GB2093413A - Retractable undercarriage for model vehicles - Google Patents

Abstract

A retractable undercarriage for a model aircraft includes a drive motor (not shown) built into the housing (2) of the retraction unit and driving the leg support block (7) by means of a reduction gear drive train (33). Power is transmitted from the reduction gear drive train (33) to the undercarriage leg support block (7) by way of a worm gear (26) and worm wheel quadrant (20) with a pin (15) and slot (13) interconnecting the worm wheel quadrant and the leg support block (7) which are pivotally mounted on parallel and spaced rotation spindles (8) and (21) respectively. Applicable to main undercarriage and to steerable nose undercarriage (Figs. 5, 6, not shown). <IMAGE>

Description

SPECIFICATION Retractable undercarriage unit for model vehicles The present invention relates to a retractable undercarriage unit for model vehicles. In particular, the undercarriage unit in accordance with the invention is suitable for use in flying model aircraft which may be powered or glider types.

It is known to provide flying models of aircraft with retractable undercarriage systems which can be operated by the controller of the aircraft. This is particularly desirable with free flight radio control aircraft, but could be adapted to other types of model aircraft, for example control line aircraft.

With the known systems it is necessary for the builder of the aircraft to incorporate a support pivot for the undercarriage leg, and a drive linkage enabling that leg to be moved between the retracted position and an extended (i.e. lowered) position with adequate provision for locking of the undercarriage leg in the "lowered" position. The constructor also needs to incorporate a motive power source, for example an electrically driven motor or electric servo which can be operated in response to a control signal, for example, a radio controlled signal picked up by the airborne receiver in the aircraft.

Particularly when constructing scale models of full size working aircraft, it is desirable to achieve compactness in the undercarriage retraction system in order to avoid having obtrusive. bulges in the fuselage or wing profile to accommodate the retraction system. Conventionally the desire to incorporate an unobtrusive retraction system in a model aircraft wing has necessitated the separate positioning of on the one hand the motive power source and on the other hand the support pivot and undercarriage leg, and to provide a suitable linkage therebetween.This is, however, disadvantageous because of the need for vibration-resisting mountings for the servo providing the motive power, and consequently the need for a lost motion linkage between the servo and the support pivot, with difficulties of achieving correct adjustment of the geometry of (a) the linkage between the servo and the support pivot and (b) the locking mechanism (for example an over centre mechanism) on the support pivot so that the undercarriage leg will correctly lock in the "lowered" position.

It is the object of the present invention to overcome the disadvantages of the known undercarriage retraction units.

Accordingly, the present invention provides a retractable undercarriage unit for a model vehicle, comprising a housing, a support pivot in said housing for receiving an undercarriage leg to allow pivoting of the leg relative to the housing between retracted and lowered positions, a drive motor in the housing, a reduction gear drive transmission in the drive train between the motor and the support pivot, and means in the housing to resist pivotal displacement of said support pivot and consequent straining of said drive train by displacement of the undercarriage leg while the drive motor is not being driven and the support pivot is in a limit position of its travel.

Preferably the drive transmission between the motor and the support pivot includes a worm and pinion mechanism with the pinion connected to the support pivot by a pin and slot linkage ailowing rotation of the pinion and the support pivot about parallel but spaced axes, the geometry being such that when the undercarriage leg is in its lowered configuration the slot is parallel to the direction of the main undercarriage loads upon landing impact so that the impact loads are not transmitted directly to the pinion.

More preferably, the arrangement is such that any flexural stress applied to the undercarriage leg in the "lowered" position will be transmitted by the pin and slot arrangement in a direction radially of the pinion, thereby ensuring that the teeth of the pinion do not absorb the landing impact load.

It is particularly convenient for the pinion to be provided in the form of a right-angled, toothed quadrant mounted on a spindle and driven for rotation by means of a speed reducing gear transmission from the motor.

