Flap angles

In article , Rick
Durden wrote:

There is no problem with slips with full flaps on a 172, it's another
of aviation's old wives tales.

Why does the 1979 C172N have a placard by the flap switch that states,
"AVOID SLIPS WITH FLAPS EXTENDED"?

"EDR" wrote in message
...
Why does the 1979 C172N have a placard by the flap switch that states,
"AVOID SLIPS WITH FLAPS EXTENDED"?

The insightful folks at Cessna were experimenting with trolling USENET.

HECTOP
PP-ASEL-IA
http://www.maxho.com
maxho_at_maxho.com

EDR wrote

Why does the 1979 C172N have a placard by the flap switch that states,
"AVOID SLIPS WITH FLAPS EXTENDED"?

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.

I would hope that everyone would copy this to their documents folder
and recall it every time that the subject comes up.

"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."

Bob Moore

zatatime wrote in message . ..
On 16 May 2004 02:06:53 GMT, (Teacherjh)
wrote:


"why do some 172's have 40 degrees of
flap avalible and others only have 38?"


Dunno about 38, but the newer ones have 30, because full 40 degree flaps were
causing problems (which I can't recall) due to poor technique of some sort.

Might have something to do with slips with flaps, IIRC.

Jose

Yep, slips with flaps was part of it, but a nose high attitude with
full flaps on go-around is what bit most of the people before they
changed to 30.

z

This month's edition of Flying has a good article by Richard Collins
about landings and a lot of the article is devoted to the use (or when
appropriate, the non-use) of flaps

Blue Skies

John

On Sun, 16 May 2004 15:14:19 GMT, Bob Moore
wrote:

EDR wrote

Why does the 1979 C172N have a placard by the flap switch that states,
"AVOID SLIPS WITH FLAPS EXTENDED"?

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.

I would hope that everyone would copy this to their documents folder
and recall it every time that the subject comes up.

"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."

Bob Moore


Thank you for this information! I've experienced this at high
altitude and try to pass along the info to others, but most of the
time I receive stubborn feedback like "I've never had a problem
so...." Now I can show documentation! One of my biggest pet peeves
are CFIs who actually teach people to slip a 172 with flaps.

Thanks again.
z

On 16 May 2004 09:17:09 -0700, (John Pelchat)
wrote:

zatatime wrote in message . ..
On 16 May 2004 02:06:53 GMT, (Teacherjh)
wrote:


"why do some 172's have 40 degrees of
flap avalible and others only have 38?"


Dunno about 38, but the newer ones have 30, because full 40 degree flaps were
causing problems (which I can't recall) due to poor technique of some sort.

Might have something to do with slips with flaps, IIRC.

Jose

Yep, slips with flaps was part of it, but a nose high attitude with
full flaps on go-around is what bit most of the people before they
changed to 30.

z

This month's edition of Flying has a good article by Richard Collins
about landings and a lot of the article is devoted to the use (or when
appropriate, the non-use) of flaps

If you are referring to the May issue (we don't all receive our issues
at the same time) then no it doesn't.

It does have one by Tom Benneson though on page 84.

There's a lot in that article to which I take issue.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

Blue Skies

John

One of my biggest pet peeves are CFIs who actually teach people to
slip a 172 with flaps.

Interesting that the only thing you picked up on was that which
supported your preconception.

"zatatime" wrote in message

Thank you for this information! .... One of my biggest pet peeves
are CFIs who actually teach people to slip a 172 with flaps.


???????

Did you read what Cpt Moore posted?

Bob,

Yeah, Bill Thompson sometimes got a little sensational to sell his
books. sigh

The POH for the new 172s deals specifically with the subject. Slips
with full flaps can cause some oscillation in the control wheel, but
it does not affect control of the aircraft. And that was only in a
very significant, controls nearly to the stop, slip. For a normal
crosswind landing, it's a non-event. Pilots are more at risk by
landing with partial flaps and losing control because they touch down
fast than landing with full flaps at a slower touchdown speed.

Ah, well, the discussion will continue without resolution forever,
while pilots continue to land with partial flaps and lose control of
their airplanes on rollout and then are puzzled as to why it happened.

All the best,
Rick

Bob Moore wrote in message .6...
EDR wrote

Why does the 1979 C172N have a placard by the flap switch that states,
"AVOID SLIPS WITH FLAPS EXTENDED"?

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.

I would hope that everyone would copy this to their documents folder
and recall it every time that the subject comes up.

"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."

Bob Moore

Hi,

Recently, Rick Durden posted:

I'm always amazed at the amount of misinformation running around here.

(snip)

There is no problem with slips with full flaps on a 172, it's another
of aviation's old wives tales.

So... I suppose that Cessna was so taken with this "old wive's tale" that
they decided to include a warning against it in the POH? ;-)

That said, I have slipped 172s with full flaps and lived to tell about it.

Neil