In this article we will look at the basic principles of landing on large jet aircraft as they apply to our environment. Although the Tu-154 was chosen as the basis for consideration, it should be taken into account that other types of aircraft generally use similar piloting principles. The information was taken based on real equipment, and we will tempt fate for now in MSFS98-2002, Microsoft has such a computer simulator, you may have even heard...
Aircraft landing configuration
Aircraft configuration- a combination of provisions for the mechanization of the wing, landing gear, parts and assemblies of the aircraft, which determine its aerodynamic qualities.
On a transport aircraft, even before entering the glide path, the wing mechanization and landing gear must be extended and the stabilizer must be repositioned. In addition, by decision of the aircraft commander, the crew can turn on the autopilot and/or autothrottle for an automatic approach.
Wing mechanization
Wing mechanization- a set of devices on the wing designed to regulate its load-bearing capacity and improve stability and controllability characteristics. The wing mechanization includes flaps, slats, flaps (interceptors), active boundary layer control systems (for example, its blowing off with air taken from the engines), etc.
Flaps
In general, flaps and slats are designed to increase the load-bearing capacity of the wing during takeoff and landing conditions.
Aerodynamically, this is expressed as follows:
- flaps increase the wing area, which leads to an increase in lift.
- flaps increase the curvature of the wing profile, which leads to a more intense downward deflection of the air flow, which also increases lift.
- flaps increase the aerodynamic drag of the aircraft, and therefore cause a decrease in speed.
Increasing the wing's lift allows the speed to be reduced to a lower limit. For example, if with a mass of 80 tons stall speed Tu-154B without flaps is 270 km/h, then after the flaps are extended completely (by 48 degrees) it decreases to 210 km/h. If you reduce the speed below this limit, the aircraft will reach dangerous angles of attack, causing stall shaking (buffeting)(especially with the flaps retracted) and, in the end, it will happen spinning.
A wing equipped with flaps and slats that form profiled slots in it is called slotted. Flaps can also consist of several panels and have slots. For example, on the Tu-154M they use double-slit, and on the Tu-154B three-slit flaps (pictured Tu-154B-2). On a slotted wing, air from the area of high pressure under the wing flows at high speed through the slots onto the upper surface of the wing, which leads to a decrease in pressure on the upper surface. With a smaller pressure difference, the flow around the wing is smoother and the tendency to form a stall is reduced.
Angle of Attack (AoA)
Basic concept of aerodynamics. The angle of attack of the wing profile is the angle at which the profile is blown by the incoming air flow. In a normal situation, UA should not exceed 12-15 degrees, otherwise flow breakdown, i.e. the formation of turbulent “burrs” behind the wing, as in a fast stream, if you place your palm not along, but across the flow of water. A stall results in loss of lift on the wing and stalling airplane.
On "small" aircraft (including the Yak-40, Tu-134), releasing the flaps usually leads to "swelling"- the plane slightly increases its vertical speed and lifts its nose. On "large" planes there are systems for improving stability and controllability, which automatically counter the emerging moment by lowering the nose. Such a system is available on the Tu-154, so the “swelling” is small (in addition, there the moment of flap release is combined with the moment of repositioning the stabilizer, which creates the opposite moment). On the Tu-134, the pilot has to dampen the increase in lift by manually deflecting the control column away from himself. In any case, to reduce “swelling”, it is customary to release the flaps in two or three steps - usually first by 20-25, then by 30-45 degrees.
Slats
Except for the flaps, almost everything transport aircraft also have slats, which are installed in the front part of the wing, and automatically deflect downward simultaneously with the flaps (the pilot hardly thinks about them). In principle, they perform the same function as flaps. The difference is as follows:
- At high angles of attack, the downward slats cling like a hook to the incoming air flow, deflecting it down along the profile. As a result, the slats reduce the angle of attack of the rest of the wing and delay the stall moment at higher angles of attack.
- Slats are usually smaller in size, which means less drag.
In general, the extension of both flaps and slats comes down to an increase in the curvature of the wing profile, which allows the incoming air flow to be more deflected downwards, and therefore increases the lift force.
