ACTIVE TWIST HOLLOW BEAM SYSTEM

• US 20130064666A1
• Filed: 08/21/2012
• Published: 03/14/2013
• Est. Priority Date: 07/29/2008
• Status: Active Grant

• Current Assignee: The Government Of The United States Of America, As Represented By The Secretary Of The Navy
• Original Assignee: The Government Of The United States Of America, As Represented By The Secretary Of The Navy
• Inventors: Thomas, James P., O'Brien, Michael J., Pogue, William R. III
• Granted Patent: US 8,721,282 B2
• Time in Patent Office: Days
• US Class Current: 416/158
• CPC Class Codes: B64C 11/20 Constructional features
• CPC Class Codes: B64C 2027/7222 using airfoil deformation
• CPC Class Codes: B64C 27/72 Means acting on blades
• CPC Class Codes: B64C 3/52 Warping
• CPC Class Codes: F01D 5/148 Blades with variable camber, e.g. by ejection of fluid
• CPC Class Codes: F03G 7/06 using expansion or contraction of bodies due to heating, cooling, moistening, drying or the like using thermal expansion of non-vaporising liquids F01K
• CPC Class Codes: Y02T 50/10 Drag reduction
• CPC Class Codes: Y02T 50/30 Wing lift efficiency
• CPC Class Codes: Y02T 50/60 Efficient propulsion technologies, e.g. for aircraft

Abstract

A system for actively controlling the span-wise rotational twist of a hollow beam along its longitudinal axis, including a hollow beam structure having a leading edge and a trailing edge region, the beam being split along its length, an actuator arranged between split surfaces of the beam, the actuator adapted to move the split surfaces in a longitudinal direction relative to each other, inducing a twist in the beam. The hollow beam is affixed to an external structure at one or both ends, with only the zero warping displacement points of the beam being attached to the external structure, material or device. In one embodiment, the actuator is a plurality of solid blocks with high thermal expansion coefficients arranged between frames of the split surfaces of the beam, with alternating blocks being heated by resistance heaters to cause expansion in the spanwise longitudinal direction.

Claims

1. An active twist hollow beam system comprising:

a hollow beam having a first end attached to an external structure, the beam being split along a longitudinal length of the beam; and

an actuator arranged to move split surfaces of the beam in a longitudinal direction relative to each other along the longitudinal length of the beam, inducing a twist in the beam,

the system configured such that the actuator moves the split surfaces in the longitudinal direction relative to each other,

wherein a cross section of the first end has a plurality of zero-warping displacement locations and maximum warping displacement locations between the zero warping displacement locations,

the first end being attached to the external structure at the zero-warping displacement locations and being free of attachment to the external structure at the maximum warping displacement locations.

2. The system of claim 1, wherein a warping displacement w(s) at a point “

s”

on a cross-section perimeter of the beam on the first end is defined by

3. The system according to claim 2, wherein the torsion constant J is equal to β

L_pt³, wherein L_p is the total length of the cross-section perimeter of the beam, t is the beam thickness, and β

is a constant between 0.14 to 0.33.

4. The system according to claim 2, wherein L_p/t is very large and J is approximated by J=⅓

L_pt³, wherein L_p is the total length of the cross-section perimeter and t is the beam thickness.

5. A system according to claim 1, wherein in operation, a shear warp actuator imposes a twist per unit length of the beam θ

and warping displacement w according to

6. The system according to claim 5, wherein the torsion constant J is approximated by J=β

L_pt³, wherein L_p is the total length of the cross-section perimeter of the beam, t is the beam thickness, and β

is a constant between 0.14 to 0.33.

7. The system according to claim 5, wherein L_p/t is very large and J is approximated by J=⅓

L_pt³, wherein L_p is the total length of the cross-section perimeter and t is the beam thickness.

8. The active twist hollow beam system according to claim 1, wherein the beam has a torsional stiffness equal to an equivalently sized closed cross-section beam, the shear-warp actuator having a resistive shear-warp stiffness K_RESIST, wherein

9. The active twist hollow beam system according to claim 1, wherein the zero warping displacement locations include a location at the leading edge of the airfoil and a location on each side of the trailing edges.

10. The active twist hollow beam system according to claim 1, wherein the beam is attached to the external structure at only the zero warping displacement locations.

