I read my ER mag yesterday and it talked about reinforcing balsa for large rockets, instead of using G10. I am in the planning/designing stage of a 29mm minimum diameter rocket, max I can go on fin thickness is 1/8" (max for PML dado slots). My preliminary rocksim file with .063" G10 fins is well below the optimal weight and that is fine, with this rocket I am going for high speed/acceleration liftoff's, doesnt even have an alt and it will be out of sight so I am not worrying about that, so going with balsa or plywood would be a much lighter option. I have some 1/8" balsa but the grain is running in the wrong direction for these fins (right triangular fins, about 6"s long and with a span of 1"). I found some 1/8" plywood, what do you think about using that? I was thinking about doing a layer of 3oz glass to the wood itself, then cutting the fins out, and last would be some heavier glass that would go from tip to tip (reinforces the fins but is mostly for the surface mounted joint)... could I use wax paper on either side of the wood? What type of wood would you recommend for the core? Remember, the lighter the better... I am also trying to reduce weight so that the coast time is lower, right now it is 1 second longer then the 14 second optimal delay of the AT 29mm motors. Thanks
extreme rocketry fin fabrication?
- Thread starter jraice
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One problem you may have with using hobby-store sheet balsa as your core material, is that the grain runs in the wrong direction.
In order to attain maximum compressive strength, the grain of the wood must run *through* the sheet... rather than with it. This is called 'End-Grain' balsa... a couple of composite shops stock it in 1/8" to 1/2" thicknesses.
For a first attempt, I'd suggest using plywood. Add a couple of layers of fiberglass to a 3/32" plywood sheet, and see how strong it is.
Good luck with your efforts.
In order to attain maximum compressive strength, the grain of the wood must run *through* the sheet... rather than with it. This is called 'End-Grain' balsa... a couple of composite shops stock it in 1/8" to 1/2" thicknesses.
For a first attempt, I'd suggest using plywood. Add a couple of layers of fiberglass to a 3/32" plywood sheet, and see how strong it is.
Good luck with your efforts.
I want thinner, 1/32" or 1/64" if I go with plywood (probably will)... then several layers of 3oz glass (one at a time or all?) and then after the fins are attached to the rocket they will have a heavy tip to tip glass, thanks for the info, keep the info coming! I am saying the above info after reading about dynastar glassing 1/64" wood for a 29mm bird... going to the wood store today so I will feel everything and make a decision.
afterburner
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I have used the "balsa core with fiberglass reinforcement" method several times. I am currently building an 6 inch upscale Quark and the fins are made of 0.375" balsa laminated with carbon fiber.
This method will produce very strong and rigid fins if done the right way. To put it simply, the rigidity of this setup is greatly based on the thickness of the fin. For thin fins you best bet is to go with G10.
I tried to laminate 1/8 inch balsa and I was very disappointed with the results. It turns out the rigidity of a laminate is proportional to the cube of the thickness. In other words, the same laminating technique on a 3/8 inch balsa core Vs an 1/8 inch balsa core will result in 27 times the rigidity.
So if your project requires fins that are 1/32 inch thick I would say stay away from balsa core and go straight to G10 or even solid carbon fiber plates from a supplier like Aerospace Composite Products ($$$).
Just my 4.5 cents
This method will produce very strong and rigid fins if done the right way. To put it simply, the rigidity of this setup is greatly based on the thickness of the fin. For thin fins you best bet is to go with G10.
I tried to laminate 1/8 inch balsa and I was very disappointed with the results. It turns out the rigidity of a laminate is proportional to the cube of the thickness. In other words, the same laminating technique on a 3/8 inch balsa core Vs an 1/8 inch balsa core will result in 27 times the rigidity.
So if your project requires fins that are 1/32 inch thick I would say stay away from balsa core and go straight to G10 or even solid carbon fiber plates from a supplier like Aerospace Composite Products ($$$).
Just my 4.5 cents
What about very thin plywood? So you think I should go with 1/16" G10 and no glass or a very thin G10 with some glass reinforcement (going for minimum weight...). I was thinking 1/64" or 1/32" plywood reinforced with glass.
KermieD
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A) Why would you glass before cutting the fins out? You can get just as good a layup with cut fins and it's much easier to cut. Besides, with a min diameter 29mm rocket, you're looking for performance, so you're going to have some considerable airfoiling on your hands anyway which will mostly negate a preshaping layup.
B) Uhhh...ok...no alt, out of sight flight...do you have a radio transmitter for this or are you considering this a disposable rocket? You're really going to want to look at an alt, even if your goal is merely causing whiplash from the launch velocity.
