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Wind Triangles Revisited

Airspeed is one of the first things we learn about in fixed-wing primary training, It’s an all-important tool for managing an airplane’s performance and helps us determine when we can do certain things, like deploying flaps or lowering landing gear. Too, pilots typically are taught to “aim” for a certain airspeed when performing various maneuvers and at various stages of normal flight. But there are different kinds of airspeed. For example, what we read directly off the instrument panel is subject to error and interpretation, and often must be corrected before it can be used for even basic tasks like navigation. Depending on the aircraft and the conditions, the airspeed instrumentation we use can be merely advisory, or it can be wildly inaccurate for our immediate needs.

Gemini Sparkle

Key Takeaways:

  • Airspeed is a fundamental concept in aviation, existing in multiple forms (Indicated, Calibrated, Equivalent, and True Airspeed), each requiring corrections for accurate flight management.
  • True Airspeed (TAS) is the most significant for navigation and calculating groundspeed, representing the aircraft's actual speed through the undisturbed air.
  • Strong crosswinds introduce "Effective True Airspeed" (ETAS), where the required crab angle to maintain course reduces the effective speed in the desired direction, becoming more significant with increased drift angles.
  • While traditional E-6B flight computers implicitly account for ETAS in wind calculations, CR-style computers may require an explicit step to determine ETAS before calculating groundspeed, highlighting its potential impact on performance.
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Airspeed is one of the first things we learn about in fixed-wing primary training, It’s an all-important tool for managing an airplane’s performance and helps us determine when we can do certain things, like deploying flaps or lowering landing gear. Too, pilots typically are taught to “aim” for a certain airspeed when performing various maneuvers and at various stages of normal flight. But there are different kinds of airspeed. For example, what we read directly off the instrument panel is subject to error and interpretation, and often must be corrected before it can be used for even basic tasks like navigation. Depending on the aircraft and the conditions, the airspeed instrumentation we use can be merely advisory, or it can be wildly inaccurate for our immediate needs.

Thankfully, these inaccuracies are well understood. Similarly, the effect of wind on groundspeed—which can translate into a headwind or a tailwind, depending on the wind and our direction of flight—is relatively easy to grasp. But something that may not be as well understood is the effect a crosswind can have on airspeed. What? How can the wind affect airspeed while in cruise? To find out, let’s start with a quick refresher on airspeed.

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