Canard (aerodynamic design)

Rutan Model 61 Long-EZ. An example of an aircraft built using the canard aerodynamic design.

"Duck"- an aerodynamic design in which an aircraft’s longitudinal controls are located in front of the wing. It was named so because one of the first aircraft made according to this design - Santos-Dumont's 14 bis - reminded eyewitnesses of a duck: forward control planes without a tail at the rear.

Advantages

The classic aerodynamic design of an aircraft has a drawback called “balancing losses.” This means that the lifting force of the horizontal tail (HO) on an aircraft with a classic design is directed downward. Consequently, the wing has to create additional lift (essentially, the lift force of the aircraft is added to the weight of the aircraft).

The canard design provides pitch control without loss of lift for balancing, because the lifting force of the PGO coincides in direction with the lifting force of the main wing. Therefore, aircraft built according to this design have better load-carrying characteristics per unit wing area.

However, ducks are practically never used in their pure form due to their inherent serious disadvantages.

Flaws

Airplanes built using the “Duck” aerodynamic design have a serious drawback called “peck tendency.” “Peck” is observed at high angles of attack, close to critical. Due to the slope of the flow behind the front horizontal tail (FH), the angle of attack on the wing is less than that of the FH. As a result, as the angle of attack increases, flow stall begins first at the PGO. This reduces the lifting force on the PGO, which is accompanied by a spontaneous lowering of the aircraft’s nose - “pitch” - which is especially dangerous during takeoff and landing.

Pilots trained to fly airplanes with a classical aerodynamic configuration, when flying a canard, complain about the limited visibility created by the PGO.

Also, the movable horizontal tail located at the front helps to increase the effective dispersion area (RCS) of the aircraft, and therefore is considered undesirable for fifth-generation fighters (examples: the American F-22 Raptor and the Russian PAK FA) and the developed promising long-range bomber (PAK DA), made in compliance with radar stealth technologies.

Tandem biplane - a “duck” with a closely spaced front wing - a design in which the main wing is located in the flow bevel zone from the front horizontal tail (FH). Saab JAS 39 Gripen and MiG 1.44 are balanced according to this scheme.

Also, various variations of the canard design are used for many guided missiles.

Literature

  • Flight tests of aircraft, Moscow, Mechanical Engineering, 1996 (K. K. Vasilchenko, V. A. Leonov, I. M. Pashkovsky, B. K. Poplavsky)

see also


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See what “Duck (aerodynamic design)” is in other dictionaries:

    Airplane. A. s. characterizes the geometric and design features of the aircraft. There are a large number of characteristics by which aircraft are characterized, but they are generally distinguished by the relative position of the wing and horizontal tail... ... Encyclopedia of technology

    aerodynamic design Encyclopedia "Aviation"

    aerodynamic design- Rice. 1. Aerodynamic designs of the aircraft. aerodynamic design of the aircraft. A. s. characterizes the geometric and design features of the aircraft. A large number of signs are known by which A. s. is characterized, but they are generally accepted... ... Encyclopedia "Aviation"

I belong to that category of modellers who are interested in designing and building an airplane themselves, and then enjoying flying it. But the main pleasure comes from the result of creative search.

After flying for several seasons on a homemade Diamant with OS MAX 50, it became a little boring. It was clear what the plane could do and what I could do. Of course, I could have honed my 3D aerobatics skills, but my soul was asking for something unusual. I wanted to build an airplane that no one else has, and which would have unique aerobatic capabilities unique to it.

Attempt 1

I watched how radio fighters fly, and the idea came up to build a “flying wing” type fanfly. No sooner said than done. The drawing was drawn, the layout worked out, and now the plane is ready.

  • Swing: 1450 mm
  • Length: 1000 mm
  • Weight: 2000 g
  • Engine: OS MAX 50

I drive out onto the field and realize that I haven’t built anything interesting. Yes, it flies, yes, it spins some figures. But nothing interesting, everything is as usual, even a little boring.

Having analyzed the situation, I understand that this was how it should have been... The classic scheme and the “flying wing” scheme have been worked out to the smallest detail, and cannot offer anything new. Creative stagnation has begun...

