The FAA 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 discret ...

charting the safe/unsafe flight profiles relevant to a specific

helicopter A helicopter is a type of rotorcraft in which Lift (force), lift and thrust are supplied by horizontally spinning Helicopter rotor, rotors. This allows the helicopter to VTOL, take off and land vertically, to hover (helicopter), hover, and ...

. 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 Commission with responsibility for civil aviation safety in the European Union. It carries out certification, regulation and standardisation and also performs inve ...

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 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 it is flying through (which itself is usually moving relative to the ground due to wind). In contrast, the ground speed is the speed of an aircraft with respect to the sur ...

, such as a hover taxi, the pilot can simply cushion the landing with

collective A collective is a group of entities that share or are motivated by at least one common issue or interest or work together to achieve a common objective. Collectives can differ from cooperatives in that they are not necessarily focused upon an e ...

by converting

rotational inertia The moment of inertia, otherwise known as the mass moment of inertia, angular/rotational mass, second moment of mass, or most accurately, rotational inertia, of a rigid body is defined relatively to a rotational axis. It is the ratio between ...

into lift. 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, bengalo in several European countries, is a type of pyrotechnic that produces a bright light or intense heat without an explosion. Flares are used for distress signaling, illuminatio ...

, 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 f of several variables is the vector field (or vector-valued function) \nabla f whose value at a point p gives the direction and the rate of fastest increase. The g ...

. 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 a Federal government of the United States, U.S. federal government agency within the United States Department of Transportation, U.S. Department of Transportation that regulates civil aviation in t ...

, 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