In order that the present invention may more readily be understood the following description is given, merely by way of example, with reference to the accompanying drawings in which: Figure 1 shows an exploded view of a retractable undercarriage used in accordance with the present invention, the unit being one primarily intended for one main undercarriage leg for underwing or under-nacelle fitting; Figures 2 to 4 show detail views of the gear wheel quadrant and the leg support block of the pivot support, in the "undercarriage lowered" position (the Figure 1 configuration) in Figure 2, in an intermediate position in Figure 3, and in the undercarriage retracted position in Figure 4; Figure 5 shows a detail of a modified undercarriage retraction unit intended for a steerable nosewheel leg; and Figure 6 shows a side elevational view of the components shown in the detail of Figure 5.

Referring now to the drawings, Figure 1 shows a retractable undercarriage unit 1 comprising a three part housing formed of a main housing block 2 of nylon, a first end plate 3 and horizontal mounting lugs 3a, of nylon, and a record end plate 4 and vertical mounting lugs 4a, also of nylon and providing a cover to the reduction gearing. A side plate 5 to the housing includes a printed circuit conductor arrangement constituting the limit switch for the undercarriage to de-activate the drive motor (not shown) at the two extreme ends of its travel.

The undercarriage leg 6 formed of spring steel piano wire is intended to be clamped in a nylon support block 7 which is rotatable on a spindle 8 housed in two bearing recesses 9 and 10 in the first end plate 3 and two bearing recesses 11 in the main housing block 2 one of which can be seen in Figure 1. The first end plate 3 includes a recess 12 to accommodate the leg support block and a similar recess (not shown) is provided in the concealed face of the main housing block 2.

Pivoting of the leg support block 7 in the clockwise direction from the Figure 1 position, through 900, will bring the undercarriage leg 6 from the vertical configuration (in this case the "undercarriage down" state) to a horizontal configuration corresponding to the "undercarriage up" position.

Such rotation of the leg support block 7 is driven by a pin and slot mechanism comprising a slot 13 in one end face of the leg support block 7 slidably receiving a brass slider 14 pivotally carried by a stainless steel pin 1 5 having one end threaded at 1 6 for cooperation with a nut 1 7 and anti-vibration washer 1 8 holding the threaded end 16 of the pin in a clearance hole 19 of a bronze gear wheel quadrant 20.

The gear wheel quadrant 20 is non-rotatably secured to one end of a driven shaft 21 of brass by means of a grub screw (not shown) engaging in a tapped hole 22 and having its inner end abutting a flat 23 on the end of the driven shaft 21. The opposite end of the driven shaft 21 has a squared end formation 24 defining flats enabling an undercarriage bay door drive mechanism to be driven from the main servo of the retractable undercarriage unit 1.

As can be seen in Figure 1, the spindle 8 for the leg support blcok 7 and the driven shaft 21 carrying the gear wheel quadrant 20 are parallel but spaced apart from one another. The cylindrical face 25 of the leg support block 7 is such that throughout the rotation of the leg support block 7 it will not foul the reduced diameter central portion of the driven shaft 21 carrying the gearwheel quadrant.

The gear wheel quadrant 20 is itself driven by a hollow steel worm gear 26 having one end supported in a bearing 27 in a bearing recess 28 of the first end plate 3 and its other end received in a bearing 29 and having a squared end 30 to receive the square central aperture 31 of a gear 32 constituting the output gear of a reduction gear drive transmission generally designated 33.

