The

FAA The Federal Aviation Administration (FAA) is the largest transportation agency of the U.S. government and regulates all aspects of civil aviation in the country as well as over surrounding international waters. Its powers include air traffic m ...

states "The height–velocity diagram or H/V curve is a

graph Graph may refer to: Mathematics *Graph (discrete mathematics), a structure made of vertices and edges **Graph theory, the study of such graphs and their properties *Graph (topology), a topological space resembling a graph in the sense of discre ...

charting the safe/unsafe flight profiles relevant to a specific

helicopter A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attributes ...

. As operation outside the safe area of the chart can be fatal in the event of a power or transmission failure it is sometimes referred to as the dead man's curve." The

EASA The European Union Aviation Safety Agency (EASA) is an agency of the European Union (EU) with responsibility for civil aviation safety. It carries out certification, regulation and standardisation and also performs investigation and monitori ...

refers to it as the "height/velocity avoid curve". The H–V curve is a diagram indicating the combinations of height above ground and airspeed that should be avoided due to safety concerns relating to emergency landings. It is dangerous to operate within the shaded regions of the diagram, because it may be impossible for the pilot to complete an emergency

autorotation Autorotation is a state of flight in which the main rotor system of a helicopter or other rotary-wing aircraft turns by the action of air moving up through the rotor, as with an autogyro, rather than engine power driving the rotor. Bensen, Igor ...

from a starting point within these regions. The H–V curve also contains a take-off profile, indicating how a pilot can start from 0 height and 0 speed, and safely traverse to cruise. At low heights with low

airspeed In aviation, airspeed is the speed of an aircraft relative to the air. Among the common conventions for qualifying airspeed are: * Indicated airspeed ("IAS"), what is read on an airspeed gauge connected to a Pitot-static system; * Calibrated a ...

, such as a

hover taxi Taxiing (rarely spelled taxying) is the movement of an aircraft on the ground, under its own power, in contrast to towing or pushback where the aircraft is moved by a tug. The aircraft usually moves on wheels, but the term also includes aircr ...

, the pilot can simply cushion the landing with collective by converting

rotational inertia The moment of inertia, otherwise known as the mass moment of inertia, angular mass, second moment of mass, or most accurately, rotational inertia, of a rigid body is a quantity that determines the torque needed for a desired angular acceler ...

into

lift Lift or LIFT may refer to: Physical devices * Elevator, or lift, a device used for raising and lowering people or goods ** Paternoster lift, a type of lift using a continuous chain of cars which do not stop ** Patient lift, or Hoyer lift, mobile ...

. Conversely, a complete power loss, and resultant crash landing, from a three-foot hover taxi at walking pace may be survivable. Multi-engine helicopters capable of flying and hovering on a single engine, don't depict this second region. As the airspeed increases without an increase in height, there comes a point where the pilot's reaction time would be insufficient to initiate a

flare A flare, also sometimes called a fusée, fusee, or bengala in some Latin-speaking countries, is a type of pyrotechnic that produces a bright light or intense heat without an explosion. Flares are used for distress signaling, illumination, ...

, and prevent a high-speed ground impact. Each increase in height increases the pilot reaction time. This is the reason the bottom right part of the H–V curve has a shallow

gradient In vector calculus, the gradient of a scalar-valued differentiable function of several variables is the vector field (or vector-valued function) \nabla f whose value at a point p is the "direction and rate of fastest increase". If the gradi ...

. If above ideal autorotation speed, a pilot can avoid the deadman's curve by flaring, converting airspeed into height, and increasing rotor RPM through coning.
Chapter 11: Helicopter Emergencies and Hazards. 6 MB
' page 11-8
Main page

Rotorcraft Flying Handbook, FAA Manual H-8083-21A. Complete manual, 84 MB
', Washington, DC: Flight Standards Service,

Federal Aviation Administration The Federal Aviation Administration (FAA) is the largest transportation agency of the U.S. government and regulates all aspects of civil aviation in the country as well as over surrounding international waters. Its powers include air traffic m ...

, U.S. Dept. of Transportation, 2012. Likewise, an increase in height without a corresponding increase in airspeed is dangerous, as a crash from this height may not be survivable. Airspeed has to increase beyond the 40–80 knot range, allowing the safe initiation of an autorotation. Thus a safe take-off profile, initiating forward flight from a low hover, involves gaining height as airspeed approaches a safe autorotation speed.

References

3. http://www.dtic.mil/dtic/tr/fulltext/u2/669481.pdf

External links

* http://www.copters.com/pilot/hvcurve.html * https://web.archive.org/web/20131217224602/http://www.magnigyro.com/features/HV%20Curve%20for%20Gyroplanes.pdf
RWS 19 – Height Velocity Diagram with Shawn Coyle
''Rotary Wing Show'', 2015. {{DEFAULTSORT:Height-velocity diagram Helicopter aerodynamics Aviation risks Diagrams

See also

References

External links