Where is the keel of the plane? Keel aircraft: construction

Even a person who has never seen the sea before, certainly knows the parting words: "Seven feet under the keel." And there are no questions. The keel of the ship is the most important constructive part, on which many details of its hull are attached. But does anyone know about where the aircraft keel is located and for what purpose?

What it is?

This is the "organ" of stability, which allows you to keep the aircraft in a given course. Unlike the ships, the keel of the aircraft is an integral part of the vertical tail feathers. At the bottom of the fuselage, there is no keel in the aircrafts! But there is one subtlety. The fact is that this part is tightly connected to the power elements of the fuselage, but because of that there is something common in the sea and air term. So where is the keel of the plane? Simply put, this is the vertical part of the tail.

It is placed motionless, fixed in three points, symmetrical axial line of the aircraft. It looks like an ideal trapezoid. Typically, the aircraft keel consists of spars, ribs and skin. This scheme is classical, little changed since the appearance of the first aircraft. The front spar is sloped (as a rule).

Layout diagrams

Most often, the keel is single, but in some cases it is made double and even triple (on propeller-driven bombers). In the latter case, this is required to ensure a high level of stability of the heavy machine. Incidentally, all aircraft at the location of the keel are divided into three types:

• Constructed according to the normal scheme. This is, for example, the keel of the A321.
• "Ducks," that is, aircraft, in which the horizontal tail of the keel is located in front of the wings.
• "Tails". From the keel there is only vertical tail, horizontal ailerons are completely absent.

Of course, the last two varieties are more characteristic for the "community" of military aircraft, since such a keel placement is necessary to make the aircraft particularly high maneuverability.

In some cases even more complex constructions are used. For example, podkilevye ridges (they are the same as the perforated carinae). They are used on some supersonic aircraft, where maintaining the ideal stability during the flight is vital. Thus, under the keel of the aircraft (this is where, we already found out) there is an additional and massive influx. More common is the situation where the horizontal tail of the tail generally has to be carried to the very top of the keel. This happens if the engines are installed in the stern of the aircraft. A similar scheme, for example, can be seen on domestic cargo and passenger planes Il.

What is it for?

As you know, windless weather is an incredible rarity, which happens not more often than once a year. In most cases, there is a wind, and its strength and direction can be radically different. When the plane flies, gusts of wind can strongly affect the direction and course. The aircraft must be designed to return to a stable position on its own. Only in this case a safe flight is possible.

Main purpose

The main rule of constructing the keel is to place it so that it does not fall under any conditions into the wake of the wing. Otherwise, a sharp violation of the exchange rate stability is possible, and in the most severe situations - physical deformation and destruction of the entire tail unit. So, the main purpose of the keel is the preservation of track stability.

The design of many aircraft is such that this part is mobile. By adjusting the magnitude of the deviation of the keel, the crew controls the heading direction. The exception is military aircraft, in which engines with a controlled thrust vector are responsible for changing the direction of flight. In their case, to make a moving keel aircraft (photo it is in the article) is stupid, since the overload during maneuvering is such that it simply collapses.

What kinds of stability are provided by the keel?

There are three types of stability, for the sake of preservation of which the keel is included in the design of the aircraft:

• Track.
• Longitudinal.
• Transversal.

We will deal with all these varieties in more detail. So, the road stability. It should be remembered that in case of loss of longitudinal stability of the fuselage in flight, the aircraft will still continue to fly for some time due to the inertial force. After that, the air stream begins to run on the rear of the aircraft, which lies behind the center of gravity. The keel in this case prevents the occurrence of a rotating force that forces the aircraft to rotate about its axis.

Longitudinal stability. Suppose an aircraft flies in normal mode, the center of gravity coincides with the center of applying pressure to its fuselage. At this point, its fuselage also operates multidirectional forces that seek to deploy the body of the aircraft. Lifting force and gravity act simultaneously. The keel of the aircraft (a photo of this detail you will see in the article) provides an equilibrium, which in this particular case is very unstable. Normal flight without tail fins, keel and stabilizers is not possible.

Other types of stability

Transverse stability. In general, this factor is a logical extension of the previous property. When the wing and cross stabilizers of the keel act in opposite directions, they "try" to overturn the aircraft. This is counteracted by the shape of the wings: if you look at them from afar, they resemble the letter "U" with strongly dilated upper "horns". This form provides an independent correction of the position of the aircraft in space. Kiel at the same time helps to maintain lateral stability.

Note that in aircraft with a swept sweep of the wing, the need for keel is not so great ... at high speeds. If it falls, then the buildup of counteraction forces occurs in a geometric progression. Therefore, for these machines, the most durable and lightweight keel is very important, which can resist such high loads. And how it can be received? Let's talk about this.

