Duck (aerodynamic design). Drawings and descriptions of the "Quickie" aircraft Tandem and canard aircraft

How to avoid balancing losses? The answer is simple: the aerodynamic configuration of a statically stable aircraft must exclude balancing with negative lift on the horizontal tail. In principle, this can be achieved using the classical scheme, but the simplest solution is to arrange the aircraft according to the “canard” scheme, which provides pitch control without loss of lift for trim (Fig. 3). However, canards are practically not used in transport aviation, and, by the way, quite rightly so. Let's explain why.

As theory and practice show, canard aircraft have one serious drawback - a small range of flight speeds. The canard design is chosen for an aircraft that must have a higher flight speed compared to an aircraft configured according to the classical design, provided that the power plants of these aircraft are equal. This effect is achieved due to the fact that on the canard it is possible to reduce air friction resistance to the limit by reducing the area of ​​the aircraft's washed surface.

On the other hand, when landing, the “duck” does not realize the maximum lift coefficient of its wing. This is explained by the fact that, in comparison with the classical aerodynamic design, with the same interfocal distances of the wing and the main body, the relative area of ​​the main part, as well as with equal absolute values ​​of the margins of longitudinal static stability, the “canard” scheme has a smaller balancing arm of the main part. It is this circumstance that does not allow the canard to compete with the classical aerodynamic design in takeoff and landing modes.

This problem can be solved in one way: increase the maximum lift coefficient of the PGO ( ) to values ​​that ensure canard balancing at landing speeds of classic aircraft. Modern aerodynamics has already given “ducks” high-load profiles with values Su max = 2, which made it possible to create a PGO with . But, despite this, all modern canards have higher landing speeds compared to classic designs.

The disruptive characteristics of the “ducks” also do not stand up to criticism. When landing in conditions of high thermal activity, turbulence or wind shear, the PGO, providing balancing at the maximum permissible Su aircraft, may have . Under these conditions, with a sudden increase in the angle of attack of the aircraft, the PGO will reach supercritical flow, which will lead to a drop in its lift, and the angle of attack of the aircraft will begin to decrease. The deep disruption of the flow from the PGO that occurs in this case puts the aircraft into a mode of sharp uncontrolled dive, which in most cases leads to disaster. This behavior of the “ducks” at critical angles of attack does not allow the use of this aerodynamic design in ultra-light and transport aircraft.

For a “standard duck” with an area of ​​horizontal tail (front wing) within 15...20% of the area of ​​the main wing and an empennage arm equal to 2.5...3 V Cach (the average aerodynamic chord of the wing), the center of gravity should be located at within the range from - 10 to - 20% VSAKH. In a more general case, when the front wing differs in parameters from the tail of a “standard canard” or a “tandem”, in order to determine the required alignment, it is convenient to conventionally bring this arrangement to a more familiar normal aerodynamic design with a conventional equivalent wing (see Fig. .).

The alignment, as in the case of the normal scheme, should lie within 15...25% of the VEKV (chord of the conventional equivalent wing), which is as follows:

In this case, the distance to the toe of the equivalent chord is equal to:

Where K is a coefficient that takes into account the difference in wing installation angles, bevels and flow deceleration behind the front wing, equals:

Please note that empirical formulas and recommendations for determining alignment are quite approximate, since the mutual influence of the wings, bevels and flow deceleration behind the front wing are difficult to calculate; this can be accurately determined only by blowing. For amateur aviators to experimentally check the alignment of an aircraft with an unusual design, we recommend using flying models, including cord models. In aircraft manufacturing practice, this method is sometimes used. And in any case, for an amateur-built aircraft, the alignment determined by the formulas should be clarified when performing high-speed taxis and approaches.

based on materials: SEREZNOV, V. KONDRATIEV "IN THE SKY TUSHINA - SLA" "Modelist-Constructor" 1988, No. 3

Based on material from the magazine "Modelist-Constructor" from the times of the USSR

Fragment of the 3rd edition of the directory "Who's Who in Robotics"

In the first decade of the 20th century. They didn’t yet know how the plane should be designed. And often on aircraft of those times the horizontal tail was placed in front of the wing on the forward fuselage. Such aircraft began to be called “ducks”, since their forward fuselage nose part in flight resembled a flying duck with an outstretched neck. This name is assigned to aircraft in which the horizontal tail is located in front of the wing. Aircraft manufacturers returned to the canard design when they began designing supersonic aircraft to eliminate the reduction in overall lift that conventional aircraft experienced from the tail. And a free-flying aircraft model, made according to the “duck” design, can be better adapted to hovering.