Being in a crisis, I leaf through old magazines and come across a model of the “Duck” scheme. This is starting to get interesting.

Idea

The weft pattern has one interesting feature. The steering surfaces are located in front of and behind the center of gravity. Accordingly, if you mix the elevator with the ailerons and do it like in line aerobatics, then the turning moment from the elevators will be applied in front and behind the center of gravity. This in turn will allow you to make loops of a very small radius. It was also known from large aviation that this scheme behaves very stably in stall modes. But the pushing propeller located at the rear did not contribute to the performance of 3D aerobatics.

The conclusion suggested itself: the engine should be placed in front, but then problems arose with alignment. Since the main wing is located at the rear (unlike the classical design, where the stabilizer does not bear the weight of the aircraft, in the canard design it creates lift), and the center of gravity is within 10-20% of the MAR, it was not possible to balance this design. Again a dead end... Leafing through further magazines, I find an old issue of "Wings of the Motherland", which talks about aircraft of special designs, and among them is the "Tandem" design. And the most interesting thing is that there are formulas for calculating the position of the center of gravity. I present an excerpt from this article.

Excerpt from an article in the magazine "Wings of the Motherland" for February 1989.

When flying at high angles of attack before stalling, stall should occur first on the front wing. Otherwise, when stalling, the plane will sharply lift its nose and go into a tailspin. This phenomenon is called “pickup” and is considered completely unacceptable. A way to combat “pickup” on canards and tandems was found a long time ago: it is necessary to increase the installation angle of the front wing relative to the rear, and the difference in installation angles should be 2-3 degrees.

A properly designed aircraft automatically lowers its nose, moves to lower angles of attack and picks up speed, thereby realizing the idea of ​​creating a non-stall aircraft. For a “standard duck” (the horizontal tail area is 15-20% of the wing area and the tail shoulder is equal to 2.5-3 MAR), the center of gravity should be located in the range from 10 to 20% of MAR. For a tandem, the centering should be within 15-20% V eq (chord of an equivalent wing), see figure. The equivalent wing chord is defined as follows:

V eq = (S p +S h)/(l p 2 +l h 2) 1/2

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

X eq = L/(1+S p /S z *K)-(S p +S z)/(4*(l p 2 +l z 2) 1/2)

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

K = (1+0.07*Q)/((0.9+0.2*(H/L))*(1-0.02*(S p /S h)))

In the given formulas:

  • S p - area of ​​the front wing.
  • S z - area of ​​the rear wing.
  • L - tandem aerodynamic arm.
  • l p - the span of the front wing.
  • l z - the span of the rear wing.
  • Q - excess of the installation angle of the front wing over the rear.
  • H is the height distance between the axis of the front and rear wings.

Final version

Now the general idea has formed. We put the engine in front, make the wings the same, and move the receiver and battery to the tail of the plane.

The aileron drive on the front and rear wings is separate. A total of 6 steering gears are used.

It was scary to immediately build a plane for the 50th engine. A whole range of questions remained unclear: on which wing to make ailerons, and on which elevator, or both; what angles of attack should the wings have; how far the wings should be spaced apart from each other; and, in general, will it fly?

But the creative itch took over the mind, and all doubts were cast aside. I am building a "Tandem" for the 25th engine. I’ll use it to check how it flies...

Attempt 2

The model is drawn, drawn and built. The following happened.

  • Both wingspan: 1000 mm
  • Length: 1150 mm
  • Wing chord with aileron: 220 mm
  • Distance between wings: 200 mm

The front wing was placed 20 mm lower than the engine axis, the rear wing 20 mm higher. The wings were absolutely identical and mutually interchangeable, only on one wing there were ailerons, and on the other an elevator.

Flight

The first flight only added confidence in the correct direction of the search. The model was absolutely predictable and adequate in the air, stable at low speeds and did not spontaneously fall into a tailspin. The scheme with the elevator on the front wing showed better results compared to the scheme when the elevator was on the rear wing. This is due to the fact that at low speeds it acted as flaps, increasing the lift on the front wing.

