Flight Training - June 2020 - 38

Engine power
and gross
weight reveal
surprisingly
little about
how much
runway an
airplane needs
for takeoff
and landing-
or the speeds
at which
it climbs,
cruises,
approaches,
and stalls.
If you want to
know those
things, pay
close attention
to an airplane's
"wing loading"
and "power
loading."

Wing loading is an
airplane's gross weight
divided by its wing area,
and it's usually expressed
in terms of pounds per
square foot. (A 1,000pound airplane with
100 square feet of wing
area has a wing loading
of 10 pounds per square
foot.) High wing loading
corresponds to higher
maximum cruise speeds
and greater stability in
turbulent air, but also
higher stall speeds and
longer takeoff and landing
distances.
Power loading is the
airplane's gross weight
divided by horsepower. (A
1,000-pound airplane with
a 100-horsepower engine
has a power loading of 10
pounds per horsepower.)
Airplanes with high power
loading typically have
lower fuel consumption and greater
endurance, but also lower cruise speeds,
longer takeoff rolls, and lower climb rates.
AOPA regularly pits similar general aviation
airplanes against each other in an ongoing Fly-Off
series-a Van's RV-7 against a Mustang II kitbuilt
airplane; a T-34 against a Nanchang CJ-6 military
aircraft; a Stearman against a Waco biplane; a Cessna
210 against a Beechcraft Bonanza A36; a Beech
Staggerwing against a Howard DGA-15; a Cessna 150
against a 152, a Cessna 182T Skylane against a Van's
RV-10, and a Cirrus SR22 against an RV-10. Myriad
other factors play into aircraft performance categories, but wing loading and power loading are critical.
In every matchup, the airplane with the higher wing
loading was shown to have a faster top speed, and
stall speed (both with flaps up and flaps down), than
its rival. And the airplane with the lower power
loading always had the better rate of climb.

FLIGHT TRAINING JUNE 2020

You almost didn't have to fly the airplanes side by
side, as we did, to know how they would stack up. But
pilots are a competitive, curious, "show me" bunch,
so we did the aerial drag races just to see if reality
matched the predictions on paper.
Before flying a Socata TB-30 Epsilon, for example,
the French military trainer's stubby wings obviously
meant it would have high wing loading, and the actual
number turns out to be 28 pounds per square foot-an
exceptionally high figure for a single-engine piston
trainer. Predictably, that high wing loading means the
Epsilon has a relatively long ground roll and relatively
high approach and stall speeds. On the positive side of
the ledger, the Epsilon's high wing loading gives it a
fast cruise speed (188 knots) and an unbelievably high
never exceed speed (282 knots).
One of the highest-performing piston warbirds of
all time was the Grumman F8F Bearcat-and its wing
loading and power loading figures show why U.S. Navy
pilots regarded it as such a beast. Small wings put Bearcat wing loading at almost 40 pounds per square foot,
and its power loading was an astonishing four pounds
per horsepower. No wonder modified Bearcats set so
many aircraft performance records, or that they later
dominated the Unlimited air racing category.
Perhaps no aircraft designer pushed wing
loading as far as Clarence Leonard "Kelly" Johnson,
Lockheed's legendary "skunk works" creator, who
dreamed up the P-38 Lightning and U-2 and SR-71
spyplanes, among others. Johnson's F-104 Starfighter
had impossibly thin, short wings (196 square feet) that
carried a mind-bending loading of 147 pounds per
square foot.
The Starfighter set multiple speed and altitude
records-but they also crashed a lot. Germany lost
about 30 percent of its 900 Starfighters in operational
accidents and darkly nicknamed them "witwenmacher," or widow maker.
Dean Stickell, a former U.S. Air Force pilot who
flew Starfighters in Europe, said the F-104's fearsome
reputation was largely undeserved. "It was an absolutely terrific airplane as long as you remembered
its limitations," he said. "As long as you didn't turn
below 300 knots or so, you'd be fine." FT
dave.hirschman@aopa.org

Flight Training - June 2020

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