Cruise Performance

Introduction:

Cruise is the predominant phase of flight by time, making cruise performance one of the most influential factors on the duration and quality of a flight
With appreciation of the drag curve, pilots configure and fly the aircraft to achieve maximum range or maximum endurance
Pilots must also consider how various factors impact cruise performance to plan for expected performance
Expected conditions necessitate certain actions, such as applying maneuvering speed to cruise

As seen in Figure 5-6, at some given airspeed, total drag is at its minimum amount
In figuring the maximum range of aircraft, the thrust required to overcome drag is at a minimum if drag is at a minimum
The minimum power and maximum endurance occur at a different point

Best range airspeed is an airspeed that should allow an aircraft to fly the farthest distance

Best endurance airspeed is an airspeed that allows for an aircraft to remain flying for the most amount of time
As seen in Figure 5-6, at some given airspeed, total drag is at its minimum amount
In figuring the maximum range of aircraft, the thrust required to overcome drag is at a minimum if drag is at a minimum
The minimum power and maximum endurance occur at a different point
As weight increases, airspeed required to maintain max endurance increases, however, the optimal angle of attack remains constant
As weight decreaes, airspeed required to maintain max endurance decreases, however, the optimal angle of attack remains constant

Wind Impacts on Cruise Flight:
- Wind direction and intensity at various cruise altitudes are an important consideration to determine cruise performance
- Winds aloft are the most direct means to plan for winds at cruise altitudes along the route of flight
- Headwinds increase flight time and therefore fuel burn, reducing range, while tailwinds do just the opposite
Icing Impacts on Cruise Flight:
- When encountering icing, additional power may be necessary to overcome the increase in drag
- Airspeed may bleed off quickly (one example saw 50 knots in under 1 minute)
- See also: Stall and Climb Performance

Maneuvering speed, or Va, is an airspeed below which full deflection of the control surfaces should not cause damage
If approaching bumpy weather, slowing to Va before penetrating turbulence should be considered
Rule of thumb: for every 2% reduction in weight, Va reduces by 1%