That case is a bugger to store isn't it?
Mine is larger than some of the rockets standing next to it in the corner
Mine is larger than some of the rockets standing next to it in the corner
CF Fin attachment
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I might just leave it in the airframe when I'm not working on it.
Do you have one? A 98mm 6XL? I would love to know what you built to fly it in. Is there a thread somewhere? Are you gonna make me search for it?
Yep, there it sits. It'll be used for the 2nd flight of my L3 project. I'll fly for Level 3 on some Red Lightning M or N, and the end goal is to fly it on the O3400 like Nick@Jet's Ultimate QCC Explorer.
Oh hey, did you get the packet of cfd results?
Oh hey, did you get the packet of cfd results?
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Hypersonic, I looked on the Composite Envisions website for spread tow fabric & there were quite a few choices. Could you post a link to the one you used on Pepe? Thanks.
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Wait, you casually mention an O motor? Is this the first you've mentioned your L3 project? This sounds very significant, we need more information! Is it L3 thread time yet?
I'll pm you so as not to derail Hyper's very excellent thread any further than I have
~A
OK, I will wait until you are ready to unveil your L3 project to us.
I'm at work right now, but when I get home I'll look at the cfd results you sent. I will let you know if I need your help understanding anything. Thank you again for doing this! I owe you one!!
You know some of my best work,or ideas about rockets have come to me when I am getting paid for it!!
Hi Greg,
Sure I'll tell you what I used. Like you said, there are many choices of the TeXtreme spread tow fabric available. The one I used may or may not be the best choice for your needs. By doing just a little bit of research (google) you will learn more about tow size, weight (thickness of fabric) modulus (Intermediate, high, or high strength) The price will vary accordingly. I did this research about a year ago, when I bought mine, and I don't remember everything I read. So I don't want to lead you in the wrong direction by misquoting something. This is what I chose to use (remember my application is for breaking speed limits!)
Htpersonic, thanks. I'm grinding/polishing/figuring an 18" telescope mirror and I want to put it on a Dobsonian truss tube mount. I hope to build the mount out of foam/carbon fiber layups to keep the weight down. Not looking for speed, just trying to gather some info.
Merry Christmas To All, and a Happy 2020!!!
I have some more pics of PePe. These are of motor retention and coupling. I remember Cj telling me to pay attention wherever a coupler is used on a stupid fast flight. Usually when Cj talks, I listen. Motor retention is a 4 inch long double walled CF coupler (one slotted and epoxied inside another) made by PML epoxied inside the airframe right after the largest case that will be used in this rocket. (the 98mm CTI 6XL) On top of that coupler there is a .250 inch bulkhead made from solid CF, with nuts epoxied on the back side for the threaded rod to hold e/bay together. In the middle is a .375 inch hole for the threaded rod that goes to forward closure of motor. I'll use a locking nut on top of bulkhead in e/bay to retain motor. On top of that bulkhead will be the 12 inch coupler/ebay (made the same way as the 4 inch coupler) with 6 inches sticking out the top of airframe to couple to payload section. Also there are some pics of the sled that goes in the e/bay, along with the electronics. Nothing is wired yet.
Make a nice stand for your rocket using an office chair base.
Keeps you rocket on display nice and stable.
Keeps you rocket on display nice and stable.
0011001100
A Person
Now that is an idea I want to steal
Me too! And the color even matches! Never thought about that before. Thanks Over The Top!
JohnCoker
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I've purchased C.F. plates from various sources over the years, but there are a couple Amazon sellers that have good products for reasonable prices:
carbon fiber plate
It's not easy to get similar results yourself and I don't think cost effective either.
As far as how much and what kind of joint reinforcement, that's one of those "feel" things that we haven't been able to quantify yet. Theoretically, we should be able to calculate all the forces and the strength of the materials, but we don't have the relevant data and at least I don't have the mechanical engineering knowledge.
FWIW, I've seen 1-3 layers of weave (plain or twill) used for joint reinforcement. I personally have never used more than 1.
carbon fiber plate
It's not easy to get similar results yourself and I don't think cost effective either.