Features of creating modern aircraft

Currently, Rosaviatsia's experts and their foreign colleagues are focusing on the creation of aircraft parts (including keel) from large-sized parts made of the latest composite materials.

The share of these compounds in the design of modern aircraft is growing steadily. According to information from specialists, their volume fraction already reaches from 25% to 50%, and small non-commercial airplanes can be composed of plastic and composites at 75% altogether. Why such an approach has become so widespread in aviation? The fact is that the same keel of the Boeing aircraft, made of polymer "alloys", has very low weight, very high strength and a resource that, using standard materials, is simply unrealistic.

Basic Materials

The most justified use of composites in the design is not only the tail fin, but also the wings and power elements of the fuselage, which should not only be very strong, but also flexible enough. Otherwise, the probability of structural failure under the influence of flight loads is not ruled out.

But it was not always so. So, the pride of Soviet aircraft construction, the Tu-160, the White Swan or Black Jack, has a keel of ... titanium alloys. Such a specific and extremely expensive material was chosen because of the huge loads on the design of this machine, which to this day retains the title of the most heavy bomber in service. But still such a cardinal approach to the creation of the keel is a rarity, and so today designers often have to deal with simpler composite materials.

What tasks do you have to solve when creating a composite keel?

In the process of development, domestic designers had to solve a whole range of complex problems:

• The creation of large-sized parts of the keel and other carbon-fiber tooling by the infusion method has been worked out.
• Also, it was necessary to almost completely rethink and re-equip the main stages of production, which were not designed for the use of composite materials.

Other features

In the production process, the latest software (FiberSim) was introduced, which allows achieving the highest possible automation levels. In addition, now the keel of the aircraft, the construction of which is described in the article, can be manufactured using such technologies, where there are practically no drawings. The production of this part with this approach is as follows:

• Designing or selecting a finished model. Today the keel (mostly) is projected in a fully automatic mode, without the participation of "human" developers.
• Cutting of used materials, also conducted in automatic mode.
• In the automatic mode, the raw materials used for the keel and its structural parts are laid out.
• Laying of layers is carried out by robotic mechanisms controlled by a computer program.

In addition, the modern approach to the production of keels suggests the following:

• Constant production of prototypes, which are tested in the most severe conditions.
• Non-destructive testing technologies are developed, which allow for constant monitoring of the condition of the keel on the aircraft.

Advanced methods for creating the tail of a plane "MS-21"

In the not-too-distant past, the aviation industry was literally stunned by the announcement of domestic developers that they were developing an entirely new aircraft, the MS-21. Its unusual is that in almost the last three decades it is the first domestic car for domestic flights. At its manufacturing, many new technologies were tested, which in many respects touched the innovative features of the keel and the entire tail empennage.

Developing and releasing the keel of the MC-21 airplane, domestic specialists were able to achieve the following:

• Full automation of cutting all parts and raw materials used in production. Due to this, it was possible to achieve no less than 50% reduction in the total cost of all tail fins and, in particular, the keel.
• In the production of tail fins, the ProDirector program is used, which allows to achieve the ideal accuracy in the machining of parts. This makes it possible to create not only strong, but extremely lightweight keels.
• Also, the keel of a modern aircraft is created using double curvature techniques. Thanks to them, it is possible to achieve a multidirectional thickness in those areas where additional reinforcement of the structure is needed (under the aircraft keel).
• Even large parts of the keel can now be "roasted" in special autoclaves. As a result, extremely durable and rigid components are obtained, withstanding loads of any degree.
• Control of the geometry of parts is also controlled by complex computerized systems.

Other features

Thanks to the use of new technologies and techniques, the labor of tail and tail fin creation was reduced by 50-70%. Today, more than four thousand parts of the keel and tail unit have passed state tests.

The main achievement was the development of a reliable and simple technology for producing keel parts of the keel size of 7.6 x 2.5 m. At present, they have already been supplied to the Irkutsk Aviation Plant. They are made of modern composite materials, and the peculiarities of this process have already been of interest to the leading foreign aircraft manufacturers.

Current problems

Why did we spend so much time discussing modern ways of designing and building a keel? The fact is that even since the 60s of the last century it became finally clear that further increase in aircraft performance is possible only if they increase their strength and introduce completely new varieties of polymer materials into production. The problem of the last generation of aircraft is that their design (and keel in particular) is highly susceptible to "fatigue". Because of this, by the 1970s, numerous techniques for controlling the state of the wing and tail were developed.

The requirements for production are also high. Each batch of details is subject to severe overloads on vibrating stands, tested by temperatures and pressure. And this is not surprising, since the slightest crack is subsequently fraught with the death of hundreds of passengers.

So you found out where the keel plane is and why it is needed!