NPTEL is lucky ..they have hv such excellent professor..dear professor..unfortunately i m not in IIT KANPUR..ur videos r far better than other stability videos on the same topic.. you are amging sir..
The moment of force causes the body to rotate about an axis. The motion will not be translational. The force is applied to the body which tends the body to twist about the axis. It is due to the unequal and opposite force the moment is produced. The magnitude of the moment of force is directly proportional to the force applied and the distance of the force from the axis. The perpendicular distance between the line of action and the center of moments can be termed as moment arm. Therefore, Moment=F×d Where F, is the force and d, is the moment arm. The center of the moment is the reference point at which the force will cause the rotation. If the rotation is clockwise about the center of the moment we can say that the moment is positive. And if the rotation is anticlockwise about the center of the moment then the moment is negative. The force will have a tendency to act opposite hence the body twists. If the moment of force is assigned a negative sign then the turning tendency of the force will be clockwise. Note: The tendency of the force to act in the opposite direction and the unequal force will create the moment of force. Hence the negative moment having rotation in anti-clockwise is having a clockwise force.
Dear sir, at 11:42 , the delta alpha made by you is going downwards, that I interpreted that you are talking about nose down condition..It's very confusing..Can't you make that delta alpha in upper direction, means nose up condition..
Sir, you said we don't want to trim ac at -ve AOA . Can you throw some light on it as to why is it so? Because theoretically at -ve AOA also we'll get trim condition of L=W & T=D.
If we need a positive lift from a cambered wing it will generate a negative pitching moment considering Cg,a/c ahead of Ac,w therefore we require horizontal stabilizer or elevator to give a pitch down moment to balance that. In the video sir mentions the Cm,cg,o to be positive and alpha trim to be positive for "The whole aircraft". Meaning, in a alpha=0 situation we will have a positive Cm,cg,o (due to pitch up elevator deflection) only to decrease to zero as the alpha increases to alpha trim, keeping alpha trim >0 for more lift due to more camber. Why is Cm,cg,o made positive? to make the alpha trim positive possible.
because for cambered airfoil there will be irregular distribution of pressure and shear forces. So if we sum up all the forces into L,D at aerodynamic center there will also be a moment cmac. For symmetric airfoil this is 0
Watched it 2x speed 👍....elaborative teaching
NPTEL is lucky ..they have hv such excellent professor..dear professor..unfortunately i m not in IIT KANPUR..ur videos r far better than other stability videos on the same topic.. you are amging sir..
got good insight with those considerations of different cases.Thank you very much sir.
great professor.
If the direction of Cmac is clockwise then how it's negative and will produce pitching down moment?
The moment of force causes the body to rotate about an axis. The motion will not be translational. The force is applied to the body which tends the body to twist about the axis. It is due to the unequal and opposite force the moment is produced.
The magnitude of the moment of force is directly proportional to the force applied and the distance of the force from the axis. The perpendicular distance between the line of action and the center of moments can be termed as moment arm. Therefore,
Moment=F×d
Where F, is the force and d, is the moment arm.
The center of the moment is the reference point at which the force will cause the rotation. If the rotation is clockwise about the center of the moment we can say that the moment is positive. And if the rotation is anticlockwise about the center of the moment then the moment is negative. The force will have a tendency to act opposite hence the body twists.
If the moment of force is assigned a negative sign then the turning tendency of the force will be clockwise.
Note:
The tendency of the force to act in the opposite direction and the unequal force will create the moment of force. Hence the negative moment having rotation in anti-clockwise is having a clockwise force.
26:41/30:28. by looking that diagram it shows that the slope is positive, but in video 26:41/30:28 diagram how come slope is negative??
Dear sir, at 11:42 , the delta alpha made by you is going downwards, that I interpreted that you are talking about nose down condition..It's very confusing..Can't you make that delta alpha in upper direction, means nose up condition..
I had the same query
Sir, you said we don't want to trim ac at -ve AOA . Can you throw some light on it as to why is it so? Because theoretically at -ve AOA also we'll get trim condition of L=W & T=D.
If we need a positive lift from a cambered wing it will generate a negative pitching moment considering Cg,a/c ahead of Ac,w therefore we require horizontal stabilizer or elevator to give a pitch down moment to balance that. In the video sir mentions the Cm,cg,o to be positive and alpha trim to be positive for "The whole aircraft". Meaning, in a alpha=0 situation we will have a positive Cm,cg,o (due to pitch up elevator deflection) only to decrease to zero as the alpha increases to alpha trim, keeping alpha trim >0 for more lift due to more camber. Why is Cm,cg,o made positive? to make the alpha trim positive possible.
Thank you sir for the nice lecture
good explanation sir, thank you sir
sir can you explain y in a cambered aerofoil cmac
because for cambered airfoil there will be irregular distribution of pressure and shear forces. So if we sum up all the forces into L,D at aerodynamic center there will also be a moment cmac. For symmetric airfoil this is 0