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main (rear) wing.
b. As the airplane’s angle of attack (AOA)
increases, the canard should stall first, lowering the
AOA of the main (rear) wing. Since the rear wing
doesn’t stall, a characteristic ‘‘buck’’ or ‘‘nod’’ takes
place. Full aft stick results in the canard alternately
stalling and flying while the rear wing never reaches
it’s critical AOA and continues to fly. This self-limiting
stall characteristic makes a properly designed and
built canard aircraft un-spinable. It should be noted,
however, that the accident rate for canard designs
are approximately the same as conventional designed
amateur-built aircraft because of the following:
(1) During take-off, the transition from
ground roll to flight can be a more critical procedure
in some canards as compared to more conventional
designs.
(2) Some canards with combinations of CG
and pitch control sensitivity will be more likely to
over rotate at lift-off.
(3) Some canards have less visible airframe
structure in front of the pilot and in his peripheral
vision. Others have more than enough. These
differences in design can produce a different reference
frame for pilots with many hours of conventional
aircraft time and may cause initial errors in
pitch attitude, such as the nose too high on takeoff
and landings.
(4) In addition, canard aircraft by design
have very different take-off characteristics than
conventional configured aircraft. Canard aircraft
with pusher propellers need a substantially higher
rotation speed on take-off.
(5) To rotate a conventional design aircraft,
all that is required is enough airspeed to provide
sufficient control to attain a positive angle of
attack due to the long moment arm from the main
gear (the axis of rotation) to the tail, a relatively
small amount of lift is required. This lift, generated
at a relatively low airspeed, makes it possible to
rotate the aircraft into the take-off position slightly
below flying speed. Allow the aircraft to accelerate
to flying speed and lift off.
(6) In contrast, the canard nose wheel will
stay firmly on the ground until an airspeed is reached
at which the canard, with full up elevator, can generate
enough lift to equal the following:
(i) the load carried by the nose
wheel, plus
(ii) the nose down moment caused by
the friction of the nose and main gear tires with the
surface, and the down-thrust vector provided by the
propeller during the take-off roll.
(7) Since the main wing may reach flying
speed before the canard, the nose wheel will stay
firmly on the runway until take-off speed is reached.
Rotation will then occur, and the aircraft will literally
jump off the ground.
(8) Canards with a thrust line above the
CG will have appreciable pitch trim change with
power. Forward stick motion is required when power
is reduced. While this may not be of any consequence
to an experienced pilot, it can be a serious surprise
to an unwary and inexperienced pilot. This unfamiliar
flight characteristic might cause pilot-induced
pitch oscillations with disturbing consequences under
some conditions (e.g., an aborted take-off).
(9) Due to its unique design, the canard
aircraft needs a higher nose up attitude when landing
compared to conventional configured aircraft. Many
canard pilots are reluctant to raise the nose high on
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AC 90-89A 5/24/95
landing due to the limited forward visibility while
the nose is up. Consequently, many canard pilots
tend to make their approach angle shallow. This shallow
angle results in approach speeds quite a few
knots faster than what is necessary. For pilots who
prefer visibility to shorter runways, it is recommended
that canard designed aircraft be tested
on runways a minimum of 1,000 feet longer than
what would be used for a conventional aircraft of
the same horsepower and performance capability.
Longer runways should be used until the pilot
becomes more experienced with the landing
characteristics of the aircraft.
(10) If the nose is held at a too high an angle
on landing, the canard will stall while the main wing
is still generating lift. The stalled canard will drop
the nose rapidly onto the runway with enough force
to damage the nose gear.
(11) Quickie (tractor engine designs)
configured canard designs have a limited ability to
rotate nose up while on the ground. This tends to
increase takeoff speeds because the canard and the
main wing angle of attack are limited while the aircraft
　
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