Yesterday, I talked about the Miracle of Lift. Today, I will pass on some of the secrets of the short field landing. We’ll also discuss how the lift equation plays so importantly in “making the point.”
One of the most fun and challenging things about flying is the short field landing. I like it because, well, I like landing on short fields. There is no more boring a place to land than an “airport” with long concrete runways. Country airports with short, grass runways are so much more interesting and fun. (For the prospective pilots who really want the greatest challenge, make the runway move up and down and left and right as you approach to land.)
When it comes to landing on a short field, it is important to land right on the end of the runway. You cannot afford “float” and you cannot land short. There is no option when it comes to touchdown; it has to be on the spot. Additionally, you have to arrive at the spot right at stall speed.
The question is how do you get the airplane on the spot?
The first thing you have to know is where to aim. There are flight instructors who say aim short of the touchdown point. This is so wrong on many levels! Pilots who aim short of their touchdown point and flight instructors who teach that technique are using speed as a crutch and improperly.
If you are aiming short of your touchdown point, don’t be surprised if, one day, you end up landing short of the runway. This is okay if the area short of the runway is grass and you can roll onto the runway. However, if there is a lip to the runway, you will be leaving your landing gear at the end of the runway on the lip, while the aircraft continues down the runway sans wheels.
You have to remember what your driver’s ed coach told you about skidding on a wet or icy road. “Don’t look at the telephone pole!” They teach this because wherever the driver’s eyes are looking, that is where the car will go.
The same holds true of landing an airplane. When you are looking short of your point, the airplane will go to that point. If you fly beyond your aim point, it is because you are flying the approach too fast and the transition is improper, resulting in “float.”
As I said yesterday in explaining the lift equation, the math can be reduced down to the concept that lift equals speed times angle of attack (L = S x AoA).
The lift required for any airspeed or glide path is dependent on AoA. For instance, for straight and level, if the airplane weighs 2400 pounds, you can say the airplane is flying at 105 knots with 22.6 units of AoA. If the airplane stalls at 42 knots, the stalling AoA is 57.1 units. (Again, we have simplified the equation, disregarding the factors of rho and wing area.)
For an airplane flown on a short field approach, we assume a short field approach speed of 60 knots. This means the angle of attack will be 40 units AoA. Keep in mind power is the element that actually determines the glide path. The more power used, the shallower the approach path. For a steep approach, you would use idle power; for straight and level at slow flight, the power setting will be high.
Now for the approach and landing on a short field, we would use a reduced power setting for the steeper approach, we maintain the airspeed at 60 knots and we have the airplane trimmed to 40 units AoA. As long as we maintain this condition with the power set for the appropriate glide path, we will continue down the proper descent angle as we approach our aim point.
If we do not adjust power, but increase the AoA by pulling back on the yoke, the airplane will climb. In the same manner, if we reduce the power and maintain both airspeed and AoA, the airplane’s descent path becomes steeper.
Now, here is the trick for aiming at the point and touching down exactly where you are aiming.
If the pilot performs the coordination of speed and AoA correctly, he or she will reach the touchdown point on the runway with an airspeed of 42 knots (stall speed) and an AoA of 57.1 units AoA (stalling AoA). Oh, and by the way, there is no float because the wing has arrived at the runway at stall. So what makes the short field approach a little more challenging?
Varying and gusting wind, of course.
© 2011 J. Clark