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Climb Performance

Introduction:

  • Climb performance is a measure of excess thrust which generally increases lift to overcome other forces such as weight, and drag
    • This is true for most aircraft although some high performance aircraft can function like rockets for a limited time, utilizing thrust to lift away from the earth vertically, with no lift required
  • Excess power or thrust, terms that are incorrectly used interchangeably, allow for an aircraft to climb

Power vs. Thrust:

  • Power and thrust are not the same, despite their use as such
  • Power is a measure of output from the engine while thrust is the force that actually moves the aircraft
    • In a piston aircraft, power is converted to thrust through the propeller
    • In a jet aircraft, the engine produces thrust directly from the engine
  • When you are moving the throttle controls inside of the aircraft, you're controlling the engine and that is why they are referred to as power levers
  • Therefore the best angle of climb (produces the best climb performance with relation to distance, occurs where the maximum thrust is available
  • The best rate occurs where the maximum power is available)

Climbs:

  • Ultimately, it is because of excess thrust that an aircraft climbs
  • For the purpose of initial climb however, we are concerned with our aircraft's performance in order to get away from the ground
  • We typically refer to best angle and best rate of climb

  • Best Angle-of-Climb:

    • Max excess thrust results in the best angle of climb
    • Occurs at L/Dmax for a jet
    • Occurs below L/Dmax for a prop

  • Best Rate-of-Climb:

    • Best rate of climb, or Vy, maximizes velocity to obtain the greatest gain in altitude over a given period of time
    • Vy is normally used during climb, after all obstacles have been cleared
    • It is the point where the largest power is available
    • Occurs above L/Dmax for a jet
    • Occurs at L/Dmax for a prop

Best Rate vs. Angle of Climb:

  • Certain conditions will call for a specific climb profile (Vy or Vx)
  • Advantages of Vy:
    • More visibility over the cowling
    • Faster time to climb
    • Increased airflow over the engine while at high power
    • More of a buffer from stall speeds
Airplane Flying Handbook, Best angle of climb verses best rate of climb
Airplane Flying Handbook
Best angle of climb verses best rate of climb

Factors Impacting Climb Performance:

  • There are several factors which can impact climb performance:

    • Aircraft Weight

      • One of the most basic considerations with regard to aircraft performance is weight, as it is a principle of flight
      • The higher the weight of an aircraft, the more lift will be required to counteract

    • Temperature:

      • Ambient air temperatures impacts your aircraft performance based on their physical properties
      • Engines don't like to run hot and if they do then reduced throttle settings may be required
      • Temperature is also a leading factor in determining the effect of air density on climb performance

    • Air Density:

      • Air density, and more specifically, density altitude, is the altitude which the aircraft "thinks" it is at
      • Performance does not depend on the physical altitude, but rather the density altitude, and the higher the temperature, the higher that altitude

    • Winds:

      • Headwinds increase performance by allowing wind flow over the wings without any forward motion of the aircraft
      • Tailwinds do the opposite

    • Aircraft Condition:

      • Smooth, parasite free wings produce the best lift
      • Anything to interrupt the smooth flow of air or increase drag will require additional forward movement, or thrust, to overcome

Conclusion:

  • Climb performance is governed by FAR Part 23, depending on aircraft weight

References: