Comment from SD

[Home] to paraglide.net [SD Log] [Amigo] [Activity] [Photo] [Comments] [Incidents] [Weather] [SBSA] [SCPA]

Sundowner Comment on Zvi's 50% asymmetric resulting in a spiral dive.

In DHV testing they check behavior in both spiral dive and 50% asymmetric collapse, but not necessarily both at the same time. Many gliders will behave quite docile if a 50% asymmetric is induced from trim. Even on a DHV 2-3 you can often seat steer without break input and maintain control.

In active air you might loose a wing due to low angle of attack as the canopy is surging forward. The increased wing loading (higher loading because you have less canopy for the same weight) can aggravate the surge. With half the wing tucked the surging canopy will want to spiral toward the tucked side due to asymmetric drag. Drag increases with the square of the airspeed and there is a lot of airspeed in a spiral dive. The high airspeed and low angle of attack will keep the tucked wing pinned under.

You reinflate a tucked wing by increasing the angle of attack. This might be accomplished without conscious pilot input if the spiral is not symmetric and the pilot oscillates through. You can also increase the angle of attack by pulling on the outside break. You want to maintain directional control anyway so it accomplishes two goals. Note that it can take a lot of force to pull the break because break pressure is dependant on wing loading and airspeed, both of which are high in the above scenario. If you increase the angle of attack too much, it is possible to stall the good side and that might result in a spin.

You want to have peripheral awareness of and manage a number of parameters during flight including:

Angle of Attack
Loading
Canopy Pressure
Energy
Airspeed
Oscillation timing & magnitude

They're all important and interdependent, but Angle of Attack awareness and management is probably the most important most of the time.
see [Asymmetric Angle of Attach Comment]

As you move up to higher performance wings, you need to react quicker because they're faster. They'll get out front more readily with more aggravated cascading consequences.

Sundowner