The reduction gear drive transmission 33 is intended to be driven by the brass pinion at the end of the drive motor (not shown) which will have one end secured in the recess 34 of the first end plate, provided with electrical contacts for energy supply to the unit, and its other end received in a bearing recess 35 formed in the main housing block 2 to locate the brass output pinion of the servo in constant meshing engagement with the larger gearwheel 36a of the first integrally formed gearwheel pair 36a--36b of the reduction gear drive 33.The reduced diameter gearwheel 36b of this integral pair is in constant meshing engagement with the larger diameter gearwheel 37a of the next integrally formed gearwheel pair 37a-37b whose smaller gearwheel 37b is in constant meshing engagement with the larger gearwheel 38a of a third integrally formed gearwheel pair. The smaller gearwheel of this third integrally formed gearwheel pair is in constant meshing engagement with the final gear 32 fixed on the square end 30 of the worm gear drive shaft. As can clearly be seen in Figure 1, the first, second and third integrally formed gearwheel pairs 36a-36b, 37a-37b, and 38a are mounted on respective shafts 36c, 37c, and 38c which are able to be received in respective apertures in the main housing block.Although not shown in Figure 1, alternative holes for the shafts 36c, 37c and 38c are provided in order to enable the gears to be positioned in a different arrangement so as to vary the reduction gear ratio between the motor pinion (not shown) and the worm gear 26, for example by using one of the three integrally formed gearwheel pairs 36a-36b, 37a-37b or 38a as an idler gear where only the larger diameter gearwheel of the appropriate pair is employed so that drive to and from that pair is by way of the same larger diameter gearwheel (for example 36a or 37a).

In order to enhance guidance of the slider 14 of the leg support block drive pin 1 5 during its sliding motion, a 900 arc slot 39 is formed in the end wall of a recess in the main block 2 in which recess the worm wheel quadrant 20 is housed. A continuation of the same recess can be seen at 40 in the first end plate 3.

The various securing screws which serve to hold the first and second end plates 3 and 4 and the printed circuit side plate 5 in place on the main housing block 2 can all be seen clearly in Figure 1 and do not require detailed description.

Figures 2, 3 and 4 show the cooperation between the worm wheel quadrant 20 and the leg support block 7 during an undercarriage leg retract operation.

The reference throughout this specification to the "undercarriage lowered" configuration is intended to denote the configuration shown in Figure 1, and that to the "undercarriage retracted" configuration is when the undercarriage leg 6 has been rotated through 900 in the clockwise direction, i.e. from the Figure 2 position to the Figure 4 position.However, in many applications of the retractable undercarriage unit it will be preferable for the retractable undercarriage unit 1 to be positioned in a configuration 900 displaced in the anticlockwise direction from the arrangement shown in Figure 1, so that the first and second end plates 3 and 4 are horizontal and consequently the overall height of the unit 1 , for example when the undercarriage is to retract into the wing, will be much less and will allow it to be installed in an "under-wing" configuration, without obtruding on the profile of the wing to any noticeable extent. The upright arrangement shown in Figure 1 is, however, preferable where the unit 1 is to be installed within the aircraft nose or a nacelle and where consequently the width or depth of the nose or nacelle is the limiting dimension rather than the thickness of the wing in the case of the under-wing mounting. However, the geometry of the preferred embodiment of the device is such that, as will be explained below, there is a secure geometric lock on the undercarriage leg 6 at both extremes of its movement and consequently unit 1 can be mounted in either of the two possible orientations (i.e. with the end plates 3 and 4 vertical as shown in Figure 1 or horizontal) according to the space available in the model.

As the gearwheel quadrant 20 begins its anticlockwise rotation from the Figure 2 position towards the Figure 3 position the drive pin 1 5 follows an arcuate path starting as a totally vertically downward movement and gradually adopting an increasing rightward horizontal component of movement. During this movement the slider block 1 4 descends along the slot 13 and drives the leg support block 7 for accelerating angular motion in the clockwise direction in so doing. By the intermediate position shown in Figure 3, the slider block 14 has attained its position which is closest to the blind end of the slot 13 and for a given rate of angular movement of the gearwheel quadrant 20 the angular velocity of the leg support block 7 has reached a maximum.

Between the Figure 3 and Figure 4 positions the slider block 14 moves away from the blind end of the slot 13 and the angular velocity of the leg support block 7 progressively reduces for constant rotation of the gearwheel quadrant 20.

The significance of the slow rotation rates of the leg support block 7 and the undercarriage leg carried thereby at each end of its travel is important where the squared end 24 of the driven shaft 21 is used to drive undercarriage bay doors.

