CHAPTER 2. Aerodynamics

Weight, Load, and Speed

Similar to airplanes, sailplanes, and PPCs, increasing weight creates increases in speed and descent rate. However, the WSC aircraft has a unique characteristic. Adding weight to a WSC aircraft creates more twist in the wing because the outboard leading edges fl ex more. With less lift at the tips, a nose-up effect is created and the trim speed lowers.

Therefore, adding weight can increase speed similar to other aircraft, but reduce the trim speed because of the increased twist unique to the WSC aircraft. Each manufacturer’s make/model has different effects depending on the specifi c design. As described in the Pilot’s Handbook of Aeronautical Knowledge, the stall speed increases as the weight or loading increases so some manufacturers may have specifi c carriage/ wing hang point locations for different weights. Some require CG locations to be forward for greater weights so the trim speed is well above the stall speed for the wing.

WSC aircraft have the same forces as airplanes during normal coordinated turns. Greater bank angles result in greater resultant loads. The fl ight operating strength of an aircraft is presented on a graph whose horizontal scale is based on load factor. The diagram is called a VG diagram—velocity versus “G” loads or load factor. Each aircraft has its own VG diagram which is valid at a certain weight and altitude. See the Pilot’s Handbook of Aeronautical Knowledge for more details on the VG diagram. Load factors are also similar to the VG diagram applicable to WSC.

Basic Propeller Principles

The WSC aircraft propeller principles are similar to those found in the Pilot’s Handbook of Aeronautical Knowledge, except there is no “corkscrewing effect of the slipstream” and there is less P-factor because the carriage is generally fl ying with the thrust line parallel to the relative wind. The wing acts independently, raising and lowering the AOA and speed. This was introduced at the beginning of this chapter when angle of incidence was defi ned.

The torque reaction does have a noticeable effect on the WSC aircraft. With the typical left hand turn tendency (for right hand turning propellers), turns are not typically built into the wing. As in airplanes, some cart designs point the engine down and to the right. Others do not make any adjustment, and the pilot accounts for the turning effect through pilot input.

It should be noted that many of the two-stroke propellers turn to the right, as do conventional airplanes. However, many four-stroke engine propellers turn to the left, creating a right hand turn. Consult the POH for the torque characteristics of your specifi c aircraft.

Chapter Summary

Basic principles of aerodynamics apply to all aircraft; however, the unique design of the wing and the separate fuselage/carriage provide a simplistic and effi cient aircraft. The following provide a summary of the unique aerodynamics for the WSC wing:

  • The WSC wing is pitch stable without a tail because of the combination of airfoil design from root to tip, sweep, twist, and planform.
  • WSC wing fl exibility allows the wing to twist from side to side by shifting the weight providing the control to roll the aircraft without control surfaces.
  • The WSC wing only has two axes of control, pitch and roll, while no yaw control is needed because it is yaw stable.
  • The WSC wing is stall resistant because under normal fl ight conditions the tip chord is still fl ying while the rest of the wing is stalled—similar to the airplane canard system.
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