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« on: May 11, 2011, 11:23:53 AM »
PankajC
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Well!!! I am kind of fascinated with this model.

After the first attempt did not succeed - it was way too heavy and lack of RC skills destroyed the model beyond repair (anyways do check out post #52 of the last build thread http://www.rcindia.org/self-designed-diy-and-college-projects/scratch-build-cub-trainer/50/)

Current attempt is has the following approx measurements

Wing span = 48 inch
Aerofoil = UC
Length = 36 inch
motor  = HK 28-30B generating about 150-160w of power
battery = 3S1P 1600mah nanotech
material = 5 mm biofoam
strengthening materials = 3 mm square tube, 5 mm tube and 2.5mm fibre rods

targetting AUW around 800gm or thereabouts

Posting some WIP pictures

fuse-01.jpg
Scratch built Cub Trainer - another attempt
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« Reply #1 on: May 11, 2011, 11:25:09 AM »
PankajC
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More pics

fuse-04.jpg
Re: Scratch built Cub Trainer - another attempt
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« Reply #2 on: May 11, 2011, 11:28:05 AM »
PankajC
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The fuse battery bay and the ESC hatch at the bottom.
The wings are to be attached by a single 6mm plastic screw
To keep the wings in place there are two 3mm CF rods going into a guide hole in a wooden strip

fuse-batterybay-01.jpg
Re: Scratch built Cub Trainer - another attempt
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« Reply #3 on: May 11, 2011, 11:30:42 AM »
PankajC
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The nose cover is detachable, I plan to put two small magnets to secure it.

fuse-nose.jpg
Re: Scratch built Cub Trainer - another attempt
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« Reply #4 on: May 11, 2011, 11:33:00 AM »
PankajC
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Wing design

wing-01.jpg
Re: Scratch built Cub Trainer - another attempt
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« Reply #5 on: May 11, 2011, 11:34:18 AM »
PankajC
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more wing pics

... thats all for now

wing-04.jpg
Re: Scratch built Cub Trainer - another attempt
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« Reply #6 on: May 11, 2011, 11:49:52 AM »
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Very beautiful build, i just wish you had made a flat bottom airfoil for this one.
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« Reply #7 on: May 11, 2011, 01:27:30 PM »
sandeepm
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i will also recomend you for a flat bottom wing
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« Reply #8 on: May 11, 2011, 02:02:15 PM »
ujjwaana
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'Never say Die'

Welcome back Pankaj sir! we missed you so much!
this build looks awesome! Esp the heat molded wing is perfect.
Is the hatch in the front for battery or ESC ? I have noticed that due to the weight of Biofoam we use in our build, most of proven design from west turn out to be too tail heavy. Give enough scope to put the battery forward so that you get the CG right.

All the best! Keep us posted!!!
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« Reply #9 on: May 11, 2011, 03:27:42 PM »
foamybuilder
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Everthing is fine but please add carbon fibre reinforcement for the fuse, two on either side should be fine. No way it could handle crashes however thick the foam is..
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« Reply #10 on: May 11, 2011, 10:57:07 PM »
PankajC
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Well, the hatch at the bottom of the fuse is for the ESC. The battery can be pushed right behind the firewall ( the top portion of the nose is detachable), so I guess there is plenty of room for adjusting the CG.

Regarding construction....
What you see as the fuse in the pic fuse-02 gives an indication of how the fust is built. The external is a 5mm biofoam sheet, but below the battery tray, starting from approx middle of the wing chord  right up to the firewall is a block of 1.5inch thermocol (the high density granular type). This is to act as the main shock absorber. This is further reinforced by a 5mm CF tube running from the firewall right to the tail fin (almost).

The entire fuse is fibreglassed - While I had the option of using light weight fiber glass cloth as I have 48gm/sq m variety, I chose to go with the cotton 'dhoti' material with WBPU and talcom powder Cheesy Cheesy. As it turned out, I cannot make the difference in the finish.

The wing was contructed as follows
cut 2 pcs of 24inch by 8 inch sheets and gave the basic round edges. Then placed them on the balcony wall - it has a well half round border. Then made the basic curve by applying even pressure across the half span of the wing. Once this was done, then I used heat to give it a more defined shape. Now, the basic problem is that I do not have a heat gun, so i substituted this with a candle. With the flame burning, there was sufficient hot air above the flame that was used to warm the biofoam (just that much ) and using hand pressure formed the aerofoil.
The LE of the wing has a 2.5mm fibbreglass rod running length wise and the stiffening is done by the 3mm sq CF tube that is visible.

