TRIPLE – SNOWMOBILE! | MODEL CONSTRUCTION

Still not having accurate information, will allow the professional micromotors in the school types of the car, we decided a new “sled” design under MDS-1,5 D of production ON Savelovsky “Progress”. If not today, then tomorrow, the race for the result will be a three-band motors in the world is simple cord snowmobile, and on trainings it is possible not to burn preparirovanie and therefore malaisrie MK-17. As you can see, the reasons for the transition to MDS we had.

Purchased several new motors were given the opportunity to begin the design of the sled. In principle this was a simple task, as we were based on a known design (see “M-K” № 8, 1989, article “speed — through simplicity”). The fact is that, we think, in her scheme of aeromodel brought to its logical perfection with the complete abolition of technical “frills”; she has no equal and adaptability. However, based on a new engine, potentially much higher turnover compared to the MK-17, we had to slightly change the cross section of the housing with simultaneous increase of the wall thickness and raise the surface of the stabilizer. After all, his main goal is to compensate for gyroscopic moments from the rotating propeller, which in turn depends on the speed. Design and materials the new pattern has repeated published in the journal.

The saved and the principle of fixing the “model engine”. Although at first we tried to draw a version with the usual under engine bars (more than usual, which can be recommended only for models beginners), in the end decided to remove the legs from the engine crankcase and cut all the motor mount on the M3 to use for his installation two dural bracket. As our sleigh strut abolished, in the sub boss now are stuck with two fat rods, which are threaded sockets and under the corners of the motor, and cord under the bar. In the manufacture of the site, it is important all work is conducted with maximum precision, so you do not have to eliminate the deviation of the axis of the shaft of the propeller. It is possible to resort to this trick: first, collect all the walk-behind tractor with a tank and only then after trying to glue the tail boom housing. Based on the logic “the model is mounted on the engine” and heavy duty construction of MDS, wire bracket main ridge is screwed directly to the cylinder head (as already mentioned, it is also used M3 screws). Power system is the most modern type, with the nozzle in the tank and pipe supply, Ø 3 mm, 2 mm incoming in the axial hole of the spool (for reference: last size equal to 6 mm). The jet is made from scratch from brass and the Assembly is soldered into the tank. The needle is withdrawn downwards, which increases the ease of adjustment because of the one-way direction with the adjustment screw compression ratio, and racing snowmobiles are not corrupted projecting parts. Of course, the power of the engine the fuel pressure bleed from the crankcase through the nozzle-valve. The deflector hood is in the winter rather for the purpose of protecting the cylinder from hypothermia than the problems of aerodynamics, so the slot for the entrance of air is cut during the selection regime of plant.

The MDS was almost ready when we slipped and began the run-in has not yet converted to the sled motor. Each individual Modeler will understand our impatience! And now…

Fig. 1. Control line racing aeromodel sleds with motor working volume of 1.5 cm3.

Fig. 1. Control line racing aeromodel sleds with motor working volume of 1.5 cm³.

A new, apparently unusual, according to passport information is very powerful and high speed motor placed on a stand. Immediately, it appears that the adjustment screw compression do not collapse even with the use of pliers (forgive us heads of clubs, no doubt correctly, prohibiting even the nuts fixing propeller tighten mites). But the impact when the rotation of the shaft it seemed that the compression is close to optimal. So we decide to try to start MDS. Flash finally appear, and nothing more. Maybe a bad copy I got?

Then someone from the guys remembered that from friends heard the conversation, such as the setback suffered by our opponents, and the club-model aircraft. What to do? I climbed into the motor, though at first it didn’t mean it…

How many “good” words were said, when it was discovered that hidden behind the beautiful appearance of the motor. First, it turned out that we were lucky because of the failure of the launch. The fact that after polishing on the cheek of the crankshaft burrs left, the size is not inferior to the cord, and after launch they are guaranteed to have fallen off. You don’t need to explain that the motor would be trashed after this whole thing? More — more…

Fig. 2. The power part of the model.

Fig. 3. Billet fuel tank.

Fig. 4. A mandrel for vyklicky tubular beam housing (housing wall thickness about 1 mm).

Fig. 5. The validation scheme the mass of the connecting rod and piston taken in the calculation of the degree of balance. To ensure accurate balancing of the shaft, put on the knives, it takes half a given mass (it can be appropriate weight to the ring worn on the finger of the crank of the crankshaft).

In short, here is a brief description of available samples of MDS. Sleeve and piston, looks very good, but even with polishing the chrome on the factory managed to polepit such burrs (or rather, nodules), any ones you want — will not succeed. Of course we took (and they fall off almost effortlessly!). Put the locking sleeve studs on all three motors, as they were planned but forgotten at the factory during Assembly. The back wall we were particularly interested in, as the host spool of special claims was not. Steel toe Carter also seemed satisfactory, and the test of balance cryoseparators group left for later.

Special but deserves a cylinder head. For unknown reasons, made of steel (by weight it is almost equal to that Carter!) and some strange form, she, along with brass controlchan by mutual adjustment called Frank amazement. Controlling was pressed into the slot, and the amount of brass that “got” was cut off by the edge of the nest and moved down counterrevolutionaries!

We were taken aback so much that I started grinding counterrevolutionaries. In principle, it is not too difficult. Especially when you consider that the slot in the head was clean enough. It is not realize that do a complete nonsense. Convincing evidence was first the start given in the order of engine-semi-finished product. Easy moving controlling immediately jammed! Otherwise, it could not be — brass in steel after warm-up sets with the same preload, there is nothing to think about trying to adjust the compression ratio. Cool motor then please adjust. But not during work!

The only way to manufacture head again, made of aluminum… However, there is another way: try to install controlling of PTFE with the top pressure washer. If you want to try, but we stopped at the famous the classic version (which, as with the concept of thermal expansion of metals unfamiliar to the developers of MDS-1,5 D? And what was the shot power characteristics of the enterprise?). Realizing that we are dealing rather than with a ready engine, and a semi-finished product, in addition to the removal of the exhaust pipe on the crankcase at the same time has presledovali boarding sock end face of the motor providing the shaft deflection under 0.2 mm in size, the seats. By the way, this was not enough: after running all the samples visible traces clamp rod to the side of the spool. It seems that low rigidity of the crankshaft and the crank of the thumb and the wrong choice crankshaft bearing, enabling greater SAG under load.

In short, in the end, MDS earned, some not even Recalling the forced “Junior”. Lifted the skirt of the piston so that there is only a wall in the area of the exhaust window, and the bottom exhaust opening 0.5 mm when the piston is at TDC. The regime has improved, but the MK-17 is far. And then pay attention: a little tight spinning shaft. The last straw was such a tight factory pressing both ball bearings, disassemble them without destruction is impossible.

What else can I say? What we never thought of the regular gitlerom node? Yes, we don’t need. I hope that you will do without him, otherwise, do not avoid the need in a number of improvements, including the preparation of a new futorki. Or back to balance? So it as such is absent, almost entirely compensated by the weight of the crank finger. Of course, the result of a lot of work to put everything in order and spent a lot of effort to force MDS to issue the passport of 0.28 kW (by the way, in the passport — not one word about the fuel or air screw, which starred features!). But… maybe not necessary to begin with this?

Reminder: the cost of the compression motor MDS-1.5 D 55 rubles! It is available Savelovsky production Association “Progress”…

DMITRIEV D., head of the self-similar mug

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