Each time you visit an airport you will notice different aircraft types, which can vary in shape, design, length, and size among other visible parameters. Similarly, whenever you take a glance at the skies a few times a plane flies past, then you’ll probably notice that it is not the same plane. Ranging from design up to the tail number, there is always a notable variance.
These variances are not by chance. The designers of the aircraft definitely had certain reasons why they thought it best to have a unique configuration for each airplane type. Perhaps it is time to give them credit considering the design of aircraft is a rather detailed process that takes years of crafting and simulation before the final rollout.
But why is this so? Usually to attain different performance capabilities, control and maneuverability, passenger comfort levels, compliance with aviation regulations, and not forgetting the aesthetic appeals to the brands.
The canard configuration is one of those designs on the aircraft’s fuselage, forward of the wings, that over the years, the aircraft designers have tinkered with for several reasons as we will see. As to whether the efforts to have canards as performance augmentation surfaces on planes have borne more fruits than setbacks, are still relevant today, or have been overtaken by newer aircraft designs, is a discussion worth having.
What are canards?
“Canard” is a French word meaning a duck. This explains why most people perceive a canard airplane as a duck, with an outstretched neck and the wings staying back. Unlike other aircraft with a conventional horizontal stabilizer and empennage that provides stability and directional control, a canard airplane has quite a large rear wing that is mounted extremely far aft. This unique design makes the canard configuration an entire redesign of an airplane instead of a plain inclusion of a control or lifting surface.
What is the use of canards?
Canard is a lift-augmentation horizontal control surface located forward of the main wing of an airplane. The canard configuration is common in combat aircraft, considering the high-performance demands such as control and maneuverability.
Canards are used for various reasons. For example, a lifting canard creates more lift, canards also help with reduction of overall drag, and improvement of aircraft control. However, this configuration comes at a cost due to the stability issues that arise. These are discussed further as we will be looking at the benefits and drawbacks of canards.
Design classes for a canard configuration
Just as typical aircraft design, canard configuration designs are of many types. However, there are two main design configurations; the lifting canard and the control canard.
A. The lifting canard
The lifting canard design is such that the wing of the aircraft and the canard share the weight of the aircraft. Notably, the horizontal stabilizer generates a negative lift or downward force. Instead, the lifting canard generates a positive lift or an upward force, which counters the weight of the aircraft that acts downwards. This canard design is common in the Rutan Long-EZ plane.
Probably one may ask the question, “Why not have a smaller main wing then considering the canard already plays an integral role in lift generation?” Well, this is not possible considering that the canard must stall ahead of the main wing while putting into perspective the capability of stall recovery and pitch stability.
As such, the wing cannot realize full lift capability, which then necessitates the need for the main wing to provide the needed lift.
Consequently, the main wing installed in such a canard-incorporated airplane is relatively larger than that of a typical airplane configuration.
B. The control canard
Unlike the lifting canard design where the wing and the canard share the weight of the aircraft, the control canard design is such that the main wing carries close to the entire weight of the aircraft with the control canard used for pitch control. That is, the angle of attack of the control canard is normally zero and is principally a control surface.
This canard aircraft design is common in combat aircraft, for example, the Eurofighter Typhoon. In these airplanes, the pitch control function of the canard is activated through the flight control systems in order to create an artificial static and dynamic stability.
Consequently, with such control surface the aircraft become more maneuverable even at high speeds, enabling the achievement of such high-performance-demanding combat missions.
Famous planes with canard designs
A list of some of the famous airplanes with a canard configuration, dating from the era of the Wright Brothers include:
Rutan Long-EZ and VariEze
Piaggio P.180 Avanti
Benefits of canards
It would be beneficial to understand the principles of flight for a conventional airplane type, with a typical empennage, especially around how they achieve stability in flight before looking at how the canard design airplane achieves better performance in this regard.
