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Title:
SYSTEM AND METHOD FOR CONTROLLING DYNAMIC ROLLOVER
Document Type and Number:
WIPO Patent Application WO/2017/081604
Kind Code:
A2
Abstract:
An anti dynamic-rollover system for an aircraft is disclosed. The system comprising a landing gear assembly comprising at least one swiveling joint connected between the aircraft and a landing gear wheel. The swiveling joint has a swiveling axis. A method for prevention of dynamic rollover in an aircraft is also disclosed comprising connecting a swiveling joint between the aircraft and a landing gear wheel, wherein the swiveling joint has a swiveling axis, and swiveling the at least one landing wheel about the swiveling axis when side force directed from the outside of the aircraft towards the center of the aircraft and substantially parallel to the ground is exerted on the portion of the wheel's circumference touching the ground wherein the swiveling axis does not cross the rolling axis of the wheel.

Inventors:
YOELI RAPHAEL (IL)
Application Number:
PCT/IB2016/056713
Publication Date:
May 18, 2017
Filing Date:
November 08, 2016
Export Citation:
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Assignee:
URBAN AERONAUTICS LTD (IL)
International Classes:
B64C25/34
Download PDF:
Claims:
CLAIMS

1. An and dynamic-rollover system for an aircraft, comprising:

a landing gear assembly comprising at least one swiveling joint connected between the aircraft and a landing gear wheel, and having a swiveling axis; and

the at least one landing wheel coupled to the swiveling joint, wherein the swiveling axis does not cross the rolling axis of the wheel,

wherein the at least one landing wheel is adapted to swivel about the swiveling axis when side force directed from the outside of the aircraft towards the center of the aircraft and substantially parallel to the ground is exerted on the portion of the wheel's circumference touching the ground.

2. The system according to claim 1, further adapted to prevent swiveling of the landing wheel beyond the direction corresponding to wheeling parallel to the longitudinal axis of the aircraft a side force directed from the center of the aircraft towards the outside of the aircraft and substantially parallel to the ground is exerted on the portion of the circumference of the landing wheel touching the ground.

3. The system according to claim 1, further comprising orienting means configured to allow rotating the wheel about the swiveling axis towards the direction of movement of the aircraft on the ground.

4. The system according to claim 1, wherein the swiveling axis is a vertical axis.

5. A method for prevention of dynamic rollover in an aircraft, the method comprising:

connecting a swiveling joint between the aircraft and a landing gear wheel, wherein the swiveling joint has a swiveling axis;

swiveling the at least one landing wheel about the swiveling axis when side force directed from the outside of the aircraft towards the center of the aircraft and substantially parallel to the ground is exerted on the portion of the wheel's circumference touching the ground,

wherein the swiveling axis does not cross the rolling axis of the wheel.

6. The method according to claim 5, further comprising directing the at least one

landing wheel towards the direction of movement of the aircraft when on the ground.

7. An anti dynamic-rollover system for an aircraft, comprising: a landing gear assembly comprising at least one swiveling joint connected between the aircraft and a landing gear wheel, and having a swiveling axis; and

the at least one landing wheel coupled to the swiveling joint, wherein the swiveling axis does not cross the rolling axis of the wheel,

wherein the at least one landing wheel is adapted to swivel about the swiveling axis when side force directed from the outside of the aircraft towards the center of the aircraft and substantially parallel to the ground is exerted on the portion of the wheel's circumference touching the ground, and,

wherein the at least one landing wheel further comprising orienting means configured to align the wheel about the swiveling axis to direction parallel to the longitudinal axis of the aircraft when the aircraft is airborne.

8. The anti dynamic-rollover system of claim 7 wherein aligning the wheel with a direction parallel to the longitudinal axis of the aircraft is not performed not before the taking off aircraft has passed at least pre-defined time from takeoff or predefined height above ground.

