WO1994010033A1

WO1994010033A1 - An ultralight aircraft, in particular a helicopter

Info

Publication number: WO1994010033A1
Application number: PCT/IT1993/000092
Authority: WO
Inventors: Alfredo Castiglioni; Angelo Castiglioni
Original assignee: Crae Elettromeccanica S.P.A.
Priority date: 1992-10-23
Filing date: 1993-09-08
Publication date: 1994-05-11
Also published as: CN1086184A; IT1255907B; BR9307278A; ITMI922433A0; ZA936671B; AR248246A1; ITMI922433A1; AU5154993A

Abstract

An ultralight aircraft is described, in particular a helicopter, falling within the limits of a basic weight ranging from 210 to 230 kg and a maximum weight of 450 kg, the length (L) of which ranges between 4950 and 5150 mm. The structure (50), constituting the characteristic framework of the helicopter, is formed by several tubular elements of titanium alloy which converge in a plurality of central knots (KC1...KC4) lying on the helicopter's symmetry plane, and of pairs of lateral knots (KL1...KL7) symmetrical with respect to said plane, the spatial position of which, referred to a triad of axes, is defined in relation to the length (M) of the structure selected as a basic parameter.

Description

DESCRIPTION

Technical Field

The instant invention relates to an aircraft falling within the ultralight (UL) class, in particular to a helicopter apt to perform hovering, rotating on its axis and translating in every direction with respect to its axis of symmetry, including rearward flight.

Background_Art

The field of the presently existing ultralight (UL) aircrafts can be divided into three classes:

a) a stiff wing conventional type aircraft;

b) a flexible wing (Rogallo wing) aircraft

c) a rotary wing gyroplane.

The structures of the above three classes of aircrafts are relatively simple and this is the reason why their weight can quite easily be contained within the limits prescribed by law. However, all these types require a flat free area, even if short, for landing and take-off, as none of them are capable of hovering or of rotating on their axis or of flying in a vertical direction like helicopters, thus substantially differing from the flexibility of use of the latter.

Deltaplanes, gyroplanes and small ultralight aircrafts have been built also by amateurs having some knowledge of flight mechanics whereas actual realizations in the field of helicopters have practically been non-existent, notwithstanding the advantageous characteristics of such vehicle, since the relevant flight mechanics and construction technologies are too sophisticated and exacting, outside the domain of a non-professional designer.

In other words, although it is all but simple to scale down the geometrical dimensions of an aircraft in order to comply with the ultralight class requirements, even reducing the maximum velocity performance, autonomy, ceiling, and similar properties, the problem of conforming a mechanically complex aircraft, such as a helicopter, is certainly even more difficult.

Disclosure of Invention

The object of the instant invention is to make a helicopter falling within the weight limits contemplated under the class of UL vehicles, i.e. having a basic weight ranging between 210 and 230 kg and a maximum take-off weight of 450 kg without floats and 500 kg in the amphibious version, apt to operate as a conventional helicopter as far as flight quality, e.g. manoeuvrability, stability and safety, are concerned.

It is a further object of the instant invention that the helicopter, equipped with the necessary accessories and control devices, with a comfortable cockpit, with simple and functional controls based on the known art, be also preset for the subsequent fitting of

special equipment depending on the end-use intended for the craft (snow skids, floats for sea-landing and other items), all of which items lie outside the scope of the present patent application.

In addition to the transportation of one or two persons, for sport or work of any kind, this type of helicopter can also be advantageously utilized in the agricultural field, e.g. for spraying pesticides.

Presently, helicopters or aircrafts are hired for such tasks, which crafts, however, apart from their high operating costs and the need of flight licenses, denote the practical problems connected with the distribution of such products. For the function of transporting persons, it is particularly important to be able to employ a lightweight craft, of very small dimensions, apt to utilize extremely limited, natural or prepared aprons, in mountain areas, along the coast or on watercrafts, for picking up wounded persons in areas of difficult access or for superintending road traffic, forests and at sea.

Some of the above tasks cannot at present be carried out, not even by conventional helicopters, whereas by using an easily manoeuvrable ultralight helicopter with reduced pilot training problems and very low operating costs, the above difficulties can be overcome with great success.

In view of what above, the commercial prospects of such a helicopter are more than favorable, taking into account also its low production costs.

