Soft/Rough Field Takeoff and Climb in Weight-Shift-Control Aircraft

Takeoffs and climbs from soft fields require the use of operational techniques for getting the WSC aircraft airborne as quickly as possible to eliminate the drag caused by tall grass, soft sand, mud, and snow, and may or may not require climbing over an obstacle. The technique makes judicious use of ground effect and requires a feel for the WSC aircraft and fine control touch. These same techniques are also useful on a rough field where it is advisable to get the aircraft off the ground as soon as possible to avoid damaging the landing gear.

Soft surfaces or long, wet grass usually reduce the aircraft’s acceleration during the takeoff roll so much that adequate takeoff speed might not be attained if normal takeoff techniques were employed.

It should be emphasized that the WSC aircraft is different from most aircraft. The high wing creates a high center of gravity in which the front wheel can bog down in soft fields and flip the WSC aircraft forward. The propeller in the back pushing down on the front wheel also contributes to this unique situation. This is a limitation for WSC aircraft that should not be ignored. WSC aircraft that land in soft fields or sand may not be able to take off. There is a wide variation of manufacturer designs with the least preferable being a skinny, high pressure, highly loaded front tire. WSC aircraft with large wide tires that can be operated at low pressure are designed for operation in soft and rough fields. [Figures 7-11 through 7-13]

Figure 7-11. Soft field takeoff limitation for WSC aircraft: front wheel digs in and WSC aircraft rolls forward.

Figure 7-11. Soft field takeoff limitation for WSC aircraft: front wheel digs in and WSC aircraft rolls forward.

Figure 7-12. Example of a WSC aircraft designed with a wide low-pressure front wheel for soft field operation.

Figure 7-12. Example of a WSC aircraft designed with a wide low-pressure front wheel for soft field operation.

Figure 7-13. Grass fields are commonly used for WSC operations but require a longer time to accelerate to takeoff speed.

Figure 7-13. Grass fields are commonly used for WSC operations but require a longer time to accelerate to takeoff speed.

Correct takeoff procedure for soft fields and rough fields 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 aircraft’s weight must be transferred as rapidly as possible from the wheels to the wings as the takeoff roll proceeds. Establishing and maintaining a relatively high angle of attack with a nose-high pitch attitude as early as possible achieves this.

Stopping on a soft surface, such as mud, snow or sand, might bog the aircraft down; therefore, it should be kept in continuous motion with sufficient power while lining up for the takeoff roll.

Takeoff Roll

As the aircraft is aligned with the takeoff path, takeoff power is applied smoothly and rapidly. As the aircraft accelerates, the control bar is moved full forward to the front tube to establish a positive angle of attack and to reduce the weight supported by the nosewheel because any lift on the wing takes load off of the landing gear.

When the aircraft is held at a nose-high attitude throughout the takeoff run and as speed increases and lift develops, the wings progressively relieve the wheels of more and more of the WSC’s weight, thereby minimizing the drag caused by surface irregularities or adhesion. If this attitude is accurately maintained, the aircraft virtually flies itself off the ground, becoming airborne at airspeed slower than a safe climb speed because of ground effect. [Figure 7-14]

Figure 7-14. Rough and soft field takeoff.

Figure 7-14. Rough and soft field takeoff.

Lift-Off and Initial Climb

After becoming airborne, the nose should be lowered very gently with the wheels clear but just above the surface to allow the aircraft to utilize ground effect to accelerate to VY, or VX if obstacles must be cleared. Extreme care must be exercised immediately after the aircraft becomes airborne and while it accelerates to avoid settling back onto the surface. An attempt to climb prematurely or too steeply may cause the aircraft to settle back to the surface as a result of losing the benefit of ground effect. An attempt to climb out of ground effect before sufficient climb airspeed is attained may result in aircraft incapacity to continue climbing as the ground effect area is traveled, even with full power for lower powered WSC aircraft. Therefore, it is essential that the aircraft remain in ground effect until at least VX is reached. This requires a feel for the WSC aircraft and a very fine control touch in order to avoid overcontrolling the pitch control as required control pressures change with aircraft acceleration. Simply getting off the ground as quickly as possible and flying in ground effect is the goal.

In addition to normal takeoffs, additional common errors in the performance of soft/rough field takeoffs are:

  • Attempting a takeoff with a WSC that is not equipped with the proper tires.
  • Minimum air pressure not used in tires.
  • Insufficient control bar forward pressure during initial takeoff roll, resulting in inadequate angle of attack.
  • Poor directional control.
  • Climbing too steeply after lift-off.
  • Abrupt and/or excessive pitch control while attempting to level off and accelerate after lift-off.
  • Allowing the aircraft to “mush” or settle resulting in an inadvertent touchdown after lift-off. 
  • Attempting to climb out of ground effect area before attaining sufficient climb speed.

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