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“G” Available

I’ve got some questions:  Howcum most CFIs think that bank angle affects stall speed?  Howcum most pilots never fly behind an accelerometer unless they are flying an aerobatic airplane.  And, speaking of accelerometers, howcum most who have one, use it to safely fly the aircraft at less than max g?

The Accelerometer.  This is a portable unit that can be put in any airplane.  Y’know what never fails to entertain the CFI when he first shows the unit to a student?  The fact that most people try to zero the instrument by finding Zero.  In fact, if the instrument indicated “zero” we’d be floating.  When it is “zeroed”, the center needle reads “1”.  ( The Lansburgh Collection, Photo by Brian Lansburgh).

Howcum most pilots don’t understand what Va is? Oh a few can actually tell you about it, but most don’t understand it.  You will.  And while you are understanding it, you’ll also learn what “G Available” is.  To understand “G Available”, we only have to practice one of our Tailwheel Town maneuvers, the YoYo.  You see, I’ve noticed something that most of my applicants do when flying the YoYo for the first time.  Instructed to pull 2.5 g’s, they will begin to pull relatively slowly and smoothly, while watching the accelerometer.  While they are pulling, the airspeed is going down.  And, without realizing it, they pull hard enough that the G available drops below 2.5.  For you see, for every airspeed there is a G available.  The higher the airspeed, the more “G” s can be pulled. The applicant normally has to be told to pull harder sooner.  The average Aeronautical Engineer knows about G Available and that has to do with the fact that the aeronautical engineer is the one who needs to calculate Va, the speed at which a sudden activation of any of the controls or entry into turbulent conditions will result in a stall at less than the maximum “G” that the airframe is designed to withstand.

Gee (you should pardon the pun), howcum more airplanes don’t have accelerometers?  They require no plumbing and are the easiest thing in the world to install.  Oh, and while I’m on the subject, howcum more CFI’s don’t teach the “Yo Yo”?  I’ll let you noodle on that and I’ll skulk off.

Happy Swooping!

Brian

2 comments to “G” Available

  • Scott Moore

    It took a while for me to understand why Va, maneuvering speed, DECREASES when you have LESS than max gross weight. It logically seemed to me that the airframe could handle more speed with the same aerodynamic force if it was not having to carry as much weight. It turns out that is has nothing to do with how much weight or force the airframe can aerodynamically carry. At max gross weight the airframe will stall at the max Gs designed. With less weight in the plane but at the same speed, it will stall at a higher G loading to create the same aerodynamic FORCE as max weight stall.

    Why is that bad if the plane will still stall with the equivalent aerodynamic load at a higher G per pound of aircraft? There are fixed loads that aren’t cargo, such as the engine. If the aerodynamic load creates 3 Gs at Va max weight, it might create 4+ Gs at the same speed but with less total weight. The engine mount is now carrying a load that is above its designed limit of 3 Gs.

    Brian, correct me if I have any of that wrong.

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