Lecture Notes on Endurance in Aviation

Introduction

• Importance of Endurance: Ability to stay airborne, crucial during busy air traffic or adverse weather.
• Endurance vs. Range: Both measure efficiency, but endurance is time-based while range is distance-based.

Key Concepts

• Endurance: Time an aircraft can remain in the air.
  • Inversely Proportional to fuel flow.
  • Equation: Endurance ∝ 1 / (Specific Fuel Consumption × Drag)
  • Fuel Flow: Product of specific fuel consumption and thrust required (drag).

Factors Affecting Endurance

• Speed for Maximum Endurance:
  • Jet Aircraft: Minimum drag speed (Vmd).
  • Propeller Aircraft: Power required is minimum at Vmp.
• Mass:
  • Heavier aircraft require more lift, increasing induced drag and power needed.
  • Estimation Trick: (New Mass/Old Mass) = (New Fuel Flow/Old Fuel Flow)

Practical Example

• Scenario: Aircraft holding at 3,000 feet with initial mass of 50,000 kg and fuel flow of 2400 kg/hr.
  • Estimation: New fuel flow when mass decreases due to burn in holding pattern.

Altitude Influence

• Jet Aircraft:
  • Better endurance at high altitudes due to lower specific fuel consumption and drag.
  • Engines operate efficiently at 90-95% max RPM.
• Propeller Aircraft:
  • Better endurance at lower altitudes; less power required at lower speeds (Vmp).

Wind Influence

• Wind: Does not affect endurance as it is concerned with time aloft, not ground speed.

Summary

• Range vs. Endurance: Range is distance, endurance is time.
• Key Equations:
  • Range: True speed/ground speed over (Specific Fuel Consumption × Drag)
  • Endurance: 1 / (Specific Fuel Consumption × Drag)
• Optimal Conditions:
  • Jets: Fly at high altitudes and Vmd for best endurance.
  • Propellers: Fly at Vmp at lower altitudes for best endurance.