||Calibrated Airspeed. Calculated as the Indicated Air Speed (IAS) corrected for position and instrument errors.Old analogue air speed indicators present IAS. Newer ASIs display CAS if:
- The airspeed value is output from an Air Data Computer (that corrects for position and configuration errors)
- The ASI is presented on a display that has (by definition) no instrument or parallax errors.
||Equivalent Airspeed (EAS) is airspeed that would be displayed on an airspeed indicator that exhibited no errors. Aerodynamicists use EAS when comparing performance, such as Stalling and Gust Values.At sea level (ISA atmosphere): EAS = CAS = TASAt any altitude: EAS = CAS corrected for compressibility error. And TAS = EAS corrected for density.This density increase (compressibility error) increases with TAS squared. This means that the CAS over indicates as airspeed increases.The relationship between EAS and CAS is shown in graph of stall speed (CAS) versus altitude. For a constant EAS stall speed, the compressibility error increases the CAS (due to decreasing temperature and speed of sound) as altitude increases.Having trouble understanding compressibility? Imaging your hand extended outside a jet’s window. At low speeds, you hand feels the stagnation pressure, which is a measure of IAS and CAS. As the speed passes M0.5, the stagnated air starts to compress and become denser, thereby further increasing the stagnation pressure.
||Airbus: Min flap retraction speed during T/O or Go Around
||Indicated Airspeed. The speed indicated on the (legacy) airspeed indicator. The total error includes position (pitot static tube location) and instrument errors. The pilot may further induce a parallax error when reading this instrument from an angle.
||Long Range Cruise Speed. The speed to maximise the Specific Range to Groundspeed ratio, provides a significant speed increase for 99% of the Max SR
||Airbus: Dynamically calculated speed that approximates the Best Lift/Drag ratio, and thus the best Climb and Drift Down Performance and approximates the min fuel consumption (
||The ratio of TAS to the LOCAL speed of sound:Speed of Sound (kts) = 644* √(1+(Temp (°C))/273.15) or more simply,Speed of Sound (kts) = 39 √ (273 + SAT)°C
||Drag Divergence Mach number . The speed at which drag increases due to Wave Drag
||RN = speed x chord x density / viscosityReynolds Number is the scale factor measuring a surface’s influence on a flow. Boundary layers change from laminar to turbulent at a particular RN, so wind tunnels and scale models must have matching RNs to ensure the model’s performance matches the final product. Old naval movies often provide a good examples of miss-matched RNs.
||Airbus only: Minimum speed to retract slats on takeoff
||True Airspeed. Calculated as the EAS corrected for density.
- TAS = EAS in the ISA atmosphere
- At 40,000’ TAS is approximately equal to twice the EAS.
||Decision speed in the event of an engine failure on takeoff at which the aircraft may successfully continue to takeoff or stop. V1 must be greater than VMCG (see Tarpini)
||Takeoff Safety Speed. The lowest speed satisfying margins above VMCA and VS/VS1G, and that provides the required climb gradients after takeoff following an engine failure.V2 is always greater than VMCA, ensuring that the aircraft is always controllable. But is usually less than the speed to achieve the highest climb gradient after liftoff. With all engines operating, the climb out at V2+10 provides a higher climb gradient than at V2.It is important for the pilot to understand this relationship. This is the reason that during takeoff, if the airspeed has settled slightly above V2 (engine out) or V2+10 (all engine), that the attitude should be maintained to hold this higher speed and ROC.
||Target speed at 50’ on landing
||Design cruise speed. One of the speeds used to define the aircraft strength. May be constrained by other speeds such as VDF.
||Maximum demonstrated flight diving speed. The maximum speed demonstrated during certification. A safety margin is required between VC/MC and VDF/MDF. So to permit a cruise at M0.85, the 747, A350 and A380 all required certification with very high VDF/MDFs.
||V Liftoff. The speed at which the aircraft becomes airborne.The aircraft is termed “Geometrically Limited” if the final rotate attitude is greater than the attitude at which the tail strikes the runway.A Geometrically Limited aircraft requires a higher VR, VLOF and thus V2 than a shorter (non geometrically limited) version of the same aircraft.
||Airbus: Lowest Selectable Speed. Minimum operating speed for the autopilot and auto-trim.Dynamically calculated speed (based upon weight, operating engines and configuration) provides a margin against the stall.