These doors will, if directly driven by the squared end 24 without any crank linkage, open at a constant rate of rotation and consequently the arrangement can be such that the doors will open from their fully closed position much more quickly than the rather sluggish initial movement of the main leg 6 and consequently, starting from the undercarriage leg raised and undercarriage bay door closed configuration, the door will be capable of clearing the path of the descending undercarriage by virtue of the slow initial movement of the undercarriage leg.

Another advantage of this configuration is that during the final stages of the undercarriage retract movement the leg will be very slowly approaching its final position whereas the undercarriage bay door moves towards its closed position at a substantially constant velocity and the arrangement can be such that it reaches its final position in advance of the end of travel of the gearwheel quadrant 20 but there is a spring in the drive to the undercarriage bay door so that the very last part of the travel of the gearwheel quadrant 20 results in straining of this spring, thereby giving a positive closing force on the undercarriage bay door and prevent it fluttering in flight.

An undercarriage door can be mounted on the leg support block 7 by means of the leg-sensing grub screw holes to allcw the main undercarriage door to be connected to the leg. Thus the undercarriage door system will comprise a main door carried by the undercarriage leg and at least partly shrouding the wheel or bogey, and the undercarriage bay door which cooperates with the main door and the perimeter of the undercarriage bay to ensure that the undercarriage bay is completely closed off to the outside airflow.

The advantage of the system illustrated in Figures 1 to 4 is that in the Figure 2 configuration the slot 1 3 of the leg support block is perpendicular to the radius joining the leg support drive pin 15 of the gearwheel quadrant 22 to the pivot shaft 21 of the gearwheel quadrant so that when the undercarriage leg 6 is in the fully lowered configuration upward shock loads which may be sustained by the leg support block 7 cannot be transmitted to the gearwheel quadrant 20.

(a) In the event of any vertical movement of the leg support block 7 (due to the inherent elasticity of the nylon leg support block) this will simply cause very small sliding displacement of the leg support block 7 with respect to the slider block 14 carried by the drive pin 1 5.

(b) Any lateral loads (i.e. loads on the undercarriage leg 6 which cause pivoting of the leg support block 7 about its spindle 8) will simply cause horizontal pressure of the slider block 1 4 against one or other of the side walls of the slot 13 and this load will be carried by the mounting boss 21a (Figure 2) around the driven shaft 21 as well as by the support bearings of the shaft 21 itself, and will in no way result in a component of movement rotating the gear quadrant and putting strain on the gear teeth at the various points of meshing of the drive transmission.The slider block 14 is designed to be rectangular (in this case square) for the purpose of providing a considerable bearing area against the walls of slot 13 to resist these lateral loads, and the width of the slider block (i.e. its dimension transversely between the slot walls) is chosen so as to allow enough clearance for free sliding movement along the slot but to prevent lost motion in the connection between the pin 1 5 and the leg support block 7 in the "undercarriage retracted" position. The slider block width is thus substantially equal to the slot width.

Any displacement of the undercarriage leg 6 about a horizontal axis in the plane of the paper of Figure 2 will be resisted by the support bearings of the leg support block spindle 8. Consequently, there is no mode of displacement of the undercarriage support leg 6 which can put strain on the engaging gear teeth of at least the worm gear 26 and worm wheel quadrant 20 and certainly not on any of the other gears of the drive transmission 33.

It is a preferred feature of the present invention that the Figure 4 position similarly has the slot 1 3 perpendicular to the radius joining the driven shaft 21 to the support block drive pin 1 5 and so the same geometric lock arises. Consequently, as indicated above, the retractable undercarriage unit 1 can be mounted either in the Figure 1 position or in an alternative configuration where the first and second end plates 3 and 4 are horizontal instead of being vertical.

