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 . 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....