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Dec 05, 2016, 12:25 AM
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Bill, what thickness balsa and what pitch angle? Have you tried 1/32 like George?

Vince
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Dec 05, 2016, 03:46 AM
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Ampbomber's Avatar
Quote:
Originally Posted by Vince Caluori
Bill, what thickness balsa and what pitch angle? Have you tried 1/32 like George?

Vince
Vince,
Don't remember too many Georges around. I've been watching but haven't gotten into building balsa props yet. Been busy with building Eagle II.

George
Dec 05, 2016, 05:06 AM
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bill clark's Avatar
Thread OP
I think he meant to say Dave.
Vince, I tried a sample of 1/32 with 2oz glass (can't find my roll of veil) on the back and didn't think it would be enough as this is a 15" prop not a 11 or 12 like Daves. I started with a piece of 1 /8 and finished with .08at the root to .025" at the tip. I don't have the correct motor or accurate current data yet so my comparisons are relative
Dec 05, 2016, 04:47 PM
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bill clark's Avatar
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Vince, on the pitch angle. I didnt measure I just eyeballed until the thrust was up around 120g's (2s voltage) and about 1800 rpm. Maybe 8-10deg but dont quote me on that.. This afternoon I set the angles to zero and ran it. About 80-90% of the current draw was the drive and blade drag. Most of that was blade drag. I estimate about 2/3rds so it appears blade efficiency needs to be top priority. My test rig currently has a gear drive not friction elements FWIW.
Dec 12, 2016, 10:38 PM
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bill clark's Avatar
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New Prop Tool


I tried to design this compression mold to give some flexibility. No helical pitch so only need one tool for CW and CCW. I will be able to try carbon only, carbon/foam, carbon/wood, etc. I put a slight amount of camber in it . The first trial run produced a nice, quality blade from 5.7oz twill. Not stiff enough and too heavy. Next I will try unidirection and see what happens. Once I get some usable blades out of this I will focus my attention on finishing the drive then I will be able to compare the 3 different blade designs using the motor and drive that will go in the plane. I hope to have all of this done by the end of the holiday break then I can move past all this and start on the plane design.
Dec 13, 2016, 06:00 AM
Hilson87
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As usual, sick work dude!
Dec 13, 2016, 04:48 PM
Risto Hölttä - F3A/P Team FIN
Finnspeed's Avatar
Very nice indeed!

Looking forward to see your results. There seems to be so many ways to make a well working prop for F3P.
Dec 13, 2016, 10:12 PM
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bill clark's Avatar
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Quote:
Originally Posted by Hilson87
As usual, sick work dude!
Seems like insanity sometimes

Quote:
Originally Posted by Finnspeed
Very nice indeed!

Looking forward to see your results. There seems to be so many ways to make a well working prop for F3P.
I won't claim to have made one that works well yet but I will keep trying. At this point it's exploration and learning. Probably not the best idea to start with 15" props either
Dec 17, 2016, 05:23 PM
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bill clark's Avatar
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Well I'm making progress.....I think. Props lettered A, B, and D are in range for weight, thickness and stiffness. i am including the following details for those interested but also so I dont forget what I did.

"A" 1.08g, Compression molded. .020" balsa core sealed with CA and a top and bottom layer of 2.6oz spread tow unidirectional tacked to 1/2oz carbon veil (to keep it in place while handling/molding). 30% resin content, .015" thick . It has adequate stiffness as is. System Three "Clear Coat" resin cured at 200f for 1.5hrs.

"B" 1.1g. This is my flat blade from earlier sanded down to a .02"-.06" taper with 1 ply on backside of 2.6oz spread tow uni. Wrap around flat surface with elastic band, 170f for 1 hour then room temp cure for 6hrs. same resin as "A"

"C" 5HS prepreg I got from work. Compression molded. The finish is nice but it was pissed when it came out of the mold. Nasty twist on the 2 pieces I tried. too heavy also.

