Engine Flashcards
What is specific fuel consumption?
Quantity/weight (lb) of fuel burn per hour / thrust of an engine
Define bypass ratio?
Ratio of the cold air mass flow passed through the bypass duct to the air mass flow passed through the high pressure system.
What is a critical Engine?
Engine that would most adversely the handling performance if it fails.
Depend o the length of the thrust arm (distance from the CG to the thrust line of the operating
engine).
Clockwise rotating propellers when view from the rear, the thrust line is displaced to the right of the engine centre line. This is because the down-going blade generates more thrust than the up-going blade.
If the left engine fails, the thrust of the right engine acts through a longer thrust arm and will give a
bigger yawing moment, hence a higher Vmc would be necessary to maintain directional control.
On a modern jet engine, which flow produces the most thrust?
The flow coming from the High Bypass Ratio.
All the air entering into the engine is given to an initial low compression, and a percentage is ducted to bypass the engine core, the remainder of the air is delivered to the combustion chamber.
The bypass air is then either mixed with the hot airflow from the engine core in the jet pipe exhaust to generate a resulting forward force.
High Bypass ratio is 5:1, they have a better SFC, better
propulsive efficiency and produces less noise. They are very efficient and are designed to operate
at high altitude at high RPM.
What is a turbo charger?
Centrifugal compressor powered by a high speed turbine that is driven by an engine’s exhaust gases.
This increase the mass of air entering the engine (forced induction), resulting in greater performance.
What is a supercharger?
Supercharger increases the air delivered to the engine cylinder above it’s normal capacity by compressing the intake air requiring more fuel to be delivered to the carburettor to maintain the correct mixture ratio.
It is connected directly to an engine. A supercharger uses mechanical energy from the engine.
A turbocharger is more efficient because it’s converts the waste heat of the exhaust gas into horse power used to drive the compressor.
Why do we takeoff with mixture full rich?
This help the engine cooling. The excess fuel helps to cool the engine.
In low density altitude this enables the aircraft to maintain the correct stoichiometric coefficient of 15:1.
Describe how a jet engine works?
Consists of a duct with a divergent entry and convergent exit.
Air is forced into the engine intake, where it loses velocity and therefore its pressure energy increases.
As it passes through the divergent duct. The total of the energy is then increased by the combustion of fuel and the expanding gases accelerate through the outlet converging duct, producing a propulsive efficiency.
What is the difference between a 2-stroke and 4-stroke engine?
Four stroke engine has one power stroke for every two crankshaft revolution
Two stroke engine has one power stroke for each crankshaft revolution.
Four stroke engine is heavier, complicated engine design, more cost, more output, engine runs cooler, water cooled, less fuel consumption, complicated
lubricating system, more thermal efficiency and less wear.
Explain Carburettor Icing?
Occurs in the engine induction system and in the carburettor of piston engines.
Particularly in the venture and around the throttle valve, where acceleration of the air can produce
a temperature fall by as much as 25°C.
We can detect carb icing with engine rough running,
reduction in RPM or MAP on constant speed propeller. Carb icing is present when the temperature
is between -10 to +25°C with relative humidty.
What is FADEC?
Full Authority Digital Engine Control
Automatically controls engine functions, start procedures, engine monitoring, fuel flow, ignition system, and power levels required.
Explain Hi Bypass Engine?
All the air entering into the engine is given to an initial low compression, and a percentage is ducted to bypass the engine core, the remainder of the air is delivered to the combustion chamber.
The bypass air is then either mixed with the hot airflow from the engine core in the jet pipe exhaust to generate a resulting forward force.
High Bypass ratio is 5:1, they have a better SFC, better
propulsive efficiency and produces less noise. They are very efficient and are designed to operate
at high altitude at high RPM.
Does a jet engine have a critical engine?
There is NO critical engine on a jet engine aircraft.
P-factor is negligible due to the higher number
of blades.
However, aerodynamically, crosswind effect can result as a critical engine: crosswind coming from the failed engine.
What is a Wet Start?
- Fuel and no ignitiion
- Fuel flow but no EGT increase
What is a Dry Start?
- Ignition but no fuel
- No fuel flow or EGT increase
