Slipping in Turns

I toke a small radius just to show, how tigth the turn must be to get about
5-10 degree angle for thread. With a 60 m radius, the angle of thread is
about 1.7 degrees, if it shows the true slipping angle of the position,
where the thread is located.

Added the asymmetric force of the air to the another side of the glider
while slipping, I doubt if there is any even small advantage to do it. It
coud be vice versa, so that there is some advantage to do skidding, because
then the air forces the glider a bit towards the core.

In either case the effect seems to be very small and question looks like
quite academic. Those opposite vectors might even summarize to absolute zero
anywhere bethween this very small angle...?

js


"Dick Johnson" wrote in message
om...
"JS" wrote in message
...
Measured with a cad-program, for a turn radius of 30 m, the thread angle
should be 3.6 degrees, if the distance of the thread from cg is 2 m.
Tighter
turn, wider angle. How precisely you can keep your thread in a 3-4
degree
angle?

js

Hello JS -You must be flying a hang glider to be capable of turning a 30
meter radius while thermalling. For a given bank angle, the theoretical turn
radius is proportional to the square of the flight velocity. Right?
My unballasted Ventus requires about 48 kts of airspeed when
performing a 45 degree banked thermalling turn. Under those conditions
I calculate my turn radius to be about 204 ft, or 62 meters.
Dick Johnsonto

A better question might be, "which is better, a slight slip or a
slight skid?" Since we try to hold the yaw string at 0 degrees in
wings level flight, holding it at 5 to 10 degrees shouldn't be any
more difficult. As others have alluded, there are safety advantages to
holding slip rather than skid in a turn, therefore, it seems
worthwhile to at least make an effort to keep the nose a little
slipped for the sake of the airflow over the wings.

As for the angle of the yaw string, first, there is no one angle. It
will change directly proportionally to increasing bank and inversely
with increasing speed. The position of the yaw string relative to the
cg is significantly different for different models. And as you have
noted, individuals' abilities to distinguish small angles varies. This
is why I suggested a broad range of 5 to 10 degrees, rather than a
single case optimization. 5 degrees is about 2 minutes sweep of the
minute hand of a clock; 10 degrees is not quite 4. These are
discernable and useful.

"JS" wrote in message ...
Measured with a cad-program, for a turn radius of 30 m, the thread angle
should be 3.6 degrees, if the distance of the thread from cg is 2 m. Tighter
turn, wider angle. How precisely you can keep your thread in a 3-4 degree
angle?

js

"Chris OCallaghan" wrote in message
om...
Jim,

There was a thread on this subject a year or two ago, you might want
to search the archives.

The simple aerodynamic answer goes like this: The circle is traced by
the glider's center of gravity, which means that your nose extends
beyond the edge of the circle. To visualize, draw a circle, then draw
a line tangent to it. You can see that the nose and tail of your
fuselage transcribe larger circles. A yaw string forward of the cg
will show a slight slip for a coordinated turn (that is, coordinated
at the cg, or wing). If your yaw string is straight, then you are, in
fact, slightly skidding the turn. This effect also exists at the tail,
requiring you to hold a little bit of rudder into the turn (but not so
much that you straighten out the yaw string). Obviously, the longer
the arm, the greater the effect.

I've tried to observe the difference between the front and rear yaw
strings on a G103, but the canopy edge generates too much turbulence
to mark any clear difference.

For practical purposes, the slip is small (5 to 10 degrees).

John,

I'm not sure that I'm understanding what you said in your note, so let
me try to rephrase, then tell me if I'm getting it...

You are suggesting that because of spiral instability that the inboard
aileron must be deflected downward (to stop overbanking), leading to
increased drag. Another way to counteract this overbanking tendency is
to use the glider's dihedral by initiating a slip. (Dihedral rolls the
glider level if slightly slipped). This eliminates the costly drag at
the wing tip for less costly drag at the tail. Do I have this right?

If this is the case, it would require a larger slip (10 - 20 degrees),
since the slip must be extended to the wings. In the previous model,
we've kept the wings coordinated by compensating for the displacement
of the yaw string from the cg. Therefore, we saw no dihedral effects.
Has this been discussed previously?

