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the blade tip. Because the gyroplane is operating in
autorotation, in forward flight there is an inherent stall
region centered inboard on the retreating blade. [Refer
to figure 16-5] As forward speed increases, the angle of
attack on the retreating blade increases to prevent dissymmetry
of lift and the stall region moves further
outboard on the retreating blade. Because the stalled
portion of the rotor disc is inboard rather than near the
tip, as with a helicopter, less force is created about the
aircraft center of gravity. The result is that you may feel
a slight increase in vibration, but you would not experience
a large pitch or roll tendency.
ROTOR FORCE
As with any heavier than air aircraft, the four forces
acting on the gyroplane in flight are lift, weight, thrust
and drag. The gyroplane derives lift from the rotor and
Forward
Driven Region
Driving Region
Stall

 

Region
Retreating

Side
Advancing

Side
Figure 16-5. Rotor disc regions in forward autorotative flight.
Forward

Flight at

42 kt
42kt
42kt
42kt
42kt
2'
Area of

Reverse flow
42kt
Rotor Speed 300 r.p.m.
Figure 16-6. An area of reverse flow forms on the retreating
blade in forward flight as a result of aircraft speed exceeding
blade rotational speed.
16-4
rotor blades turn, rapid changes occur on the airfoils
depending on position, rotor speed, and aircraft speed.
A change in the angle of attack of the rotor disc can
effect a rapid and substantial change in total rotor drag.
Rotor drag can be divided into components of induced
drag and profile drag. The induced drag is a product of
lift, while the profile drag is a function of rotor r.p.m.
Because induced drag is a result of the rotor providing
lift, profile drag can be considered the drag of the rotor
when it is not producing lift. To visualize profile drag,
consider the drag that must be overcome to prerotate
the rotor system to flight r.p.m. while the blades are
producing no lift. This can be achieved with a rotor system
having a symmetrical airfoil and a pitch change
capability by setting the blades to a 0° angle of attack.
A rotor system with an asymmetrical airfoil and a built
in pitch angle, which includes most amateur-built
teeter-head rotor systems, cannot be prerotated without
having to overcome the induced drag created as well.
THRUST
Thrust in a gyroplane is defined as the component of
total propeller force parallel to the relative wind. As
with any force applied to an aircraft, thrust acts around
the center of gravity. Based upon where the thrust is
applied in relation to the aircraft center of gravity, a relatively
small component may be perpendicular to the
relative wind and can be considered to be additive to
lift or weight.
In flight, the fuselage of a gyroplane essentially acts as
a plumb suspended from the rotor, and as such, it is
thrust directly from the engine through a propeller.
[Figure 16-7]
The force produced by the gyroplane rotor may be
divided into two components; rotor lift and rotor drag.
The component of rotor force perpendicular to the
flight path is rotor lift, and the component of rotor force
parallel to the flight path is rotor drag. To derive the
total aircraft drag reaction, you must also add the drag
of the fuselage to that of the rotor.
ROTOR LIFT
Rotor lift can most easily be visualized as the lift
required to support the weight of the aircraft. When an
airfoil produces lift, induced drag is produced. The
most efficient angle of attack for a given airfoil produces
the most lift for the least drag. However, the airfoil
of a rotor blade does not operate at this efficient
angle throughout the many changes that occur in each
revolution. Also, the rotor system must remain in the
autorotative (low) pitch range to continue turning in
order to generate lift.
Some gyroplanes use small wings for creating lift when
operating at higher cruise speeds. The lift provided by
the wings can either supplement or entirely replace
rotor lift while creating much less induced drag.
ROTOR DRAG
Total rotor drag is the summation of all the drag forces
acting on the airfoil at each blade position. Each blade
position contributes to the total drag according to the
speed and angle of the airfoil at that position. As the
Lift
Resultant
Thrust
Resultant
Thrust
Lift
Resultant
Drag
Rotor

Drag
Fuselage

Drag
Resultant
　
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