Spinning (mis)concepts

Eric Greenwell wrote:

Marc Ramsey wrote:
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.

Yes, I use the spoilers at the same time. The spoilers work fine if you
are making a shallow approach at 60 knots or so. They are marginal,
at best, when making a high close-in approach at 70+ knots (typical
Truckee afternoon landing).

Marc

Getting down fast! I was getting ready to enter the
wave window at Mt. Mitchell, NC, and the cold suddenly
told me my bladder was about to let go. Full divebrakes
in a slipping turn got me on the runway in time, but
I had to jump out and run to a ditch beside the runway;
at 75 yards, the FBO toilet was just too far away.

At 20:48 29 January 2004, Eric Greenwell wrote:
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

Marc Ramsey wrote:
Eric Greenwell wrote:

Marc Ramsey wrote:

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.


Yes, I use the spoilers at the same time. The spoilers work fine if you
are making a shallow approach at 60 knots or so. They are marginal, at
best, when making a high close-in approach at 70+ knots (typical Truckee
afternoon landing).

If I understand this right:

1) you are coming down more steeply at 70 knots than you did at 60
knots, but it's still not steep enough;
2) and that's because at Truckee, you want to come in _very_ steeply
over/near the threshold to avoid the downwash off the end;
3) and at 80 knots, the descent would be steep enough, but you'd be
stopping wwaaayyy at the other end.

I've only made a couple of landings at Truckee, so I'm trying to picture
the situation.

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Eric Greenwell
Washington State
USA

Nyal Williams wrote:

Getting down fast! I was getting ready to enter the
wave window at Mt. Mitchell, NC, and the cold suddenly
told me my bladder was about to let go. Full divebrakes
in a slipping turn got me on the runway in time, but
I had to jump out and run to a ditch beside the runway;
at 75 yards, the FBO toilet was just too far away.

What speed did you use? Could you have just used full spoilers and
spiralled down at 90 knots or so (or faster, if air was smooth), and had
the same descent rate?
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Eric Greenwell
Washington State
USA

Eric Greenwell wrote:
If I understand this right:

1) you are coming down more steeply at 70 knots than you did at 60
knots, but it's still not steep enough;
2) and that's because at Truckee, you want to come in _very_ steeply
over/near the threshold to avoid the downwash off the end;
3) and at 80 knots, the descent would be steep enough, but you'd be
stopping wwaaayyy at the other end.

You've got it. The spoilers don't provide a lot of drag, so it takes a
bit of distance to burn off the extra 10 to 20 knots before making a
normal touchdown. You can fly it on and hit the fine hydraulic brake,
but then it will slam down on the nosewheel, making your partners nervous...

I've only made a couple of landings at Truckee, so I'm trying to picture
the situation.

For those who don't know, gliders at Truckee (near Lake Tahoe, elevation
5900 feet) normally use runway 19, which features a cliff-like drop off
at the threshold. In the afternoons, the winds are often between 15 and
30 knots right down the runway, which sets up an interesting rotor-like
condition just before the threshold, resulting in big sink and a
significant wind gradient. We normally try to arrange things on windy
days so the turn from base to final is over the numbers. But sometimes,
circumstances prevent that, like a Skyhawk put-putting along on final,
in which case you want lots of extra energy. Let me just say, if you
ever find yourself below the threshold of 19, *push*, then pull at the
last moment, and if you're lucky, you'll end up making a very low energy
landing right on the numbers...

Marc

(Mark James Boyd) wrote in message news:40194105$1@darkstar...
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


OK, I'll bite again.

Dutch rolls are, by definition, uncoordinated. So I would expect the
yaw string to be behaving as you said. It is your perception that is
wrong.

Tom

At 20:30 29 January 2004, Mark James Boyd wrote:

Perhaps (slipping turns for descent are) 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.


See the US Private & Commercial Glider Practical Test
Standards, Area of Operation IV on landings, Task R,
Slips to Landings. See also the Soaring Flight Manual
and its new FAA-published successor (whose name escapes
me).

Judy

At 21:00 29 January 2004, Marc Ramsey wrote:
Eric Greenwell wrote:
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.


Our Club Duo had iniffective airbrakes when we bought
it, and it also was standard practice to side-slip
on final (ie: not turning, going in a straight line).
We discovered that there was some packaging that prevented
the full travel of the airbrake. You should have your
glider checked out, as once we had our problem identified,
the airbrakes were quite good.

Pete Zeugma wrote:
We discovered that there was some packaging that prevented
the full travel of the airbrake.

What do you mean by "some packaging"?

Marc

At 04:30 30 January 2004, Marc Ramsey wrote:

For those who don't know, gliders at Truckee (near
Lake Tahoe, elevation
5900 feet) normally use runway 19, which features a
cliff-like drop off
at the threshold.

How long is your runway? Club I fly fairly often at
in Scotland, Deeside GC (Aboyne), has quite wonderful
rotor/curlover/wind shear right down to the deck in
strong southerlies. It has two thin (5m and 7m ish)
parallel runways about 500m long (all figs approx)
situated between two ridgelines. There are two windsocks
either side of the runways, and in these strong southerlies
the socks are generally pointing in opposite directions.
I've had many a fast landing there in these conditions,
80-90knots is quite typical. It is common practice
to run on all the way to the end of the runway, to
keep it clear at all times. Of course, what you forget
to mention is that these are airspeeds, not ground
speeds. Landing a glider at 90knots ground speed is
very exciting!