Fluid reaction surfaces (i.e. – impellers) – Articulated – resiliently mounted or self-shifting impeller... – Sectional – staged or nonrigid working member
Patent
1992-09-23
1994-02-08
Kwon, John T.
Fluid reaction surfaces (i.e., impellers)
Articulated, resiliently mounted or self-shifting impeller...
Sectional, staged or nonrigid working member
F03D 306
Patent
active
052844196
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a propeller with blades which can be twisted.
If a propeller is operated for producing the forward-drive force of an aircraft, optimum blade pitch angles can be maintained over the entire blade length in different flight situations (takeoff, climbing flight, cruise flight) in the case of a propeller with blades which can be twisted, with the advantage of a thrust and efficiency which are favourable in each case for these different flight situations, and as little noise generation as possible. When using a propeller with blades which can be twisted in so-called VTOL aircraft, the propeller is used as a rotor in hovering flight, in a position pivoted through 90 angular degrees with respect to that in cruise flight. A variable blade twist makes possible an optimum blade pitch angle over the entire blade length in such a case as well, both in the different phases of forward flight and in the hovering flight phase, in contrast to a propeller with a rigid blade twist which has an optimum setting with the most favourable thrust and efficiency and as little noise generation as possible only in a single operating situation which is predetermined by the design point.
Design solutions for a propeller with blades which can be twisted have been proposed many times. For example, DE-OS 2,164,648 discloses the facilitating of a variable twist of the blade via a strip system within the propeller blade in conjunction with a rigid main spar and conical adjusting tubes resting thereon. DE-OS 1,531,475 and DE-AS 1,531,476 describe a propeller having a variable blade twist, in which the twist is achieved by means of ribs which are guided on a spar in helical grooves and can be displaced axially on the spar. According to DE-AS 1,281,271, blade cavities can be rotated around the blade axis by means of a different fluid filling, as a result of which it is intended to facilitate a variable blade twist.
Disadvantages of the known design proposals for the construction of a propeller with blades which can be twisted are the suitability, which is only limited, for operation under high centrifugal-force stresses and, furthermore, the highly complex blade construction.
A propeller of the type mentioned initially has been disclosed in U.S. Pat. No. 2,627,928. The individual ribs which are arranged on the blade spar such that they can rotate are connected at the leading edge of the blade to in each case one reinforcing element and at the trailing edge to in each case one leaf spring element. During an adjustment process of the outermost rib with respect to the innermost rib, the intermediate ribs are also moved by the elastic outer skin enclosing the blade. Since, in particular, the leaf spring elements form a type of chain which deforms in an unpredictable manner under the influence of the centrifugal force, bending and torsion oscillations occur in operation which negate the advantages of the adjustment capability again.
The object of the invention is to create a propeller of the type mentioned initially in which, on the one hand, the high centrifugal-force stresses of the blade are adequately absorbed despite the elastic regions which are required for variability of the twist, and in which, in particular, the coupling between adjacent ribs takes place such that an undesired adjustment of the elastic regions under the influence of the centrifugal force and an undesired adjustment of the blade geometry resulting from this are prevented, with a simple blade construction.
Design solutions for a propeller with blades which can be twisted have been proposed many times. For example, DE-OS 2,164,648 discloses the facilitating of a variable twist of the blade via a strip system within the propeller blade in conjunction with a rigid main spar and conical adjusting tubes resting thereon. DE-OS 1,531,475 and DE-AS 1,531,476 describe a propeller having a variable blade twist, in which the twist is achieved by means of ribs which are guided on a spar in helical grooves and can be displaced axially on the spar. According to DE
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