Page 92 - Understanding Flight

CH03_Anderson 7/25/01 8:56 AM Page 79

Wings 79

NASA X-29 experimental aircraft shown in Figure 3.8 and the Long-
EZ in Figure 3.19.
Canards have the advantage that the horizontal stabilizer is lifting
up rather than down, as it does on a conventional airplane. This
reduces the load on the wing. Thus, the canard appears to be more
efficient. Both the wings and the horizontal stabilizers provide lift.
But canards must be designed such that the horizontal stabilizer
stalls before the wing. If the wing stalled first in the canard
configuration, the rear of the airplane would drop, increasing the
angle of attack further, and stall recovery would be impossible. The
canard is designed such that the horizontal stabilizer stalls first,
dropping the nose of the airplane. Thus, the airplane’s wing will not
stall. This safety feature has encouraged many modern designers to
favor canards.
Canards are touted as being more efficient than conventional
airplanes because all surfaces are lifting. This conclusion ignores
power. The horizontal stabilizer is at a higher angle of attack so it is
working harder than the wing. By comparison, the wing is loafing.
The lift from the horizontal stabilizer is generated by increased
downwash because of the higher angle of attack. From a power
standpoint, this is inefficient. The more efficient wing is allowed to
generate less lift, as a result of the load carried by the canard. For

Fig. 3.19. A home-built Long-EZ illustrating a canard configuration. (Photo
courtesy of Sandy DiFazio.)