Cruise Performance

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 an 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 specific actions, such as applying maneuvering speed to cruise.

Cruise Performance

Cruise Performance

As seen in Figure 5-6, at some given airspeed, total drag is at its minimum amount.
In determining the maximum range of aircraft, minimizing drag minimizes the thrust to overcome it.
The minimum power and maximum endurance occur at different points.

Cruise Performance

The best endurance airspeed is an airspeed that allows an aircraft to remain flying for the longest time.
As weight increases, the airspeed required to maintain max endurance increases; however, the optimal angle of attack remains constant.
As weight decreases, airspeed required to maintain max endurance decreases; however, the optimal angle of attack remains constant.

Cruise Performance

Wind Impacts on Cruise Flight:
- Wind direction and intensity at various cruise altitudes are essential considerations 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.

Cruise Performance

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

Cruise Performance

Cruise Performance
Cruise performance data enables pilots to plan long-distance, cross-country flights while simultaneously allowing pilots to determine fuel reserves.
Cruise Performance Chart Example:
- Start by choosing the chart that meets the prerequisites (i.e., weight, temperature).
- Choose the cruise altitude flown and move right to the appropriate temperature at altitude.
- The RPM dictates the desired performance.
- Fuel burn understandably increases with RPM setting:
  - Using 6,000 feet at standard temperature, 2100 RPM is 5.4 Gallons Per Hour (GPH) at 92 knots.
  - Increasing by 100 RPM increases fuel burn to 5.7 GPH (+6%) at 98 knots (+7%).
- As you increase RPM, the aircraft (at least in our example) will experience diminishing returns where fuel burn increases are larger, and speed benefits are less.
Cruise Performance

Cruise Performance

Cruise Performance