picked up 1 of the 2 Altimeters (Marsa54LHD 100G version) have not decided on the backup, and the CTI 98mm 6XL case with tailcone. I have also decided that Kate will be on-board for real-time telemetry/tracking, a camera will be in the airframe facing out. and I will use CO2 for primary and a traditional BP backup charge for both main and apogee.

Beyond the choices above I have a preliminary design which has been simmed in both OR and RASAero to ensure it stays within the waiver, and maintains 2 Calibers of stability, etc. I have also downloaded AeroFinSim but have yet to get into it, which will help me with the final fin design, plate thickness and layup decisions. I just picked up a copy of SolidWorks to learn and use to design my AV bays, recovery components as well as any other components that will benefit from CAD, and if required to perform some analyses on any component where there may be a concern. Other choices I am leaning towards are that this is not likely to take place until 2019 at Airfest.

I have reviewed every possible N5800 launch on this forum, as well as anything I could find on the web and YouTube, all in an attempt to get as much of a feel for this motor as I can...and it deserves a lot of respect. In doing so I am happy with my preliminary choices, 4 fins, the fin size the realization that the fins ripping off is a contributing factor for failure, etc. However I am starting to question using the tubing that I originally purchased for a much less extreme purpose and less extreme motor choices. I have no issue saving that tubing for another project at this stage if it is not up to this task.

So the purpose of this thread for me was not to make this about my L3, not to get into the nuts and bolts about leading edge and aero heating and erosion, 3 fins vs. 4 fins, etc., I will save those for future threads as well as possibly a build thread. I was looking to make this thread a sole subject thread in order to get a feeling if I am being short-sighted on using the tubing, just because I already own it, or should I roll my own, or look for another off the shelf solution such as the Wildman tubing mentioned. Not to ignore the obvious, which is in order to make a proper evaluation numbers would help, but so would anecdotal experiences from those who have survived this motor. Unfortunately I don't have any specs on the existing tubing except that it was purchased from Rocketry Warehouse so I am assuming that it is the same stuff that Madcow is now offering. If anyone has any specifications on the tubing then great, and no I have not tried to reach out to Curtis, or Mike but I may if this does not yield and results.
I will say it again, your body tubes will hold up just fine. I am far from this flight that I am wanting to do, but I already prepared a design in Fusion 360, Rocksim, and RASAero.

Shoot me up if you want to exhange some ideas.


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patelldp

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I will say it again, your body tubes will hold up just fine. I am far from this flight that I am wanting to do, but I already prepared a design in Fusion 360, Rocksim, and RASAero.

Shoot me up if you want to exhange some ideas.


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I don't think you can confidently say that without data to back it up. I'd be very concerned about single thickness, unsupported spans of hobby "grade" tubing or components under those types of loads. Maybe someone can provide data to help you figure it out, but it's unlikely.

This project is extreme for the hobby, it's not prudent to assume off-the-shelf components will work in a "big Estes rocket" type of configuration.
 

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I don't think you can confidently say that without data to back it up. I'd be very concerned about single thickness, unsupported spans of hobby "grade" tubing or components under those types of loads. Maybe someone can provide data to help you figure it out, but it's unlikely.

This project is extreme for the hobby, it's not prudent to assume off-the-shelf components will work in a "big Estes rocket" type of configuration.
Assuming the airframe is built straight and no kinks in a coupler, crooked nosecone, bend tubes, I'll second that the tubes will hold up fine. I've done a ton of research on axial compression and Euler's buckling, and I'm impressed at how robust both fiberglass and carbon fiber tubes really are. I put out a calculator showing how much force they can take, and you won't come near the limits of a carbon fiber tube. A 4' long fiberglass tube is almost beefy enough to take the force, but not quite.

Your carbon tube can take over 2x the force it will experience before it will buckle. (2,261 drag+inertia lbs force limit vs 993 lbs force from the flight)

2016-12-15 08_14_04-Rocket Safety Checks - Google Sheets.png
 

patelldp

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Assuming the airframe is built straight and no kinks in a coupler, crooked nosecone, bend tubes, I'll second that the tubes will hold up fine. I've done a ton of research on axial compression and Euler's buckling, and I'm impressed at how robust both fiberglass and carbon fiber tubes really are. I put out a calculator showing how much force they can take, and you won't come near the limits of a carbon fiber tube. A 4' long fiberglass tube is almost beefy enough to take the force, but not quite.

Your carbon tube can take over 2x the force it will experience before it will buckle. (2,261 drag+inertia lbs force limit vs 993 lbs force from the flight)

View attachment 307449
Cool, data! I'm happy someone commented with more than a "I think it'll work." Can you clarify a few things?

