The Wind Gradient
We refer to THE WIND GRADIENT the situation when during a short final you encounter a head wind that sensibly diminish in strength with the altitude.
As an example lets put down some numbers:
at 300 feet 30 knots
at 250 feet 25 knots
at 150 feet 22 knots
at 100 feet 7 knots
at 50 feet 6 knots
on the ground 5 knots
in this case you see that at 100 feet there is a significant change of the wind force.
Suddenly the wind is changing from 22 to 7 knots, 15 knots drop of the air ventilating the wings, it means that if you were flying at 50 knots suddenly the air speed drop at 35 knots.............. very, very close to stall speed.
With the Sinus on short final if you encounter such condition you better be prepared, particularly if you are in a downdraft at that point. What will happen is that you will see the Sinus dropping very quickly and if you are tempted to pull on the stick to stay in the normal descending path you may be in trouble.
In such a case the right air speed must be kept pitching the nose down, preventing the plane to stall and having sufficient inertia to carry out the flaring.
I did encounter such situation three times, I was very surprised and my passenger was impressed too.
From 150 feet I had the impression of descending almost vertically.
I did pitch the nose down and I did not gain any speed.
Flaring and touch down were normal.
As an example lets put down some numbers:
at 300 feet 30 knots
at 250 feet 25 knots
at 150 feet 22 knots
at 100 feet 7 knots
at 50 feet 6 knots
on the ground 5 knots
in this case you see that at 100 feet there is a significant change of the wind force.
Suddenly the wind is changing from 22 to 7 knots, 15 knots drop of the air ventilating the wings, it means that if you were flying at 50 knots suddenly the air speed drop at 35 knots.............. very, very close to stall speed.
With the Sinus on short final if you encounter such condition you better be prepared, particularly if you are in a downdraft at that point. What will happen is that you will see the Sinus dropping very quickly and if you are tempted to pull on the stick to stay in the normal descending path you may be in trouble.
In such a case the right air speed must be kept pitching the nose down, preventing the plane to stall and having sufficient inertia to carry out the flaring.
I did encounter such situation three times, I was very surprised and my passenger was impressed too.
From 150 feet I had the impression of descending almost vertically.
I did pitch the nose down and I did not gain any speed.
Flaring and touch down were normal.