Slipping with flaps....Cessna test pilot

The following paragraph is copied from the book "Cessna, Wings for the
World" written by William D. Thompson, an Engineering Test Pilot and later
Manager of Flight Test and Aerodynamics at the Cessna Aircraft Co.


With the advent of the large slotted flaps in the C-170, C-180, and C-172 we
encountered a nose down pitch in forward slips with the wing flaps
deflected. In some cases it was severe enough to lift the pilot against his
seat belt if he was slow in checking the motion. For this reason a caution
note was placed in most of the owner's manuals under "Landings" reading
"Slips should be avoided with flap settings greater than 30° due to a
downward pitch encountered under certain combinations of airspeed, side-slip
angle, and center of gravity loadings". Since wing-low drift correction in
cross-wind landings is normally performed with a minimum flap setting (for
better rudder control) this limitation did not apply to that maneuver. The
cause of the pitching motion is the transition of a strong wing downwash
over the tail in straight flight to a lessened downwash angle over part of
the horizontal tail caused by the influence of a relative "upwash increment"
from the upturned aileron in slipping flight. Although not stated in the
owner's manuals, we privately encouraged flight instructors to explore these
effects at high altitude, and to pass on the information to their students.
This phenomenon was elusive and sometimes hard to duplicate, but it was
thought that a pilot should be aware of its existence and know how to
counter-act it if it occurs close to the ground.

When the larger dorsal fin was adopted in the 1972 C-172L, this side-slip
pitch phenomenon was eliminated, but the cautionary placard was retained. In
the higher-powered C-172P and C-R172 the placard was applicable to a mild
pitch "pumping" motion resulting from flap outboard-end vortex impingement
on the horizontal tail at some combinations of side-slip angle, power, and
airspeed.

Karl
"Curator"

And this was posted why?

"karl gruber" wrote in message
...
The following paragraph is copied from the book "Cessna, Wings for the
World" written by William D. Thompson, an Engineering Test Pilot and later
Manager of Flight Test and Aerodynamics at the Cessna Aircraft Co.


With the advent of the large slotted flaps in the C-170, C-180, and C-172
we encountered a nose down pitch in forward slips with the wing flaps
deflected. In some cases it was severe enough to lift the pilot against
his seat belt if he was slow in checking the motion. For this reason a
caution note was placed in most of the owner's manuals under "Landings"
reading "Slips should be avoided with flap settings greater than 30° due
to a downward pitch encountered under certain combinations of airspeed,
side-slip angle, and center of gravity loadings". Since wing-low drift
correction in cross-wind landings is normally performed with a minimum
flap setting (for better rudder control) this limitation did not apply to
that maneuver. The cause of the pitching motion is the transition of a
strong wing downwash over the tail in straight flight to a lessened
downwash angle over part of the horizontal tail caused by the influence of
a relative "upwash increment" from the upturned aileron in slipping
flight. Although not stated in the owner's manuals, we privately
encouraged flight instructors to explore these effects at high altitude,
and to pass on the information to their students.
This phenomenon was elusive and sometimes hard to duplicate, but it was
thought that a pilot should be aware of its existence and know how to
counter-act it if it occurs close to the ground.

When the larger dorsal fin was adopted in the 1972 C-172L, this side-slip
pitch phenomenon was eliminated, but the cautionary placard was retained.
In the higher-powered C-172P and C-R172 the placard was applicable to a
mild pitch "pumping" motion resulting from flap outboard-end vortex
impingement on the horizontal tail at some combinations of side-slip
angle, power, and airspeed.

Karl
"Curator"

Bob,

Your posts are always so good that I've taken up posting them again a week
later.

Karl


"Bob Moore" wrote in message
46.128...
BT wrote

And this was posted why?

"karl gruber"wrote in message
The following paragraph is copied from the book "Cessna, Wings for
the World" written by William D. Thompson, an Engineering Test Pilot
and later Manager of Flight Test and Aerodynamics at the Cessna
Aircraft Co.

Probably because I posted the same excerpt a week ago ???? Wonder
where Karl was?

Bob Moore