Don't Try It If The Outcome Isn't Obvious
So, you're sitting on the end of the runway. It's 98 degrees; there's no wind; the runway is 2,200 feet long, paved, and has pine trees at the end. The elevation is 2,800 feet above mean sea level, and you're loaded to maximum gross weight. You look in the pilot's operating handbook and it says you'll clear a 50-foot obstacle in 1,900 feet. According to the POH you have a 300-foot runway margin, so it looks like a go. Or does it?
First, you should know something about POHs. They don't really lie, but they aren't accurate, either. They aren't accurate because none of us is the equivalent of the experienced test pilot who generated those numbers, and we aren't flying a brand-new airplane like he or she was (see "POH Hype," September AOPA Flight Training). Yes, the airplane has performed as the POH says it can, but probably only once, while the tests were being conducted. We all know we can't expect those numbers. What we don't know, however, is exactly what we can expect.
One of the unknowns is how much of your airplane's performance has been stolen by the aging process. For another, you can be pretty certain you won't fly the airplane as well as the test pilot did. Plus, you don't actually know how tall the trees are - you only know that they are taller than you wish they were. In addition, the engine won't be putting out maximum power because you probably won't be able optimize it for the conditions even by leaning. You'll come close, but it won't be perfect. Questions, questions.
So, what do you do? This is a real judgment call. A guess, actually. The POH says you have 300 feet of runway length to spare, but that doesn't sound like much, does it? Do you try it?
The quick answer is that if you have to ask yourself whether or not you're cutting it too close, then you're cutting it too close. If there's any question, you simply don't do it. You wait until either the temperature goes down or the wind comes up, or both, so that the POH gives you a bigger margin. Even then, you should pick a go/no-go point where you can abort and still get stopped on the runway.
Takeoff Goals
In doing either a short- or a soft-field takeoff, remember what you're trying to accomplish. Also, notice that the goals of the two types of takeoffs are wildly different, which is why the techniques are so different.
The goal of a short-field takeoff is to get up to best angle (not best rate) of climb speed as quickly as possible. Yes, we are concerned about the amount of runway we use, but we are even more concerned about the distance to the trees at the end. It doesn't do any good to get off early if, in the process of doing so, we build up so much drag that we lounge around nose-high in ground effect and eat up valuable distance between us and the trees.
The only number that counts in a short-field takeoff is that magic best-angle-of-climb speed. Anything above or below that number means we're moving closer to the trees than we would at best angle. Trying to climb the second we get off the ground actually hurts us when trying to clear an obstacle. The technique is simple enough: We want to maximize the engine's effect on our acceleration by directing the thrust vector in the optimum direction while minimizing the drag generated by our contact with the runway and the aerodynamic drag of the airplane.
Runway drag is minimized by reducing our contact with the surface. That means getting the little wheel, whether it's in front or back, off the runway as soon as practical. At the same time, however, we don't want to introduce too much drag in the process of picking the wheel up. Starting with full aft elevator (nosewheel) or full forward stick (tailwheel) means the tail surfaces are fully deflected and producing maximum drag, which slows our acceleration. It's better to wait just a few seconds until there is more wind over the tail before we change its position. Then, as soon as the wheel is off the runway, we want to hold a low angle of attack. When taking off from a soft field we need maximum lift, but in short-field takeoffs, remember that we're going for maximum acceleration. We want to keep the drag lower, so we keep the angle a little flatter, which also points the thrust vector more nearly horizontal and helps acceleration. The angle is a compromise between an early liftoff and maximum acceleration.
The POH will tell you what amount of flaps to use, but lacking that information, use the number of notches that give you the closest to 15 degrees. That is the most efficient lift deflection for most airplanes. As you go past 15 degrees, many flaps start generating increasing amounts of drag.
As soon as the airplane is off the ground with a positive rate of climb, the nose should be lowered. We don't want to settle back on, but we do want the thrust vector from the engine as close to horizontal as we can get it and still stay in the air. We want that thrust dedicated entirely to building speed.
Incidentally, the technique we're discussing here is for "normal" airplanes, not those with serious performance. Short-field take-off technique in an Aviat Husky, for instance, is to simply hold three-point and thunder along until the main gear lifts off first, then relax and enjoy the ride. Every airplane has a different recommended method.
Soft-Field Objectives
The soft-field takeoff is the flip side of the short field. When the runway is producing excess wheel drag because it is soft, muddy, or snow-covered, we want to lighten the load on the wheels as soon as possible. It doesn't make any difference how much runway it takes or doesn't take. We're willing to accept high drag in exchange for high lift.
