Playing around with the pitch phugoid

This sounds very interesting for a pilot testing a new design or getting
to know his new glider. It certainly doesn't seem to me to have any
relationship with day to day soaring. Or is this simply a mind experiment?

On 7/9/2015 8:51 AM, wrote:
Interesting replies, thanks for chiming in.

I certainly agree that the phugoid is HUGELY damped by adding drag.

I would suggest that even some pilots who consider themselves well trained in "partial panel" flying, may not be really be familiar with the best way to end a pronounced pitch phugoid. And also may not appreciate the fact that in some sailplanes at some loadings, in the absence of pilot inputs, the pitch phugoid can tend to slowly get larger and larger, to the point where there is a stall break at the point of minimum airspeed. Even in a glider that seems quite well-behaved in normal visual flying.

If you disagree with my suggested inputs, I'd invite you to explore the phugoid a bit yourself. Accelerate or decelerate to 20 mph/ knots above or below the trimmed speed, let go the stick, and watch what happens.

I'd suggest that during a well-developed phugoid, if the airspeed is increasing (or is momentarily frozen and about to increase), the pilot ought be applying aft pressure on the stick, and if the airspeed is decreasing (or is momentarily frozen at a peak value and about to decrease), the pilot ought be applying forward pressure on the stick. I'd suggest that the very best opportunity for decisively breaking the phugoid is the moment where the airspeed peaks and as about to start decreasing. The glider is in a nearly level attitude at the "bottom" of an oscillation cycle at this instant. I'd suggest that if the airspeed is well above the trimmed airspeed at this moment, it will indeed take quite an "aggressive" push on the stick to freeze the airspeed at this moment. Then the glider can be slowly eased back to trim speed.

If this seems wrong to you, I'd invite you to explore the phugoid a bit yourself the next time you fly-- you might find the suggestion makes more sense after some hands-on explorations.

Or you may find that your glider is so dynamically stable at your loading, that the pitch phugoid is a non-issue.

S

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Dan Marotta