SCHOOL AIRCRAFT

SCHOOL.You decide to build an airplane. And immediately before you the first issue – what will it be? Single or double? Often it depends on capacity of the engine, availability of necessary materials and tools, as well as the size of the “Angara” for the construction and storage of the aircraft. And in most cases the designer has to opt for a single aircraft type training.

According to statistics, this class of aircraft is the most widespread and popular among designers and enthusiasts. For such machines used a variety of schemes, types of structures and engines. Equally often there are biplanes, monoplanes with low – and high-wing single – and twin-engine, with pulling and pushing propellers, etc.
This new series provides an analysis of the advantages and disadvantages of the main aerodynamic designs of aircraft and their constructive decisions that will allow readers to independently assess the strengths and weaknesses of various Amateur designs that will help choose the best one and most suitable for construction.
 
WITH THE AIRCRAFT -ONE ON ONE
 
One of the most common ways Amateur single aircraft is a strut-braced monoplane with a high wing and a tractor propeller. It should be noted that this scheme appeared in the 1920-ies and for all time of its existence remained virtually unchanged, becoming one of the most studied, tested and worked constructively. The characteristic features of this type of aircraft – wooden two-spar wing, welded steel truss fuselage, fabric covering, pyramid chassis and enclosed cab with door car type.
 
In the 1920-ies – 1930-ies became widespread version of this diagram – the plane of the “parasol” (FR. parasol – a parasol), representing a high-wing monoplane with the wing attached to the uprights and the struts above the fuselage. The “parasols” in Amateur aircraft construction meeting today, however, they are usually structurally complex, less perfect in relation to aerodynamic and less comfortable to use than the classic vysokopilya. In addition, such devices (especially small sizes) is very difficult access to the cabin and, as a consequence, the complexity of its emergency escape.
 
A parasol
 
B - high
 
Single aircraft vysokopilya:
 
And – parasol “Kid”:
 
engine – LX-2 with 30 HP design L. Komarov, wing area – 7.8 m2 wing profile is Clark takeoff weight of 220 kg (pilot – 85 kg, the power plant is 32.2 kg, the fuselage – 27 kg chassis with skis -10,5 kg horizontal tail is 5.75 kg, wing struts – 33 kg) maximum speed — 130 km/h, flight range with fuel reserve-10 l-180-200 km
 
B – high “Leningrad”:
 
engine – “Zundapp” capacity 50 HP, wing area – of 9.43 m2 take — off weight- 380 kg, the empty weight is 260 kg, a top speed of 150 km/h, climb rate near the ground is 2.6 m/s, the flight duration -8 h stall speed 70 km/h

 
The plane-vysokoplan V. Frolov
The plane-vysokoplan V. Frolov
 
The advantages vysokopreosv can be attributed to the ease of piloting, particularly if the specific load on the wing does not exceed 30 – 40 kg/m2. Vysokopilya are highly resistant, excellent landing characteristics, they allow the rear alignment up to 35 -40% mean aerodynamic chord (SAH). From the cockpit of such a device the pilot provided the optimum downward visibility. In short, for those who are building their first aircraft, besides going on their own to master his flying, the best scheme is not to come up.
 
In our country, to the schema of the strut-braced high-wing monoplane aircraft designers-fans were treated repeatedly. So, at one time there was a whole squadron of planes-“umbrellas”: “Baby” from Chelyabinsk created by a former pilot L. Komarov, “Leningrad” from St. Petersburg, built by a group of modelers, headed by V. Taciturnity, high-wing monoplane, designed by mechanic V. Frolov from Moscow, the village of Donino.
 
About the last machine I should tell more. Having studied the most simple scheme of a strut-braced high, the designer has carefully planned its work. The wing is made from pine and plywood, the fuselage is welded steel tubing and covered these elements of the plane of the canvas classic of aviation technology. Wheels for the chassis picked up large to be able to fly from unprepared ground sites. The power unit is based on a 32-horsepower engine MT-8 equipped with a gearbox and a propeller of large diameter. The aircraft’s takeoff mass is 270 kg, in-flight alignment – 30% of SAH, the specific wing loading of 28 kg/m2, a wing span of 8000 mm, traction screw in place – 85 kgf, maximum speed – 130 km/h, landing 50 km/h.
 
Test pilot V. Zabolotsky, who circled this unit, delighted with its capabilities. According to the pilot, they will be able to manage even a child. The aircraft was operated at V. Frolov more than ten years and participated in several gatherings of ALS.
 
