98mm Min Dia L3 Build

[A5tr0 An0n]

CCotner and I trusted RASAero which declared that Bare Necessities would always have at least 2 calibers of stability... OpenRocket predicted 0 calibers of stability >M4.2. It went unstable.

Since the cat is out of the bag lol… I am primarily using OR… and I mean mostly using it. I am only using RASaero for a cross reference. I actually have your OR file and have play around with it. IMO the vehicle was unstable for that type of velocity. The CP most been moving fast towards your CG at that velocity. It is a shame that the vehicle went unstable… you guys did such a great job! I hope you are going to give it another go? I am sure you will be successful the next time around.

 

[CarVac]

Since the cat is out of the bag lol… I am primarily using OR… and I mean mostly using it. I am only using RASaero for a cross reference. I actually have your OR file and have play around with it. IMO the vehicle was unstable for that type of velocity. The CP most been moving fast towards your CG at that velocity. It is a shame that the vehicle went unstable… you guys did such a great job! I hope you are going to give it another go? I am sure you will be successful the next time around.

Maybe we will eventually. It needs a new fincan but the front end is still in good shape. Probably four thinner fins of the same dimension, since 1/4" was way overkill, would help maintain the altitude. The fincan itself could be an inch shorter, helping reduce the mass gain.

But of course now we have new jobs so taking a long trip to Black Rock isn't so easy. Next year, perhaps. We'll see; I do want to do it as well.

 

[CCotner]

Astro Anon, very, very interesting. Of course, I wish you the best of luck in all your endeavors. I'm impressed by the amount of initial, up-front planning and thinking ahead problem solving you've done. I haven't looked through your posts yet-not in great detail, just a quick read-through-but I hear you talking about all the things that I, in my limited experience, think you should be.

I would guess that by relying on RASAero alone, we pushed our design configuration into a corner where RASAero wasn't as accurate as it claimed to have been. If you want, PM me/CarVac and we can share the data files from our instability and our analysis of the departure, they might be useful to you.

For survival, weight is your friend-the heavier it is, even if it lowers max-V to mach 3.5 instead of 4, will make a big improvement in your chances. On that note, I'd highly, highly recommend certifying with this rocket on an N2540 Green3, or another slow N, instead of the 5800-you're much more likely to get it back, and you'll have more confidence in the recovery system and thermal protection going into the N5800 flight. On the other hand, big motors are very, very expensive, so I completely understand wanting to do it all at once-it's what CarVac and I did, after all.

I'm pretty busy right now finishing up my MS.E degree on Wednesday (other than finals), and I am traveling from Thursday through Monday, and then moving to LA to start work in June. But in the meantime I'll try to find a chance to read through your plan more thoroughly and see if I have anything helpful to add.

It's going to be an adventure! Remember to have fun on it! =)

 

[MClark]

Your sim shows over 50K-- remember it must be run through the TRA class 3 committee,
If you are launching at BALLS you will be at 2000' due to bad track record of N5800 flights.

M

 

[CarVac]

If you are launching at BALLS you will be at 2000' due to bad track record of N5800 flights.

M

A good idea.

Bare Necessities's motor core sampled ~1200 feet from the pad, IIRC. Somewhat closer to the flight line than the 1000-foot M and N pads.

 

[A5tr0 An0n]

Maybe we will eventually. It needs a new fincan but the front end is still in good shape. Probably four thinner fins of the same dimension, since 1/4" was way overkill, would help maintain the altitude. The fincan itself could be an inch shorter, helping reduce the mass gain.

But of course now we have new jobs so taking a long trip to Black Rock isn't so easy. Next year, perhaps. We'll see; I do want to do it as well.

I did not realize that your fins were 0.25" thick. That is understandable… well I hope you get to give it another go soon. I think it goes without saying, be sure to document it here on the forum!

Astro Anon, very, very interesting. Of course, I wish you the best of luck in all your endeavors. I'm impressed by the amount of initial, up-front planning and thinking ahead problem solving you've done. I haven't looked through your posts yet-not in great detail, just a quick read-through-but I hear you talking about all the things that I, in my limited experience, think you should be.