According to the instant invention, the reduction of the helicopter to the desired dimensions and weight has been achieved by complying with specific aerodynamic ratios, with ratios of dimensions and weights and shape of the basic tridimensional structure, the distribution of the propulsion members and principal masses, as will be disclosed in the description

hereinbelow. Yet these ratios are not an object per se but they characterize this type of helicopter.

As a rather complex type of construction is involved, only the essential parts of the structure will be described, its basic dimensions and the distribution of the masses, particularly in the form of ratios between these quantities which have often proven to be surprisingly critical and decisive for the realization of the intended object of the invention.

The drawing attached hereto illustrate, in no limitative way of example, in particular the structure of an ultralight two-seater helicopter of more general use, comprising within the scope of protection itself the structure of a single-seater helicopter, slightly more reduced in width but still characterized by the same fundamental ratios.

Brief Description of the Drawings

As to the drawings:

- Fig .1 is a schematic elevation side view of the complete helicopter, with its internal members shown in transparency, according to one form of embodiment;

- Fig.1B is an enlarged detail of the top part of Fig.l, showing in particular the main rotor head;

- Fig.2 is a complete side view of the basic structure including the landing gear;

- Fig.3 is a partial elevation front view of the structure shown in Fig.2 taken along line III-III of Fig.2;

- Fig.4 shows a rear view of the structure of Fig.2, complete with landing gear, according to the direction IV-IV of Fig.2; - Fig.5 is a top view of the structure shown in Fig.2;

- Fig.6 is a schematic perspective front/side view of the structure shown in Figs. 2 thru 5;

- Fig.7 is a schematic side view of the arrangement of the centers of gravity of the main masses, such as the engine, fuel tank, gear reduction unit, pilot and passenger;

- Fig.8 is a schematic plan view, similar to Fig.7, of the arrangement of the main masses; and

- Fig.9 is an elevation front view of the arrangement of the main masses.

Fig.1 is an elevation side view of the ultralight helicopter, identified in its entirety by numeral 1, wherein a front zone A, a central zone B and tail zone c are evidenced.

Zone A houses cockpit 10, including seats for the crew, flight controls, such as control stick 12 which operates in a known manner, causing the rotor plane to tilt for the forward, reverse or side motion of the aircraft, as well as the pedal 14 for the directional control, affecting the pitch of tail rotor 26. The set of instruments includes the most essential indicators of a known type, assembled on an instrument panel 16 located opposite the pilots' seats. In the case of a two-seater helicopter, the controls are duplicated so as to allow both occupants to pilot the aircraft. These components are of the known type.

Cockpit 10 is protected by composite fairing 13 of the quick assembly/ disassembly type, the front part of the cockpit being provided with large windows 15 which ensure excellent visibility. Access to the cockpit is gained via two doors 17, which may also be removed without jeopardizing the flight operation.

The helicopter's load bearing structure, consisting of a metal framework of tubulor elements, is globally identified in Figs.2 thru 6 by numeral 50.

Although the framwork is formed of one single assembly of interconnected tubular elements, in said framework can be identified an elevated part 50B located essentially in the center zone B of the helicopter, and a front ejecting part 50A which supports the seats and the floor of the cockpit and to which the flight controls and the instrument panel are secured. The function of part 50B, in particular, is to ensure the necessary stability and rigidity with the least possible weight, and to said part are connected engine 44 with centrifugal clutch, the fuel tank, the main gearbox 40 with freewheel unit and the starter battery. Said framework also supports sleeve 45 of the main rotor shaft. Through said framework pass also the tension rods of the flight and engine controls.

Still according to the invention, rear zone C comprises tail-boom 20 consisting of a self-supporting steel plate cylinder, secured directly to part 50B of structure 50 and supported by two rod-like elements 22 anchored to the structure itself. To the end of said tail-boom is secured empennage 24, apt to ensure the required longitudinal and lateral stability, as well as the countertorque rotor assembly 26 complete with 90° miter gears bearing the numeral 25. The shaft 47 which transmits the torque to the rotor as well as its controls pass through tail-boom 20.

The dynamic part includes the main rotor 30, consisting of two symmetrical blades, which rotor is connected to the transmission shaft by means of a two-degree freedom cardanic hub(known as rocker arm rotor). The rotor blades can be folded backwards to reduce the overall dimensions. The flight controls for the main rotor, consisting of a longitudinal and lateral cyclic device and of a collective pitch change, control, via the oscillating plate of rotor head 31, the geometrical pitch of the main propeller.

