1st rc build ever a kfm3 - RC Groups
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Nov 21, 2013, 12:54 PM
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1st rc build ever a kfm3

I have been looking into this for a while now and finally started it. I have glued up the foam together and inserted some aluminum spars. The leading edges are almost shaped now. I used dollar tree foam and home depot pink foam. It is a kfm3 airfoil. Now trying to get it all shaped up and balanced. I don't have any electronics yet so still need to get all of that. WOW took much longer than I thought to get to this point. I am going to eventually use this for fpv.
Last edited by jmar595; Feb 19, 2014 at 09:13 PM.
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Nov 23, 2013, 05:01 PM
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This is the buildup so far. I was sanding the T.E. of the right wing to be even with the left wing and sanded a contour into it. Now I have to find a filler that I can straighten out the T.E. with. I am thinking of covering it with monokote, Prob. black on the bottome with a bright thin pin stripe and blue and red on the top. Is monokote a good covering for this. Initially I was thinking of covering it with fiberglass, but that would take the weight up a lot. I may also, cut out some triangles along the top of the pink foam to lighten it up a bit. What do you think so far? The guy at the hobby shop suggested a 2000mah battery, 30-35amp esc and a 400-450 engine with small servos. He said heavy for fast planes and light for slower planes.
Last edited by jmar595; Nov 24, 2013 at 01:32 AM.
Nov 23, 2013, 06:12 PM
serial scratchbuilder
Granted's Avatar
Looks good so far.
Use econokote, it has a lower working temperature and you won't be melting the foam before the covering sticks.
Glue another piece of foam along the TE and trim back to original size/shape.
Nov 30, 2013, 05:34 AM
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So, I ordered the components for it. I went with a Turnigy Park 450 1050kv motor, a Turnigy plush 30amp ESC, and I got 2 diff batteries, a 4000mah and a 5000 mah. I am going to fix the T.E. and cover it soon. Make the bottom black with some stripes coming from the nose and fanning out, then blue for the top step, red for the middle and blue for the back of the top. Prob do red for the fan pattern on the bottom. I am waiting on a guy that has a ton of stuff, hopefully get the Spectrum DX6 from him.
Jan 14, 2014, 11:19 AM
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So I got a bit farther on it. I put winglets on and it is now 51" It is very tail heavy and I am trying to find a way to balance it without adding a lot of weight. I will prob add another battery and put a go pro on the front. I am thinking of making an aluminum battery box and another spar that goes in front of that and ties bak to the other spars. If I don't have enough weight by adding the battery and go pro, I was thinking of mounting the camera forward of the wing on a boom mount. That should give me the moment I would need. I am going to sculpt a cowl and add pylons that would act as skids on it also. So what do ya think so far? It is pink in those areas because I did some hand tosses to check it all out and found that it was very tail heavy, will balance it out really well before I do that again.
Feb 18, 2014, 04:59 PM
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So I build an alum. battery box for the front end that will hold 2 batteries. I was going to mount a go pro on an extension arm forward of the plane itself, but when I plugged in my numbers in the flying wing calc. It put my cg at 8.03. Is this 8" aft of the nose? Also, the wing calc didn't have a way that I saw to put in a body section, would this make any difference? It just looks really far aft for the cg, I thought the cg should be 15% of the root cord and the root cord on mine is 13.5" from nose the t.e. of elevons, 11.5" to t.e. of body.
Feb 19, 2014, 09:11 PM
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Here is what I have so far. It should be flyable, but I think it is underpowered. It is 4lb. 1 oz or 1865 grams and has a Tunrnigy Park 450 1050 kv motor with a 35amp esc and a 10x7 prop. I think I have the cg close is a bit nose heavy now. I did some throw tests and it dives a bit. Tried giving some power but I think it is underpowered. What do ya think? It also has a 5000mah 2s 25-50c battery.
Feb 20, 2014, 04:16 AM
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That motor is way to small for that size wing, and it will never work with the prop on backwards
Look for a 3536 size motor 1000 -1250KV

Feb 20, 2014, 07:32 PM
Just another FPV addicted teen
EpicRC's Avatar
And 3s
Feb 25, 2014, 04:02 PM
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That was bad, what a stupid noob with the prop on backwards. So, I found a good prop calc and found the Turnigy G10 1200kv with a 4s and 70amp esc would give me some good power with a good choice of range in props. I just ordered the motor, esc, and battery, so hopefully I can try to get it flying soon.
Feb 26, 2014, 03:20 PM
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What is a good thrust/weight ratio? Also, what is the lowest end of that that is safe and flyable?
Mar 07, 2014, 12:55 PM
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Ok, I put on a Turnigy G-10 1200kv with 80 amp esc and a 4s 4500 mah battery and a sf 10x3.8 prop. It has loads of power now. Just have to glue in the battery box and balance it out. What is a good place to start with initial setup for rigging the control throws? I am trying to figure out how much throw and how much to put in for the dual rate and expo. I am new to this all and this is a scratch design. Any help would be appreciated.
Mar 18, 2014, 02:09 AM
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So I had a friend tell me that it will not fly. I cant wait to prove him wrong! He has never heard of the kfm airfoils and thinks they cant fly. I am trying to figure out if I should lower the motor closer to c.l. and make a different cowl.

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