פורסם עם: General Aviation
August 2008
THE WHEELBARROW
What do a porpoise and a wheelbarrow have in common? An airplane can do a convincing imitation of either when problems crop up during ground runs. Touching down in an improper attitude, with too high an airspeed and rate of descent, famously leads to porpoising and accidents involving pilots in training. Learn more about porpoising in the April 16, 2004, "Training Tip."
Less recognized because of its less-spectacular symptoms is the problem of wheelbarrowing. But to anyone who has spent time pushing a real wheelbarrow, the term authentically depicts an airplane speeding along the runway with its nosewheel planted too firmly on the ground and its tail surfaces and main gear constrained from performing their functions.
That's why it's worth taking some time to understand wheelbarrowing, its causes, and its possible results. "Normally, 'wheelbarrowing' may be encountered if the pilot is utilizing excess approach speed in a full flap configuration that results in the aircraft touching down with little or no rotation," explains an FAA advisory circular. "After this touchdown, the pilot may then try to hold the aircraft on the ground with forward pressure on the control wheel. Under these conditions, braking and steering capability is severely diminished and 'wheelbarrowing' is likely to result." This is particularly so in crosswind conditions.
Wheelbarrowing is a takeoff hazard as well. Note that the effect "can occur at lower speeds than during landing due to the propwash increasing the lifting power of the horizontal stabilator. The use of excessive forward stick pressure during takeoff to hold the airplane on the ground to speeds above normal takeoff speed is not recommended," adds the advisory circular.
When landing, a good roundout is always the proper first step. It's also insurance against the wheelbarrow because it sets you up to touch down in the correct nose-up attitude, as Tom Horne explains in "Touchdown" from the September 2003 AOPA Pilot. Another resource for studying the wheelbarrow phenomenon, and how to steer clear of it, is the discussion in Chapter 8 of the Airplane Flying Handbook. Note the proper and simple wheelbarrow-repair techniques given: Smoothly apply back-elevator pressure, or, if it's too late for that, go around!