In
helicopter aerodynamics, the Lock number is the ratio of aerodynamic forces, which act to lift the
rotor blades, to inertial forces, which act to maintain the blades in the plane of rotation.
It is named after
C. N. H. Lock
Christopher Noel Hunter Lock (21 December 1894 – 27 March 1949) was a British aerodynamicist, after whom the Lock number is named.
Biography
Lock was born at Herschel House, Cambridge, the youngest son of John Bascombe Lock (18 March 1849 – ...
, a British aerodynamicist who studied
autogyros in the 1920s.
Typical
rotorcraft blades have a Lock number between 3 and 12,
usually approximately 8.
The Lock number is typically 8 to 10 for articulated rotors and 5 to 7 for hingeless rotors.
High-stiffness blades may have a Lock number up to 14.
Larger blades have a higher mass and more inertia, so tend to have a lower Lock number. Helicopter rotors with more than two blades can have lighter blades, so tend to have a higher Lock number.
A low Lock number gives good
autorotation characteristics due to higher inertia, however this comes with a mass penalty.
Ray Prouty writes, "The previously discussed numbers: Mach, Reynolds and Froude are used in many fields of fluid dynamic studies. The Lock number is ours alone."
See also
*
Coning
*
Mach number
Mach number (M or Ma) (; ) is a dimensionless quantity in fluid dynamics representing the ratio of flow velocity past a boundary to the local speed of sound.
It is named after the Moravian physicist and philosopher Ernst Mach.
: \mathrm = \frac ...
*
Froude number
In continuum mechanics, the Froude number (, after William Froude, ) is a dimensionless number defined as the ratio of the flow inertia to the external field (the latter in many applications simply due to gravity). The Froude number is based on t ...
*
Reynolds number
In fluid mechanics, the Reynolds number () is a dimensionless quantity that helps predict fluid flow patterns in different situations by measuring the ratio between inertial and viscous forces. At low Reynolds numbers, flows tend to be domi ...
References
Helicopter aerodynamics
Engineering ratios
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