Similarly to the main rotor, also the countertorque rotor 26 consists of two blades of symmetrical profile.

Main gearbox 40, operated through belt pulley 42 from engine 44, controls both main rotor 30 and, via the horizontal shaft 47, tail rotor 26. In case of engine failure, the gearbox through the free wheel unit automatically disengages the power transmission, enabling the main and tail rotors to rotate freely with the least internal resistance (self-rotation manoeuvre).

The construction parameters, according to the invention, are provided hereinunder.

Overall Sizing

Again with reference to Fig.1, the overall dimensions of helicopter 1 are governed by the following ratios:

ranging from 0.4 to 0.47, preferably from 0.43 to 0.45.

ranging from 1.4 to 1.5, preferably from 1.42 to 1.46.

The dimensional values L and W given in the above ratios are intended excluding the blades; specifically, the length dimension L, measured between the crosspiece 55 of the front framework 50A and the box of the miter gears 25 of the tail rotor, ranges from 4800 to 5300 mm, preferably from 4950 to 5150 mm, whilst the maximum width W corresponds to the cross-distance between the landing skids 56 (v. Fig.4) and ranges from 1400 to 1600 mm, preferably from 1450 to 1550 mm.

Height H is measured between the rest plane of skids 56, 56' and the axis of the cardanic joint 29;

ranging from 5.5 to 6.5, preferably from 5.9 to 6.2; Ratios of the Masses

ranging from 0.08 to 0.15, preferably from 0.09 to 0.12

ranging from 0.02 to 0.07, preferably from 0.038 to 0.045.

ranging from 0.05 to 0.08, preferably from 0.050 to

0.060,

where, in the ratios R₄ to R₆, the basic weight

(P_v) is the weight of the helicopter ready for take-off without crew, fuel and possible ballast, while the operating weight (P_M) is the weight of the helicopter ready for take-off with full fuel tank load and

complete crew on board.

Aerodynamic Ratios

ranging from 15 to 25, preferably from 16 to 18;

ranging from 4 to 6, preferably from 4.2 to 4.4;

R₉= Main rotor solidity

ranging from 0.033 to 0.056, preferably from 0.035 to

0.042.

R₁₀= Tail rotor solidity

ranging from 0.12 to 0.19, preferably from 0.13 to

0.15, the solidity value being defined by the ratio between the surface of the blades and the surface of the related rotor disc;

R₁₁= Rotor load ranging from 8 to 16 kg/m , preferably from 11 to 14 kg/m², by rotor load being meant the ratio between the operating weight of the helicopter and the main rotor disc surface.

ranging from 0.01 to 0.02, preferably from 0.013 to 0.016, wherein (with reference to Fig.1B) "h_c" is the distance of the axis of the cardanic joint 29 from the axis of symmetry of the hub bearing the blades of the ma in rotor 30;

of center of gravity

ranging from 0.03 to 0.07 °/mm;

Power and Weight Ratios

ranging from 0.40 to 0.60, preferably from 0.45 to

0.55; '

ranging from 0.30 to 0.50 kW/kg, preferably from 0.35 to 0.45 kW/kg;

ranging from 0.15 to 0.25 kW/kg, preferably from 0.18 to 0.23 kW/kg;

R₁₇= Efficiency factor ranging from 0.5 to 0.85, preferably the maximum

possible, where by efficiency factor is meant the ratio between the minimum theoretical power needed at a hover (set point), outside the ground effect, and the power actually required ;

R ₁₈ = Coefficient of advancement

ranging from 0.15 to 0.35, preferably from 0.20 to

0.28, the advancement coefficient being the ratio between the translational speed of the helicopter and the peripheral speed of the main rotor blades.

Figures 2 thru 6 show the tridimensional loadc a r r y i n g structure of the ultralight helicopter according to the invention, globally identified by numeral 50, Said structure consists of a metal framework of tubular elements preferably made of a titanium alloy, by means of which it is possible to attain a maximum resistance with minimum weight. Said framework illustrates, solely by way of example, the embodiment of a two-seater helicopter. To spatially define the characterizing elements of such a structure, the latter will be referred to a triad of Cartesian axes, wherein Z, or the vertical axis, coincides with the axis of the shaft of the main rotor 30 located on the vertical symmetry plane of the framework, while the axes X and Y, completing the triad and shown by way of example in Fig.5, are taken along the horizontal plane formed by the substantially horizontal tubular elements 52,54, parallel to the plane of skids 56,56' , forming the supporting base of the cockpit floor (v. Fig.2). The overall length M of structure 50, measured between the front rod 55 of the front projecting part 50A and the extreme vertical plane of part 50B of the structure itself, is substantially equal to 40% of the helicopter's total length L (v. Fig.1). In the case of the embodiment described herein, M preferably ranges from 2000 to 2060 mm. The very complex spatial arrangement of the tubular elements of structure 50 can at any rate be better understood from the perspective view of Fig.6 in conjunction with Figures 2, 3, 4, 5 which provide to scale the actual dimensions of the elements of such structure.

