Airwork, 4 June

There’s an old saw in aviation: to be a successful pilot, all you have to do is make sure that your lifetime total of takeoffs and landings match. With that in mind, student pilots spend a fair amount of time practicing various kinds of takeoffs and landings to become proficient. In this particular session, we worked on soft-field takeoffs and landings.

One thing that many non-pilots assume is that airplanes can take off or land pretty much anywhere. This is true for some values of “airplanes” and “pretty much anywhere.”  It’s true that almost any reasonably level surface of sufficient length can be used as a landing strip, but some airplanes are much better suited to what we call unimproved strips– those that aren’t paved– than others.  If you watch almost any TV show involving Alaska, for example, you’ll see lots of video of airplanes landing on grass strips, dirt, gravel or sandbars in rivers, snow, and ice. Some of these airplanes will have tricycle gear (meaning a nose wheel and two main gear located under the fuselage), while others will be taildraggers (which use a steerable wheel under the tail, along with two main gear). Some will have skis, while others will have big bush tires. But what about your everyday, run-of-the-mill Cessna or Piper? It turns out that they can operate just fine from many kinds of unimproved runway, including grass and dirt strips. More to the point, though, in case of a precautionary or forced landing, it’s really important to know how to take off and land safely on soft-surfaced runways, so we practice it.

For a soft-field takeoff or landing in a tricycle-gear airplane, one key is to try to keep the nose wheel off the ground as much as possible by keeping the yoke back. As airspeed increases, keeping the yoke back raises the nose, lessening the load on the nose wheel and reducing the chance that it will dig in to the surface and flip the plane over. As you land, keeping the yoke back allows you to convert forward airspeed into lift, which has the beneficial effect of slowing the airplane down quickly without using brakes and while keeping the nose wheel out of the mud, or whatever is on the surface.

To accomplish a good soft-field takeoff, there are a few other things to do. First, momentum is your friend. Once you begin to turn onto the runway, you don’t stop to line up (provided, of course, that ATC hasn’t told you to “line up and wait,” which means that they’ve cleared you to line up on the departure end of the runway and wait for clearance to actually take off while another aircraft lands), and you control your taxi speed such that you don’t have to use the brakes as you turn to align with the runway. As you’re completing your turn, you advance the power smoothly to takeoff power while keeping the yoke back. Once you gain sufficient speed to take off, you add enough up-elevator to leave the runway surface and then immediately push forward so that you don’t climb.

“Wait, what?” I can hear you asking.

Flying machines can benefit from something known as ground effect. This is what makes hovercraft work; an airfoil moving within a certain distance off the ground will generate a sort of cushion of air that provides additional lift and reduced drag, beyond what the airfoil generates on its own. You might remember from a previous discussion that every airplane has a characteristic speed at which it climbs best– it gains the most altitude for each foot of forward motion at that speed. The goal of keeping the aircraft in ground effect is to keep it off the muddy/sticky/grassy surface– which would just slow it down– and allow it to accelerate to best-climb speed as quickly as possible, while surfing the cushion of ground-effect air. This takes some getting used to because your learned reaction to leaving the ground is to put in enough pitch to climb at the desired speed. Instead of doing that, you have to force the aircraft to stay close to the ground until it’s time to climb. This is easy to do; it just requires some extra thought. Once you’ve reached best-climb speed, you can trim the aircraft to maintain that speed, retract the flaps (if you added any), and transition to a normal climb.

Soft-field landings are all about speed. If you’re landing on a soft field it’s a good bet that the field is also shorter than you might like, so you’ll want to slow down your approach. Even if the field is long, though, you’ll still carry 5-10 knots less speed into the approach. For short-field approaches in the 172, I fly 70 knots with the first 10° of flaps, then I slow to 65 knots with 20° flaps and 60 knots with full flaps. If you do it right, you’ll end up in your landing flare doing no more than about 40 knots. Think of what this means in practical terms: if you’re landing on a plowed field (let’s say) because of an engine failure, if you can cut your touchdown speed by 20 knots, you’ve reduced the kinetic energy you’re carrying by a large amount, given that kinetic energy changes as the square of velocity (remember good ol’ KE = 1/2mv^2!)

Short-field takeoffs and landings are different beasts; here the goal is to take off or land within the minimum distance possible, perhaps including clearing an obstacle on the approach or departure. For example, the airfield at Milton, Florida (2R4) is a great place to practice short-field work because there are trees several hundred feet from each end of the runway. These don’t present any real danger, but they make a great target; in a short-field approach, you fly a steeper than usual descent to clear any obstacles, then land a bit firmer than usual– your goal is to avoid any unnecessary float, because float translates to additional distance flown down the runway. You may not have any additional distance to spare. Because it’s late, and I’m sleepy, rather than go on about short-field work I’ll leave this AOPA Flight Training article for those who are interested; it’s pretty good.

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