I would guess that by relying on RASAero alone, we pushed our design configuration into a corner where RASAero wasn't as accurate as it claimed to have been. If you want, PM me/CarVac and we can share the data files from our instability and our analysis of the departure, they might be useful to you.

For survival, weight is your friend-the heavier it is, even if it lowers max-V to mach 3.5 instead of 4, will make a big improvement in your chances. On that note, I'd highly, highly recommend certifying with this rocket on an N2540 Green3, or another slow N, instead of the 5800-you're much more likely to get it back, and you'll have more confidence in the recovery system and thermal protection going into the N5800 flight. On the other hand, big motors are very, very expensive, so I completely understand wanting to do it all at once-it's what CarVac and I did, after all.

I'm pretty busy right now finishing up my MS.E degree on Wednesday (other than finals), and I am traveling from Thursday through Monday, and then moving to LA to start work in June. But in the meantime I'll try to find a chance to read through your plan more thoroughly and see if I have anything helpful to add.

It's going to be an adventure! Remember to have fun on it! =)

Thank you very much! That was a very thoughtful post and I would look forward to your input when you get the chance. I hope you and CarVac's jobs are as fun as building rockets!

One a more serious note I have tried to identify other failures in the past and design a vehicle to deal with it and hopefully overcome it. Still will need the help of the forum though! I do believe that this build is not something to take lightly. I feel the adventure coming on already. I will shoot you a pm for some of that data. It will be very valuable to me and this build.

 

[gtm3323]

:eyeroll:



op:

good luck!

 

[A5tr0 An0n]

Your sim shows over 50K-- remember it must be run through the TRA class 3 committee,
If you are launching at BALLS you will be at 2000' due to bad track record of N5800 flights.

M

On that matter, I do believe you are one of the folks that is involved in the operations at BALLS? Do you have any advice in how I need to go about the TRA class 3 committee? Is it just a matter of filling out the form? This is my first time going to BALLS and I apologize if this seems blatantly obvious.

I think being 2kft back is smart… I don't think I want to be so close to it once it lights

 

[CarVac]

On that matter, I do believe you are one of the folks that is involved in the operations at BALLS? Do you have any advice in how I need to go about the TRA class 3 committee? Is it just a matter of filling out the form? This is my first time going to BALLS and I apologize if this seems blatantly obvious.

I think being 2kft back is smart… I don't think I want to be so close to it once it lights

The motor isn't so scary, but rather the rain of parts. I would have been happy to be closer to BN but logistics dictated that we be on the flight line.

 

[A5tr0 An0n]

:eyeroll:



op:

good luck!

Nice to meet you too Gerald lol and congrats on your successful N5800 attempt!

Thanks.

 

[MClark]

On that matter, I do believe you are one of the folks that is involved in the operations at BALLS? Do you have any advice in how I need to go about the TRA class 3 committee? Is it just a matter of filling out the form? This is my first time going to BALLS and I apologize if this seems blatantly obvious.

I think being 2kft back is smart… I don't think I want to be so close to it once it lights

I have been the BALLS launch director since 1998.
Fill out the form, send everything you have on the rocket and materials, previous experience with similar rockets. They will contact you and ask questions/ request other info.
Send as soon as you can, I think there is a 30 day cut off. No class 3 approval= no launch.

M

 

[A5tr0 An0n]

I have been the BALLS launch director since 1998.
Fill out the form, send everything you have on the rocket and materials, previous experience with similar rockets. They will contact you and ask questions/ request other info.
Send as soon as you can, I think there is a 30 day cut off. No class 3 approval= no launch.

M

That is a pretty awesome gig you've got there. I take it you live close to Black Rock? Wish I did…

Yes I see there is a 30 day cut off. I will make it for sure before that. I will till the vehicle is more underway. Thank you very much for the advice Mark! I look forward to meeting you out there.

Mat

 

[A5tr0 An0n]

Updates:
Seeing as pictures are worth a lot of words… or at least to some.