Said structure consists of a number of tubular elements - defined for the sake of brevity as tubes - concurring in a plurality of knots K. These knots will be identified as KC, if a central knot is involved, viz. lying on the longitudinal symmetry plane of the helicopter, and as KL, if the knots are lateral, always symmetrically spaced from said longitudinal symmetry plane.

The top knot KCl, located on axiz Z, consistutes the topmost point of the framework. It coincides with the ideal point of concurrence, on sleeve 45 of the main rotor shaft, of three tubes 60,60' and 62 and it is located at a distance z ranging from 0.63 to 0.67 M from the reference plane of axes X and Y.

In one embodiment, KCl has co-ordinates where x = 0; y = 0; z = 1330 mm.

Tubes 60, 60' , rising from symmetrical knots KLl, are continuous with tubes 64, 64' coming from knots KL2 and they are bent at a point coinciding with said knots KL1. Seven tubes concur with knots KL2, whereof tubes 66, directed downwards from knots KL2 towards knots KL3 located on reference plane X-Y, with coordinate z = 0, are coplanar with tubes 64,60 and

60', 64', said plane being inclined towards the helicopter's tail by an angle ranging from 8º to 12°, preferably 10° with respect to the vertical.

Other basic knots are a complex rear knot KC2, adequately reinforced, the co-ordinate x of which being approx. equal to 800 mm, i.e. ranging from 0.37 to

0.40 M, its co-rdinate z ranging from 950 to 865 mm, i.e. from 0.42 to 0.46 M; symmetrical knots KL4 with co-ordinates × = approx. 800 mm, y = ± 300 mm, z = 315 mm, i.e. in the order: × ranging from 0.38 to 0.41 M, y ranging from ± 0.14 to 0.15 M, and z ranging from 0.13 to 0.16 M. Knots KL4 are connected with knot KC2 by a continuous tube bent as an inverted V forming branches 68,68', to which tube is secured an element 69 (v. Fig.5) constituting the coupling of tail-boom 20.

Branches 68, 68' are stiffened by horizontal crosspieces 70,71; said branches 68,68' i.e. the symmetrical knots KL4, are joined at their lower end by a crosspiece 72 to which in turn in secured by coupling 73 (v. also Fig.2) the horizontal tube 74 of a rear stand 75, the lower ends of which retain skids 56,56' engaged at their opposite end with a similar stand 76, secured substantially to the mid-part of projection 50A which develops forward starting from knot KL3, which will be described hereinafter. Skids 56,56' are interspaced by a value W (v. Fig.4) ranging (again by way of an embodiment) from 1450 to 1550 mm, i.e. from 0.72 to 0.75 M, W being the maximum width of the helicopter, while distance G between said stands 75 and 76 (v. Fig.2) is approx. 0.71 M, i.e. ranging from 1440 to 1460 mm.

The supporting plane formed by skids 56,56' is situated substantially at a co-ordinate value-z ranging from 0.24 to 0.26 M. It must also be noted from Fig.2 that the bent tube 68,68' and the stand 75 lie on the same extreme vertical plane of structure 50B.

Knots KL4 are engaged with knots KL2 and KL3 by tubes 80,82; 80' , 82' , which form, symmetrically on the two sides, a triangular structure with tubes 66,66' , while the pairs of knots KL1 and KL2 are isostatically connected by crosspieces 84 and 86 which join at a central knot KC3, said central knot being in turn connected to tubes 88 and 88' forming a triangle with transversal-horizontal tube 90 which directly joins knots KL2.

