Lecture on Calculating Aircraft Range
Introduction
- Purpose of Lecture: Understanding how to calculate the range for the fuel onboard or the maximum fuel capacity.
- Importance: Range determines how far an aircraft can fly and which airports it can visit.
Definitions
- Specific Range: Distance flown through air per unit of fuel used.
- Specific Ground Range: Distance over ground accounting for wind.
- Units: Nautical miles per kilogram of fuel.
Formulas
- Specific Range (Air Distance): True Air Speed (TAS) / Fuel Flow.
- Specific Ground Range: (TAS ± Wind Component) / Fuel Flow.
- Factors impacting fuel flow include specific fuel consumption and drag/thrust requirements.
Factors Affecting Range
- Mass: Heavier aircraft need more lift, creating more drag, reducing specific range.
- Speed for Max Range (VMR): Occurs at 1.32 VMD for jets.
- Propeller Aircraft: Maximize thrust-to-power ratio, occurs at 1.32 VMP.
- Altitude: Ideal altitudes reduce drag and optimize engine efficiency.
- Jets: High altitudes optimize RPM and fuel consumption.
- Propeller Aircraft: Manufacturer-tested altitudes for efficiency.
- Wind: Affects specific ground range but not specific air range.
- Tailwind increases ground speed; headwind decreases it.
Practical Application
- Step Climb: Adjusting altitude as fuel weight decreases to maintain engine efficiency.
- Optimum altitude increases as weight decreases during flight.
- Commercial Considerations:
- Long Range Cruise (VLRC): Slightly faster speed for a small increase in fuel consumption to save time.
- Econ Speed: Determined by cost index (1-50), balancing speed and fuel consumption.
Summary
- Specific Air Range: TAS divided by fuel flow; influenced by mass, altitude, and engine efficiency.
- Specific Ground Range: Adjusted for wind factors.
- Speeds: MMR for max range; VLRC and Econ speeds for commercial operations.
Understanding these principles helps in planning efficient flight operations and ensuring fuel sufficiency for the journey.