11 Endurance Flashcards
What is Endurance?
The maximum time an aeroplane can remain airborne with the avalaible fuel irrespective of distance covered.
What is flying for maximum endurance?
Flying for minimum fuel flow.
Endurance ~ 1 / Fuel Flow
Where is Endurance for a jet?
Endurance ~ 1 / (SFC x Drag)
Therefore for endurance to be greatest, drag must be minimised. So to achieve maximum endurance, a jet aeroplane must fly at Vmd.
Theoretically optimum altitude for endurnace is actually higher than the optimum altitude for range.
Endurance for a propeller driven AC?
Achieves maximum endurnace when the fuel flow is minimum. The fuel flow is minimum when the power required is minimum.
Endurance ~ 1/Fuel Flow
Fuel Flow = SFC x Power Required
Endurance ~ 1 / (SFC x Power Required)
Speed for maximum endurance for a prop AC?
Minimum power required speed, Vmp. 0.76Vmd.
Optimum Alitude for range and endurance?
At increased altitude, drag curve moves up and left. Therefore Vmp increases.
Effect of Mass on endurance?
A lighter AC has less drag, therefore less thrust is required. Less thrust means less fuel flow.
A lighter AC has a greater endurnace then a heavier AC.
Fuel Flow and AC mass in the hold?
Jets hold at Vmd
New fuel flow / Old fuel flow = New Mass / Old Mass.
Effect of wind of endurance?
Wind doesn’t affect endurnacve because the horizontal position of the AC is irrelevant for endurnace.
To minimise fuel costs an aeroplane flies at:
- Best range speed (minimum fuel for distance covered)
- Holds at the best endurance speed (minimum fuel used with time). Max range speed is faster than max endurance speed.
The optimum speeds and altitudes for range and endurance for jet a prop AC:
As a flight progresses the optimum speeds for range and endurance…
reduce
As a flight progresses the optimum altitude for a jet…………… . A step climb is the operational method for staying close to optimum altitude whilst complying with the ATC requirement to fly flight levels.
increases.
Econ settings in a jet?
In a jet LRC and ECON settings are faster speeds than 1.32 V_MD.
Fuel flow at Vmd?
At V_MD fuel flow is proportional to aircraft mass. At speeds faster than V_MD, fuel flow is less affected by a change in aircraft mass.
