[Music] welcome back to helicopter lessons in ten minutes or less I'm Jakob and today I just wanted to put out a short video that labels all of the forces that act on an airfoil now up to this point I've kept the airfoil terminology fairly simple but I think it's about time to just kind of expand this a little bit more and show a little bit more detail now starting off with the basics we have our airfoil so looking at space careful right here they can come in either symmetric or asymmetric shapes each with their own different benefits but from the leading edge to the trailing edge we have a cord line talk about that in my other video on the types of air foils but from the leading edge to the trailing edge we have a chord line and now this is going to give us our baseline for how to measure a lot of the other forces in relation to the blade now as the rotor turns around the mass it creates a rotational relative wind this is generally perpendicular to the axis of rotation when the aircraft is level so what we have right here is the axis of rotation so as the aircraft rotates around the mast this is its axis of rotation and now it's going to be impacting our rotational relative wind once again axis of rotation and I should have labeled it earlier but here's their cord line alright now this rotational relative wind sometimes called as the the tip path plane it's the the path that all the blades follow around the mast now do the fact that the rotor blades follow each other along the same path around the mast with increases in pitch angle it creates a downward flow of air through the through the rotor system so the blades are actually experiencing induced flow or downwash and deuced rag there's a lot of different names for it but this X on the airfoil something like this we're gonna have our induced flow all right so what's left over from this is going to give us a resultant relative wind so if we were to draw this right here intercepting that we're gonna have our resultant relative wind and just like the name and Plus this is the result of the the relative a wind of the relative wind as we modify it for induced flow now it's from here that we can find things like our angle of attack which is going to be where we get a lift from now our angle of attack this is the angle between the chord line and the resultant relative wind and it depicts the amount of lift that the airfoil is producing so this is going to be the angle like I said before between the chord line and the resultant relative wind so this angle right here is our angle of attack this is our lift this is where we're getting that lifting force on the airfoil now the difference between the chord line and the rotational relative wind is going to be our actual pitch angle this angle of attack we don't directly affect but this angle between the chord line and the rotational relative wind we do affect so this angle right here is our angle of incidence now this is usually confused fairly often the difference between angle of attack and angle of incidence so I'll just kind of talk about that a little bit more the angle of incidence is going to be a mechanical angle we directly control this with collective and cyclic inputs we are changing the pitch angle in the blade and adjusting this angle of incidence the angle of attack is an aerodynamic angle which is a product of our angle of incidence and our induced flow so we may want to increase our angle of attack but we actually control it by our angle of incidence by increasing that pitching we adjust this angle which then broadens this angle even more potentially affecting the amount of induced flow depending on the flight profiler and but from here it's necessary to note that lift X perpendicular to the resultant relative wind so what we're going to do we followed this resultant relative wind all the way back and just like the forces with lift weight thrust and drag this is bringing it opposite of the resultant noting our drag vector and then perpendicular to this we're having our lift vector alright so from this lift vector is where we're able to find our total aerodynamic force so based on the two vectors between our drag vector and our lift vector if we were to put those both together we generate what's called our total aerodynamic force vector now this is sometimes referred to as the resultant force and it's generally directed up and aft of the airfoil now you may notice that these angles over here are roughly the same as these angles over here this is just an easier way to depict it so we know of our lift and drag you know lift being generally up drag generally being aft this is an easier way for us to identify where those lift and drag variables come from whereas on this side of the chart it's kind of an easier method to depict how this air flow is actually impacting our airfoil so just it's the same angles that we're seeing right here it's just depicted slightly different ways to explain different things so as you notice right here these differences in lift and drag this induced flow right here now being this induced drag right here if you want to calculate it for your your lift and drag but from here we have the basic structure of the aerodynamic forces as they interact on the airfoil now if I say induced flow is increased without a change to angle of incidence it goes to say that that must be a reduction in angle of attack so if this gets larger without this increasing we're losing angle of attack so in essence we're losing lift so what does this mean this was this would be like if you were flying along and straight and level flight and then you decided to stop moving in forward flight and just make an approach to an out of ground effect hover without adjusting the collective this induced flow is going to increase if you didn't adjust collective your angle of attack would say right here your angle of or your angle of incidence would stay right here your angle of attack would actually be reduced and you would not be producing as much lift so you're going to note that the helicopter is falling and like what I said before angle of attack we control this mechanically with our flight controls so we need to increase this angle of attack in order to main or increase our angle of incidence in order to in order to maintain our angle of attack in order to continue flying and not fall out of the sky doing this maneuver now I don't expect every pilot to actively think about this chart anytime you're doing a take-off but it's good to understand these diagrams so that you can have a better understanding of how lift changes when going through things like ETL or the differences in air flow at hover especially the difference between say an inground effect and an outer ground effect over you know some of my other videos show about how this induced flow angle adjust you have differences in angle of attack and the differences in angle of incidence so this just kind of sets the framework for depicting how the forces act on the airfoil but that wraps up this video this that concludes the forces acting on an airfoil thanks again for watching helicopter lessons in ten minutes or less be sure to hit like and subscribe below and as well as leave a comment if you enjoyed or if you didn't enjoy what you like once again I'm Jacob thanks for watching and stay flying [Music]