What is a bearingless rotor?
A bearingless rotor is a special case of a hingeless rotor, in which the pitch bearing as well as the flap and lag hinges are eliminated (see Figure 1). Pitch control from the pitch link to the main blade is transmitted via a torsionally stiff torque tube.
What is a semi-rigid rotor system?
Semi-rigid Rotor System. A semi-rigid rotor system is usually composed of two blades which are rigidly mounted to the main rotor hub. The main rotor hub is free to tilt with respect to the main rotor shaft on what is known as a teetering hinge. This allows the blades to flap together as a unit.
What do you mean by dissymmetry of lift?
Dissymmetry of lift (also known as asymmetry of lift or asymmetric lift) in rotorcraft aerodynamics refers to an unequal amount of lift on opposite sides of the rotor disc. It is a phenomenon that affects single-rotor helicopters and autogyros in forward flight.
Do helicopter blades change speed?
Most helicopter rotors spin at constant speed. However slowing the rotor in some situations can bring benefits. As forward speed increases, the advancing rotor tip speed soon approaches the speed of sound.
What is rotor configuration?
The rotors on a helicopter can be configured in several ways. The most common configuration is the combination of one main rotor and one tail rotor. The tail rotor compensates for the torque that is produced by the main rotor. The tail rotor also controls the helicopter along the vertical axis during hover flight.
What are the differences of a semi rigid and rigid rotor system?
The semirigid rotor design is found on aircraft with two rotor blades. The blades are connected in a manner such that as one blade flaps up, the opposite blade flaps down. The rigid rotor system is a rare design but potentially offers the best properties of both the fully articulated and semirigid rotors.
What are the three basic classifications of a main rotor system?
Main rotor systems are classified according to how the main rotor blades are attached and move relative to the main rotor hub. There are three basic classifications: rigid, semirigid, and fully articulated, although some modern rotor systems use a combination of these classifications.
How are helicopter blades designed?
The blades of a helicopter are long, narrow airfoils with a high aspect ratio, a shape that minimizes drag from tip vortices (see the wings of a glider for comparison).
What is the difference between a fully articulated rotor system and rigid rotor system?
The rigid rotor system is a rare design but potentially offers the best properties of both the fully articulated and semirigid rotors. In this design, the blade roots are rigidly attached to the rotor hub. The blades do not have hinges to allow lead-lag or flapping.
In a bearingless rotor the flap and lag hinges, as well as the pitch bearings, have all been replaced by a torsionally soft flexbeam between the blade and the hub (Figs. 1 and 2). Pitch control is applied to the blade through a torsionally stiff torque tube by rotating the tube with a pushrod.
What are the Lag dampers for bearingless rotors?
For articulated rotors, the instability problems are taken care of by adding mechanical lag dampers. Since there is no lag hinge on bearingless rotors, traditional lag damper can not be effectively used.
What are the different types of rotor trim?
In forwardflight, two typesof rotor trims were employed. One method was to adjust the longitudinalcyclic to obtainthe propulsiveforce andmomentthat werenecessaryto overcomethe hypotheticalaircraftdrag and down-toadsof the horizontal tail stabilizer. This is generally refered to as propulsive trim, or H-force trim.