As far as is known so far, the slats are not highlighted separately in the air file.
To understand why such complex mechanization is used on airplanes, watch the birds land. You can often notice how pigeons and similar crows land with their wings fluffed out, tucking their tail and stabilizer under themselves, trying to get a wing profile of great curvature and create a good air cushion. This is the release of flaps and slats.
Mechanization of a B-747 on landing
Interceptors (spoilers)
Interceptors, they are spoilers are deflectable brake flaps on the upper surface of the wing, which increase aerodynamic drag and reduce lift (unlike flaps and slats). Therefore, interceptors (especially on “silts”) are also called lift dampers.
Interceptors are a very broad concept, into which there are many different types of dampers, and different types they may have different names and be located in different places.
As an example, consider the wing of a Tu-154 aircraft, which uses three types of spoilers:
1) external aileron spoilers (spoilers, roll spoilers)
Aileron spoilers are an addition to ailerons. They deviate asymmetrically. For example, on the Tu-154, when the left aileron is deflected upward by an angle of up to 20 degrees, the left aileron-interceptor automatically deflects upward by an angle of up to 45 degrees. As a result, the lift on the left wing decreases and the plane rolls to the left. The same for the right half-wing.
Why can't we just use ailerons?
The fact is that in order to create a roll moment on a large aircraft, a large area of deflected ailerons is needed. But because jets fly at speeds close to the speed of sound, they need to have a thin wing profile that doesn't create too much drag. The use of large ailerons would lead to its twisting and all sorts of bad phenomena such as aileron reverse (this, for example, can happen on the Tu-134). Therefore, we need a way to distribute the load on the wing more evenly. For this purpose, aileron interceptors are used - flaps installed on the upper surface, which, when deflected upward, reduce the lift force on a given half-wing and “sink” it down. The rotation speed along the roll increases significantly.
The pilot does not think about the aileron interceptors; from his point of view, everything happens automatically.
In principle, aileron interceptors are provided in the air file.
2) middle spoilers (spoilers, speed brakes)
Medium spoilers are what are usually understood as simply “interceptors” or “spoilers” - i.e. "air brakes". The symmetrical activation of spoilers on both halves of the wing leads to a sharp decrease in lift and braking of the aircraft. After the “air brakes” are released, the aircraft will balance at a higher angle of attack, begin to slow down due to increased drag, and descend smoothly.
On the Tu-154, the middle spoilers are deflected at an arbitrary angle of up to 45 degrees using a lever on the middle pilot console. This is about the question of where the stop valve is on the plane.
On the Tu-154, the outer and middle spoilers are structurally different elements, but on other aircraft the “air brakes” can be structurally combined with aileron spoilers. For example, on the IL-76, spoilers usually operate in aileron mode (with a deflection of up to 20 degrees), and, if necessary, in braking mode (with a deflection of up to 40 degrees).
There is no need to deploy the middle spoilers during landing. In fact, releasing spoilers after releasing the landing gear is usually prohibited. In a normal situation, spoilers are released for a faster descent from flight level with a vertical speed of up to 15 m/s and after the aircraft has landed. In addition, they can be used during aborted takeoff and emergency descent.
It happens that “virtual pilots” forget to turn off the throttle when approaching the landing, and keep the mode almost on takeoff, trying to fit into the landing pattern with a very high speed, causing angry screams from the dispatcher in the style of “Maximum speed below ten thousand feet is 200 knots!” In such cases, you can briefly release the middle interceptors, but in reality, this is unlikely to lead to anything good. It is better to use this crude method of reducing speed in advance - only when descending, and it is not always necessary to extend the spoilers to the full angle.
3) internal spoilers (ground spoilers)
Also "brake flaps"
Located on the upper surface in the inner (root) part of the wing between the fuselage and landing gear nacelles. The Tu-154 automatically deviates to an angle of 50 degrees after landing when the main landing gear struts are compressed, the speed is more than 100 km/h and the throttle is in the “idle” or “reverse” position. At the same time, the middle interceptors also deflect.
