17.1 Fundamentals Flashcards
what is the design and function of a propellor?
it takes a large quantity of air and pushes it backwards slowly rather than a small amount quickly like that of a turbojet
what speeds are propellors most efficient at?
lower speeds
what was the initial design of propellors?
originally they were designed as small aerofoils wish merely pushed air back
what improvements have been made to modern propellors?
they are now made of aluminium with thinner aerofoil sections and greater strength
what did the introduction of gas turbine engines allow for?
efficient operation at medium altitudes and speed
what is Propeller?
A device, consisting of a rotating hub with two or more radiating blades; used to propel an aircraft.
what is the Hub?
The central portion of a propeller which carries the blades.
what is the blade?
Aerofoil section that is attached to the hub.
what is the blade butt?
The base of the propeller blade where the root ends.
what is the Blade root/shank?
The thickened portion of the blade nearest to the hub.
what is the Blade station?
A distance measured from the centre of rotation, normally measured in inches or centimetres.
what is a master reference station?
A distance is measured from the centre of rotation where all measurements are taken from.
where is a master reference system usually?
Normally 75% from the centre of rotation on a fixed-pitch propeller and can be 50–75% on a variable pitch propeller.
what is the blade face?
The flat thrust producing side of a propeller blade.
what is the blade back?
The curved side of the propeller blade facing the direction of flight.
what is the blade chord line?
A line through the blade profile at the points between the face and back surfaces.
what is the plane of rotation?
The plane in which the propeller rotates. This is 90° to the engine centreline.
what is blade angle?
The angle between the blade chord line and the plane of rotation.
what is pitch?
Distance advanced in one complete revolution.
what is the function of the pitch change mechanism?
a device to alter blade angle
what does fine pitch mean?
Vertical blade angles. Also referred to as “Low pitch”.
what does coarse pitch mean?
Horizontal blade angles. Also referred to as “High pitch”.
what does reverse pitch mean?
Turning the propeller blades to a negative angle to produce braking or reversing thrust.
what is the dome assembly?
Encases the pitch change mechanism.