As far as how much and what kind of joint reinforcement, that's one of those "feel" things that we haven't been able to quantify yet. Theoretically, we should be able to calculate all the forces and the strength of the materials, but we don't have the relevant data and at least I don't have the mechanical engineering knowledge.
FWIW, I've seen 1-3 layers of weave (plain or twill) used for joint reinforcement. I personally have never used more than 1.
By making my own plate, or tip to tip, I'm able to use the epoxy of my choice (high temp) along with my choice of fabric, rotating the tows every layer. I agree that my homemade stuff is not made with as much pressure during construction as maybe the Dragon Plate is. Look at the price for 3/16" Quasi-Isotropic high temp CF sheets. I just make mine a little thicker with more layers. Mine is rotated every 45 degrees instead of 90. Will any of this matter? We will see when launch day arrives and its time to light a real fire under PePe. I will be holding my breath with my fingers crossed!!
Andrew_ASC
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Even with engineering knowledge composite structure design is no walk in the park. With basic mechanics materials you have like Mohr’s circle. With composites in advanced mechanics which is like an “optional elective for 4 yr mech students” this Mohr’s circle has stresses in like 9 freaking directions. And throw basic algebra equation out the window they wanted tactic of Elementary Linear Algebra which wasn’t Y=Mx+b slope of line and more like matrices of numerical values and matrix ops (More math or just start using excel spreadsheets.) These along with compressible gas dynamics were more hardcore mech electives for seniors at end of graduating. Some profs joked welcome to the grad course undergrads... I enjoyed compressible flow much more than this composite design stuff.
As far as force loadings hobbyists have tons of motor thrust data etc. The serious issue arises if need of accurate CFD/wind tunnel data arises for aerodynamic forces at higher Mach. The drag coefficient itself is hard to analyze/get for new geometry. Basically when you want to optimize airframe structure thickness for forces. OR may spitball a guessing number that could be close. It’s just a CFD is so much more. 3D models and engineering software plugins professional/educational packages plus enough theory understanding to not Bork your boundary layer/control volumes so it tells you the correct values in the end and simulated at exact Mach ranges the rocket will fly. Oh yeah computer wind tunnels hate large angle of attack changes. Hardest part is Cd varies. That’s just so you can complete your force models and start the structural analysis. Hit a curve shape and just do yourself a favor and throw basic mechanics in trash can resort to computer FEA methods not shown in all undergrad courses.
Theory loves to assume materials are all perfectly uniform and void free. In reality imperfections are everywhere lol. Ultimately it’s throw math at it. Break part in failure testing. Iterations later something works. If you start adding in flutter stuff then there’s entire classes on vibrations and harmonics. Yuk. And just don’t spin stabilize because your gonna add more force components to make life difficult.
/RANT...
I wanna say Burt Rutan learned a lot more from hands on shop experience on composite structures than just theory classes. I’d imagine a lot of it needs very precise processes and quality control to ensure part uniformity and strength.
People that professionally work with composites would be the kinda people we should be asking questions too. Even factory workers. Because I guarantee they have process knowledge we don’t on how to make it better. And sorry if I derailed it a tad.
Yes, this can be done fairly easily with the tools you already have at your disposal, i.e. OpenRocket or RockSim and a spreadsheet. I can point you in the right direction if you're interested but I won't derail this thread with it. Just be confident that most of your intuition, experience, and tribal knowledge are really good enough to cover the vast majority of this hobby.
That part is true. Everything that follows that sentence is just asinine gibberish.
Andrew, at the risk of my words echoing around in the ether and never landing on a willing receptor in your head, I'm going to give you some advice. I've been in the aerospace industry for 22 years as an aircraft structures engineer, and now as a manager of structural engineers. When you apply for engineering jobs in the aerospace industry, I'm the guy across the table from you. When you get a job, I'm the guy you work for, just to give you some perspective on where I'm coming from...
My advice to you is this - use these forums to learn instead of trying to sound smarter than everyone around you. Vomiting out a bunch of words you heard in a class once does not make you sound smart. It makes you sound like an ignorant fool who is scared of math. You might very well be the smartest guy in the room but if nobody respects you or listens to you, then you become a fly that people swat away. Use this forum to learn how to talk to people and simplify things so they understand you, not rant about a bunch of BS that sounds so scary that non-engineers couldn't possibly understand it. You aren't increasing anyone's understanding of the subject matter by spewing that garbage. If you have real knowledge and experience, simplify it before you pass it on. Otherwise, just be seen and not heard.
