The Cruise Flashcards
Max time in the air
Endurance
Range
Min fuel per distance
Max S+L speed for a prop
Where the Pr meets the Pa curves
For a jet, max S+L speeds for both TAS and CAS
TAS - increases with altitude
CAS - remains constant with altitude
SAR
Specific air range, relative to the air
= NAM/KG
=TAS/thrust x SFC
As thrust = drag in the cruise it can also be written
=TAS/drag x SFC or = TAS/drag
SGR
Specific ground range
= NGM/kg
FF for a jet and prop are based on
Prop - power
Jet - thrust
Jet FF
=Thrust x SFC
Difference in efficiency characteristics between jet and prop
Jet - compresses the air so it is more efficient at alt where the air is colder
Piston prop - less efficient at alt due to lesser molecules
Turbo prop - jet and prop so it is more efficient at mid alt due to them leveling out
Design RPM
Where they design the engine to be the most efficient
90 - 95% RPM
Vmr for a jet
Best TAS to drag ratio - SR = TAS/drag
Tangent to the drag curve = 1.32 Vmd
Indicated speed
Optimum altitude
At a high alt where the Vmr and the 90-95% RPM meet
SAR for a prop
=TAS/Pr x SFC
Or
=TAS/Pr
Vmr for a prop
Tangent to the Pr curve
At Vmd
Long range cruise (Mmlc)
Mmr x 1.04
Flying 4% faster will reduce range by 1% but we can save time for a small fuel penalty
Cost index
Ratio between revenue and operating costs
0 = most efficient = 1.32vmd
If operating costs are reduced we can fly faster and reach the dest quicker
When to fly at endurance
Rescue duties or holding as we want to stay in the air for the most amount of time
Endurance for a jet
= 1/thrust x SFC or 1/drag x TAS (1/FF)
So min drag = min FF
Higher than the max range height due to flying at vmd which requires less thrust than 1.32 vmd
Endurance for a prop
= 1/Pr x SFC
Increase in alt - Pr moves along the its tangent = endurance will be lower than its range alt §
Effect of wind on endurance
Has no effect
