Documenting my Level3 and for sharing with my advisor.

[Steve Shannon]

Tripoli prohibits the use of commercial fin cans on L3 certification flights. I believe NAR does also. The ability to design and construct fins that won’t fail are considered a basic important skill for people who will be entrusted with M, N, O and above motors. Slapping on a commercial fin can demonstrates no skill in designing or building. Fin failures are probably the most frequent cause of rocket flight failures during the up part. I don’t think I know of frequent failures of nosecones.

 

[Steve Shannon]

And for future reference people have brazed on aluminum fins and flown them above mach2. I actually read about that here.

Yes, indeed. Mike Fisher did it among others. Brazing works better than welding for aluminum fins.

 

[NickG]

I see the problem as people thinking that a cert flight is different than any other project (it’s fundamentally not)

Yes, safety is everyone’s concern, and if the person is doing something unsafe, then people should speak up. But, really, what is the difference if the OP certs on a BDR & a 1%M motor, then goes on to build the proposed MD project? Why waste your time and money on a BDR if that is not what your into?

I like the cert process, and the extra formality involved. I don’t want any of my rockets to fail. I just think some people are adverse to risk/failure, especially when it is a formalized cert failure and they transpose that fear onto others.

 

[boatgeek]

NAR rules dictate that you can’t use a commercial off the shelf fincan for your L3. It does not however say that you can’t use a fincan. I had to clarify this before making my decision.


My understanding, and I agree, is that they don’t want people doing a pure bolt together L3. They want me to invest time and effort. I’m ok with this.

Tripoli prohibits the use of commercial fin cans on L3 certification flights. I believe NAR does also. The ability to design and construct fins that won’t fail are considered a basic important skill for people who will be entrusted with M, N, O and above motors. Slapping on a commercial fin can demonstrates no skill in designing or building. Fin failures are probably the most frequent cause of rocket flight failures during the up part. I don’t think I know of frequent failures of nosecones.

Thanks to both of you for fact-checking me.

 

[Ez2cDave]

With due respect, I felt that come off as a little harsh/condescending

Nytrunner,

Thank you for saying that about yourself. . . It's a rare quality, nowadays !

I, too, was a "little harsh" in my reply to you and, for that, I apologize !

Dave F.

 

[blackjack2564]

Mike P was the first to successfully tame the N-5800 beast in a minimum.
The fins are brazed with aluminum brazing rods ,search for "Don't Debate This" name of rocket.

 

[Nytrunner]

Nytrunner,

Thank you for saying that about yourself. . . It's a rare quality, nowadays !

I, too, was a "little harsh" in my reply to you and, for that, I apologize !

Dave F.

*I wasn't the poster you replied to originally

 

[Ez2cDave]

*I wasn't the poster you replied to originally

Thanks for letting me know . . .

BTW - Keep that apology for yourself, in case I ever owe you one in the future . . . LOL !

Dave F.

 

[levi seaton]

Yes, indeed. Mike Fisher did it among others. Brazing works better than welding for aluminum fins.

Why would brazing work better than welding

 

[Steve Shannon]

Why would brazing work better than welding

My understanding is that the lower temperatures result in much less distortion and stress. Mike Fisher was actually brazing fins directly to the outside of motor cases.

 

[TimothyG]

Yes, indeed. Mike Fisher did it among others. Brazing works better than welding for aluminum fins.

Thanks a bunch. I have been trying to find the article about it and couldn’t remember the name. Found the Australian forum discussion I was looking for. Gives me previous work to site in my decision matrix.

 

[cwbullet]

Good luck with your level 3 - subscribed.

 

[levi seaton]

My understanding is that the lower temperatures result in much less distortion and stress. Mike Fisher was actually brazing fins directly to the outside of motor cases.

Placing a heat sink on the back side made of copper, stainless, or brass can control or stop the distortion or at least minimize it. Not arguing. I’m just courious because of the difference in strength.

 

[TimothyG]

Placing a heat sink on the back side made of copper, stainless, or brass can control or stop the distortion or at least minimize it. Not arguing. I’m just courious because of the difference in strength.

There’s also the possibility of not destroying the T6 rating of the aluminum with brazing which means no treatment required. Hence the attractiveness of the brazing over welding.