Again according to an embodiment of the instant invention, knots KL1 have the following co-ordinates: x ranging from -85 to -95 mm, i.e. from - 0.04 to -0.05 M:

y ranging from ^390 to 410 mm, i . e . from ±0.19 to o.21 M;

z ranging from 820 to 860 mm, i.e. from 0.40 to 0.42 M,

while knots KL2 have the following co-ordinates: x ranging from -175 to -195 mm, i.e. from -0.085 to -0.10 M ;

y ranging from ± 460 to 490 mm, i.e. from ±0.22 to 0.24 M;

z ranging from 275 to 295 mm, i.e. from 0.13 to 0.16 M.

Knots KL3 have the following co-ordinates:

x ranging from -225 to -245 mm, i.e. from -0.11 to -0.12 M;

y ranging from ± 465 to 485 mm, i.e. from ± 0.23 to 0.24 M;

z = 0.

Knots KC3 have the co-ordinates:

x ranging from -90 to -100 mm, i.e. from -0.044 to -0.048 M;

z ranging from 790 to 810 mm, i.e. from 0.37 to 0.42 M.

A similar stiffness is provided in the parallelogram of tubular elements lying between the pairs of knots KL2 and KL3, starting from central knot KC4 located midwaytube 90, which is secured by tubes

92,92' to said knots KL3, which in turn are trrnsversally joined to each other by tube 94. To complete structure 50B. knot KC2 is further secured to the pair of knots KL1 by means of tubes 100,100' lying in a plane descending slightly forwards, and substantially inclined by 5° to 9°, preferably 7°, with respect to a horizontal plane ( v.Fig.2) as well as by means of a pair of tubes 102,102' to knots KL2.

Co-ordinates x and z of knot KC4 are the same as those of knots KL2.

The front part 50A of structure 50 (again with reference to Fig.6) is applied to the pair of knots KL2 and KL3. Said front part, starting from knots KL3 onwards, with an overall projection N (v. Fig.1) substantially equal to 0.5 M, is laterally shaped as an obtuse triangle, the lower side of which consists of two continuous tracts 52-54 and 52'-54' , each formed by the same horizontal tube terminating in extreme knots KL5 which are connected transversally by crosspiece 55 and which in turn are secured to knots KL2 by means of tubes 58,58' ; 59,59' . Substantially in the middle part of projection N of the front part 50A an intermediate vertical reinforcing structure is provided, identified by the letter P, which is delimited by lower and upper knots, KL6 and KL7 respectively, the first two being connected transversally by tube 110 and the others by tube 112. Said intermediate struc ture P is interconnected within its limits by several reinforcing tubular elements which can also be

exploited, in known manner, for example as a support, e.g. for the control tension rods, while the lower transversal tube 110 is connected longitudinally by tubes 120, 120' , reciprocally interspaced by a distance n ranging from 0.08 to 0.09 M, to the front crosspiece 55 and to the transversal tube 94 joining

knots KL3. The top tube 112 of structure P is in turn connected by bars 124,124' , with interspacing substantially as the preceding tubes 120,120' , to the transver sal tube 90 joining knots KL2. Tubes 126, 126' , more-over, connect knots KL7 to knots KL3.

Knots KL5 and KL6, as defined hereinbefore, lie on plane X,Y of the triad of axes X,Y,Z of reference of structure 50 and hence their co-ordinate z = 0, while knots KL 7 have a co-ordinate z ranging from 0.065 to 0.075M.

The co-ordinates x and y of knots KL5 and KL6 have, respectively, the following values:

KL5 : x ranges from -0.58 to -0.62 M;

y ranges from ±0.190 to 0.215M:

KL6 : x ranges from -0.34 to -0.36 M

y ranges from ±0.23 to 0.24 M.

Knots KL7 have co-ordinates x and y equal to those of knots KL6.

The distance between knots KL5 corresponds to 0.42 M.

Regarding the distribution of the main masses, (having reference to Figs. 7, 8, 9), the center of gravity of masses S1 and S2 constituted by the pilot and the passenger ( transversally adjacent to each other in the cockpit) is situated at a distance Q from the plane of reference X, Y, ranging from 0.23 to 0.270 M, said masses S1 and S2 being separated by a distance y of ± 280 mm approx., with respect to the symmetry plane, i.e. by a distance y ranging from ± 0.12 to 0.15 M, the co-ordinate x ranging from

-0.22 to -0.25 M.

The center of gravity of the engine, identified by numeral S3, has a co-ordinate z substantially equal to that of masses S1 and S2 cited above and a co-ordinate x substantially ranging from 0.20 to 0.22 M.

