SOFT FIELD TECHNIQUES

Before setting off to visit a small grass or gravel airstrip, it’s not a bad plan to review the soft field techniques, if you haven’t been using them on a regular basis. Like any other technique, unless you stay current you may have allowed the finer points to slip.

Practice in a safe and controlled environment before you need a technique is always an excellent plan. That way, when you get to that lovely, little strip, you will be able to land, taxi and take off with confidence.

When we speak of soft field techniques for taxiing, taking off and landing, it isn’t necessarily the take off or landing surface that is “soft”. A grass or gravel strip can be not only quite hard, it can be bumpy and rough and uneven. When we refer to “soft field” techniques, what we are directing attention to is the need to keep interactions between the machine and the surface as gentle as possible to prevent damage and the risk of losing control.

An unimproved surface can be uneven, bumpy, can include significant potholes and may include loose surface material that can be sucked into the engine or picked up be the propeller and tossed about. With a tricycle gear aircraft, the nose wheel is particularly vulnerable to damage and must be protected. With conventional gear aircraft, visibility can be a problem and a pilot must take the necessary measures to ensure he or she doesn’t inadvertently taxi into an obstacle.

When taxiing on a rough surface, the keys are to proceed slowly and to keep going. We taxi slowly to keep the whole process as gentle as possible. Many rough surfaces will develop over time undulating bumps just like you see on a beach as a result of wheel traffic and the movement of the surface material. This wave-like surface profile can result in an increasing porpoising movement of the aircraft as you taxi. Not a good scenario. Keep the speed down to dampen the effects of the uneven surface. Protect the propeller. Protect the nose gear with a tricycle gear aircraft.

Uneven surfaces can have potholes or other difficult to traverse spots. If is has been raining, things tend to be worse. Keep the aircraft moving to avoid becoming stuck in a soft spot or hole. The extra thrust required to extract an aircraft from a hole can result in damage to the propeller or other parts of the airframe from loose rocks or other particulate matter thrown by the propeller wash.

With a tricycle gear aircraft, taxi with the elevators in the full up position. This helps keep excess weight off the nose gear. When taxiing a conventional gear aircraft, keep the stick full back, taxi slowly and perform ‘S’ turns to ensure good visibility of potential hazards. Some tail draggers have miserable forward visibility in the taxi.

Pick your run-up spot with care and attention. You may or may not have an appropriate area available for a power run-up. Once again, we don’t want to run the engine at a high rpm and risk damage to the propeller or the airframe from flying debris. If you do increase rpm, do it slowly to reduce the risks involved.

You may not want to open carburetor heat on the ground unless absolutely necessary. We want to avoid unfiltered air being sucked into the engine. Loose grass clippings, dust, gravel particles: all very bad news for the insides of your engine.

Takeoff is the process of transferring the weight of the aircraft from its wheels to its wings. On a “soft field”, we want to accomplish this as gently and safely as possible. Making certain it is safe to do so and that the strip itself is safe to take off from—remember most unimproved strips will have no air traffic control—we want to line the aircraft up with the departure path and find appropriate reference points.

We will not have the nice, white lines painted on hard surface runways to assist us. We must make do with trees, telephone poles, clouds, mountains, whatever may be available. Reference points must include those above the surface; we will lose sight of the ground as we assume a climb attitude.

Use appropriate flap setting as specified in the aircraft POH. Apply power gently to accelerate at a controlled rate. We don’t want to suck up any unnecessary debris as a result of the increasing propeller rpm. With a tricycle gear aircraft, hold the elevators in the full up position until the nose wheel leaves the ground. We want to achieve a nose high attitude with the nose wheel off the ground but not so nose high that we lose visual contact with the strip. If a cow or coyote steps into our path we would certainly like to see it so we can respond appropriately.

Do not rotate as you would on a paved surface. Allow the aircraft to lift itself off the ground. Once airborne, level off right above the ground. We would like the aircraft to accelerate to climb speed while still in ground effect to reduce the chance of a stall. At Vy, allow the aircraft to begin a climb. At a safe altitude, retract flaps and carry on your way.

If we are flying one of those silly aircraft with its third wheel at the back end, we apply power gently, holding the stick well back to keep the nose high and the tail wheel on the ground. As the aircraft begins to pick up speed, raise the tail wheel just above the ground to reduce its rolling resistance while still maintaining a high angle of attack and protecting the propeller from damage.

Allow the aircraft to fly itself off the ground. Once airborne, lower the nose to level and remain in ground effect, allowing the aircraft to accelerate to Vy. Initiate a climb and away you go. Flaps up at a safe altitude.

Landing on an unimproved or unpaved airstrip can be a challenge unless you are current and properly prepared. Once again, we are transferring the weight of the aircraft: this time from the wings to the wheels. We want to achieve this transfer as gently as possible to prevent damage to the aircraft or any potential loss of control.

Have a very good look at the strip before you commit yourself to landing. Make certain that the strip is usable, that there are no obstacles, that you understand what the wind is doing and that the surface is safe to land on. Remember the OWLS checks from training: Obstacles, Wind, Length, Surface?

Approach at the specified speed as per your aircraft’s POH. Normally, we will use full flaps, if we are so equipped, for a soft field landing unless the wind is strong or gusty. As we round out over the surface we reduce power somewhat but retain sufficient power to maintain a very low rate of descent. Essentially, we level off just above the ground and fly the aircraft into a slow flight condition, maintaining our approach with power.

As the aircraft enters slow flight, we may even choose to add a touch of power to control our rate of descent.

If your normal procedure is to use carburetor heat on approach, it isn’t a bad plan to close it on short final or just prior to touch down. We would like to avoid sucking particles of grass or dust into the engine if we can avoid it.

With a tricycle gear aircraft, fly the aircraft on to the ground, allowing the main gear to make contact while holding a nose up attitude. It’s nice to be hearing the stall warning horn as we are touching down. As soon as the wheels make contact, gently begin reducing power while maintaining a nose up attitude with elevator. We would like to keep that vulnerable nose wheel in the air until we have pretty much run out of speed and the elevators are in the full up position. Once all three wheels are down, retract the flaps and taxi with elevators in the full up position to protect the nose gear.

Conventional gear aircraft will want to land in the three point or full stall configuration at as low an airspeed as is consistent with safety. Use power to control your rate of descent; pitch controls our airspeed. We want to touch down as slowly and gently as possible. Once down, keep the stick full back—elevators full up—to protect the propeller and keep the tailwheel firmly on the ground.

Flaps can come up as soon as things are under control to protect them from damage and reduce any unwanted lift. Make certain you can retract the flaps by feel. I had a couple of exciting moments once when I looked down to find the flap extension lever on a C-170 a little sooner than I should have. If in doubt, wait until the aircraft is rolling very slowly or is stopped.

Making use of unimproved airstrips will give you all sorts of interesting additional destinations during these months of delightful weather. Making sure before you set out that you are current and comfortable with the necessary procedures and techniques can help reduce the risks and ensure you will enjoy your adventures.