Photograph by Chris Rose. |
Don't tell us that you've never bounced, ballooned, skipped, or floated like crazy on a landing. Anyone who says that has not made more than two landings in an airplane. So, what can we do to eliminate these missteps? And, what's the best way to handle each when they do happen?
Balloons, bounces, skips, and floats have nuances that make handling each a little different. However, the root cause of all of them is energy management: We either have too much energy--or not enough--and the mismatches invariably occur at exactly the wrong time.
In the final stages of a landing, with the power off as we come into ground effect, our energy comes from two sources: altitude (potential energy) and speed (kinetic energy). These two energy sources are intertwined in a fairly complex relationship, and the relationship is continually changing as we come closer to the ground and slow down. Then ground effect further complicates the relationship, and as if life at that moment isn't complex enough, aerodynamics comes into play, making things that much more fun. Understanding the concept of handling energy, as it changes, is central to eliminating those embarrassing and potentially dangerous landing mistakes.
Excessive floating
Floating is not particularly dangerous, assuming you have plenty of runway, but it is the primary reason people can't put an airplane in the first 500 to 800 feet of the runway--which is what makes a 2,000-foot runway seem short to some people when it really isn't (density altitude notwithstanding). A float comes almost exclusively from one factor: too much speed over the threshold, and that usually comes from too much speed on final. Fly the correct airspeed over the threshold and roughly 20 to 30 feet high, and you should touch down 500 to 800 feet beyond the numbers--and be able to turn off at 1,500 feet. And yes, it really is as simple as that.
Balloons
Ballooning is the result of getting impatient while fighting your way through excessive float. The initial cause is extra speed, but this is made worse if you lose your patience and try to bring the nose up before the airspeed will let you. It's a delicate balance, trying to bring the nose up to slow the airplane down without causing it to balloon. If you do balloon, however, it's generally not dangerous, as long as you recognize what is happening and ease off the back pressure to stop the altitude increase. Ballooning can become dangerous if it leads to a potentially damaging bounce. That happens when you don't recognize that you've pulled the airplane away from the ground, don't release the back pressure, and start a deceleration too high above the runway. Airplanes can sustain damage that way: The flare is started normally, but the speed is too high, the airplane balloons higher, the pilot doesn't release backpressure, and the airspeed begins to fall rapidly--followed immediately by the airplane.
First, don't be that fast; and second, be patient and just nibble at the backpressure, being sensitive to the airplane's attempts to climb as you change nose attitude. And don't force it onto the runway. If it's not working out, power up, go around, and try it again.
Bounce versus skip
Of the four factors, bounces have the highest embarrassment quotient and, depending on their severity and how we handle them, they also are potentially the most dangerous. Unfortunately, they are sometimes misdiagnosed because there is a subtle difference between a skip and a bounce, which makes one harmless and the other a potential problem. The biggest differences between the two are energy--specifically, what's happening to that energy (how quickly is it decreasing)--and the resulting relative angle of contact with the ground.
First a skip. You're on short final and either you're fast or you're on the correct approach speed but little or no deceleration is taking place because you didn't break the glide early enough. Either way, rather than slowly bleeding off speed for a gradual reunion with the ground, you're late applying just a little backpressure to check the rate of descent and the airplane bumps into the ground. It is, however, instantly back in the air again. This is not a bounce.
The identifying characteristics of a skip is what the energy (read that as speed; the terms are almost interchangeable in this situation) is doing just before touchdown and right after accidental liftoff. Because the airplane is descending to the ground for the inadvertent touchdown, the speed remains relatively constant: It's literally flying into the ground. So the airplane hits while it is still carrying more energy than we'd like. Because it still has high energy, much of which is oriented in a forward direction rather than in a vertical direction, it literally skips off the ground having made a light contact.
