Philip Greenspun’s Weblog » Cirrus SR20 crash in Manhattan:
My preliminary best guess (and at this point it can only be a guess) is that the two pilots on board the accident SR20 were cruising slowly up the East River. At some point, they decided that they’d reached the end of the little cut-out tongue of uncontrolled airspace over the East River. They attempted a 180-degree turn in an attempt to get southbound down the river toward uncontrolled airspace. An airplane in a sharp turn stalls at a much higher airspeed than when straight and level. Merely by putting the airplane into a steep bank and trying to hold altitude, they could have gone from flying to an aerodynamic stall (wings at too high an angle to the relative wind or, in simpler terms, air not moving fast enough over the wings) in a matter of seconds. At this point, the airplane is not easily controlled and a lot of bad things can happen. Low-speed low-level maneuvering, which typically happens when aircraft are trying to land, is the leading cause of plane crashes.
[It is possible to turn an airplane tightly and safely and is commonly done inside mountain valleys in Alaska (where guys just love to take off and head towards a pass to see if there is any separation between the clouds and the terrain; if not, they turn around and go back to their cabin). The trick is to slow down as much as possible. An ice skater going fast will use up a lot more ice in a 180-degree turn than an ice skater going very slowly. In an airplane, this means putting out flaps so that you can fly slower without stalling and slowing down to maybe 1.5 times stalling speed (in the Cirrus SR20 this would be about 75 knots with two people on board). At a slow speed, you have to be somewhat careful with bank angle because you are closer to the stalling speed. On the other hand, you don’t need a steep bank angle to make a tight turn because you’re only going about as fast as a car.]
8:25 AM
Dilettante Archives