Unlike a short-field takeoff, we want the little wheel out of the mud immediately - no matter what the cost - because its drag plowing through the mud could be enough to make the takeoff impossible. So, the yoke is hugged to the chest (stick is forward on a taildragger) as soon as the takeoff roll is started. You can feel the prop blast hammering at the tail as it forces the little wheel into the air.
We want the nose angle to be high, as close to the maximum angle as we can get it - but at the same time, we don't it want it so high that the airplane will never get off the ground. In most airplanes, however, the design of the gear makes it impossible to get the angle too high because the tail will touch the ground first. We want to be short of that angle. As a nosewheel airplane speeds up, the nose is going to try to keep coming up because the tail is getting more and more efficient. We don't want the nose too high, so we pick an attitude and, as the nose tries to climb, we ease off the back pressure to nail the angle.
Holding the angle is no big deal when practicing on a paved runway, but in a real-world soft-field situation it can be a challenge. Actual soft runways are never consistent in their texture. They have puddles and soft spots mixed in with harder areas. The result is that the drag on the tires is not constant, and every time the gear hits a soft spot, the nose will try to go down, and every time you hit a hard spot the reverse happens. You can't let the nose bob up and down. If it touches the ground again, even for an instant, it'll eat up a lot of runway. You can't let it bob up, or it may suck the airplane off the ground momentarily and drop it back in a mighty splash. The airplane will plow along, slowly gaining speed until it finally waddles into the air. It's flying, but barely, and this is where we find out how sensitive you really are as an aviator. The airplane is clinging to flight by its fingernails, and it is your job to ever so slowly ease the nose down, allowing it to accelerate while at the same time keeping it from touching the runway again.
Even though the airplane is super slow, it'll fly in ground effect just fine, but all bets are off if it's allowed to climb out of ground effect too early. The trick is to picture ground effect as meringue on an asphalt pie (the runway); we want to skip along right on the top edge of it.
The critical period is the first few seconds after liftoff. If you ease off the back-pressure too quickly, it'll sag back into the quicksand. If you wait too long, it'll climb out of ground effect and sag back into the quicksand. Look around the nose at the edges of the runway and, as you ease off (we repeat, ease off) the back-pressure slightly, try to judge whether the airplane is losing altitude or not. Usually the feeling in your butt will tell you you're going downhill before your eyes do. Your control inputs at this point are minuscule. You aren't moving anything, and you aren't asking the airplane to do anything. You make subtle suggestions to it, but that's about it.
In a matter of seconds, as you ease off the back-pressure, you can take a breath because the airspeed will start building and you're comfortably in the air. At the same time, you'll let it climb high enough to bring the flaps in. Bring them in really slowly and stop if the airplane starts downhill and doesn't immediately recover.
Before taking off from a field that is really mushy, it is a good idea to find out if the owner is going to resent having a pair of deep ruts to deal with after you have left and the ground has hardened to the consistency of cement again. If so, plan your flight for a better day.
Energy Management
Here again, it's important to remember what your goals are. In a short-field landing, the goals are:
- Have zero doubt of the outcome from the beginning.
- Leave as little runway behind on touchdown as is practical, not possible.
- Hit a given spot.
- Touch down at minimum speed.
Part of the bit about knowing the outcome at the outset is recognizing both the airplane's limitations, as they relate to the field in question, and your own limitations.
The limitations of the airplane change with both with the airplane type and with the environment. A runway that's short to a Beech Bonanza is unbelievably long to a Piper Cub. A runway that is plenty long during the winter becomes a push in August, and runways of the same length seem to get shorter as they are moved up into the mountains of the West. In addition, a short runway with no obstacles is longer than a bigger one that has trees at the end. There are many factors that make a runway short for a given airplane, and most of those factors aren't in the POH. Even if they are in the POH, they can't be trusted.
Other factors that can make a given runway shorter include surface conditions and grade. A wet grass runway gives no braking, and a runway with a slight downgrade gets really short regardless of its actual length. If the runway is rough, then your braking is also in question and it becomes short.
