‫Welcome back.
‫So let's analyze our airfoil now and let's see what forces it experiences.
‫So here you had one velocity vector or mega times R that was horizontal and then you had another velocity
‫vector, which was in red V.
‫V.
‫Omegle times are came from the fact that the model was actually rotating and then we saw we came from
‫this dream tube effect and so our airfoil saw two types of air velocities.
‫And since they are both vectors, then we could have a resultant velocity, which is this you?
‫This is the resultant air velocity that the airfoil sees.
‫And now we have to define a couple of angles.
‫The first angle that we're going to define, we're going to define a Seeta angle.
‫This is an Air Force pitch angle, and so you get it if you take your airfoil and this is your cord
‫length in green and it ends here at its nose at the Air Force nose.
‫So if you project this green line further than the air for a pitch angle is defined from this horizontal
‫line up until this green line.
‫So it gives you an idea of how much this airfoil is twisted upwards.
‫Then you have another angle, which is from here to here, and let's call it Alpha, this angle is called
‫the angle of attack is the angle that forms between this result and air velocity vector and then this
‫green line that goes along the core length of the airfoil.
‫In other words, you want to know how much the airfoil is twisted with respect to this resultant air
‫velocity.
‫And that's actually the most important angle in aerodynamics, because it's this angle.
‫What determines what kind of aerodynamic forces your airfoil experiences because aerodynamic forces
‫come from.
‫Airflows or er velocity's, and then we can define another angle here, and that would just be the difference
‫of Theta minus Alpha so we can say that it's PHI.
‫So due to this resultant air velocity, this airfoil will experience and aerodynamic force that we're
‫going to call the F sub A and now we have to decompose this vector and we're going to decompose it in
‫two different ways.
‫You can decompose it along horizontal and vertical axis.
‫So this would be the horizontal component.
‫And this would be the vertical component, so the horizontal component is along the same dimension,
‫like the rotation of the airfoil around the center of the motorised rotation.
‫And then the vertical component is perpendicular to that, we're going to call this component the DH
‫and this H is not angular.
‫Momentum is just a capital letter that I'm using to name this horizontal component of this D.F. sub
‫a vector.
‫And we're going to come back to this component later.
‫But this component, the vertical one that's called the T., which is the differential thrust.
‫So this is your aerodynamic force and this vertical component of it, this is what forms the thrust
‫force.
‫But that's not the only way you can decompose this force vector.
‫You can also define to access that are parallel to this U vector and perpendicular to it.
‫So this axis here would be parallel to the U vector.
‫So this would be your fly angle then like here.
‫And this axis here would be perpendicular to the U vector.
‫So if you shift your you vector here, then you would have 90 degrees here.
‫And now you can decompose this dates up a vector like this along these two axis.
‫In orange.
‫You have one vector here, which is this one perpendicular to the vector.
‫And the other component would be parallel to the new vector, so it would be like this.
‫So the component that is perpendicular to the vector, we call it the D.
‫L, which is a differential lift force.
‫So just for your knowledge, the lift force in general in aerodynamics is defined in such a way that
‫it is perpendicular to the resultant air velocity vector that the airfoil sees and then the component
‫parallel to the vector, that's what we call Didi's or differential drag.
‫So again, in general, in aerodynamics at drag force is a force vector that is parallel to the vector.
‫And so our objective now is to find the total thrust force that the entire blade generates, and once
‫we know that, then we can simply multiply by two and then we'll know how much thrust the entire model
‫will generate because each murder, remember, has two blades.
‫You find thrust for one blade and then the other blade will have the same thrust.
‫So that's why you can just multiply this by two and then you will know the total thrust force generated
‫by one more.
‫And then, of course, you find the thrusts of other three murders as well, and then you will sum them
‫all up, thrust one plus thrust two, plus thrust three and plus four.
‫And then you will know the total thrust that they are generating to lift the drone.
‫But let's go back to our airfoil now.
‫The thing is that in order to find the differential thrust force, you first have to express it in terms
‫of differential lift and differential drag force.
‫So you have to find DETI as a function of DL and D.
‫D, so this will be your little exercise.
‫So a little bit of work out in geometry.
‫Based on this information here, you see the angles, right, and you see the vectors, so based on
‫that, how would you write this DTA in terms of DL?
‫And so try it out yourself and then you'll see the solution in the next video.
‫Thank you very much.