Method of determining an initial leading edge circle of airfoils of a blade and of improving the blade in order to increase its negative stall angle of attack

Patent metadata

Field	Value
Publication number	US-11148794-B2
Application number	US-201916273576-A
Country	US
Kind code	B2
Filing date	Feb 12, 2019
Priority date	Feb 15, 2018
Publication date	Oct 19, 2021
Grant date	Oct 19, 2021

Abstract

A method of determining an initial leading edge circle for airfoils of a blade and 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 determined and then 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 improving a blade, the blade extending in a longitudinal direction (X) spanwise from a first end to a second end, and in a transverse direction (Y) from a leading edge to a trailing edge, the blade having 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 a leading edge segment, an intermediate segment, and a terminal segment, wherein the method includes:
a first step of determining an initial leading edge circle for at least one of the two half-airfoils of at least one airfoil, each initial leading edge circle being attached to a respective half-airfoil;
a second step of modifying at least one half-airfoil of at least one airfoil;
a third step of moving the leading edge for each airfoil of the blade; and
a fourth step of fabricating the blade with the modified airfoils;
the first step of determining an initial leading edge circle having the following substeps:
defining a straight line segment connecting the leading edge to the trailing edge of the airfoil;
creating a construction circle passing through the leading edge, the center of the construction circle being situated on the straight line segment, the construction circle being inscribed in the half-airfoil;
increasing the radius of the construction circle, the center of the construction circle being moved along the straight line segment and the construction circle continuing to pass through the leading edge until the construction circle intersects the half-airfoil, the construction circle no longer being inscribed inside the half-airfoil; and
determining the initial leading edge circle of the half-airfoil, the initial leading edge circle being the largest construction circle inscribed inside the half-airfoil, the center of the initial leading edge circle being the center of the largest construction circle inscribed inside the half-airfoil and situated on the straight line segment, the radius of the initial leading edge circle being the radius of the largest construction circle inscribed inside the half-airfoil;

the second step of modifying at least one half-airfoil having the following substeps:
replacing the leading edge segment of the at least one half-airfoil by a portion of the initial leading edge circle attached to the at least one half-airfoil;
increasing the radius of the initial leading edge circle of the at least one half-airfoil, the center of the initial leading edge circle being moved along the straight line segment so as to form a new leading edge circle of the at least one half-airfoil having a portion that constitutes a new leading edge segment of the at least one half-airfoil; and
defining a new intermediate segment of the at least one half-airfoil replacing the intermediate segment of the at least one half-airfoil and connecting the new leading edge circle of the at least one half-airfoil to the terminal segment of the at least one half-airfoil in order to increase the negative stall angle of attack of the blade;

the third step having the following substeps:
moving the leading edge of each airfoil of the blade through a third distance d perpendicular to the straight line segment, from the pressure side half-airfoil towards the suction side half-airfoil, the initial leading edge segment or else, where appropriate, the new leading edge segment, of both of the half-airfoils of the airfoil also being moved likewise; and
defining a new intermediate segment for each of the two half-airfoils respectively connecting the initial leading edge segment or else, where applicable, the new leading edge segment of the two half-airfoils to the terminal segment of the two half-airfoils.

2. The method according to claim 1 , wherein during the first step, respective initial leading edge circles are determined for both of the half-airfoils.

3. The method according to claim 1 , wherein during the second step, both of the half-airfoils of each airfoil are modified.

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

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

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

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

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

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

10. An improved blade for an aircraft, the blade extending in a longitudinal direction spanwise from a first end to a second end, and along a transverse direction 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 a leading edge segment, an intermediate segment, and a terminal segment, the blade being made using the airfoils modified by the method according to claim 1 .

11. The blade according to claim 10 , the blade including at least one modified airfoil having the following points constituting it in a (u, v) reference frame:

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

Assignees

• Airbus Helicopters

Inventors

• Fukari Raphael
• Eglin Paul

Classifications

• B64C27/467 Primary

  Aerodynamic features · CPC title

• B64C2003/146

  comprising leading edges of particular shape · CPC title

• B64C3/14 Primary

  Aerofoil profile · CPC title

• B64C11/18

  Aerodynamic features · CPC title

• B64C27/473

  Constructional features · CPC title