Crab, slips, and crossed controls

Amine wrote in news:18e46a13-6294-4b68-9775-
:

Hey,

Some of you may have heard of Air Canada 143 [http://www.youtube.com/
watch?v=dfJIpA2gv1g] which ran out of fuel in mid air and had to make
an emergency descent at velocities way above the normal limits. The
pilot's makeshift technique was to engage a sideslip to decelerate the
aircraft (which by then had no flaps, and only minimal hydraulics).

Now I thought that sideslips (and crabs--whatever the difference
between the two is...) were only to be used to handle crosswinds.

They're different and they aren't just used for crosswinds.


I
didn't read anywhere that they could be used to bleed excessive speed,
although it makes sense from an aerodynamics perspective. Anyone out
there used sideslips for anything other than crosswind approaches?

PS: I have read about many cases of jetliners that had to make
emergency descents at abnormally high speeds, but the AC143 seems the
only one to have used the sideslip.



it isn't.


Bertie

Robert Moore wrote in
2.60:

Stealth Pilot wrote
Sideslips are a very useful tool because they allow you to
substantially increase the drag, which makes you descent like a
plumbers toolbag, but doesnt change the forward speed. so you have no
increased risk of stalling as you wash off the height.

What you have described is the "forward slip". Although control usage
is the same in both, a "side slip" is used to correct for a crosswind,
and a "forward slip" is used to descend more rapidly on final without
having the airspeed increase. If one is not landing, I suppose that it
would just be a "slip".

Airliners normally do not use either because of the increased discomfort
caused the passengers....both being uncoordinated flight.

Actually, they do. The 72 and 70 were kind of excepetions because of the
risk of dragging a flap or pod, but most jet airliners land better in
crosswinds when slipped.
Even the autopilot will slip it if you're doing an autoland



Bertie

Stefan wrote in news:1fb3$48d7ad48$54487392$9846
@news.hispeed.ch:

Robert Moore schrieb:

What you have described is the "forward slip". Although control usage
is the same in both, a "side slip" is used to correct for a crosswind,
and a "forward slip" is used to descend more rapidly

A slip is a slip is a slip.


No it isn't.


Bertie

Stefan wrote in news:9cc9b$48d7b746$54487392
:

Robert Moore schrieb:

A slip is a slip is a slip.

From The FAA H-8083-3a, Airplane Flying Handbook

Ok, so in the USA there exist several different brands of slips.

In the rest of the world however, a slip is a slip is a slip. Which is
how airplanes see it, too, I suppose.


You're full of ****, stefan.

Slips are slips no matter where you are and slips, while aerodynamically
identical have different references.






Bertie

Hi Amine,
I'll sometimes use a sideslip on final when I want to practice an approach
without using any flaps. When I was flying gliders I used to use a slip
often to augment the spoilers, especially while flying gliders that had no
flaps. Using a sideslip is a great way to control your rate of descent. But
be sure to read the aircraft POH to make sure that you understand the
conditions where a sideslip may not be recommended. The POH for a Cessna 172
does not recommend forward slips with the flaps down.

Randy L.

--
Remember: Any landing that you can walk away from,
is a landing that you can be fined, sued, or prosecuted for.

"Amine" wrote in message
...
Hey,

Anyone out
there used sideslips for anything other than crosswind approaches?

"RandyL" rlink(AT)cableone(DOT)net wrote in
:

Hi Amine,
I'll sometimes use a sideslip on final when I want to practice an
approach without using any flaps.

That's actually a forwad slip.




Bertie

Bertie the Bunyip schrieb:

You're full of ****, stefan.

Still better than completely hollow like you.

Slips are slips no matter where you are and slips, while aerodynamically
identical have different references.

Of course they have different references... visual references, that is:
In one, you look straight ahead, in the other, you look slightly to one
side. I'm fully aware that this difference is enough for simple minded
like you to think they are two different maneuvres.

Stefan wrote in
:

Bertie the Bunyip schrieb:

You're full of ****, stefan.

Still better than completely hollow like you.

Slips are slips no matter where you are and slips, while
aerodynamically identical have different references.

Of course they have different references... visual references, that
is: In one, you look straight ahead, in the other, you look slightly
to one side. I'm fully aware that this difference is enough for simple
minded like you to think they are two different maneuvres.


Yeah, right backpedaling boi.


Bertie

"RandyL" rlink(AT)cableone(DOT)net wrote
The POH for a Cessna 172 does not recommend forward slips
with the flaps down.

About once-a-year I post the following excerpt from "Cessna, Wings for
the World", a book by William D. Thompson.

Bill Thompson is an Aeronautical engineer from Purdue University and
worked for Cessna Aircraft Company for 28 years as an engineering test
pilot and later as the Manager of Flight Test & Aerodynamics.

-------------------------------------------------------------------
"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 ATP/CFI
12 years slipping with flaps in Skyhawks

Gig 601Xl Builder wrote in
m:

Once we were back on the ground and with his boss close by I left
him reading about them in the FAA Airplane Flying Handbook they
had in the office.

That's incredible. When I took my CFI Ride, I had to demonstrate a
maximum effort forward slip on final. Kicked out when I was over the
fence and hit the numbers. Seems as if your instructor didn't know the
difference between a slip and a skid.

--