O3400 Min Diameter L3

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airforcetp1991

airforcetp1991

Cave Putorium
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I am designing a L3 build for this summer, for a BALLS launch or locally if the waiver is approved. The overall concept is a 60" carbon airframe from Wildman with a 2" switch band and a 24" VK nosecone. Redundant Raven4 altimeters and Raptors for the drogue deployment. It is a head-end dual deployment concept with a Sim max altitude of ~85,000 according to RASAero II (rounded fin edge for a conservative estimate) with a max Mach of ~3.6. Planning on 3 or 4 #6 shear pins for each section.

One of the biggest things I am struggling with is the fin attachment method. I am not planning on a tip to tip, mainly due to lack of the equipment to make this happen to be completely honest. The fin design right now is 0.1875" G10 with a 1" bevel (made by PML). The question I would like some help with is will a solid fillet be sufficient using hysol loctite ea e-120hp epoxy? The other option I am looking into is drilling and tapping holes in the fin and using steel screws through the tube wall to help reduce the chance that the peel strength of the tube wall will be the limfac. I am not set on the number of screws but from an engineering point of view I like the concept. I can't help but feel like this would be more common if it was really necessary though...

Any additional BS flags would be greatly appreciated. Thanks!

-Tony
 

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If I recall correctly, anything over 50k feet must be approved by a Tripoli committee, and I'm going to guess that they won't approve something like this without the person already having their L3 and having flown high already. Might be wrong, but I think that's the case.

Don't get me wrong, I love the idea of the rocket in general, but for an L3 Cert flight it's probably not what you want to do. Plus, getting a TAP to sign off on this might be a trick and a half too.
 
I acknowledge that this is a very ambitious project and that it could very well be a struggle to get approval. I am also well aware of the fact that many many people on this forum have more experience than I do. With that said my philosophy behind doing this as a L3 project is that if I intend to fly a rocket like this as a L3 why should it not have the higher level of review and approval required of a cert flight. Building a large diameter rocket and flying it on a small M is not easy and I have a huge amount of respect for those who have done this and earned their L3, something I have not done, but would it really be better for me to do that and then later build something like I described above without the oversight? If the intent of a L3 cert is to show competence, and I intent to fly similar projects in the future, I would submit doing this type of build as a cert is a valid way to demonstrate that competence. Again, BS flags are welcome.

-Tony
 
airforcetp1991 said:
I acknowledge that this is a very ambitious project and that it could very well be a struggle to get approval. I am also well aware of the fact that many many people on this forum have more experience than I do. With that said my philosophy behind doing this as a L3 project is that if I intend to fly a rocket like this as a L3 why should it not have the higher level of review and approval required of a cert flight. Building a large diameter rocket and flying it on a small M is not easy and I have a huge amount of respect for those who have done this and earned their L3, something I have not done, but would it really be better for me to do that and then later build something like I described above without the oversight? If the intent of a L3 cert is to show competence, and I intent to fly similar projects in the future, I would submit doing this type of build as a cert is a valid way to demonstrate that competence. Again, BS flags are welcome.

-Tony
Click to expand...


I've heard this discussion before and it legit resonates with me - I'm working on an L3 that is a tank of a LOC Bruiser EXP that's going to go, MAYBE, 5k feet up on an M. Totally different philosophy, and the reason I'm doing it is because where I live the closest 4 fields are all 15k feet or less...this is what I'll be flying in the future, so this is what I'm building for Cert. So, I'm certainly not calling BS on that idea.

What if you build the rocket but put a bigger M or something in it? You're gonna have a better chance of the cert going well, it would fit your anticipated build style in the future, and you can take smaller steps in getting there.

...I guess what I'm saying is, maybe look at getting your L3 as the first step to going 80k feet, not the only step to getting there? I have some crazy flights I want to do in the future (a 1:10 scale of a Delta II 7925 comes to mind), but I'm looking at my L3 project as the first step in getting there, not the only step.
 
My only question is: is that a tracker up in the NC, and will it be a metal-tipped NC? If so, make sure the NC tip won't interfere with your tracker. Check specs, or do some experimentation.
 
Dustin Lobner said:
I've heard this discussion before and it legit resonates with me - I'm working on an L3 that is a tank of a LOC Bruiser EXP that's going to go, MAYBE, 5k feet up on an M. Totally different philosophy, and the reason I'm doing it is because where I live the closest 4 fields are all 15k feet or less...this is what I'll be flying in the future, so this is what I'm building for Cert. So, I'm certainly not calling BS on that idea.

