The present invention is directed to a unique foldable winglet assembly adaptable for use with an aircraft for maximizing the wing span of the aircraft during cruise operation while reducing wing bending moment during extreme flight maneuvers. A foldable winglet is pivotally joined to the aircraft wing and is rotatable during flight between a retracted position and a fully extended position. An actuator is mounted on the aircraft wing and attached to the foldable winglet. When the aircraft reaches cruise operation, the actuator can be manually or automatically energized to pivot the winglet from a substantially vertical, retracted position to a fully extended position wherein the winglet becomes an extension of the wing. During cruise, the wing and winglet form an enlarged wing that serves to maximize lift of the aircraft. When loads more severe than would occur at or near cruise, such as dive, are encountered, the loads overcome the action of the actuator and pivot the winglet to its initial, vertical position. This action, serves to reduce the bending moment acting on the wing as well as increase aerodynamic efficiency of the aircraft.

BACKGROUND OF THE INVENTION 
The present invention relates generally to the concept of airplanes having 
folding winglets, and more particularly, to winglet assemblies which can 
be extended during cruise to increase span and automatically/passively 
retracted to an upright position as needed to reduce the wing bending 
moment and aircraft weight when subjected to large loads at conditions 
such as dive. 
Because of the reduced size of the flight deck and reduced hangar space, it 
has long been known to fold the wings of fighter aircraft when stored 
onboard aircraft carriers. Such aircraft normally include a power driven 
actuator system which functions to move an outboard portion of the 
aircraft wing between an extended position suitable for flight and a 
retracted storage position. U.S. Pat. No. 5,310,138 entitled "Wing Fold 
Actuator System for Aircraft" issued May 1994 to Thomas F. Fitzgibbon is 
believed to be typical of such an aircraft. It is noted that the actuator 
system is provided to pivot the wing from a folded position when stored to 
an extended position prior to flight. The disclosure of the '138 patent is 
herein incorporated by reference. There is no suggestion in the '138 
patent of pivoting the wing between deployed and retracted positions 
during operation of the aircraft. 
It is known that having an aircraft's winglets extend at an angle to the 
remaining portion of the wing can affect the flight characteristic of the 
aircraft. U.S. Pat. No. 5,072,894 entitled "Apparatus and Method for 
Increasing the Angle of Attack Operating Range of an Aircraft" issued 
December 1991 to Daniel R. Cichy, the disclosure of which is herein 
incorporated by reference, teaches that the by employing vertically 
downwardly extending tip fins, it is possible to increase the angle of 
attack operating range of an aircraft. At high angles of attack, the tip 
fins extend approximately 90.degree. to the inboard portion of the wing. 
There is no suggestion of raising the tip fins above the wing nor is there 
any suggestion of extending the tip fins during flight. 
Commercial aircraft have been known to employ foldable wing tips which can 
be raised to reduce the landing space occupied by the aircraft. By raising 
the wing tips, aircraft having large wings, such as the Boeing 777, can 
reach current loading gates that would otherwise be unavailable. A 
latching mechanism for locking the wing tips in their upright position 
when on the ground is taught in U.S. Pat. No. 5,427,329 entitled "Locking 
Hydraulic Latch Pin Actuator" issued June 1995 to Michael E. Renzelmann et 
al, the disclosure of which is herein incorporated by reference. A 
hydraulic actuator is employed to move the primary lock member between 
locked and unlocked positions when the aircraft is on the ground. There is 
no suggestion in the '329 patent that the wing tips are movable when the 
aircraft is in flight. 
None of the cited patents employs a wing including a foldable winglet that 
can be folded while the aircraft is in flight. As a result, none of the 
cited patents can take advantage of the extended winglets during cruise 
and folded winglets during more severe load conditions. 
The present invention overcomes the size and structural weight problems 
associated with a large span while retaining the reduced drag benefit of a 
large span during cruise. 