Engineering structures and materials that we deal with in industry and this hobby is hard. But real engineers use simplifying assumptions to make the hard things easy. They don't rant about "like nine freaking directions". They use a simple loads model to understand the load path then spreadsheets or progressively finer models to calculate the internal forces in every direction. They calculate laminate properites in every ply in every direction and calculate stress and strain in every ply in every direction. When failure modes predicted by the simple analysis doesn't line up with test data, they build more complex finite element models. My team is doing this right now - they're modeling laminates ply by ply and adhesive layers between parts with 3D solid elements at microscopic element sizes to try to design some of the most complex bonded composite structures ever made. And they make it look easy because they're professionals.
You are right about skilled composites workers in that they know the process...but not necessarily how to make it better. They follow the instructions that the manufacturing and process engineers laid out for them. Everything we need to know about the process for hobby pursuits is in that "Properly bonding composites" thread at the top of this forum.
Andrew_ASC
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Optimizing a composite tube wall thickness with math to save weight while retaining structural integrity is not asinine gibberish. There is a lot of math that goes into that. Without force loadings computed you won’t know when the tube fails in theory until you flight test it. You think they just GUESS tubing sizes and composite flaring wall thickness at spaceX!? Let me go laugh more.
There were seven students in the composite structure class and half of us dropped that. Professor was douche. Taught from three different text books and never would accept partial credit making passing likely improbable. Many of those problems had 20 x 20 matrix math. Half of seventeen in compressible flow class failed first exam and never came back. They thought they were dumb. I said bro this is hard sh*t your not dumb. It was designing supersonic wind tunnel systems on paper. I outlied details more of math processes more in depth to analyze those structures than your average hobbyist would ever see or even want. Coker was right about at some point it’s hard to get all the numerical inputs when you don’t know everything to start with.
You can input turbulence data into a FEA. Had an aerospace prof laugh and say good luck knowing the data to input until you’ve tested it. Professionally speaking there’s even cases of wind turbines structurally failing at center of tube and composite aircraft breaking up tail first in flight from composite structural design errors. But go ahead call it gibberish. Rest of the planet calls it engineering.
Rather than flight testing ten thousand different tube wall thicknesses and angled layer combinations somebody else uses more numerical methods to design one first without making it and iterates that design later after manufacturing it from specifications set forth in theoretical design. Revisions are made after testing. As far as building tubes fine, Hobbyists have that down no questions at all. It’s much harder to design said tube especially if you lack force data. That’s why I rant about it.
You can always ignore engineering gibberish. The tube will structurally fail at some force loading in reality. You won’t know what point it fails without math gibberish as you call it until you physically break it. Engineering let’s you better understand when and why things break. Especially mechanical engineering.
There were seven students in the composite structure class and half of us dropped that. Professor was douche. Taught from three different text books and never would accept partial credit making passing likely improbable. Many of those problems had 20 x 20 matrix math. Half of seventeen in compressible flow class failed first exam and never came back. They thought they were dumb. I said bro this is hard sh*t your not dumb. It was designing supersonic wind tunnel systems on paper. I outlied details more of math processes more in depth to analyze those structures than your average hobbyist would ever see or even want. Coker was right about at some point it’s hard to get all the numerical inputs when you don’t know everything to start with.
You can input turbulence data into a FEA. Had an aerospace prof laugh and say good luck knowing the data to input until you’ve tested it. Professionally speaking there’s even cases of wind turbines structurally failing at center of tube and composite aircraft breaking up tail first in flight from composite structural design errors. But go ahead call it gibberish. Rest of the planet calls it engineering.
Rather than flight testing ten thousand different tube wall thicknesses and angled layer combinations somebody else uses more numerical methods to design one first without making it and iterates that design later after manufacturing it from specifications set forth in theoretical design. Revisions are made after testing. As far as building tubes fine, Hobbyists have that down no questions at all. It’s much harder to design said tube especially if you lack force data. That’s why I rant about it.