Aerobatic aircraft model "UII-GBird" with a 2.5 cm³ engine, having a "duck" design. The horizontal tail with the elevator is attached to its aerobatic wing on two beams. The engine with a pulling propeller is located in the nose of the short fuselage. The nose wheel strut is mounted directly behind the engine. The main landing gear struts are located at the beam attachment points. On the trailing edge of the wing there are two fins, deflected asymmetrically, as shown in the drawing.

The painstaking work to select the position of the center of gravity paid off and led to success in competitions. During testing of the model, another significant advantage of the “duck” scheme was revealed. If the engine suddenly stopped while performing aerobatic maneuvers, having lost control, it went into a dive, and then, without the intervention of the modeller, it came out of it and made a safe landing. This is explained by the fact that when diving without control, the weight moment of the elevator around the axis of its hinged suspension causes the steering wheel to deflect downward with the trailing edge. As a result, a moment arises that causes the “duck” to exit the dive, and then a smooth landing.

A canard cord model built and successfully tested by Japanese aircraft modellers.

When designing any canard model, to ensure stable flight it is very important to correctly select the center of gravity relative to the leading edge of the wing chord. The distance from the tip of the wing chord to the center of gravity of the model, necessary for stable flight, is determined by the formula: X = 70Lgo x Sgo/Scr - 0.1b, where: Sgo - area of ​​​​the horizontal tail in square decimeters, Sc - wing area in square decimeters, Lth is the horizontal tail arm, that is, the distance from the toe of the stabilizer chord to the toe of the wing chord, in decimeters, b is the wing chord in mm.

This formula is given for the case when a pushing screw is used on the model. For example, for a model with Sgo = 10.5 dm²; Lgo = 6.3 dm; Skr= 31.9 dm²; X = 126 mm. If, on a model made according to the “duck” scheme, a pulling screw is used, placed in front of the wing, then X is found using an even simpler formula: X = 70Lgo x Sgo/Scr

In the United States, two experimental models of the F-16XL fighter, created on the basis of the F-16 fighter-bomber, are being tested. If it was previously reported that the power plant of the new fighter remained the same, now, according to the foreign press, it is planned to use a more powerful F-101DFE engine, created on the basis of the F-101 engine of the B-1 strategic bomber. Compared to the base model, the wing area of ​​the new aircraft was significantly increased (it amounted to 60 m2), the length of the fuselage increased by 1.4 m. Thanks to such changes in the design, the fuel capacity increased by 80%.

It is hoped that the F-16XL fighter will be capable of long-term flights at supersonic cruising speed. For takeoff and landing, it will require a runway less than 600 m long.

The aircraft's avionics are planned to include an upgraded AN/APG-66 radar station, an AN/ALQ-165 electronic suppression station, the Lantirn electro-optical system and a new digital computer for the weapon control system. Magazine "Equipment and weapons" from the times of the USSR

The history of this project dates back to the early 80s. At the experimental machine-building plant named after V. M. Myasishchev, design and research work was carried out to develop the concept of a new heavy-duty aviation transport system.

In the early 80s of the last century, similar work was carried out in several aviation design bureaus and, of course, in the scientific center of domestic aviation TsAGI.

The concept of a heavy transport aircraft developed at TsAGI is quite well known in aviation circles; the author of the development was the head of design research, Yu. P. Zhurikhin.

The demonstration model of the TsAGI transport system has been repeatedly demonstrated at international aviation exhibitions.

Design developments of EMZ named after. V. M. Myasishchev were carried out within the framework of the topic, which received the index “52”. They were carried out under the leadership of the chief designer of the EMZ V. A. Fedotov, the theme leader at the initial stage was the deputy chief designer R. A. Izmailov. The leading designer on the topic and essentially the author of the concept was V. F. Spivak.

The concept of the “52” project included the creation of a unified transport aircraft with unique transport capabilities. The main objective of the project was to ensure the air launch of a reusable aerospace rapid response aircraft. It would not be economically feasible to create such a unique aircraft with a take-off weight of 800 tons for only one task. Therefore, from the very beginning, the concept of the “52” project provided for the use of this aircraft for unique transport operations, including the transportation of military equipment and military units, industrial cargo beyond large sizes and weight.

The design concept of “52” was based on the “external load” principle. Only this principle makes it possible to place loads of completely different shapes and dimensions. In this case, the aircraft fuselage practically degenerates as a means of accommodating the load, therefore, by maintaining the minimum required size of the fuselage, it would be possible to significantly reduce the weight of the aircraft structure. That's all, it would seem a very simple idea on the basis of which the entire project is built.

