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In article <31a67daa.219667…@news.atcon.com>, gt…@ips.ca (GT) writes:
>Subject:    Slipping
>From:       gt…@ips.ca (GT)
>Date:       Sat, 25 May 1996 03:28:19 GMT

>When slipping in a C172 (left) usually so I can see better I find the
>air speed drops so I tend to push the nose down. Is the speed really
>dropping or is it due to the air being fowled around the pitot tube.

>Glenn Tate gt…@ips.ca

>GT Management Systems
>PO Box 222, SAckville, NS.
>Canada   B4E 2S9

<Install emoticon for surprise here, followed by <G> then, entering
reminder mode:>
Questions concerning aircraft systems:
On a C-172:
Where is the static source located? (Preflight checklist item)
What is it connected to (instruments)?
When in a left slip, what is the relationship between airflow and static
source?
(When in a right slip, what happens to the air near the static source?)
What effects will a left slip have on what is connected to the static
source?

Don’t read further for the fast answer. Consider it a mind problem.
——————————————————-

Where is the static source located? (Preflight checklist item)
Left side in front of door, behind firewall.
What is it connected to (instruments)?
Airspeed, Altimeter, Rate of Climb.

When in a left slip, what is the relationship between airflow and static
source?
Airflow is hitting (somewhat) the left side of the aircraft, causing a
higher pressure on the left side of the aircraft, increasing the pressure
at the static source.

(When in a right slip, what happens to the air near the static source?)
The airflow is hitting (somewhat) the right side of the aircraft, causing
a higher pressure on the right side, and a diminished pressure on the left
side, decreasing the pressure at the static source.

What effects will a left slip have on what is connected to the static
source?
Increased static pressure will cause the differential pressure between the
static source and the pitot (ram) pressure to diminish, the airspeed will
read lower than actual when not slipping to the left. When in a right slip
the airspeed will read higher due to reduced pressure at the static
source. (Yes, there is a small effect due to a different angle of airflow
at the pitot tube, but the effect is minor considering the changes in
static air source pressure. If you are attempting approaches at stall
speed then I don’t want to be there doing slips (see stall/spin entry
technique and "don’t do this near the ground" warnings))

The altimeter will read lower in a left slip, higher in a right slip.
The vertical velocity indicator will read an increased descent _while
entering the left slip_ and the actual rate of descent (+- instrument
errors) during the slip. A right slip will read less than actual rate
during entry into the slip. Since the time to get established in a slip is
longer than a second or two, this effect is usually unnoticed.

Question: why is the C-206 uneffected by this problem (more mind game,
some technical knowledge, or a good guess, is required)?

Stan

Question: If, at an altitude sufficent to recover from any possible
result, the aircraft is flown level at final approach speed and at a power
setting to sustain level flight, and then the elevator is not allowed to
change position further and the throttle is gently advanced to climb power
(aileron and rudder as required to maintain heading and compensate for
p-effect), when the climb stabilizes, what changes, if any, will there be
in airspeed? If the throttle were reduced from the approach speed level
flight, what changes would occur in airspeed? Would this happen in a jet?

At altitude, enter a slip, don’t change the position of the elevator, and
recover from the slip, again, without moving the elvator. Was the recovery
airspeed different from the entry speed? (Prior to entry, and after
recovery. Don’t consider indicator changes due to effects of slipping.)

The above question is for mental gymnastics only. Professional pilots on a
closed course. Do not attempt this at home. Seek and use Professional
Help. Your results are the result of your decisions and actions and not
mine, the pilot is in command and responsible for the ship, its contents,
crew, and passengers, where it goes, what is does, and how it arrives.
Your milage may vary. Some settling of the contents may have occurred
during shipment. Contents measured by wait, not VOLUME. Caution: Birth
causes Death, except in rare instances.

PPS: The C-206 has dual static sources, located on either side, with a "T"
connector which reduces any effect due to slipping.

GS

> GT wrote:

> > Is the speed really
> > dropping or is it due to the air being fowled around the pitot tube.