As of now, the wing and the fuse (sans the tail fin) weight about 340gms

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« Reply #11 on: May 11, 2011, 11:08:06 PM »
SunLikeStar
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I chose to go with the cotton 'dhoti' material with WBPU and talcom powder Cheesy Cheesy. As it turned out, I cannot make the difference in the finish.
Clap the fuse in picture fuse-06, is it already glassed?  how much rigidity did you get compared to fiber glass?
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« Reply #12 on: May 12, 2011, 07:09:57 AM »
PankajC
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since I use WBPU even with fiber cloth, the rigidity with the cotton cloth is almost the same - at least thats what it appears to me
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« Reply #13 on: May 12, 2011, 10:58:24 AM »
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Very Nice Build Pankaj.

Your wing building method shows, the way to all the scratch builders that scratch building requires determination than any thing else.

Candle for heating wings to bend, great.
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« Reply #14 on: May 15, 2011, 02:54:20 PM »
PankajC
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Well. my daughter is helping me on this this thread. He school closed for summers and she has taken it on herself to paint this one.

So the model just became more special

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« Reply #15 on: May 16, 2011, 02:20:32 AM »
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Pankaj, quite a co-incidence.....i too am working on the cub trainer.... i found the plan on rcgroups.....attached is the plan i am using....guess its the same one you used in yr previous attempt too...

i have just managed to cut out and assembled (not glued) the former, but have made one mistake...have stuck the bottom and sides of the fuslage together before sticking the former to the bottom... but ...it seems to fit in somehow.

still cant find some piano wire for the landing gear.....anyone in Mumbai can help me with this ?

attached is the image of what i have done till now..... will need yr support during this build !



DSC00443.jpg
Re: Scratch built Cub Trainer - another attempt
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« Reply #16 on: May 16, 2011, 01:40:03 PM »
PankajC
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jits,
yes, seems to be the same as my previous attempt. I feel that the build is not for newbies and hance I had landed in problem.
For the landing gear contact rcforall
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« Reply #17 on: May 23, 2011, 04:25:58 PM »
PankajC
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Some more WIP of the fuse

fuse-wip-01.jpg
Re: Scratch built Cub Trainer - another attempt
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« Reply #18 on: May 23, 2011, 04:29:57 PM »
PankajC
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Posting pics after my daughter had her fill of painting the bird. Done quite a good job I must say (speaking like a proud father)...

Well the pictures are not of a very good quality, but are uploaded just the same.

The overall weight is 845gm as of now and with watt meter, the max the motor is generating is around 180w. So technically, this thing should fly. Lets see how the maiden goes, will be asking Divay to do the maiden

Pankaj

finished_fuse-01.jpg
Re: Scratch built Cub Trainer - another attempt
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« Reply #19 on: May 23, 2011, 08:24:23 PM »
ujjwaana
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 Bow Bow
Hail!! Its looks so fantastic!! the fuse looks like made of Balsa. Fantastic trim scheme. The wing also looks solid!
I bet this time things would be fine. Just CG and Thrust angle is all you need to take care of now.
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« Reply #20 on: May 23, 2011, 08:47:26 PM »
PankajC
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thanks Ujjwaana, The CG is kind of taken care of with the 1600mAH battery right behind the firewall. I am going with a slightly nose heavy setup and then maybe adjust the CG a bit. I don't want the plane to be tail heavy on maiden
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« Reply #21 on: May 23, 2011, 10:58:15 PM »
ujjwaana
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Great going Pankaj. I was reiterating because I have noticed that purely Sticking to plans from West and no leaving scope to further place battery often leave planes way tail heavy.
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« Reply #22 on: May 24, 2011, 10:07:42 AM »
PankajC
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yup - my experience exactly...

To counter this, I have done two things
1) increased the length of the nose which in turn increases the distance between the CG and the prop thereby giving more room for weight adjustments by shifting the battery rather than by adding weight
2) mounted ESC below and battery above to ensure the heaviest components are right up.

If these do not work, I got a heavier motor Cheesy
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« Reply #23 on: May 30, 2011, 04:36:47 PM »
PankajC
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Well, the bird was flown on Sunday by Divay. Less than a minute flight. The following points were noticed
1) Ailerons were not effective, had to use Rudder to turn
2) The wing's trailing edges were vibrating.
3) Also noticed that while on ground, if I hold the wing tips, then the dihedral seems to increase meaning the stiffeners are not solid.

Regarding the first issue, I will first attempt to increase the throw. However I am concerned with the 2nd problem and am wondering how to determine the root cause.
I have in the meantime tried to strengthen the TE by gluing a glass fibre rod and also applied a 3mm CF rod on the top of wing to address point #3.

Hope this helps, but not sure......

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« Reply #24 on: May 30, 2011, 05:21:29 PM »
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Fiber tape can be used to reduce flutter on the TE.
This is why I don't like undercamber wings, they flutter like a butterfly, are unable to handle wind properly, only the rising aileron does actual work and very poor glide ratio.
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