In this article we will not consider the “52” project in detail. We will refer those interested to the multi-volume publication “Illustrated Encyclopedia of Aircraft EMZ named after. V.M. Myasishchev”, where the development of the project is described in sufficient detail.

The author of these lines had to directly participate in these works, and in this article I would like to talk about those projects, or more correctly, ideas that were also considered in the process of developing the concept, but were not developed and were not worked out in sufficient detail.

The very idea of ​​​​creating a super-heavy transport aircraft did not arise on its own. The Ministry of Aviation Industry (MAP) set the specific task of transporting large cargo in the interests of the national economy of the country.

The USSR, with its vast territories and large industrial centers scattered throughout the country, needed a solution to this problem, because it is obvious that it is more economically profitable to transport ready-made and assembled units.

Nuclear reactors, convectors of metallurgical production, gas tanks and distillation columns of chemical production and many other cargoes, all of them, when transported assembled “by air”, could be put into operation quite quickly, which means less time and correspondingly lower costs.

Any transport operation “on the ground” is a whole event for many transport services. Detailed study of the route, demolition of bridges and overpasses, power lines if they interfere with transportation, and so on... These are the timing, these are the costs, in some cases this is simply an insoluble problem.

Cargoes weighing from 200 to 500 tons, with overall dimensions ranging from 3 to 8 m in diameter and 12 m to 50 m in length were intended for transportation. It is clear that, of course, not all of the proposed cargo could be transported by air, but the project “52” could transport most of the cargo if it were implemented.

So the idea arose not only to reduce the size of the fuselage to the minimum possible, but to abandon it altogether. Why not make the transported cargo itself “work”? This idea was prompted by the fact that many cargoes intended for transportation looked like elongated cylindrical bodies, that is, they looked like a fragment of the fuselage.

Of course, the cargo itself, the material from which it was made and its design had to satisfy the strength conditions when installing it on an aircraft. The inclusion of cargo in the aircraft's power circuit promised a significant gain in the aircraft's weight efficiency and, accordingly, increased its transport efficiency.

How can the transported cargo itself be included in the power scheme of a transport aircraft? It’s very simple, you need to make the transported cargo winged! There is such an aerodynamic design of the aircraft called “tandem”. In this scheme, the aircraft's load-bearing system consists of a pair of wings arranged tandemly behind each other with longitudinal spacing. The transported cargo is located between the wings precisely in the center of gravity of the entire supporting system of the aircraft, everything is very simple, although it is well known what a big problem solving the problem of centering a heavy load poses.

The tandem scheme has a slightly larger area of ​​the aircraft's load-bearing system compared to the classical scheme, but this scheme turns out to be the most suitable for cargo transportation tasks.

Both wings produce lift without losing lift to the longitudinal trim inherent in a classic aircraft design. Optimal profiling of both wings and degradation of their installation angles make it possible to minimize the negative impact of wing interference and therefore reduce aerodynamic losses.

One of the variants of the tandem aircraft consisted of two independent sections with a full-fledged wing with mechanization of the leading and trailing edges. The wing of the front section is made according to a low-wing design to reduce the effect of the flow bevel on the rear wing. The power plant engines are installed on vertical pylons on top of the front section wing. The pylon engine suspension is considered to be quite universal, allowing the required number of engines to be varied during the development process.

The location of the engines above the upper surface of the wing made it possible to use the effect of increasing the lifting force of the wing due to the jet blowing over the engines (Coanda effect). Due to the greater load on the front wing, the front wing was made with a slightly smaller area compared to the rear wing.

The front section is equipped with its own chassis - the main one, consisting of two four-wheeled main supports and two two-wheeled underwing supports. The spacing of the main and underwing landing gear along the longitudinal axis of the aircraft ensured the longitudinal stability of the front section at the airfield in the undocked position.

On top of the front section behind the cockpit there is a rear-facing glazed cabin for the load operators, who monitor the condition of the cargo and the load securing systems during the flight.

The rear section of the tandem aircraft is similar to the front. The wing of the rear section is overhead, with a slightly larger span. Vertical tail washers are installed on the rear wing. Due to the small effective shoulder, the vertical tail is made of a large area, with two fins.

The rear section of the tandem aircraft does not have engines; the landing gear is designed similarly to the front section. Due to the high location of the wing on the rear section, the underwing landing gear is attached to the vertical tail washers.

