Patent Application
20190283864
This application relates to counter-rotating propeller systems, such as for use on aircraft where one of the rows can be selectively stopped from rotating and its blades utilized as guide vanes during lower power operation.
Propeller systems are known and often utilized to provide propulsion to aircraft. One known type of propeller system has two co-axial sets of rotating blades rotating with separate hubs. In many cases, the two sets of blades rotate in opposite directions. These are called counter-rotating propeller systems.
It is also known to provide guide vanes either upstream or downstream of a propeller, which may have a variable angle of incidence, such as to redirect flow upstream or capture swirl downstream of the propeller blades. In at least one known system, there are dedicated guide vanes positioned downstream of the rotor and blades.
A propeller system has a pair of rotors and a pair of blade sets and at least one drive input to drive a first of the rotors and blade sets and a second of the rotors and blade sets. The blade sets are positioned such that when both are driven, air will be driven across the first blade set and then across the second blade set. There is a pitch change mechanism to change an angle of incidence of the blade in at least one of the first and second blade sets. There is a device for selectively stopping rotation of the at least one of the first or second rotor and blade set while still allowing rotation of the other rotor and blade set. The pitch change mechanism of the stopped blade set can still change the angle of incidence when the device has stopped rotation.
A method is also disclosed.
These and other features may be best understood from the following drawings and specification.
Air is driven by blades 24 and then across blades 28 which drive additional air flow.
A pitch change mechanism 41 can change the pitch angle of the blades 28 about their respective axis 30.
Pitch change mechanisms are known, and mechanisms 40/41 may be known.
The pitch change of propeller systems in normal operation serves two functions. One is to allow for efficient conversion of power into thrust over a range of operating conditions including varying forward speeds by properly aligning the propeller blades with the incoming flow.
The second is to allow the propeller system to control its speed of rotation.
The clutch 109 is shown as being controlled by a control 300. The control 300 further controls the pitch change mechanisms 40 and 41.
Now, at lower power operation, the control 300 may open the clutch 109 stopping rotation of the hub 22 and blades 24. The angle of the blades 24 can still be changed by pitch change mechanism 40, such that the now stopped blades 24 can provide the function of guide vanes, as described below. Thus, the guide vane function is provided without the requirement of having a separate guide vane row. The use of such guide vanes becomes particularly valuable at lower power operation, and when it is not necessary to have both blade sets 24 and 28 to provide sufficient propulsion. The lower power operation could be cruise of the associated aircraft, and the higher power operation could be take-off of the associated aircraft.
Allowing the stopped blade row to change pitch is intended to allow the blades to operate efficiently as guide vanes over a range of operating conditions including varying flight speeds. In the case where the guide vanes are aft of the rotating row, the vanes turn the swirling flow from the propeller in the axial direction converting some of the wasted energy in the swirling flow into thrust. Similarly, in the situation where the guide vanes are in front of the rotating blade row, the flow is swirled coming into the rotating row such that the flow exiting the rotating row is more predominantly in the axial direction, and thus generating more thrust, than it would have done without the guide vanes. A skilled worker in this art would recognize when a particular angle is desirable.
In another embodiment, a clutch could be positioned to stop the rotation of the hub 26 and blades 28 which would then serve as guide vanes for the flow exiting the rotating front blade set 24.
As can be appreciated, any number of mechanisms can be employed to stop drive of one of the blade sets. Those disclosed here are examples.
Although embodiments have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the true scope and content of this disclosure.
