Friday, August 24, 2012

Pussy Footing Around - Detecting a Cushion

Sensing Float (Buoyancy)

In landing an airplane sensations you receive from the plane to you are very important. Short fields require sensitivity to the subtle clues that affect lift. Floating is not nice as you run out of runway.

You want a slight cushion, when you land, to flare out, check the descent of your plane and contact the ground. This is the very slight touch of your wheels in a perfect landing. The "Ahh, what a landing" reaction from pilot and passengers. 

This is "flying the edge" to some folks. To arrive at the edge and not drop off the cliff is the goal in every landing.

We talked about lift reserve before. The perfect landing results from a cushion of reserve lift that allows the plane to touchdown quickly with as little float when you pull back on the stick or wheel and stall.

When you pull back on the stick you don't want to feel a surge of lift that requires a checking of the descent from you!

At altitude you can test the effect by flying a slow glide at the very edge of a stall. When you pull the stick back a few inches the flight path of the plane does not go up. Instead the plane begins to stall and settle. The flight path goes down. In a fast glide, with lots of reserve lift, when you pull back on the stick a few inches, the plane balloons with a firm push into your bottom. Net result is an upward flight path and a much longer movement forward before the plane settles down to land.

At altitude you can't  really see the deflection of the aircraft upward. You feel it. In an actual landing flare, near the ground, the slightest ballooning or settling of the plane is very apparent to the eye. You feel the changes you make in the stick position by sensing the slight weight changes (lightness or heaviness) that occur from stick handling.

If a pull back on the stick makes you feel slightly heavier you are gliding too fast and the plane "floats" until the glide slows.

If you pull back on the stick and you feel lighter, like going down in a fast elevator, your reserve of lift is limited and you descend.

Your perception of weight change is very sensitive. You make a conscious effort to pay attention to that "sense" and act accordingly. If you are a passenger in the right seat of a small plane during the final stages of a landing you will see the pilot make small changes in the stick position (both back and forward) as he "senses" the planes descent to a perfect landing.

This gives credence to the term "flying by the seat of your pants" when landing an airplane.

In conclusion, sensing the cushion effect is important to a good approach and landing. Your senses become very sensitive as you glide lower to the ground and control movements are limited to prevent major changes in flight attitude (up and down).