Extract from a NASA technical paper "A Look at Handling Qualities of Canard Configurations", by Seth B. Anderson.
The comments on controllably, and the use of anhedral are worthy of note, given the diatribe by
simplex on these two elements.
At the start of powered flight, most new aircraft copied the Wright Brothers canard design; however, only tail aft configurations were produced during the WW I years, 1914-1918, and only a few copies of canard designs invaded the market for the next 50 years. In those early days of flight, most aircraft were designed and built without the benefit of wind tunnel tests, and documentation of stability and control characteristics did not exist. The first systematic stability and control flight test results were conducted by NACA5 in 1919 using a Curtiss JN4H aircraft. Handling qualities measurements correlated with pilot opinion did not take place until the late 1930s.
Although a great number of canard-equipped aircraft have flown throughout the years, it is only recently that stability and control data have become available to provide a clearer understanding of the relative merits of this concept. As a result, only a select few of the many canard concepts that have demonstrated successful flight are reviewed.
In the early struggles to achieve powered flight, the canard concept proved to be popular. The Wright Brothers designed their 1903 canard "Flyer" by appropriately blending knowledge of structures, power plant, and aerodynamics to construct a machine that had enough power to offset the drag and sufficient control to trim over a wide AOA range. They did not, however, understand or appreciate the need for stability and this was reflected in problems encountered in developing their concept. Not only was their aircraft unstable longitudinally and laterally, but also the elevator hinge moments were overbalanced, and large adverse yaw complicated turn entries.
An examination of a two-view drawing of the 1905 aircraft reveals features which are of special interest from the stability and control (handling qualities) standpoint. Foremost is the use of the foreplane, which led to the configuration coined "canard," a French word for a hoax or tall story. In fact, their accomplishment of powered flight was not completely believed until Wilber Wright demonstrated their aircraft in many European countries in 1908. The reason for the choice of the canard control was not based upon measured data (the Wrights' wind tunnel tests did not include pitching moment), but more upon intuitive reasoning. Good control was uppermost in their minds. Wilber had expressed a concern that an aft tail configuration had an intrinsic danger that was associated with Lilienthal's loss of control and death while flying his glider in 1896.
The stall behavior of their aircraft was never well documented. The relatively constant chord planform would normally provide good stall characteristics by virtue of center-section flow breakdown, except that downwash from the canard would unload the wing root area and tend to cause loss of lateral stability at stall. Stalls had been encountered in the 1901 glider (configured similarly to the 1903 powered vehicle), which was observed to "mush" to the ground with little damage. A more serious stall did occur with the 1903 Flyer when Wilber allowed the aircraft to pitch up to the stall in a moment of confusion when he inadvertently stopped the engine. The stall occurred at low altitude, resulting in a nose-down impact with considerable damage, but Wilber was not hurt. The nose-down behavior is normally a desired stall recovery response, except when flying close to the ground.
Pursuing the pitch characteristics further, recent data obtained on a one-eighth-scale model show that pitching moment characteristics were relatively linear up to CLmax . In fact, a pitch down at the stall normally max associated with a canard control losing effectiveness (by stalling before the wing) is not evident. Flight stall behavior would be altered by the c.g. location used. In the Wrights' case, the c.g. was not far enough forward to highly load the canard and cause it to stall first. Although the Wrights may have wanted more stability, it was not possible to move the c.g. farther forward because of the inability to trim out the large nose-down pitching moment associated with the highly cambered airfoil. It should be noted that even though the flyer was highly unstable, a large upload on the canard was required to provide trim at a cruise CL of approximately 0.6.
The Flyer's instability was a major handling qualities problem as evidenced from comments by Orville Wright in a letter to Wilber in 1909. "The difficulty in handling our machine is due to rudder (horizontal tailor canard) being in front, which makes it hard to keep on a level course. If you want to climb you must first give the front rudder a larger angle, but immediately the machine begins to rise you must reverse the rudder and give a smaller angle. The machine is always in unstable equilibrium. I do not think it necessary to lengthen the machine but to simply put the rudder behind instead of before." From the recent wind tunnel data it was estimated that they were flying with a negative static margin of approximately -20%. The derived pitch dynamic stability showed that the short period mode was aperiodic and doubled amplitude in about 0.5 sec. This calculated divergence rate is considerably greater than that judged acceptable. In reality, the behavior would be subdued by apparent mass and inertia effects. A skilled pilot could learn to cope with this behavior, but undoubtedly the pilot workload was high.
As their flights progressed, the Wrights recognized the need for more stability. By reducing the wing camber and providing a more favorable hinge moment balance, they were able to add 70 lb of cast iron at the nose to improve stability. Eventually, one of the canard surfaces was moved to the rear and made movable, improving stability so that hands-off flight was possible.
The lateral/directional stability and control of the Flyer were marginal and early attempts at turning flight were fraught with danger. In fact, it was not until September 1904 that a 360° turn was accomplished. Part of the problem was lateral stability. Although dihedral invented by Cayley around 1800 was known to produce positive lateral stability, the Wrights chose to use anhedral because their glIder experiments had shown adverse bank angle effects when flying in ground effect in cross wind operation with positive dihedral.
Although anhedral tended to help the airplane turn by virtue of an unstable spiral mode, Wilbur noted in his diary, "Unable to stop turning." It was fortunate that directional stability (CNB ) was neutral to low, since a large CNB would have aggravated the spiral instability. In part, the poor yaw (turn) behavior was due to the interconnect system used to improve turn entry. The Wrights discovered early in their glider tests that wing warping provided good roll effectiveness, but it also produced adverse yaw. By interconnecting the rudder with wing warp, adverse yaw effects were reduced, but yaw control power was marginal. In 1905 they decided to operate the rudder control independently with improved turn capability.
Although the 1903 Flyer did achieve success in ushering in the era of powered flight, the canard concept did not appear to have enough merit to prevail beyond 1910. The 1911 model B aircraft had a conventional (aft) tail.