RC India

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

More pics

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

The nose cover is detachable, I plan to put two small magnets to secure it.

Wing design

more wing pics

... thats all for now

Very beautiful build, i just wish you had made a flat bottom airfoil for this one.

i will also recomend you for a flat bottom wing

'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!!!

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..

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 :D :D. 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

{:)} the fuse in picture fuse-06, is it already glassed?  how much rigidity did you get compared to fiber glass?

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

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.

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

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 !

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

Some more WIP of the fuse

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

 :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.

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

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.

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 :D

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......

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.

What exactly can be the cause of this ?  That ailerons have virtually no effect, and rudder is a must for turns.

Ailerons on under camber wings never work well, the main reason is adverse yaw. The aileron going down becomes continuation of the camber creating huge amount of drag which causes the plane to just "slip" through air without turning.

More discussion...

Here is a clear explanation of what adverse yaw is, and how to correct it.

http://www.mountainflying.com/Pages/mountain-flying/adverse-yaw.html


So what it really needed is differential aileron throw (more up than down), not just more throw.  Not sure if this plane uses dual aileron servos, if indeed, then achieving differential throws would be easy with radio ATV/EPA setup.

Well, if I just add a sheet of wrapping paper on the UCto make it flat bottom aerofoil, will this help?

Wrapping paper might not work, but you can use 3mm foam sheet to cover the UC or as Anwar suggested you can use differential to correct it. UC wings are not that bad if you want a slow flyer, but flat bottom wings are much more fun to fly.

Another attempt was made after programming ailerons for differential throw. However the ailerons are still not effective.
So have done the following
1) increased the length of the aileron
2) increased the up throw to about degree.

Now to try it out.

good luck on the flight........ im still working on my firstr plane....

actually increasing the size of the aileron did not have much effect.
Had read somewhere that for high wingers with aileron it is better to have very little dihedral. So knocked off the dihedral.
NOW IT RESPONDS to aileron controls

However, the single sheet UC wing is turning out to be a problem. Yesterday again, inspite of having reinforced the foam, the trailing edge started vibrating and then the plane lost control. Divay managed to bring it down by what I call - a gentle crash :D. Still quite repairable

Anyway, I am now convinced that UC works best for 3 ch birds. So am changing the wing shape to flat bottom one. Will post what happens.

The effort that you put into R&D and the patience with which you work your models ... is commendable pankaj .... kudos to you bro !!!

Question  on aerodynamics.  Why would knocking off dihedrals help with aileron authority ? :)

well from what I gather the lift of a clark-y wing is max when it is parellel to ground. Now in a dihedral situation, both halves of the wings are at a slight angle. So when the plane banks on one side, that side now becomes parallel to ground and produces max lift thereby automatically correcting the bank. So if the dihedral is not there, this self correction does not occur.

While is common to both high and low winger, the high winger has the CG below the wing so the weight acts as a pendulum as well. for this reason, a high winger would have lesser diherdral than a low winger

put a CF rod along trailing edge using fibre tape.....same has to be done in a slow stick since its has a flat bottom under-camber and also has a dihedral doing that will do the job....