​

is the completed NC. Both the NC and shoulder are G10 FG; the NC has black dye in it and not graphite. [Middle] I have not yet permanently bonded the shoulder to the NC yet. I will finish the design on the internal bays and recovery and then cut down the should. I am thinking the shoulder will ultimately be ~10" in length.

​

Note this is left over material from the cut of the shoulder tube; I am only using it to show the wall thickness (~3mm).

​

is the completed AF. It is FWCF and ~66" in length. [Middle] Here you can see the mock fin design. There is one last thing I have to do with the fins before they are final… but +/- a little, that is what they will look like.

​

This shows the thickness of the AF (~3mm). This entire rocket is reinforced per se, so I do not expect it to "buckle," under force.

Note:
*These parts have not received their baths yet. I just thought I would throw that out there.



More to come soon….

Mat​

 

[MarkH]

Where are you sourcing the thick walled tubing? The common performance rocketry/ proline tubes have only 0.06 inch (about 1.5mm) thick walls.

 

[dixontj93060]

Where are you sourcing the thick walled tubing? The common performance rocketry/ proline tubes have only 0.06 inch (about 1.5mm) thick walls.

Performance Rocketry has this as an option on their 98mm tube size.

 

[babp1011]

Also on a sourcing note, where were you able to get a 6:1 FWFG nosecone? The only one I was aware of that was 6:1 was from shockwave, but theirs aren't fiber wound.

 

[MClark]

That is a pretty awesome gig you've got there. I take it you live close to Black Rock? Wish I did…

Yes I see there is a 30 day cut off. I will make it for sure before that. I will till the vehicle is more underway. Thank you very much for the advice Mark! I look forward to meeting you out there.

Mat

It is about 800 miles to Black Rock, Phoenix area

M

 

[butalane]

...

Note: I also considered 4 fins, btw.

Cool project. Good luck!



Maybe consider it some more?...

Jeroen

+1.

 

[CCotner]

Hahaha I love the subtle hinting toward 4 fins =)

I'll try to summarize this, but it is in no way my area of expertise and I may be wrong; feel free (butalane or Jeroen another) to correct me.

Rigid-body dynamics is the field of study of the motion of 'rigid' bodies; you stop assuming nice symmetries that lead to things like moments of inertia being a number instead of a tensor. three fins, while symmetric enough to ensure good flight characteristics, has more complicated inertial behavior coming from an inertia tensor with more cross terms that are non-zero-I think? I was hoping to take a class on it, but USC, amazingly, didn't offer one. Basically, proper tensor-based motion analysis leads to interesting and unanticipated behaviors and instabilities that don't show up with a simple static "CP-CG" kind of stability check, like coupling between pitch and yaw on an aircraft (or the rocketry equivalent of pitch-roll coupling). It is plausible to me, without understanding the details very well yet, that 4 fin rockets have neater inertia tensors and therefore show fewer troubling behaviors.

If/When CarVac or I or both of us together refly BN, it will have 4 fins instead of three. They will be thinner, closer to 3/32" thick; and they will probably be composite fins with metallic leading-edge inserts, still compression-mounted and pin-mounted in an aluminum 'can.

I like what I see-double-thick AF tube, double-thick full-length shoulder, for redundant loadpaths... everything looks right so far. Have you thought about thermal protection for the nosecone?

 

[CarVac]

Rigid-body dynamics is the field of study of the motion of 'rigid' bodies; you stop assuming nice symmetries that lead to things like moments of inertia being a number instead of a tensor. three fins, while symmetric enough to ensure good flight characteristics, has more complicated inertial behavior coming from an inertia tensor with more cross terms that are non-zero-I think?

Going from two to three fins wouldn't mess up the inertia tensor; you can always pick a linear transformation (rotation of the axes, in particular) which will diagonalize the tensor. Even on a 3-finned rocket, those axes would still be lined up with the body.

However, it's almost certainly something in the forcing: nonlinearities that enable stable oscillatory modes such as dependence of the normal coefficient on the roll angle relative to the angle of attack. A linear system is ALWAYS either statically stable or divergent, but nonlinear systems can oscillate stably.

