17.2 Flashcards
What is the most common wood used to make a wooden propeller?
Birch
A minimum of 5 laminates are bonded with what?
Aeroglue
A minimum of how many laminates is bonded with aero glue?
5
How long are wooden propellers left for and why in construction?
Left for one week for even moisture distribution
What is it known as when a wooden propeller has been left for a week for even moisture distribution?
Propeller white
What is added to wooden propellers for added strength?
Fabric sheathing
How is metal tipping secured at leading edge of wooden propeller?
Tipping secured using countersink screws
Tips secured with copper rivets
What can tipping be made from?
Brass
Stainless steel
Monel (nickel and copper alloy)
Terneplate (steel coated with a lead/tin alloy)
Why are three 3/16” holes drilled in wooden propellers?
Draining
Allow wood to breathe
Final stages of wooden propeller construction?
Balanced and varnished
Modern propellers are painted with what for mechanical and ultraviolet protection?
Polyurethane
What is metal spar made from?
Titanium
Aluminium
Stainless steel
What is a composite propeller filled with?
Low density foam or honeycomb
On a composite propeller what is the shell made from?
Fibreglass
Kevlar
Carbon fibre
Does composite propeller always have a metal spar?
No
Some just filled with complete foam or honeycomb
What is an aluminium blade made from?
Made from extruded formers of aluminium alloy
Shaped from a master blade
Most common surface finish process for aluminium propellers?
Anodising
Stops corrosion
Two grinding methods for aluminium propellors?
Manual grinding by a master blade as a template
Modern grinding done by CNC machine as more accurate
Where are steel propellers found?
Old propeller aircraft
Advantage of hollow steel propeller?
Saves weight
Propeller blade station
Numbered from 1 onwards or the number of inches or centimetres from the root to its tip
Propeller master reference station?
Measured from the centre of rotation
Normally 75% in a fixed pitch propeller
Can be 50%-75% on variable pitch propeller
Propeller blade angle?
The angle between the blade chord line and the plane of rotation
Propeller face?
The flat thrust producing side of a propeller blade
Propeller blade root/shank?
The thickened portion of the blade nearest to the hub
Propeller blade butt?
The base of the propeller blade where the root ends
Propeller back?
The curved side of the propeller blade facing the direction of flight.
Propeller hub?
Central portion of a propeller which carries the blades.
Dome assembly?
Encases the pitch change mechanism
Fixed pitch propellers are used up to what speeds?
250km/h
Fixed propellers are favoured why?
Easier to produce
Cheaper to maintain
What conditions are fixed pitch propellers best suited for?
Best suited for cruising conditions
Optimum angle of attack for fixed pitch propellers?
4 degrees
What are disadvantages of a fixed pitch propeller?
-Maximum propeller efficiency only achieved in one phase of flight (take off or cruise)
-Power available at take off is reduced because of lower RPM
-The efficiency of propeller widely fluctuates
-Pilot intensive (Must constantly be checking engine output power to RPM keeping within acceptable ranges)
Why are blade angles adjusted on ground?
Change for desired conditions such as needing a short take off
Variable blade angles change between what degrees?
7 and 15 degrees
New blade angle is checked with what?
A propeller protractor at the master reference station
There should be no more than what degrees variation between individual blades and desired blade angle?
0.1 degrees
Two propeller aircraft controls?
-Throttle control, regulates power output of engine, registered on the manifold pressure gauge
-Propeller control which is regulates engine RPM and therefore propeller RPM
Constant speeding propellers are designed to do what?
Automatically change its blade pitch to allow it to maintain a constant RPM
-Accomplished by means of constant speed unit or governor
How does constant speed unit work?
Work on principle of centrifugal force
Uses a speeder ring and a set of fly weights
Can be electronically governed
Advantages of constant speeding propeller?
-Maximum power in a narrow speed band
-allows efficient use
-Blade angle reduced torque required reduced- increase in RPM/ airspeed
-Allowing propeller and engine to be set to optimum
A spinner does what for the engine?
Gives better aerodynamics
Protects the hub
Aesthetic reasons
Is the dynamic loads on spinner very high or low?
High
Inspected regularly
A spinner has no wobble on rotation, how will this help at higher RPM?
Magnify stresses
What is the critical engine?
The engine that causes the smallest yaw moment
