Re: Slips?

From:         barr@netcom.com (Keith Barr)
Organization: Netcom Online Communications Services (408-241-9760 login: guest)
Date:         07 Jul 94 00:13:06 
References:   1
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In article <airliners.1994.1418@ohare.Chicago.COM> chris.wesley@tiuk.ti.com writes:
>ON my first flight ever (a Braniff 747 to Dallas from London), I was
>alarmed when the pilot did several things which might have been "slips".
> 
>The [plane] was banked to about 45 degrees, and my perception was that it
>fell quite dramatically, before the plane was righted. he did this maybe
>4 times.

There are two types of slips (which are both basically the same 
maneuver, they just accomplish different things).  The forward slip is
used to lose altitude rapidly, and the side slip is used to remain 
aligned with the runway during a crosswind landing.

Generally a forward slip is entered by pressing one rudder all the way to
the stop, by pushing the nose down, and by applying enough opposite
aileron (opposite in the sense that if right rudder is applied, you
move the ailerons as though you were entering a left turn) to remain in
control of the aircraft.  You will be descending very quickly and the
nose of the aircraft will be pointed in a direction not aligned with
the runway (in fact, as a pilot you are sometimes watching the runway
through a side window).

A side slip is accomplished in a similar manner.  When flying in coordinated
flight (rudder position appropriate to aileron position) in a crosswind, the
aircraft must be crabbed into the wind.  You tend to lose style points if
you attempt to land in a crab as it can be quite hard on the landing gear and
tires, and it tends to alarm any passengers.  The best thing to do then,
is to come out of the crab by pressing enough rudder to align the longitudinal
axis of the aircraft with the runway, but when the pilot does this, the 
crosswind will try to blow the aircraft off the side of the runway.  To offset 
this effect, the pilot should then add enough opposite aileron to hold the
airplane in position over the runway, all the way to touchdown (n.b. in a 
well accomplished crosswind landing, the aircraft will touch down on the gear
on the windward side of the aircraft first).

In *large* aircraft side slips are much more common than forward slips, because
needing to use a forward slip would generally indicate botched planning on
the approach.  Most airlines require pilots to be established in a stabilized
approach for some distance out, therefore a forward slip is not usually 
necessary.  Forward slips are much more common in light aircraft, especially
older models that are not equipped with flaps (an invention that can be used
to take the place of the forward slip to some extent).
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