# How do helicopters handle P-Factor?

Propeller-powered aircraft have a "problem" called P-Factor, where the descending blade of the prop is generating more lift (a.k.a. thrust) then the ascending blade due to a higher angle of attack when the angle of attack of the wings is high. (I hope I summed that up properly.)

How about helicopters? For this example let's say the blades turn counterclockwise when seen from the top. When the helicopter is accelerated, the blades on the right side of the helicopter are faster then the ones on the left side. Thus they should be generating more lift. The higher the speed, the higher the difference in lift on both sides would be.

What mechanism handles corrections that have to be made due to this lift difference? How does it work?

• See this and a number of questions on here that already discuss dissymmetry of lift. Search for "retreating blade" and see the corresponding answers. Commented Jun 22, 2015 at 10:49
• Okay, that's a start, I didn't know own that word yet and hence couldn't search for it... Will rephrase my question later, I am more lookin on how they achieve the corrections made. As they must be different for different speeds and pitch attitudes. Commented Jun 22, 2015 at 10:54
• Note that P-Factor is an issue in multi-engine aircraft too
– Ben
Commented Jun 22, 2015 at 11:17
• For corrections, see this Commented Jun 22, 2015 at 13:39

This was one of the primary problems that needed to be solved in helicopter flight.

In my example, I'll use a 2 bladed helicopter, but this holds true with all helicopters, and I'll explain some of the different rotor types later on. The blade that is moving forward, relative to the direction of the helicopter, is called the advancing blade. The opposite is called the retreating blade, and you are correct in assuming that they would generate different amounts of lift. As a previous commenter noted, the term used for this is "dissymmetry of lift", and is the same thing that limits the maximum speed of a helicopter.