You can always ignore engineering gibberish. The tube will structurally fail at some force loading in reality. You won’t know what point it fails without math gibberish as you call it until you physically break it. Engineering let’s you better understand when and why things break. Especially mechanical engineering.
WoW!! Way to go guys. Now I feel like a kindergartner playing with tinker toys! I never said once that anything I do can be proven by the numbers. The math involved is WAY over my head! I will NEVER let that stop me from doing anything that I "feel" has a good chance of success. A man must know his strengths and his weakness and rely on help from others when it comes to his weaknesses. I learned a long time ago (from this forum) that you should try and keep it simple stupid. PePe is as simple as Mach1, Mach2, Mach3. Since I've already been to Mach1, I'm going to leave that out. His first flight will be a Mach2, then "IF" things look good enough without any tweaking, he will attempt to go Mach3.
My biggest fear is trying to get the nosecone tip in perfect alignment with the center of the airframe. I think you guys call this "coning". Should PePe develop a spin at Mach3 and my alignment is off even a little, this could be the beginning of the end for PePe. This cork screwing effect will stress the fins to there breaking point, and I don't need numbers to tell me that. Even a few degrees of AoA at these speeds could be the end.
So how do I get my couplers in the airframe and in the nosecone to be as straight as possible, so when I check the runout at the nosecone tip, when spinning the airframe in a lathe or on rollers, it will be as small as possible?
I never said once that anything I do can be proven by the numbers. The math involved is WAY over my head! I will NEVER let that stop me from doing anything that I "feel" has a good chance of success. A man must know his strengths and his weakness and rely on help from others when it comes to his weaknesses. I learned a long time ago (from this forum) that you should try and keep it simple stupid. PePe is as simple as Mach1, Mach2, Mach3. Since I've already been to Mach1, I'm going to leave that out. His first flight will be a Mach2, then "IF" things look good enough without any tweaking, he will attempt to go Mach3. My biggest fear is trying to get the nosecone tip in perfect alignment with the center of the airframe. I think you guys call this "coning". Should PePe develop a spin at Mach3 and my alignment is off even a little, this could be the beginning of the end for PePe. This cork screwing effect will stress the fins to there breaking point, and I don't need numbers to tell me that. Even a few degrees of AoA at these speeds could be the end.
So how do I get my couplers in the airframe and in the nosecone to be as straight as possible, so when I check the runout at the nosecone tip, when spinning the airframe in a lathe or on rollers, it will be as small as possible?
You're doing fine. Those tip to tip plies forgive a lot of sins if everything else is straight.
Centerless grinding is probably the best way to get a round straight coupler, but you may not be able to have that done on a short tube section. In that case, chucking it in a lathe may be the best bet, but wait and see if anyone else has a better idea first.
Centerless grinding is probably the best way to get a round straight coupler, but you may not be able to have that done on a short tube section. In that case, chucking it in a lathe may be the best bet, but wait and see if anyone else has a better idea first.
Please keep in mind that Andrew is the kid who zip tied a bunch of electronics to a sled and called it good. Among other construction atrocities.
Moving on, I think the issue with doing any meaningful analysis is the variation in technique and ability. In the absence of ovens and autoclaves, emperical evidence rules. Not mechanical engineering, but mechanical imagination. You can throw all the math you want at it you want, but none of it will apply if your technique is bad.
So Hypersonic, you're definitely not a kindergartner playing with tinker toys. Your technique is sound. You've got a rocket that probably really can go Mach 3. It's also dang near a work of art.
As far as centering the nose tip in the rocket, others have made jigs that held everything straight with tip centered. Jim Jarvis also has a pretty novel method for squaring the ends of tubes. He also does a pretty good job of emphasising the importance of square tubes, if I remember correctly. I'll try and find some examples in the morning. I've got them all saved somewhere.
Moving on, I think the issue with doing any meaningful analysis is the variation in technique and ability. In the absence of ovens and autoclaves, emperical evidence rules. Not mechanical engineering, but mechanical imagination. You can throw all the math you want at it you want, but none of it will apply if your technique is bad.