It's decided! I am studying the behavior of this model in the air and starting to build a model for 61 engines. While the big plane is being built, we fly on the small one. During the flights we find another interesting feature of the model. She could stop and stand in the air against the wind. When pulling the stick toward itself at low throttle, it showed a tendency to parachute.

The result is the following:

  • Swing: 1400 mm
  • Length: 1570 mm
  • Chord with aileron: 300 mm
  • Distance between wings: 275 mm

The first flight is carried out with ailerons on the rear wing and elevator at the front.

Impression:

Steady, stable at all speeds, very predictable. However, the flight of the large model revealed one peculiarity. The plane reacts very sensitively to the elevator. That is, I brought it into horizontal flight, trimmed it at medium throttle - it flies smoothly and steadily, but as soon as you touch the altitude control, it abruptly, but at a small angle, changes the direction of flight. It’s not that it’s annoying or dangerous, you just need to take into account that the model reacts very sensitively to the elevator.

This is of course unacceptable for a training aircraft, but our FAN is designed for an advanced pilot.

Now I'm trying to mix the elevator and ailerons. That is, when I pull the handle towards myself on the front wing, both ailerons go down, and on the rear wing they go up. But when I roll, the ailerons work in parallel on both wings.

The model's unstable behavior in horizontal flight was most likely due to incorrect wing angles. Unfortunately, it was not possible to change them without significant alteration.

The model is finally set up, I’m trying out what it can do in the air.

  1. I'm taking off the gas. I pull the handle towards myself (squeezed expenses). The model slows down almost to a stop, then smoothly nods, accelerates and repeats the same thing. No tendency to spin. That is, if you do not deliberately disrupt the flow from the wing, then the stall occurs very smoothly and is immediately restored with a set of speed.
  2. I'm taking off the gas. I pull the handle on myself (full expenses). The model stops in the air and, maintaining a horizontal position, begins to descend like a parachute. Parachute figure. I give the handle from myself - she turns over on her back and continues her descent vertically downwards (it’s just some kind of plague). "Shifter" figure. That is, the model is capable of being controlled by rudders in the mode of 100% flow separation from the load-bearing planes!
  3. Expenses to the maximum - I'm twisting the loop. True, this cannot be called a loop. Rather, it is a classic “waterfall” from a 3D complex. The model spins around the lantern, while slowly descending. Moreover, there is no need to work with gas. And it is very easy to change the direction of rotation when shifting the rudders. Shaker figure.
  4. I make a “parachute” and deflect the rudder. I get a very slow flat corkscrew - a "dry leaf" figure.
  5. Such a figure as the “harier” goes into the category of children’s.
  6. A “square loop” turns out to be exactly square, since the turning radii at the corners are almost unreadable.

It would take a very long time to describe the figures. I'll just say one thing. This plane can do more than I can, and is capable of teaching an advanced pilot several more new maneuvers that are inaccessible on conventional aircraft. And I especially want to note the predictability and stability of the aircraft, no matter what you do with it.

Looks like I got what I WANTED!

Attempt 4

Although the second and third aircraft showed excellent flight performance, one more very important question remained: what are the optimal angles of attack for the wings? To solve this problem, it was decided to build a model for the 50th engine, with the ability to change the angle of attack of the wings on the ground. In addition, model No. 3 was destroyed due to hardware failure.

It was also decided to place the front wing above the engine axis, and the rear below (on the previous model it was the other way around, I just wanted to check - I’ll say right away that I didn’t notice any changes in the behavior of the model.) and make a slight bevel along the leading edge, the front wing received an implicit the pronounced positive "V" and the posterior negative "V". This was supposed to give stability at low speeds in forward and reverse aerobatics, respectively.

I will not dwell in detail on the description of the design and manufacturing process. She is no different from the usual Fanfly and is clear from the photographs.

