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8 Answers

Pivotal Altitude for Eights on Pylons

Asked by: 5211 views Commercial Pilot, FAA Regulations, Flight Instructor, General Aviation

I am currently training a student for a commercial single-engine add-on and am trying to decide the proper altitude for eights on pylons.  According to the equation (GS x GS)/15 for MPH our pivotal altitude in the Champ we are flying should be somewhere in the 350' AGL range.  However I know the FAA standards for ground reference maneuvers say that you need to be between 600' and 1000' AGL.  So would the proper altitude for this aircraft be 350' or 600'?

8 Answers



  1. John D. Collins on Mar 08, 2011

    Lance,

     

    I can’t find your reference in the Commercial PTS to “between 600′ and 1000′ AGL” for ground reference maneuvers.  Pivotal altitude is determined by ground speed and there is no way you can complete the maneuver without being at pivotal altitude when turning on the pylon.  If you have a slower aircraft, your pivotal altitude will be lower and you have to use the appropriate altitude to comply with the requirement.

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  2. DeAnn Crowley on Mar 08, 2011

    Looking at the most current Commercial PTS … area of operation VI and no reference is to 600′-1000′AGL. “Holds pylon using appropriate pivotal altitude …” is mentioned and I think it’s a bit more than a recommendation.
    FAA-H-8083-3A pg 6-14 says, “There is a specific altitude at which, when the airplane turns at a given groundspeed, a projection of the sighting reference line to the selected point on the ground will appear to pivot on that point. Since different airplanes fly at different airspeeds, the groundspeed will be different. Therefore, each airplane will have its own pivotal altitude.”  … and it goes on to give the formula you’ve mentioned and a table where the slowest mph is 100 with an approx pivotal alt. of 670″agl.
    This maneuver can not be properly executed unless the aiplane is at the appropriate altitude for a given (PTS says airspeed) groundspeed. FAA says this is the standard: VI.4. “Enters the maneuver at the appropriate altitude and airspeed and at a bank angle of approx. 30-40 degrees at the steepest point.” 5. “…necessary corrections so that the line-of-sight reference line remains on the pylon.”
    So, you already know, if you want higher you’re going to have to fly them faster (with the host of problems that may load you up with).  It seems like the real question here is how low and slow can you safely go to fly the snot out of your airplane? Seems like your groundspeed has part of the answer.  I sure would make sure that I had my area for an emergency approach and landing firmly established! The Airplane Flying Handbook lists inability to select a pivotal altitude among the common errors.

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  3. Matthew Waugh on Mar 08, 2011

    As John said – you can’t perform the maneuver unless you are at pivotal altitude, so trying it at 600 feet if the PA is 350 feet will be, at a minimum, frustrating.
     
    So the difficulty is making sure that you can find a place to practice that don’t fall foul of any of the regulations about how close you get to people etc. I have seen the 600-1000 feet reference in FAA materials, but it was related to the Private Pilot maneuvers. I’ve not seen anything regulatory.

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  4. MaggotCFII on Mar 08, 2011

    A point of view from the “old” days!
    This from circa 1941: “Flying Questions”, Carlton Wheeler-CFI”:
    “16. WHAT IS THE PROPER METHOD OF DETERMINING THE PROPER ALTITUDE FOR EIGHTS-ON-PYLONS?”
    “At a low altitude it can be demonstrated that no matter what the degree of bank of the airplane, the lower wing tip of the airplane appears to move forward over the ground.  If this process is repeated at progressively higher altitudes the same action will be noted until the proper altitude is reached.
    At this altitude the wing tip will appear to pivot “on” the point selected.  This is the pivotal altitude and the one to be used for eights on pylons.
    If the altitude is then increased, it will be noted that the lower wing tip appears to move backward over the ground no matter what degree of bank is being used, shallow, medium, or steep.
    Below this pivotal altitude the pylon can be held only by skidding.  As the altitude is decreased the amount of skidding necessary to hold the pylon must be increased.
    Above the pivotal altitude the pylon can be held only be slipping.  The greater the increase in altitude above this point the greater the amount of slipping necessary to hold the pylon.”
    Enjoy!

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  5. Brian on Mar 09, 2011

    The majority of flight training probably occurs in ‘other than congested’ areas. So if we bust the PTS 600’ AGL to accomplish the maneuver, ok. However, FAR 91.119 requires 500’ AGL in ‘other than congested’ areas. This is the training environment I grew up in and instruct in.
     
