Where is the keel of the plane? Aircraft keel: design

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

Even a person who has never seen the sea probably knows the parting word: "Seven feet under the keel." And there are no questions here. The keel of a ship is the most important structural part on which many parts of its hull are attached. But does anyone know where the keel of the aircraft is located and what it serves for?

What is this?

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

It is placed motionless, fixed at three points, symmetrical to the center line of the aircraft. In appearance, this detail has the shape of an ideal trapezoid. As a rule, the keel of an aircraft consists of spars, ribs and skin. This scheme is classic, little changedsince the appearance of the first aircraft. The front spar is placed obliquely (as a rule).

Layouts

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

• Built in a normal pattern. Such, for example, is the keel of the A321 aircraft.
• "Ducks", that is, aircraft in which the horizontal tail of the keel is located in front of the wings.
• "Tailless". From the keel, only the vertical tail remains, the horizontal ailerons are completely absent.

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

In some cases, even more complex designs are used. For example, under-keel crests (they are also ventral keels). They are used on some supersonic aircraft where maintaining perfect stability during flight is vital. Thus, under the keel of the aircraft (this is where, we have already found out) there is an additional and massive influx. A more common situation is when the horizontal plumage of the tail generally has to be transferred to the very top of the keel. This happens if the engines are installed at the rear of the aircraft. Such a diagram can be seen, for example, indomestic cargo-passenger aircraft "Il".

What is it for?

As you know, calm weather is an incredible rarity that happens no more than a couple of times a year. In most cases, there is wind, and its strength and direction can vary dramatically. When an aircraft is flying, gusts of wind can greatly affect the direction and course. The aircraft must be designed to return to a stable position on its own. Only in this case is a safe flight possible.

Main purpose

The main rule for designing a keel is to place it in such a way that it does not, under any circumstances, fall into the wake from the wing. Otherwise, a sharp violation of directional 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 to maintain directional stability.

The design of many aircraft is such that this part is movable. By adjusting the keel deflection, the crew controls the course direction. The exception is military aircraft, on which engines with a controlled thrust vector are responsible for changing the direction of flight. In their case, making a movable keel of the aircraft (there is a photo of it in the article) is stupid, since the overloads during maneuvering are such that it will simply collapse.

What kind of stability does the keel provide?

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

• Track.
• Longitudinal.
• Transverse.

Let's deal with all these varieties in more detail. So, directional 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 forward for some time due to inertial force. After that, the air flow begins to run into 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 around its axis.

Longitudinal stability. Assume that the aircraft is flying in normal mode, the center of gravity coincides with the center of pressure application to its fuselage. At this moment, multidirectional forces also act on its fuselage, which tend to deploy the body of the aircraft. Lift and gravity act simultaneously. The keel of the aircraft (you will see a photo of this part in the article) provides balance, which in this particular case is very unstable. Normal flight without tail, keel and stabilizers is impossible.

Other sustainability

Shear stability. In general, this factor is a logical continuation of the previous property. When multidirectional forces act on the wing and lateral stabilizers of the keel, they "try" to overturn the aircraft. The shape of the wings counteracts this: if you look at them from a distance, they resemble the letter “U” with strongly separated upper “horns”. This form provides self-correction of the positionaircraft in space. The keel helps to maintain lateral stability.

Note that swept-wing aircraft don't need the keel as much…at high speeds. If it falls, then the growth of counteraction forces occurs exponentially. Therefore, for these machines, the most durable and lightweight keel is very important, which can resist such high loads. And how can you get it? Let's talk about this.

Features of creating modern aircraft

Currently, Rosaviation specialists and their foreign colleagues are focusing on the creation of aircraft parts (including the keel) from large parts made from the latest composite materials.

The proportion of these compounds in the design of modern aircraft is steadily growing. According to information from experts, their volume fraction already reaches from 25% to 50%, and small non-commercial aircraft can even consist of plastic and composites by 75%. Why is this approach so widespread in aviation? The fact is that the same keel of a Boeing aircraft, made of polymer "alloys", has a very low weight, very high strength and a resource that is simply unrealistic to achieve using standard materials.