Description:
SYSTEM AND METHOD FOR CONTROLLING DYNAMIC ROLLOVER

FIELD OF THE INVENTION

[001] The present invention relates to aircraft safety equipment More particularly, the present invention relates to safety equipment for prevention of dynamic rollover in aircraft.

BACKGROUND OF THE INVENTION

[002] Many aircraft, and particularly helicopters and other types vehicles capable of vertical takeoff and landing, are susceptible to lateral rolling tendency, usually called dynamic rollover, when lifting off the surface (or during final phase of landing). For dynamic rollover to occur, the aircraft has to have a pivot point on the landing pad/ground to which its landing gear is pivotally engaged, and it further has to be subject to lateral force(s), such as side-wind or side-acting component of the lifting force. When these conditions exist and at least some of the lifting force of the aircraft is still acting (i.e. the aircraft is not leaning with full weight on the ground) an initial roll movement sideward may occur about the pivot point This can happen for a variety of reasons, including the failure to remove a tie down or landing gear securing device, or if the landing gear contacts a fixed object while translating sideward in a hover very close to the ground, or if the landing gear is stuck in ice, or mud. Whatever the cause, if the contact point of the landing gear with the ground becomes a pivot point, dynamic rollover may occur if proper corrective maneuver is not timely provided. For example, if the right skid contacts an object and becomes the pivot point while the helicopter starts rolling to the right even with full left cyclic control applied, there may be strong enough right-side component of the main rotor thrust vector that will provide right-side moment which will contribute to the tendency of rolling to the right. When the helicopter crosses a peak point on the graph of acting forces - lateral, vertical and gravity forces - combined with the speed of the angular movement dynamic rollover occurs. Dynamic rollover usually takes place when the aircraft is 'light on its landing gear', i.e. a large portion of the aircraft' s weight is supported by the aircraft' s hovering force and only small portion is supported by the landing gear.

[003] Beyond that peak point, the main rotor thrust (of the helicopter) and/or side wind continues to provide rolling momentum and any recovery is impossible (with the helicopter rolling on its side). Dynamic rollover can occur in both skid and wheel equipped aircraft and all types of rotor systems or other systems producing vertical lifting force. It would therefore be advantageous to provide safety equipment in order to prevent the dynamic rollover phenomenon. SUMMARY OF THE INVENTION

[004] An object of the present invention is to provide safety equipment for aircraft, which overcomes the limitations and disadvantages of prior aircraft

[005] A further object of the present invention is to provide a method for prevention of dynamic rollover in aircraft

[006] There is thus provided, in accordance with a preferred embodiment of the present invention, an ami dynamic-rollover system for an aircraft, comprising a landing gear assembly comprising at least one swiveling joint connected between the aircraft and a landing gear wheel, and having a swiveling axis and the at least one landing wheel coupled to the swiveling joint, wherein the swiveling axis does not cross the rolling axis of the wheel, and wherein the at least one landing wheel is adapted to swivel about the swiveling axis when side force directed from the outside of the aircraft towards the center of the aircraft and substantially parallel to the ground is exerted on the portion of the wheel's circumference touching the ground.

[007] According to additional embodiment the system is further adapted to prevent swiveling of the landing wheel beyond the direction corresponding to wheeling parallel to the longitudinal axis of the aircraft a side force directed from the center of the aircraft towards the outside of the aircraft and substantially parallel to the ground is exerted on the portion of the circumference of the landing wheel touching the ground.

[008] According to additional embodiment the system further comprises orienting means configured to allow rotating the wheel about the swiveling axis towards the direction of movement of the aircraft on the ground.

[009] According to yet additional embodiments the swiveling axis is a vertical axis.

[010] Furthermore a method for prevention of dynamic rollover in an aircraft is thus provided, the method comprising connecting a swiveling joint between the aircraft and a landing gear wheel, wherein the swiveling joint has a swiveling axis, and swiveling the at least one landing wheel about the swiveling axis when side force directed from the outside of the aircraft towards the center of the aircraft and substantially parallel to the ground is exerted on the portion of the wheel's circumference touching the ground, wherein the swiveling axis does not cross the rolling axis of the wheel.