I'm unable to do the fluid dynamics computations which would show what these forcing functions are, but I'm certain that that is the problem.

 

[grouch]

Not being classically educated in the matter, I would pick 4 over 3 fins based one two factors. First, the bulk of the go fast sounding rockets use 4 not 3. Secondly, many have tried 3 and failed. I tend to model "copy" what has worked in the last then go from there. It will be years before I am the position to try a flight like this if ever but of the time does come, the rocket will be loosely based off the D region Tomahawk.


Sent from my iPhone using Rocketry Forum

 

[g zilla]

What would a N-10,000 sim to

 

[botscott08]

What would a N-10,000 sim to

Considerably lower altitude and velocity since its half the impulse of the N5800.

 

[performancerocketry]

Where are you sourcing the thick walled tubing? The common performance rocketry/ proline tubes have only 0.06 inch (about 1.5mm) thick walls.

We will make almost anything custom, custom wall thickness thin - thick and custom nosecones filament wound in almost every size and shape. You pick your material fiberglass and/or carbon and temp rating. We also manufacture a full line of Carbon Fiber Sheet - High Temp rating and made from high end Boeing Carbon used in the 787.

Contact Gary T at [email protected] for pricing.

Thanks
Curtis

 

[G_T]

Hmmm, I'm going to have to contact you on that one for a project of mine.

Gerald

 

[GaryT]

As Curtis pointed out almost anything is possible, just shoot me and email or give me a call and we'll see what we can do. Matt and I have been talking for about a year now on his project, can't wait to see it fly.

Thanks again Matt, Gary T.

 

[botscott08]

I'll vouch for Curtis and the quality of his custom work. He made me a whole bunch of fantastic parts and everything fit dead nuts.

 

[A5tr0 An0n]

I have been busy lately, hence the delayed responses. As the airframe and NC are done, I am focusing all my attention on another 1/2 way done project and the epoxy testing. This must be complete before I even begin to think about attaching the fins. I might some time this week or next build the payload section and machine the retainer.

Where are you sourcing the thick walled tubing? The common performance rocketry/ proline tubes have only 0.06 inch (about 1.5mm) thick walls.

Also on a sourcing note, where were you able to get a 6:1 FWFG nosecone? The only one I was aware of that was 6:1 was from shockwave, but theirs aren't fiber wound.

I had them both custom made from PR.

I'll vouch for Curtis and the quality of his custom work. He made me a whole bunch of fantastic parts and everything fit dead nuts.

I have had the same experience.

 

[A5tr0 An0n]

Hahaha I love the subtle hinting toward 4 fins =)

I'll try to summarize this, but it is in no way my area of expertise and I may be wrong; feel free (butalane or Jeroen another) to correct me.

Rigid-body dynamics is the field of study of the motion of 'rigid' bodies; you stop assuming nice symmetries that lead to things like moments of inertia being a number instead of a tensor. three fins, while symmetric enough to ensure good flight characteristics, has more complicated inertial behavior coming from an inertia tensor with more cross terms that are non-zero-I think? I was hoping to take a class on it, but USC, amazingly, didn't offer one. Basically, proper tensor-based motion analysis leads to interesting and unanticipated behaviors and instabilities that don't show up with a simple static "CP-CG" kind of stability check, like coupling between pitch and yaw on an aircraft (or the rocketry equivalent of pitch-roll coupling). It is plausible to me, without understanding the details very well yet, that 4 fin rockets have neater inertia tensors and therefore show fewer troubling behaviors.

If/When CarVac or I or both of us together refly BN, it will have 4 fins instead of three. They will be thinner, closer to 3/32" thick; and they will probably be composite fins with metallic leading-edge inserts, still compression-mounted and pin-mounted in an aluminum 'can.

I like what I see-double-thick AF tube, double-thick full-length shoulder, for redundant loadpaths... everything looks right so far. Have you thought about thermal protection for the nosecone?