11. The system according to claim 1, wherein the actuator is arranged between a first split surface and a second split surface, the actuator including:

solid blocks of material having a linear thermal expansion coefficient of at least 10×

10<sup>−

6</sup> per degree Kelvin,

each of the solid blocks being in contact with an electrical resistance heater, each of the solid blocks being located between at least one protrusions on the first split surface and at least one protrusion on the second split surface,

wherein in operation, the electrical resistance heater heats only alternating solid blocks, causing expansion of the heated solid blocks in the longitudinal direction, thereby moving the split surfaces relative to each other in the longitudinal direction.

12. The system of claim 11, wherein the solid block of material is a metal alloy.

13. The system of claim 11, wherein the solid block of material is an elastomer or polymer, and has a linear thermal expansion coefficient of at least 30×

10<sup>−

6</sup> per degree Kelvin.

14. The system of claim 1, wherein the actuator is arranged between split surfaces of the beam.

15. The system according to claim 1, wherein the beam has an airfoil shape.

16. The system according to claim 1, wherein the split along the longitudinal length of the beam is in the trailing edge of the beam.

17. The system according to claim 1, wherein the split along the longitudinal length of the beam is in a vertical spar of the beam.

18. The system according to claim 1, wherein the actuator is a shear-warp actuator.

19. The system according to claim 1, wherein the beam is an aircraft propeller, wing, control surface or rotor blade.

20. The system according to claim 1, wherein the beam is a helicopter rotor blade, turbine blade, underwater vehicle control surface, or robotic appendage.

21. The active twist hollow beam system according to claim 1, the system comprising a plurality of actuators, each actuator arranged at a beam section at a different longitudinal position along the beam, each actuator independently controlled to induce different twist amounts to the beam sections.

22. The active twist hollow beam system of claim 11, wherein the solid blocks consist essentially of polyethylene.

23. The active twist hollow beam system of claim 1, wherein the actuator comprises thermal actuator blocks and an electrical resistance coil, piezoelectric or magnetostrictive material blocks, a hydraulic actuator, a pneumatic actuator, or a threaded screw extending along the longitudinal direction of the hollow beam.

24. The system according to claim 1, the beam having a first longitudinal spit in a forward section of the beam and having a second longitudinal split in after section of the beam, and the actuator arranged to move the split surfaces of the forward and after sections of the beam in a longitudinal direction relative to each other along the length of the beam, causing the forward and after sections of the beam to warp.

25. The system according to claim 1, wherein the hollow beam has a second end attached to a second external structure at a plurality of zero warping displacement locations, the second end being free of attachment to the second external structure at the maximum warping displacement locations.

26. The system according to claim 1, wherein the second external structure is a beam cap.

27. The system according to claim 1, wherein the attachments between the beam and the external structures at the first and second end are sufficient to transmit applied loads on the beam to the external structures without failure.

28. The active twist hollow beam system according to claim 1, wherein attachment or connection of the beam at the first end and the second end with the external structure, materials, or devices occurs only the zero warping displacement locations.

29. An active twist hollow beam system comprising:

a hollow beam having a first end attached to an external structure, the beam being split along a longitudinal length of the beam; and

an actuator arranged to move split surfaces of the beam in a longitudinal direction relative to each other along the longitudinal length of the beam, inducing a twist in the beam, the actuator positioned between a first split surface and a second split surface of the hollow beam and configured to move the split surfaces in the longitudinal direction relative to each other, the actuator including;

solid blocks of material having a linear thermal expansion coefficient of at least 10×

10<sup>−

6</sup> per degree Kelvin,

each of the solid blocks being in contact with an electrical resistance heater, each of the solid blocks being located between at least one protrusions on the first split surface and at least one protrusion on the second split surface,

wherein in operation, the electrical resistance heater heats only alternating solid blocks, causing expansion of the heated solid blocks in the longitudinal direction, thereby moving the split surfaces relative to each other in the longitudinal direction.

30. The active twist hollow beam system of claim 29, wherein the solid blocks consist essentially of polyethylene.

31. The system of claim 29, wherein the solid block of material is a metal alloy.

32. The system of claim 29, wherein the solid block of material is an elastomer or polymer, and has a linear thermal expansion coefficient of at least 30×

10<sup>−

6</sup> per degree Kelvin.