Internal spoilers are designed to dampen lift after landing or during an aborted takeoff. Like other types of spoilers, they do not so much dampen the speed as they dampen the lifting force of the wing, which leads to an increase in the load on the wheels and improved traction of the wheels with the surface. Thanks to this, after releasing the internal spoilers, you can proceed to braking using the wheels.
On the Tu-134, brake flaps are the only type of spoilers.
In the simulator, internal interceptors are either absent or recreated rather conditionally.
Pitch trim
Large aircraft have a number of pitch control features that cannot be ignored. Trimming, centering, balancing, stabilizer repositioning, steering column consumption. Let's look at these questions in more detail.
Pitch
Pitch- the angular movement of the aircraft relative to the transverse axis of inertia, or, more simply, “bully”. Sailors call this bullshit "trim". Pitch opposed bank And yaw, which respectively characterize the position of the aircraft during its rotation around the longitudinal and vertical axis. Accordingly, pitch, roll and yaw angles are distinguished (sometimes called Euler angles). The term "yaw" can be replaced with the word "course", for example they say "in the course channel".
I hope there is no need to explain the difference between the pitch angle and the angle of attack... When the plane falls completely flat, like an iron, its angle of attack will be 90 degrees, and the pitch angle will be close to zero. On the contrary, when a fighter is climbing, in afterburner, at good speed, its pitch angle can be 20 degrees, but the angle of attack, say, is only 5 degrees.
Trimming
To ensure normal piloting, the force on the control wheel must be noticeable, otherwise any random deviation could send the plane into some kind of bad tailspin. As a matter of fact, this is why on heavy aircraft that are not designed to perform sharp maneuvers, yokes are usually used rather than sticks - they are not so easy to accidentally roll over. (The exception is Airbus, which prefers joysticks.)
It is clear that with heavy control, the pilot’s biceps will gradually develop quite decent ones, moreover, if the aircraft unbalanced in effort it is difficult to pilot because any weakening of the force will push steering column (SHK) not where it should be. Therefore, so that during the flight, pilots can sometimes slap flight attendant Katya on the ass, trimmers are installed on airplanes.
Trimmer is a device that in one way or another fixes the steering wheel (control stick) in a given position so that the papelats can descend, gain altitude and fly in horizontal flight, etc. without applying any force to the steering column.
As a result of trimming, the point to which the steering wheel (handle) is pulled will not coincide with the neutral position for a given steering wheel. How further from the trim position, the big effort has to be made to hold the steering wheel (handle) in a given position.
Most often, by trimmer they mean a trimmer in the pitch channel - i.e. Elevator trimmer (ER). However, on large aircraft, just in case, trim tabs are installed in all three channels - there they usually perform an auxiliary role. For example, in the roll channel, trimming can be used when the aircraft is longitudinally unbalanced due to asymmetrical fuel production from the wing tanks, i.e. when one wing pulls the other. In the heading channel - in case of engine failure, so that the plane does not yaw to the side when one engine is not working. Etc.
Trimming can be technically implemented in the following ways:
1) using a separate aerodynamic trimmer, as on the Tu-134 - i.e. a small “knob” on the elevator, which holds the main rudder in a given position using aerodynamic compensation, i.e. using the force of the oncoming flow. On the Tu-134, such a trimmer is used to control trimmer wheel, on which the cable going to the RV is wound.
2) by using MET (trimming effect mechanism), as on the Tu-154 - i.e. simply by adjusting the tension in the spring system (it would be more correct to say spring loaders), which purely mechanically holds the steering column in a given position. When the MET rod moves back and forth, the loaders are either loosened or tightened. To control the MET, small push switches are used on the steering wheel handles, when turned on, the MET rod, and behind it the steering column, slowly move to a given position. There are no aerodynamic trim tabs like on the Tu-134 or on the Tu-154.
