PPL AIRCRAFT GENERAL KNOWLEDGE

What does a positive load factor mean in regards to the wings?

The higher the positive load factor, the higher the upward bending force on the wings.

Name the four main parts that combine to create the structure of the wings.

The main spar, the secondary spar, the stringers and the ribs.

What do the ribs of the wing add to the structure?

The ribs add the aerofoil shape to the wings.

What is the stressed skin condition?

the stressed skin condition is known as a monocoque structure - most of the aircraft load / stress is placed on the outer metal skin of the aircraft.

What's an advantage of the stressed skin condition?

The internal construction of the aircraft can be modified as it no longer takes the stresses of the aircraft.

What's the difference between a monocoque structure and a semi-monocoque structure?

A monocoque structure- all of the load on the aircraft is placed on the metal skin whereas a semi-monocoque structure, only some of the stress is put on the aircraft skin and most of it is placed on the internal structure.

What's the equation for aspect ratio?

Aspect ratio = wings span/wing chord

What is aspect ratio?

Aspect ratio is a measure of the wings shape.

What kind of wing section implies safe slow flight?... why is this?

No sharp curvature of the aerofoil... because it is harder for the air flow to separate from the wing.

Where is the ideal separation of airflow on a wing at high angles of attack?

The ideal separation of airflow begins at the rear inboard part of the wings.

What is washout?

A twist in the wing section.

What is a wings angle of incidence?

The angle between the chord line and the fuselage.

What does washing mean regarding the wing and stalling characteristics?

Washing means that the inner wing will reach the stalling angle of attack before the wing tips, which provides lots of warning and characteristics of the stall.

What do stall strips do?

They make airflow separation more likely to happen at the leading edge of the wing.

What is the boundary layer?

A layer of air passing over a surface through which velocity slows from free stream speed to zero.

What types of air layer flows over the wings in the boundary layer at which points?

Smooth laminar flow flows over the leading edge of the wing. This changes to turbulent flow around the trailing edge of the wing.

What's the difference between laminar and turbulent flow during a stall?

Laminar flow is quick to separate from the wing which makes stalls more likely to occur with less notice. Turbulent flow is more sticky and therefore is less likely to seperate from the wing, making the stall less likely and with lots of warning.

What does a vertical wing tip do?

Produces a component of lift in the forward direction.

What are the three main parts used in the construction of the fuselage?

Longerons, cross bars and ventral strakes.

What do ventral strakes do?

Provide stability in the yaw, practically at high angles of attack.

What does wrinkling in the metal skin show?

The aircraft has been over stressed in some way by exceeding the load factor.

How does corrosion show on an aircraft?

Bubbled and flaking paint.

What is delamination? How is it detected?

One of the layers of a laminated material seperates. Detected by tapping it with a metal coin and listening for a thud sound.

What's the elevators main use?

Allows the pilot to alter the angle of attack. It is also the airspeed control.

What does a horn balance do?

Aids the movement of the rudder.

What does mass and balance do?

Prevents flutter.

What are the signs of stall in a side slip?

Lessening the angle of foot-load on the rudder pedal followed by the pedal locking over at full deflection.

What does aileron deflection do?

Reduces adverse yaw.

What is adverse yaw?

The tendency of an airplane to yaw opposite the direction it is rolling.

What do flaps do?

Improve slow speed behaviour and reduce take off and landing distances.

What happens to the load factor limit when flaps are extended?

Load factor limits are reduced when flaps are extended.

What's the difference between slats and slots?

Slots work well at low air speeds but add a lot of drag and cannot be retracted. Slats can be retracted and can move automatically at slow airspeeds.

What effect does damage to the trailing edge have?

Very serious flutter.

What is flutter?

Serious vibrations.

Describe how a oleo undercarriage works when a landing load is placed on it.

Oleo undercarriage consists of a piston and cylinder. The piston is filled with air,and on landing the aircrafts weight pushes the piston into the cylinder, which forces oil through a small opening. This transfer of oil under pressure absorbs the landing load. The air in the cylinder is compressed which takes the load of the aircraft taxiing.

