Landing Gear Mechanism for Model Airplane
A radio controlled model airplane has landing gear including a wheel rotatably mounted on a strut. The wheel and strut are retractable into the airplane wing. The strut is angled forwardly relative to the wing surface where the strut is attached such that the wheel is forward of the airplane center of gravity just prior to takeoff and touchdown. The landing gear includes a control assembly mounted on the wing. The control assembly includes a housing and a pivot pin on which the strut is mounted. The pivot pin is rotatable and pivotable around one of its ends. The control assembly also includes a cam which causes the pivot pin to pivot upon rotation, thereby causing the strut to move through a plane oblique to the wing.
This application claims the benefit of U.S. Provisional Application No. 61/165,208 filed Mar. 31, 2009, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTIONThis invention relates in general to landing gear for radio controlled model airplanes, and more particularly to an improved structure for retractable landing gear.
Most radio controlled model airplanes are equipped with landing gear to facilitate take-offs and landings. Typically, the landing gear includes a wheel supported on the end of a strut. Generally, the landing gear struts are perpendicular to the airplane wings to which they are attached. Some landing gear is permanently fixed in position. Other landing gear is retractable and folds up into the wing after take off. Retractable landing gear is desirable in many types of radio controlled airplanes for reasons such as authenticity, maneuverability and handling.
The center of gravity or balance point of many radio controlled model airplanes is substantially directly over the wheels just before takeoff and just prior to touchdown. This can cause the plane to teeter on the wheels and often creates “nose over” conditions during both take-offs and landings. In a “nose over” condition, the tail of a radio controlled model airplane will rise, and the nose of the airplane will hit the ground and stall the engine. Most runways are grass, causing increased drag and exacerbating the nose over condition because of the higher rolling resistance.
To avoid a nose over condition during take-off, a radio controlled model airplane can be positioned on a runway, and then be caused to “blast off,” which is accomplished by immediately applying both full throttle and up elevator (the control surface that makes the plane go up or down). The plane blasts down the runway a few feet and jumps skyward like a rocket. This can be dangerous, as the model airplane may be somewhat uncontrollable for the first few seconds of flight. This type of take-off also looks unnatural. Landings are easier than take-offs, but as a radio controlled model airplane touches down and its speed decreases, the airplane can stop in a “nose over” condition.
One way to alleviate the problems caused by “nose over” conditions is to used fixed landing gear struts angled forwardly, as opposed to generally vertically oriented, therefore positioning the wheels forward of the center of gravity. In these fixed landing gear type of radio controlled model airplanes, the “nose over” condition does not tend to occur as frequently.
Currently available mechanisms for retractable landing gears are simple. They generally consist of an actuating arm and a pivot on top of the strut. The pivot has a pin about which the strut rotates. The pivot is housed in a small box or case. The mounting bores for the pin, and therefore the pin axis, are aligned (i.e. parallel) to the fuselage of the plane, restricting the strut and wheels to swing or parallel to the wing. No commercially satisfactory design has been made to adequately retract landing gear having forwardly angled struts.
SUMMARY OF THE INVENTIONMy invention is a retractable landing gear assembly for model airplanes having a strut angled forwardly relative to the wing surface where the strut is attached. The landing gear includes a control assembly mounted on the wing. The control assembly causes the strut to move through a plane oblique to the wing. Preferably, the control assembly includes housing and a swivel to which the strut is attached. The swivel is mounted for rotation in the housing. The swivel has a fixed end and a free end which allows pivoting relative to the housing. The swivel includes a cam which pivots the free end of the swivel from a first position to a second position upon rotation.
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A bushing 63 is positioned in a housing bore opposite bushing 62. Bushing 63 is solid except for a conical drill indentation 65 which provides clearance for the cap screw 64, even though such clearance is generally not needed to allow a full extension of the actuator shaft 60. By reversing the solid bushing 63 and the bored busing 62, the landing gear may operate with an outboard servo instead of an inboard servo as will be described later.
Swivel 80 includes an integral cam 90 having upper and lower cam surfaces 92, 94. Swivel includes an integral fork 96 engageable with wiper 66 upon axial movement of the actuator shaft 60 in either direction. Upon movement of wiper 66 from one end of the housing as seen in
Front housing portion 54 having an inner front surface 53 is shown in
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Alternatively, two servo motors can be used, one for the landing gear of each wheel. Generally two servos would be used only if the airplane is not suited to accommodate a single inboard servo for any reason, for example limited inboard space. Two inboard servos could be used, but more typically two outboard servos would be used. The control assembly 50 described herein can easily be adapted for an outboard servo motor by reversing the bushings 62, 63 and flipping the actuator shaft 60.
In summary, when the landing gear is in the retracted, wheel up position, the pivot pin 70 is in essentially the same position as a pivot pin used in prior art devices, allowing the strut and wheel to align with the wing surface and landing gear well for a flat fit. However, in the extended, wheel down position, the cam 90 causes one end of the pin 70 to raise and lower in the front bore 74 while the other end remains stationary. The forward tilting of the pivot pin 70 causes the strut and wheel to tilt forward. The cam has a flowing angle to accommodate the gradual tilt as the landing gear moves to an from extended and retracted positions. The relief angles on the swivel surface 97 also accommodate this movement.
