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PRINCIPLES OF ROTORCRAFT FLIGHT
Class 8 – Helicopter Performance
Prof. Assoc. Fl´avio D. Marques
Universidade de S˜
ao Paulo
Escola de Engenharia de S˜
ao Carlos
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Prof. Fl´
avio D. Marques
SAA 121 – Dinˆ
amica de voo de helic´
opteros
Content (class 8)
Summary
Introduction on helicopter/rotorcraft;
Fundamentals on rotor aerodynamics;
Rotor dynamics, torque compensation, and control;
Helicopter Components – Structures, engines, and trasmission systems.
For this class ...
Helicopter Performance
1
2
3
Required power;
Available power;
Some examples of performance
parameters.
Juan de la Cierva y Codorn´ıu – Spanish
engineer; the autogyro inventor in 1920
Cierva C6 – 1924
Prof. Fl´
avio D. Marques
SAA 121 – Dinˆ
amica de voo de helic´
opteros
Helicopter Performance
Helicopter performance features depend on the flight condition, that is,
hovering;
pure vertical fight;
level forward flight;
climbing flight;
...
To assess the performance values it is usually necessary to calculate de
power relation between required and available powers.
REQUIRED POWER
Prof. Fl´
avio D. Marques
vs
AVAILABLE POWER
SAA 121 – Dinˆ
amica de voo de helic´
opteros
Helicopter performance – cont’d
REQUIRED POWER
It represents all those power values to be overcome to produce flight.
For helicopter the required power (mainly due to rotor motion and
fuselage interference) is divided into:
Power required to overcome PROFILE DRAG;
Power required to overcome PARASITE DRAG;
Power required to overcome INDUCED DRAG.
One must be aware of the need for power to overcome tail rotor
aero-mechanical dissipations, as well as in the transmission systems.
Prof. Fl´
avio D. Marques
SAA 121 – Dinˆ
amica de voo de helic´
opteros
Helicopter performance – Required Power ... cont’d
AIRPLANE
HELICOPTER
PP + PI
PPr + PP + PI
(parasite drag includes
profile drag)
(typically in hover, helicopter profile power
corresponds to 35%, while the induced power
is 65% of the total required power)
where PP denotes Parasite Power, PPr denotes Profile Power, and PI denotes Induced
Power.
DRAG FORCES
Parasite Drag – drag force related to helicopter components that do not generate lift,
that is: fuselage, fairings, nacelles, etc...;
Profile Drag – drag force due to the turning rotor blades through the air. Similar to
the parasite drag, but its source is related exclusively to the rotor
blades in motion;
Induced Drag – drag related to lift production.
Prof. Fl´
avio D. Marques
SAA 121 – Dinˆ
amica de voo de helic´
opteros
Helicopter performance – Required Power ... cont’d
PARASITE POWER
Parasite power is a function of the cube of the airspeed.
Prof. Fl´
avio D. Marques
SAA 121 – Dinˆ
amica de voo de helic´
opteros
Helicopter performance – Required Power ... cont’d
PROFILE POWER
at zero airspeed still necessary a substantial amount of power to drive the rotors
through the air;
slight changes in profile power with airspeed is observed, except for very high
velocities and at severe stall regime;
in stall condition drag increase rapidly; 3 to 4 degrees in AoA in the stall region
can cause the profile drag to double!
Prof. Fl´
avio D. Marques
SAA 121 – Dinˆ
amica de voo de helic´
opteros
Helicopter performance – Required Power ... cont’d
INDUCED POWER
at zero airspeed the induced power presents its higher values, because the rotor
must impart considerable amount of energy to get the air moving through the
rotor;
increasingly forward speed leads to a reduction in induced power;
ground effect acts in favor of reducing induced drag.
Prof. Fl´
avio D. Marques
SAA 121 – Dinˆ
amica de voo de helic´
opteros
Helicopter performance – Required Power ... cont’d
TOTAL REQUIRED POWER
Prof. Fl´
avio D. Marques
SAA 121 – Dinˆ
amica de voo de helic´
opteros
Helicopter performance – cont’d
AVALIABLE versus REQUIRED POWER
Available Power: the power of the engine less the power required to
operate the tail rotor, transmissions, frictional losses, etc..
Excess Power
Prof. Fl´
avio D. Marques
SAA 121 – Dinˆ
amica de voo de helic´
opteros
Helicopter performance – Available vs Required Power ... cont’d
Insufficient Power
observe that overloaded or underpowered flight is possible, but vertical flight and
hovering is impossible;
if some source of airflow is provided to the rotor, e.g. by taxiing the helicopter,
insufficient power region can be overcome and flight can be sustained. This
phenomenon is known as transitional or translational lift.
Prof. Fl´
avio D. Marques
SAA 121 – Dinˆ
amica de voo de helic´
opteros
Helicopter performance – Available vs Required Power ... cont’d
Forward Flight Performance
Level Flight Maximum Speed:
Maximum Ratio of Climb and Climbing Angle:
ratio of climb =
available power - required power
excess power
=
weight
weight
sin γ =
ratio of climb
velocity
Prof. Fl´
avio D. Marques
SAA 121 – Dinˆ
amica de voo de helic´
opteros
Helicopter performance – Available vs Required Power ... cont’d
Forward Flight Performance (cont’d.)
Ceiling:
Absolute:
Service:
maximum ratio of climb is zero;
ft
maximum ration of climb is 100 min
(regulations).
Prof. Fl´
avio D. Marques
SAA 121 – Dinˆ
amica de voo de helic´
opteros