[Bob Kuczewski]

Thanks to Doug and Joe for suggesting this topic for the training manual.

Let me just start off with some advice that was given to me by John Heiney when he was mentoring me many years ago. This is from memory so it's not an exact quote.

I was trying out a new glider that I hadn't flown before and John warned me that a pilot will often fly a glider like this for a long flight near minimum sink and get the false impression that they've got it "dialed in". Then they pull on some speed for landing and find the glider is "all over the place". John advised me that I should try flying the glider fast at various times during my flight so I could get a feel for handling it under those conditions.

I took John's advice, and by the time I was ready to land, there were no surprises.

This chapter of the training manual should discuss various aspects of pilot induced oscillation (PIO).. We should include explanations, animations, and analogies. For example, a playground swing demonstrates how the timing of small inputs (bending and unbending at the knees) can build up to support large oscillations in position. Videos of PIO in flight might be augmented with diagrams and animations. Discussions of natural frequency might include everything from guitar strings to the Tacoma Narrows bridge.

Good topic Doug!!!   

[Bill Cummings]

PIO Can also result from not understanding the lag time from when a pilot shifts his/her weight until the glider responds to that weight shift.
https://youtu.be/sXk5Bg3QvMY

[dhmartens]

Sport 2 / 2C
https://www.willswing.com/hang-gliders/sport-2/

"... and an effective VG system, the Sport 2 offers glide performance across the speed range that is just slightly below that of the U2! The Sport 2 tracks straight and true at any speed, with no tendency towards oscillations. The Sport 2’s “on rails” directional stability makes aerotowing a breeze, and allows for confident, accurate landing approaches. .."

Willswing says it doesn't oscillate.

[Bill Cummings]

Pilot Induced Oscillation (P.I.O.)
Design Induced Oscillation (D.I,O.)
The old Airwave K-2 was near the best example of P.I.O. and D.I.O. all rolled into one glider.
During an early morning or late afternoon flight over a long ridge with laminar air holding me high above the terrain I’ve climbed up and stood on the base tube of the control frame. Also I wedged my neck and shoulders into the narrow apex of the down tubes (also called uprights). My body was locked stationary inside the control frame. The glider would continuously yaw left, right, left, right for four miles west then four miles east on Frontenac Ridge between Red Wing and Lake City, Minnesota.
No matter what the glider manufactures tell you this is not P.I.O.
I named it D.I.O.
When bored with that a pilot can go prone in the harness and still flying just as fast try to make it stop the adverse yawing with pilot input. Control then goes from bad to worse. Now you have P.I.O enhanced D.I.O. (Exciting.)
It takes longer figuring out how to control this situation at high speed than is does to either panic, throw your reserve parachute, or slow down. Slowing down works best until you can land and install a vertical stabilizer.