No less enthusiasm among the test pilots called the aircraft PMK-3, created in the suburban town of Zhukovsky group of aircraft enthusiasts under the leadership of N. Prokopto. The machine had a kind of nose of the fuselage, a very low chassis and was designed according to the scheme of strut-braced high-wing monoplane with an enclosed cockpit; on the left side of the fuselage provided for the door. Wing are beveled back to ensure the necessary alignment. Aircraft design – solid wood with fabric cording. The wing is single-spar with pine shelves, a set of ribs and forehead of the wing is sheathed with plywood.
 
The plane PMK-3
The plane PMK-3:
 
wing area is 10.4 m2 wing profile – R-h, take – off weight- 200 kg, fuel capacity – 13 liters, the flight alignment 27% SAH, static thrust of a propeller is 60 kg, stall speed: 40 km/h, the maximum speed is 100 km/h, range 100 km

 
The base of the fuselage – three of the spar, and therefore the fuselage had a triangular cross section. Empennage and control system aircraft PMK-3 is made as a famous training glider B. Oskinis BRO-11 M. the Basis of the power plant – a 30-horsepower outboard motor “Whirlwind” liquid cooled; the radiator were a little from the right side of the fuselage.
 
An interesting variation of a strut-braced high Amateur-built was the “don Quixote”, developed in Poland by Y. Yanovsky. With a light hand of an Amateur enthusiast of aviation famous pilot-glider pilot-investigator and journalist G. S. Malinowski, published in the journal “modelist-Konstruktor” drawings “don Quixote”, this, in General, not very successful the scheme has received very wide circulation in our country at conventions SLA sometimes there were more than four dozen similar devices. Professional aircraft designers, however, believe that the pilots-fans in this scheme attracted primarily to the unusual appearance of the aircraft, but it has some hidden pitfalls.
A characteristic feature of “don Quixote” was the forward cabin, which provides excellent visibility and convenient location of the pilot. However, for very light aircraft weighing up to 300 kg alignment has changed significantly in the case when in the cockpit instead of the 80 kg pilot sat a more slender, weighing 60 kg to the machine when it suddenly turned from an overly stable to absolutely unstable. To avoid such a situation, followed even at the design stage of the machine – it was only necessary to set the pilot’s seat in the center of gravity.
 
A -
 
B -
 
In - plane A-12
 
Aircraft with pusher propeller designed by the scheme of the aircraft “don Quixote”:
 
A – “don Quixote” by Y. Yanovsky and layout of the cubicle:
 
motor power — 25 HP, wing area is 7.5 m2, the empty weight is 150 lbs., takeoff weight of 270 kg, maximum speed – 130 km/h, climb rate at ground level — 2.5 m/s, ceiling 3000 m, range is 250 km away. machine Design – solid wood
 
B – “Polonaise” Me. Yanovsky:
 
engine power – 30 HP, wingspan -7 m, wing area – 7 m2, the empty weight is 105 kg, takeoff weight of 235 kg, maximum speed – 160 km/h, climb rate is 3 m/s, the flight duration – 3 hours
 
In – plane A-12:
 
construction – fiberglass, engine power – 35 HP, wingspan — 8 m, wing area is 8 m2 wing profile Clark YH, takeoff weight – 246 kg, empty weight – 143 kg, in-flight alignment – 20% SI, maximum speed – 130 km/h

 
Another feature of “don Quixote” – chassis with the tail wheel. As is known, such a scheme in principle does not provide directional stability of a light aircraft while moving on the airfield. The fact that the movement of the aircraft with the decrease of mass and moments of inertia become quick, sharp, short-period, and the pilot has his attention to be focused on maintaining the direction of takeoff or mileage.
 
The aircraft a-12 club “Aeroprakt” (Samara), representing one of the copies of “don Quixote” had the same congenital defect as the first-born of this galaxy, but the designers after testing machine professional pilots Makagonov V. and M. Molchanka quickly found the error in the design. Replacing the A-12 tail wheel bow, they completely eliminated one of the main disadvantages of the aircraft the Polish scheme.
 
Another drawback of “don Quixote” – the use of a pusher propeller, shaded in flight, the cockpit and the wing. The efficiency of screw fell sharply, and the wing, not blown airflow from the propeller, provides the estimated lift force. As a result, growing the takeoff and landing speeds, which resulted in a lengthening run and run and reduced climb rate. At low thrust-weight ratio, the plane could never get off the ground. That is what happened at one of the gatherings of ALS with the plane “Elf”, built under the scheme of “don Quixote” students and staff of MAI.
 
Of course, to build machines with pusher propeller is not forbidden, however, the need and feasibility of creating aircraft with such power plant in each case should be carefully evaluated, as this inevitable loss of thrust and wing lift.
 