However, it is possible for the design of the retractable undercarriage unit 1 to be modified so as to allow for the positioning of the axis of the leg support block spindle 8 to be adjusted to allow the travel of the undercarriage leg 6 between its "undercarriage retracted" and "undercarriage lowered" positions to be less than 90" of angular movement, for example where the undercarriage is intended to retract into the wing of an aircraft having appreciable wing dihedral but is nevertheless intended to have the leg vertical when in the "undercarriage lowered" position.In this variation there will be one limit of leg travel (the "undercarriage lowered" limit) which provides the "lock" configuration of the slot 13 being perpendicular to the radius 8-21 and the other limit will be variable so that the geometric lock at that end of travel will be optional.

The arrangement illustrated in Figures 1 to 4 is intended for a nosewheel undercarriage leg with the undercarriage leg clamped in position in its socket in the leg support block 7 by means of grub screws (shown at 42 in Figure 1).

This system can be used, with slight adaptation, for a steerable nosewheel undercarriage system by providing the leg support block 7 with at least one recess in which a retaining collet of the undercarriage support leg 6 can be received so as to allow the support leg 6 to be rotatable about its own axis with respect to the support block 7, while at the same time providing adequate transmission of vertical axial impact loading on the leg 6 and of flexural loading either rearwardly or sidewardly on the leg 6 to the support block 7. Such an arrangement is illustrated in Figure 6 where the support block 7 has recesses to accommodate upper and lower retaining collets 43 and 44, respectively, clamped on the leg 6 so that upthrust on the steeringly rotatable leg 6 is sustained by the lower collet 44 and downthrust is sustained by the upper collet 43.

The overhead view of this same arrangement is shown in Figure 5 where the leg 6 is shown as having a non-rotatably secured thereto a steering collet 45 having the diamond with parallel side flats. In the "undercarriage lowered" configuration the steering collet 45 is, as shown in Figure 6, positioned just into an arcuate guide 46, but when the leg 6 is retracted by anticlockwise movement around the spindle 8 of the leg support block 7, the steering collet 45 enters the spatula-shaped slot (47 in Figure 5) defined between the two arcuate limbs of the guide 46 to be constrained by sliding engagement of the parallel sides of the collet with the parallel walls of the slot 47 so that the axis of rotation of the nosewheel will remain parallel to the orientation it has in the "straight ahead" steering configuration when lowered.

The steering arm 48 of the nosewheel mechanism has a circular boss 49 at its pivot with a V-shaped recess to receive the one end apex of the steering collet 45 when the nosewheel leg is in the lowered configuration shown in Figures 5 and 6. Provided the steering arm 48 is maintained at a deflection of not more than 300 from the "dead ahead" position of Figure 5 during retraction and lowering of the undercarriage leg 6, and since at this stage the steering collet 45 is in the widened "head" of the slot 47, the steering collet will cleanly enter and leave the corresponding recess of boss 49 upon lowering and retraction of the undercarriage despite 1300 of steering deflection.When the undercarriage leg support block 7 is in the Figure 6 "undercarriage lowered" configuration rotation of the boss 49 of the steering arm 48 will drive the now vertical steerable nosewheel leg 6 for rotation about its own vertical axis for steering of the aircraft on the ground. It will of course be appreciated that, with the limited number of control channels of an airborne radio control receiver, the steering arm 48 will in practice be driven by the same servo which is responsible for operation of the rudder so that in flight the servo in question will rotate the steerable arm 48 and the rudder but not the nosewheel leg 6, whereas when the nosewheel leg 6 is in the "undercarriage lowered" configuration shown in Figures 5 and 6 the same servo will then be driving not only the rudder and the steering arm 48, but also the steering collet 45 and the steerable leg 6 (to provide more positive ground handling characteristics in the yawing mode).

Because the steering collet 45 is a sliding fit in the recess of the boss 49 of the steering arm 48, there will be no transmission of vertical shock loading from the nosewheel leg 6 to the steering arm 48 as the nosewheel deflects rearwardly on touchdown, and any lateral flexure of the leg 6 on landing will readily be absorbed by the pivot (not shown) for the boss 49. There will not be much likelihood of torsional deflection of the leg 6 about its own vertical axis and consequently there is little likelihood of impact loading being transmitted to the nosewheel steering arm 48 and drive mechanism therefor.