B) Uhhh...ok...no alt, out of sight flight...do you have a radio transmitter for this or are you considering this a disposable rocket? You're really going to want to look at an alt, even if your goal is merely causing whiplash from the launch velocity.
The alt would just make the prep of the rocket take much longer, yes it has a RF HAM radio tracker onboard. My goal is to build a rocket that can be easily preped (motor ejection) and still have the enjoyment of extreme speeds, mile high flights and costs under $20 per flight... I have a K flight and a complex L flight planned for may and want something on the cheap side but still with some serious fun. I plan on glassing the "core" then cutting out the fins, after the fins are attached to the body tube and there are fillets in place I will tip to tip glass them (airfoilded before body tube attachment). Nomatter what I will have to order the core online (lumber store has no plywood smaller then 1/8") so what would you recommend for a strong, lightweight core material that will be no larger the 1/8" thick after laminating? How many layers of 3oz would you apply before cutting the fins out (heavier layer from PML will be used for tip-tip glassing)? Thanks
Mcmaster has some G10 1/32" thick, but something cant be right, it is showing the 1/32" G10 has the same tensile strength as 1/8" G10... how can this be? So should I go with the 1/32" G10? It is only $2 for a 6" by 6" piece and for these small fins that is all I will need. There are so many options, I just cant seem to find which is best, if you wanted to make strong, but VERY light fins, how would you do it? What thickness of G10 would you use if you were not going to use any glass at all? I am attaching the fins similar to the way the cirrus dart's fins are attached, with a dado slot, with a small 29mm rocket on maybe an H268R will any tip to tip glass be needed to keep them attached to the rocket? I am thinking it might be best, and easiest, to just use G10, and have one layer of 3oz glass tip to tip, just to hold the fins on, that would be very strong and the 3oz glass would not add a ton of weight. The fins have a very small span so I dont think they need to be super strong, 1/16" G10 is probably overkill...
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I just got done building a 29mm min dia rocket. I played around with various fin materials..looking for the thinest/strongest. I had some .033 G10 that I put one layer of carbon fiber on each side..they came out about .060 thick. and are very strong. The body tube is two layer of carbon fiber. One problem with all this high tech stuff is now my optimal weight is to low..they rocket ready to fly with electronics less motor was just over 8 oz..which is good for the I69 ellis motor but I needed to place a 7 oz weight to bring it up to optimal mass for the H268. Took some doing to get all this stuffed into a 26.5" rocket.
Tony
Tony
Wow, that is pretty short, I was thinking about doing a 36" tube (10" transmitter bay, room for recover stuff and an EM I69) with the PML cone. So do you think maybe a G10 inbetween the .063" and the .033", plus the tip to tip glass would be pretty good? Thanks...
edwardw
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Jordan,
The tensile strength of a material is in lbs/in^2. So G10 of any thickness (as long as they are the same spec G10) is the same. To determine the strentgh of the material - you need to know how many in^2 you are. So - if you are using it as a fin - you have a shear plane that the force is acting on. Usually the thickness of the G10 times length of the root of the fin gives you in^2. Then you multiply the tensile strength by the area (in^2) and you will get a number. That will tell you how much force you can apply to the joint before it fails.
Edward
The tensile strength of a material is in lbs/in^2. So G10 of any thickness (as long as they are the same spec G10) is the same. To determine the strentgh of the material - you need to know how many in^2 you are. So - if you are using it as a fin - you have a shear plane that the force is acting on. Usually the thickness of the G10 times length of the root of the fin gives you in^2. Then you multiply the tensile strength by the area (in^2) and you will get a number. That will tell you how much force you can apply to the joint before it fails.
Edward
dbarrym
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FWIW I have made any number of balsa (and honeycomb) cored FG and CF parts, if you have access to a decent table saw, making end grain core sheets is not too difficult. I use a thin kerf formica saw blade to cut the end grain 'slices" from a 6" to 8" square balsa blocks.. no need to glue the slices together, just cut to fit the necessary shape and assemble over your composite layup base like a jigsaw puzzle.
FWIW my method for making flat surface laminates (fins, bulkheads, and the like) is to wet lay out the inner/outer composite cloth on waxed 3/16" glass sheets and 'assemble' the honeycomb or end grain balsa on one side, then lay the other glass sheet/composite side over the core and insert into a vacuum bag.