What are the two types of undercarriage?

Spring leaf and oleo

What is shimmy?

High frequency oscillation of the nose wheel in a yawing plane which occurs at certain speeds.

How do brakes work?

Brakes work by producing a frictional force within the brake unit attached to the wheel. The brakes turn the kinetic energy of a moving aircraft into heat.

What 2 types of brakes are there?

Drum brakes and disc brakes.

Describe how disc type brakes work.

A brake disc is attached to each wheel so it rotates with it. Either side are brake linings or pads. When applied, the pads press against the disc and generate friction.

Describe how brakes work in terms of the hydraulic system.

When the pedal is pressed, a piston moves down the master cylinder and creates a pressure in the hydraulic fluid. This pressure is transmitted rough the system via fluid pressure in the brake pipes to the unit.

How much tread should a tyre have?

2mm over a depth of 75% of the tyre.

How does the parking brake work?

The parking break is applied via a valve that traps the fluid in the system, maintaining the pressure on the brake units and holding the breaks on.

What kind of engine is in an aeroplane?

Piston

Describe the simple process of how a piston engine works

The engine is fed with with flammable liquid and mixed with air. It is then ignited and burnt causing it to expand.

Where is the fuel and air ignited in the engine?

The cylinder

Where is the energy created in the engine turned into a rotary movement?

The crankshaft

Whats the four stroke cycle known as?

The Otto cycle

Where does the Otto cycle take place?

The engine cylinder

Describe how the fuel and air mixture is introduced into the cylinder.

The piston moves down the cylinder, creating a suction. The intake valve opens at the top of the cylinder allowing the mixture to come in. As the piston reaches the bottom, the intake valve closes and the piston moves up which compresses the mixture.

Where in the engine is a spark created?

In the ignition system inside the cylinder.

How is a spark created inside the engine?

Magnetos provide a high voltage current which leads to a spark plug, at the end of which jumps a small gap. This jumping of the gap creates a spark which ignites the flammable liquid.

What are the four stages of the Otto cycle?

Induction, compression, expansion, exhaust.

What is compression ratio?

Ratio of the total cylinder volume to clearance volume.

What is compression ratio used for?

Used for calculating the efficiency of the engine.

What does the induction system do?

The induction system takes in air from the atmosphere and adds liquid fuel.

What does mixture control vary?

Mixture control varies the ratio of fuel to air.

How are most engines cooled?

They are mostly air cooled, meaning air flow is directed over the engine to carry away the heat.

How is the engine lubricated?

Using oil

How many power strokes does a four stroke engine provide?

One power stroke in every 4 strokes.

What is engine pressure measured in?

Manifold pressure.

As an aircraft climbs, what happens to the manifold pressure?

As the aircraft climbs, manifold pressure will reduce due to the decreasing air density.

What happens to the engine power output when the aircraft climbs to high altitudes?

The power output decreases.

What is a supercharger? What does it do?

A supercharger is a compressor in the intake manifold driven by a linkage in the crankshaft. The pressure increases the manifold pressure at all altitudes and therefore increases engine power.

What is a turbocharger?

A turbocharger is driven by a turbine which receives rotational energy from the exhaust gas pressure.

What two engine systems does a pilot have the greatest amount of control over?

The fuel system and the induction system.

What does a mismatch of the fuel system and the induction system cause?

Engine failure.

Describe how a gravity feed system works?

Th fuel tank is located some vertical distance above the engine and a fuel line down. Fuel flows by gravity through a filter into the carburettor.

Describe what oil canning is in the engine and why it is used.

Oil canning is where there is a ventilation hole where the fuel flows out, meaning the pressure is restored to normal and fuel can flow by gravity. It is used because departing liquid from the tank leaves an area of flow pressure behind it. This low pressure causes a suction and therefore fuel won't be able to flow out, even if it is full.

Why is the fuel drain done at the very bottom of the fuel tank?

Water is heavier than fuel therefore it tends to collect at the bottom of the tank, underneath the fuel. The drain is done at the bottom so that if there is any water contamination, it can be seen clearly to the pilot.