(John Firth) wrote in message ...
Todd is quite right about the exagerated slip shown by the yaw string.
AS for slipping in turns, deliberately, I think the reason is to
counter the spiral instability; if you use opposite aileron input to
counter the bankinbg tendency then the inboard aileron (downward deflection)
will stall earlier then the outboard one; the objective is to fly as
slowly as possible for min. turn radius so leave the ailerons neutral
and slip to hold the bank angle.
Made a big difference in the Std Libelle. in circling speed.
John Firth
an old no longer bold soaring pilot.

Measured with a cad-program, for a turn radius of 30 m, the thread angle
should be 3.6 degrees, if the distance of the thread from cg is 2 m. Tighter
turn, wider angle. How precisely you can keep your thread in a 3-4 degree
angle?

The typical canopy shape causes the airflow to split which
appears to amplify the yaw string angle for small slip
angles.
Todd Pattist - "WH" Ventus C
(Remove DONTSPAMME from address to email reply.)

Just by talking to several world class glider pilots (including the
current world champion) in Leszno this summer and based on the
presentation given by Prof.M.D.Maughmer (The design and testing of a
winglet airfoil for low-speed aircraft)it turns out that gliders
equipped with winglets do not favor flying in a slip. In other cases
(gliders with no winglets), especially the open class gliders do favor
thermaling with a slight slip. Again, this is based on talking to and
observing those who know much more than an average glider pilot.
Milan Air
Robert John wrote in message ...
Because the turn you are creating by banking into the
thermal is soooooooo much bigger than the tiny turning
effect of the slip and, as has been said before, you
are slipping towards the centre of the thermal, which
has to be good. (Actually, you are slipping towards
a point that is always a little in front of the core,
but -hey- I can't fly that accurately either!)
Rob
At 10:42 26 November 2003, Js wrote:
What about this: when I press another pedal slowly
down an keep it there,
holding wings level, plane begins to fly round a point
at the noses and
pressed pedals side. Thread shows I am skidding to
opposite side. I could
allmost thermal like this, holding wings in level.

So why shoud I slip into thermal, becouse skidding
out of it turns the plane
into the direction of thermals core.

Complicated...

js


'Bert Willing' wrote in
message ...
I'm anyway too stupid to fly coordinated, so I choose
to better slip into
the thermal than skidding out of it :-)

--
Bert Willing

Jim Hendrix wrote:

I'm wondering if many people hold a mild slip in turns and why they do it.
Please reply to this post if you do this and give your reason(s).

I do.

Reason : it's easier... and why shouldn't I ?

Symmetrical flight is optimal in straight flight, not in turn. Even with
no slip nor skid (at the wings), a turn flight is NOT symmetrical (it is
either to the right, either to the left, never both !). The inner wing
goes slower than the outerwing, dihedral effect with slip helps
couteracting this dissymetry.

How much slip is optimal is another question, but SOME slip is
definitely optimal.

--
Denis
Private replies: remove "moncourrielest" from my e-mail address
Pour me répondre utiliser l'adresse courriel figurant après
moncourrielest" dans mon adresse courriel...

you plonkers! the only reason slipping into the turn works is,the glider
airspeed is controlled a lot better due to the fact the fuz is still trying to
climb, if you watch the asi you can see a closer smoother air speed thus stopping
the pilot from making to many corrections and chasing the asi.Moffit touched
on it in the 70s

noitall

I can't (plonk) seem to get (plonk) my arms (plonk) around this one.
Sadly, I need to see it discussed to its bitter end.

Could someone please elucidate... or translate. All I've got so far is
that if I slip my turns, my nervous tick won't be so grossly echoed by
the asi needle.

Young Pratt wrote in message ...
you plonkers! the only reason slipping into the turn works is,the glider
airspeed is controlled a lot better due to the fact the fuz is still trying to
climb, if you watch the asi you can see a closer smoother air speed thus stopping
the pilot from making to many corrections and chasing the asi.Moffit touched
on it in the 70s

noitall