Aerodynamic Forces Flashcards
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tip path
The circular path described by the tips of rotor blades
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Tip path plane
The plane within which the tips of rotor blades travel. It is parallel to the plane of rotation which acts through the rotor head.
How can a pilot change tip path plane?
a pilot my out of this plane for movement of the cyclic control
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axis of rotation
The line through the rotor head at right angles to the plane of rotation. blades actually rotate around this axis.
What does POR stand for?
Plane of rotation
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What is the shaft axis
The lion consistent with the rotor shaft mast.
What is the disc area?
The area contained within the tip path plane. In flight, this area is not constant since it is affected by the coning angle of blades
What is a chord?
The straight line between the blades leading Edge and its trailing Edge
What is Blade angle (aka Pitch angle)?
The angular difference between the chord of a blade and the plane of rotation (POR).
How can the pilot change the blade angle?
This angle may be altered by the pilot through movement of the collective lever or through cyclic control.
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Angle of attack
The angular difference between the code of a blade and a relative airflow
What is coning?
Coning is an upward sweeping angle of the rotor blades as a result of lift and centrifugal force.
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Feathering axis
The straight-line axis between the root of the blade and it’s tip about which the blade can alter its blade angle
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Feathering
The movement of a blade about it’s feathering axis.
Which results in pitch angle changes
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Disc loading
The gross weight of a helicopter divided by the disk area.
Is disc loading constant during a flight?
No. A helicopters disc area is not constant in flight so it follows that disc loading cannot be a constant
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Blade loading
The gross weight of the helicopter divided by the combined area of the helicopter blades
What units are used for disk loading?
Expressed as pounds per square inch (lb/sq inch) or kilograms per metre squared (kg/m^2)
What units are used to express blades loading
Expressed as pounds per square inch (lb/sq inch) or kilograms per metre squared (kg/m^2)
What is flapping?
Movement of a blade in the classical sense relative to the plane of rotation.
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Lead-Lagging
Movement of a blade forward or aft in the plane of rotation
Leading - would be on the leading edge moving forward
Lagging - on the other bit of the rotor blade
Give some examples of rotor systems
Fully articulated rotor
Semi rigid rotor
Rigid rotor
What is a fully articulated rotor
A rotor system allowing blades to flap, feather, and lead-lag, allowed by hinges or bearings
Generally, where can you find a fully articulated rotor?
Give an example
In helicopters with more than 2 blades
Cabri G2 which has three blades
What is a semi rigid rotor?
A rotor system that allows the blade to flap and feather but not lead lag.
In what type of helicopter is a semi rigid rotor system usually found?
It is a common system used in two blade rotors
What does a rigid rotor system allow on a helicopter
The blades to feather only
