Spinning (mis)concepts

Todd Pattist wrote:
(Mark James Boyd) wrote:

I think a slip is an uncoordinated manuever where both wings
are at the same airspeed. A skid is an uncoordinated
manuever where the wings are at different airspeeds.

A slip can occur while you are flying straight or while
turning. By definition, a skid can *only* occur in a turn.

Aha. Quite true. I suppose I didn't include the slipping turn
because it is not generally taught, and could be a little
hard to grasp for brand new pilots...

I've also seen new pilots do skids on base to final, and tell me
they were doing a slip from base to final, and this was OK
because their previous instructor said slips are perfectly
safe. A+ for theory, D- for application...so I only teach
the kind of slips where both wings have the same airspeed...

In article ,
Jim wrote:
On Wed, 28 Jan 2004 16:32:45 -0500, Todd Pattist
wrote:

(Mark James Boyd) wrote:

I think a slip is an uncoordinated manuever where both wings
are at the same airspeed. A skid is an uncoordinated
manuever where the wings are at different airspeeds.

A slip can occur while you are flying straight or while
turning. By definition, a skid can *only* occur in a turn.


Well, maybe so, but my understanding of a skid is a little
different. In my notion of a skid it is a flight condition in which
the amount of rudder applied is too great for the amount of bank
applied.

I think a lot of this thread is about what exactly "the right
amount of rudder" is. String centered? Does wingspan matter?
Does angle of bank matter? Does roll rate matter? But these
are real nuances, so what you write above is something I'd
believe is fine...

Thus, in my thinking, if you are flying at zero bank -
not in a banked turn - ANY application of rudder will result in a
skid, not a slip.

Ahhh...mostly. I've flown some hella misrigged stuff (including my
own 172) and if you have more drag on the left aileron/flap/tip fairing/etc.
you may have to put in rudder even with the wings perfectly level
(0 bank). And I would call this a slip, in this case a straight slip
(even though the nose is cocked to the side) and the ground track
follows a straight line and both wings have the same airspeed. Jump planes
do this too when they have some yahoo hanging on the wing strut
hoping the pilot is holding the wheel brake for another few seconds...
(since the yahoo is standing on the wheel). As another poster mentioned,
this may not be the most aerodynamically clean slip, but I bet
the jumper prefers it to any bank angle...


Please let me know if I have this mixed up!

It seems like you have it well in hand, except for the
squirrel cases bored winter pilots come up with...

In article ,
Tom Seim wrote:

What is coordinated? Well, if the yaw string or ball were
at the CG, and centered, that would be coordinated. But
the string isn't. It is often in front of and higher than
the CG. When this is the case, at high roll rates,
and steep banks, keeping the yaw string
perfectly centered means I am in a skid.

Humm, so we are all flying uncoordinated in a turn?

I couldn't pass this up, so I calculated how much the yaw string is
off. Assume a 300' turn radius, the yaw string is 5' ahead of the CG
and is 4" long. With these numbers the yaw string is off by 0.033
inch, much smaller than the diameter of the string itself!

Tom

Several posters pointed this out. In my defense, I've seen
this sitting in the back seat of a glider with two yaw strings,
and I know it is real. However, as someone else pointed out,
the string is made even more sensitive by the canopy
splitting the airflow a little, so miniscule angles can
be detected.

I'm going to look a little more at how large of an impact
this really has. It may simply be dwarfed by the other effects,
and so small as to be insignificant, as Tom seems to suggest.

I'm still convinced of the second part though. I think there is
some significant error caused on the yaw string at slow airspeeds
with high roll rates when the string is above the
center of gravity...er...center of pressure (thanks for the
correction to this one too).

When I do high rate dutch rolls, the glider seems to
perfectly rotate around the axis, but the string is way
all over the place. Explain THAT whydontcha? :PPP

In article ,
Doug Taylor wrote:
(Mark James Boyd) wrote in message news:401810d2$1@darkstar...

Now I go up in my glider, and I get in straight flight,
and I pull the stick back to the stop, and hold it
perfectly centered for about a minute. If the CG or design
don't allow a continual stall, the glider bucks up and down
in pitch. I try my best to keep it straight, but eventually
a wing drops, and it goes into a bucking spin/spiral.
If the CG or design allow a continued
stall, I try my best to keep it straight, and a wing drops,
and it goes into a spin. If I keep the stick all the way
back and centered, I can change the direction of the
spin with rudder (including a momentary straightness)
but can't keep it straight consistently.

The only aircraft I've been able to do a true full stall
straight falling leaf is in Cezzna 150/152/172s.
Washout, dihedral, huge vertical stab, huge rudder, CG hanging low.
I've never been able to do a straight ahead stall, stick back and
centered for a full minute, in any glider.



You haven't flown a SparrowHawk yet! Couldn't resist a short remark
here. You can even hold the stick full aft AND be fully cross
controlled through a number of pitch breaks in the SparrowHawk.

Doug Taylor

I can imagine that with some dihedral, at some weight, and
with certain limits to the full travel of the controls,
one could design a glider to do this. If the sparrowhawk
also does this through the full range of pilot weights and
CG as well, that would be even more interesting.