 

[jjwb22101]

As someone working on a similar (somewhat less ambitious, but still definitely not a BDR) L3 project, I'd like to shed a bit of light on why people might decide to fly high and fast for a cert flight. In terms of the practical considerations, you always have to start with cost. A larger rocket is more expensive, because it takes more raw materials to make. I got my entire airframe for about $300 (motor mount, airframe tubes, couplers, centering rings, and a sheet of fiberglass to cut my own fins). A similar 6" airframe would cost double that, at least. Smaller (and thus, lighter) rockets also don't need as large a parachute, or as strong of recovery harnesses/attachment points, which also saves money. As a college student, I'm already spending basically my whole 'fun' budget (plus some) for this year on my L3, and making it larger just wouldn't be financially feasible, even if I wouldn't want to then build a high-performance rocket later.

Let's talk about safety and experience. I'd be surprised if the safety incident rate for high-performance models (not including research motors) was significantly higher than for 'low and slow' rockets, since the vast majority of failures are recovery failures, and the recovery subsystem would be basically identical between high performance and 'low and slow' rockets (see the NAR's 2005 special committee report). Yes, it's more likely that you don't find the rocket, but the extra $150 you might spend to install a tracker in the rocket to mitigate that risk is still significantly less than the cost difference of a larger rocket. As for airframe failures, yes, they're going to be more common in a high performance rocket, but the risk is still very small, and can be mitigated by a good understanding of the flight performance, which is one of the few things that I've found student groups to be significantly better at than a lot of the rocketry community (seriously, most rocketeers, even experienced HPR fliers, haven't done fin flutter analysis, FEA, CFD, and thermal analysis before).

So here's my advice - you should know exactly what's going to happen with any rocket you're going to fly before you push the launch button. The vast majority of certifications that I've seen fail have been because of inexperience. If you don't know what you're doing, ask. Also, make sure to take a step back when that happens and make sure you haven't gotten in over your head. But if you're comfortable that you know how everything is going to perform, go for it. That goes for both high performance cert flights as well as for a 'low and slow' project. Best of luck on your cert! Also, for your fin attachment - is there a reason you want to go with welding or brazing rather than just a mechanical attachment (I'm thinking L-brackets to hold the fins to the airframe, or maybe something akin to the max-q fin cans that Binder Design sells)? I haven't done anything with metallic fins, and am curious about your design process.

 

[levi seaton]

As someone working on a similar (somewhat less ambitious, but still definitely not a BDR) L3 project, I'd like to shed a bit of light on why people might decide to fly high and fast for a cert flight. In terms of the practical considerations, you always have to start with cost. A larger rocket is more expensive, because it takes more raw materials to make. I got my entire airframe for about $300 (motor mount, airframe tubes, couplers, centering rings, and a sheet of fiberglass to cut my own fins). A similar 6" airframe would cost double that, at least. Smaller (and thus, lighter) rockets also don't need as large a parachute, or as strong of recovery harnesses/attachment points, which also saves money. As a college student, I'm already spending basically my whole 'fun' budget (plus some) for this year on my L3, and making it larger just wouldn't be financially feasible, even if I wouldn't want to then build a high-performance rocket later.

Let's talk about safety and experience. I'd be surprised if the safety incident rate for high-performance models (not including research motors) was significantly higher than for 'low and slow' rockets, since the vast majority of failures are recovery failures, and the recovery subsystem would be basically identical between high performance and 'low and slow' rockets (see the NAR's 2005 special committee report). Yes, it's more likely that you don't find the rocket, but the extra $150 you might spend to install a tracker in the rocket to mitigate that risk is still significantly less than the cost difference of a larger rocket. As for airframe failures, yes, they're going to be more common in a high performance rocket, but the risk is still very small, and can be mitigated by a good understanding of the flight performance, which is one of the few things that I've found student groups to be significantly better at than a lot of the rocketry community (seriously, most rocketeers, even experienced HPR fliers, haven't done fin flutter analysis, FEA, CFD, and thermal analysis before).

