Canard Airplane Spin Recovery
Aerodynamic and mass criteria for good spin recovery of tail-last configurations are well known, as a result of years of experience and testing. A builder of a conventional tail-last configuration can rely on NASA spin recovery design charts with a fair degree of confidence. The NASA design charts specify minimum rudder and fuselage areas in certain locations, depending on calculated airplane moment of inertia parameters. The point is that airplane designers who cannot afford the expense of testing their designs in specialized spin-tunnel facilities or in model drop tests can still be reasonably assured of safe spin recoveries by using the NASA design charts and other guidelines.
The NASA spin recovery design charts do not specifically apply to canard configurations and can only offer the most general guide in those cases. A canard airplane designer should count on spin-tunnel or drop model tests, in order to ensure safe spin recoveries. Canard
Figure 17.2 The canard six-place Jetcruzer, the first airplane to be granted a spin-resistant certification under FAA Part 23. Numerous attempts to spin the airplane were unsuccessful. (From AOPA Pilot, Aug. 1994)
surface tests by Neihouse in 1960 showed prospinning or propelling yawing moments for some canard sizes and locations on the fuselage nose.
Possible spin recovery problems are of course avoided if the airplane’s longitudinal control power is limited sufficiently so thatthe airplane cannot be stalled. An airplane’s main wing must be stalled and autorotation (Jones, 1934; McCormick, 1979) must be initiated before an airplane can spin. Even if the airplane stalls, spinning might still be avoided if rudder power is limited or coordinated with the ailerons, as in two-control airplanes such as the Ercoupe. Control limiting without penalty to the airplane’s utility is altogether feasible for modern computer-controlled fly-by-wire machines, such as the Northrop B-2 and Grumman X-29A.
For ordinary fly-by-cable airplanes, limiting longitudinal control power to that just needed to attain maximum lift coefficient can be defeated by loading the airplane to have a more aft center of gravity. Otherwise stated, limiting longitudinal control power to avoid stalling and spinning inevitably cuts down an airplane’s usable center-of-gravity range, reducing its utility. Some form of control limiting through center-of-gravity range has apparently been used in a recently certificated canard airplane. This is the six-place turboprop Jetcruzer, a product of Advanced Aerodynamics and Structures, Inc., of Burbank, California (Figure 17.2). Numerous attempts by test pilots to stall and spin the airplane were unsuccessful. The FAA granted the airplane a “spin-resistant”-type certificate, under the Federal Airworthiness Standards, Part 23.