It should be noted that designers, creatively approached to the use of the power plant with pusher propeller, was able to overcome the shortcomings of such a scheme and create some interesting options. In particular, some good machines under the scheme of “don Quixote” was built by a mechanic from the city of Dniprodzerzhyns’k P. Atemov.
 
Plane
The Plane “Crystal” P. Alimarina:
 
the wing area is 8 m2 takeoff weight – 215 kg, maximum speed – 150 km/h, stall speed – 60 km/h, climb rate near the ground – 1.5 m/s, the range of operating overloads from +6 to -4

 
Aircraft design
 
The design of the aircraft “Crystal”:
 
1 – metal toe wing; 2 – tubular wing spar; 3 – flap; 4 – tubular spars Aileron and flap; 5 – Aileron; 6 – lever engine control; 7 – the front door of the cockpit (right side); 8 – engine; 9 – control rod Aileron; 10 – brace in the plane of the wing; 11 – riveted duralumin fuselage beam; 12 – tubular side members; 13 – speed indicator; 14 – the ignition switch; 15 – altimeter; 16 – variometer; 17 – gauge slide; 18 – gauge cylinder head temperature; 19 – handle flap; 20 – dorsal parachute

 
Well flying a plane with a pusher propeller was created by a team of Amateur aircraft club “Flight” Samara aviation plant under the supervision of P. Aparina – this car has received the name “Crystal”. Fly around its test pilot Vladimir Gorbunov has not stinted on the high rating according to reviews, the car had good stability, was easy and simple to manage. The samarians were able to ensure high efficiency of the flaps, otklanyatsya at 20° for takeoff and 60° during landing. However, the rate of climb of this aircraft was only 1.5 m/s due to shading pusher propeller wide cockpit. However, these parameters proved to be quite sufficient for the Amateur design – and this despite the fact that take-off it had been difficult.
 
Attractive appearance of Crystal is combined with a great production and performance all-metal monoplane. A glider fuselage is a duralumin I-beam, riveted from the 1-mm sheets D16T. In the power set of I-beam also included several curved sheet of aluminum walls and frames.
 
It should be noted that in Amateur structures instead of metal, it is possible to use plywood, pine sticks, plastics and other materials available.
 
In the curve of the fuselage beams in the bow part, was located the cabin, closed a big transparent faceted lantern shape and a light fairing of D16T sheet thickness of 0.5 mm.
 
Strut-braced wing is an original single-spar design with spars of duralumin tubes 90×1,5 mm, perceiving the load from bending and torsion of the wing. The set of ribs of 0.5 mm D16T, stamped in the rubber, are fixed on the spar with rivets. The wing strut is made of dural tube 50×1 and improved fairing from the D16T. In principle, dural spars and struts, you can replace the wooden, box-section.
 
The wing was equipped with ailerons and flaps with mechanical hand drive. Wing profile – R-III. Aileron and flap had spars of duralumin tubes with a diameter 30×1 mm. the Forehead of the wing – from 0.5 mm sheet D16T. The surface of the wing tight fitting cloth.
 
Tail – cantilever. Keel, stabilizer, rudder and Elevator – also odnalezienie, with spars of pipes D16T diameter 50×1,5 mm. Tail tight fitting cloth. Control wiring ailerons were hard thrust and rocking wiring to the rudder cable.
 
Chassis – tricycle, with steerable nose wheel. Depreciation chassis on the plane is due to the elasticity of the wheels-tires with dimensions 255×110 mm.
 
The basis of the power plant of the aircraft – 35-HP two-cylinder engine RMZ-640 from a snowmobile “Buran”. The propeller is of wooden construction.
When comparing the pulling and pushing propellers you need to keep in mind that for devices with a small power capacity of the first is more efficient that at one time showed great French aircraft designer employee of the company “Aerospatiale” Michelle Colombian – Creator of a small and very elegant aviette “CRI-CRI” (cricket).
 
Will not be superfluous to remind that the creation of small-sized aircraft with engines of minimum power at all times attracted both Amateurs and professionals. Thus, the large aircraft designer O. K. Antonov, has already built a flying giant An-22 “Antey” takeoff weight of 225 tons, in his book “Ten times first” told about his dream plane, the little engine 16 HP unfortunately, to create such a device Oleg Antonov doesn’t have time…
 
To construct a compact plane – the task is not so simple as it might seem at first glance. Many have conceived it in the form of ultra-light machines with extremely low wing loading. The result is an ultra-lightweight vehicles that are capable of flying only in the complete absence of wind.
 
Later, the designers came to the idea of using such devices for wings of small area and high specific load, which allowed to significantly reduce the size of the machine and increase its aerodynamic quality.
 
