“DROP” ON TRACK | MODEL CONSTRUCTION

A lot of history in the fate of the car racing! Even now, when they are built almost the same pattern, in conversations the athletes to hear the terms “boat”, “drop”, “arrow”, meaning certain areas in the layout. Remember that was a “drop”. The name itself speaks about the shape of the hull. Aerodynamics have always maintained that the teardrop body has the lowest drag, to overcome which spent a large part of engine power. The advantage of “drop” and that it is well located for the centre of gravity of the car: it is very close to the drive wheels. This means that irregularities of the track model of this type will respond much less.

But this scheme has not withstood the test of time and practice. The fact that the midsection of this model was prohibitively large due to the lack of special engines, and therefore better aerodynamics simply could not occur. Yes, and very much uncomfortable mounted the “filling”: had a lot of free space, what should be the modern model.

At a time when many athletes have learned to do the engines, nothing to inferior to the best serial samples, “drop” again attracted attention. The fact that you can make a motor with a length not more than the width of a conventional engine with legs attachment. Therefore, it can be easily placed so that the axis of the shaft became perpendicular to the longitudinal axis of the model. In the end, again, “drop”, but with completely new properties.

Carefully comparing the model of the modern school and the proposed option, it is impossible not to pay attention to the following.

The engine can almost “put”, then the area midleware cross section is reduced approximately two times. Aerodynamic calculations show (taking into account the changes of elongation of the hull, the bow and the full wetted surface), it reduces the resistance of 1.89 times. A lot of it? Yes, if you take into account that, according to experimental data, the model with the engine a working volume of 10.0 cm³going at a speed of 300 km/h, the aerodynamic resistance of the hull is approximately 0.5 kg. To overcome it consumes 0,55 HP engine! Don’t you need the “extra” 0,26 HP!

At new configuration to the model “asking” cylindrical gears. According to handbooks on mechanical engineering, the efficiency of such transfers, the above tapered by 2.5% (the same as debugging). You can proceed to setting more comfortable under the new scheme of two-stage cylindrical gear without power loss.

The advantages of the scheme “drop — small distance between the center of gravity of the model and the drive shaft. And this condition is sustained during the course.

Fig. 1. Size comparison of models old and new type.

A racing model of a new type of horizontal engine;— racing model of the old type with vertically mounted engine.

Fig. 2. Racing model with front-wheel drive and horizontally placed engine with minimal aerodynamic drag.

The angle between the axis of the cylinder and the exhaust pipe can be achieved. Studies of large internal combustion engines has shown that when opening the exhaust window edge moving down of the piston the exhaust gases flow at an angle equal to the average of 30° relative to the axis of the cylinder. For model engines the terms of expiration are the same, so the new position of the nozzle eliminates a kind of throttling of the exhaust caused by the abrupt reversal of the jet exhaust gases in the normal version. At the same time improve the working conditions of a resonant tube in combination with the engine. Reflected from the reverse cone muffler pressure wave directs the gas stream is not to boost the channel, and almost along the wall of the sleeve.

Optimum conditions of blowing the motor. The head is cooled efficiently and, most important, evenly, which is not the traditional blowout. What has not been done before, in order to avoid warping of the motor caused by uneven cooling of engine with rear exhaust! Tried to apply and pull back the ribs, and powerful fins with special nozzles on the exhaust pipes, in particular chiseled carters, tried to close the front part of the jacket of the cylinder against the back of the part. But… uneven heating of the still was led to a different thermal expansion plots of the crankcase and causes a change in the geometry of the sleeve and the piston, the distortion of the parallelism of the axes of the shaft and the piston pin. Because of this increased mechanical losses, and the connecting rod started to “slide” with the crank. The new scheme provides, in addition to uniform cooling of the head, that section of the crankcase in the area of the exhaust window is not in the “shadow” shirts, and in clean air flow. All of this reduces warping. Any knowledgeable Modeler will tell you the value of this option blowing. It is particularly important that as a result of warping, you may receive only a very small descsize (the displacement of the axis of the cylinder relative to the axis of the crankshaft), which will not affect the operation of the engine.

Let’s go further in our reasoning. If you decide to make the drive axle suspension,… along the way, it is possible to use the energy that was previously extinguished by the springs or the rubber ear pendants.

And here is another dignity of cylindrical gear.

There is no need of installation of the cardan, which was a mandatory element of the transmission. Now it will not “eat” their interest in engine power. Fading influence of the gyroscopic moment of the rotating flywheel on the load distribution between the rear and front axles of the wheels of the model. Be only heeling moments that are easy to deal with the selection of attachment points and a cord strap. No connection of the axes with the body. As Moto-set along with axle is collected separately, eliminates the influence of the deformation of the structure upon arrival.