Very little of its speed is lost in the contact and the airplane skips off the ground in a flat angle. In that kind of situation, the energy going in is high and the angle leaving the ground is low; as a result, as the airplane leaves the ground, the deceleration rate is quite low--it maintains much of its speed. The airplane is still flying, however, and all we have to do is relax the backpressure just enough that it doesn't go any higher and fly it back down to the ground, flaring as we get closer. If we relax the pressure and don't pull the airplane away from the runway (an easy thing to accidentally do, given the excess energy), it's a simple matter of landing the airplane again. No power will be needed because the energy is allowing us to fly quite nicely.
The set-up for a bounce is quite different. In this case, just before touchdown the airspeed has been allowed to degrade too much, too high above the ground. As the airspeed continues to deteriorate, sufficient lift is no longer being generated, and the airplane literally falls onto the ground. Here, the vertical vector is a sizeable part of the energy equation and the horizontal portion is less significant. The result is that the airplane is coming down at a steeper angle with less kinetic energy. Here, the contact with the runway is much harder than with the skip because the deceleration has also stolen part of our ground effect--which usually softens the landing--and the rate of descent is higher.
Because we're literally falling at the ground with a higher rate of sink, when we hit the landing gear is compressed much more than what it would have been on a skip. The tires, in combination with the shock struts, are also compressed more. Then a portion of the energy that was absorbed by the tires and shock struts is immediately released when the landing gear and tires go back into their original position, resulting in an upward motion of the airplane.
As the airplane leaves the ground, the airspeed, which had already been decelerating, continues to slow even more. As a result, when it reaches the top of its bounce the airspeed is even slower, and aerodynamics do nothing to support the airplane--if we don't add more energy in the form of power, it flops back onto the ground. This time the hit is softer than the first one, but often there is still enough force to produce another vertical component and the airplane bounces off the ground again, and we dribble down the runway until gravity finally sorts things out for us.
The initial fix is to not let it happen in the first place: Don't let the airplane slow down too much, too high. The most common cause for this is that, after leveling the airplane in ground effect, we misread its tendency to sink and started pulling the nose up a little too early in relation to the airspeed decrease. The visual key that it's OK to start bringing the nose up is when the airplane starts to move down. If it's not moving down, and it's just skating along in ground effect and not losing altitude, just sit there and watch it; wait for it to slow down and make the first move toward the ground, which you then check with a little back pressure.
The next opportunity to prevent a bounce is to develop an awareness of that sinking feeling, where we can clearly tell the airplane has begun to settle in an abnormal manner, as if the bottom has fallen out. This is generally the result of holding it too high, too long. Right at that point, when that sinking feeling sets in--both physically and psychologically--is the time to soften the landing with power. We have to fight the natural urge to pitch the nose up even further, which is usually the wrong thing to do: The airplane is already decelerating too quickly, and any pitch up of the nose will rob even more speed, making the hit that much harder. When in doubt, add a little power.
Anywhere in the landing, if you know something's wrong but you're not sure what to do about it, add power and go around. That's never the wrong decision. It may not be necessary, but it's never wrong.
If you bounce
As you're bouncing up off the runway, first drop the nose very slightly to keep the bounce to a manageable height. Don't push forward; just ease off the back pressure so you don't make a bad situation much worse very quickly. Then, assuming you don't want to go around, ease in just a little power. Once the power has arrested the bounce, ease off the power very slowly and let the airplane ride the throttle to the ground. When you see you are no longer falling, don't abruptly yank the throttle thinking you've just saved the situation. If you do, you'll hit really hard because the power is the energy that is keeping the airplane up. So bleed it off gently, reaching idle just as the wheels touch.
If we can't prevent the hard hit and we're leaving the runway in a well-developed bounce, we must treat the situation much differently than we do a skip. As we leave the runway and our airspeed continues to decrease, we are rapidly becoming a dynamic object rather than an aerodynamic one. In other words, we're becoming more like a rock than a Frisbee. There is no doubt that the airplane is going to immediately return to Earth. Here, too, err on the side of safety and conservative flying--apply power and go around.
Budd Davisson is an aviation writer/photographer and magazine editor who has written approximately 2,200 articles and has flown more than 300 different types of aircraft. A CFI since 1967, he teaches about 30 hours a month in his Pitts S-2A Special. Visit his Web site.
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