I can't wait to try it! Sparrowhawk world tour?

Todd Pattist wrote:
(Mark James Boyd) wrote:

A+ for theory, D- for application...so I only teach
the kind of slips where both wings have the same airspeed...

I find that very odd. The slipping turn is a highly useful
maneuver.
Todd Pattist - "WH" Ventus C
(Remove DONTSPAMME from address to email reply.)

Perhaps this is something I will look more at.
I was never taught this, I was never asked to
demonstrate it during a dozen check rides, and
I haven't ever seen a written reference to a slipping
turn, so I perhaps haven't thought about it
much.

Hmmm...

Todd Pattist wrote:
A skidding turn, as you described is the opposite of a
slipping turn. The student needs to be taught the
difference. If he is doing a slipping turn, the yaw string
will be out of the turn, if he's skidding it will be inside
the turn.


A+ for theory, D- for application...so I only teach
the kind of slips where both wings have the same airspeed...


I find that very odd. The slipping turn is a highly useful
maneuver.

Refresh my memory, which doesn't seem to include this. Under what
circumstances and glider types would this be true? If I'm too high, I
adjust the pattern or open the airbrakes. I will slip on final for
crosswind compensation, but why would I want make slipping turns in the
pattern or elswhere?

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Eric Greenwell
Washington State
USA

Eric Greenwell wrote:
Refresh my memory, which doesn't seem to include this. Under what
circumstances and glider types would this be true? If I'm too high, I
adjust the pattern or open the airbrakes. I will slip on final for
crosswind compensation, but why would I want make slipping turns in the
pattern or elswhere?

When I'm flying our Duo, a slipping turn from base to final is my
standard procedure. I like to carry extra energy in the pattern (too
much flying at Truckee), but the airbrakes aren't terribly effective, so
I use a slipping turn to dissipate the excess energy, and hold it
until I'm at an acceptable (shallow) approach angle. It also makes it a
lot easier to see what's happening on the runway from the back seat.

Marc

Marc Ramsey wrote:

Eric Greenwell wrote:

Refresh my memory, which doesn't seem to include this. Under what
circumstances and glider types would this be true? If I'm too high, I
adjust the pattern or open the airbrakes. I will slip on final for
crosswind compensation, but why would I want make slipping turns in
the pattern or elswhere?

When I'm flying our Duo, a slipping turn from base to final is my
standard procedure. I like to carry extra energy in the pattern (too
much flying at Truckee), but the airbrakes aren't terribly effective, so
I use a slipping turn to dissipate the excess energy, and hold it until
I'm at an acceptable (shallow) approach angle. It also makes it a lot
easier to see what's happening on the runway from the back seat.

Are you using the spoilers at the same time? Of course, they won't help
the view from the back seat.

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Eric Greenwell
Washington State
USA

Todd Pattist wrote:

Eric Greenwell wrote:


Refresh my memory, which doesn't seem to include this. Under what
circumstances and glider types would this be true? If I'm too high, I
adjust the pattern or open the airbrakes. I will slip on final for
crosswind compensation, but why would I want make slipping turns in the
pattern or elswhere?


I suppose it's like asking why you would ever want spoilers
in a turn. You can retract them if you want, but I like
having some extra descent rate as an option. If your
spoilers are frozen shut, you can fly a normal pattern and
just substitute slip wherever you'd use spoilers.

We've got a short runway perpendicular to the ridge that
starts near the ridge base. It's nicely aligned with the
wind on a ridge day, but you have to fight the ridge lift on
base, hold your speed for safety in the turbulence, and you
can't open up your pattern due to the proximity of the
ridge. You need maximum descent rate if you want to land
short. I often slip through the base-final turn there.

Is it practical to just do a lower pattern, knowing the ridge lift is
there? Or is it not there once in a while?

Would it be practical to use a full spoiler "dive" (say, 70 knots) on
final to increase your approach angle, rather than slipping plus some
spoilers at a slower speed?

Plus, there are times when I can see the runway better in a
slipping turn.

In a two seater, like Marc?
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Eric Greenwell
Washington State
USA

In article ,
Todd Pattist wrote:

As a matter of interest, how did you handle the request to
demonstrate a "no airbrakes" landing where you needed a
forward slip on both base and final? Did you bring the
rudder fully through to the opposite side (inside of the
turn) to intersperse a coordinated turn between your forward
slips?

Yep. Exactly. I've used slips in taildraggers extensively,
during no-flap demonstrations, and on lots of checkrides.
Always interspersed a coordinated turn. Kinda funny
to write it here now that I think about it. Just something
I haven't done before, I can't really explain why...

And I've never been in a situation where this has been insufficient.
Combined with adjusting more by flying faster or slower than
best glide on final, this has worked ok.

A coupla aircraft (Katana, PW-5) have such little pipsqueak
popsicle stick rudders that slips seem to do VERY little,
and I've had to mostly use airspeed control for glideslope.
God forbid I hit positive shear or updrafts with no spoilers/flaps
in these ships: overshoot of even a long runway seems likely...