There are many terms and acronyms in aviation that can be confusing, and V speeds are no exception. The first thing you should know is that the V in this term stands for Velocity, a very standard term for speed in the scientific lexicon. However, some people also claim that the V stands for “Vitesse” a French word for speed.
V speeds are standard airspeeds for each airplane to operate at the highest possible performance level within the established safety standards. Therefore, V speeds are determined by manufacturers after performing test flights and identifying the aircraft limitations.
The main intention of these test flights is to provide the required information for pilots to learn the best practices for the safe operation of the aircraft they fly, where V speeds play an important role. But why are V speeds so important for flight performance and safety? Keep reading as we disclose all the details for you.
Which V speeds are on the airspeed indicator?
As mentioned above, V speeds are standard airspeeds. Therefore, it is no surprise that they can be found on the airspeed indicator. Now, the important thing for any pilot is learning to identify and read the V speeds that are shown in any airspeed indicator.
Different aircraft will have different airspeed indicator designs, but the information shown is standard. This means that all indicators have things in common and those are the characteristics you will need to identify the different V speeds on the indicator.
The standardized code uses colors to illustrate the V speeds that are most relevant for safety and performance. And numbered lines are used to represent the values of those speeds.
In dial indicators, you will find colored arcs. However, the most recent aircraft might use glass cockpits where the code is represented by a colored bar, but the basic principle is the same.
There are four colors that are used, white, green, yellow, and red. So, let’s take a look at what does each color represents.
Image source: Oona Räisänen (Mysid)
White coded speeds
The main V speeds found in white are the VSO, VS1, and VFE. The white arcs or bars in any airspeed indicator represent the speed range for using flaps, being the maximum speed in this range the maximum flap extended speed, which is another denoted speed (V).
What are VSO and VS1?
These are two of the V speeds coded with the white color.
VSO is defined as the stall speed in landing configuration, or with the landing gear and flaps fully deployed which is the same. When looking at the white range in the indicator, the VSO can be identified at the lower end of the white arc or bar. It is also known as the minimum steady flight speed, which is the minimum speed at which aircraft is controllable in landing configuration. For example, the maximum stall speed allowed for single-engine and light twin-engine aircraft in this configuration is 61 knots.
On the other hand, VS1 is defined as the stall speed with the landing gear and flaps fully retracted. In this case, there will be a specific configuration that must be different from the landing configuration mentioned above. This said, it is also defined as the minimum steady flight speed in a given configuration.
Another name given to VS1 is the “clean” stall speed, which makes reference to the landing gear and flaps being retracted and not creating any added drag or turbulent airflow. However, the configuration could be not necessarily completely clean, as VS1 could refer to stall speed with flaps in takeoff position or any other specific configuration that is not the landing one. Although it is part of the white-coded speeds, the VS1 can be identified at the lower end of the green arc in a dial airspeed indicator or the beginning of the green bar in the indicator usually found on the left of a glass cockpit. For example, VS1 for a Cessna 172 in a no-flaps configuration is 47 knots.
What about the maximum speed with flaps extended?
The maximum speed with flaps extended is the VFE. It is usually defined as the Maximum Flap Extended Speed, thus representing the limit for extending the flaps. If the flaps were extended at a speed that is higher than the given VFE, serious structural damage could happen which could turn into a catastrophe. However, some aircraft are designed so that they can use a specific type of flap, generally called approach flap, at higher speeds with the purpose of having a quicker approach to the landing area.
The VFE can be identified as the speed measured at the top end of the white arc or the white bar in the case of a glass cockpit.
Green coded speed
In general, the green scale in any airspeed indicator represents the range of normal operation for the aircraft. While some of the white-coded speeds use the green scale as a reference, the truth is that there is only one denoted speed (V) in the green scale. The VNO.
What is VNO?
Since this is a green coded speed and the green scale represents the range of normal operations, it is easy to understand that VNO is the speed (V) defined as Velocity of Normal Operation.
While this sounds as it could be any speed in the green range, the reality is that VNO is at the top of the green scale to refer to the maximum structural cruising speed.
Maximum structural cruising speed
The top speed of the green range takes this name because it represents the maximum speed the aircraft can reach without compromising the structure while in cruise flight mode. The VNO represents the limit to fly within the FAA-certified range of wind gusts, with a top measure of 50 fps.
Although modern aircraft are designed to resist high levels of wind gusts, the pilot has no way of measuring the intensity at any given moment, which is why keeping the speed below this limit is so important. And this is also the reason why the yellow color is used after the VNO, as it represents a warning signal.
While operations above the VNO are possible, they are discouraged and should be performed only in case of emergency and knowing that the wind is not so strong.
Yellow and red coded speed
Putting these two codes together makes sense because the yellow color is already a warning, while the red represents a final alert.
