I'm waking up, I feel it in my bones, come to make my system grow, welcome to the new age, to the new age, welcome to the new age Hey guys It's Jacob here. Welcome to Helicopter Lessons in 10 Minutes or Less. This is my first video on what I hope will be a long series of videos explaining the topics that helicopter pilots need to know in order to fly, but also to pass check rides and academic evaluations. What I want to do here is take topics one by one in each video and teach them in a format that viewers can easily grasp the concepts.
From there you guys and gals can recreate the drawings, the diagrams, and the teaching aids to show your knowledge to pass check rods. So a quick background about me. I absolutely love flying.
I've loved it since I was a kid. It's just nothing like it in the world. It's always been my passion in life, and so when I was old enough, joined the Army, and I've been flying helicopters for the past four years now. I'm currently in the instructor pilot course and still refining my teaching techniques. So if you guys have any questions, comments, concerns, just want to talk to me about anything, feel free to let me know in the comments section below.
Today we're going to be talking about dissymmetry of lift. It's one of the most basic concepts that all helicopters have. pilots need to know.
So unlike an airplane or a fixed wing where you have the same amount of airflow over each side of the wing at all times, for the helicopter you have an advancing blade and a retreating blade that are getting different amounts of airflow depending on how you move through the air. So, the symmetry of lift, what is it? It's when the helicopter moves through the air, the relative airflow through the main rotor disc is different on the advancing side than on the retreating side.
The relative wind encountered by the advancing blade is increased by the forward speed of the helicopter. while the relative wind speed acting on the retreating blade is reduced by the helicopter's forward airspeed. Therefore, as a result of the relative wind speed, the advancing blade side of the rotor disc produces more lift than the retreating blade. Alright, so that is dissymetry of lift.
There is dissymetry in the lifting parts of the helicopter. So let's show what does that mean. Now I've got spectacular drawings, hope you guys can bear with me. I don't claim to be an artist by any means.
Alright, so we have the... helicopter fuselage and this is the area that the rotor blades turn in. So American-made helicopters turn in a counterclockwise fashion, European ones turn clockwise. We won't get into that. For the purposes of this and the next few lessons we'll be talking about American-made counterclockwise rotor systems.
So let's say that the rotor disc is turning at 300 knots. That's 300 knots of airspeed that these blades are turning into. Now we'll get into the dissymmetry of lift.
when we move in any kind of direction. So say the helicopter now is moving forward at, say, 100 knots. What this means is you have 100 knots of relative wind coming at the rotor disc, and it's affecting it differently on different sides. For the advancing side, this blade is already traveling 300 knots, and it's advancing into another 100 knots.
So what is that doing? It's adding that to it, and now it's like the blade is, it's traveling at 400 knots. 400 knots through the air.
Now the retreating side, you have that same rotational velocity of 300 knots, but now it's retreating away from that relative wind, so it's losing that airspeed. So now you have 200 knots on the retreating side. So what does this mean?
Well, your advancing side rotating, or the airspeed, the relative wind on the advancing side is 400 knots, the retreating side 200 knots, so you're getting, in essence, double the lift on that advancing side than you are the retreating side. retreating side. So this applies to any kind of forward motion, any kind of wind change, anything like that. So for sake of clarity we'll draw one more helicopter.
Do another example. Say this helicopter is sitting in the middle of a open field surrounded by trees and he's wanting to slide to the right, you know, maybe he wants to reposition for a takeoff or something. So he's going to just do a sod step to the right.
So he's moving this way. So our advancing and retreating side is determined by the direction of travel. So now we're sliding this way, this rear half of the disc is now the advancing half, the forward half of the disc is now the retreating half as it relates to the relative wind. So say we're sliding to the right 20 knots. So we still have the rotational speed say 300 and it's advancing into the 20 knots for 320 knots of airspeed on the advancing side.
And the retreating side, doing the reverse 300 minus the 20 for 280 knots. So here we see on the rear half of the rotor disc, it's producing more lift than that retreating side. So this is a quick, clear, concise definition of what is the symmetry of lift. I hope you enjoyed it.
Thanks for watching. Check out more of my videos and we'll go into more concepts and helicopter aerodynamics and whatnot later on. Thank you again.