Pivotal Altitude Explained
Teaching eights on pylons the easy way
Eights on pylons is an advanced training maneuver required to earn commercial pilot and flight instructor certificates. The purpose of this maneuver is to further develop piloting skills and to provide a flight test maneuver worthy of advanced pilots.
To get started, the student must master basic training maneuvers. To learn quickly, the student must be proficient in straight-and-level flight and turns, as well as S-turns, turns around a point, eights along a road, slow flight, stalls, and other maneuvers that support the development of pilot skills.
Also required is skill in concentration and handling distractions-specifically holding altitude while making good turns and thinking about other traffic and the aircraft's position over the ground.
The maneuver involves flying around pylons at a specific pivotal altitude, going from one pylon to the other and adjusting altitude as speed changes require. It is similar to eights around pylons, but with a distinctly different objective. For eights around pylons, the pilot flies a circle around each pylon while maintaining a constant altitude and distance from the pylon. This involves making constant corrections for wind drift by varying the bank-shallow into the wind, steeper going downwind.
The objective of eights on pylons is to fly around each pylon at the exact pivotal altitude. Pivotal altitude depends on groundspeed. The faster the groundspeed, the higher the pivotal altitude. The altitude must be varied with changes in groundspeed. Faster speed, such as downwind, means higher altitude; slower speed, such as heading into the wind, means lower altitude. The steeper bank will be on the upwind side where the track is closer to the pylon.
While circling the pylons, if the wing tip, or reference point, moves behind the pylon, that is an indication that you are flying higher than pivotal altitude and you must fly lower to reach pivotal altitude. If the wing tip moves ahead of the pylon, then you are flying below pivotal altitude and must climb to reach the correct altitude. The trick is to identify changes in speed and react quickly by adjusting altitude.
A good training device is to use a model airplane to show how to circle the pylon. It is useful to go to the parking lot and walk around pylons with the model, pointing the wings toward pylons, demonstrating how the student should correct altitude for changes in groundspeed.
As you take to the air to demonstrate the concept, forget pylon selection at first. Simply select a single point some distance away and dip the wing to capture the pylon. The bank should be shallow. It is easier that way. The objective at this stage is to establish the pilot's ability to determine pivotal altitude, to detect changes in speed, and to correct altitude. Show the student how to sense that a change is occurring.
Show the student how to select pylons, choosing a location with a suitable landing field nearby in the event that the engine fails during instruction or testing.
To estimate pivotal altitude, square the groundspeed and then divide by 15 if you use mph, or 11.3 if you prefer knots. That will provide a starting altitude. For example, 100 mph times 100 equals 10,000, divided by 15 equals 666 feet approximate pivotal altitude. A groundspeed of 95 mph results in a pivotal altitude of 600 feet. Hence, traveling at 100 mph on the fast side, pivotal altitude is 666 feet. On the slower side-the side into the wind-95 mph results in a pivotal altitude that is 60 feet lower than the fast side.
Finally, show your students how to fly straight ahead at a 45-degree angle downwind between the pylons. It is a good idea to pick pylons along a road or other straight line. This makes it easier to find the other pylon. Remember that your first teaching objective is to identify pivotal altitude and correct altitude for speed changes. That takes lots of practice. You and your students will be better pilots when you have mastered this maneuver.