3) using adjustable stabilizer, as on most Western types (see below)
In the simulator it is difficult to recreate a real elevator trimmer; for this you will have to use a fancy joystick with a trimming effect, because what is called a trimmer in MSFS, in fact, should not be perceived as such - it would be more correct to cover the joystick with plasticine or chewing gum or simply put mouse on the table (in FS98) - here you have a trimmer. I must say that management is generally sore spot all simulators. Even if you buy the most sophisticated steering wheel and pedal system, it will still most likely be far from the real thing. An imitation is just that, an imitation, because to get an absolutely exact copy of a real plane you need to spend the same amount of effort and process the same amount of information as to build a real plane...
Centering (CG)
Center of Gravity (CG) position- the position of the center of gravity, measured as a percentage of the length of the so-called mean aerodynamic chord (MAC)- i.e. chords of a conventional rectangular wing, equivalent to a given wing, and having the same area as it.
Chord is a straight segment connecting the leading and trailing edges of the wing profile.
center of gravity position 25% MAR
The length of the average aerodynamic chord is found by integrating over the lengths of the chords along all half-wing profiles. Roughly speaking, the MAR characterizes the most common, most probable wing profile. those. it is assumed that the entire wing with all its diversity of profiles can be replaced by one single averaged profile with one single averaged chord - MAR.
To find the position of the MAR, knowing its length, you need to intersect the MAR with the contour of the real wing and see where the beginning of the resulting segment is located. This point (0% MAR) will serve as a reference point for determining alignment.
Of course, a transport aircraft cannot have a constant alignment. It will change from departure to departure due to cargo movements, changes in the number of passengers, and also during the flight as fuel is used up. For each aircraft, an acceptable range of alignments is determined, which ensures its good stability and controllability. Usually distinguish front(for Tu-154B - 21-28%), average(28-35%) and rear(35-50%) alignment - for other types the numbers will be slightly different.
The alignment of an empty aircraft is very different from the alignment of a fueled aircraft with all cargo and passengers, and to calculate it before departure, a special centering chart.
An empty Tu-154B has an alignment of about 49-50% of the MAC, despite the fact that at 52.5% it already tips over onto its tail (the engines on the tail are pulled). Therefore, in some cases it is necessary to install a safety rod under the rear fuselage.
Balancing in flight
An airplane with a swept wing wing lift center located at a point of approximately 50-60% of the MAR, i.e. behind the center of gravity, which in flight is usually located in the region of 20-30% of the MAR.
As a result, in horizontal flight a lift lever who wants to tip the plane over on its nose, i.e. in a normal situation the aircraft is under the influence diving moment.
To avoid all this, you will have to counter the resulting diving moment throughout the flight. balancing deviation РВ, i.e. The elevator deflection will not be zero even in level flight.
Basically, in order to keep the plane from “pecking” you will need to create pitching moment, i.e. The RV will need to deflect upward.
To trim - from fr. cabrer, "to rear."
Always up? No, not always.
As the speed increases, velocity head will increase, which means the total lift force on the wing, stabilizer and elevator will increase proportionally
F under = F under1 – F under2 – F under3
But the gravity will remain the same, which means the plane will go into climb. To rebalance the papelats in horizontal flight, you will have to lower the elevator lower (move the steering wheel away from you), i.e. reduce the term F sub3. Then the nose will drop, and the plane will again balance in level flight, but at a lower angle of attack.
Thus, for each speed we will have our own balancing deviation of the RT - we will get quite a whole balancing curve(dependence of the deviation of the aircraft on the flight speed). At high speeds, you will have to push the steering column away from you (RV down) to keep the Samik from pitching up; at low speeds you will have to take the steering column toward you (RV up) to keep the Samik from diving. The helm and elevator will be in a neutral position only at one specific indicated speed (about 490 km/h for the Tu-154B).
Stabilizer (Horizontal Stabilizer)
In addition, as can be seen from the diagram above, the aircraft can be balanced not only by the elevator, but also by an adjustable stabilizer (component Fpod2). Such a stabilizer can be completely installed at a new angle using a special mechanism. The efficiency of such a transfer will be approximately 3 times higher - i.e. 3 degrees of deflection of the radio will correspond to 1 degree of deflection of the stabilizer, because its area of the horizontal stabilizer at the “carcass” is approximately 3 times larger than the area of the RV.
