Assessing helicopter main rotor blade critical area using blade element theory in the cases of forward speed and blade collective pitch angle increments

The critical area on the main rotor blade when a helicopter is in forward flight conditions was assessed in this research using Blade Element Theory program. Two cases have been analyzed in this studied which are the effects of increasing forward speed and blade collective pitch angle. The Blade Element Theory was used throughout in the research. The validation of the Blade Element Theory program showed that the computed results were in good agreement with published data of Prouty’s. Furthermore, it was evident that in forward flight, the retreating blade experiences high angle of attack and low lift, in contrast to the advancing blade. The increment of the helicopter speed affected the lift distribution along the blade and also the reverse flow area at retreating blade. The increment of collective pitch angle changes the angle of attack distribution and lift of the rotor blade. In addition, it is proven that to ensure safety, every helicopter has its limit of speed called Velocity Never Exceed.