WO2007114803A1

WO2007114803A1 - Landing gear wheels with side-mounted airfoils

Info

Publication number: WO2007114803A1
Application number: PCT/US2006/011371
Authority: WO
Inventors: Gecheng Zha
Original assignee: University of Miami
Current assignee: University of Miami
Priority date: 2006-03-30
Filing date: 2006-03-30
Publication date: 2007-10-11
Anticipated expiration: 2008-09-30

Abstract

An aircraft wheel assembly (100) includes a hub (102) and a tire (110). The hub (102) is adapted to be connected to a shaft (104), and the tire (110) is around the hub (102) and has a bearing surface (116) and opposing side surfaces (114). A plurality of airfoils (112) are attached to either one or both of the side surfaces (114). The plurality of airfoils (112) are evenly distributed about the side surface(s) (114), and the plurality of airfoils (112) are integrally formed with the side surface(s) (114). The plurality of airfoils (112) extend substantially perpendicular to the side surface(s) (114). A ratio of a width of the tire (110) without the plurality of airfoils (112) to a width of the tire (110) with the plurality of airfoils 112 is less than 0.93.

Description

LANDING GEAR WHEELS WITH SIDE-MOUNTED AIRFOILS

BACKGROUND OF THE INVENTION

Field of the Invention

The disclosure relates generally to aircraft tires and, more specifically, to an aircraft tire having side-mounted airfoils to pre-rotate the tire prior to landing.

Description of the Related Art

A well-known issue associated with tires of an aircraft occurs when the aircraft tire is not rotating as the aircraft touches down. If the aircraft tire is not rotating at a speed such that the velocity of the outer circumference of the aircraft tire equals the relative velocity of aircraft to the surface upon which the aircraft lands, then skidding between the tire and the surface occurs until the velocity of the tire matches the velocity of the aircraft. The skidding of the tire creates excess stress and wear on the tire, which can greatly reduce the expected usable lifetime of the tire and, in certain circumstances, cause the tire to rupture.

Many different systems have been employed in attempts to address this issue. For example, many systems use electro-mechanical or hydraulic systems to pre-rotate the aircraft wheel during flight. Alternatively, many systems employ the use of impellors/airfoils positioned on the hub of the wheel to use the oncoming air stream to rotate the wheels. For example, U.S. Patent No. 4,040,582, entitled "Wind Power Accessory For A Vehicle Wheel" and issued August 9, 1997, to Krauss, discloses an annular disc with spaced cups to catch head winds and covert their forces into rotation torque. The disc is secured to a wheel by clamping segments having flanges engaged between the tire side wall and the wheel rim. Also, both U.S. Patent No. 4,491,288, entitled "Aircraft Landing Wheel Rotating Means" and issued January 1, 1985, to Sinclair and U.S. Patent No. 4,061,294, entitled "Aircraft Wheel Rotator" and issued December 6, 1977 to Hawkins, disclose impellers/blades positioned at the hub of the aircraft wheel. Other systems employ the use of a specific tread design on the tire itself to initiate rotation of the wheel. For example, U.S. Patent Publication No. 2002/0157748, entitled "Aircraft Tire Having Tread Providing Self-Rotation," published on October 31, 2002, to Weller, discloses a tread surface of a tire having a plurality of cavities formed with the bearing surface. The cavities are shaped so that the tire experiences self -rotation upon being exposed to an airflow.

These attempted solutions, although being capable of pre-rotating the tire, also create additional issues to be addressed. For example, those solutions that use electro-mechanical or hydraulic devices to rotate the tire require extensive refitting of the wheel assembly if these devices are not already included. Also, these devices can add significant weight to the aircraft, which is also not desirable. Those solutions that employ impellers located at the hub may also require extensive refitting/redesign of the wheel assembly since these impellers need to be large and/or require additional equipment to redirect airflow to the impellers to create sufficient torque to rotate the wheels.

Those solutions that employ a special tread surface on the tire address the issues associated with refitting/redesigning the wheel assembly and additional weight created by the additional equipment; however, systems utilizing special tread designs have different issues associated with them. For example, as the tire wears, the effectiveness of the tread design in rotating the wheel may be compromised. Also, the tread design used to rotate the wheel may interfere with other purposes for having a tread (e.g., for directing water away from the tread), and the torque create by the tread is limited in that the tread is still part of a substantially flat surface. There is, therefore, a need for an improved aircraft wheel that is capable of producing substantial torque to pre-rotate the wheel without requiring extensive refitting/redesign of the wheel assembly and altering the effectiveness of the tread on the tire. BRIEF SUMMARY OF THE INVENTION

Embodiments of the invention address deficiencies of the art in respect to aircraft wheel assemblies and provide a novel and non-obvious aircraft wheel system for pre-rotating the wheel prior to an aircraft touching down. The aircraft wheel assembly includes a hub and a tire. The hub is adapted to be connected to a shaft, and the tire is around the hub and has a bearing surface and opposing side surfaces. A plurality of airfoils are attached to either one or both of the side surfaces. The plurality of airfoils may be evenly distributed about the side surface(s), and the plurality of airfoils may be integrally formed with the side surface(s). The plurality of airfoils may extend substantially perpendicular to the side surface(s). A ratio of a width of the tire without the plurality of airfoils to a width of the tire with the plurality of airfoils may be less than 0.93.

