A small balance tab on the wing trailing edge near the root operates in the opposite direction to the wing.
Aircraft information
The Mistral is a three-axis, tricycle landing gear, microlight biplane, built by Aviasud Ltd in France.
It is powered by a Rotax 532 two-stroke engine, located in the nose, and is fitted with a fixed pitch three bladed propeller of composite construction.
The aircraft has side by side seating for the two occupants, with a single control column located in the centre between the two seats.
Fuel is carried in plastic tank(s) located behind the seats.
The aircraft is highly unusual in two particular respects: firstly, in having swept forward wings and secondly, in having all-flying lower mainplanes in lieu of ailerons for roll control. Each of the lower mainplanes is pivoted on a pair of ball and socket joints positioned at approximately 30% chord, one at the wing root and the other at approximately mid span. The latter joint is supported by a vertical bracing strut connected at its top end to the upper mainplane spar, at the lift strut
attachment point. The incidence of each lower wing is controlled directly by the pilot, via a system of rods and bellcranks linking the control column to the trailing edge of each wing, such that lateral movements of the control column move the trailing edges of the lower mainplanes in opposition to one another, in the manner of very large ailerons.
The inboard end of each lower wing is fitted with a servo tab hinged to the trailing edge. With a ground-adjustable, fixed geometry, linkage to this tab a non-linear relationship between servo tab position and wing incidence is achieved. A specific aircraft's servo tab control characteristic will depend on the rigging of the wings and how the tab linkages have been adjusted. The overall characteristic of the system is such that the servo tabs will act primarily in opposition to pilot inputs (i.e. as an anti-balance tab) whenever the wing is at significant positive or negative angles of incidence. The servo control moments opposing pilot inputs are more pronounced in the positive wing incidence regime than for negative wing incidence and the wing incidence at which the servo tab control moment passes through zero will depend upon the individual linkage adjustment settings.
Pitch control is achieved via a conventional all flying tailplane, also equipped with an anti-balance tab, the linkage anchor point of which is adjustable in flight to trim the aircraft in pitch. The rudder is conventional and is operated by cables.
*PS. Although Aviasud was based in France I believe the designer was Belgian.
Bar by Mees