An important feature of the “tandem” scheme is also that when the aircraft takes off from the runway, the aircraft takes off flat-parallel, with virtually no pitch angle; this feature of the “tandem” is ideal for transporting long cargo, since the explosion of an aircraft on takeoff with a long externally slung cargo becomes problematic for a classic aircraft.

To secure various loads, transitional ring trusses were provided, adapted to the specific load.

In order to increase the transport efficiency of the tandem aircraft, it was also planned to use a passenger module closed between the front and rear sections of the aircraft.

The open-loop design of the tandem aircraft made it possible to adapt the aircraft to loads of varying lengths, this made the aircraft an efficient transport vehicle. In the case of an empty aircraft, both sections were joined using connecting ring trusses.

The design of a tandem aircraft with a truss fuselage looked less radical.

Fundamentally, the idea of ​​the concept remained the same, but the fuselage was still preserved, albeit in a somewhat exotic form - two fuselage beams in the form of spatial trusses. A special feature of this tandem aircraft design was that the rear wing with its landing gear and cargo fastening units could move along the trusses to the desired position, depending on the size of the cargo being transported and its alignment. In all other respects, the concept repeated the first scheme. The shortcomings of this scheme were clearly visible, but the only positive thing was that the search for further productive ideas lay through these schemes.

The “tandem” scheme has not yet exhausted itself, perhaps it will find a worthy application in the very near future, we’ll see.

Source. V. Pogodin Valery Pogodin. Tandem - a new word in aviation? Wings of the Motherland 5/2004

Ideas from our readers

YUAN-2 "Sky Dweller" at the MAKS-2007 air show

YaptsrnatiZnar

This aircraft will not yet be at MAKS 2009 - the design is being improved, and its next version is created largely from parts and components of the previous one. But at the last MAKS, the ultra-light YuAN-2 aroused great interest, despite its appearance being spoiled by numerous tests. Because this is not just another SLA. The aircraft has an aerodynamic design - the so-called “vane canard” - which without exaggeration can be called revolutionary. In this article, the author of the idea and the head of the construction of experimental aircraft, young aircraft designer Alexey Yurkonenko, substantiates the advantages of the new scheme. In his opinion, it is ideal for non-maneuverable aircraft, and in this category - very broad, by the way - it can become the basis of a new direction in the development of world aircraft manufacturing.

The use of modern aircraft design technologies has led to a result that, at first glance, is paradoxical: the process of improving the performance of aircraft has “lost momentum.” New aerodynamic profiles have been found, wing mechanization has been optimized, and principles for constructing rational structures of aviation constants have been formulated.

ructions, the gas dynamics of the engines have been improved... What's next, has the development of the aircraft really come to its logical conclusion?

Well, the evolution of the aircraft within the framework of the normal, or classical, aerodynamic scheme is really slowing down. At aviation exhibitions and salons, the mass spectator finds a huge and colorful variety; experience

the same specialist sees fundamentally identical aircraft, differing only in operational and technological characteristics, but having common conceptual shortcomings,

“CLASSICS”: PROS AND CONS

Let us recall that the term “aircraft aerodynamic design*” refers to a method of ensuring static stability and controllability of the aircraft in the pitch channel 1.

The main and, perhaps, the only positive property of the classical aerodynamic design is that the horizontal tail (HO) located behind the wing makes it possible to ensure longitudinal static stability at high angles of attack of the aircraft without any particular difficulties.”

The main disadvantage of the classical aerodynamic design is the presence of so-called balancing losses, which arise due to the need to ensure a margin of longitudinal static stability of the aircraft (Fig. I). Thus, the resulting lift force of the aircraft turns out to be less than the lift force of the wing by the amount of the negative lift force of the aircraft.

The maximum value of balancing losses occurs during takeoff and landing modes with the wing high-lift devices extended, when the lifting force of the wing and, consequently, the diving moment caused by it (see Fig. 1) have a maximum value. There are, for example, passenger aircraft in which, with fully extended mechanization, the negative lifting force of the aircraft is equal to 25% of their weight. This means that the wing has been oversized by approximately the same amount, and all the economic and operational indicators of such an aircraft, to put it mildly, are far from optimal values.

AERODYNAMIC DESIGN “DUCK”

How to avoid these losses? The answer is simple: the aerodynamic configuration of a statically stable aircraft must exclude balancing with a negative lift force on the horizontal

"Pitch is the angular movement of the aircraft relative to the transverse axis of inertia. Pitch angle is the angle between the longitudinal axis of the aircraft and the horizontal plane.

1 The angle of attack of an aircraft is the angle between the direction of the oncoming flow velocity and the longitudinal cmpoume.tbHuu axis of the aircraft.

 

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