Speed, Lift, Weight And Drag Flashcards
CAS
Instrument and pressure error
Relationship of increasing mass on VMD speed
Increases by half of the % increase
E.g 10% increase in mass = 5% increase in vmd speed
Effect of altitude and speed on thrust
Reduces due to the momentum drag and the reduction in air molecules with altitude
Intake Momentum drag
Due to the air being pushed out the engine being constant but the forward velocity of the air is being increased
RAM effect
Due to the air being pre compressed at high speeds. So when the air enters the engine, it reduces the workload on the turbines.
It increases thrust at high speeds
Flat rating
Limiting thrust by the amount of RPM
Below ISA +15 you are limited by flat rating
Above ISA + 15
Limited on temperature rather than flat rating
Standard time on TOGA
5 mins for all engines
10 mins for an engine failure
MCT
Max continuous thrust
Used in the cruise
Power =
F x speed (TAS)
Power available
Thrust x TAS
Power required
Drag x TAS
Power available with a jet
PA = Thrust x TAS
As thrust is constant, pa has a linear increase
Power available for a prop
Pa = thrust x TAS
However, as thrust decreases with increasing TAS, the pa forms a curve
Pr curve
Similar to the drag curve
Vmp is at the trough and vmd is on the tangent
What happens to the Pr curve with altitude
Tracks along its own tangent due to
D = pr/TAS so as both of them increase with altitude the ratio stays the same
Fuel flow
Mass of fuel consumed in a given time
M/time
Units for FF
Kg/hr for big a/c
Lbs/hr for small a/c
FF formulas
M/time
Thrust x Efficiency (SFC)
Low SFC = more efficient
SFC is always lower than 1
SFC formula for a prop
As thrust comes from the prop,
SFC = FF/Power
Reversed command
A reduction in speed requires an increase in thrust
