98mm Min-Diameter Composite Mach 3 Build

LandonC

Well-Known Member
Joined
Sep 19, 2022
Messages
54
Reaction score
14
Location
Austin, TX
Hi everyone, I just wanted to get people's opinions/tips on a "little" project that my college rocketry team is working on. Intended to test our manufacturing capabilities in hopes that the lessons learned can be applied to our much larger competition multi-stage rocket, this project is currently in the design stages. I had a few questions for some of the more seasoned veterans on here.

  1. Achieving Mach 3 obviously no small task, and quite honestly I'm not sure how many people have done it using commercially-available motors (design is constantly changing, but M-motors are likely going to be used). Our current design features low-profile swept delta fins with a considerable root chord length for strength. It's worth noting that we're making a min-diameter rocket at 75mm made almost entirely out of carbon fiber manufactured in-house. Our goal is to form the fins with a fiberglass core and carbon overlay but is there other materials that could give them the necessary strength to basically not disintegrate on launch (yes, I've had this happen on a smaller L2 rocket before and it was a sight to behold).
  2. Fin design is still up in the air. Any recommendations on general shape/profile for the lowest drag while still maintaining stability? I assume that the final design will feature a knife-edge on both the leading and trailing edges of the fins.
  3. One of the issues I've read about that other high-powered rockets encountered was structural failures of the nose cone. Typical off-the-shelf plastic cones won't cut it. As of right now, our two options are to source a reinforced cone with a composite tip (http://www.compositewarehouse.com/index.php?route=product/product&path=34_43&product_id=99), or to prototype and manufacture our own cone. Any feedback on reinforcing nose cones is appreciated. Heat shielding paint of some type will likely be applied at the end as well.
  4. Any and all feedback/advice is greatly appreciated. We're basically working from the ground up and I'm looking forward to going through the design and testing phase of this project. Happy to keep anyone interested up-to-date on our progress.
 
Last edited:

sharkbait

Well-Known Member
Joined
Aug 6, 2013
Messages
590
Reaction score
113
Hi everyone, I just wanted to get people's opinions/tips on a "little" project that my college rocketry team is working on. Intended to test our manufacturing capabilities in hopes that the lessons learned can be applied to our much larger competition multi-stage rocket, this project is currently in the design stages. I had a few questions for some of the more seasoned veterans on here.

  1. Achieving Mach 3 obviously no small task, and quite honestly I'm not sure how many people have done it using commercially-available motors (design is constantly changing, but M-motors are likely going to be used). Our current design features low-profile swept delta fins with a considerable root chord length for strength. It's worth noting that we're making a min-diameter rocket at 75mm made almost entirely out of carbon fiber manufactured in-house. Our goal is to form the fins with a fiberglass core and carbon overlay but is there other materials that could give them the necessary strength to basically not disintegrate on launch (yes, I've had this happen on a smaller L2 rocket before and it was a sight to behold).
  2. Fin design is still up in the air. Any recommendations on general shape/profile for the lowest drag while still maintaining stability? I assume that the final design will feature a knife-edge on both the leading and trailing edges of the fins.
  3. One of the issues I've read about that other high-powered rockets encountered was structural failures of the nose cone. Typical off-the-shelf plastic cones won't cut it. As of right now, our two options are to source a reinforced cone with a composite tip (http://www.compositewarehouse.com/index.php?route=product/product&path=34_43&product_id=99), or to prototype and manufacture our own cone. Any feedback on reinforcing nose cones is appreciated. Heat shielding paint of some type will likely be applied at the end as well.
  4. Any and all feedback/advice is greatly appreciated. We're basically working from the ground up and I'm looking forward to going through the design and testing phase of this project. Happy to keep anyone interested up-to-date on our progress.
Check out the Wildman Mach 3 and the Wildman Falcon 3
 

JackC

Well-Known Member
TRF Supporter
Joined
May 2, 2020
Messages
497
Reaction score
349
You can do it with a fiberglass nosecone with an aluminum tip. I would also use a Von Karman nosecone. You can find them at Composite Warehouse or Wildman Rocketry. For a commercial motor, try a Cesaroni M2245.
 