     
    In other words, when I was taught the maneuver, and when I’ve taught it, we had to stay above 500’ AGL. To figure this out I first need to know that pivotal altitude equals the sum of groundspeed squared divided by 11.3. With some basic algebra, we can rewrite this to say that groundspeed, for a given pivotal altitude, is the sum of the square root of pivotal altitude multiplied by 11.3.  Mathematically written as:
     
     
    Ground speed = √(Pivotal altitude * 11.3)
     
    Here are a few pivotal altitudes with corresponding ground speeds:
     
    500′ = 75 knots
    600′ = 82 knots
    1000′ = 106 knots
     
    Keep in mind, all altitudes are based off feet above ground level and speeds are in knots groundspeed.
     
    Now we must figure out what airspeed we will do the maneuver at, calculate our ground speed, and ensure it is greater than 75 knots. I’ve never done the maneuver under 100 knots airspeed. The result was, as long as winds were under 20 knots, I knew I could maintain a ground speed corresponding to a pivotal altitude greater than 500′ AGL.
     
     
    On an aside, a WWII veteran once told me that knowledge of pivotal altitude was necessary in the war days. If the pilot could properly fly pivotal altitudes, the gunnies job would be easier as the targets remained relatively fixed. I’ve yet to hear or see a practical application for such knowledge in real world, not killing people, flying.
     
    Though, if anyone does know a real world application for this knowledge, I’d love to hear it so I can teach future students. I dislike teaching any topic that I can’t specifically cite a purpose for learning. A student is bound to ask and ‘because the PTS says so’ is a distasteful reply in my opinion.
     
    Sorry to hijack your post with another question and thank you, I hope this helps.
     
     

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  6. Lance on Mar 09, 2011

    Thanks guys that was the answer I wanted to hear, because I was having a terrible time practicing higher up so that I was sure I showed it to him properly.

    Brian, the reason I used 15 in my equation is because I was using MPH. The reasons I have heard (and give myself) for using this technique usually correspond to photography and wildlife spotting, both things that a commercial pilot could do as a job.

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  7. Paul Buller on Feb 13, 2012

    Brian, the practical application of a pylon turn is this. I you are wanting to look at something on the ground and you can establish the pivital altitude you can fly the turn around the thing you want to look at totaly by outside reference. There is no need to look back inside the airplane if you maintain the object on the sight reference line. It would be impossible to fly into the ground (CFIT). I would suggest that in reality one would cross check airspeed and altitiude once every 30 seconds or so. But either way you could go around the point without looking back inside for as long as you want to go around in circles. I use plylon turns whenever I am checking out something on the ground. The pivital turn allows me to adjust my altitude above the object up or down simply by increaseing or decreasing airspeed and therefore the groundspeed.
    Paul

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  8. Dudley R. Briggs on Aug 29, 2012

    Brian, an early practical use of turns about a pylon was trading with Central & South American natives back in the early days of flying. You could safely fly a J-3 at 60 IAS and the pivotal altitude would be about 300 feet. Once established in your turns, your passenger could lower a basket on a rope of say 400 ft. and the basket would assume a near stationary point on the ground where those down below could hold the basket still. Broken Coke bottles or similar valuables were exchanged for whatever the natives thought the offering worth, sometimes something valuable.

    As recently as the 1960s I had a Cub for going fishing down on the Texas coast and with it occasionally flew free-lance for the U.S. Fish & Wildlife Service to pick up from remote areas aquatic samples using the pylon turn maneuver to get the samples to the lab guys in good time. We used a teardrop-shaped canvas bag with a ring at the top and a zipper in the side.

    I found the discussions of formulas for speed and altitude interesting. They were a new one on me inasmuch as I had never been exposed to them. We did a lot of pylon turns using the wingtip’s position relative to the point to arrive at the altitude, as described by MaggotCFII. I knew about what the pivotal altitude was for the plane at hand, so I would begin a bit above that and when that certain picture of wingtip and point locked on you were there.

    Speaking of “that certain picture”, I learned that from an interesting little article in Flying Magazine back in the 1950s that led me to see “that certain picture” for any practical speed and it solved for me the altitude equation . The trick was to learn by a fair amount of trial and error to observe when the wingtip is locked in relative to the point. Not locked on the point, but relative to it. The picture was elusive at first and I spent a lot of time chasing the point, but getting it down was like turning on a light bulb. Once I had it, it worked in any airplane and when the point was pinned you could forget about altitude and airspeed because neither could change without losing the point.

    Paul Buller said it for me: “You could go around the point without looking back inside for as long as you want to go around in circles. . . The pivital turn allows me to adjust my altitude above the object up or down simply by increaseing or decreasing airspeed and therefore the groundspeed.”

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