"D" 1.86g. Compression molded. 24k strands of standard modulus tow with 2pcs of 2.6oz spread tow on bias tacked to 2oz carbon veil. This is vey stiff and super thin, .010" thick . We have some HM prepreg tape coming in to work. I want to try that with .5oz veil or 1.8oz spread tow on top and bottom. I might be willing to take a bit of a penalty on weight with this layup if it works out. .010" or less. Would probably by as efficient as I am going to get

"E" is 1 ply of 5.7oz twill (see above post)
Last edited by bill clark; Dec 18, 2016 at 04:43 PM. Reason: corrected veil weight
Dec 18, 2016, 04:40 PM
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bill clark's Avatar
Thread OP
Work for today....
Any of these 3 options appear light enough, stiff enough and a good foundation to fine tune. From left to right is the Rohacell 31 foam core (depron would give similar results but not quite as good as the Rohacell) with 1/2 oz veil and 3 single layer strips of carbon between core and veil, top and bottom. Center is balsa core with 1/2 oz veil only. No additional carbon. The right blade is balsa core "A" from above. All are right around 1 gram and are very similar in stiffnes. Refine the layup, add 2mm tube and hub and should be around 2.5g
Some notes to pass along,
I can see why the guys from Russia have settled on the veil. Its easy to handle wet or dry i.e. doesnt fall apart. The stiffness at these thicknesses are coming from the epoxy not so much the fibers. Thin sections really cant take advantage of the tension/compression qualities of fibers (I think KK made that observation a while back).
Getting rid of as much excess resin with a roller then a paper towel is a real good idea. It takes very little resin to get the job done and less for the core to soak up. About 50% of the blade weight is resin. I need to try to reduce this further. I mix up 4ml to layup a blade.
All of these came out .015-.020" thick even though the cores started out thicker in the middle. I may be squeezing them too hard in the tool.
At this point I plan to work with these 3 layups. Maybe do something similar to the latest AL props and dont crush it so much. A little thicker should add some stiffness specially along the center of the blade. The good news is I can make the core, cut the veil and get it all in the mold in about 20 minutes. I am expecting an AP05 and AP03 this week would should keep me on track for spending the holiday break finishing the props. Then back to the drive.
Last edited by bill clark; Dec 18, 2016 at 04:46 PM.
Dec 18, 2016, 04:45 PM
I don't want to "Switch Now"
pmackenzie's Avatar
They might be using carboline, rather than veil. That is what Glavak appears to be using on their 16" props. Veil has very little strength because the fibres are so short and randomly oriented.
Dec 18, 2016, 09:31 PM
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bill clark's Avatar
Thread OP
Thanks for the info Pat. I sent them an inquiry. I am really interested in getting my hands on some non impregnated, high modulus single layer which they may have. Seems to be rare as Hens teeth in small quantities.
Dec 18, 2016, 09:46 PM
I don't want to "Switch Now"
pmackenzie's Avatar
Another one is Carboweave. Some say it is better and more uniform than Carboline. The guy who sells it posts on here and sells small quantities as DLG repair kits.

https://www.rcgroups.com/forums/show...my-website-now

Probably easier than ordering from Ukraine
Feb 14, 2017, 09:45 PM
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bill clark's Avatar
Thread OP

Servo Gear Drive Contra


My new job has kept me insanely busy for the last couple of months but I have not let up on this project. I have made progress and present my servo gear drive contra. I felt early on that high reduction was (and will be) the way to go. Unfortunately, after spending many hours trying I could not come up with a good design using friction elements to achieve this. Other than copying a hybrid design like the guys from Finland (which is awesome BTW) I decided to take another look at gears. Popping open one of the many Hitec HS65 servos I had on hand (among others)presented a nice 12:1 gear set. Some initial durability testing to see if the gears where adequate, many hours of CAD work and machining netted a result that I am very happy with at least at this early stage. I will post some numbers once I find the best wind/prop/pitch combo but so far i am very pleased with the static testing. Shocked, actually. About a half hour total running at different throttle settings shows no signs of wear. Also these small toothed gears are extremely quite. All I hear is the motor wine. And a few pictures.........
Feb 14, 2017, 10:45 PM
Senior to who? Member
crossup's Avatar
Apologies for going off topic but could you tell us a little of what you use in the way of machine tools. I'm in the process of setting up my shop and trying to get all those pesky major purchases out of the way so I can use the equipment as soon as possible and for as long as possible. I suspect you have some high end gear and I'm whistling up a tree but one doesnt know if one doesnt ask


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