SUMMARY OF THE INVENTION 
The present invention is directed to an articulating winglet which is 
adaptable for use on commercial aircraft. The winglet consists of a 
winglet attached to a wing by a conventional hinge. An actuator mounted in 
the wing assembly can be powered to raise or lower each winglet about its 
hinge. Where airport compatibility issues restrict the wing span of the 
aircraft, the winglets can be rotated to vertical or nearly vertical 
positions. 
Once the aircraft has climbed to its cruise altitude, the actuators can be 
energized to extend the winglets. As long as the aircraft remains near 
cruise conditions, the winglets will remain extended, reducing the drag 
and thereby increasing the aerodynamic efficiency of the aircraft. In 
effect, the winglets allow use of greater span than do wings of 
conventional design. This results in aircraft with articulating winglets 
outperforming aircraft with standard wing configurations. 
By design, the actuators are capable of holding the winglets in their 
extended positions only when confronting aerodynamic loads no more severe 
than the conditions encountered at or slightly beyond cruise condition. 
When the aircraft begins to perform a maneuver that would substantially 
increase the load condition on the wing, the aerodynamic loads will 
overcome the actuators and automatically return the winglets to their 
nearly vertical positions. This greatly reduces the structural weight 
penalty encountered by the winglets when extended. 
The present invention increases the aerodynamic efficiency of the aircraft 
by extending the winglets during cruise to reduce drag. At the same time, 
automatic retraction of the winglets i.e., passive load alleviation, 
reduces the wing bending moment and aircraft weight as occurs during 
severe load conditions, without imposing an undue weight penalty.

DETAILED DESCRIPTION OF THE INVENTION 
While the present invention is described herein with reference to 
illustrative embodiments for particular applications, it should be 
understood that the invention is not limited thereto. Those having 
ordinary skill in the art and access to the teachings provided herein will 
recognize additional modifications, applications, and embodiments within 
the scope thereof and additional fields in which the present invention 
would be of significant utility. 
With reference now to FIG. 1, there can be seen a schematic view of a jet 
aircraft having winglets constructed in accordance with the present 
invention. Aircraft 10 includes a pair of wings 11 having at their 
outboard ends a pair of foldable winglets 12 and 14. The solid lines show 
the winglets 12 and 14 in their upwardly-folded or retracted positions. 
The winglets assume this position when aircraft 10 is parked to load and 
offload passengers at a conventional airport. In addition, the winglets 12 
and 14 will assume their retracted positions when the aircraft 10 is 
undergoing severe flight loads as will be explained below. 
The dashed lines 12a and 14a show the same winglets fully extended and 
aligned with the axis of the wing inboard portions 20 and 22, 
respectively. As will be explained, the winglets may assume the positions 
shown in 12a and 14a when there is no restriction on the size of the 
airport requiring the winglets to be retracted. More importantly, when the 
aircraft reaches cruise, the winglets may be extended to the positions 
shown at 12a and 14a in order to maximize lift while reducing drag. Each 
of the winglets 12 and 14 is attached to an end of a wing 11 by means of a 
hinge assembly 15 positioned between a wing and winglet. Each hinge 
assembly 15 preferably extends substantially parallel to a longitudinal 
axis of aircraft 10 in order that each of the winglets 12 and 14 may be 
pivoted into vertical or nearly vertical positions with respect to the 
substantially horizontal positions of the wings 11. 
FIG. 2 depicts a conventional mechanism for operating the winglets 12 and 
14. An actuator 24 may be selectively energized to rotate the winglets 
between the retracted positions 12 and 14 and their extended positions 12a 
and 14a. Actuator 24 may comprise any well known assembly which may be 
mechanical, fluid, electrical or a combination thereof. 
