M17.2 Construction Flashcards by Meg Bazeley

What are the 3 categories of propeller constructions?

. Wooden
. Composite
. Metal propellers

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What two types of metal are used for metal propellor?

. Aluminium alloy
. Steel

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What types of wood are used on wooden prop?

. Birch
. Mahogany
. Cherry
. ash
. beech
. Oak
. Walnut

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What is the most common type of wood used?

Birch

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At least 5 laters of wood are layer down and then glued together, what does this from?

A blank that is roughly shaped

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How long is a blank left to sit?

7 days then formed a white

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What is applied after white?

A cotton fabric sheathing applied to the outer 12-15 inches of the tip to reinforce the strength of thin section

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How can you protect the fabric from deterioration of weather?

Doping it

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What is tipping?

A metal tip strip is rebated into the leading edge of the propeller to prevent damage from small stones

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What 5 metals are used for tipping?

. Brass
. Stainless steel
. Monel
. Terndplate

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How is the tipping secured to the blade?

Using countersink screws at the thick blade section

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What is the last stage of wooden propeller construction?

It is balanced and then a finishing coat is added

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What are the advatanges of composite propellers?

Lightweight and stronger than metal props

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What de icing do composite props use?

Have an external boot but some do have internal heating elements

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What is the basic composition of a composite prop?

. The spar is made from titanium, aluminium alloy of stainless steel. It runs through tye centre of the blade
. It then has low density foam or honeycomb in front and behind as it’s filling material.
. With fibreglass, Kevlar or carbon fibre shell

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How do composites without a metal spar work?

There are two carbon fibre components in the blade which form the spar, it’s then hollow centre is filled with polyurethane foam

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What is the most common propeller used?

Aluminium alloy propeller

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Once the aluminium prop has been grounded to final size what happens next?

Pre balanced by hand and anodising is taken place

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Where are steel props normally found?

Older aircraft

What is the construction of steel props?

Hollow steel propellers are made from folded sheet welded over a ribbed structure which is foam filled in the outer section of the blade

What does the propeller blade station denote?

The location of various points on a prop blade.
Numbered 1 onwards from root to tip

What does the prop master reference station denote?

A distance measured from the centre of rotation where all measurements are taken.
. 75% from the centre of rotation in a fixed pitch propeller.
. 50-75% for variable pitch prop

What does propeller blade angle denote?

The angle between the blade chord line and the plane of rotation

What does propeller face denote?

The flat thrust producing side of a propeller blade

What does the propeller blade root/shank denote?

The thickened portion of the blade nearest to the hub

What does propeller blade butt denote?

The base of the propeller blade where the root ends

What does propeller back denote?

The curved side of the propeller blade facing the direction of flight

What does propeller hub denote?

Central portion of a propeller which carries tye blades

What does the dome assembly denote?

Encases the pitch change mechanism

What type of pitch propeller is more favourable?

Fixed pitch propellers, decrease maintenance, less cost

Can you change the angle on a fixed pitch propeller?

No, it is only set to one specific angle

What is the optimum angle of attack for fixed pitch propellers?

4 degrees, which maximum RPM is available

What are ground- adjustable propellers designed for?

So blade angle can be adjusted on the ground to give the desired performance characteristics for various conditions

What type of aircraft are ground- adjustable propellers found on?

Older aircraft of low - moderate performance

What is the angle range for ground- adjustable propellers?

7-15 degrees

What must you use to check the blade angle?

A propeller protractor at the master reference station

What is the allowable blade angle differences on ground- adjustment propellers?

No more than 0.1 degrees

What are the two different types of controllable - pitch propellers?

. Controllable pitch propellers . Variable pitch propeller

What does the controllable pitch propellers allow?

The pilot to change the pitch of the blades in flight

How many different pitch stages do controllable pitch propellers have?

2 - high and low pitch Whereas the variable can adjust to any pitch

What two controls does a controllable pitch propeller have?

. Throttle control - which controls the power output of engine, register on the manifold pressure gauge . Propeller control - regulates the engine RPM and in turn the propeller RPM.

What is a constant speeding propeller designed to do?

To automatically change it blade pitch to allow it to maintain a constant RPM

What is the constant speeding propeller governed by?

. A constant speed unit or propeller governor

What principle does the constant speed unit work on?

. Centrifugal force Incorporates a speeder spring and a set of fly weights

What are the advantages of a constant speed propellor?

. Maximum power in a narrow speed band . Allows efficient use . Allows prop and engine to be set at an optimum

Why do we have mounted spinner?

For better aerodynamics and as a mechanical protection for the hub and aesthetic reasons

What happens if there are cracks in the blade recesses if spinners.

Repairs are limited, must be replaced. (Drill stoping a crack is allowed)