[011] According to additional embodiment the method further comprising directing the at least one landing wheel towards the direction of movement of the aircraft when on the ground.

[012] According to yet further embodiment an anti dynamic-rollover system for an aircraft is thus provided comprising a landing gear assembly comprising at least one swiveling joint connected between the aircraft and a landing gear wheel, and having a swiveling axis and the at least one landing wheel coupled to the swiveling joint, wherein the swiveling axis does not cross the rolling axis of the wheel, wherein the at least one landing wheel is adapted to swivel about the swiveling axis when side force directed from the outside of the aircraft towards the center of the aircraft and substantially parallel to the ground is exerted on the portion of the wheel's circumference touching the ground, and wherein the at least one landing wheel further comprising orienting means configured to align the wheel about the swiveling axis to direction parallel to the longitudinal axis of the aircraft when the aircraft is airborne.

[013] According to further embodiment the anti dynamic-rollover system wherein aligning die wheel with a direction parallel to the longitudinal axis of the aircraft is not performed before the taking off aircraft has passed at least pre-defined time from takeoff or predefined height above ground.

BRIEF DESCRIPTION OF THE DRAWINGS

[014] The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the appended drawings in which:

[015] Fig. 1 shows a frontal view of a commercially available helicopter, tilting on its side;

[016] Fig.2 shows a frontal view of an aircraft capable of vertical takeoff, tilting on its side;

[017] Fig. 3 illustrates frontal and side views of swiveling landing gear, according to a preferred embodiment of the present invention;

[018] Fig. 4 illustrates a frontal view of an anti-dynamic rollover system, with a swiveling landing gear assembled onto the aircraft, according to another preferred embodiment of the present invention;

[019] Figs.5 A -SC depict an aircraft with vertical takeoff capability subject o side forces keeping equilibrium of tilting forces using anti roll-over system, according to a further preferred embodiment of the present invention;

[020] Figs. 5D-5F depict an aircraft with vertical takeoff capability subject o side forces avoiding dynamic roll-over using anti roll-over system, according to a further preferred embodiment of the present invention;

[021] Fig.6A illustrates a schematic top view of the landing gear of the aircraft of Fig. SA when side force starts acting on the landing wheel due to side acting forces, according to a further preferred embodiment of the present invention; and

[022] Fig. 6B illustrates a schematic top view of the landing gear of the aircraft of Rg. 5A in an intermediate state while a counter force exerted upon the landing wheel causes its swiveling, according to a further preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE PRESENT INVENTION

[023] Reference is now made to fig. 1, which shows a frontal view of a commercially available helicopter, generally designated 10, tilting on its side and illustrating the dynamic rollover phenomenon. The helicopter 10 has a rotor 12 and landing gear 14 (e.g. skids), wherein the helicopter 10 tilts on its side upon the landing gear 14 (e.g. skid). Such tilting may occur as a result of crosswinds, andVor maneuvering by the pilot (hat produces side component of the lifting force, while the weight of helicopter 10 is partially supported by the ground 4, with the rotor 12 providing lift force 13 which is smaller but close to die weight of helicopter 10 acting at the center of gravity CG (note that the arrows representing the acting forces are not drawn to a scale. For example, lift force 13 is drawn relatively long, in order for its horizontal component, 13B, will be clearly visible in the drawing). It should be noted that the general direction of the thrust (created by the rotor 12) is indicated with an arrow 13, which is substantially perpendicular to the rotor 12. Thrust 13 may be represented by its vertical component 13A and its horizontal component 13B.

