Slipping in Turns

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).

Thanks, Jim Hendrix

Yes many do, me included. In the gliders I've tried it in, Grob 103 Ventus b and Mosquito, I find I have much better pitch control when turning steeply e.g. 45 deg. People argue the aerodynamic pros and cons. I figure if I can stay in a tight thermal more easily, or a more powerful core, I'll climb faster. Works for me.

Cheers,

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).

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

I'm anyway too stupid to fly coordinated, so I choose to better slip into the thermal than skidding out of it

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' < This e-mail address is being protected from spam bots, you need JavaScript enabled to view it > wrote in

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

I see it all the time in the L-23. The string in front shows a slight slip while the one for the back seat shows a coordinated turn.

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.

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

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.