Los Alamitos Glider Training Squadron 41
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Instructor Tips

The Magic of Ground Effect

Flight Instructor: Capt. Rhon WIlliams

 

Have you ever been on short final and realize that you are sinking too much and are unlikely to reach the runway? You have checked that the spoilers are closed and speed is set for best speed to fly and it is still not enough, what now? It can happen to any of us due to unexpected sink on final, poor planning earlier in the pattern, or stronger winds than expected.

Fortunately, there is often a magic trick available to the clever glider pilot – ground effect.

Hopefully you may remember from ground school that ground effect is a phenomenon that occurs when an aircraft wing is less than one wingspan from the ground. In simple terms, being very close to a relatively smooth surface changes the aerodynamic flow around a wind, significantly reducing the drag without changing the lift. The result is that a wing in ground effect has less drag and will fly further without slowing as much as it would outside of ground effect. Just what you may be wishing for on short final.

So now that we know there is an aerodynamic condition that can help save a landing, how do we make use of this tool? The challenge is that the pilot must overcome the strong urge to stay away from the ground, and must fight off the impulse to pull back on the stick. In most realms of flight, pulling back on the stick makes the aircraft go up, and when we are getting too close to the ground, there is the extreme urge to use this technique. Unfortunately, when getting “low and slow” pulling back on the stick only makes the aircraft fly slower, be less efficient, and sink more. The answer is for the clever pilot to keep up the best speed to fly given the wind, fly down near the ground with the landing gear only a few feet from touching, and maintain a level attitude. If the pilot can resist pulling back and slowing down, they will be rewarded with s surprising amount of float that will often carry the glider all the way to the runway threshold. This scenario does assume that there is a flat area without obstructions leading up to the runway, but even if not paved, a level touchdown in this area may just be a gentle bounce to the pavement, and is better than most any other alternative once in this situation.

Another possible tool for extending your glide is the use of flaps. Although a training glider like the Schweitzer SGS2-33, does not have flaps, many other gliders do. So if you have this option, consider that adding a small amount of flaps will reduce the stall speed with little drag penalty, and thus also extend the point of touchdown. Keep in mind that once flaps are added, leave them in until the glider is on the ground.

So the next time you find yourself feeling the runway seems a little too far away, resist pulling back on the stick, snuggle down into ground effect, and be rewarded with a gentle float to the runway.

Yaw String as Attitude Indicator

Flight Instructor: Capt. Rhon WIlliams

For a Schweizer 2-33 glider use the knot on yaw string as an attitude indicator.

Set up straight and level flight at desired airspeed such as 55 mph. Memorize the position of the yaw string knot on the pitot tube relative to the horizon. Depending on your height in the glider the spot may be slightly above or below the horizon. Then any time you want the airspeed to be 55 mph, just set the yaw string knot at the memorized position, and the glider airspeed will soon return to 55 mph. Since the airspeed indicator has an inherent delay, setting the yaw string knot position on the horizon is an immediate and reliable way to set the attitude for the target airspeed. For other commonly used speeds such as speed for minimum sink, the knot can be set just above the horizon (a quick trial will allow you to memorize the correct spot).

Using the yaw string knot as an attitude indicator also works during turns. At any given airspeed, note the knot position on the horizon and as you roll into the turn, keep the knot at the same relative height on the horizon, and you will maintain the desired speed during the turn. Similarly, when rolling out of a turn, keeping the knot in the position will avoid airspeed deviations.

Since you are already looking at the yaw string it is also a good time to check your turn coordination, and "step on the knot" if needed. This works because if the yaw string is off to one side, the knot (forward end of the string) indicates which rudder pedal needs more pressure.

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