  • Where are you deriving the axial load limit and Euler buckling limit? I'm guessing this information is hard to come by even for commercially made tubing as it's rarely, if ever, used in applications aside from piping.
  • What manufacturing method do your tubes emulate? I see you have a material selection, but do you have a manufacturing provision, i.e. filament wound, convolutely wound, spiral wound, etc.?
  • Flights are basically never straight and never void of lateral forces on a tube. Can you model the approximate lateral force in conjunction with the column loading that will lead to failure? To Bob's earlier point, a bit of coning or wind shear response is the death knell of a project not adequately designed.

Thanks!
 

markkoelsch

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I don't think you can confidently say that without data to back it up. I'd be very concerned about single thickness, unsupported spans of hobby "grade" tubing or components under those types of loads. Maybe someone can provide data to help you figure it out, but it's unlikely.

This project is extreme for the hobby, it's not prudent to assume off-the-shelf components will work in a "big Estes rocket" type of configuration.
The tubing will very likely by fine. The load a tube, especially a carbon tube, can take longitudinally is quite a lot. Now, if you lose a fin or start coning bets are off.

That said, I think the choice of four fins is a good choice.

Attachment is the thing, in my opinion. I believe any layup done will need to be post cured to maximize it.
 

patelldp

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The tubing will very likely by fine. The load a tube, especially a carbon tube, can take longitudinally is quite a lot. Now, if you lose a fin or start coning bets are off.
So that's my point, it may not be fine.

As I stated: unsupported, single thickness spans of tubing should be kept to a minimum length or eliminated wherever possible.
 

mccordmw

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Cool, data! I'm happy someone commented with more than a "I think it'll work." Can you clarify a few things?

  • Where are you deriving the axial load limit and Euler buckling limit? I'm guessing this information is hard to come by even for commercially made tubing as it's rarely, if ever, used in applications aside from piping.
  • What manufacturing method do your tubes emulate? I see you have a material selection, but do you have a manufacturing provision, i.e. filament wound, convolutely wound, spiral wound, etc.?
  • Flights are basically never straight and never void of lateral forces on a tube. Can you model the approximate lateral force in conjunction with the column loading that will lead to failure? To Bob's earlier point, a bit of coning or wind shear response is the death knell of a project not adequately designed.

Thanks!
The reference formula tab on the calculator shows all the calculations I brought together that are underneath the spreadsheet for determning axial compression and buckling limits

The resources tab has links to all the descriptions on the theory and the math. It also links to the several databases used to record the compression limits and the Young's modulus of elasticity needed for compression and buckling calculations. Most of that data was found, but some had to be extrapolated. For example, Quikrete tubes. I had to read the research paper on Modulus of Elasticity Data and measure a square inch of the tube to get its density. That was cross checked on a table in that paper for cardboard tubes to get the approximate Young's modulus. Most other data was directly from matweb or matbase and some from the axial compression archive on rocket tubes. That reference data is on the reference data tab which can always use real-world verification. Can also use more material entries on it to make it more useful.

My manufacturing method for tubes is click>buy. :-D I'm also learning to do better FG layups, and there is an entry for glassed Sonotube as an approximation of what I have with 2 wraps of 6 oz. FG and one wrap of 2.5 oz veil. That one is a guess.

The force calculation is for an angle of attack of 0 degrees. It can be updated to include AoA, but I was assuming if that deviated much, the build was screwed anyway. I do use FinSim separately to calculate if my fins will survive a wild flight.
 

mccordmw

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So that's my point, it may not be fine.

As I stated: unsupported, single thickness spans of tubing should be kept to a minimum length or eliminated wherever possible.
+1 to that. I found the buckling limits dropped very fast when the length increased. Axial compression is way way higher than buckling limits. Long tubes are like wet noodles. :-D

For example, a 4" x 4' CF tube can take 2200 lbs force before buckling.
A 4" x 3' tube goes up to 4000 lbs force. Cutting length by 25% doubled the resistance to buckling. While the numbers may be approximations, it hammers home the scientific theory behind what makes our models strong or weak.

A 4" x 6' tube will buckle at 1000 lbs force. That's about the same force load you'd get from the N5800. Shred likely.
 

mccordmw

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So that's my point, it may not be fine.

As I stated: unsupported, single thickness spans of tubing should be kept to a minimum length or eliminated wherever possible.
And the rub here is that shortening your tubes means more couplers. Those are a point of instability if you aren't laser straight. Tolerances on subsonic flights is much greater that mach 2-3 N5800 flights. Build quality is at a premium.

Internal reinforcement will let you build longer tubes, but that's more weight and internal build complexity. Also, more chance to tangle cords and chutes if there is stuff in the tube.
 

patelldp

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And the rub here is that shortening your tubes means more couplers. Those are a point of instability if you aren't laser straight. Tolerances on subsonic flights is much greater that mach 2-3 N5800 flights. Build quality is at a premium.

Internal reinforcement will let you build longer tubes, but that's more weight and internal build complexity. Also, more chance to tangle cords and chutes if there is stuff in the tube.
I meant essentially double walling, not separation points.
 
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