You can also make airfoil shaped fins and flying surfaces by shaping the core as needed and using precut Mylar sheet (about .015 to .04" depending on the size of the surface and amount of curvature) to lay up the composites. Just need to be careful to not introduce any warps while pulling the vacuum or while it is curing - I wire-cut foam "beds" to lay them in and weight the bed/part/bed sandwich down on a flat concrete floor while curing.
Barry
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You want the fins to be as thin as you can get them to reduce drag. The fin design will also effect how strong (thickness wise) the fin needs to be. Nike style fins are hard to make thin becasue of the short cord and longesh spans. Your 'tip to tip' glassing will also an strength to the fin. I used 3 layers for tip to tip glassing but in a weird way. The tips of the fins do not need to be as strong (thick) as the root cord. So I place a very narrow strip of glass on top of my carbon fiber filet. The next layer runs up the fin about 2/3 of the way to the tip. and maybe about halfway around the body tube..the last and top layer does go tip to tip and ties everything together. the filets and all 3 layers are all done at the same time so that there are no 'cold' joints. Layering it like this also make sanding easier becasue the layers are under each other. I use system three T-88 epoxy that I can thin with denatured alcohol. so far this method hase held up to mach 1.98.
So to answer your question as to what thickness G10 you should use. I'd go with the thin stuff..cut out the fins..flex it in your hand and see what it feels like..if it's to weak..maybe a thin layer or two of extra glass or carbon will make it perfect
So to answer your question as to what thickness G10 you should use. I'd go with the thin stuff..cut out the fins..flex it in your hand and see what it feels like..if it's to weak..maybe a thin layer or two of extra glass or carbon will make it perfect
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here's the 29mm min dia rocket..close to being done.
Tony
Tony
How long is that tube CF tube? I am thinking the 1/32" CF might be a good start for the fins, then some glass... the span is VERY small so I think it should work great... I need to mount a transmitter somewhere in the rocket, was going to make a transmitter bay but that just add's to the weight... and the solid resin cast cone cant store it, any hollow 29mm cones that would work well? Ognive might be faster, but conical does look really cool... Thanks... I wish I had the $$$ to make the rocket all CF, but with my 2.5" CF rocket, I want this to be a simple cheap phenolic rocket...
SARocketMan
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Nice rocket how high do you think it will go ?
Alex
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Alex, Good question...I would like to see it go 10,900' to beat the current H record. I have been to 9,275 with a different 29mm min dia rocket that was not as 'sophisticated' as this one. This rocket has zero free space. is as small in diameter as can be, is adjustable weight wise and has an optimal nose cone design, has OK fin design and has thin material for the fins. Another trick I'm trying is I'm planning on ejecting the motor out the bottom of the rocket pulling out the chute. The reason being every time you have a seam or joint on a rocket there is drag associated with it. I have ground tested it 3 times now and so far so good. Also, I have 3 different G-Wiz's that I can chose from to use in it. Next step is to make a testing devise to see which G-Wiz unit I should use in it. And the biggest thing is getting it back and that is where luck comes into play.
Tony
Tony
Chris TNR
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quote:
Originally posted by: jraice
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I need to mount a transmitter somewhere in the rocket, was going to make a transmitter bay but that just add's to the weight... and the solid resin cast cone cant store it, any hollow 29mm cones that would work well?
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Either Sandman or myself could turn you a nose from balsa. However the difference about this nosecone is it has to be hollowed out to provide room for the transmitter. A little bit more work but not too bad. Being a 29mm x 36" rocket, (please correct me if I'm wrong) I would assume the nose length at 7-8".
I'd make it (s/h included) for $20 bucks---either balsa or pine.
Let us know if we can help........nice project you have going here.
Curious to see what your highest altitude is....
email>>[email protected]
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Chris Emich
NAR #84102
TNRocketry
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Originally posted by: jraice
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I need to mount a transmitter somewhere in the rocket, was going to make a transmitter bay but that just add's to the weight... and the solid resin cast cone cant store it, any hollow 29mm cones that would work well?
_____________________________________________
Either Sandman or myself could turn you a nose from balsa. However the difference about this nosecone is it has to be hollowed out to provide room for the transmitter. A little bit more work but not too bad. Being a 29mm x 36" rocket, (please correct me if I'm wrong) I would assume the nose length at 7-8".
I'd make it (s/h included) for $20 bucks---either balsa or pine.
Let us know if we can help........nice project you have going here.
Curious to see what your highest altitude is....
email>>[email protected]
_____________________________
Chris Emich
NAR #84102
TNRocketry
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