LandonC

Well-Known Member
Joined
Sep 19, 2022
Messages
54
Reaction score
14
Location
Austin, TX
You can do it with a fiberglass nosecone with an aluminum tip. I would also use a Von Karman nosecone. You can find them at Composite Warehouse or Wildman Rocketry. For a commercial motor, try a Cesaroni M2245.
Aluminum tip is enough for the heat? Good to know. Thanks.
 

dhbarr

Amateur Professional
TRF Supporter
Joined
Jan 30, 2016
Messages
8,472
Reaction score
2,866
You can do it with a fiberglass nosecone with an aluminum tip. I would also use a Von Karman nosecone. You can find them at Composite Warehouse or Wildman Rocketry. For a commercial motor, try a Cesaroni M2245.
That's like a 45k shot, so ~50k waiver or so?
 

tfish

Well-Known Member
Joined
Dec 7, 2009
Messages
3,038
Reaction score
1,385
I've done 'lots" of mach flights on plastic nose cones and a few to mach 2..

but yes to FG or better for an M3 attempt for sure

Things start getting serious about mach 2.7 and that's when things heat up and melt, or collapse, or grow from heating and become loose (aluminum nose cone tips) etc etc etc etc..

Tony
 

StreuB1

Well-Known Member
Joined
Aug 28, 2007
Messages
830
Reaction score
885
Location
Illinois
As an aside to what Tony mentioned about things getting real above M2.7. Consider bonding your eyebolt (welded, of course) into the aluminum tip with JB weld and use a loop of Kevlar as a leash through the eyebolt for attaching your cord. Once the eyebolt is in for good, a leash is the only means to attach anything to it. You can always cut the aluminum tip off and buy/make another if you REALLY need to.

Loctite can be used but the aluminum tip will sink a lot of heat and could loosen up. Its a long way down from 50k and lines will be wound up like crazy which could back out your eyebolt. The chance is extremely unlikely but on projects like this, the least possible thing to happen, will happen.

Leave no stone unturned and speak softly, Murphy is always around the corner.
 

QFactor

L2 - NAR & TRA
TRF Supporter
Joined
Nov 6, 2019
Messages
445
Reaction score
246
Location
Ohio
Since you are in the design phase, and will be trying your hand at laying up the components, be sure to review
your motor selection for a rocket that could weigh noticeably more than your "calculated" weight.
 

LandonC

Well-Known Member
Joined
Sep 19, 2022
Messages
54
Reaction score
14
Location
Austin, TX
Since you are in the design phase, and will be trying your hand at laying up the components, be sure to review
your motor selection for a rocket that could weigh noticeably more than your "calculated" weight.
Definitely considered this possibility. Plenty of experience laying up fiberglass and carbon so we should have predictable build quality.
 

LandonC

Well-Known Member
Joined
Sep 19, 2022
Messages
54
Reaction score
14
Location
Austin, TX
As an aside to what Tony mentioned about things getting real above M2.7. Consider bonding your eyebolt (welded, of course) into the aluminum tip with JB weld and use a loop of Kevlar as a leash through the eyebolt for attaching your cord. Once the eyebolt is in for good, a leash is the only means to attach anything to it. You can always cut the aluminum tip off and buy/make another if you REALLY need to.

Loctite can be used but the aluminum tip will sink a lot of heat and could loosen up. Its a long way down from 50k and lines will be wound up like crazy which could back out your eyebolt. The chance is extremely unlikely but on projects like this, the least possible thing to happen, will happen.

Leave no stone unturned and speak softly, Murphy is always around the corner.
That's a great point, thanks. Sounds like you've had some unlikely complications happen?
 