How many fuel pumps does an aircraft have? What are the differences between them? Why is this designed like this?

An aircraft has two fuel pumps, one is engine driven and one is electric driven. The engine fuel pump is used whenever is engine is running, but the electric one is operated by a switch in the cockpit. This is turned on during take off and landing, any aerobatics or stalls and anything below 1000ft. It is used as a back up just in case of a failure from the other one.

When are you supposed to use the electric fuel pump?

Take off, landing, aerobatics, stalls or PFL's, any manoeuvre at or below 1000ft.

What does fluctuating fuel pressure indicate?

Fluctuating fuel pressure indicates a blockage in the fuel system or fuel drying up ... it indicates that you should divert or land as soon as possible.

What does AVGAS stand for?

Aviation Gasoline

How is AVGAS graded?

AVGAS is graded according to its octane rating : the higher the grade, the higher the octane rating. The octane rating is a measure of its anti-detonation characteristics - the higher the grading, the better anti-detonation characteristics.

What colour is AVGAS?

Blue

Why is it important to use the correct grade of AVGAS?

Using AVGAS with a lower octane rating gives a risk if detonation. Using AVGAS with a higher rating gives a risk of deposits on the spark plugs due to added TEL.

What is added to AVGAS to reduce the detonation characteristics?

TEL.

What does the induction system do?

Brings the fuel and air together.

What effect does the Venturi have on the airflow in the induction system?

The Venturi has the effect of increasing airflow and reducing air pressure.

Describe Bernoulli's Principle

As the speed of a fluid increases, the pressure within the fluid decreases. (The higher the speed of the airflow, the lower the airs pressure will be.)

How does differential pressure aid the fuel flow to the venturi in the engine?

The low pressure draws fuel from the float chamber of the carburetor.

What is the flow of fuel to the venturi in the engine controlled by?

the butterfly valve.

why is an accelerator pump needed?

the accelerator pump is needed because when the throttle goes from idle to full power, there is a lag when the butterfly valve is opened. The accelerator pump injects a shot of fuel into the venturi if the throttle is opened rapidly.

What does the butterfly valve do?

the butterfly valve controls the throttle - moving the throttle forward opens the butterfly and increases the engine power.

whats the ideal mixture of fuel to air? (ratio)

1:12 (fuel:air)

as altitude increases, what happens to the air density?

as altitude increases, the atmosphere becomes less dense.

what are the two forms of carb icing?

impact icing that is caused by flight in icing conditions and ice that forms on the venturi itself.

Describe the two types of carb icing

Impact icing is the icing of the air filter caused by flight in known icing conditions. This occurs when ice forms over the air intake valve and blows the flow of air into the induction system.

Normal more common carb icing is when ice forms on the venturi itself. The decrease in pressure implies a decrease in temperature also. The evaporation of fuel also decreases the temperature. This can cause the moisture in the air to freeze and form as ice on the sides of the venturi and the throttle valve.

As pressure decreases, what happens to temperature?

As pressure decreases, the temperature decreases.

As altitude increases, what happens to pressure?

As altitude increases, pressure decreases.

where does carb ice mostly form?

the sides of the venturi and the throttle valve.

Describe the best conditions for carb icing. (exact)

temperatures between 10 and 30 degrees C and humid

Describe the best conditions for carb icing (general).

Warm temperatures and large amount of water content in the air. (humid)

by how many degrees does carb ice raise the temperature?

30 degrees

what does it indicate when the rpm is higher after using carb heat?

ice was present

what does the ignition system do?

ignites the fuel and air mixture within the cylinder

describe how a spark is created in the ignition system

an electric current is generated by the magneto. The magnet is rotated, which provides a flow of electrical current and a magnetic field. the electric current travels along leads, and at the end of the spark plug the current has to jump a gap, which produces a spark and ignites the fuel air mixture within the cylinder.

what do the magnetos do?

generates the electric current within the ignition system - the magnet rotates providing both an electrical current and a magnetic field.

what is pre-ignition?

early burning of the incoming fuel-air mixture