[024] The contact between the landing gear 14 and the ground 4, creates a pivot point 11. As thrust 13 grows bigger and/or as thrust 13 is directed more to the right of the page, its horizontal component 13B grows similarly, thus providing a growing rolling momentum. As a result, the helicopter 10 may tilt further about the pivot point 11 , until the combination of side-acting forces is large enough to move the center of gravity of helicopter 10 beyond an imaginary vertical line passing through pivot point 11. At that point the dynamic rollover phenomenon occurs (indicated with corresponding arrows). It should be noted that at the pivot point 11, the helicopter 10 experiences a counter-force having a horizontal component IS, which is exerted by the ground 4 on the landing gear 14 (due to friction, blocking protrusion or other local structure that holds landing gear 14 from moving away from pivot point 11. The combined linear forces at pivot point 11 sum to zero (since there is no relative linear movement of landing gear 14 with respect to pivot point 11). The sum of moments about pivot point 11, however, is different from zero and as a result rotating force acting about pivot point 11 on helicopter 10 to the right of the page, thereby causing it to rollover.

[025] Reference is now made to Fig. 2, which shows a frontal view of a vertical takeoff aircraft, generally designated 20, tilting on its side and illustrating the various forces involved in causing the dynamic rollover phenomenon. Similarly to the commercially available helicopter 10 (as shown in Fig. 1 ), the aircraft 20 has at least one rotor 22 or any other system capable of producing vertical lifting forces, and landing gear 24 (e.g. wheels), wherein a ground contact point 21 of aircraft 20 may be formed or established (e.g. when landing gear 24 is stuck in the mud, or leans sideward on a stone or tied down), which may prevent side drifting or sliding or rolling of aircraft 20, thereby causing side-tilting of the aircraft on its side about the contact point of landing gear 24 (e.g. a wheel) with the ground. Under Newton's third law of motion when aircraft 20 tilts about tilting point 21, a counter force is applied on landing gear 24, having a horizontal component 21A. The counter force acting at point 21 is parallel and equal to the combination of tilting forces exerted on aircraft 20. The direction of me counter force 21 A is therefore opposite to the horizontal component of the tilting forces.

[026] It is appreciated that the dynamic rollover phenomenon can occur in various types of vertical take-off and landing aircrafts, generally having substantially vertically acting lifting force that may either be close to zero or on the other extreme close to or even larger than the weight of the aircraft, and not just helicopters. Such aircraft may be provided with one, two or more rotors or fans, or jet-based lifting force power sources or the like. Similarly, such aircraft may have their vertical lift sources of power arranged side-by-side, in tandem or otherwise. These aircrafts may be equipped with rotor having long blades (which extend outside of the dimensions of the body of the aircraft), or having rotors or fans with short blades (which are confined within die dimensions of the aircraft's body). Accordingly, the various types of vertical takeoff and landing aircrafts may have wide range of dynamic reaction to corrective maneuverings. For example. VTOL aircraft with short blades will typically have a more dynamic nature of reaction than a VTOL aircraft with long blades, h will be noted that a general solution according to embodiments of the present invention may be usable for aircrafts that are capable of vertical takeoff and landing and of hovering near the ground 4, and are in risk of dynamic rollover. For instance, aircraft 20 may be an unmanned aerial vehicle (UAV) with payload ranging from few hundreds of grams, similarly to commercially available quadcopters, to hundreds of kilograms and also to all vertical takeoff and landing aircraft manned or unmanned that are configured after or similar to the classic helicopter configuration. It will be further noted that the risk of evolving of dynamic rollover is high during the beginning of a vertical takeoff, when the aircraft reduces its actual weight on the ground/landing pad and only one of either the right or the left main landing gear assemblies touches the ground. The risk for dynamic rollover is further high when the aircraft at the final part of vertical landing. Each of these scenarios is typically very short (as short as few seconds). As a result, applying of corrective maneuvering commands may be difficult, specifically if the aircraft is remotely controlled.

