Whether you're working on your commercial certificate now, going to be, or already have then you'll find this useful.
As part of the Commercial ACS, we as pilots have to learn Eight's-on-Pylons. This is a maneuver in which the plane flies around two pylons maintaining a visual sight reference with each one in relation to the lateral axis of the airplane. Drawing the plane's ground track, it looks like a figure 8, thus the term Eight's-on-Pylons.
Picture from the Airplane Flying Handbook
One of the most important concepts to take from this maneuver is pivotal altitude.
So what is it?
Pivotal altitude is the altitude at which, for a given groundspeed, the projection of the visual reference line to the pylon appears to pivot. Simply put, it's what the plane keeps coming back to each time you're able to maintain the pylon off the wingtip and hold it.
This is also something that is calculated before the maneuver is begun using the airplane's groundspeed. It's the groundspeed squared divided by either 15 for miles per hour or 11.3 for knots.
Some things to note about pivotal altitude is it does not change with the angle of bank, given that it is not steep enough to affect the groundspeed (but if you do the maneuver and correct for wind properly you shouldn't have to over-steepen the bank where this happens).
Pivotal altitude can be noted very easily while flying around the pylons. All you have to do is get the plane stabilized where you're holding the pylon off the wingtip with no pitch up or down correction, then look at your altimeter and note the altitude! This is what the plane will keep coming back to.
You should also enter and exit the maneuver at the pivotal altitude; how close or far you are from it when exiting can exhibit how well the maneuver was performed.
If you're needing help with commercial maneuvers, or just want to pursue a commercial certificate, take a look at our Aviation Training Directory to find somewhere near you to train.
Best of luck with your Eight's-on-Pylons and happy landings!