pilot continues the descent below the pivotal altitude, the  projected visual reference line with respect to the pylon will  begin to move forward. airplane flies a prescribed path over the ground and the pilot  attempts to maintain the track by correcting for the wind.  With eights-on-pylons, the pilot maintains lateral orientation  to a specific spot on the ground. This develops the pilot’s  ability to maneuver the airplane accurately while dividing  attention between the flightpath and the selected pylons on  the ground. The altitude at which the visual reference line ceases to  move across the ground is the pivotal altitude. If the airplane  descends below the pivotal altitude, the pilot should increase  power to maintain airspeed while regaining altitude to the  point at which the projected reference line moves neither  backward nor forward but actually pivots on the pylon. In this  way, the pilot can determine the pivotal altitude of the airplane. An explanation of the pivotal altitude is also essential. First,  a good rule of thumb for estimating the pivotal altitude is to  square the groundspeed, then divide by 15 (if the groundspeed  is in miles per hour) or divide by 11.3 (if the groundspeed is  in knots), and then add the mean sea level (MSL) altitude of  the ground reference. The pivotal altitude is the altitude at  which, for a given groundspeed, the projection of the visual  reference line to the pylon appears to pivot.  [Figure 6-12]  The  pivotal altitude does not vary with the angle of bank unless  the bank is steep enough to affect the groundspeed.  The pivotal altitude is critical and changes with variations  in groundspeed. Since the headings throughout turns  continuously vary from downwind to upwind, the groundspeed  constantly changes. This results in the proper pivotal altitude  varying slightly throughout the turn. The pilot should adjust  for this by climbing or descending, as necessary, to hold the  visual reference line on the pylons. This change in altitude  is dependent on the groundspeed. Selecting proper pylon is an important factor of successfully  performing eights-on-pylons. They should be sufficiently  prominent so the pilot can view them when completing the  turn around one pylon and heading for the next. They should  also be adequately spaced to provide time for planning the  turns but not spaced so far apart that they cause unnecessary  straight-and-level flight between the pylons. The selected  pylons should also be at the same elevation, since differences  of over few feet necessitate climbing or descending between  each turn. The pilot should select two pylons along a line that  lies perpendicular to the direction of the wind. The distance  between the pylons should allow for the straight-and-level  flight segment to last from 3 to 5 seconds. Distance from the pylon affects the angle of bank. At any  altitude above that pivotal altitude, the projected reference  line appears to move rearward in a circular path in relation to  the pylon. Conversely, when the airplane is below the pivotal  altitude, the projected reference line appears to move forward  in a circular path.  [Figure 6-13]  To demonstrate this, the pilot  will fly at maneuvering speed and at an altitude below the  pivotal altitude, and then placed in a medium-banked turn.  The projected visual reference line appears to move forward  along the ground (pylon moves back) as the airplane turns.  The pilot then executes a climb to an altitude well above the  pivotal altitude. When the airplane is again at maneuvering  speed, it is placed in a medium-banked turn. At the higher  altitude, the projected visual reference line appears to move  backward across the ground (pylon moves forward). After demonstrating the maneuver at a high altitude, the pilot  should reduce power and begin a descent at maneuvering  speed in a continuing medium bank turn around the pylon.  The apparent backward movement of the projected visual  reference line with respect to the pylon will slow down as  altitude is lost and will eventually stop for an instant. If the  The pilot should estimate the pivotal altitude during preflight  planning. Weather reports and consultation with other pilots  flying in the area may provide both the wind direction and  velocity. If the references are previously known (many  flight instructors already have these ground-based reference  selected), the sectional chart will provide the MSL of the  references, the Pilot’s Operating Handbook (POH) provides  the range of maneuvering airspeeds (based on weight), and  the wind direction and velocity can be estimated to calculate  the appropriate pivotal altitudes. The pilot should calculate  the pivotal altitude for each position: upwind, downwind,  and crosswind. The pilot should begin the eight-on-pylons maneuver by  flying diagonally crosswind between the pylons to a point  downwind from the first pylon so that the first turn can be  made into the wind. As the airplane approaches a position  where the pylon appears to be just ahead of the wingtip, the  Figure 6-12.  Speed versus pivotal altitude. 6-16 Approximate Pivotal Altitude Groundspeed Knots 87 91 96 100 104 109 113 MPH 100 105 110 115 120 125 130 670 735 810 885 960 1050 1130