Welcome back to Helicopter Lessons in 10 minutes or less. It's Jacob here and this video is all about the lift equation. Now this subject can go pretty detailed if you ask aerodynamicists, but for this lesson I just want to keep it just to the basics.
Now it's important to understand where lift comes from as a helicopter pilot because then you can realize what you can and can't affect in the cockpit, either directly or indirectly. So, let's check it out. Now, lift is going to be made up of four key elements, and we're going to be using this formula. So, lift equals the coefficient of lift times surface area times 1 half row. also known as air density times the velocity squared.
Now let's break it down. We'll break it down into segments right here just to make it easy to understand. First part is gonna be coefficient of lift. Now, coefficient of lift is a measure of the amount of lift a particular airfoil shape can produce.
Now, this is going to be determined by things like the shape of an airfoil in conjunction with its angle of attack. Now, when you talk about shape of the airfoil, we're talking about things like your blade span, your camber, whether it's symmetrical or not. So there's a lot of different shape designs. You know, maybe you have a symmetrical versus an asymmetrical blade.
different cambers, different characteristics in the blade. But obviously we cannot affect this while we're in flight, but what we can affect is going to be angle of attack. While not directly because this is an aerodynamic angle, we can affect it via the angle of incidence. So as we manipulate our flight controls, the angle of incidence changes.
So looking at a basic airfoil, let's say we've got the cord line, got our rotational relative wind, and we have a resultant relative wind corrected for this induced flow in here. This first angle is going to be the difference between the chord line and the rotational relative wind. It's going to be your angle of incidence. This line in between the resultant relative wind and the chord line is going to be your angle of attack.
So this angle of attack is where your lift is because it's being adjusted for this induced flow, but what we actually control is our angle of incidence. So although... Like I said earlier, the angle of attack is an aerodynamic angle, which we don't directly control. It is affected by our angle of incidence, a mechanical angle, which we control with our cyclic and collective inputs.
Now, for a better look at this, I recommend checking out some of my other videos. Something like my compensation for dissymmetry of lift video kind of breaks down this a little bit more. But I'll put that link in the description below, as well as a link should pop up in the video above. Now, the next element of the lift equation is going to be surface area. Alright, so surface area.
This refers to the general surface area of the airfoil or the rotor disc. Now the larger the area, the more lift with all other parts constant and vice versa. Now this is generally thought to be unchanged and unaffected by the pilot.
However, I'd like to consider rotor coning. Now as the rotor cones, its surface area decreases. So during normal rotation, the rotor system usually holds about, you know, about a 2 to 5 degree cone. But it's generally regarded as pretty... pretty fixed out to the left and right around the disc due to the centrifugal force holding it rigidly outward.
But as the rotor starts to cone, potentially coning up like this, and obviously this is a little bit drastic of an example, but we're looking at things like the difference in the surface area, the diameter difference in this rotor like this. As it starts to cone, it starts to decrease in surface area. So during normal rotation, the rotor system usually holds maybe a 0 to 2 degree coning attitude, but this indicates that there's more centrifugal force than lifting force. Now if the lifting force is greater than the rotational force, like in this coning example, a coning angle increases and the surface area decreases, and therefore lift is reduced.
Now some factors that affect the rotor coning, we'll just go ahead and write those out. Rotor coning. is going to be things like low rotor RPM. So as the rotor slows down, it's not able to hold its rigidity, and it starts to cone up. Things like high gross weights and also excessive g-forces.
Now all these factors affect the amount of rotor coning. So although we don't directly affect surface area, we can directly affect the amount of coning angle in the blades and thereby have secondary effects that affect our surface area. Now as a pilot, it's important to understand what are the factors you can and cannot affect, but these factors right here we definitely do have control of as we're flying the aircraft.
Alright, so that concludes the first part of the lift equation. We talked about the coefficient of lift as well as the surface area. In the next video, I want to start to cover the air density as well as velocity squared and kind of wrap all this up as far as what you can and cannot affect in the cockpit but stay tuned the next video should come up in the link should be in the description as well so stay tuned for that next video thanks for watching