I am trying to make a concept for a small UAV. The UAV shall be flying at Mach=0.75 , shortly 0.9
For this, I am looking for an adequate airfoil, which allows me, to avoid Mach=1 on the airfoil. From airfoiltools I have chosen the rae2822 , said to have a high critical mach number. I plotted my cp curve for alpha=0 and calculated the critical mach number which is 0.736 for sweep angle=5 degree.
So I this will not work. I also tested the sc2 0714, originally made as supercritical airfoil, which gives me a value of Mach=0,56 as critical mach number.
Either I made a mistake in calculation or I do not know how commercial aircraft fly at 0.8 or 0.9 ? I do not want to have a big sweep angle in order to have a good lift/drag ratio.
Can you recommend any airfoil?