The center of gravity of the reduction unit identified by numeral S4, is substantially aligned with the axis of transmission shaft 47 operating the tail rotor, with a co-ordinate z of approx. 880 mm, i.e. ranging from 0.42 to 0.44 M.

Fuel tank S5 is also practically vertically aligned underneath the reduction unit S4, the center of gravity of said fuel tank being approx. at the same height z as the centers of gravity of the passengers and of the engine.

Regarding the value of the masses of the pilot and the passenger, these are each considered, as is usual, to be variable between 75 and 85 kg, with the possibility of a total excursion of the weight up to one half if the pilot alone is present on the helicopter. Generally, ail the masses considered, referred to value P_v of the basic weight characterizing the class of the helicopter, range within the following values:

S1 and S2 (taken alone) 0 to 0.38 P_v

S3 0.125 to 0.25 P_v

S4 and S5 0.10 to 0.27 P_v

In all, the maximum excursion of the center of gravity longitudinally is estimated to range between ± 240 mm, while the lateral excursion of the same ranges between ± 150 mm; the centers of gravity are measured with the reference being axis Z, coincident with the main rotor shaft.

Although the invention has been illustrated and described particularly with reference to a preferred embodiment, the skilled artisan will realize that various changes can be made without departing from the scope of protection of the invention as claimed. *****

Claims

C L A I M S

1. An ultralight (UL) aircraft, in particular a helicopter, falling within the limits of maximum weight P_M of 450 kg at take-off, in the version without floats, and a basic weight P_v ranging from 210 to 230 kg, including a structure (50) made of tubular elements constituting the framework of the aircraft, to which are secured tail-boom (20), the rear end of which is provided, in a known manner, with an empennage (24) and a countertorque rotor (26) actuated by means of a miter gearbox (25), as well as a main rotor (30), said structure being generally formed by a plurality of tubular elements acting as push-rods and tension rods, converging into a plurality of central knots (KC1... KC4), located on the longitudinal symmetry plane of the helicopter, and lateral knots (KL1...KL7), symmetrically set on the sides of said symmetry plane; the spatial position of said knots (KC...) and (KL...) of structure (50) and of other elements such as the main masses (S1 ....S5) being referred to a tridimensional triad of coordinated axes X,Y,Z, the vertical axis Z of which coincides with the geometrical axis of the shaft of main rotor (30), while axes X and Y, longitudinal and transversal respectively, lie on the horizontal plane formed by the lower tubes of front part (50A), the latter part, together with part (50B), more developed in height, forming the entire structure (50), characterized in that: I) length (L) of the helicopter, excluding the rotors, measures starting from front crosspiece (55) of part (50A) of structure (50) up to the miter gearbox (25) of countertorque tail rotor (26), ranges from 4800 to 5300 mm, preferably from 4950 to 5150mm;

II) length (M) of structure (50), measured from said piece (55) to the extreme vertical plane of structure (50) is substantially equal to 0.40L, i.e. ranging from 1920 to 2120 mm, preferably from 2000 to 2060 mm;

III) maximum width (W), representing the cross-distance between landing skids (56,56'), ranges from 0.70 to 0.80 M, preferably from 0.72 to 0.75 M;

IV) height (H), measured between the oscillating plate of head (31) of main rotor (30) and the resting plane of said skids (56,56'), preferably ranges from 0.43 to 0.45 L, while height (H) with respect to the maximum width (W) ranges from 1.4 to 1.5 W, preferably from 1.42 to 1.46 W;

V) central knots (KC1...KC4) of part (50B) of the structure, referred to the triad of axes X,Y,Z, have their co-ordinates, with respect to length (M) of structure (50) ranging between the following values: (KC1 ) × = 0 z = 0.63 to 0.67 M

(KC2) × = 0.37 to 0.40 M z = 0.42 to 0.46 M (KC3) × = -0.044 to -0.048 M z = 0.37 to 0.42 M (KC4) × = -0.08 to 0.10 M z = 0.13 to 0.16 M

VI) lateral knots (KL1 ...KL4) of part (50B) of the structure have their co-ordinates, with respect to length (M) of structure (50), ranging between the following values:

