JByrd
03-11-2006, 04:25 PM
I have a request for your comment. In the Part 141 class my son and I are taking at the Langley Aero Club we are using the Jeppesen course.
I have had the course before, about 22 years ago. I am still puzzled at the description of induced drag. It is rather interesting as though it is treated in the literature as if induced drag only appears at high angles of AOA.
I am more inclined to describe it as a rotation of the lift line from the CP location to a more aft angle with respect to the chord line. If split into a perpendicular to chord and parallel to chord component it describes a lift and drag vector. However these are only components of the true lift line.
In some aircraft such as the F-18 there is a near continuous deployment of the leading edge slat to 6 degrees down. This does not reduce drag, it actually increases it slightly. The overall effect is that it rotates the lift line from the cp forward more perperdicular to the chord. The plane actually speeds up with little penalty in increased drag from deployment of the slat. This was discovered quite by accident in flight tests. It was seen in wind tunnel data and not fully exploited.
It is interesting to note that on some commuter aircraft and especially the B-52 deploying the flaps to full position rotates the lift vector so far aft that the airplane trims nose down in level flight. What is more odd is to see a B-52 climbing rapidly with the nose down.
Any comments?
We had a beautiful 73F day here in NNVA.
Jim
I have had the course before, about 22 years ago. I am still puzzled at the description of induced drag. It is rather interesting as though it is treated in the literature as if induced drag only appears at high angles of AOA.
I am more inclined to describe it as a rotation of the lift line from the CP location to a more aft angle with respect to the chord line. If split into a perpendicular to chord and parallel to chord component it describes a lift and drag vector. However these are only components of the true lift line.
In some aircraft such as the F-18 there is a near continuous deployment of the leading edge slat to 6 degrees down. This does not reduce drag, it actually increases it slightly. The overall effect is that it rotates the lift line from the cp forward more perperdicular to the chord. The plane actually speeds up with little penalty in increased drag from deployment of the slat. This was discovered quite by accident in flight tests. It was seen in wind tunnel data and not fully exploited.
It is interesting to note that on some commuter aircraft and especially the B-52 deploying the flaps to full position rotates the lift vector so far aft that the airplane trims nose down in level flight. What is more odd is to see a B-52 climbing rapidly with the nose down.
Any comments?
We had a beautiful 73F day here in NNVA.
Jim