Takeoffs and climbs from soft fields require techniques that help the airplane become airborne as quickly as possible. These techniques reduce drag caused by tall grass, soft sand, mud, and snow and may also be necessary when an obstacle must be cleared. They make careful use of ground effect to reduce landing gear drag and require an understanding of the airplane’s low-speed characteristics and responses.
The same techniques are useful on rough fields, where getting the airplane off the ground as soon as possible can help avoid landing gear damage.
Soft-Field Takeoff Procedures
Taking off from a soft surface, or through soft or long wet grass, reduces the airplane’s ability to accelerate during the takeoff roll. With normal takeoff techniques, the airplane may not reach an adequate takeoff speed.
Soft-field takeoff procedures differ significantly from those used for short-field takeoffs on firm, smooth surfaces. To reduce the hazards associated with soft or rough fields, the pilot should transfer the airplane’s weight from the wheels to the wings as rapidly as possible during the takeoff roll. This is accomplished by establishing and maintaining a relatively high angle of attack (AOA), or nose-high pitch attitude, as early as possible.
If recommended by the manufacturer, the pilot should lower the wing flaps before starting the takeoff to provide additional lift and help transfer the airplane’s weight from the wheels to the wings.
The pilot should maintain continuous motion with sufficient power while lining up for the takeoff roll. Stopping on a soft surface, such as mud or snow, may cause the airplane to become bogged down.
Takeoff Roll
As the airplane is aligned with the takeoff path, the pilot should apply takeoff power smoothly and as rapidly as the powerplant can accept without faltering.
As the airplane accelerates, the pilot should apply sufficient back-elevator pressure to establish a positive AOA and reduce the weight supported by the nosewheel.
When the airplane is held at a nose-high attitude throughout the takeoff run, the wings increasingly relieve the wheels of the airplane’s weight as speed increases and lift develops. This minimizes drag caused by surface irregularities or adhesion.
If the nose-high attitude is maintained accurately, the airplane will virtually fly itself off the ground. It may become airborne at an airspeed slower than a safe climb speed because of ground effect. [Figure 1]
Lift-Off
After the airplane becomes airborne, the pilot should gently lower the nose, with the wheels clear of the surface, to allow the airplane to accelerate to a minimum safe climb speed.
During acceleration, the pilot should be aware that the airplane may tend to settle back onto the surface while transitioning out of ground effect, even with full power applied. Therefore, the airplane must remain in ground effect until at least (V_X) is reached.
This requires a good understanding of the control pressures, aircraft responses, visual cues, and acceleration characteristics of the particular airplane.
Initial Climb
After a positive rate of climb is established and the airplane has accelerated to (V_Y), the pilot should retract the landing gear and flaps, if equipped.
When departing from an airstrip covered with wet snow or slush, the landing gear should not be retracted immediately. This allows the wet snow or slush to be air-dried.
If an obstacle must be cleared after a soft-field takeoff, the pilot should climb at (V_X) until the obstacle is cleared. The pilot should then adjust the pitch attitude to maintain (V_Y) and retract the landing gear and flaps. Power can then be reduced to the normal climb setting.
Common Errors
Common errors during soft/rough-field takeoffs and climbs include:
- Failure to review the AFM/POH and performance charts before takeoff.
- Failure to adequately clear the area.
- Insufficient back-elevator pressure during the initial takeoff roll, resulting in inadequate AOA.
- Failure to cross-check engine instruments for indications of proper operation after applying power.
- Poor directional control.
- Climbing too high after lift-off and failing to level off low enough to maintain the ground-effect attitude.
- Abrupt or excessive elevator control while attempting to level off and accelerate after lift-off.
- Allowing the airplane to “mush” or settle, resulting in an inadvertent touchdown after lift-off.
- Attempting to climb out of ground effect before attaining sufficient climb speed.
- Failure to anticipate an increase in pitch attitude as the airplane climbs out of ground effect.