The one thing that doesn't change about a given airplane on a given runway is the amount of energy that airplane is carrying on touchdown and how much resistance, as supplied by the brakes and surface friction, is available to counter that energy. At a given speed and weight, an airplane is going to have a certain amount of energy. Normally, other than burning off fuel, we can't do much about the weight, but we can definitely change the touchdown speed. This is good because speed has much more effect than does weight - the force required to stop the airplane goes up as a square of the speed. Add a little speed and the energy goes up a lot. Fortunately, the reverse is also true, which is why a major goal of a short-field landing is to touch down as slowly as possible.
There's a misconception that the proper way to land slowly is to fly final as slowly as possible. That's not entirely true. We want to arrive at the minimum safe speed (stall plus a comfortable margin for bumpy air, gusts, and you not being on your game), but that doesn't require flying the entire final that slowly. We only need to be that slow when over the threshold. During the approach, we'll start out at normal approach speed and gradually slow to a predetermined minimum speed over the threshold. As we slow down, at some point we'll see the airplane become more of a brick, and glideslope control will be slowly transferred to the throttle. Then we will use the throttle to keep the threshold/runway numbers stationary in our windshield.
Watching the threshold/numbers move is the key to our success. Just remember: If they appear to be moving toward us (or down in the windshield), we will land beyond them. If they are moving away (or up), we will land short. The goal is to hold them stationary with subtle movements of the throttle. The closer we get, the more obvious the movements become.
We've said that one of our goals is to leave as little of the runway behind us as possible, but that does not mean hanging the tail over the threshold on touchdown. Serious bush flying sometimes requires flying on the ragged edge, but few of us are likely to land on a runway that absolutely requires we use every inch. The average light airplane doesn't need much more than 500 to 800 feet to stop, so unless the runway is 1,000 feet long, it doesn't make sense to try to use every foot. Besides, trying to plant it right at the end of the runway exposes us to the risk of landing short. If you're going to make a mistake, it's better to roll off the other end at a slow speed than drop it in the trees right at the approach end.
At a minimal approach speed the airplane won't have enough energy to flare normally, so fight the urge to bring the nose up until nearly the last second. And don't suddenly chop the throttle. Gradually close it so the airplane eases onto the runway, rather than flops on and bounces. Bounces take up runway length and ruin braking.
Once down, raise the flaps to transfer all the weight to the gear and smoothly get on the brakes. Try hard to avoid sliding a tire because a sliding wheel isn't doing anything to slow you down.
Gradual Touchdown
A short-field landing is an "arrival." You clunk on. A soft-field landing, however, should be a gradual merging of the airplane with the soft surface. The theory is that we're going to ease our way onto the runway so gradually that we minimize the chance of the surface's grabbing a wheel.
To accomplish this we're going to fly what starts out as a normal approach, but as we come into ground effect we're going to start flying in formation with the ground, doing our best to get closer and closer to it but never touching it. Obviously, we are going to touch it, but we're going to delay it to the last second by using throttle throughout the flare.
This is really a neat game where, as the airplane tries to slow down and settle onto the runway, we keep adding just enough power to hang it in the air only inches above the runway. But we don't want to keep it there. Gradually ease the throttle back just a little and let the airplane barely touch. The throttle will stay where it is or will be slightly increased, as you try to soften the touchdown and keep the nose up. Slowly ease the power further back and let the wheels settle on the rest of the way. Then, while the power is being brought further back, gradually lower the nose to the ground - don't let it drop of its own accord. Everything we're doing here is an effort to stop the tires from penetrating any deeper than necessary into the quicksand.
Once you're down, keep the yoke back to keep pressure off the nosewheel and stay off the brakes unless they are needed because they probably won't grab evenly and will cause you to slip and slide.
Soft, Short Fields
First of all, there are some takeoffs and landings that shouldn't be made. When the runway is both soft and short, the best you can do is use a modified soft-field technique for either landing or takeoff, but it's a serious compromise in both cases and the ramifications should be closely considered. If it's a soft, short field and you realize on takeoff that you aren't going to make it, you have to abort much earlier because the braking won't be there to stop you. Landing in the same situation is even worse because by the time you realize you can't get stopped, you probably can't go around either.
Any runway longer than 1,800 feet generally will accommodate most small airplanes without using special techniques, as long as the density altitude isn't too high and the obstacles aren't very tall. Still, using short-field techniques can't hurt. Even though 1,500 feet isn't really short, it is short to the pilot accustomed to landing on a mile of concrete. "Short" is a personal definition. If the runway looks and feels short to you, or if it may be soft, treat it accordingly.
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 for 36 years, he teaches about 30 hours a month in his Pitts S-2A Special. Visit his Web site ( www.airbum.com ).
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