By locating the airfoils on the side surfaces of the tire and farther away from the wheel shaft, these airfoils generate higher torque than if the airfoils were mounted on the wheel hub. Additionally, by forming the airfoils integrally with the tires using, for example, a rubber compound, the wheel assembly enjoys significant weight savings compared to a configuration in which metal blades (or other devices) are attached to the hub of the wheel to generate pre-rotation of the wheel.

Additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The aspects of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of the invention. The embodiments illustrated herein are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown, wherein:

Figure 1 is a perspective view of an aircraft wheel assembly in accordance with the inventive arrangements;

Figure 2 is a graphical illustration of the forces generated by the airfoils on a tire;

Figures 3A-3D are side views of tires having different airfoil configurations;

Figure 4 is graph showing revolution per minute versus wind speed for the data found in Tables 1 and 2;

Figure 5 is graph showing tire speed versus wind speed for the data found in Tables 1 and 2.

DETAILED DESCRIPTION OF THE INVENTION

An aircraft wheel assembly for an aircraft according to the invention is disclosed in Fig. 1. The aircraft wheel assembly 100 includes a hub 102 and a tire

110. The hub 102 is adapted to be connected to a shaft 104, and the tire 110 is positioned around the hub 102 and has a bearing surface 116 and opposing side surfaces 114. A plurality of airfoils 112 are attached to either one or both of the side surfaces 114. The bearing surface 116 is not limited as to a particular configuration; however, in certain aspects, the bearing surface 116 may include a tread. The airfoils 112 are positioned on the tire 112 so as to pre-rotate the tire 110 while the aircraft is in flight. By locating the airfoils 112 on the side surfaces 114 of the tire 110 and farther away from the shaft 104, these airfoils 112 generate higher torque than if the airfoils 112 were mounted on the hub 102 of the wheel 100. By pre- rotating the tire 112 prior to landing, it is expected that the lifespan of the tire 110 may be increased by at least 10%.

In certain aspects of the wheel assembly 100, the airfoils 112 are evenly distributed about the side surface(s) 114 of the tire 110; however, the wheel assembly 100 is not limited in this manner. By evenly distributing the airfoils 112 about the tire 110, the forces generated by the airfoils 112 are evenly balanced. In other aspects of the wheel assembly 100, the airfoils 112 may extend substantially perpendicular to the side surface(s) 114; although the wheel assembly 100 is not limited in this manner.

Certain characteristics of the airfoils 112, such as number, relative flow angle, type, and size, are not limited as to particular combinations. Depending upon the particular needs of a particular wheel assembly 100 and aircraft, these characteristics may vary. However, in certain aspects of the wheel assembly 100, at least two airfoils 112 are located on a single side surface 114 of the tire 110. In other aspects of the tire 110, a ratio of a width of the tire 110 without the plurality of airfoils 112 to a width of the tire 110 with the plurality of airfoils 112 is less than 0.93, and in other aspects, the ratio is less than 0.88. In yet other aspects of the tire 110, a relative flow angle is between about 10° to about 50°.

Although the tire 110 and airfoils 112 are not limited in the manner in which airfoils 112 are positioned on the tire 110, in certain aspects of the tire 110, the airfoils 112 are integrally formed with the tire 110. For example, shapes for the airfoils 112 can be included within the mold used to manufacture the tire 110. By forming the airfoils 112 from the same material that the tire 110 is formed, for example, a rubber compound, the airfoils 112 weigh less than if formed from a denser material. Also, since fasteners are not required to attach the airfoils 112 to the tire 110 additional weight savings may be realized.

The underlying aerodynamic concept associated with the modifications to the tire 110 can be described with regard to Fig. 2. The airfoil is oriented at a certain angle of attack to the relative incoming velocity, V_rei, which is determined by the vector subtraction as: V_rei = V_M - u. V_M is the incoming velocity or the aircraft flying velocity, and u is the linear rotating velocity of the wheel assembly 100 at the leading edge of the airfoil 112. If the radius of the leading edge is r, then: u = ω r, where ω is angular velocity.

