Dissymmetry of lift
The CAA recently set this as an engineering question
What is the advancing blade on a helicopter doing
a Increasing in lift
b Going to the highest point
c Increasing in drag
Its option B that is causing the confusion. For the advancing blade which direction is the blade flapping ? After reading Mr Coyles book it is evident that for the advancing blade, two mechanisms are occuring.
Cyclical change of pitch which gives the advancing blade a lower angle and less lift and the retreating blade a higher angle and thus more lift. This is accomplished via the mechanics of the pitch change system. The overall effect here is for gyroscopic precession to put the advancing blade at its lowest point at 180 deg rotor azimuth.
The second mechanism is flapping to equal out the lift on opposite sides of the rotor disc. The advancing blade flapping up and thus reducing in lift and the retreating blade flapping down and thus increasing in lift. The two effects, on opposite sides of the disc help keep the lift equal between the two halves.
These two seem to contradict each other somewhat and after reading the description of flapback/blowback it turns it on its head.
Could someone please explain which way the advancing blade is flapping
Many thanks
GR (fixed wing !)