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SpinningWing > Helicopters > Helicopter Performance > Important Helicopter Airspeeds

Important Helicopter Airspeeds

In this article, we discuss special airspeeds that are useful in helicopter flight. They are called V-speeds and are provided by helicopter manufacturers for both safety and performance specification. Some V-speeds are used in the certification process and defined by the government or certifying authority (e.g. Title 14 of the Code of Federal Regulations in the US).

V-speeds are typically provided in knots of indicated airspeed, or KIAS for short. Although sometimes one number will be provided / known, most V-speeds vary with weight (cargo, passengers, ...) and weather (temperature, pressure altitude). Some V-speeds used in fixed wing aircraft, like the stall speeds (Vs), are not applicable to helicopters. The table below summarizes the useful speeds for helicopter flight, and more details are provided below.

\(V_{be}\) velocity of best endurance, at which the helicopter can maintain altitude the longest
\(V_{bg}\) velocity of best glide range, at which the helicopter can fly the maximum distance without power (autorotate)
\(V_{br}\) velocity of best range, at which the helicopter can fly the longest distance given limited gas
\(V_{c}\) velocity of cruise, a convenient overall speed accounting for fuel efficiency, transit time, maintenance and handling qualities
\(V_{g}\) velocity of glide, at which the helicopter has the smallest descent rate (best endurance) without power (in autorotation)
\(V_{h}\) velocity of max continuous power (MCP), at which the helicopter will consume the max power it can sustain level flight
\(V_{aft}\) Velocity to never exceed in aft flight. A helicopter should not exceed this speed when flying aft.
\(V_{lat}\) Velocity to never exceed in lateral flight. A helicopter should not exceed this speed flying laterally (left or right).
\(V_{mini}\) minimum velocity in IFR flight
\(V_{ne}\) Velocity to never exceed. A helicopter should not exceed this speed, even in a dive.
\(V_{nea}\) Velocity to never exceed in autorotation. A helicopter should not exceed this speed in autorotation.
\(V_{neao}\) Velocity to never exceed with augmentation (SAS, SCAS or other) off. A helicopter should not exceed this speed without the augmentation system.
\(V_{nei}\) Maximum allowed velocity when flying IFR.
\(V_{neoei}\) Velocity to never exceed with one engine inoperative (OEI). A helicopter should not exceed this speed in OEI flight.
\(V_{taxi}\) Velocity to never exceed in taxi operations. A helicopter should not exceed this speed when taxiing.
\(V_{x}\) velocity at which the steepest climb angle is obtained (typically 0, giving a 90deg vertical climb)
\(V_{y}\) velocity at which the helicopter can climb fastest
\(V_{tocs}\) recommended velocity for takeoff and climb out

Level flight

Flying level at a speed between 45-75 KIAS will typically allow a helicopter to stay aloft for the longest amount of time (given a fixed amount of fuel). The specific speed that allows the longest time in air is called the maximum endurance speed and is denoted Vbe. This is also the speed at which the helicopter burns fuel the slowest.

At a speed above Vbe a helicopter will be capable of flying the longest distance. This is called the maximum range airspeed, denoted Vbr or MRA. At this speed, the helicopter burns fuel faster than at Vbe, but it's able to fly further because the distance traveled per unit time more than offsets the faster fuel burn.

Endurance versus range (a common confusion)

Since they're often confused, let's clarify the difference between endurance and range with an example. We have a helicopter that burns 200 pounds of fuel per hour (PPH) at 50 KIAS, and 300 PPH at 100 KIAS. Of course, the helicopter can fly for a longer time at 50 KIAS because less fuel is burned per second. However, it can fly further at 100 KIAS. The math follows.

While any amount would work, let's just assume the helicopter has 300 pounds of fuel. It can fly at 50 KIAS for 300/200 or 1.5 hours, but it can only fly at 100 KIAS for 300/300 or 1.0 hours (i.e. it has better endurance at 50 KIAS). However, notice that it can only fly 50 KIAS times 1.5 hour or 75 nautical miles in the 1.5 hours at 50 KIAS, while it can fly 100 KIAS times 1 hour or 100 nautical miles at 100 KIAS (i.e. it has a better range at 100 KIAS)!

Helicopters typically fly at a speed above Vbr, just as highway drivers typically drive faster than their cars best range speed (often around 50 mph). Saving time in travel is typically desirable as long as fuel efficiency is reasonable. This is where the cruise speed—Vc—comes in.

Cruise speed is a kind of overall ideal speed taking into account convenience, fuel consumption, and other costs. For example, higher speeds may allow pilots to fly more trips and increase their revenue per hour. Helicopters should fly safe and have good handling qualities around Vc.

At a higher speed, still in level flight, a helicopter may reach its maximum continuous power MCP—the maximum amount of power the helicopter can fly at for more than a few minutes. This speed is denoted as Vh.

There is yet a higher speed at which the manufacturer recommends never exceeding, even in a dive. This is called the never exceed speed and denoted Vne. Exceeding this speed could result in poor handling qualities and even damage the helicopter (e.g. due to retreating blade stall). This speed may only be attainable in a dive.

In summary, important speeds in level flight include the following, ordered from least to greatest.

  • Vbe < Vbr < Vc < Vh < Vne

In addition to these speeds, there is a minimum speed, denoted Vmin or Vmini, for flying a helicopter using instrument flight rules (IFR). There is also a maximum speed, denoted Vnei, that should not be surpassed when flying with IFR.

Climb, descent and autorotation

We've thus far focused on speeds in level flight (although Vne is more likely to be encountered in descent). Here we'll discuss a few important speeds in climb / descent.

Probably the most important speed in climb is Vy, the best climb rate speed. This is the speed at which the helicopter can ascend fastest, but also where climbing is safe and efficient. Once free of obstacles, a pilot will typically fly at this speed while climbing to a target cruise altitude.

It's important to understand that Vy does not provide the steepest climb angle. In fact, helicopters can typically climb vertically from a hover (90 degree climb angle). This consumes more power due to induced drag, and in some cases (e.g. high gross weight) may not be feasible. Vx is the speed at which the helicopter can make the steepest ascent. So Vx is often 0 for a helicopter, but may be a higher speed (below Vy) when vertical climbs are not possible.

In some cases, a recommended takeoff and climb out speed will be published for a helicopter. This speed is often abbreviated as Vtocs.

Three more speeds are important for autorotation: Vg, Vbg, and Vnea. Vg is the speed that minimizes descent rate, giving the pilot the most time until landing. Vbg provides the maximum range in autorotation. A pilot would fly close to Vbg to reach a distant location for landing. Vnea is the maximum recommended speed in autorotation. One reason for Vnea can be a lack of pedal authority (in high speed autorotation the pedal approaches the end of its range, limiting maneuverability).

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