Vfs Speed Aviation

[Jarvarious Hunsaker]

Inaviation, V-speeds are standard terms used to define airspeeds important or useful to the operation of all aircraft.[1] These speeds are derived from data obtained by aircraft designers and manufacturers during flight testing for aircraft type-certification. Using them is considered a best practice to maximize aviation safety, aircraft performance, or both.[2]

The actual speeds represented by these designators are specific to a particular model of aircraft. They are expressed by the aircraft's indicated airspeed (and not by, for example, the ground speed), so that pilots may use them directly, without having to apply correction factors, as aircraft instruments also show indicated airspeed.

In general aviation aircraft, the most commonly used and most safety-critical airspeeds are displayed as color-coded arcs and lines located on the face of an aircraft's airspeed indicator. The lower ends of the white arc and the green arc are the stalling speed with wing flaps in landing configuration, and stalling speed with wing flaps retracted, respectively. These are the stalling speeds for the aircraft at its maximum weight.[3][4] The yellow band is the range in which the aircraft may be operated in smooth air, and then only with caution to avoid abrupt control movement. The red line is the VNE, the never-exceed speed.

The most common V-speeds are often defined by a particular government's aviation regulations. In the United States, these are defined in title 14 of the United States Code of Federal Regulations, known as the Federal Aviation Regulations (FARs).[7] In Canada, the regulatory body, Transport Canada, defines 26 commonly used V-speeds in their Aeronautical Information Manual.[8] V-speed definitions in FAR 23, 25 and equivalent are for designing and certification of airplanes, not for their operational use. The descriptions below are for use by pilots.

These V-speeds are defined by regulations. They are typically defined with constraints such as weight, configuration, or phases of flight. Some of these constraints have been omitted to simplify the description.

In discussions of the takeoff performance of military aircraft, the term Vref stands for refusal speed. Refusal speed is the maximum speed during takeoff from which the air vehicle can stop within the available remaining runway length for a specified altitude, weight, and configuration.[19]Incorrectly, or as an abbreviation, some documentation refers to Vref and/or Vrot speeds as "Vr."[29]

V1 is the critical engine failure recognition speed or takeoff decision speed. It is the speed above which the takeoff will continue even if an engine fails or another problem occurs, such as a blown tire.[9] The speed will vary among aircraft types and varies according to factors such as aircraft weight, runway length, wing flap setting, engine thrust used and runway surface contamination; thus, it must be determined by the pilot before takeoff. Aborting a takeoff after V1 is strongly discouraged because the aircraft may not be able to stop before the end of the runway, thus suffering a runway overrun.[50]

Vy and Vx make sense to me. They are used for fastest height gain at a given time and biggest angle of climb. But what is the purpose of that speed (it's from DA20 POH)? It's only 3 kts faster than Vx.

In the absence of POH guidance normally Vx is the target airspeed for a 50ft obstacle. However, when the 50ft speed is included in the POH, as it is in modern aircraft, it is based upon empirical data from flight tests. Essentially, the test pilot flies the plane searching for the best technique to offer the best performance. When that is determined, the procedure and speeds are worked into the POH, usually in procedures and tables of speeds, but sometimes in graphs.

Also, published speeds may have a buffer in them to avoid significant performance loss, if for example a maneuver puts one close to a point where sink might be higher if the pilot's airspeed control is slightly off.

So to summarize, different manufacturers have different methods of determining what their recommended procedures and speeds are. Sometimes there are buffers built in for speeds, and sometimes not. Sometimes a skilled pilot can outperform the recommended POH procedure. That doesn't happen often, because POH figures are competitive and are used to sell planes.

Side story: I was evaluating a PC-12 and C-208 as platforms for scientific instruments, and flew each one with a sales man. The PC-12 came back with a factory test pilot to fly with me. I wanted to fly at speeds between 61 and 64k, in the Caravan, at 500 ft AGL, and 67 to 70k in the PC-12. The Cessna Caravan would do it comfortably all day long. Neither the salesman nor the factory test pilot was willing to fly (or let me fly) the PC-12 at those speeds at that altitude. I did with the PC-12 at 3500 ft AGL, and it simply didn't have the stability that the Caravan did at the lower envelope.

