Takeoffs and climbs from soft fields require the use of operational techniques for getting the airplane airborne as quickly as possible to eliminate the drag caused by tall grass, soft sand, mud, snow, etc., and may or may not require climbing over an obstacle. These same techniques are also useful on a rough field where it is advisable to get the airplane off the ground as soon as possible to avoid damaging the landing gear.
Soft surfaces or long wet grass usually retard the airplane's acceleration during the takeoff roll so much that adequate takeoff speed might not be attained if normal takeoff techniques were employed.
The correct takeoff procedure at fields with such restraining conditions is quite different from that appropriate for short fields with firm, smooth surfaces. To minimize the hazards associated with takeoffs from soft or rough fields, support of the airplane's weight must be transferred as rapidly as possible from the wheels to the wings as the takeoff roll proceeds. This is done by establishing and maintaining a relatively high angle of attack or nose high pitch attitude as early as possible by use of the elevator control. Wing flaps may be lowered prior to starting the takeoff (if recommended by the manufacturer) to provide additional lift and transfer the airplane's weight from the wheels to the wings as early as possible.
The airplane should be taxied onto the takeoff surface at as fast a speed as possible, consistent with safety and surface conditions. Since stopping on a soft surface, such as mud or snow, might bog the airplane down, it should be kept in continuous motion with sufficient power while lining up for the takeoff roll.
As the airplane is aligned with the proposed takeoff path, takeoff power must be applied smoothly and as rapidly as the powerplant will accept it without faltering. As the nosewheel type airplane accelerates, enough back elevator pressure should be applied to establish a positive angle of attack and to reduce the weight supported by the nosewheel. In tailwheel type airplanes, the tail should be kept low to maintain the inherent positive angle of attack and to avoid any tendency of the airplane to nose over as a result of soft spots, tall grass, or deep snow.
When the airplane is held at a nose high attitude throughout the takeoff run the wings will, as speed increases and lift develops, progressively relieve the wheels of more and more of the airplane's weight, thereby minimizing the drag caused by surface irregularities or adhesion. If this attitude is accurately maintained, the airplane will virtually fly itself off the ground. It may even become airborne at an airspeed slower than a safe climb speed because of the action of "ground effect." This phenomenon produces an interim gain in lift during flight at very low altitude due to the effect the ground has on the flow pattern of the air passing along the wing. "Ground effect" is further explained in the chapter on Principles of Flight.
After becoming airborne, the nose should be lowered very gently with the wheels just clear of the surface to allow the airplane to accelerate to the best rate of climb speed (Vy), or best angle of climb speed (Vx) if obstacles must be cleared. Extreme care must be exercised immediately after the airplane becomes airborne and while it accelerates, to avoid settling back onto the surface. An attempt to climb prematurely or too steeply may cause the airplane to settle back to the surface as a result of losing the benefit of "ground effect." Therefore, it is recommended that no climb to an altitude higher than barely clear of the surface be attempted at an airspeed slower than the best angle of climb airspeed (Vx).
After a definite climb is established, and the airplane has accelerated to the best rate of climb speed (Vy), retract the landing gear and flaps, if so equipped.
In the event an obstacle must be cleared after a soft field takeoff, the climbout must be performed at the best angle of climb airspeed (Vx) until the obstacle has been well cleared. After reaching this point the airspeed may then be accelerated to the best rate of climb (Vy) and the flaps and gear retracted. The power may then be reduced to the normal climb setting.