> Actually, it’ll only get "fowled" if you catch a bird on the pitot tube.
> <g>

One thing I think you guys are forgetting is that the static port is
on the left side of the nose in the Cessna aircraft I uusually fly.  In
any slip with right rudder, some dynamic air pressure is transferred
to that port, which makes the difference between it and the the pitot
pressure lower, giving a lower airspeed indication.  If you had left
rudder, there might well be negative pressure around the static port,
increasing the airspeed indication.  I’d bet that that has more effect
than any disturbance over the pitot.  Also, in the glider instance,
I was taught to use a slip with top rudder in a turn to lose altitude
fast, such as when finding myself too high on downwind or base.  I have
done this many times, and you will literally fall out of the sky in
that condition.  (It also works fantastically well in airplanes, like
trying to get back to the strip from a jump run without shock cooling
the cylinders.  You can descend at a great rate with cruise power.)

–
Ed Winchester,   CFI (A&G)
edwin@vl_wssf_mail.chinalake.navy.mil
ed…@ridgecrest.ca.us
http://www1.ridgecrest.ca.us/~edwin

(Dave Russell) writes:
>(I have flown a glider ’round and ’round in a circle, full rudder, full
>opposite aileron, and full aft stick to loose altitude fast.

To lose altitude in a hurry, I was taught to pull into a 60 degree bank
and use the spoiler/dive brake.  It works.  –Bill

_________________________________________________________________________
Wm W. Plummer, 7 Country Club D., Chelmsford MA  01824  508-256-9570
PP-ASEL,G

The 150 and 172 have a single static port on the left side of the
fuselage, forward of the pilot’s door.  
If you stomp on the right rudder (left slip), the left side of the
fuselage is pointed into the wind and has high pressure on it.  The
indicated airspeed (pressure difference between pitot and static ports)
drops.
If you stomp on the left rudder, the static port is on the low pressure
side and the indicated airspeed jumps up.

The 182 has dual static ports, one on each side, to minimize these
anomalous airspeed indications in slips.  When slipping a 172, ignore
the ASI and maintain pitch attitude.

> Is the speed really
> dropping or is it due to the air being fowled around the pitot tube.

Actually, it’ll only get "fowled" if you catch a bird on the pitot tube.
<g>

Walt
—
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Author:  "Cessna Warbirds, A Detailed and Personal History
          of Cessna’s Involvement in the Armed Forces"
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Shoemaker) writes:
> Yes, it is partially due to the angle of the pitot. But, if you want
> to see the effect of slipping and you want to make sure you don’t spin
> a hole into the ground, take it up to altitude and slip the hell out of
> it.

Three points…

1.  Yes, I agree.  Go up *high* and practice your slips first (as you practice
anything new, of course).

2.  I was told that it is hard for most GA aircraft to be stalled from a deep
slip, and I’ve found it true for every aircraft I’ve had the opportunity to
test it on.  Without a helpful wind gust, you tend to run out of elevator
authority before you can stall the wing.  Go up high and try it!

(I have flown a glider ’round and ’round in a circle, full rudder, full
opposite aileron, and full aft stick to loose altitude fast.  Very stable,
very easy, and it came down like a ROCK.  No hint of stalling or spinning.)

3.  I have flown airplanes where the ASI went wild when you slipped the ship
(like backwards past zero!).  My favorite instructor once told me that the
pitch attitude/airspeed doesn’t change in a slip.  Look at the horizon in
normal, coordinated flight, then fly that pitch attitude in your slip to get
the same airspeed; just remember to ignore the ASI.  It has always worked well
for me! (If anybody has a way to test this, I’d love to hear about it…)

Dave Russell        voice: 908 519-3965
druss…@synapse.bms.com
In God we trust, everything else we check.

Yes, it is partially due to the angle of the pitot. But, if you want
to see the effect of slipping and you want to make sure you don’t spin
a hole into the ground, take it up to altitude and slip the hell out
of it.

A lot of people make the mistake of practicing these things on
approach. Some of ‘em are dead. Take it up to altitude and work on it.

-john