LandonC

Well-Known Member
Joined
Sep 19, 2022
Messages
54
Reaction score
14
Location
Austin, TX
3D printed an 18 in. nosecone as the basis for the carbon fiber mold. We’ll probably lightly coat in epoxy and sand it down smooth to remove some of the steps before making the form. The cut off on the top is for the 2in. machined aluminum tip.
 

Attachments

  • 958BB88C-3D4C-42CD-8EEE-EFA15ADC05AE.jpeg
    958BB88C-3D4C-42CD-8EEE-EFA15ADC05AE.jpeg
    1.5 MB · Views: 0

robopup

Well-Known Member
Joined
Oct 7, 2021
Messages
54
Reaction score
91
Lookin' good! Did you leave yourself a little extra nosetip on the plug compared to the 2in tip? So you can trim the edges of parts pulled from the mold.
 
Joined
Dec 19, 2011
Messages
271
Reaction score
177
Location
Lebanon,IN
Look at threads by Jim Jarvis. He has been fabricating his own carbon airframes and shows his building approach in the thread. Jim is covering the leading edge of his fins with Cotonics (high temp epoxy) as an ablative. You might consider that in your design.
 

G_T

Well-Known Member
Joined
Dec 29, 2011
Messages
2,772
Reaction score
728
Instead of epoxy for your plug prep, consider using sandable primer, then auto paint, then let cure, then polish it out with conformal sanding blocks and very fine wet sandpaper to render a glass smooth surface. You can get fine sandpaper at auto parts stores since it is the same thing for auto paint work. Go at least to 4000 grit IMHO. Then coat with a mold release wax, then probably PVA. Or use a semi-permanent mold release, two coats.

Note, in the primer stage you want to eliminate every pinhole. Spraying more paint at a pinhole won't remove it. A very fine drill bit spun by the fingers to clean the pit, and a toothbrush to dab in primer, should work. That's if you have pinhole issues show up. Don't be shocked if they do. More layers of paint will just make the surface worse so don't try to fix that way!

Gerald
 

Chris_H

Well-Known Member
Joined
Sep 13, 2017
Messages
540
Reaction score
105
Instead of epoxy for your plug prep, consider using sandable primer, then auto paint, then let cure, then polish it out with conformal sanding blocks and very fine wet sandpaper to render a glass smooth surface. You can get fine sandpaper at auto parts stores since it is the same thing for auto paint work. Go at least to 4000 grit IMHO. Then coat with a mold release wax, then probably PVA. Or use a semi-permanent mold release, two coats.

Note, in the primer stage you want to eliminate every pinhole. Spraying more paint at a pinhole won't remove it. A very fine drill bit spun by the fingers to clean the pit, and a toothbrush to dab in primer, should work. That's if you have pinhole issues show up. Don't be shocked if they do. More layers of paint will just make the surface worse so don't try to fix that way!

Ge
This...
A quality polished automotive urethane is good to at least mid M2 unscathed. A near perfect finish will give more altitude, also. I am not sure where it will begin to fail because of heating, but somewhere past M2.5 if you do a good job.
To reiterate.. perfect in the filler primer before moving into basecoat. Get it perfect early, ASAP in the building of coats. For the finish, at least two fully wet coats of a high quality urethane. The polishing stage starts with 1000, wet, then onto 3000 grit Trizact pad, wet. Then the 3M perfect it system, #1, and at least #3 on a mini polisher, with a foam pad. You can skip #2 to cut cost.

There is a video on youtube of someone flying an M2245 min dia. I think it went a little past 30k, and maybe not M3, maybe just over, I do not recall. Either the Loki M1378 or L2050 would be a cool motor.
 

G_T

Well-Known Member
Joined
Dec 29, 2011
Messages
2,772
Reaction score
728
I think this was for preparing a plug for making a mold, not flying that part directly. But I could be mistaken; I haven't gone back and reread the previous posts.
 

