Preparation for the launch of the UAV “Eleron-3”. Photo by the Ministry of Defense of the Russian Federation / mil.ru
To date, a great many unmanned aerial systems for various purposes have been created in our country and abroad. During the construction of the UAV, a wide range of ideas and solutions are used, incl. all major aerodynamic schemes. The “flying wing” layout is quite popular because it offers well-known advantages – and at the same time leads to some limitations.
In our country, the theme of the flying wing was taken up several decades ago, but this direction did not have much success. In the field of manned aviation, other schemes were developed, incl. structurally similar, such as tailless or integral layout.
However, the situation changed dramatically with the start of active and mass development of unmanned aerial vehicles. In this area, it was possible to more fully realize – and bring to operation – all the main advantages of the “flying wing” in different classes of equipment. Let’s consider the most interesting examples of the use of such a scheme in domestic UAVs.
At the beginning of the 2000s, the first UAV of the future Eleron family from the ENIX company appeared. It was an ultralight vehicle weighing 3400 g with a wing span of less than 1.5 m. With the help of an electric propeller-driven group, it could reach speeds of more than 100 km / h and fly for 70-75 minutes. The drone’s payload was day and night cameras.
UAV “Eleron-10D”. Photo Vitalykuzmin.net
Later, new samples of the family appeared, such as “Eleron-10”. Its wing has increased to 2.2 m in span, and its mass has increased to 15.5 kg. Due to larger and more capacious batteries, it is able to stay in the air for 2.5 hours and work at a distance of at least 50 km from the operator (with video signal transmission). All samples of the Eleron family have found application in the army and law enforcement agencies.
You can also note the UAV line ZALA 421 from the company ZALA Aero Group. This family includes tailless, flying wings and even a tiltrotor and multicopter. Devices weighing in kilograms are capable of flying tens of kilometers and carrying reconnaissance equipment. Some of these samples are accepted for supply and are mass-produced. The loitering ammunition ZALA KUB stands apart. This product also has the features of a flying wing.
For a number of reasons, the “flying wing” scheme did not find application in domestic projects of the middle class, but it came in handy when creating some heavy samples. Due to the size and function offered, such projects have consistently attracted the attention of the public and professionals.
In 2007 RSK MiG presented a full-size model of the Skat heavy attack UAV. The project provided for the construction of a machine weighing 20 tons with a wingspan of 11.5 m and a turbojet engine. The design speed reached 850 km / h, the range was 4000 km. The drone was supposed to take on board up to 6 tons of weapons at 4 points of internal suspension. Together with the “Skat” mock-up, several types of guided aircraft weapons were demonstrated, compatible with it.
Ultra-light drone ZALA 421-08M – it can be launched “hand-held”. Photo ZALA Aero Group / zala.aero
In the future, the fate of the project remained vague. He was remembered every few years, but without mention of any progress. At the same time, as it was stated, the work stopped and continued. The latest news of this kind appeared a year ago – and there have been no new messages since then.
In June 2018, an experienced heavy UAV S-70 “Okhotnik” developed by the “Sukhoi” company was taken out of the assembly shop. The wingspan of this machine is estimated at 18-20 m, the take-off weight is at least 20 tons. One turbojet engine is used. The payload is several tons in the internal compartments. According to various sources, the UAV is made sub- or transonic. An advanced automatic control system is used, capable of interacting with the operator or other aircraft.
The first flight of the Okhotnik took place on August 3, 2019, and flight tests are still ongoing. The S-70 operates independently and in conjunction with the Su-57 fighter. It is not known when the development work will be completed and mass production will begin.
Benefits in context
The advantages of a flying wing design over other aerodynamic arrangements are well known. Let’s consider why exactly it turned out to be useful in the creation of some domestic (and not only) unmanned aerial vehicles.
Loitering ammunition ZALA KUB. Photo ZALA Aero Group / zala.aero
The main advantage of the scheme is the ability to transform the entire or almost the entire surface of the airframe into a load-bearing surface – with a corresponding increase in flight characteristics and / or carrying capacity. This design feature allows relatively light UAVs with low fuel reserves or limited capacity batteries to remain in the air longer than traditional designs of similar size and weight.
The flying wing offers advantages in terms of available layout spaces. The necessary components and assemblies can be placed not only in the fuselage, as in the normal scheme, but also in the center section smoothly conjugated with it or in the wing of increased thickness. Such opportunities are best demonstrated by the heavy “Skat” and “Hunter”. Inside their gliders, it was possible to place fairly large turbojet engines, cargo compartments and tanks with a large amount of fuel. Light UAVs are built in a similar way, albeit with understandable differences.
An important feature of the flying wing is its potential in terms of stealth. Smooth contours of the desired configuration, combined with the correct choice of material, can drastically reduce the effective scattering area. According to various estimates, such techniques were used in the Hunter and Skat projects. The same applies to a number of foreign developments.
Dealing with imperfections
For all its advantages, the flying wing is not without its disadvantages, which have to be dealt with. Often, such problems are too serious and lead to the abandonment of such a scheme in favor of other layouts.
A prototype UAV “Skat” from RSK “MiG”. Photo Airwar.ru
One of the biggest challenges when creating flying wings, incl. UAV is associated with the layout of the necessary units within the volumes of a specific configuration. The largest units can be placed only inside the fuselage protrusion or center section, the volume of which is not infinite. Expanding the available compartments requires aerodynamic redesign, which is not always possible or advisable.
Fortunately, these issues are successfully addressed early in the design phase. In addition, in the field of UAVs, there are some features that facilitate the layout of the units. So, the drone does not need a cockpit and related systems, and the control is carried out by electronics that do not require much space.
A serious problem is the behavior of a flying wing in the air. Having no vertical tail, such an aircraft cannot demonstrate acceptable track stability. There is also a problem with the provision of control. Traditional elevons on the trailing edge of the wing do a good job of roll control, but can show insufficient pitch control due to insufficient offset from the center of mass. Without vertical tail, there is a problem of yaw control.
Heading stability can be ensured with the help of curved tips, as on some Elerons and part of the ZALA UAV. Heading control can be carried out by splitting elevons, like the “Skat”. A radical solution could be the abandonment of the “flying wing” scheme in favor of a tailless one with a keel and a full-fledged rudder.
The newest heavy UAV S-70 “Okhotnik”. Photo by the Ministry of Defense of the Russian Federation / mil.ru
The solution to all problems with stability and controllability is facilitated by the active development of autopilots and electronics in general. Modern UAVs of all main classes use high-speed automation and advanced algorithms capable of maintaining flight with specified parameters and reacting to undesirable phenomena.
One of the options
In general, the “flying wing” scheme at the current level of technology development is useful and can be used in certain projects. Its characteristic features can be used to solve certain problems, receiving serious benefits and advantages over other schemes. However, due to the presence of limitations and disadvantages, the flying wing does not become a universal and unequivocally positive solution – and therefore cannot displace other schemes.
UAVs of other schemes are still being created and implemented. So, along with the flying wing “Eleron”, “Eagles” of the normal layout are actively used. Altius with a full-fledged fuselage and a narrow straight wing is being tested simultaneously with the strike Hunter. Moreover, in some classes of drones, the flying wing has not yet found application, for example, in the field of long-range medium-altitude vehicles (MALE).
Thus, the creators of new aviation technology need to remember the existence of different aerodynamic schemes and understand their characteristic features, which will make it possible to choose the optimal solutions for specific projects. With this approach, new samples of unmanned or other equipment will have an optimal appearance and characteristics – regardless of the presence or absence of a pronounced fuselage and empennage.