FLY, BASED ON KNOWLEDGE

 

FLY, BASED ON KNOWLEDGEThe results of the last three meetings, which were attended by hundreds of aviation enthusiasts, showed that the majority of the devices is executed at a high professional level. But there were planes, which the creators clearly lacked basic knowledge and experience. These machines, made in violation of the laws of aerodynamics and theory of strength, to fly is not allowed.
We hope that the published material engineer V. P. Kondratyev, member of the technical Committee of ALS-and ALS 84 and 85, to help Amateur designers to avoid many mistakes in the development of ultralight aircraft.
 
Technical job — this is what usually starts the design of the aircraft. Suggest to articulate it. Above all, it should reflect the purpose of the aircraft type and engine power, operational overload, the equipment and payload. In the present TOR, there are other characteristics — maximum speed, climb rate and others, and the result of the study defines the parameters of the power plant. But the “homebrew” choose the engine is not necessary. And the power of the motor in conjunction with stall speed almost uniquely identify the flight data. This is the algorithm of the proposed method of finding the parameters and flight characteristics of the aircraft Amateur
 
 
A few comments on the selection of stall speed. Keep in mind, depends on the difficulty of piloting your machine. From experience with Amateur devices know that the pilot passed the training course at the flying club DOSAAF, not too difficult to fly a plane with a stall speed of 100-110 km/h, for a beginner I need a machine with the value of this parameter 50-60 km/h. But in any case, home machine is not worth to choose it above 90 km/h.
 
The essence of the algorithm design will help to understand a specific example. For example, it was decided to build a single training aircraft under the engine RMZ-640 35 HP from a snowmobile “Buran” (by the way, this is probably the only available engine which can be used for such purposes almost without modifications). Take SKO-
the stall speed of 75 km/h, the wing flap is a simple flap nedelevo. Operational overload of +6 to -3: these will allow your machine to perform aerobatics. Load: pilot (75 kg), fuel (10 kg), parachute (the most suitable glider dorsal PLP-60 -9 kg, either C-4 or C-5 — 12 kg). Equipment: airspeed indicator, altimeter, slip indicator, tachometer, cylinder head temperature, the system receivers air pressure (LDPE). Along with dash it all weighs 3.5 kg. Good to equip the aircraft radio and light (4 kg with power supply).
 
Of course, on the basis of the data of TK can be done a number of rather complex calculations, however, to define the characteristics of a small Amateur aircraft classical scheme better
 
use of statistical recommendations, summarized in a series of nomograms (Fig. 1), which will allow you to quickly and accurately determine all the necessary parameters of the aircraft and its flight data.
 
 
Characteristics obtained by using nomograms, assuming installation of the propeller meet-
the emergence of this regime of flight. In principle, this means that for maximum speed one screw, the maximum rate of climb — other, minimum take — off distance- third… of selecting the optimal propeller in the future we will return.
 
Nomograms (see Fig. 1) allow to compare the influence of various parameters on the performance characteristics and selection to achieve the best results. Defining the parameters of the aircraft, use the diagrams in figures 1 and 4 and watertite preliminary layout (Fig. 2).
 
Now count the weight, and determine alignment.
 
 
At this stage it is necessary to accurately determine the weight of the power plant and equipment for the weighing results or passport. To determine the weight of aircraft assemblies use the nomograms (Fig. 3).
 
Keep in mind that in small planes many elements, the dimensions of which are determined not by calculations, but by “{constructive reasons.” Indeed, the walls of the ribs or lining could be done with a thickness of few tenths of a millimeter, however, it is still much thicker. And such variation is very difficult to consider weight formulas and nomograms, so the weight calculation requires accuracy.
 
Use a more powerful engine, or increase the wingspan and wing area. More accurate take-off weight determined at the element weight calculation after identifying the power of the cross-sections of structural elements for the strength calculation. Weight control spend in all phases of design and construction of the aircraft.
 
The next stage is the calculation of alignment. According to preliminary layout determined the location of the wing, empennage, fuselage and cockpit, which should be as close as possible to the desired center of gravity (15-25% )” Now, mark on the drawing the center of gravity (CG) of the individual units and zcoordinate them as shown in figure 2.
 
In the process, almost all the parameters of the aircraft, including scale, elongation, contraction and the area of the wing and shoulder feathers and other characteristics can be changed within ±5% aerodynamics readily admits it. Can even perform Kry-
lo tapered or swept. But do not make the narrowing more than 2 and the sweep on the leading edge of more than 15°. Choosing the shape of the aircraft, it is not necessary to draw it in perspective. Because the Park is perceived lateral projection, and in-flight planning. And if they both are graceful and beautiful — so you managed to portray a good plane.
 
In the process of design development do not forget about the structure of the aircraft set main power components: spars, ribs, frames, junction nodes, and then watertite the layout of the aircraft in scale of 1 : 5 and in 1:10 scale, as shown in figure 4. Recheck the weight and precise alignment. If it is slightly deviated from a preset, adjust it, moving certain units of the power plant or equipment.
 
 
If alignment must be correct within wide limits, it is more efficient to slightly move the wing.
 
So, you painted your plane. Carefully examine the drawings, analyze all its advantages and disadvantages. And after some time start the development of the second variant: probably, you will have new ideas. Bad, if “regular” development will be the first, nor bad when the new layout has no end…
 
Vladimir KONDRATYEV

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