So here's my advice - you should know exactly what's going to happen with any rocket you're going to fly before you push the launch button. The vast majority of certifications that I've seen fail have been because of inexperience. If you don't know what you're doing, ask. Also, make sure to take a step back when that happens and make sure you haven't gotten in over your head. But if you're comfortable that you know how everything is going to perform, go for it. That goes for both high performance cert flights as well as for a 'low and slow' project. Best of luck on your cert! Also, for your fin attachment - is there a reason you want to go with welding or brazing rather than just a mechanical attachment (I'm thinking L-brackets to hold the fins to the airframe, or maybe something akin to the max-q fin cans that Binder Design sells)? I haven't done anything with metallic fins, and am curious about your design process.

I agree with the cost difference. My level three was about 80$ minus the motor, electronics, and recovery gear.

 

[cherokeej]

Timothy, document your build. Ignore all the negatives.

Bring it out to the playa and fly it. Up fast, down slow.

 

[DRAGON64]

Very ambitious certification project to say the least... looking forward to reading more, as I love extreme rocket projects! Best of luck with your level 3!

 

[mpitfield]

Hats off to you for taking unnecessary risks when it counts the most. I am looking forward to your progress and results. At the end of the day if you fail then you learn something and try again. Assuming the failure doesn't represent a safety issue.

Good luck

 

[Tyler P]

Now that all the naysayers have weighed in, can we move ahead with this project? I love learning new things and following a thread about many things that are above my current level is a way to learn. Obviously, safety is always of highest concern, but the OP isn't doing this on his own...his advisors/mentors are not likely to let something go along the way that isn't safe.

So let the fun continue! I want to see some progress!

 

[TimothyG]

Adding some pictures from phone. I’ll add text in an edit later today to explain what all I was doing/thinking.

 

[Nytrunner]

Nice rocket room, wish my school had that when I was competing (we had to squat in the instrumentation lab). Phoenix!

Camera cutout and chute cannon development?

 

[Ez2cDave]

Now that all the naysayers have weighed in, can we move ahead with this project? I love learning new things and following a thread about many things that are above my current level is a way to learn. Obviously, safety is always of highest concern, but the OP isn't doing this on his own...his advisors/mentors are not likely to let something go along the way that isn't safe.

So let the fun continue! I want to see some progress!

Tyler,

I noticed in your signature that you are going for Level 1 this year . . . Best wishes for success !

Certification is merely the "Entry Point" to each Level . . . It is NOT meant to demonstrate "Mastery" of the Certification Level being sought.

Each person is entitled, within the "boundaries" set by their TAP or L3CC, to fly in whatever manner they choose, be it "Low & Slow" or a Mach 2 flight !

My personal suggestion is to fly the bare minimum impulse level, in a non-minimum diameter rocket, with a slightly oversized chute ( landing damage ) and, if electronics are used, the least complex setup possible. Once the next Level is attained, "Let her RIP", if that is your "style" !

I wish the OP success in his Certification attempt, also !

Dave F.

 

[Tyler P]

Tyler,

I noticed in your signature that you are going for Level 1 this year . . . Best wishes for success !

Certification is merely the "Entry Point" to each Level . . . It is NOT meant to demonstrate "Mastery" of the Certification Level being sought.

Each person is entitled, within the "boundaries" set by their TAP or L3CC, to fly in whatever manner they choose, be it "Low & Slow" or a Mach 2 flight !

My personal suggestion is to fly the bare minimum impulse level, in a non-minimum diameter rocket, with a slightly oversized chute ( landing damage ) and, if electronics are used, the least complex setup possible. Once the next Level is attained, "Let her RIP", if that is your "style" !

I wish the OP success in his Certification attempt, also !

Dave F.

Yes, I agree that certifying is the first step, and I feel the same as you as far as complications are concerned. My L1 rocket is pretty much ready, and will be a fairly simple affair. 3" LOC IRIS, single use H135, motor ejection, and a JLCR for simple "dual deploy".

I actually prefer the low and slow methodology, but I feel the OP has a right to choose and he will do what he thinks is best under his advisors watchful eye. I personally love watching a launch and keeping the rocket in sight.

Edit: Also, L3 isn't even on my radar, at the moment. I just enjoy watching the process, even if it is different from the way I would likely want to do it myself.