The invention relates to aircraft with a front horizontal tail. The canard aircraft includes a wing, fuselage, propulsion system, landing gear, vertical tail and a biplane front horizontal tail (FH). The aircraft has a uniform loading of the wing and the airfoil per unit area, with the ratio of the distance between the airfoil planes to the arithmetic mean of the chord values ​​of each of the planes equal to 1.2. The invention is aimed at reducing the size of the aircraft. 1 ill.

The invention relates to aircraft with a front horizontal tail, mainly ultra-light, sport aircraft.

A canard-design aircraft is known, including a wing, fuselage, propulsion system, landing gear, vertical tail and biplane front horizontal tail.

For a canard-type aircraft, the load on the front horizontal tail (FH) per unit area is significantly less than that of the wing. This situation is a consequence of the fact that the ratio of the distance between the PGO plans to the arithmetic mean of the chord values ​​of these plans is only 0.7. Since the bearing area of ​​the PGO is used inefficiently, an increase in the size of the wing area and front horizontal tail is required, which increases the size of the aircraft.

The technical problem solved by the present invention is to reduce the size of the aircraft.

The problem is solved due to the fact that according to the invention, in a canard aircraft, including a wing, fuselage, propulsion system, landing gear, vertical tail and a biplane front horizontal tail (FH), there is a uniform load of the wing and FH per unit area, ensured by the ratio of the distance between the plans of the PGO to the arithmetic mean of the values ​​of the chords of each of the plans, equal to 1.2.

This design of the aircraft makes it possible to reduce its size.

The invention is illustrated by a specific example of its implementation and the accompanying drawing.

In fig. 1 shows a cross-section of a biplane front horizontal tail of a canard-type aircraft along a plane parallel to the base plane of the aircraft made in accordance with the invention.

The “canard aircraft” device includes a wing, fuselage, propulsion system, landing gear, vertical tail and a biplane front horizontal tail, consisting of a lower plane and an upper plane. In this case, the specific load of the PGO is equal to the specific load of the wing and is, for example, 550 newtons per 2.2 square meter. That is, there is a uniform load on the wing and PGO per unit area.

In fig. 1, the value of the chord of the lower plan 1 PGO is indicated by the letter bн, and the value of the chord of the upper plan 2 is indicated by the letter bв. The distance between the top 2 and bottom 1 plans is indicated by the letter h.

The chord bн of the lower plan 1 is equal to the chord bв of the upper plan 2 and is, for example, 300 mm. The distance h between plans 1 and 2 is, for example, 360 mm. In this case, the ratio of the distance h to the arithmetic mean of the plan chords is 1.2.

The value of this ratio ensures uniform loading of the wing and PGO for ultra-light sports aircraft. This follows from the following circumstances.

A decrease in the value of h leads, on the one hand, to a rearward shift of the aircraft's focus, which is positive until the load on the airborne space becomes equal to the load on the wing. On the other hand, a decrease in the value of h is accompanied by an increase in the inductive reactance of the PGO, which is certainly negative. In this regard, it is clearly impossible to determine exactly what distance between the PGO plans should be chosen. At the same time, it must be borne in mind that from the point of view of reducing the total area of ​​the wing and the anti-aircraft platform and, consequently, the size of the aircraft, the condition of uniform loading of the wing and the anti-aircraft platform per unit area must be met.

With the same or almost identical loading of the wing and the landing gear, the condition is met that the critical angle of attack of the wing is exceeded by three degrees over the critical angle of attack of the landing gear in their landing configuration. This condition is mandatory to prevent “pitch” - a sharp lowering of the aircraft’s nose due to a stall in the flow at the PGO. In this case, a slight difference in load is possible both in favor of the PGO and the wing.

The value of the above ratio was revealed through analytical studies and verification of their results through flight tests of an aircraft model, on which it was possible to change the distance between the PGO plans.

INFORMATION SOURCES

An aircraft with a canard design, including a wing, fuselage, propulsion system, landing gear, vertical tail and a biplane front horizontal tail (FH), characterized in that it has a uniform loading of the wing and FH per unit area, ensured by the ratio of the distance between the plans of the FH to the arithmetic mean of the chord values ​​of each of the plans, equal to 1.2.

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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