SLEIGH KMD-2,5

SLEIGH KMD-2,5A number of recent publications in “M-K” on the cord design racing cars and snowmobiles helped us in creating equipment and more heavy class — under the engine working volume of 2.5 cm3. Despite the fact that the published information has mostly referred to “trucks”, most of nodal solutions have been shown to be beneficial in the classroom as-2 and AM-2. Sharp weight reduction and a simultaneous simplification of the circuit and process of manufacture, the almost total absence of metal and processed by machines details helps aeromarine with “paper” beam and a kind of motor mount on three points and remain leaders in technology, accessibility of buildings and possibilities of achievement of high sports results.
Of course, the ultimate goal of creating such machines — that athletic performance — in the first place depends on the maturity and the bringing of the engine. But the model itself needs to be under a good engine. We therefore believe that the time searching for the optimal design of cars has passed (though it’s not pleasant…), and it makes no sense to build new “experimentally” when there is brought, the debugged technology and very simple technique. I would like to note that, as can be seen from the publications in the end it turned out that the aerodynamics to increase the rapidity of the models is insignificant; with satisfactory streamlining in front of the athlete-designer, there is only one task — to ensure sustainable progress for all modes.
 
That’s exactly what this feature of aeromodel we wanted to talk with the followers of aviamodelirovaniya. The fact is that, despite the typing scheme, in competition you can find quite a variety of focal solutions machinery. “Fuselage” — wooden dugout, fiberglass, mixed designs (although most of it is still Vileika of Kraft paper offered by the journal). Against this diversity, I have nothing, as the weight of the body on all driving performance is affected little, and here it is only important to provide rigidity for satisfactory processability. But the stabilizers… the Most common “tails” of duralumin sheet, although not as rare and solid wood or plywood options. But from the point of view of stability of the course none of the above is simply unacceptable! As most distant from a center of gravity detail, the stabilizer and the tail defines a large part of the total moment of inertia of the whole model, and this is the main characteristic vibrational stability of the device on the go.
 
Control line racing model snowmobiles with the engine working volume of 2.5 cm3.
Control line racing model snowmobiles with the engine working volume of 2.5 cm3:
1 — front point of support (ridge or pair of wheels), 2 — tail boom (tube made of Kraft paper with a thickness of about 0.8 mm), 3 — eyelet engine model 4 — engine fairing, 5 — strut engine mounts, 6 — spinner, 7 — propeller (birch), 8 — main landing gear, 9 — cord strap, 10 — screw carb adjustment, 11 — stabilizer (original version), 12 — plate with screws of fastening of the stabilizer.
Fuel tank (tin tin).
Fuel tank (tin tin).
 
Installer for vyklicky tail boom from Kraft paper.
A mandrel for vyklicky tail boom from Kraft paper.
 
Cord strap (D16T).
Cord strap (D16T).
 
Sub boss Assembly.
Sub boss:
1 — sleeve (dural tube), 2 for the side cheeks (plywood thickness 1,5…2 mm), 3 — insert (dural core), 4 — the base of the boss (beech, birch).
 
The construction of the extension nozzle, built-in tank.
The design of the extension nozzle, built-in tank:
1 — feed tube, 2 — wall fuel tank, 3 — reinforcing tin clamp, 4 — nozzle, 5 — nut 6 — washer (soldering, together with parts 4, 5 and 2), 7 — wire, latch needle, 8 — needle nozzle, 9 — drain pipe, 10 — clamping nut 11 — tail boom, 12 — spraying tube.

 
To better understand the problem, try to imagine a pendulum attached to a flat plate-“stabilizer”. If a thread is to leave a “tail”, any fluctuations will calm down almost instantly. A little utilite pendulum — everything will change immediately, the process of attenuation will noticeably stretch of time. Exactly the same happens on running the model. The only difference in the oscillation frequency. Unfortunately, the eyes, everything happens completely transparent, and the effect is only in the lack of speed.
 