- A380: Minimum value of VMCL2 if two engines inoperative.
||Minimum control speed (a critical engine failed) in the air in a TAKEOFF configuration at which the aircraft can maintain a heading with the rated takeoff thrust, takeoff configuration, gear up and five degrees of bank into the failed engine.Certification requirements only allow for only one engine failure during the takeoff, so VMCA3 will be published for 4 engine aircraft, and VMCA1 for 2 engine aircraft.
||Minimum Control Speed in the air in the APPROACH or LANDING configuration enables (at least): Straight and Level flight then a rolling turn through 20 degrees away from the inoperative engine within 5 seconds.VMCL (all engine) and VMCL-1 (one engine inoperative) will always be publishedVMCL-2 will be published for 4 engine aircraft.
||During a max thrust takeoff , the minimum speed on the ground, at which with the critical engine failed, it is possible to maintain control of the aeroplane with rudder only and remain within 30’ of runway centreline).
||Maximum operating speed/mach number that may not be deliberately exceeded, and is sufficiently below VD/MD, to make it highly improbable that VD/MD will be inadvertently exceeded in operations.
||Rotation speed. During takeoff, the speed at which the aircraft is rotated for takeoff. The selected VR ensures:
- in case of an engine failure, V2 is reached at 35’
- the aircraft lifts off at a speed greater than VMU.
||VSTALL or Stall Speed. The speed at which the aircraft exhibits qualities equated to the stall.Some operating speeds were expressed as functions of VS. For example, Vs influences the minimum takeoff (1.2VS) and approach (1.3Vs) speeds, and thus takeoff and landing performance. With this in mind, there was a clear incentive for the manufacturer to obtain the slowest Vs possible. The problem is that when test pilots flew aircraft to determine this speed (with personal pride in obtaining the lowest speed), their “careful” maneuvers resulted in the load factor being less than 1g at the time of the stall.To correct for this anomaly, the certifying authorities required a new stall speed (called Vs1g), calculated at 1g. All aircraft certified after this change publish only the VS1G speeds (not Vs). Older aircraft certified before this change continue to refer to VS.Since Vs1g is always > Vs, takeoff and landing performance would be reduced for newer aircraft using VS1G with the original takeoff and approach minimum speed margins (1.2 and 1.3). To alleviate this problem, certifying authorities defined a VS/VS1G ratio of 0.94 that could be used to factor the speed margins accordingly.Thus when using VS1G, the minimum:
- takeoff speed is 1.13 VS1G (1.2 x 0.94)
- approach speed is 1.23 VS1G (1.3 x 0.94)
Practically, all aircraft certified since the mid 1990s use VS1G (ie B747-400 and newer and all Airbus A320, derivatives and newer). Older aircraft continue to use VS (747-100,200,300)
||VS1G Stall Speed with a load factor of 1. The speed at which the aircraft exhibits qualities that equate to the stall. VSR (JAR) VS1G (FAR)
||Airbus: The target airspeed speed displayed on the air speed tape. During approach, is equal to the approach speed (Vapp), corrected for wind gusts
||Minimum Unstick Speed. The lowest speed at which the aircraft can safely lift off the ground. For Geometrically Limited aircraft, this speed is obtained with the tail of the aircraft touching the runway. By deduction, it is impossible to lift off below VMU.
||Screen Height Heights used in defining takeoff and landing performance.
- 35’ above the runway for takeoff
- 50’ above the runway for landing