 

[TimothyG]

Last night I had enough time to take a closer look with hands on for parachutes. My plan is to protect the parachutes inside of a tube epoxied to the bulkhead with a slip fit cap. This completely encloses the parachute and nylon shock cord and leaves only the more heat resistant Kevlar out where it's exposed to black powder burning. My problem is that it takes a 3" coupler 7" in length just o hold the fruity chute without the nylon shockcord. Reading up on HED a little, I found that the only justification for putting drogue in main airframe and main in nosecone was a second redundancy in the motor ejection. My drogue parachute with full nylon shockcord will fit easily inside of a section of 54mm bluetube I have here that is uncut and this allows me more room on the bulkhead for charge tubes and possibly a place to put my antenna for the tracker.

You can see the camera cut out (This is the madcow camera set up I'm not the maker or designer just the builder) in the picture at the top. I'm modifying this by having the hood mount to the 3D printed sled on a 3D printed arm that will spring the hood into position once sled is inserted. This will make it possible to only insert the sled in a single orientation. I'll have two nuts pressed into the print that will allow me to bolt the hood into position solidly once sled is inserted to help get rid of vibrations from having a camera floating on a spring.

Fincan has been the biggest demon on my plate and my three options have become more thought out and planned out. This has led me to rearrange them in priority.

• First option is now braising on the fins as this option is the cheapest one present. This also comes with lowest risk of warpage as well as allowing me more freedom in my fin design without added complexity.
  
• Second option is machining a traditional bolt together fincan that I machine from 1" flat stock for the can components and 3/16 flat for the fins. I've machined stuff like this for years so it's sounding more like work and less like learning something new and having fun.
• Third option has the highest learning potential but also the greatest risk of failure and greatest cost. I've made friends with an instructor at school that teaches an entry level casting course in aluminum and he's interested in helping with this project, so I have a teacher. I'd 3D print the fincan in 5 components, one tube, and four fins. Gluing or hotair-welding them together and then casting in investment plaster. Cast the entire fincan as a single component and do final finishing work such as boring and polishing. This option requires I buy PLA printing filament, investment casting plaster, appropriate aluminum for casting, and finishing materials. This is also the slowest to progress option and the one least likely to be realistically finished in time for test launching in april-may.

 

[Steve Shannon]

Another significant reason for breaking the rocket apart midspan is because that’s almost certainly going to ensure instability even if the chute doesn’t make it out, whereas HED (just like single deployment) can and has resulted in stable airframes falling straight downward, resulting in zippers or lawn darts.

 

[TimothyG]

Another significant reason for breaking the rocket apart midspan is because that’s almost certainly going to ensure instability even if the chute doesn’t make it out, whereas HED (just like single deployment) can and has resulted in stable airframes falling straight downward, resulting in zippers or lawn darts.

Problem is that in using HED it doesn't matter if it comes out of the nosecone or airframe in regards to the remaining airframe still being stable. If I break it at the end of the fuselage it's going to be stable and if I pop the nosecone it's still going to be stable. A part of this has me leaning towards going with a larger drogue chute than I normally would. I'm thinking 24"-36" range instead of my current 18".
This is also leading me to ponder having an extra layer of redundancy for the apogee charge. I have the room on the sled and the altimeters.

 

[Steve Shannon]

Problem is that in using HED it doesn't matter if it comes out of the nosecone or airframe in regards to the remaining airframe still being stable. If I break it at the end of the fuselage it's going to be stable and if I pop the nosecone it's still going to be stable. A part of this has me leaning towards going with a larger drogue chute than I normally would. I'm thinking 24"-36" range instead of my current 18".
This is also leading me to ponder having an extra layer of redundancy for the apogee charge. I have the room on the sled and the altimeters.

Right, that’s exactly what I’m saying (airframe stability).
I tend to use very small drogues but I break at the midpoint. The drogue just falls out as long as the airframe separates.

 

[TimothyG]

It's definitely something I'm worried about even more then fin failure or electronics failure. One of the many reasons I'm supper glad to have the opportunity to fly this rocket on J-L motors as much as I want before certifying. Best of all flying on a K motor will give me lots of hang time to watch how the air frame behaves under drogue and how stable it is. This will help me to modify my drogue requirements for when I fly on the baby M motor and then a green M.

 

[blackjack2564]

Alumiweld brazing rods. Mike [if I remember correctly] pre heated the tube by placing on a grill and heating slowly to 400 degrees to prevent distorting tube while brazing the fins on...find his full up report in how to do it..Australian Forum...."Don't Debate This", as I previously mentioned. Full write up on how to do it and his testing method.