Aero-Tips!
A good pilot is always learning -- how many times have you heard
this old standard throughout your flying career? There is no truer
statement in all of flying (well, with the possible exception of
"there are no old, bold pilots.")
Aero-News has called upon the expertise of Thomas P. Turner,
master CFI and all-around-good-guy, to bring our readers -- and us
-- daily tips to improve our skills as aviators. Some of them, you
may have heard before... but for each of us, there will also be
something we might never have considered before, or something that
didn't "stick" the way it should have the first time we memorized
it for the practical test.
Look for our daily Aero-Tips segments, coming each day to you
through the Aero-News Network.
Aero-Tips 09.04.06
A question came across my desktop:
I'm looking for data on Vyse as a function of gross vehicle
weight. I frequently fly alone and am wondering if I'm carrying
more speed than necessary on final approach to stay above blue
line.
First, let's define our terms. VYSE is the indicated airspeed
that results in the best rate of climb with one engine inoperative
in a twin-engine airplane. VYSE is usually depicted by a
blue-colored radial line on the airspeed indicator-hence "blue
line" speed. "Best rate of climb" is something of a misnomer, too;
in many cases VYSE is the speed that provides the least rate of
descent with an engine out.
I wrote back:
VYSE is by definition an airspeed determined under worst-case
conditions, which includes maximum takeoff weight. Like other
angle-of-attack-related airspeeds, there are no published
correction values for VYSE at lighter weights because by definition
VYSE exists only at maximum weight.
However, the effect of VYSE does decrease with a reduction in
aircraft weight. As a rough estimate in most light twins the
indicated airspeed drops at the rate of approximately two knots for
every 100 pounds below maximum takeoff weight.
Why don't you try an exercise? With a qualified multiengine
instructor along to help keep you out of trouble and to record data
as you fly, establish a safe altitude, put the left engine into
zero thrust (or even shut it down and feather the propeller for
maximum realism, doing so over an airport just in case practice
turns into a real single-engine landing), and establish VYSE /blue
line attitude. Note the rate of climb. Then increase pitch a degree
or two to reduce airspeed slightly and see what steady-state climb
rate results. Done safely this can be a fun and informative
flight.
And lastly, once you're committed to landing you need to reduce
airspeed below "blue line" to safely land. Flying in fast will
cause you to use a lot of excess runway to flare and stop. Typical
POH landing speed is 1.3 times the VMCA, the minimum controllable
airspeed with the critical engine inoperative…and "effective
VMCA" drops with a reduction in aircraft weight, too!
Aero-tip of the day: Understanding the
certification basis of performance speed helps you design carefully
controlled, safe experiments to determine the "best" technique for
nonstandard conditions.