Cord speed model. Drawing, description

MODELING
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Cord speed model. Tips for a modeller

Modeling

The model consists of a low spar, a fuselage cowl and a removable wing. The low is machined on a lathe from a magnesium alloy MA 8-MA12 and milled in such a way that the engine legs do not protrude beyond the split axis, which is 5 mm above the low axis. The spar of the same alloy is attached from the inside low with four countersunk screws (argon-arc welding can be used). In the groove in the rear part, a fork is mounted on the K-153 glue, it is fixed from the end surface with two wire pins. The tail pylon is also glued into the groove.

A rocking chair made of D16T sheet alloy is installed in the spar. A control cable Ø 0,7-0,8 mm is fixed in it, on which a bowden wound from OBC wire Ø 0,25-0,3 is put on. The ends of the bowden are glued to the inner plane of the low and the pylon. The hood of the fuselage is type-setting, it has load-bearing frames - hornbeam and lime - with a balsa bar glued to them. Seven fungi, planted in a frame with glue, are securely connected low to the hood. The stabilizer is balsa, reinforced with lime edging and a spar. Installation angle 0°. Thickness in the middle 4,5 mm, at the end 2 mm Profile - symmetrical. On the hood there is a small extension of the wing at an angle of 1,5°, which insures the model from stalling when the engine is stopped.

The wing is made of D16T sheet alloy. Profile - biconvex, symmetrical, relative thickness - 7%.

Rice. 1. Fuel tank and its elements (click to enlarge): 1 - filling tube, 2 - rubber tube, 3 - suspension bracket, 4 - power tube, 5 - drain tube, 6 - special nut, 7 - cambric (Ø=9, l=3), 8 - glass, 9 - cambric (Ø=9, l=23), 10 - coupling screw

The manufacturing technology of the wing is not particularly difficult. For bending the workpiece, it is convenient to use the simplest fixture. These are two boards 500x120x250 mm in size, well fitted to each other and connected by four hinged loops (Fig. 2). From plywood 10 mm thick, make a mandrel (Fig. 3) with a height greater than the chord of the wing, planing one of its sides into a cone resembling a wing profile.

Cord speed model
Rice. 2. Wing bender

Cord speed model
Rice. 3. Mandrel

Then, between the two halves, lay the wing blank so that the axis of the latter is on the edge (Fig. 4). This operation must be done together: one holds the workpiece, the other mandrel bends the sheet at a right angle, and then, laying it in the fixture, press it together to an angle of 15-20 ° (Fig. 5).

To obtain the desired radius on the leading edge, insert a strip of plywood 1 mm thick into the workpiece and press it to the stop (Fig. 6). You will get an inner radius of 0,5 mm. You can not reduce it, as the edge begins to crack.

Open the workpiece with a mandrel (Fig. 7), cut to the desired size and glue the rear edge (it is best to use PU-2 glue). After drying, glue the spars along the leading and trailing edges, and a lime boss with holes for the cord at the end of the wing.

Rice. 4, 5, 6, 7. Wing blank bending process

Low with hood sandpaper and cover with one layer of fiberglass with epoxy.

In the bow of the hood, cut a window for the diffuser and engine cooling. Glue the landing ski from OBC O 2,3 wire, and solder a carbide reinforcement to its end. This design will allow you to make many flights without changing the ski.

Cover the front of the hood with 0,05 mm thick fiberglass and finish the surface with sandpaper.

Cover the model with polyurethane paint and polish. A tank (Fig. 1) made of 0,3 mm thick sheet metal is hung on a rubber cambric at a low position. Glue the air intake into it by connecting it with an elastic rubber tube to the tank drain tube.

It's time to install the wing and cord leads. To do this, assemble the model completely and hang it by the cord (steering wheel in the neutral position). To compensate for the deflection of the line during flight, select such a position of the wing, in which the nose of the model will fall 2-3 mm below the horizon line (Fig. 8). Then drill holes for the wing mount.

Cord speed model
Rice. 8. Installation of the wing (hanging)

The next stage includes the manufacture and preparation of propellers and the launch cart. The latter should be relatively easy, reliable in operation. It is equipped with two grips, which are held by the "saber" and are released when the model is lifted together with the trolley to a height of 20 cm. This ensures a reliable take-off and eliminates propeller breakage.

Screw: two-bladed - Ø 150 mm, pitch 165 mm; single-bladed - Ø 176 mm, pitch 190 mm. When using the latter, one must be very careful, since its breakdown during the flight leads to the complete death of the entire structure.

Model debugging is usually carried out on an engine with a very weak pair, while it is desirable to have a pipe length of at least 315 mm (from the cylinder axis to the end of the pipe). The tank is put on enrichment, and the engine is brought to almost maximum speed. This mode provides a fast and safe takeoff.

With a well-adjusted tank, the speed of the model should not change throughout the flight (25-30 laps). This setting allows assistants to detect the speed and give a signal to the athlete. If the speed is unsatisfactory, you can turn off the engine by forced stop and, after making an adjustment, try again. All this makes it possible to make up to 6 takeoffs during one attempt, which contributes to the achievement of a high result.

Author: V.Maslenkin

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