Method of improving a blade so as to increase its negative stall angle of attack

Patent metadata

Field	Value
Publication number	US-11225316-B2
Application number	US-201916274302-A
Country	US
Kind code	B2
Filing date	Feb 13, 2019
Priority date	Feb 15, 2018
Publication date	Jan 18, 2022
Grant date	Jan 18, 2022

Abstract

A method of improving a blade and also an improved blade and a advancement propeller including the improved blade. The radius of the initial leading edge circle of each airfoil of the blade is increased, and its leading edge is moved away from a pressure side half-airfoil towards a suction side half-airfoil, thereby modifying the airfoil of each cross-section of the blade and modifying the camber of each airfoil. Consequently, the absolute value of the negative stall angle of attack of the blade is increased, thus making it possible to increase the aerodynamic performance of the blade under a negative angle of attack compared with a blade that is not modified, and without significantly degrading its aerodynamic performance under a positive angle of attack.

First claim

What is claimed is:

1. A method of designing a propeller blade based upon a predetermined basis blade, the predetermined basis and propeller blades extending in a longitudinal direction (X) spanwise from a first end to a second end and in a transverse direction (Y) from respectively basis and resulting leading edges to respectively basis and resulting trailing edges, the predetermined basis and propeller blades having respective basis and resulting cross-sections, succeeding along the longitudinal direction (X), each basis and resulting cross-sections being defined by respectively basis and resulting airfoils, such that each basis and resulting airfoil is respectively defined by two respectively basis and resulting half-airfoils, including a respectively basis and resulting suction side half-airfoil and a respectively basis and resulting pressure side half-airfoil, the respectively basis and resulting two half-airfoils each comprising, respectively: a basis and resulting leading edge segment, a basis and resulting intermediate segment, and a basis and resulting terminal segment, the resulting leading edge segment of each half-airfoil being formed by a portion of a basis leading edge circle of the predetermined basis blade, the basis leading edge circle having a basis radius; wherein the method comprises:
a first step of modifying at least one basis half-airfoil of each basis airfoil to obtain the at least one resulting half-airfoil of each resulting airfoil;
a second step of moving the leading edge for each resulting airfoil of the resulting blade, relatively to the basis leading edge for each basis airfoil of the basis blade; and
a third step of fabricating the resulting blade with the resulting airfoils;
the first step having the following substeps of:
increasing for the at least one resulting half-airfoil, the basis radius of the basis leading edge circle for the at least one resulting half-airfoil so as to form a resulting leading edge circle having an increased resulting radius; the at least one resulting half-airfoil having a portion that constitutes the resulting leading edge segment, the resulting leading edge circle being tangential to the basis leading edge circle of the at least one basis half-airfoil at the resulting leading edge; and
defining a new intermediate segment for the at least one resulting half-airfoil by replacing the basis intermediate segment connecting the resulting leading edge circle to a terminal segment of the at least one half-airfoil in such a manner to increase a negative stall angle of a resulting attack angle with respect to a basis attack angle of the basis blade; and

the second step having the following substeps:
moving the leading edge for each resulting airfoil of the resulting blade, relatively to the basis leading edge of each basis airfoil, through a third distance d perpendicularly to a straight line segment connecting the basis leading edge to the basis trailing edge, from the resulting pressure side half-airfoil towards the resulting suction side half-airfoil, with the resulting leading edge segment of the resulting airfoil also being moved; and
refining a resulting intermediate segment for each of the resulting two half-airfoils by connecting the basis leading edge segment of both of the resulting half-airfoils to the resulting terminal segments of both of the resulting half-airfoils.

2. The method according to claim 1 , wherein during the first step, both of the two basis half-airfoils of each basis airfoil are modified.

3. The method according to claim 1 , wherein for each resulting airfoil of the resulting blade, the resulting radius of the resulting leading edge circle of the resulting suction side half-airfoil lies in the range 110% to 140% of the basis radius of the basis leading edge circle of the basis suction side half-airfoil, and the resulting radius of the resulting leading edge circle of the resulting pressure side half-airfoil lies in the range 115% to 220% of the basis radius of the basis leading edge circle of the basis pressure side half-airfoil.

4. The method according to claim 1 , wherein for the at least one resulting half-airfoil of each resulting airfoil of the resulting blade, the new intermediate segment begins on the resulting leading edge segment at a first distance from the resulting leading edge, which first distance is a minimum transverse distance lying in the range 0.5% to 5% of a chord ( c ) of the resulting airfoil and connects with the resulting terminal segment at a second distance from the resulting leading edge, which second distance is a transverse distance equal to at most 25% of the chord ( c ), the chord ( c ) being equal to the distance between the resulting leading edge and the resulting trailing edge of the resulting airfoil.

5. The method according to claim 1 , the third distance d lying in the range 0.5% to 2% of a chord ( c ) of the resulting airfoil, the chord ( c ) being equal to the distance between the resulting leading edge and the resulting trailing edge of the resulting airfoil.

6. The method according to claim 1 , wherein for the at least one resulting half-airfoil of each resulting airfoil of the resulting blade, the new intermediate segment does not have any point of inflection.

7. The method according to claim 1 , wherein for the at least one resulting half-airfoil of each resulting airfoil, of the resulting blade, the new intermediate segment is formed by a polynomial of degree 3.

8. The method according to claim 1 , wherein a thickness ( e ) equal to the maximum distance between the resulting suction side half-airfoil and the resulting pressure side half-airfoil of the resulting airfoil being unchanged for each airfoil.

9. An improved blade for an aircraft, the blade extending in a longitudinal direction (X) spanwise from a first end to a second end, and along a transverse direction (Y) from a leading edge to a trailing edge, the blade comprising successive cross-sections, each cross-section being defined by an airfoil, each airfoil being defined by two half-airfoils including a suction side half-airfoil and a pressure side half-airfoil, each of the two half-airfoils comprising respectively a leading edge segment, an intermediate segment, and a terminal segment, the leading edge segment being formed by a portion of an initial leading edge circle for each half-airfoil, the blade being made using the airfoils modified by the method according to claim 1 .

10. The blade according to claim 9 , the blade including at least one modified airfoil having the following points constituting it in a (u, v) reference frame, where the (u,v) reference frame is positioned at the leading edge of the airfoil:

u
v
u
v

1
−0.001786945
0.898362357
−0.010840856

0.993196671
−0.001985598
0.891597532
−0.011590451

0.986394068
−0.002207676
0.884831428
−0.012328409

0.979593055
−0.002474188
0.878063944
−0.013053601

0.972797017
−0.002846444
0.871295153
−0.013766489

Assignees

• Airbus Helicopters

Inventors

• Fukari Raphael
• Eglin Paul

Classifications

• B64C27/473

  Constructional features · CPC title

• B64C11/18 Primary

  Aerodynamic features · CPC title

• B64C3/14

  Aerofoil profile · CPC title

• B64C27/467 Primary

  Aerodynamic features · CPC title