Any one who has flown in an airplane in turbulent air recalls that experience with distaste. Prior to jet transports that cruise at altitudes above turbulent air, every airplane was equipped with "sick sacks" in the pocket on the back of each seat. Even the invention of dramamine did not effectively relieve this dark side of flying.

The goal of a smooth-riding airplane has been pursued since the first low-wing-loading biplane took off from a pasture. Extensive research has been conducted on this topic, and many attempts have been made to build a smooth-riding airplane. One of the most effective approaches was tested by NACA (the predecessor to NASA) in 1956, as described in Reference 7. This report describes an experiment in which a Beech Model 18 was equipped with a servo-controlled flap that could be deflected in response to a gust that was sensed by a vane on a mast ahead of the airplane.

Results of this experiment were impressive. Normal (vertical) accelerations were reduced by over 60% and pilots reported favorably on the control response of the airplane. Research on the reactions of humans to vertical accelerations has indicated that individuals feel an even greater reduction.

The NACA Model 18 experiment required that the original flaps had to be modified to span the entire wing. This was because the conventional flaps were not effective enough to produce incremental positive or negative lift coefficients large enough to counter the change of wing angle of attack produced by the gust (page 2 of Reference 7). This required a servo system with sufficient power to deflect the entire flap.

This deficiency is remedied with the PWCR^TM airplane. Blowing over the flap increases flap effectiveness, and a small chord flap is sufficient to change wing lift coefficient. Power required to deflect this small chord flap is reduced, and the servo-system is simpler. Modern developments in sensors and control systems enable a simpler and more effective response to gusts, and the full advantage of gust alleviation is achieved.

The gust alleviation system is shown in the following diagram. Either vanes on booms or embedded sensors detect gusts (upward or downward wind flow). The gust strength and direction is fed into a computer that controls a servo motor to change the angle of the gust alleviator flap. If the gust is upward (increasing the wing angle of attack) the gust alleviation flap is deflected upward to decrease the wing lift coefficient. Flap deflection is a function of the intensity of the gusts as sensed by the vanes or sensors.

This "smooth ride" gust alleviation system is made practical by a combination of increased flap effectiveness from blowing and by modern developments in sensors and control systems. Just as certified engines now exist for the main and blowing power plants, "off the shelf" equipment is now available for the gust alleviation system.