What if you build the rocket but put a bigger M or something in it? You're gonna have a better chance of the cert going well, it would fit your anticipated build style in the future, and you can take smaller steps in getting there.

...I guess what I'm saying is, maybe look at getting your L3 as the first step to going 80k feet, not the only step to getting there? I have some crazy flights I want to do in the future (a 1:10 scale of a Delta II 7925 comes to mind), but I'm looking at my L3 project as the first step in getting there, not the only step.
Click to expand...

That is valid and I considered this. My concern would be stressing the rocket on a smaller motor before asking it to handle the much greater stress of an 80K flight. If I was going to do a smaller motor I would be more inclined to build a 75mm MD rocket for the cert, if that is what the TAPs decide I should do I will absolutely respect that and build it the best I can. That said any MD build flying on an M or larger is going to be beyond visual range at apogee so if I am trusting the tracker data why not go for it. That is just my opinion/philosophy though.
 
I am far from an L3, so I can only touch one piece of the project: the tip to tip. You mentioned not having the equipment to do it. While I love me a good vacuum bag setup, you don't really need that to do a decent T2T. A decent grooved roller (see here for an example) will get you 75%-ish of the way there. It won't be the lightest it could be, but I'd expect it to be good enough.

I'd also fly the cert on an M and hit it with the O3000 on the second flight, but I'm cautious like that. No harm in going full bore if your TAP agrees and you're willing to take the added risk.
 
boatgeek said:
I am far from an L3, so I can only touch one piece of the project: the tip to tip. You mentioned not having the equipment to do it. While I love me a good vacuum bag setup, you don't really need that to do a decent T2T. A decent grooved roller (see here for an example) will get you 75%-ish of the way there. It won't be the lightest it could be, but I'd expect it to be good enough.

I'd also fly the cert on an M and hit it with the O3000 on the second flight, but I'm cautious like that. No harm in going full bore if your TAP agrees and you're willing to take the added risk.
Click to expand...

That's good advice. What do you primarily use T2T to achieve in your builds? Are you worried most about fin rigidity or attachment, or both?

-Tony
 
To the OP. First if you are going to stress the airframe on a smaller M class motor, it will never handle an "O".
Second, on a MD build you can slot the airframe the size of the root of the fins and inset them into the slot. I also like to drill holes through the fins to act as " fingers " in the fillet.
 
David Schwantz said:
To the OP. First if you are going to stress the airframe on a smaller M class motor, it will never handle an "O".
Second, on a MD build you can slot the airframe the size of the root of the fins and inset them into the slot. I also like to drill holes through the fins to act as " fingers " in the fillet.
Click to expand...

I 100% agree I should have used a better word than stressed, I was mainly thinking of a hard landing or slight damage during deployment that isn’t catastrophic but would not allow for a flight on an O.

I like the “fingers” idea a lot!

Tony
 
airforcetp1991 said:
That's good advice. What do you primarily use T2T to achieve in your builds? Are you worried most about fin rigidity or attachment, or both?

-Tony
Click to expand...
Honestly, none of my builds have been pushed hard enough to really need T2T. I have done it off and on for extra peace of mind around fin attachment, plus it looks cool.
 
I've not used it myself, but I've worked with a lot of hysols and have been uniformly impressed. Those automatic-metering syringes are expensive, but it's truly a "you get what you pay for" in that you get a) the correct mix ratio and b) a proper mix through the mixing tip.
 
Dustin Lobner said:
I've not used it myself, but I've worked with a lot of hysols and have been uniformly impressed. Those automatic-metering syringes are expensive, but it's truly a "you get what you pay for" in that you get a) the correct mix ratio and b) a proper mix through the mixing tip.
Click to expand...

That checks, I would hate to lose a $1,000+ build trying to save $50 on epoxy... Do you normally trust the mixing that that nozzle does or do you mix it extra to be sure?

-Tony
 
I have used Hysol for many years. It is the best I have ever used. Many applications on RC jets. I also like it the best to do fillets on rockets. Will not run or drip. Wipe it with your finger for a glass smooth surface. Dreamworks RC sells it for 85 bucks for 5 tubes.
 

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