David Schwantz

Well-Known Member
TRF Supporter
Joined
Jul 22, 2018
Messages
3,180
Reaction score
2,047
Location
MN
This works quite well for pin holes.
 

LandonC

Well-Known Member
Joined
Sep 19, 2022
Messages
54
Reaction score
14
Location
Austin, TX
I think this was for preparing a plug for making a mold, not flying that part directly. But I could be mistaken; I haven't gone back and reread the previous posts.
Since this is our first time manufacturing our own nosecones, (this whole project is to test manufacturing capabilities to improve our main Spaceport America rocket) we are trying a few different methods to see what gives us the best result. The 3D-printed cones will be used for a few things, mainly as plugs to make molds. The entire body of our rocket will be carbon fiber, with the fins having G10 cores and a machined aluminum nosecone tip.
 

LandonC

Well-Known Member
Joined
Sep 19, 2022
Messages
54
Reaction score
14
Location
Austin, TX
Finished designing the mold for the nose cone. Still deciding how to manufacture the mold, whether it's 3D printed in PETG, SLS printed, or CNCed out of aluminum (worst-case scenario). We'll do the full carbon fiber layup and ultimately chop the tip and attach a 2-inch machined aluminum tip. This should get the ball rolling pretty quickly.FNC Mold.png
 

plugger

Well-Known Member
Joined
Apr 30, 2009
Messages
716
Reaction score
381
Current sim with the M2245, which we plan to use, puts us at ~46k @Mach 3.2
I've done this flight (custom CF rocket with M2245) and it folded up right around Mach 3. I rolled my own airframe (4 layers 2x2 200gsm twill) and had a bare (rolled CF airframe only) section between the forward closure and the aft end of my AV bay. That's where the vehicle folded. I was able to recover the NC and AV bay but the rest of the rocket (basically everything up to the top of the casing) just kept scootin.
I used a COTS FWFG nose cone for this and it survived going sideways at nearly M3. It strained some of the filaments but it didn't pop. A nominal flight with a COTS FWFG NC should be fine. No need for reinforcement, ablative, etc. You'll only just kiss M3 most likely and then decelerate quite quickly.
 

robopup

Well-Known Member
Joined
Oct 7, 2021
Messages
54
Reaction score
91
@robopup ,

About 3D printing: We can do SLA, PLA, ABS, PETG, etc. on the main printers (Craftbot XLs). We have smaller printers that can print carbon, but it's too small for this application. There's a handful of Raise3D Pro3s as well as some higher-end SLS and metal printers. There's a huge industrial printer we could use but there are a few hurdles to getting approval for it. We do have budget constraints, so machining a mold out of aluminum would take a significant amount of convincing to get approval for, although we do have the CNC capability. Now that I think about it, an SLS print of the mold would be a lot more practical than a standard PLA or PETG print, since it could give us a longer lifetime of use.

About the mold: I'll adjust the Solidworks part to reflect your comment. Seems obvious now that you mention it. Did you have any issues fastening the aluminum tip to the rest of the carbon cone?

I have a part sitting on my desk which is from an SLS machine which I can at least wrap my head around being stiff enough to use for a tool. I believe it's aluminum+nylon. For my personal projects, I probably still wouldn't go this route but my requirements are likely different from yours.

Another couple comments on your mold:
  • I would not print male keys into mold halves. They're going to be a pain to finish and finish around, and look like they have the potential to break. It's also going to be really hard to both put mold halves together and take them apart because the mold will only move along the axis of your keys. I also wouldn't use a square profile, it will be hard to finish. For tools which are directly cut, I've used both the marble method @G_T shows pictures of in my thread and had holes through each half which pins push through. Both have been successful.
  • Your keys are getting kinda close to your part edge. Epoxy tends to squeeze into these areas and stick to your keys if you don't have a plan to deal with it.
  • If you 3d print your mold, do you have a plan to keep your nosecone shoulder feature sharp while you're finishing and polishing? I omitted this altogether and built the nose and lower tube as a single part.
 
Top