The relative flow angle f between the relative velocity and incoming flow velocity is determined by: f = arctan (u/V_inf). If the wheel front surface rotating linear speed is equal to the incoming flow speed, f = 45°, which is what occurs when the speed of the tire 110 matches the flying speed of the aircraft. Matching the speed of the tire 110 to the speed of the aircraft at touch down is desirable, but not necessary, to reduce skidding between the tire 110 and the surface upon which the tire 110 contacts. In certain aspects, to avoid over-speeding, u may be controlled to be less than VM-

By treating V_M as a constant, f and u have an one-to-one relationship. If the tire speed is larger than the incoming flow speed, f > 45°, the tire is rotating too fast, and the tire speed will be reduced to the flying speed of the aircraft at touch down by friction between the tire 110 and the surface. However, if the tire speed is lower than the incoming flow speed, f < 45°, the tire speed is rotating too slowly, and tire speed will be increased to the flying speed of the aircraft at touch down by the friction between the tire 110 and the surface.

Airfoil orientation may defined by the angle between the chord line and incoming flow direction, β. Lift L is determined by the angle of attack between the relative velocity and the chord line. If f < β, the airfoil 112 has positive angle of attack. If f > β, the airfoil has negative angle of attack. To generate sufficient lift and torque to rotate the tire 110 in the direction of flight, f should remain not greater than β-

EXAMPLES

Figs. 3A-3D respectively illustrate four different types of airfoils that were tested. Figs. 3A-3C are Clark Y airfoils respectively at 15°, 25°, and 45°, and Fig. 3D is a blade (hereinafter Blade 2) having a higher degree of camber than a Clark Y airfoil. Each wheel assembly 100 was made of wax using stereo lithography and tested in a wind tunnel at speeds varying from 0 to 100 miles per hour (MPH) at intervals of 5 MPH.

The wheel assembly 100 has an outer diameter of 6 inches and a thickness of 2.22 inches. With these dimensions, the wheel assembly 100 is approximately a 1:8 scale of a Boeing 747 wheel, which has an outer diameter of 49 inches and a thickness of 18 inches. The airfoils 112 attached to the side walls 114 of the tires 110 added 0.15 inches to each side of the tire 110, which increase the total tire thickness by about 13.5%. The diameter to thickness ratio of the wheel assembly 100 with the airfoils 112 attached to the side wall 114 of the tires 110 is about 2.72, which is comparable to the actual diameter to thickness ratio of a typical tire used with a Boeing 747.

The wheel assembly 100 using Clark Y airfoil at 45° is approximately twice as heavy as the wheel assembly 100 using the Blade 2 airfoil. Also, although both designs used 16 airfoils 112 on each side 114 of the tires 110, the Clark Y airfoil at 45° design has airfoils 112 with a thickness of about 0.10 inches, and the Blade 2 airfoil design had airfoils 112 with a thickness of about 0.15 inches.

Tables 1 and 2 contain the test results for the Clark Y airfoil at 45° and Blade 2. For each of the measure velocities, the maximum variation is approximately 0.5 MPH. Table 1: Results obtained for Clark Y airfoil at 45^C

Table 1 shows that the Clark Y airfoil at 45° started to rotate at wind speeds of approximately 55 MPH. Table 1 does not include speeds lower than 55 MPH because the tire 110 was not rotating, which is likely because the torque generated by the airfoils 112 was not able to overcome the friction between the wheel assembly 100 and the shaft about which the wheel assembly 100 rotated. As the wind speed increased from 55 MPH to 100 MPH, the revolutions per minute (RPM) of the tire 110 increases somewhat linearly from 490 RPM to 1150 RPM. Also, the speed of the tire 110 increased from 8.8 MPH to 20.65 MPH. The last column of Table 1 shows the ratio of the wind speed to the tire speed. As evident from the computed values, this ratio was substantially constant, having a maximum ratio of 6.2:1, a minimum ratio of 4.8:1, and an average ratio of 5.5:1. Thus, on average, the wind speed was 5.5 times larger than the linear velocity of the tire 110.

Table 2 shows that the Blade 2 airfoil started to rotate at wind speeds of approximately 44 MPH. As the wind speed increased from 44 MPH to 100 MPH, the RPM increases linearly from 675 RPM to 1730 RPM, and the linear speed of the tire increases from 12.1 MPH to 31 MPH. The ratio of the wind speed to tire speed varies from 3.9:1 to 3.2:1, and has an average ratio of 3.5:1. Thus, on average, the wind speed was 3.5 times larger than the linear velocity of the tire 110.