(KL1) x = -0.04 to -0.05 M

y = ±0.19 to 0.21 M

z = 0.40 to 0.42 M

(KL4) x = 0.38 to 0.41 M

y = ±0.14 to 0.15 M

z = 0.13 to 0.16 M

(KL2) x = -0.085 to -0.10 M

y = ±0.22 to 0.24 M

z = 0.13 to 0.16 M

(KL3 ) x = -0.11 to -0.12 M

y = ±0.23 to 0.24 M

z = 0

VII) lateral knots (KL5...KL7) of front part(50A) of structure (50) have their co-ordinates, with respect to length (M) of said structure (50) ranging between the following values:

(KL5) x = -0.58 to -0.62 M

y = ±0.190 to 0.215M

z = 0

(KL6) x = -0.34 to -0.36 M

y = ±0.23 to 0.24 M

z = 0

(KL7) x = -0.34 to -0.36 M

y = ±0.23 to 0.24 M

z = 0.065 to 0.075M.

2. An ultralight aircraft, in particular a helicopter, according to Claim 1, characterized in that knot (KC1) is coincident with the point of concurrence of three tubes (60, 60' , 62) on the guide sleeve (45) of the vertical shaft transmitting torque to the blades of main rotor (30), the first two mentioned tubes (60,60') being secured with their other end to symmetrical knots (KL1) and the other tube (62) to knot (KC2).

3. An ultralight aircraft, in particular a helicopter, according to Claims 1 and 2, characterized in that knot (KC2) is connected to knots (KL4) by means of a continuous tube bent to form an inverted V, the branches (68,68') of said bent tube being stiffened by horizontal cross pieces(70,71), and in that at the bent vertex of V formed by said tube is applied a reinforcement (69) for coupling tail-boom (20) of the helicopter.

4. An ultralight aircraft, in particular a helicopter, according to Claims 1 thru 3, characterized in that symmetrical knots (KL4) are linked to each other by a crosspiece (72)secured in turn by couplings (73) to the horizontal tube (74) of a stand (75), the lower ends of which retain in the rear the skids (56, 56'), said knots (KL4) and knot (KC2) lying on one only vertical plane together with said stand (75).

5. An ultralight aircraft, in particular a helicopter, according to Claims 1 thru 4, characterized in that knots (KC1, KL1, KL2, KL3) lie on a plane inclined towards the rear part of the structure (50) at an angle ranging from 8° to 12°, preferably 10°, with respect to the vertical direction.

6. An ultralight aircraft, in particular a helicopter, according to Claims 1 thru 5, characterized in that knots (KL1) are connected to knot (KC2) by means of tubes (100,100') lying on a plane descending slightly forward and inclined from 5° to 9°, preferably approx.7°, with respect to the horizontal direction

7. An ultralight aircraft, in particular a helicopter, according to Claims 1 thru 6, characterized in that knots (KL1) are connected to knot (KC3) by means of tuoes (84,86), knot (KC3) being connected to knots (KL2) by means of tubes (88,88'), forming a triangle with transversal-horizontal tube (90) which joins knots (KL2).

8. An ultralight aircraft, in particular a helicopter, according to Claims 1 thru 7, characterized in that knots (KL4) are connected with knots (KL2) by means of tubes (80,80' ) and with knots (KL3) by means of tubes (82,82' ), forming on two sides of structure (50) a triangular structure with tubes

(66,66') which join knots (KL2) and (KL3).

9. An ultralight aircraft, in particular a helicopter, according to Claims 1 thru 8, characterized in that knot (KC2) is connected to knots (KL1) by means of tubes (100,100'), forming substantially the corners of a tetrahedron with tubes (60, 60' , 62) which concur on the topmost vertex (KC1) of structure (50).

10. An ultralight aircraft, in particular a helicopter, according to Claims 1 thru 9, characterized in that front part (50A) of structure (50), housed in front zone (A) of the helicopter, forms a projection secured to knots (KL2) and (KL3) of part (50B) of structure (50), the longitudinal length (N) of said projection part (50A), measured between crosspiece (55)and knots (KL3), being substantially equal to 0.5 M.

11. An ultralight aircraft, in particular a helicopter, according to Claims 1 thru 10, characterized in that in part (50A) of structure (50) the substantially horizontal base of the projecting part, consists of two continuous tubes (52,54) and (52' ,54' ) parallel to each other in the first tracts (52,52') and symmetrically converging forwards in their subsequent front tracts (54,54' ) to form knots (KL5) connected to each other by a crosspiece ( 55 ) the length of which is substantially 90% of the distance between said parallel tracts (52,52'), which distance corresponds substantially to 0.42 M.