As shown in Figure 5, the steering arm 48 has a set of three holes at several different radial distances with respect to the centre of the boss 49 and consequently the mechanical advantage of the steering mechanism can readily be adjusted by attachment of the drive linkage (not shown) of the steering arm 48 to a different one of these holes.

The undercarriage retraction unit shown in Figure 1 is intended for both fixed nosewheel application and port main wheel application. For main wheel use (i.e. mounting in the wing) the second end plate 4 will be without the drilled mounting lugs 4a shown in Figure 1 and will terminate at the dotted line in the drawing, the first end plate 3 being provided with drilled mounting lugs 3a as shown. For nosewheel use, the I 'gs 3a are omitted from the first end plate 3 and he drilied mounting lugs 4a of the second end7plate 4 will be reinstated.

Claims (11)

1. A retractable undercarriage unit for a model vehicle, comprising a housing, a support pivot in said housing for receiving an undercarriage leg to allow pivoting of the leg relative to the housing between retracted and lowered positions, a drive motor in the housing, a reduction gear drive transmission in the drive train between the motor and the support pivot, and means in the housing to resist pivotal displacement of said support pivot and consequent straining of said drive train by displacement of the undercarriage leg while the drive motor is not being driven and the support pivot is in a limit position of its travel.

2. A retractable undercarriage unit according to claim 1, wherein said means resisting pivotal displacement of the support pivot includes a worm gear and worm wheel quadrant in which drive from the motor to the support pivot is transmitted from the worm gear to the worm wheel quadrant.

3. A retractable undercarriage unit according to claim 1 or claim 2 wherein said means to resist pivotal displacement of said support pivot includes a pin and slot linkage connecting the support pivot and a pivotal member of the drive train thereto whereby in an extreme position of the pivotal travel of the support pivot the slot is parallel to the position of the axis of an undercarriage leg intended to be secured to said support pivot so that the forces transmitted between the slot and the pin by pivotal displacement of the undercarriage leg are resisted by the pivot of said pivotal member and not by the teeth of the reduction gear drive transmission.

4. A retractable undercarriage unit according to claims 2 and 3, when taken together, wherein said worm wheel is the said pivotal member of the drive train and the pin is carried by said worm wheel and the slot is formed in said support pivot, and wherein the arrangement is such that the slot is perpendicular to the radius joining the axis of the pin to the axis of the worm wheel in said limit position of the support pivot.

5. A retractable undercarriage unit according to claim 4, wherein suid support pivot is a leg support block pivotal around a first axis of rotation, and said worm wheel is a worm gear quadrant pivotal around a spaced, parallel axis of rotation.

6. A retractable undercarriage unit according to claim 4 or claim 5, wherein said slot is perpendicular to said radius at both limit positions of the pivotal travel of said support pivot.

7. A retractable undercarriage unit according to any one of claims 3 to 6, wherein said pin carries a slider which is slidably received in said slot and is of rectangular cross section having at least one major axis substantially equal to the width of said slot.

8. A retractable undercarriage unit according to claim 2 or to any one of claims 3 to 7 when claim 3 is appendant to claim 2, wherein said pivotal member is mounted for rotation on a shaft having at one end means for an auxiliary drive take off, for example for undercarriage bay doors.

9. A retractable undercarriage unit according to any one of the preceding claims, and including a limit switch for deactivating said drive motor at each limit position of the pivotal travel of said support pivot.

1 0. A retractable undercarriage unit according to any one of the preceding claims, wherein said support pivot is adapted to have an undercarriage leg secured in said support pivot so as to be rotatable about the axis of the leg, for the purposes of providing steerable undercarriage.

11. A retractable undercarriage unit substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.