04 Thrust And Power Flashcards
What is the definition of Intake Momentum Drag?
Intake Momentum Drag is caused when the speed of the air entering the engine increases.
But the exit speed of the air remains constant.
This means that the amount the engine increases the air speed by is decreased.
Thus thrust is decreased, which is known as Intake Momentum Drag
What is the definition of the Ram Effect?
As the air speed increases, compressibility causes the the density of the air in the intake to increase and so the mass flow increases.
Ram effect is the increased thrust due to the increase of the mass flow.
What is the overall effect on thrust of Intake Momentum Drag and the Ram Effect?
They cancel each other out and so it can be assumed that thrust remains constant as air speed increases
What assumption can be made about the thrust during the take-off run?
It decreases slightly as speed increases
How does Available Thrust vary at temperatures equal to and below ISA standard 15 degrees and why?
Available thrust does not change as the engine is RPM limited
How does Available Thrust vary at temperatures above ISA standard 15 degrees and why?
As temperature increases the Available Thrust decreases due to the decreased air density and so the decreased mass flow
What does Flat Rating and engine mean?
Limiting the available thrust from an engine by limiting the max RPM.
Becomes a limiting factor below ISA standard 15 degrees.
What are the two main engine thrust settings?
- TOGA (Take-off Go Around)
- MCA (Maximum Continuous Thrust)
- Aka CON
What are the time limits normally imposed on the TOGA thrust setting for all engine and one engine?
- 5 mins for all engines
- 10 mins for one engine
What is the equation for Power?
Power = Force x Speed
What is the equation for Power Available?
Power Available = Thrust x TAS
What is the equation for Power Required?
Power Required = Drag x TAS
What is the definition of Fuel Flow?
Fuel Flow is the rate at which a mass of fuel is used with time (normally kg or lbs per hour)
What is the definition of the Specific Fuel Consumption?
The Specific Fuel Consumption (SFC) is a measure of an engines efficiency.
A lower SFC, a more efficient engine.
Two engines with the same SFC will only have the same Fuel Flow if they are producing the same amount of thrust.
What is the formula for the Specific Fuel Consumption (SFC) for:
- Jet
- Prop
- Jet SFC = Fuel Flow / Unit of Thrust
- Prop SFC = Fuel Flow / Unit of Power