[027] It should be noted that the general direction of the thrust (created by the rotor(s) 22) is indicated with an arrow 23, which is substantially perpendicular to an imaginary line connecting the left and right bottom portions of landing gear 24 of the aircraft 20. While the aircraft 20 tilts about the tilting point 21, the dynamic rollover phenomenon occurs when the aircraft 20 experiences drift and/or roll forces due to side wind, and/or the movement in the direction of the rotor's thrust 23 further sideways and/or due to the increasing of the thrust 23 and a counter force 21A is exerted at the pivot point 21 (collectively denoted side-rolling or laterally-acting momentums), until the combined rolling momentums are large enough to cause rollover (indicated with corresponding arrows). Therefore, by changing the conditions at the pivot point 21, the dynamic rollover phenomenon may be better controlled and eventually prevented. For example, by limiting the size of counter force 21A exerted at pivot point 21 in response to the side rolling force, dynamic roll-over may be prevented.

[028] Reference is now made to Fig. 3, which illustrates frontal and side views of landing gear, generally designated 34, according to a preferred embodiment of the present invention. The landing gear 34 is intended to prevent dynamic rollover in aircraft, further described hereinafter. The landing gear 34 may comprise a strut 31 connectable to the body of the aircraft, a swiveling landing wheel 30, and a swiveling joint 32 connecting strut 31 to swiveling fork 35 accommodating swiveling wheel 30. With the swiveling joint 32, wheel 30 may yaw or turn around a substantially vertical swiveling axis 33 indicated with a dashed line in Fig. 3. For example, wheel 30 may have optimal performance when the applied side force (e.g. due to a cross wind) is in the range of 10%- 100% of the full weight of the attached vehicle. Preferably, swiveling axis 33 does not cross roll axis 30A of the wheel 30 in order to allow the required swiveling operation of the landing gear 34 in response to counter forces exerted on wheel 30 via tilting point 4A. Thus, rolling axis 30A of wheel 30 is at a distance Dl from the vertical swiveling axis 33. The rolling axis of the wheel 30 is indicated by a dashed line and is denoted as 30A. It is appreciated that the contact point between the wheel 30 and the ground 4 (denoted 4A) is at the bottom of the wheel 30 and therefore also at a distance of Dl from the vertical swiveling axis 33.

[029] In some embodiments, the swiveling axis is not exactly vertical but rather is slightly tilted from the vertical line, whereby such design may provide a significant advantage with stabilizing forces around the swiveling axis.

[030] Reference is now made to Fig. 4, which illustrates a frontal view of an anti-dynamic rollover system, generally designated 40, with a landing gear 34 assembled onto the aircraft 20, equipped with a swiveling wheel, according to a preferred embodiment of the present invention. It is appreciated that once the landing gear 34 is assembled onto the aircraft 20, the occurrence of dynamic rollover may be minimized. Specifically, in case that the aircraft 20 contacts the ground 4 in only one point 41, then the contact point 41 shall not become a pivot point causing dynamic rollover phenomenon once the wheel of this landing gear turns, or yaws, to align with the direction of the sideward force acting on it and that force overcomes the stationary friction force of the wheel, which is typically much smaller than the counter force 21 A developing at point 21 of Fig. 2. As a result wheel 30 starts rolling on the ground, and since the landing gear 34 swivels wheel 30 may adapt its direction of rolling to align with the side forces exerted on the aircraft. When wheel 30 rolls on the ground the counter force exerted by the ground is minimized to close to zero . It is appreciated that with such anti-dynamic rollover system 40, there is only the drift effect caused by the thrust of the rotors and the contact with the ground, whereas there is no longer a roll effect to tip the aircraft 20 as depicted in more details in Figs 5A-5C and Figs. 5D-SF. Figs SA-5C describe three consecutive stages of aircraft SO after takeoff process started and the lift force LI has a right-acting (with respect to the page) component When the magnitude of LI is high enough to lift the left wheel (in the drawing) off the ground aircraft SO will start rolling to the right of the page as described in Figs.5B and 5C. In case the side-acting component of LI is high enough aircraft SO will continue rolling to the right (and may even accelerate its side velocity). While this scenario is not typical, since when close-to-rollover conditions evolve limiting control actions are expected to be taken, manually or automatically, yet this scenario exemplifies the immunity of aircraft SO to dynamic rollover according to embodiment of the present invention. A slightly different scenario is presented in Figs. SD-SF. Aircraft 56 is subject to the action of lift force L2 having a side-acting component aimed to the right of the page. If L2 is slightly smaller than LI the equilibrium depicted in Figs.5A-5C will not exist. If following the exertion of L2 aircraft 56 will tend to tilt to the right of the page (in the direction of the side- acting component of L2) and the left wheel (in the drawing) of the landing gear of aircraft 56 will leave the ground, aircraft 56 will roll to the right of the page, and the change of friction force at wheel 58 from stationary to moving friction coefficient will cause substantial reduction of the counter force exerted by the ground on wheel 58. As a result aircraft 56 will gradually tilt back towards horizontal position, as depicted, in stages, in Figs. SD, SE and SF.