So Hypersonic, you're definitely not a kindergartner playing with tinker toys. Your technique is sound. You've got a rocket that probably really can go Mach 3. It's also dang near a work of art.
As far as centering the nose tip in the rocket, others have made jigs that held everything straight with tip centered. Jim Jarvis also has a pretty novel method for squaring the ends of tubes. He also does a pretty good job of emphasising the importance of square tubes, if I remember correctly. I'll try and find some examples in the morning. I've got them all saved somewhere.
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Thank you for the kind words! If you guys see anything that looks wrong to you, I'm hoping you will say something, as I know that most all of you have flown more flights than me. I may be a speed junky, but that makes it more of a challenge to me. If it wasn't challenging enough, I probably would not be doing it. And with all of you watching my back sort of speak, I like my odds!
I've read lots of things from Jim J over the years, but I need to read them again to refresh my memory. I think he used a laser level if I remember right to square tubes up. I also need to reread his paper on burning BP at altitude. I remember some stuff, but not everything. I had this thought about maybe substituting a different oxidizer than BP uses, to reduce the effect of less pressure on burning rate or heat transfer between the particles. Maybe even a different fuel. I'm no chemist, but it's something to think about. I would imagine if there was a better composition than BP at altitude, somebody would have thought about it by now.
If you find some of Jim's stuff, point me in the right direction so I can reread them. I always loved the look of his TooCarbYen! And Thank You again.
JimJarvis50
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Thanks HyperSonic. Looks like it's been over three years since the links were posted, so here is one set of them (for Part 1 and Part 2). The laser level method is in Part 2, and it's still how I do it.
https://www.raketenmodellbau.org/repository/archive/167792?view=true
https://www.raketenmodellbau.org/repository/archive/167793?view=true
The high altitude BP method is attached. The only thing I would add to that method is to put the ematch on top of the powder instead of underneath of it. That helps for larger charges. Also, look for Tony's version of this method.
Jim
Thank You Jim!
Hello everyone,
It has been a while since I posted anything here, so I want to bring you up to speed on things. I know a lot of you are waiting to see if I launched PePe yet. My plan was to launch him at Airfest this year. Then came the Covid and life has changed. PePe will have to wait until next year to fly. I have most of the harder stuff done and ready to go, like the fins, the tower, all the electronics are ready to be tested. I will take some pics of the chute cannon, my double barrel shotgun ejection at apogee method, (thats just what I call it) in the next couple of days.
I want everyone to know that when PePe finally does fly, I will post all the data from many different systems here on TRF. (thats if he doesn't shred!) I have learned so much from all of you and I want to give back. There will be a Marsa54, Raven 4, Telemega, BRB GPS, and a GO Pro shooting at 1080P at 60 fps. There's also a RDF beacon that pulses every couple of seconds.
When the time comes to fly the 5800, I may have to go to BALLS because RASAero 2 puts it close to 50k. I'm not sure on the exact final weight of rocket and built motor. I'm guessing the CTI N5800 complete motor weight is 33 pounds (from thrustcurve) and the rocket weight at 14 pounds.
It has been a while since I posted anything here, so I want to bring you up to speed on things. I know a lot of you are waiting to see if I launched PePe yet. My plan was to launch him at Airfest this year. Then came the Covid and life has changed. PePe will have to wait until next year to fly. I have most of the harder stuff done and ready to go, like the fins, the tower, all the electronics are ready to be tested. I will take some pics of the chute cannon, my double barrel shotgun ejection at apogee method, (thats just what I call it) in the next couple of days.
I want everyone to know that when PePe finally does fly, I will post all the data from many different systems here on TRF. (thats if he doesn't shred!) I have learned so much from all of you and I want to give back. There will be a Marsa54, Raven 4, Telemega, BRB GPS, and a GO Pro shooting at 1080P at 60 fps. There's also a RDF beacon that pulses every couple of seconds.
When the time comes to fly the 5800, I may have to go to BALLS because RASAero 2 puts it close to 50k. I'm not sure on the exact final weight of rocket and built motor. I'm guessing the CTI N5800 complete motor weight is 33 pounds (from thrustcurve) and the rocket weight at 14 pounds.