The speeds in the yellow arc or bar are already excessive for the aircraft. It means that the aircraft has overpassed the maximum operating limit speed set by the VNO which is not recommended. However, it may be possible for some aircraft to fly above that maximum operating limit speed, but only for a short period of time and under smooth wind conditions. This range is found in the indicator starting at the end of the green arc or bar.
On the other hand, the red-coded speed is known as the VNE. This acronym stands for Velocity that you Never Exceed. In other words, is the maximum speed the aircraft could reach without serious structural damage, even under smooth wind conditions. While it is true that designers and manufacturers add a margin for safety, it is a very small one and no one should test it.
The VNE is represented in any indicator as a red line at the end of the yellow range to highlight the criticality of this V speed.
Other V speeds
Apart from the stalling speed with landing gear extended and flaps deployed and another reference stall speed, the minimum speed for steady flight, and all the V speeds we have mentioned, there are others that are worth mentioning. Although these are not clearly shown in the airspeed indicator, the following are also very important for different flight stages.
Maneuvering Speed (VA)
Also known as Velocity of Acceleration, VA refers to the design maneuvering speed. This design speed represents the maximum speed for the aircraft to go through sudden and brusque movement without suffering any structural damage. Similarly, no aircraft should be piloted above its VA under turbulence or high wind gust conditions.
At this point, it is also important to highlight that these speeds are usually given according to the weight. If only one value is provided, it must be assumed that it refers to the maximum landing weight.
Maximum Landing Gear Operating Speed (VLO)
The maximum landing gear operating speed or Maximum Velocity for Landing Gear Operation (VLO) is a denoted speed (V) for retractable gear aircraft only. This means that fixed landing gear aircraft will not have this speed (V) provided in their operational manual.
The VLO represents the speed (V) that makes extending or retracting the landing gear safe. Therefore, none of these operations should be performed above this speed (V), as it will create the possibility of damage to the system. This is only understandable in case of an emergency when trying to land the aircraft is more important than saving the structure of the gear.
Maximum Landing Gear Extended Speed (VLE)
The maximum landing gear extended speed or VLE is the top speed the aircraft can reach to fly safely with the landing gear fully extended.
Best rate of climb (VY)
This V speed is the one configured after takeoff when the aircraft needs to reach the desired level of altitude in the shortest time possible. Usually refers to flaps and gear-up configuration, and it is directly proportional to weight and inversely proportional to the altitude. In other words, the heavier the aircraft the higher the speed (V), and the higher the altitude, the lower the speed you need to finish your climb.
Minimum Control Speed (VMC)
Minimum control speed is another type of a V speed that indicates a speed at which an aircraft can be kept in control directionally and laterally in an engine failure event. There also is a VMCA (minimum control speed with critical engine inoperative) which shows at what speed an aircraft can be controlled directionally.
Best Angle of Climb (VX)
Although the name seems to have no relation to speed, the best angle of climb or VX is another V speed that can be critical in more than one situation. Why? Because Vx is the speed to achieve the maximum possible altitude in the shortest possible horizontal distance, something crucial for clearing any obstacle that may be found shortly after the takeoff at the end or beyond the runway.
For the best angle of climb, a high forward speed is not necessary, which is why VX is slower than VY. This is because the lower amount of speed to move forward provides a better chance to reach altitude in a shorter horizontal distance, thus making sure the obstacle will be cleared. However, if time is more important because there is no obstacle, this speed would not be the best choice as it will take longer to reach the cruise altitude. Normally, VY will replace VX after the obstacle is cleared.
It is important to highlight that the best angle of climb or VX speed found in any manual refers to takeoff at sea level, at max gross weight, and with flaps in takeoff position. VX is directly proportional to altitude (about ½ knot per 1,000 feet) and inversely proportional to weight.
Rotation speed (VR) indicates aircraft rotation on the runway, specifically upwards and downwards. VR shows the pilots when they should begin pitching up the aircraft for takeoff.
The rotation speed should be monitored closely in order to smoothly lift the nose of the airplane instead of suddenly yanking it up. The VR should assist in lifting the aircraft making the takeoff smooth and natural.
The V speeds defined until this point are not really all those that exist. There are others such as the minimum takeoff safety speed (V2MIN), design speed for maximum gust intensity for cargo aircraft (VB), design diving speed (VD), final takeoff speed (VFTO), maximum speed in level flight with maximum continuous power (VH), and many more.
However, all those speeds are mainly used by advanced pilots and we just wanted to give you an overview of the most relevant ones. If you are studying to become a pilot, be sure that you will be studying all the V speeds more in depth during your courses.
Now, if you are interested in learning more about the aviation industry, or you want to launch or scale your career within the industry, we recommend you take a look at the different courses we offer dictated by our expert lectors. We are sure that you will find one for yourself, so go check them out here.
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Jet pilot @NASA
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