What is the advantage of using an adjustable stabilizer? First of all, in this case Elevator consumption is reduced. The fact is that sometimes, due to too forward alignment, in order to keep the plane at a certain angle of attack, you have to use the entire stroke of the control column - the pilot chose control completely over himself, and the plane can no longer be lured upward by any carrot. This can especially occur on landings with extremely forward centering, when when attempting a go-around, the elevator may not be sufficient. As a matter of fact, the value of the maximum forward alignment is set on the basis that the available deflection of the elevator is sufficient in all flight modes.
Since the RV deviates relative to the stabilizer, it is easy to see that the use of an adjustable stabilizer will reduce steering wheel consumption and increase the available range of alignments and available speeds. This means it will be possible to take more cargo and arrange it in a more convenient way.
In horizontal flight at flight level, the Tu-154 stabilizer is at a pitch-up angle of -1.5 degrees relative to the fuselage, i.e. almost horizontal. On takeoff and landing, it is further shifted to pitch up at an angle of up to -7 degrees relative to the fuselage in order to create a sufficient angle of attack to maintain the aircraft in level flight at low speed.
A special feature of the Tu-154 is that the stabilizer is rearranged only on takeoff and landing, and in flight it is retracted to position -1.5 (which is considered zero), and the plane is then balanced with one elevator.
At the same time, for the convenience of the crew and for a number of other reasons, relocation combined with the release of flaps and slats, i.e. when moving the flap handle from position 0 to the release position, automatically The slats are extended and the stabilizer is moved to the agreed position. When retracting the flaps after takeoff, do the same in reverse order.
Let's give a table that hangs in the cockpit to constantly remind him that they don't produce a damn thing...
Thus, everything happens by itself. On the circle before landing at a speed of 400 km/h, the crew only needs to check whether the balancing deviation of the aircraft corresponds to the position of the stabilizer adjuster and, if not, then set the adjuster to the desired position. Let's say the arrow of the position indicator of the PV is in the green sector, which means we set the set pointer to the green “P” - everything is quite simple and does not require significant mental effort...
In case of automation failures, all releases and relocations of mechanization can be done manually. For example, if we are talking about a stabilizer, you need to fold back the cap on the left in the photo and move the stabilizer to the agreed position.
On other types of aircraft, this system works differently. For example, on the Yak-42, MD-83, B-747 (I find it difficult to say for the whole of Odessa, but this should be the case on most Western aircraft) the stabilizer deflects throughout the flight and completely replaces the trimmer. This system is more advanced because it allows you to reduce drag in flight, since the stabilizer, due to its large area, deflects at smaller angles than the flywheel.
On the Yak-40, Tu-134, the stabilizer is also usually adjusted independently of the wing mechanization.
Now about MSFS. In the simulator we have the situation of a “trimming stabilizer”, as on Western types. There is no separate virtual trimmer in MSFS. That rectangular thing (like on a Cessna), which Microsoft calls a “trimmer,” is actually a stabilizer, which is noticeable by its independence of operation from the radio.
Why is this so? Probably the whole point is that initially (in the late 80s) FS was used as a software base for full-featured simulators on which there were real steering columns and real METs. When MS bought (stole?) FS, it did not delve deeply into the features of its operation (and perhaps did not even have a complete description for it), so the stabilizer began to be called a trimmer. At least, this is the assumption I would like to make when studying MS+FS, because the description for the air file has never been published, and judging by the quality of the default models and a number of other signs, we can conclude that Microsoft itself is not particularly versed in it.
In the case of the Tu-154, you should probably set the microsoft trim once before landing in level flight, so that the elevator indicator is approximately in the neutral position, and not return to it again, but work only with the joystick trim, which no one has.. Or work with the “rectangular thing”, close your eyes and repeat to yourself: “This is not a stabilizer, this is not a stabilizer...”