Figure 4 is a graphical representation of the data found in Tables 1 and 2 and shows a relationship between tire speed (MPH) and wind speed (MPH). Figure 5 is similar to Figure 4 and shows a relationship between tire speed (RPM) and wind speed (MPH). As graphically illustrated in Figs. 4 and 5, Blade 2 has a higher speed

(RPM or MPH) than Clark Y at 45° for any given wind speed. At lower speeds, the difference between Blade 2 and Clark Y at 45° is less than at higher speeds, as evident from the slopes of both lines. The slope of the equations for each trend line shows a change in RPM or MPH for a unit change in wind speed. The slope of the test of the line using the test data from Blade 2 is higher than the slope of the line using the test data from Clark Y at 45° by a factor of 1.35. The Clark Y airfoil at 45° rotates slower than the Blade 2 airfoil. This may be explained in that the Clark Y airfoil 45° is twice as heavy as the Blade 2 airfoil; and thus, additional force is necessary to overcome the inertia of the tire 110 and rotation friction between the tire 110 and the shaft. Another factor in determining at what air speed the tire 110 begins to rotate is the total frontal area of the tire 110, which is increased by adding the airfoils 112 to the side walls 114. Both designs tested involved the use of 16 blades on each side, but the thickness of those airfoils

112 were 0.10 inches, for the Clark Y airfoil and 0.15 inches for the Blade 2 airfoil.

Thus, the Blade 2 airfoil has a total of 0.1 inches more in blade thickness for creating the net force to rotate the tire 110.

Claims

What is claimed is:

1. An aircraft wheel assembly 100, comprising: a hub 102 adapted to be connected to a shaft 104; a tire 110 around the hub 102 and having a bearing surface 116 and opposing side surfaces 114; and a plurality of airfoils 112 attached to at least one of the side surfaces 114.

2. The aircraft wheel assembly 100 of claim 1, wherein each of said opposing sides surfaces 114 includes a plurality of opposing airfoils 112.

3. The aircraft wheel assembly 100 of claim 1, wherein the plurality of airfoils

112 are evenly distributed about the at least one of the side surfaces 114.

4. The aircraft wheel assembly 100 of claim 1, wherein the plurality of airfoils 112 are integrally formed with the at least one of the side surfaces 114.

5. The aircraft wheel assembly 100 of claim 1, wherein the at least one of the side surfaces 114 includes at least two of the airfoils 112.

6. The aircraft wheel assembly 100 of claim 1, wherein the plurality of airfoils 112 extend substantially perpendicular to the at least one of the sides surfaces 114.

7. The aircraft wheel assembly 100 of claim 1, wherein a ratio of a width of the tire 110 without the plurality of airfoils 112 to a width of the tire 110 with the plurality of airfoils 112 is less than 0.93.

8. An aircraft tire 110 adapted to be connected to a hub 102 of an aircraft wheel assembly 100, comprising: a bearing surface 116; opposing side surfaces 114; and a plurality of airfoils 112 attached to at least one of the side surfaces 114.

9. The aircraft tire 110 of claim 8, wherein each of said opposing sides surfaces 114 includes a plurality of opposing airfoils 112.

10. The aircraft tire 110 of claim 8, wherein the plurality of airfoils 112 are evenly distributed about the at least one of the side surfaces 114.

11. The aircraft tire 110 of claim 8, wherein the plurality of airfoils 112 are integrally formed with the at least one of the side surfaces 114.

12. The aircraft tire 110 of claim 8, wherein the at least one of the side surfaces 114 includes at least two of the airfoils 112.

13. The aircraft tire of claim 8, wherein the plurality of airfoils 112 extend substantially perpendicular to the at least one of the sides surfaces 114.

14. The aircraft tire of claim 8, wherein a ratio of a width of the tire 110 without the plurality of airfoils 112 to a width of the tire 110 with the plurality of airfoils 112 is less than 0.93.

15. A method of manufacturing an aircraft tire 110, comprising the step of: integrally forming a plurality of airfoils 112 to at least one of opposing side surfaces 114 of the tire 110.

16. The method of claim 15, wherein each of said opposing sides surfaces 114 includes a plurality of opposing airfoils 112.

17. The method of claim 15, wherein the plurality of airfoils 112 are evenly distributed about the at least one of the side surfaces 114.

18. The method of claim 15, wherein the at least one of the side surfaces 114 includes at least two of the airfoils 112.

19. The method of claim 15, wherein the plurality of airfoils 112 extend substantially perpendicular to the at least one of the sides surfaces 114.

20. The method of claim 15, wherein a ratio of a width of the tire 110 without the plurality of airfoils 112 to a width of the tire 110 with the plurality of airfoils 112 is less than 0.93.