## Interpreting Tow Position Several visual elements are considered when interpreting the vertical and lateral position of the glider on tow. The exact references used will vary with the specific towplane and glider, but conceptually these elements are consistent: ### Vertical Position When interpreting the glider's vertical position, the pilot must consider: - the towplane's apparent position relative to the horizon (if the horizon is clearly visible) - the towplane's apparent position relative to a fixed reference point on the glider - the angular perspective of the towplane ### Lateral Position and Alignment When interpreting the glider's lateral position and alignment, the pilot must consider: - the angular perspective of the towplane - the glider's longitudinal alignment relative to the towplane ![[Sugarbush tow SP.png]] ## Glider Control On Tow Elevator is used to control the vertical position of the glider on tow. Aileron is generally used to match the bank angle of the tow plane, while rudder is used to control lateral position and longitudinal alignment. Tow rope tension tends to return the glider to a centered lateral position, while any sustained bank or rudder application will move the glider away from center. In the case of a large lateral movement (such as correcting an abnormal tow position, or [[Boxing the Wake]]), aileron and rudder may be used together, however, the pilot must use caution not to overcontrol the aircraft, and remove the bank/rudder as the glider arrives at the desired position. Additionally, changing vertical position will affect the tension on the tow rope. If the glider climbs, it will decelerate and temporarily increase tow rope tension. If the glider descends, it will accelerate and temporarily decrease tow rope tension, possibly inducing [[Slack Line]]. ## Basic Tow Positions ![[GFH tow positions.png]] ### High Tow Position In the United States, the high tow position is considered the standard vertical tow position for normal operations. High tow position is defined as a position just above the wake of the towplane. Specific visual references for the towplane's apparent position relative to a fixed reference point on the glider, and the angular perspective of the towplane are aircraft specific, but the towplane should appear just above the horizon to the glider pilot. ### Low Tow Position In the United States, the low tow position is only used for special circumstances: demonstrating proficiency on tow (such as when [[Boxing the Wake]]), and during extended towing operations (such as a cross-country tow) to reduce the tail-down force required by the towplane during high tow operations. The disadvantages of the low tow position include reduced visibility of the glider by the tow pilot, and greater risk of glider entanglement in the event of a rope break or towplane release. Low tow position is defined as a position just below the wake of the towplane. Again, specific visual references will be specific to the towplane and glider. ### Lateral Position The most basic lateral position for the glider is centered behind the towplane. Visually: - the angular perspective of the towplane should be directly ahead of, and aligned with the glider; the vertical stabilizer should be in-line with the entire fuselage, and the nose or tailwheel exactly between the main wheels - the glider's longitudinal alignment should match the towplane's; the nose of the glider should point at the center of the towplane Some operators encourage gliders to maintain a slightly left-of-center lateral tow position, to alleviate the [[Aerodynamics and Flight Maneuvers/Left Turning Tendencies|Left Turning Tendencies]] experienced by the towplane, especially if the towplane does not have rudder trim. In this case: - the glider's longitudinal axis should be parallel to the towplane's longitudinal axis, but offset to the left; the glider's nose should be aligned with the mid-point of the towplane's left wing, or strut-to-wing attachment point - the angular perspective of the towplane should be slightly left of center; the vertical stabilizer should appear slightly right of the towplane's fuselage ### Example In the image below, note the following: - the horizon is obscured by a mountain, and there are no visible reference points visible from the glider - vertical position can be interpreted by the angular perspective of the towplane: the horizontal stabilizer is in-line with the wing root, consistent with a high tow position for the Pawnee - lateral position can be interpreted by the angular perspective of the towplane: the entire right side of the towplane is visible, consistent with an extreme right lateral position ![[N8514L right side.jpg]] ## Turns Turns should be made in the high tow position. The glider pilot should match the bank angle of the towplane, and align the nose of the glider with the towplane's **outside** wingtip - this can be accomplished by smoothly rolling into the appropriate bank approximately 1-2 seconds after the towplane initiates the turn, when the glider's nose nears alignment with the towplane's raised wingtip. If the glider turns too early or the bank is too steep, the glider turn radius becomes smaller than the towplane turn radius; [[Slack Line]] will develop, and the glider will decelerate and sink. If the glider turns too late or the bank is too shallow, the glider turn radius becomes larger than towplane turn radius; towline tension increases, and the glider will accelerate and climb. ![[GFH aerotow turns.png]] ## Additional Considerations Interpreting and maintaining the appropriate tow position is relatively easy in concept when the proper references and control philosophy are learned; in practice, maintaining tow positions is a continual process of identifying small deviations and making constant corrections to keep the glider precisely in the desired position. Particularly in turbulent conditions, this will require constant attention and corrections made along all three axes of control. It is helpful to note that any atmospheric disturbance will affect the towplane first - with a typical [[Aerotow Rope]] length, at most tow speeds, whatever disturbance the towplane encounters, the glider will encounter approximately **2 seconds later.** If the glider pilot ever loses sight of the towplane, is in an unrecoverable abnormal tow position, or the safety of the tow is in question, **the glider pilot MUST [[Tow Release]] IMMEDIATELY!** ## Common Errors - Failure to maintain proper vertical and lateral position - Inadvertent entry into towplane wake - Failure to maintain proper alignment during turns - Using too much aileron, and/or not using enough rudder to control lateral position - Overcorrecting vertical position; climbing or descending on tow causes changes in towline tension, coupled with out-of-phase corrections can lead to *pilot-induced oscillations (PIOs)*