Fig. 3. Scheme the advent of the “twist” when encountering an obstacle:

1 — absorber, 2 — wheel, 3 — gear, 4 — pinion. A — fixed position, B — when lifting-wheel drive models gear wheel runs in gear, turning at a certain angle.

Fig. 4. Racing model with the engine a working volume of 10 cm3

1 — resonance of the exhaust pipe 2 clamp pipe 3 is shock absorber, assy, 4 — drive wheel, 5 — engine, 6 — channel for supplying cooling air, 7 — fuel tank 8 — automatic stop engine 9 — front wheel, 10 — fork in the front axle, 11 — front shock absorber, 12 — frame (tray), 13 — axle front fork, 14 — fairing (body).

The crankcase is made of heat-treated steel 30KHGSA. It has a fairly simple form, but a small thickness of several changes in the technology of its processing. In the roughly machined workpiece are milled channels of the bypass, and on the same machine is brought the external form. Then follows a thermal process of normalization and only after it — boring cylindrical inner surfaces and the landing ends.

The bearing wall of the same steel. It is made nests under the bearings No. 1000900 (10X22) of the crankshaft. The mounting feet machined on a milling machine. The wall is attached to the crankcase with screws M4.

Distribution is also a wall of steel 30KHGSA. Inlet drilled, using cutters it is given the desired form. Attached the item is as same as bearing: four M4 screws. You can understate the inner end wall of 0.5 mm, leaving intact only a two-millimeter band width around the inlet and along the edge of this end.

The crankshaft is made of steel 38ХМЮА, nitrided, polished and peel plies are treated in the mandrel. Features of which is a toothed belt, a threaded socket in the shaft and the crank pin, a tapered entrance into the slot in the finger is subjected to a preliminary rolling. Preparation of the crankshaft ends sealing zapressovkoj the belt at the same time acts as an additional flywheel. Gear: Z = 30, module — 1.0.

The connecting rod and both heads have pressed bronze bushings made with one hand (the external the motion model for annular track of the track) flange.

Spool is a curly polished plate of stainless steel with the thickness 0.4—0.5 mm. It is welded to the flange, the cone which is pressed by screw M3,5 to the knurled surface of the socket in the crank pin. When assembling the engine, make sure that between the spool and the end distribution wall there is a gap equal to 0.08—0.1 mm.

The piston pin is facilitated by drilling, peel plies are treated and polished. Material SHKH15.

The piston is extremely lightweight. Large recesses in the skirt are designed not only to reduce weight, to and for efficient cooling of the flow entering the crankcase fresh mixture. Threaded ring, lock insert with your finger and the rod, at the same time protects the finger from axial movement. Maximum relief piston group allows you to make centrifugal load longitudinal low, to increase the operating speed of the motor and to limit vibrations. Balancing is carried out by pressing on the cheek of the crank tubes of an alloy of VNM type. Piston material — al-26.

Casing from brass LS-62. The working surface (mirror) is chrome-plated and prichert. In steel, the shirt is inserted freely.

The head to reduce stresses in the sleeve are made navertyvajut on a shirt. Different from conventional designs are relatively powerful radial cooling fins and videobrasil grooves on the inner surface. Made on material of AK4-1T.

Fig. 5. The engine with axle and wheels:

1 — wheel with welded rubber and glued balsa bosses, 2 — gear, 3 — key, 4 — axle wheels, 5 — cheek 6 — intermediate gear 7 — a protracted bolt, 8 washer-screw, 9 — columnar shaft 10 — bearing wall, 11 — sealing ring 12 — shirt cylinder, 13 — cylinder, 14 — head engine, 15 — piston and connecting rod Assembly 16, the nozzle 17 distribution drive, 18 — pin, 19 — distribution wall, 20 — Carter, 21 — a protracted bolt, the 22 — plug 23 — spacer, 24 — supporting washer 25, the shoulder of the shock absorber.

Fig. 6. Dukhobory the engine with the crankshaft of the engine and a single-stage gearbox (flap valve suction mounted on the wall of the booster channel).

The drive axle is no different from the usual. Fork (30KHGSA) as easy as possible and has bronze bushings.

Bearings-axles — No. 1000098 (8X19). The same in the intermediate gear. Its axis, simultaneously serving as a finger attachment plugs, made of steel, the Assembly is pressed into the eyelet of the crankcase. Is on both sides of the slot under the locking bolts.

Gear made of steel 40X. Hardness after carburizing and Kalki 45НRС. Intermediate Z=40 and counter shaft Z = 45. Width of the crown in all cases is equal to 4.3 mm.

