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Educational Materials

These are training aids and other items pertinent to PPG that may be helpful in explaining various phenomenon.

Power & Understanding

May 4, 2007

Adding throttle makes you climb. That's easy enough, but what about angle of attack and flight path.

Anatomy of a Paraglider Collapse

Feb 18, 2006

Using speedbar below 100 feet is never recommended. Using speedbar while the trimmers are set fast is worse and doing so with the power off is worse yet. 

During a competition, pilot Stanley Kasica was about to enter the fast part of the slow/fast task. Most pilots fly this part with the speedbar pressed and trims up (their fast setting). That leaves the pilot vulnerable to a frontal collapse which is exactly what happened as photographer Jim Farrel snapped off pictures.

Most collapses are some form of this. Since the only way the wing can collapse is down, frequently it is the leading edge that starts or continues to fold, bringing more of the wing down before falling changes the relative wind and it re-inflates. Even in this one, the altitude loss was minimal and he landed on his feet. Stanley is a highly experienced competition pilot who acted correctly by immediately releasing the speedbar and avoided overreacting on the brakes. There was very little turn and he landed on his feet. In the vast majority of wing malfunction incidents, the pilot over-controls and makes the problem worse.

"Hands up, power off" is the normal emergency response but, when low to the ground, use whatever steering input is necessary to assure a safe course while being mindful that less is almost always better than too much.

Correcting Misconceptions

Feb 25, 2005

A recent poll revealed there are some misconceptions on where we can fly. The blessedly simple and ONLY FAA rule we must comply with is FAR part 103. It references a very few rules from other parts. Other rules, such as not disturbing wildlife, may also apply.

Our great latitude comes with great responsibility. Pilots get in trouble when they annoy or endanger people regardless of whether an actual rule is violated. If the police get called because of your flying and the FAA gets involved, they will FIND a rule to use.

Here is a quick summary to help correct some common misconceptions.

Really Understanding of Torque

Feb 12, 2005

Torque is the force that tries to spin the pilot/motor opposite the direction of prop spin. It's just like a hand drill where the drill bit spins one way and tries to spin your hand the other way. But it has some interesting traits when put to a paramotor. These are excerpted from "The Powered Paragliding Bible" by Jeff Goin.

Weight Shift

The most simple element of turn induced by torque makes one riser go up and the other go down. On machines with higher hook-ins, this happens less but it still happens. By pulling one riser down more than the other a "weight shift" turn is induced. It is a relatively weak force and is easily overcome by brake application.

Twisting Under the Risers

Any force that can twist the pilot under the risers will redirect the thrust. This becomes VERY powerful and can quickly render the craft uncontrollable!

There are several forces that cause this. 

Lean-Back: Anytime the motor is leaning back (not hanging vertical) there are two forces at work; P-Factor, a very minor force, and the horizontal component of torque - a very powerful force.

1. "P-Factor" happens whenever the propeller is not hitting the air head-on. When angled back, the descending blade is taking a bigger "bite" of faster-moving air and so produces more lift. It is a very small force for PPG's because it is based on the speed difference created by forward motion. We just don't have much speed to give much difference.

2. The Horizontal component of torque is just the motor's torque that acts on the horizontal plane. Hang the motor so that the thrust line is pointing straight down (like the pilot at right) - and the spinning prop will try to twist the pilot under the risers. As you angle the motor up, this becomes less of a factor until it goes away completely on an upright motor.

Asymmetric: Another powerful force that can arise is Asymmetric thrust. It happens when the motor's thrustline is not centered on the pilot's back. Every time he powers up it's like someone shoving him on a shoulder blade - he wants to twist. While powerful, it is usually the easiest to fix.

Gyroscopic: This is almost negligible but it can play a small part during the take off run. The odd trait of spinning bodies that keep a top top upright works on our spinning prop too. If you apply a force perpendicular to the plane of rotation (like pushing down on the edge a spinning bicycle wheel) the force will act 90 degrees away in the direction of rotation. If, when launching, you go from being upright to leaning back, the motor will want to twist due to this force. But once leaned back, this force has no beaing.

Fixing It

In flight, the only fix is to reduce power. Reduce it gradually then hold it for to let any swings stabilize. Modulating the power can aggravate the problem, causing you to swing all the way around so that the thrust is pointing backwards. Oops.

Better yet, fix it on the ground. If you hang back too much, adjust. If the motor is not centered adjust. Note that some machines might hang fine with centered thrust but then the torque moves the motor over. Hang in a simulator and have someone physically twist the motor to see if it moves. If so, secure it, usually an easy operation that can be done with the straps or wire ties.

All Contents Copyright © 2007 USPPA