I am inclined to believe that is a misprint from either an earlier POH or a non-OEM approved flight manual. Here's an excerpt from the current OEM-approved DA-20 POH for the normal operating procedures.

Note here, the figure listed for the short field takeoff climb speed of 58KIAS refers to a best rate of climb using takeoff flaps whereas Vx of 60KIAS in the manual is the best rate of climb in a cruise configuration (flaps up).

The screenshot you posted seems to indicate a climb speed for a standard takeoff as oppos d to using a short field procedure. However the OEM manual doesn't seem to list anything like that for takeoff roll and obstacle clearing distances.

As always, this data presented here is for informational purposes only; always use the manufacturer approved flight manual, supplemental data and approved cockpit placards specific to the airplane you are operating.

In small GA airplanes, I teach my students to rotate around $1.3V_S0$ which really means to slowly bring the nose up to the takeoff pitch attitude. Under no circumstances do I want them to yank the airplane off the ground. If done correctly, the airplane will naturally lift off when it is ready to.

You need to add some time for the rotation to gather enough angle of attack change so the aircraft can lift off. While the pilot pulls to lower the tail and rotates around the main gear, the aircraft continues to accelerate. Also, the 1.3 factor is only required to be reached once the aircraft climbs through 35 ft (or 50 ft, depending on the certification). What happens is that the pilot starts pulling right around stall speed, the aircraft starts to produce more downforce at the tail until the nose gear lifts off, then rotates until the angle of attack has grown to maybe 10 so the wings create enough lift for take-off. At this time, the aircraft will have accelerated to around 1.15 times stall speed and starts to climb, which requires still more pitch change. Now drag will increase by the amount of induced drag produced by the added lift so the rate of acceleration slows down. Still, until the 35 ft are reached the aircraft will accelerate further to 1.3 times stall speed at this point.

That is how the take-off distance is flown for certification to achieve the minimum distance. Depending on the rotation rate (typically 3 to 5 per second) and excess engine thrust, the optimum take-off might require to start the rotation process at less than stall speed. For added safety, it is advisable to stay a little longer on the ground if the available runway permits it.

The FAA requires that aircraft manufacturers provide certain V-speeds to ensure the safest and most efficient flow of air traffic. They are standard aviation terms used to identify the critical operational airspeeds for various phases of flight. V-speeds are valuable tools that help pilots responsibly and effectively operate their aircraft.

However, aircraft weight is not the only factor to consider; there is also the weight of the cargo, the configuration of the airplane, runway slope, wind speed, and temperature (including the presence of rain or ice).

If one engine fails (in a multi-engine aircraft) during takeoff, V2 is the speed at which this disabled aircraft can still safely climb. V2 will vary depending on the position of the flaps at the time of the engine malfunction.

The minimum speed at which an aircraft can maintain controlled flight with one engine inoperative. This speed is crucial for multi-engine aircraft, as it helps to ensure that pilots can maintain control of the aircraft even if an engine fails. In a twin-engine airplane, for example, if one engine fails, the other will produce thrust asymmetrically, causing the plane to yaw towards the dead engine.

Vx is the maximum altitude gain in the shortest horizontal distance (knowing this metric is the key to calculating this speed). Pilots use VX to avoid obstacles such as tall buildings or cell phone towers.

This is the maximum speed for an aircraft in flight during turbulence or heavy wind gusts. The manufacturer usually determines this speed based on the maximum gross weight of the aircraft. However, the VA changes when the plane is being operated at less than max gross.

VMAX refers to the maximum speed at which an aircraft can safely operate under normal conditions. This term is often interchangeable with VMO (Velocity Maximum Operating) or MMO (Mach Maximum Operating).

Pilots extend the flaps of the airplane to create an increase in drag, which slows the aircraft in preparation for landing. But how will the pilot know how slowly the aircraft may go before it stalls?

This speed is not random or arbitrary, but rather a carefully calculated value that is typically set slightly above the VREF, or Reference Landing Speed. The reason for this is to establish a safety buffer.

It is typically the speed at which a transport aircraft is flown during the final stage of its approach to landing. The VREF is usually set at 1.3 times the VS0, also known as the stalling speed or minimum steady flight speed at which the aircraft is controllable in the landing configuration.

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