One such well known actuator adaptable for moving a portion of an aircraft 
wing 11 to control the outboard ailerons is manufactured by Parker Bertea, 
employed on the MD-11 and identified as part number P/N BRG002. In order 
to prevent damage to the aircraft during extreme operating conditions of 
the MD-11, such as may occur during dive or high speed buffeting, the 
outboard ailerons are designed to float trailing edge upward. This float 
is not commanded by any active load alleviation system. Rather, the 
actuators BRG002 employed to control the position of the ailerons are 
unable to resist the aerodynamic hinge moments acting on the ailerons that 
arise during dive or high speed buffeting. As a result, the moments acting 
on the aileron during extreme conditions overpower the torque supplied by 
the actuator and pivot the aileron to a predetermined upward float 
position in an attempt to return the aircraft to a more stable flight 
condition. It has been discovered that the same type of actuator employed 
for aileron control in the MD-11 can be utilized in a new and unique way 
for controlling the movement of articulating winglets attached to the 
aircraft wings. Regardless of the form of actuator 24, its operation in 
controlling the winglets is the same. 
During operation, it will be assumed that aircraft 10 is on the ground and 
has taxied to the terminal to load passengers. Winglets 12 and 14 are in 
their vertical or almost vertical positions in order to minimize ground 
space at the terminal. Once aircraft 10 has been loaded, taken-off and 
climbed to near cruising altitude, actuator 24 is selectively energized to 
pivot the winglets from their fully retracted positions to their fully 
extended positions 12a and 14a. Actuator 24 may be actuated by the flight 
crew depressing button 26 or automatically actuated by a sensor 28 shown 
in phantom when it determines that the aircraft 10 is at or near cruise 
condition. Regardless of what energizes actuator 24, pivoting the winglets 
12 and 14 to their extended positions acts to maximize the wing span of 
aircraft 10 while, at the same time, reducing the drag effect of the 
vertically extending winglets, thereby improving the aerodynamic 
efficiency. As aircraft 10 continues in cruise, the winglets 12 and 14 
remain in their fully extended positions 12a and 14a under pressure of 
actuators 24. 
It is important to note that winglets 12 and 14 are not locked in their 
extended positions but only remain extended as long as the torque supplied 
by actuators 24 to extend the winglets is greater than any opposing 
aerodynamic moment tending to rotate the winglets back to their retracted 
positions. Each actuator 24 is carefully calibrated to assure that it can 
supply adequate torque to force a winglet to remain extended when the 
aircraft is in cruise. However, once a maneuver begins which increases the 
load on the wings, the aerodynamic moment of the winglet will overcome the 
effect of actuators 24 and pivot the winglets from their extended 
positions back to their retracted positions. This passive design feature 
causes the winglets to automatically retract in response to extreme loads, 
thereby reducing the wing bending moment and aircraft weight. Because the 
forces acting on the wings function to rotate the winglets, the effect is 
that of passive load alleviation which eliminates the need to command 
actuators 24 to return the winglets to their retracted, nearly vertical 
positions. 
Actuators 24 supply the torque for extending the winglets and the dynamic 
load conditions encountered during flight supplies the power for 
retracting the winglets. By calibrating the torque capability supplied by 
actuators 24, it is possible to dispense with a separate locking mechanism 
for holding the winglets in their extended positions. However, it is 
considered within the scope of the present invention to incorporate a 
removable lock which can be withdrawn when it becomes necessary to pivot 
the winglets between their retracted positions 12 and 14 and their 
extended positions 12a and 14a, respectively. 
By design, the actuators 24 are capable of holding the winglets in their 
extended positions only for structural load conditions no more severe than 
encountered at or slightly beyond cruise conditions. When more severe 
conditions arise, the aerodynamic moments will overpower the torque 
supplied by actuators 24, causing the winglets to move in a steady manner 
towards their retracted positions. This feature of the present invention 
reduces the structural weight penalty otherwise resulting from extending 
the winglet. 
In general, although a preferred embodiment of the present invention has 
been described in detail hereinabove, it should be clearly understood that 
many variations and/or modifications of the basic inventive concepts 
herein taught which may appear to those skilled in the pertinent art will 
still fall within the spirit and scope of the present invention, as 
defined in the appended claims.