Main Materials

The most justified use of composites in the design of not only the tail, but also the wings and fuselage power elements, which must be not only very strong, but also sufficientlyflexible. Otherwise, the probability of destruction of the structure under the action of flight loads cannot be ruled out.

But it wasn't always like this. So, the pride of the Soviet aircraft industry, the Tu-160 aircraft, also known as the White Swan or Blackjack, has a keel made of … titanium alloys. Such a specific and extremely expensive material was chosen because of the enormous stresses placed on the design of this machine, which to this day retains the title of the heaviest bomber in service. But still, such a radical approach to creating a keel is rare, and therefore today designers have to deal with simpler composite materials much more often.

What challenges do you face when creating a composite keel?

During the development process, domestic designers had to solve a whole range of complex tasks:

• The creation of large-sized parts of the keel and other carbon-fiber equipment using the infusion method has been worked out.
• Also had to almost completely rethink and retool the main stages of production, which were not designed for the use of composite materials.

Other Features

The latest software (FiberSim) has been introduced into the production process, which allows to achieve the highest degree of automation. In addition, now the keel of the aircraft, the design of which is described in the article, can be made using technologies where there are practically no drawings. The production of this part with this approach is as followsway:

• Designing or choosing a finished model. Today, the keel is (mostly) designed in a fully automatic mode, without the participation of "human" developers.
• Cutting used materials, also carried out in automatic mode.
• In the automatic mode, the raw materials used to create the keel and its structural parts are laid out.
• Laying 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:

• Continuously building prototypes that are tested under the toughest conditions.
• Non-destructive testing technologies are being developed that allow continuous monitoring of the state of the keel on an aircraft.

Advanced methods for creating the tail unit of the MS-21 aircraft

In the not so distant past, the aviation industry was literally stunned by the announcement of domestic developers that they are developing a completely new aircraft, the MS-21. Its unusualness is that for almost the last three decades this is the first domestic car for flights within the country. During its manufacture, many of the latest technologies were tested, which largely affected the innovative features of the keel and the entire tail assembly.

Developing and producing the caisson of the keel of the MS-21 aircraft, domestic specialists were able to achieve the following:

• Full automation of cutting of all parts and raw materials used in production. Due to this, it was possible to achieve at least 50% reduction in the total cost of the entire tail unit and especially the keel.
• ProDirector software is used in the production of the tail unit, which allows you to achieve perfect precision in the processing of parts. This makes it possible to create not only strong, but also extremely light keels.
• Also, the keel of a modern aircraft is created using double curvature techniques. Thanks to them, it is possible to achieve multidirectional thickness in those areas where additional structural reinforcement is needed (under the keel of the aircraft).
• Even large parts of the keel today can be "fried" in special autoclaves. The result is extremely strong and rigid components that can withstand loads of any degree.
• The control of the geometry of parts is also controlled by complex computerized systems.

Other Features

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

The main achievement is the development of a reliable and simple technology for the production of keel box parts measuring 7.6 x 2.5 m. At present, they have already begun to be delivered to the Irkutsk Aviation Plant. They are made from modern composite materials, and the features of this process have already attracted the interest of leading foreign manufacturers of aviation equipment.

Modern Issues

Why did we spend so much time discussing modern ways of designing and building a keel? The fact is that since the 60s of the last century it has become completely clear that a further increase in the speed performance of aircraft is possible only if their strength is increased and completely new types of polymeric materials are introduced into production. The problem with aircraft of the latest generations is that their design (and the keel in particular) is highly susceptible to "fatigue". Because of this, by about the 70s of the last century, numerous methods for monitoring the condition of the wing and tail were developed.

Production requirements are also high. Each batch of parts is subjected to the most severe overloads on vibration 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 plane's keel is and what it is for!