12. An ultralight aircraft, in particular a helicopter, according to Claims 1 thru 11, characterized in that knots (KL5) are secured to knots (KL2) by means of tubes (58,59; 58' , 59' ), having - seen in projection on the horizontal plane - an identical arrangement as the underlying ones (52,54;52' ,54' ), the bending point of the tube tracts (52,54) forming knot (KL6) and the bending point of the tube tracts (58,59) forming knot (KL7) and their symmetrical ones, said knots being interconnected, respectively, by tubes (110) and (112) constituting an intermediate vertical structure (P) which is interconnected within its limits by a plurality of vertical and oblique reinforcing tubular elements.

13. An ultralight aircraft, in particular a helicopter, according to one or more of Claims 1 thru 12, characterized in that:

- the diameter (E) of the main rotor disc is preferably from 5.9 to 6.2 times the diameter (F) of the tail rotor(26);

- the radius (E/2) of the main rotor ranges from 15 to 25. times, preferably from 16 to 18 times, the width of the corresponding blade (30);

- the radius (F/2) of the tail rotor ranges from 4 to 6 times, preferably from 4.2 to 4.4 times, the width of the corresponding blade (26);

- the ratio between the surface of the blades (30) of the main rotor and the surface of the main rotor disc ranges from 0.033 to 0.056, preferably from 0.035 to 0.042, while the ratio between the blades (26) of the tail rotor and the surface of the tail rotor disc ranges from 0.12 to 0.19, preferably from 0.13 to 0.15;

- the weight of the structure (50) ranges from

0.08 to 0.15 the basic weight (P_v) prescribed for aircrafts falling within the UL class, preferably from 0.09 to 0.12 P_v;

- the weight of the tail-boom (20) together with the empennage (24) ranges from 0.02 to 0.07 the basic weight P_v , preferably from 0.038 to 0.045;

- the ratio between the operating weight of the aircraft and the surface of the main rotor disc ranges from 8 to 16 kg/m², preferably from 11 to 14 kg/m²;

_ the distance (h_c) between the axis of the cardanic joint and the axis of symmetry of the hub ranges from 0.01 to 0.02 ( E/2), pre ferably from 0.13 to 0.016 (E/2), (E) being the diameter of the main rotor disc;

- the ratio between the maximum flapping angle of the main rotor and the maximum longitudinal displacement of the center of gravity ranges from 0.03 °/mm to 0.07 °/mm;

- the ratio between the engine power and the basic weight P_v has a value of from 0.30 to 0.50 kW/kg, preferably from 0.35 to 0.45 kW/kg, while the corresponding ratio with respect to the maximum operating weight P_M ranges from 0.15 to 0.25 kW/kg, preferably from 0.18 to 0.23 kW/kg;

- the ratio between the minimum theoretical power necessary at a hover, outside ground effect, and the actually needed power ranges from 0.5 to 0.85;

- the ratio between the translational speed of the ultralight helicopter and the peripheral speed of the main rotor blades, i.e. the "coefficient of

advancement" has a value ranging from 0.15 to 0.35, preferably from 0.20 to 0.28.

14. An ultralight aircraft according to Claims 1 thru 13, characterized in that the centers of gravity of the main masses represented by the pilot and passenger (S1 and S2), respectively, by the engine(S3), by the reduction unit (S4) and the fuel tank (S5) have co-ordinates ranging within the following values: (S1 and S2) x = -0.22 to -0.25 M

y = ±0.12 to 0.15 M z = 0.23 to 0.27 M

(S3) X = 0.20 to 0.22 M

y = 0

z = 0.23 to 0.27 M

(S4) X = 0

y = 0

z = 0.42 to 0.44 M

(S5) X = 0

y = 0

z = 0.23 to 0.27 M

15. An ultralight aircraft according to Claims

1 thru 14, characterized in that with reference to the basic weight P_v of the helicopter, the mass of the pilot (S1) and of a possible passenger (S2) has a maximum value each of 0.38 P_v; the mass of the engine (S3) ranges from 0.125 to 0.25 P_v, while the sum of the reduction unit (S4) plus the fuel tank (S5) ranges from 0.10 to 0.27 P_v.

16. An ultralight aircraft according to Claims 1 thru 15, characterized in that the tubes forming the structure (50), including the elements (22) supporting the tail-boom (20), the stands (75,76) and the landing skids (56,56') are titanium alloy tubular elements.