In a preferred embodiment, the control assembly 50 components are made of lightweight metal such as aluminum. However, the housing 52, 54 and the swivel 80 may be made from plastic, with the cam surfaces, rails, etc. being precisely machined with CNC equipment.
The landing gear of the present invention may be used as either original equipment, such as in a model airplane kit, or as a retrofit assembly. For a typical model airplane, an optimum forward tilt for a strut is about nine and one-half degrees from its original position. For a typical strut length of about 6.5 inches and wheel diameter of about 3 inches, this amount of tilt will move the wheel forward slightly over one inch (1.0672 inches). This forward movement is sufficient to keep the airplane center of gravity behind the wheel just priot to takeoff and touchdown of the airplane.
The principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.
Claims
1. A model airplane comprising an elongated fuselage having a longitudinal axis, a wing oriented transversely to the fuselage along an axis generally transverse to the fuselage axis, and a retractable landing gear assembly attached to the airplane, the landing gear assembly comprising an elongated strut having a longitudinal axis with one end of the strut pivotally mounted on the airplane the other end of the strut rotatably attached to a wheel, wherein the strut is movable from a retracted position in which the strut axis is substantially parallel to the wing axis to an extended position in which the strut axis is substantially oblique to the wing axis.
2. A model airplane as defined in claim 1 wherein the strut is pivotally mounted on the wing, wherein the wing surface defines a landing gear well, and wherein the strut axis is substantially oblique to the plane of the wing surface adjacent the well when the strut is in the extended position.
3. A model airplane as defined in claim 1 wherein the strut axis when, the strut is in the extended position is substantially perpendicular to the wing axis when viewed along an axis parallel to the fuselage axis, and skewed with respect to the fuselage axis and wing axis when viewed along an axis parallel to the wing axis.
4. A model airplane as defined in claim 3 wherein the strut axis is skewed about 9.5 degrees with respect to the fuselage axis and wing axis.
5. A model airplane as defined in claim 1 comprising two struts, wherein each of the two struts is operated by a servo positioned inboard of each strut.
6. A model airplane as defined in claim 1 having radio controls and a servo to move the strut to and from the extended and retracted positions.
7. A model airplane as defined in claim 1 wherein the airplane is a tail dragger type airplane.
8. A retractable landing gear control assembly for a model airplane, the assembly comprising:
- a housing having a cam rail,
- a swivel having a substantially fixed end mounted in the housing and a free end mounted in the housing for pivotal movement about the fixed end, the swivel including cam engageable with the cam rail, an actuator engageable with the swivel to rotate the swivel, wherein upon rotation of the swivel, the cam causes the free end of the pivot pin to move from a first position to a second position.
9. A retractable landing gear control assembly as defined in claim 8 wherein the housing further comprises a second cam rail, the cam engageable with the second cam rail.
10. A retractable landing gear control assembly as defined in claim 8 wherein a landing gear strut is attached to the swivel.
11. A retractable landing gear control assembly as defined in claim 8 wherein the actuator comprises a shaft mounted in the housing transverse to the pivot pin.
12. A retractable landing gear control assembly as defined in claim 9 further comprising a wiper affixed to the actuator shaft, the wiper engageable with the swivel.
13. A retractable landing gear control assembly as defined in claim 10 wherein one of the wiper and swivel includes a fork engageable with the other one of the wiper and swivel.
14. A retractable landing gear control assembly as defined in claim 11 wherein the wiper rides in a housing track.
15. A retractable landing gear control assembly as defined in claim 8 wherein the actuator comprises a shaft having a longitudinal axis, and further comprising a servo motor for moving the actuator shaft along the longitudinal axis.
16. A retractable landing gear assembly as defined in claim 13 wherein the housing further comprises bushings for facilitating axial movement of the actuator shaft relative to the housing.
17. A retractable landing gear assembly as defined in claim 8 wherein the swivel comprises a pivot pin.
18. A retractable landing gear assembly as defined in claim 17 wherein the pivot pin is integrally formed with the swivel.
19. A model airplane comprising a longitudinally oriented fuselage, a wing oriented transversely to the fuselage, and a retractable landing gear assembly attached to the wing, the landing gear assembly comprising a strut mounted on the wing, a wheel rotatably attached to the strut, and a pivot pin having a first end and a second end, wherein the strut is rotatable around the pivot pin, and wherein the first end of the pivot pin is substantially fixed relative to the wing and the second end of the pivot pin is movable with respect to the wing.
20. A model airplane as defined in claim 19 wherein the airplane is a tail dragger type.
Type: Application
Filed: Mar 29, 2010
Publication Date: Sep 30, 2010
Inventor: Jerry L. McNutt (Walbridge, OH)
Application Number: 12/748,569
International Classification: A63H 27/32 (20060101);