Wat should be the thickness of the plywood tat can be used for spar?

2.5 to 3mm should be fine. but make sure you select light plywood, because some are really heavy.

Now I got what you are looking for. You could use a wood called 'Reeper' by the local carpenters. It is a white coloured wood with grains running nearly straight along the lenth of the wood. It looks some what like pine. A second option is as once Ismail had told me, is to use the wood that is used by frame makers (Photo frames). This is the same wood. You will have to reenforce the center with pieces of the same wood lengh about 6 -7 inches. Place one piece of wood flat on the floor and place the second length of wood at the height that is in the plan. Again the 2nd piece is flat on the floor. mark the angle the 2nd piece is making with the 1st and then cut/ sand the first piece at the correct place. Keep the length of the pieces slightly longer than that is in the plan. U can cut the extra later.
Another option is to use 'Multiwall Polycarbonate sheet' for the spar. You can find it any place that stocks Coro. This sheet comes in a size of 4.6 and 6 mm. It is lighter than coro and when 2 pieces with flutes running perpendicular to each other are stuck together, are as strong as light wood.
A photograph of the material that I am talking about. (And the SPAD Extra I'm working on)

Thanks doc..I'll check all the three options soon..

Back to build after a gap..I've cut the elevator n rudder..When i inserted the ele for checking in it's slot as per the plan,one half of the ele is going down n not balanced one..Will it be ok after gluing correctly? Uploading the pics

Just glue it, we will find a way if it droops at one side. Have you finished the wing?

U can see the ele position in the following pic

Hi sun,i'Ve just cut down the wing pieces n spar pieces from coro..Gonna glue the spar first..

Hello frnds,finished the wing last week..uploading pics:

This is a 2piece wing..The spar is made from 3mm coro,idea given by mr.Edwin(martian2121)..Spar is built by sticking a layer of coro flutes running cord-wise between 2layers of coro flutes running span-wise..I've to glue the center wing wrap n ailerons..Glues used:Fevibond,Feviquick..

beautiful wing, by 2 piece do you mean detachable 2 piece?

pretty nice built all the best for maiden!!

Thanks sun&ash..No it's not detachable..I mean it made from 2 separate pieces of 625length coro,as per plan it should be built from a single piece of length 1250 mm..is it possible to build a detachable wing with dihedral?

i was just asking because i am planning to build one with 2M detachable wings, but right now i am out of coro

is it with dihedral?

right now its hypothetical, but want it to be polyhedral. 

Built another set of wing..

is this air-foil ok??

I'm confused abt the aileron dimensions..can any one help me regarding this?? I also want to know abt placing the aileron servos..planning to use Turnigy eco micro servo..is it suitable for this?

how did you stick the body?
i mean the sides of the 90deg?
please explain in detail!

@prateek:u mean the sides of the fuse?

yeah

Why did u build another wing? I mean was there a problem with the first wing?

Actually i'm buildin one plane at my home town n another one at Hubli..

@prateek: I just scored the flutes to be fold n applied feviquick,then kept between bricks..U can see tat pic in my earlier post..