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Blade pitch acts much like the gearing of the final drive of a car. Low pitch yields good low speed acceleration (and climb rate in an aircraft) while high pitch optimizes high speed performance and fuel economy. It is quite common for an aircraft to be designed with a variable-pitch propeller, to give maximum thrust over a larger speed range ...
The propeller characteristics are commonly expressed as dimensionless ratios: [31] Pitch ratio PR = propeller pitch/propeller diameter, or P/D; Disk area A 0 = πD 2 /4; Expanded area ratio = A E /A 0, where expanded area A E = Expanded area of all blades outside of the hub.
An alternative design is the controllable-pitch propeller (CPP, or CRP for controllable-reversible pitch), where the blades are rotated normally to the drive shaft by additional machinery – usually hydraulics – at the hub and control linkages running down the shaft. This allows the drive machinery to operate at a constant speed while the ...
A controllable-pitch propeller is one where the pitch is controlled manually by the pilot. Alternatively, a constant-speed propeller is one where the pilot sets the desired engine speed ( RPM ), and the blade pitch is controlled automatically without the pilot's intervention so that the rotational speed remains constant.
Early pitch control settings were pilot operated, either with a small number of preset positions or continuously variable. [1] The simplest mechanism is the ground-adjustable propeller, which may be adjusted on the ground, but is effectively a fixed-pitch prop once airborne. The spring-loaded "two-speed" VP prop is set to fine for takeoff, and ...
This is a two-bladed propeller 3 ft. in diameter, with a uniform geometrical pitch of 2.1 ft. (or a pitch-diameter ratio of 0.7). The blades have standard propeller sections based on the R.A.F-6 airfoil (Fig. 6), and the blade widths, thicknesses, and angles are as given in the first part of Table I.
Due to the pitch rotation at takeoff, the propeller diameter may have to be reduced (with a loss of efficiency [22]) and/or landing gear made longer [6] and heavier. Many pushers [note 8] have ventral fins or skids beneath the propeller to prevent the propeller from striking the ground, at an added cost in drag and weight.
Its 190-inch propeller diameter (4.7-metre) was smaller than the NK-12's 220–240 in (5.6–6.2 m) diameter, but it produced a power output of 21,007 hp (15,665 kW), delivering a takeoff thrust of 40,000 pounds-force (177 kilonewtons). [12] Even more powerful was the NK-62, which was in development throughout most of the decade.
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