Retreating Blade Stall

[@rotorkid2457]

I’ve always had a hard time understanding retreating blade stall but I understand now, great video 👍

[@garycleveland2989]

Thank you

[@PandaCola100]

Thanks! Explanation also explains why helicopters have taken so long to reach today's level of sophistication. Complexities of helicopter flight also mean limitations. E.g. the presented retreating blade stall limits cruising speed severely. That is why tiltrotors are needed.

[@mikesilman6456]

Gary just wanted to drop you a line to say "GREAT JOB" on your explanation of Retreating Blade Stall. I've been involved with helicopters for 28yrs, a Commercial Helicopter Pilot for 23yrs and I must say that your explanation of Retreating Blade Stall is the BEST I've ever seen. You made it so easy to understand whether a person is a brand new student or an old timer just brushing up on the books and I know that your students have a real appreciation for your teaching style. Keep up the Great Work and Fly Safe.

[@garycleveland2989]

Thanks for taking time to give that feedback. I really appreciate it!

[@piconazzaro]

great lesson, well presented just want to be clear on the tail rotor thrust vector your diagram shows the arrow pointing in the same direction as the rotation of the main rotor. the resulting force (thrust) of the tail rotor pushing the tail (to the right with a counter-clockwise rotating main rotor) means the air flow is to the left and tail rotor thrust to the right is pulling the tail in the opposite direction of the main rotor torque (or same direction as main rotor rotation depending on how one looks at it).

[@garycleveland2989]

Correct. The tail rotor is pushing on the tail boom on counter clockwise helicopters with the tail rotor on the left side. Thanks for the comment!

[@williambogacki1687]

@@garycleveland2989 that is not correct, if the main rotor is anti clock rotation as viewed from top down, the fuselage will rotate nose right. we apply left pedal to stop this. to make the noise go left we push the tail right by blowing air to the left. thus getting translating drift to the right. your arrow is showing thrust not the direction of airflow.

[@garycleveland2989]

@@williambogacki1687 thrust is towards the tailboom (to the right if seated in the helicopter), airflow is to the left if seated in the helicopter. Hope that helps.

[@cavassini]

Tks for the video!

[@garycleveland2989]

Pilot Cesar appreciate the feedback 👍🚁

[@mxrriderr]

I'm still confused on the idea of blade flapping and how it is affected by gyroscopic precession: With the advancing blade creating more lift because of its speed, wouldn't that cause the advancing blade to flap up in the front of the helicopter due to gyroscopic precession? The way I understand it now is that the blade would have to immediately flap up due to the increased lift on the advancing side which doesn't make sense. Thanks for the help.

[@mxrriderr]

And in the context of transverse flow - when the front half of the rotor begins to enter cleaner air, therefore creating more lift, why doesn't the front half of the rotor simply flap up?

[@garycleveland2989]

In my opinion, you are overthinking this. You are holding yourself to a standard of understanding that is not necessary for a pilot. Many things explained in the helicopter flying handbook and the airplane flying handbook are explained in a way that is not technically correct from a physics standpoint, but made simpler for the average person to understand. I learned this from a student that I had who had a PHD in physics. He understood aerodynamics to a level that only confuses me. But I understand if you desire in depth knowledge and encourage you to investigate. I am sorry that my understanding is pretty basic.

[@mxrriderr]

@@garycleveland2989 That's interesting how the helicopter flying handbook isn't always technically correct, but I guess it makes sense just to convey the principle ideas without getting too in depth. Thanks for the response.

[@Climbontrack]

Please can you explain the difference between fixed and rotor wing benefit from TAS with altitude and why the VNE in fixed stay the same with increasing Altitude while in rotary A/C VNE gets lower with increasing Altitude.

[@garycleveland2989]

@@Climbontrack I am not a fixed wing instructor. But I can tell you that true airspeed is calculated to be faster than indicated and indicated air speed is all that we have to see in the aircraft. Some advanced avionics show both

[@waltercastillo1713]

Is this a potential situation with the Kobe Bryant helicopter incident? When the pilot attempts to climb fast at last minute but then abruptly descends quickly?

[@garycleveland2989]

Walter Castillo No, I think you will find that the NTSB will rule it as weather related spatial disorientation, unless the pilot had some medical event occur.

[@JoseHernandez-eo3wu]

Please i Need whats means lead lag

[@garycleveland2989]

A fully articulated rotor system allows each blade to flap independently which creates moments where blade tip speeds vary from one another. The lead/lag hinge overcomes “Coriolis effect”. The helicopter flying handbook also has an explanation to reference.

[@diegobeatrice5257]

Hi, it is my understanding that the difference in lift between the advancing and the retreating blades it is not affected by the angle of attack until the upflap/downflap effect comes into play but due to the change in velocity as per the lift equation L = 1/2 Cl V squared density S resulting in tge advancing blade to generate more lift due to the combined effect to the forward aircraft velocity and to the rotor rpm’s, than the retreating blade. Am i correct?

[@garycleveland2989]

Diego Beatrice I would recommend that you read it first hand in the Helicopter flying handbook. My explanation is good enough for all examiners that I have used for private and commercial students. I find that keeping it simple is best. If you wish to have a deeper understanding that involves equations, that is wonderful but not necessary to be a pilot.

[@diegobeatrice5257]

Gary Cleveland thanks for your prompt reply. A little bit about myself - i am an 8000 plus hour fixed wing training captain with less than 20 hours of heli under my belt, fascinated by the helicopter aerodynamics and i do agree with you that while taking a checkride the safest option is to keep it simple as you dont want to expose yourself to thorny subjects you might not have a solid grasp on, however for sake of information i think that sharing the sources where some effects stem from, it helps to clarify them, for the more technically inclined amongst us.