Retractable racing chassis. Drawing, description

MODELING
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Retractable racing chassis. Tips for a modeler

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About 190 km/h! This is the technical average speed of a modern racing model with a powerful engine. Moreover, the maximum operating speed of the model exceeds 170 km / h, and this is not the limit. By constantly improving the miniature aircraft, athletes strive to further reduce the time it takes to cover a ten-kilometer distance. As a rule, the modeller has three ways: changing the layout scheme, forcing the engine and improving the aerodynamics of the model.

(click to enlarge)

A significant proportion of the total aerodynamic drag is drag. By removing protruding parts from the model, you can significantly reduce it. One of the few nodes that significantly protrude beyond the contours of the fuselage is the landing gear. The proposed design of the retractable landing gear (Fig. 1) just allows you to achieve the result.

The landing gear retraction mechanism is driven by a "floating" model control rocker. At the same time, its axis is attached not to the wing (as usual), but to the drive rocking chair mounted on the wing.

The kinematics of lifting the landing gear leg is simple: when the centrifugal force acting on the model reaches a certain value, the cord is stretched, and the rocker, overcoming the force of the spring that restrains it, deflects the rocker with the help of thrust and removes the rack. At the same time, the rear flap also rises, while closing the fuselage cavity.

The landing gear also performs an aerodynamic function - it is the front brake flap, due to which, when landing, the speed is quickly extinguished. A model with this chassis has a soft "sticky" fit. This is due to the shock absorber located in the rack.

The landing gear retract mechanism usually works already at a speed of 110-115 km/h. This can be achieved by adjusting the spring or by choosing the point of its attachment to the drive rocker.

Knowing the approximate flight speed of the model and its weight, it is easy to determine the force of the spring tension. To do this, you can use the following formulas:

Now about some technological subtleties. Chassis frame is milled from D16T material. When processing, special attention should be paid to drilling and reaming holes Ø 3 mm and 2,5 mm, cutting grooves 10 and 12 mm wide, since their non-parallelism or non-observance of the mentioned dimensions can lead to distortions of the mechanism parts and failures in operation.

Landing gear - from the same material. When selecting a workpiece, do not forget to take into account the direction of the fibers - otherwise this may lead to a loss of stability of the material under load and failure of the part.

The backstage is processed on a lathe from steel U8 or 30KhGSA, after which the groove and the outer contour are marked and milled. And finally, heat treatment. The temporary tensile strength of the material must be at least 120 kgf/mm2.

The drive rocker arm is made of D16T alloy. The correct choice of the direction of the fibers is also essential for this part, since it is one of the most loaded. Like the rocker, the yoke is first machined on a lathe; dimensions 10, 2 and Ø 2,5 mm should be made as accurately as possible. Next, the part is marked out, holes are drilled and deployed in it, and it is cut down along the outer contour.

Rice. 1. Retractable landing gear (click to enlarge): 1 - control rocker, 2 - axis of attachment of the power spring on. drive rocker, 3 - power spring, 4 - axis of the control rocker, 5 - drive rocker, 6 - axis of the thrust attached to the drive rocker, 7 - thrust, 8 - frame, 9 - frame, 10 - nuts, 11 - thrust attachment axis to the rocker, 12 - drive rocker, 13 - drive rocker axle, 14 - rocker, 15 - rocker axle, 16 - damping springs, 17 - landing gear, 18 - bushing., 1.9 - wheel, 20 - wheel axle, 21 - hub wheels

Damping springs made of OBC wire are wound on a mandrel, the diameter of which should be chosen 1,5 mm less than the true inner diameter of the spring. Further, unnecessary turns are cut off, and finally, heat treatment - hardening and tempering.

Similarly to the drive rocker arm, rocking chairs - control and drive - are machined from D16T material.

A mold is required to make a wheel. It can be machined from D16T material. The wheel hub is from the same alloy. For more reliable contact with rubber, it must be sandblasted or chemically treated. The hub prepared in this way and raw rubber are placed in a mold and vulcanized.

All screws and axles of the mechanism are made of U8 or 30KhGSA steel with subsequent heat treatment.

Now you can proceed to the control assembly of the chassis units. First of all, a frame is glued from three plywood plates. Please note that the direction of the fibers on the middle plate must be perpendicular to the directions of the fibers on the outer ones. When connecting blanks, it is best to use K-153 glue, which consists of two components - resin and hardener. For preparation, its components are mixed in a ratio of 6: 1.

The finished frame is processed along the contour of the fuselage with an underestimation of 1 mm per side. After that, a chassis frame is installed on it - on K-153 glue and four rivets Ø 2 mm. To facilitate, as well as for a stronger grip with the frame, several holes can be drilled in the frame. Next, a chassis rack with shock-absorbing springs fixed in it, a backstage and a pin limiting its movement and a drive rocker, which is connected to the backstage groove with an axle Ø 2 mm, are installed on the frame.

The assembled mechanism should be checked for smoothness and ease of movement of the levers, after which it can be glued into the wing (on glue K-153) with an axle with a drive rocker installed on it.

Rice. 2, 3 (click to enlarge)

After finishing the details (if there were, for example, sticking of the levers), the mechanism is assembled and glued to the model body so that the straight end of the plywood frame lies on the leading edge of the wing. Then, having set the landing gear to the extended position, and the drive rocker to the initial position, it is necessary to determine the length of the future thrust and bend it from the OBC wire Ø 2-2,5 mm. By connecting it with a drive rocking chair and a rocker, they check the ease of operation of the entire structure.

The power spring can be wound from OBC wire Ø 0,4 mm on a mandrel Ø 2 mm and length 40 mm. After heat treatment (quenching and tempering), the spring is installed on the model and its tension is selected, measuring the cord tension with a dynamometer. It must correspond to the values calculated according to the above formulas.

After calibrating the spring, the mechanism is disassembled. All parts should be washed with gasoline and lubricated with CIATIM-201 grease, and then reassembled. The most lightweight round nuts are screwed onto all axles and soldered with POS-40 solder. After the final check of the ease of movement of the entire mechanism and adjustment of the power spring, the fuselage cavity is sealed. A rear shield (Fig. 1) made of magnesium alloy MA3 is installed along the rear edge of the chassis compartment on an axle Ø 8 mm. After checking the operation of the chassis together with the rear shield, the fuselage is pasted over with fiberglass 0,02 mm thick and painted.

Author: N.Komarov

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