If the Accelerometer is the Rodney Dangerfield of instruments, perhaps it’s because “G” force is the Rodney Dangerfield of forces. Hell, it’s not even included in the “four forces”. But it should be, perhaps as a sub-force of gravity. “G” force is nothing more than the force caused by acceleration or change of direction. It can be felt by us or indicated by an instrument like the “G” meter. “G” force has some effects other than making centrifuge pilots pass out and passengers to throw up. The Yo Yo is a maneuver designed to help us learn how to feel a specific amount of “G” force. Think of it as a butt-calibrator.
Let’s take one of the sacred mantras repeated by virtually every flight instructor at some point. They will tell you that in a 60 degree level banked turn, the stalling speed will increase by about 40 percent and the airplane will experience 2 “G”s. They are correct. BUT, the average pilot soon forgets part of that truism. He forgets the part that says “level”.
Everyone knows that lift is the force which makes an airplane turn, but in order for it to turn, we must borrow some of its vertical component. That’s why the nose drops when we bank…the vertical component of lift is diminishing. And, you see, in order to maintain the starting altitude, the elevator must be deflected in order to keep the airplane’s nose from dropping. And in order to maintain that attitude which will result in a level turn, the airplane will experience positive “G” force. Here comes the part they never tell you. And I’m afraid that in some cases the reason they don’t tell you this is because they don’t know! The fact is that it is “G” force which increases stall speed, not angle of bank. After the usual test of stalling with a steep bank, simply allow the altitude to decrease instead of hauling back on the elevator. That’ll keep “G” force from increasing with an increase in stall speed. That’s why we teach pilots at tailwheel town to stop trying to climb during that initial turn after takeoff.
If there is one thing that truly separates the way flying is taught at Tailwheel Town and the way it is taught at Acme, it’s the way we use maneuvers. Critical to the philosophy of learning here is that for every skill we want to teach, there is a maneuver which can, through practice, make that skill easier and more logical to learn. And so we have “The Yo Yo”. With the exception of the steep
turn, most fliers rarely have a chance to play with “G” force. Why limit that experience to providing zero “G” to your dog or some giggling little kid (little kids LOVE zero “G”)? The Yo Yo provides a way to experience “G” force and more than simply experiencing it, you’ll learn to recognize a couple of conditions. They are .5 “G” and 2.5 “G”. These two landmarks have been chosen for a reason. If we actually push to zero “G”, we will not only cause everything on the dashboard to float. We will also cause the oil to flow out of the crankcase through the breather, and the carburetor float to lose its reason for being and your engine will quit.. That’s kinda bad for engines and it makes a big mess that someone has to clean up. But by limiting the lower side to .5, we can come really close to zero, keep the engine running and the oil where we added it. On the other side, by limiting the positive pull to 2.5 “G”, we give ourselves a cushion and pretty much guarantee that we won’t see the “wing-off” light begin to flicker.
We can’t perform the Yo Yo in an airplane without a “G” meter. I carry a portable one in my flight bag. I find it interesting how few fliers are familiar with it. That may be because it is normally not found in any of the airplanes they fly. It should be. One of the ways in which I tell if a flier knows about the instrument is how they deal with it on the pre-takeoff checklist. The “G” meter’s “tell-tales” are zeroed by simply pushing the reset knob. Those not familiar with it will attempt to turn the knob as if it’s like a Kollsman knob on an altimeter. They will also remark that there must be something wrong with it because it’s on “one” instead of “zero”. I patiently point out to them that if it were on zero, we’d be floating in the cockpit, since we normally have one “G” on us when at rest.
Now one of the things that every pilot should know is that for every airspeed there is an amount of “G available”. You might try to pull more “G”s than that, but you won’t have much luck… the airplane will stall before you reach it if your speed is not high enough. That’s why aeronautical engineers specify a maneuvering speed, or VA for every airplane produced. So to make sure that there is a sufficient “G” available, we’ll set an airspeed range for this maneuver. That speed range will vary with aircraft model, so I’ll be a bit vague about it in this little description of this maneuver.
Here’s how the maneuver works: In flight, initially we’ll lower the nose and allow the speed to increase. When it reaches an airspeed that will provide the “G” available of well over 2.5, we’ll pull and watch the “G” meter. We’ll stop our pull at 2.5 and we’ll note what it felt like in the seat of our pants. Right now the nose is up and the speed is decaying. So we’ll now push and once more we will watch the “G” meter. We’ll stop the push at .5, hold that pitch attitude and allow the airplane to accelerate. When it reaches that aerobatic entry speed that we previously decided on, we’ll pull and
repeat the process. Just a word about those “tell-tales”. Every “G” meter has “tell tales”. These are needles that only increase and stay at the maximum they’ve reached. The center dial remains “alive”, indicating what we’re pulling at every moment. Once we’ve established a range and rhythm, we’ll simply keep pulling and pushing, accelerating and decelerating while we peg the max negative of .5 and the max positive of 2.5 “G”. And we’ll find that we are maintaining a pitch attitude no higher than 45 degrees up and no lower than 45 degrees down.
As a flight instructor, I supervise this rhythmic maneuver until I think the student has
educated the seat of his pants. Then I simply zero the tell tales and place my hand over the “G” meter so he can’t see it. I allow the applicant to zoom to one more cycle, then I remove my hand, exposing the tell tales. They should be at .5 and 2.5 “G”s. And the flyer used the seat of his pants to set those values, because now he knows how they feel.