But clark y aerofoil is not under camered or just eleminating bottom makes is do the job. I thought an under chambered wing gives slow speed .

No KalyanDa, the first graph is from the book of Anderson, second one I googled. we haven't tested flat plates, however I have written Matlab codes for the pressure distribution around many airfoils(including flat plate) but to save time I googled those graphs.


This is not true. First of all building an undercambered airfoil will be more difficult than building a flat bottomed airfoil, secondly how fast your plane flies depends on how much thrust(i.e the power system) you apply not the airfoil. I mean, if I were to attach a Rolls Royce turbojet engine( ok its way too exaggerated  but bear with me) to your model plane, then will it matter, what airfoil you put? That plane is going to shoot past you. The undercambered airfoil will have more drag but that doesn't necessarily mean slow speed!

Ok, I must now stop, otherwise I might overcomplicate things and unnecessarily bombard you with too much information which would infuriate our aerodynamics guru rcpilotacro.  I therefore request rcpilotacro to take charge from here. I must guide you to his aerodynamics thread which, I feel, you should go through. Here it is : http://www.rcindia.org/rc-general-topics/basic-aerodynamics-for-rc-flying/

I get what u say but ideally if I have 2 planes with same engine same wing span same chord but one Clark y with flat and one under cambered then what will be difference in flight. Simple question.

Hmm. The undercambered airfoil will produce more lift than the clark y airfoil but it will stall faster than the other one.