So what still needs to be a stabilizer? The figure shows the basic power circuit of lightweight options (by the way, even the worst of them is about five times lighter than metal!). In the initial model, we used the simplest celebarty stabilizer. But the weight of timber shall not exceed 0.1 g/cm3, the exterior and interior is neat pasting fiberglass thickness of 0.03 mm on a parquet varnish. Otherwise, they would have to go on the matched plane.
 
The design of the stabilizer in the original version.
The design of the stabilizer in the original version:
1 — ending (balsa), 2 — stabilizer (balsa), 3 — wedge insert (Linden), 4 — front edge (birch). The thickness of the finished stabilizer is about 3 mm.
 
The basic structural layout of the stabilizers lightweight type.
The basic structural layout of light stabilizers:
1 — metal (foil D16T with a thickness of 0.2…0.3 mm) power paneling, wooden FALCONIERE, 2 — power metal sheathing, the foam filler forehead, 3 — Styrofoam head (foam stamps PVC), wooden dial with ribs, made of Mylar film, 4 — solid wood set with the skin of the forehead from plywood with a thickness of 1 mm, the rest of the film 5 is a stacked structure with ribs and a full covering of film 6 — finished structure made of balsa with a partially covering film.
On the choice of the size of the stabilizer you need to make a few comments. Do note that his profile efficiency is almost independent. Angles of attack even with the buildup of the model are within the boundaries under which the work of the flat plate equivalent profiled wing. But much more important is the extension of the stabilizer. Damping properties of the long narrow plane themselves above (albeit with a “round” of the stabilizer it is possible to achieve satisfactory characteristics of the model, but due to a sharp increase leverage — the distance between the stabilizer and the center of gravity of the machine). But the main advantage of the plane-a”knife” in the other. If “circle” is guaranteed to be intense air jet from the propeller, the “knife” in large end sections of the exit area of the jet. In case of any deviations of the housing from the horizontal such knife will clearly take into account the change in blow-out of the undisturbed surrounding air will create power, levelling position of your body. Short stabilizer, no one will notice the tilt, as with the hull and propeller jet leaving the horizontal (real length of the shoulder surrounding air has little effect on the slant of the jet). The result is that “circle” is only able to dampen vibrations of the body, and not so effectively.
 
About the thickness of wing plate: from the viewpoint of ease of the stabilizer but it is more advantageous to use a symmetrical profile relative thickness of about 8…10% of its chord. The plate plane is a good technology; but if you need to remove a few unnecessary grams of weight from the tail of the model, will have to return to the stacked profiled options. The required strength and stiffness will be provided here either langeronii elements, or the subtle working hard covering. The resistance of the profiled plane in comparison with a flat plate with the same shape in plan has the same with her air resistance (oddly enough in the opinion of automodellista).
 
Good quality model and good engine. On our model was mounted a modified KMD-2,5. Here’s just the list of modifications: due to the lapping cylinder end of the crankcase cylinder axis sloped back to prevent slipping of the connecting rod with the crank; the bore is chrome-plated and peterto; the piston is facilitated by removing the entire skirt, also located in the area of exhaust window; both the connecting rod is cut with the cutting melodiewinawer “pockets” that are absolutely essential for the highly loaded racing engines; rear spool wall of the crankcase drained and rotated 90° counter-stroke engine; factory carb completely abolished — its functions are now performed by two parts of the motor (more precisely, the motor and tank, as the cavity along the axis of the spool was in fact futorki, and a discharge tube tank nozzles — the nozzle). By the way, last revision made on the recommendations of the journal for the “lorry”, in combination with the rotation of the walls completely transformed KMD. He was easy to reach a high speed without the slightest sign of overload or “zadavlivaniya”. The impression is that even on standard fuel he had large reserves of power.
 
When calculating the speed of 200 km/h it is useful to perform another operation domainservice engine. Even with a lightweight piston KMD needs it, and therefore on the cheek of the crank in the pre-made channels zapressovyvajutsja tube of alloy type of VNM. Then again controlled by the degree of balance. It should be equal to 0,46 0,49…. And, of course, the most attention requires the selection and workmanship of the propeller. According to our observations, are better than wooden screws nothing. Stekloplastikov much more “touchy” to use and unstable geometry, which is much variability in practice.
 
Yury YURYEV, head of the society

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