That is interesting… I need to see data on that, perhaps I will take that class with you. It still seems to me (with my current understanding) that this is only a "necessity," for flights maybe M4+. That statement is not based on nothing other than my opinion; I just like being able to have slightly smaller fins and thus reducing the aero loads they will be subject to. Like CarVac said, with 3 fins they have to substantially get "bigger," to become more effect. Although still true with 4 fins per se it is not as substantial.

Now I am building this rocket slightly different (duh), but what I mean is that I have a preliminary design and that I will build the vast majority of the vehicle before attaching the fins. This will allow me to accurately measure the dimension and the mass of the vehicle, thus allowing me to "optimize," my fin design for this flight. I have not given up on the 4 fins, but still am leaning towards 3 fins for this flight.

The nosecone has been cured to withstand up to 600F, that with High temp paint (similar to Nic's paint on Mad Max) I was thinking I do not need anything else. His held up extremely well, yes he had a lot of paint burn of under his Al tip, but he also used a extra material with a lower Tg after the Al tip. Even if the paint still burns right below the Al tip (which it will) the material underneath it is good for 600F and in my mind have no problem for those few seconds. It only needs to survive once…. maybe twice (after care of course).

Not being classically educated in the matter, I would pick 4 over 3 fins based one two factors. First, the bulk of the go fast sounding rockets use 4 not 3. Secondly, many have tried 3 and failed. I tend to model "copy" what has worked in the last then go from there. It will be years before I am the position to try a flight like this if ever but of the time does come, the rocket will be loosely based off the D region Tomahawk.


Sent from my iPhone using Rocketry Forum

I would argue that most of the failures on this motor failed not because of the use of 3 fins but because of a lack of understanding on the CP shift on higher velocity flights thus leading to instability. That and the coupled NC and/or AF areas give out. I see those 2 reasons being the most common. I could be wrong. On a flight like this there are many things that can go wrong quickly and without an actual thorough investigation, we may not truly understand what is the root initiating cause of failure. Have fins fluttered on the N5800 MD flights, yes. Have fins survived a N5800 flight, yes. One thing I will say though and is what has kept me up thinking is even if the fins did not fail first, that does not necessarily mean they were not about to fail. For example, the instability or weak coupler section could of gave first, but would the fins have failed if those first did not?

 

[A5tr0 An0n]

UPDATE:
I have since updated the DD section of this thread (under the picture). Still need to make the CADs for it. I am mostly working on the experiments for the best fin attachment method. This can be found here https://www.rocketryforum.com/showthread.php?65106-Battle-of-the-Epoxies-A-Road-to-BALLS-Experiment. Therefore this thread will remain a little action free until the fin attachment methods are sound. In the mean time I plan on working on the electronics for this flight and will post that once finished. Once the fin attachment experiments and the NC payload are finished I will then refine the fin design and proceed to work on them. The reason for this is that it allows me to take into account all the actual measurements and the mass of the components, thus allowing me to incorporate the best fins for this flight.

Mat

Fins fins fins. If you have sufficient thickness, I don't think flutter and material strength is an issue anymore, but rather you need to focus on attachment.

As of right now, no minimum-diameter N5800 has successfully (or semi-successfully, either) flown that had all-epoxy fin attachment: Don't Debate This had a brazed fincan, Kari Pill and Bare Necessities had all-aluminum fincans (the latter of which survived corkscrewing at M4), and Mad Max had aluminum fin brackets bolted to the airframe from the inside.
Project60K in 2012 didn't use any tip-to-tip, but their fins' bonds exceeded the peeling strength of the FWCF airframe.

I must admit that I have been toying around with the idea of using metal brackets in addition to the large carbon reinforced fillets and possible t2t. However I am not totally convinced to there usefulness. From my quick thoughts, it seems that these brackets (under the large fillets) are not under any load during the flight and therefore are extra unneeded mass. Now if the fillets fail then the brackets are under load. I think at this point in the flight the forces will be so strong that the brackets will be useless. This thought has kept me from wanting to use them. Any thoughts here guys?

It seems brackets may increase the pull strength but not prevent flutter (since that is dependent on the natural resonance of the fin material or mixtures there of). I do not think flutter will be an issue and I am more concerned with the adhesion strength of the fillets.