[031] In some embodiments, the swiveling landing gears, such landing gear 34 of Fig. 3, or landing gears 52 and 56 of Figs. 5A-SF, are assembled with directing means (for example a physical barrier) such that a side force applied onto the wheels from the center of the aircraft 20 towards the outer regions does not allow rotation of the wheel 30 around the swiveling axis 33 (as shown in Fig. 3) beyond the angle where wheel 30 is aligned with the longitudinal axis of aircraft 40, and the wheel remains directed towards the movement direction of the vehicle.

[032] According to some embodiments, the landing gears with swiveling wheels may be assembled with straightening means that may be adapted to direct the wheels 30 towards the direction forward movement of the vehicle, if no additional forces are applied. Such straightening means may comprise a return spring, a controlled hydraulic or pneumatic actuator, an electrical actuator, etc., as is known in the art. According to additional embodiment, the swivcling axis may be formed with a protrusion and the housing of the swiveling axis maybe formed with a compatible notch so that when the wheel is free of vertical pressure, e.g. when the aircraft is off the ground, the self-weight of the wheel and its fork and its swiveling axis may exert the required substantially vertical force to cause the protrusion on the axis to glide into the notch in the axis housing thus directing the wheel to be aligned with a pre-defined direction, for example the longitudinal center line of the aircraft.

[033] Reference is now made to Figs. 6A and 6B, which illustrate a top view of one side of landing gear 34 of aircraft 40 in initial and in half-way to its final state (respectively), while counter force 21A is exerted upon the wheel 30, according to embodiments of the present invention.

[034] It is appreciated that with the abovementioned operation of the swiveling joint of gear 34, a wheel 30 may turn about the swiveling axis 33 (axis 33 is perpendicular the page, in Figs SA, 5B) in response to force 21 A acting on the wheel 30, for example in point 4A. The wheel 30 turns substantially until it is, at least partially, aligned with the direction of that force 21A thus allowing the aircraft 40 to roll in that direction, as shown in Fig. 5B. according to further embodiments of the present invention swiveling joint 32 may be designed to allow swiveling of wheel 30 when force, such as force 21 A, is acting laterally from the outside of aircraft 40 towards its center, from a position in which wheel 30 is aligned with a longitudinal axis of aircraft 40 until it is aligned with force 21 A, but to prevent turning outwardly from a position in which it is aligned with a longitudinal axis of aircraft 40 when force such as force 21 A is acting on it from the center of aircraft 40 outwardly, thus providing further stability of aircraft 40 when side-acting forces are exerted on aircraft 40.

[035] It will be appreciated mat the present invention is not limited by what has been described hereinabove and that numerous modifications, all of which fall within the scope of the present invention, exist. For example, while the present invention has been described with respect to aircraft and helicopters, the same may apply to other vehicles experiencing the dynamic rollover phenomenon.

[036] It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described herein above. Rather the scope of the invention is defined by the claims which follow: