Les Glatt, Ph.D., ATP/CFI-AI, AGI/IGI
Ground reference maneuvers are maneuvers that are required for both the Private Pilot and the Commercial Pilot Certificate. In the case of the Private Pilot Certificate, the Pilot must satisfactorily demonstrate: (a) Rectangular Course, (b) S- Turns across a Road, and (c) Turns around a Point. In the case of the Commercial Pilot Certificate, the Pilot must satisfactorily demonstrate Eights-On Pylons. In a previous White Paper (Ref. 1), we discussed in significant detail, Turns around a Point. We showed the key parameter in all ground reference maneuvers is the windspeed ratio, which is defined as the ratio of the windspeed to the aircraft’s TAS.
Prior to teaching Eights-on-Pylons, we usually introduce the Student to the simple On-Pylon Turn maneuver. This maneuver allows the Student to understand the concept of pivotal altitude, which is the altitude that allows an imaginary line extended from the Pilot’s eye to the pylon, which is parallel to the lateral axis of the aircraft, appears to pivot around the pylon. It also introduces the Pilot to the key observations which are used to determine whether the aircraft is above or below the correct pivotal altitude. In the Airplane Flying Handbook (FAA-H-8083-3A, 2004, Ref. 2), the pivotal altitude was estimated as the square of the TAS divided by 11.3, where the TAS is in knots. However, in the latest version of the Airplane Flying Handbook (FAA-H-8083-3B, 2016, Ref. 3), the pivotal altitude was estimated as the square of the groundspeed divided by 11.3, where the groundspeed is in knots. Although the results are identical when the windspeed is zero, we will show that the pivotal altitude in the presence of a wind is incorrect as given in both versions of the Airplane Flying Handbook.
In Section 2 we introduce the dynamics of the turn and the concept of pivotal altitude. We derive the correct expression for the centripetal acceleration during the On- Pylon Turn maneuver. This result is then used to derive the correct formula for the pivotal altitude. In Section 3 we derive the ground track of the On-Pylon Turn maneuver as a function of the angular position relative to the downwind. In Section 4 we derive equations for the required (1) bank angle, (2) rate of turn and (3) rate of climb/descent as a function of the position relative to the downwind in order for the Pilot to hold the pylon. We also show how to select the combination of both airspeed and the radius on the downwind such that aircraft can meet both the maximum required rate of climb during the maneuver and keeping the bank angle below a specified maximum value. In Section 5 we describe how to determine whether the aircraft is above or below the pivotal altitude, and what corrections are necessary to bring the aircraft back on the pylon. In Section 6 we discuss a different method for holding the pylon in the presence of a wind at a constant pivotal altitude by varying the TAS. In Section 7 we show how to utilize the derived turn dynamics of the On-Pylon Turn maneuver to deduce the turn dynamics of Turn around a Point maneuver, which is consistent with the results in Ref. 1. We summarize the results in Section 8 and provide references in Section 9.
In addition, we have highlighted important formulas and statements in red, which are the takeaways that all Pilots/Instructors should understand in order to fly the On- Pylon Turn with precision.
Download the paper here: On-Pylon-Turn.pdf