A - plane
 
B - plane
 
The twin-engine diskoplana:
 
A – plane “Cree-Cree” of Michel Colomban (France);
 
B – plane “Grazing” Edward Magnascope (Poland) — a good example of creative development of the scheme “Cree-Cree”:
 
powerplant – two engine KFM-107E with a total capacity of 50 HP, wing area is 3.5 m2, the elongation of the wing – 14.4 V, empty weight – 180 kg; takeoff weight – 310 kg; maximum speed – 260 km/h; stall speed – 105 km/h; range – 1000 km

 
Aircraft
 
The layout of the aircraft “Cree-Cree”:
 
1 – priends air pressure speed indicator; 2 – duralumin rotor (maximum speed – 1000 rpm); 3 – engine “Rowena” (the working volume of the cylinder 137 cm3, 8 HP, weight 6.5 kg); 4 – resonant exhaust pipe; 5 – a diaphragm carburetor; 6 – heating fuel – flexible hoses with weights on the ends (one per engine); 7 – Gaza (left side); 8 – crank mechanism of trimmer effect (adjustment spring segregates rudder); 9 – reset of the lamp; 10 – unsupported rocking in cable wiring control rudder; 11 – rigid wiring control stabilizer; 12 – cable runs actuator rudder; 13 – all-moving horizontal tail; 14 rocking of the rudder; 15 – longitudinal keel; 16 – gear in the compressed position of the cushioning; 17 – spring of the main landing gear; 18 – drain pipe of the fuel tank; 19 – control knob that is stuck Aileron-flap (left side); 20 – fuel tank capacity 32 l; 21 – cable wiring control nose landing gear; 22 – adjustable pedals; 23 – segregating pedals (rubber shock absorber); 24-rubber damper right landing gear; 25 – frame installation engines (a steel V-shaped pipe); 26 – rocking control bow stand; 27 – wing spar; 28 – hovering Aileron (deflection angles from -15° to 8°, hanging – +30°; 29 – foam frame; 30 – wing; 31 – headstock hanging Aileron; 32 – the foam ribs; 33 – ending of the stabilizer (balsa); 34 – stabilizer spar; 35 – toe Aileron (trim – aluminum, filler – foam)

 
As already mentioned, one of the most successful aircraft constructed in accordance with this concept was a twin-engine airplane had “KRI-KRI”, created M. Colombana. This camera for its size resembles a large flying model, rather than a manned aircraft. Its takeoff weight of only 170 kg, empty weight – 70 kg, wing area – 3.1 m2. However, excessively reduce the wing span, as it sometimes makes novice aircraft designers, Colomban did not, believing that the load-bearing properties of the wing is primarily determined by its absolute scale, not a square. So, the “KRI-KRI” wingspan is 4.9 m, length – 3.9 m, height – 1, 22 m
 
The aircraft has two single-cylinder air-cooled engine with a total capacity of 16 HP In the subsequent numerous variants, the “KRI-KRI” used engines with a capacity of 8 to 10 HP a Characteristic feature of this aircraft is the front-engine V-shaped rack, which creates good conditions for their cooling and for the air screws.
 
In parallel with the design of ultra-small machines with high specific load on the wing in the West has evolved and the opposite direction – design “butterflies” is an ultralight aircraft with a huge wing. As a rule, the tubular aircraft conceptual design with a soft covering, created at deltaplano technology. However, the performance of “CRI-CRI” has advantages with a much smaller capacity power plant. Concedes he is “butterflies” only at minimum speed and landing characteristics, significantly exceeding them in all other flight parameters. And, above all, due to the high aerodynamic perfection compact apparatus.
 
“Cricket” is made mostly of metal. Sheet duralumin made the wing spars, empennage and fuselage, as well as all plating, the thickness of which does not exceed 0.5 mm. In our time, many of the homebrew I try to use plastic in the hope to obtain a significant reduction in the mass of the apparatus. However, the analysis of the structures of these aircraft shows that the bulk of them on 15 – 20% more than the car Colomban. Non-force elements of a glider “KRI-KRI”, including wing ribs, tail and some fuselage frames, made of dense foam. All the connections are thin metal plating with a frame made using bonding, which contributed to obtaining a clean and smooth aerodynamic surfaces.
 
The plane Colomban is very popular among Amateur aircraft designers. The simplicity and adaptability of its design contributed to the spread of “Cricket” in many countries – according to the drawings Colomban was built dozens (if not hundreds) of this type of device.
 
Handling qualities “KRI-KRI” was quite high: it can perform aerobatics in the range operational overloading and from +6 to -3 and such stunts as flying the same two cars “head to head”.
 
(To be continued)
VYACHESLAV KONDRATYEV

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