The drive wheels lightweight design, dural, devulcanizing rubber. The hubs are fastened with screws. Window relief cut and after balancing the wheels sealed the balsa plugs, which greatly reduces disturbances introduced into the ambient flow.

MODEL DESCRIPTION

Frame (tray) is milled from a block of duralumin (D16T). Has a relatively large compared to the size of the whole body height. This allows you to make it more hard and well to make a motor mount. When processing of the frame is particularly careful to the landing places of the plant: notch under the bearing wall and the hole for the pin junction of the wall. From the material of the pallet is machined and the intake to the carb. The gap between them to seal. This will ensure full use of the energy flow for a naturally aspirated engine. it is not so small — velocity head when the model of 300 km/h is equal to 0.04 ATM. Want to imagine what kind of pressure? Then try to clamp a hand outlet home vacuum — pressure there is the same.

Upper fairing (body) hollowed out of basswood and covered on all sides with Fiberglass 0.2 mm thickness for epoxy resin. Channel for supplying to the head of the motor cooling air is made of three layers of the same fiberglass on foam mandrel and glued into the body.

The front wheels of the knife-like shapes are made by conventional techniques. Their distinguishing feature is a small diameter and a sufficiently large distance between them. The first aerodynamically allows to correctly resolve the forward part of the model (the most important in relation to the flow) and reduce the weight of unsprung parts, although places high demands on the rubber. The second gives you the opportunity, strangely, to get rid of extra air resistance. The fact that closely spaced wheels, result in rotation of the entire annular layer of flow between the disks. The result is the same as if we put one nose wheel, but with the width of the treadmill equal to the distance between the discs.

Front axle — conventional pendulum-type plug with the machined sockets for bearings No. 1000095 (5X13). Careful selection of the material of the shock absorber. The size and elasticity of the rubber from which it is made, depends the whole bridge with different quality coatings kartodromo.

Tank with a volume of 80 cm3 soldered tin with a thickness of 0.4 mm. It is mounted on rubber pads, dramatically reducing foaming of the fuel. A stopping device operates on the principle of the latch, pressing the rubber feeding tube.

Shock absorber axle ordinary spring Tina. It is necessary to provide the ability to adjust the torque of the spring itself — this is useful when debugging “shell”.

Pay attention to two specific details. First, the air intake is located on the inner side of the model, and the exhaust channel of the resonance tube is bent in the outside. This is done in order to try to avoid running the course in a cocurrent stream of exhaust gases. After all, our “shell” is one and the same location in a matter of seconds! And getting exhaust gases into the intake can not be considered useful. The second — on the model of flywheel. The calculations showed that for normal operation is sufficient available rotating parts. So, if you are concerned about the low weight of this little micro-car, to improve traction with the track, use the extra load.

In conclusion, I would like to appeal to those who are not afraid to experiment. We want to offer the scheme with front-wheel drive. Using a horizontal motor with a split in the center of the wheel (or gently envelope them) resonant exhaust pipe, can dramatically improve the aerodynamics of the model. Compressed the front wheels closed bottom front wedge-shaped divider of the air, most of them located inside the body, and the protruding upper zakoptelova well streamlined “light” type aircraft. This allows you to make the area of the midsection is even less when a good elliptical sectional shape. Fully enclosed the wheels are to mix the incoming air, even their sides and create a vortex trail, which hides the entire tail section of the model, nullifying the effect of its shape on the magnitude of the total aerodynamic drag. But the creation of such a vortex tail takes considerable energy! If the wheels are closed and only a small part of them meets the incoming flow for its rectangular “heads”, it makes sense to do and licked the back of the body. By the way, this model has another advantage: it has no tendency to raise the nose, lifting the wheels from the track Assembly.

Certain interest and unusual power system using the most promising design of the crankshaft — two-post. The advantage of this motor — the volume of the crankcase can be reduced to the minimum that will provide the most rational form of the overflow channels. If you think that there is no need to make a longer connecting rod thus reduced in comparison with conventional motors side loading on the piston. Suction goes through the flap valve, ending in the cavity of the booster channel. In addition, with a slight increase in gauge, you can go to a single-stage cylindrical gearbox, fully using the advantage of such gears. Winning with the power of motor 3 HP compared to the bevel gearboxes will be almost a 0.1 HP! However, it does not dispense with the flywheel, since the mass and the number of rotating elements is small. However, it’s easy — just a cheek of the crank install ring, machined alloy type of VNM, and having a large specific gravity.

V. TIKHOMIROV, master of sports of the USSR

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