Four forces act on an aircraft in flight – weight or gravity, which is the downward acting force; lift, which is the upward acting force; thrust, which is the forward acting force; drag, which is the reward acting force. In this case, let’s focus on the weight and the lift.
The magnitude of the weight of the airplane relies on the mass of the plane, the fuel loaded, and the payload onboard. Even though there is the distribution of weight in the entire aircraft, it is often thought to act through a single point called the center of gravity, COG or CG, through which the aircraft rotates in flight.
On the other hand, the lift is the upward acting force that ensures the aircraft remains afloat and doesn’t stall. It overcomes the downward acting force, weight, which means it must be greater than the weight for the aircraft to take off and keep flying.
Lift relies on several factors such as the velocity of the airflow around the wings, and the shape and size of the airfoil. Primarily, the lift is generated by the wings.
Therefore, in a conventional horizontal and vertical stabilizer airplane, the weight and lift are generated as follows:
Upward force, lift, is generated by the wings.
Downward force, the CG and weight of the airplane.
Downward force, is additionally generated by the horizontal stabilizer.
During a flight, the pilot can maintain the plane in a stable and level position to counter the tail-down force actuated by the horizontal stabilizer and correct any weight shifts as long as the aircraft is properly loaded.
However, in a canard design aircraft, there is a change to the equation as follows:
Upward force, lift, is generated by the wings.
Downward force, the CG and weight of the airplane.
Upward force, an additional lift generated by the canard.
Take notice of item 3. in a typical aircraft versus a canard aircraft because it forms the basis of the benefits of a canard. Whereas there is more downward force generated to counter the lift produced by the wings in a typical aircraft with the extra requirement of the main wings to generate enough lift to keep the aircraft airborne, in a canard design aircraft, the canard offers additional upward force, lift, sharing the function with the wings.
As such, both surfaces work in tandem to maintain the airplane airborne. That is, during takeoff, the canard helps to lift the nose, complementing the main wing rather than adding to its load.
Additionally, unstable canard aircraft designs offer a larger control authority at higher coefficients of lift than in unstable aft-tail configurations of comparable typical aircraft. As such, for unstable airplanes, there is an advantage of a high coefficient of lift in canard designs than is the case of a conventional airplane.
Drawbacks of canards
Well, if the canards were super excellent then most modern aircraft would have them installed. This is not the case.
A canard design is technically believed to be “stall proof.” The design is such that the canard should stall ahead of the main wing, making the nose of the plane drop as the airspeed builds up again, and the airplane recovers.
However, to guarantee this capability, the canards must have a very high wing loading, which makes the canard sizing more critical than the sizing of the aft tail. As such, having an optimized sizing of the canard can prove difficult because a slightly small or very large size could alter its performance, which is a headache that is very much avoidable in conventional airplanes.
Additionally, the canards still require the rudder surface and the vertical stabilizer, the empennage. However, locating the vertical stabilizer, in this case, may be difficult considering the distance from the CG of the airplane to most of the aft surfaces of the plane is relatively smaller in canard planes than in conventional planes.
The consequence of this is that it can result in quite large vertical surfaces, which can then be corrected using winglets as common to the Rutan Long-EZ. However, this may require a high sweepback of the wings to ensure that the vertical surfaces are far behind the COG as necessary.
In consequence, such a sweepback does not favor low-speed flights, which basically are low-altitude flights, raising the approach and stalling speeds of the plane.
Even more, although canard designs can produce equal or better values of coefficient of lift, which is beneficial in the lift generation equation, such designs with higher values of coefficient of lift tend to have higher induced drag values than that of a comparable conventional plane.
Well, you can probably tell that despite the benefits of the canard designs, there is just too much effort needed in terms of design complexity to achieve the same level of stability as would be the case in a comparable conventional aircraft, beating the benefits of incorporating the design in modern aircraft.
Despite the striking appeal when a canard-equipped airplane is placed side by side with a typical airplane, for most designers, it is not worth the effort.
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Jet pilot @NASA
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