Auto Throttle
In helm mode, KVS or 2P controls the engines using Thrusters (motor control levers) on the middle console or by giving commands to the flight engineer: “Mode such and such”
Sometimes it is convenient to control engines not manually, but using automatic traction (auto throttle, AT), which tries to keep the speed within acceptable limits by automatically adjusting the engine mode.
Turn on AT (Shift R key), set desired speed on US-I(speed indicator), and the automation will try to maintain it without pilot intervention. On the Tu-154 speed when turned on AT-6-2 can be adjusted in two ways: 1) by rotating the ratchet on the left or on the right US-I 2) by rotating the regulator on PN-6 (= remote control for STU and autothrottle).
Types of landing systems
Distinguish visual approach And instrument approach.
Purely visual approaches are rarely used on large aircraft and can cause difficulties even for an experienced crew. Therefore, entry is usually carried out by instruments, i.e. using radio systems under the direction and control of an air traffic controller.
Air Traffic Control (ATC)- control of aircraft movement in flight and on the airfield maneuvering area.
Radio-technical landing systems
Let's consider approaches using radio-technical landing systems. They can be divided into the following types:
“according to OSB”, i.e. using DPRM and BPRM
“according to RMS”, i.e. using ILS
“according to RSP”, i.e. by locator.
Entry using OSB
Also known as "approach by drives".
OSB (landing system equipment)- a complex of ground-based equipment, including two drive radio stations with marker radio beacons, as well as lighting equipment (STO), installed at the airfield according to the approved standard layout.
Specifically, NSP includes
"distant" (locator beacon) (DPRM, Outer Marker, OM)- a long-range radio station with its own marker, which is located 4000 (+/- 200) m from the runway end. When a marker passes, a light and sound alarm is triggered in the cockpit. The Morse code of the signal in the ILS system looks like “dash-dash-dash...”.
"near" (locator beacon) (BPRM, Middle Marker, MM)- a near-range radio station, also with its own marker, which is located 1050 (+/- 150) m from the runway end. Morse code in the ILS system looks like “dash-dot-...“
Drive radios operate in the range of 150-1300 kHz.
When flying in a circle, the first and second sets automatic radio compass (ARK, Automatic Direction Finder, ADF) are tuned to the frequencies of DPRM and BPRM - in this case, one arrow on the ARC indicator will point to DPRM, the second to BPRM.
Let us recall that the arrow of the ARC indicator always points to the radio station, just as the arrow of a magnetic compass always points to the north. Therefore, when flying according to the pattern, the moment of the beginning of the fourth turn can be determined according to the heading angle of the radio station (KUR). Let's say, if the DPRM radio station is exactly on the left, then CUR = 270 degrees. If we want to turn towards it, then the turn needs to start 10-15 degrees earlier (i.e. at CUR = 280...285 degrees). Flying over the radio station will be accompanied by a 180 degree turn of the needle.
Thus, when flying in a circle, the heading angle of the DPRM helps to determine the moments when turning turns on the circle begin. In this regard, the DPRM represents something like a reference point, relative to which many actions during the landing are calculated.
Also attached to the radio station marker, or marker beacon- a transmitter that sends upward a narrowly directed signal, which, when flying over it, is perceived by aircraft receivers and causes the indicator light and electric bell to go off. Thanks to this, knowing at what height the DPRM and BPRM should be passed (usually this is 200 And 60 m respectively) you can get two points from which you can build a pre-landing straight line.
In the west, at airfields of categories II and III with difficult terrain, at a distance of 75..100 m from the end of the runway, they also install internal radio marker (Inner Marker, IM)(with Morse code “dot-dot-dot...”), which is used as an additional reminder to the crew that they are approaching the point at which visual guidance begins and the need to make a landing decision.
The OSP complex is a simplified landing system; it must provide the aircraft crew with a drive to the airfield area and a descent maneuver to the visual detection altitude of the runway. In practice, it plays an auxiliary role and usually does not replace the need to use an ILS system or landing radar. They enter purely using OSB only in the absence of more advanced landing systems.
When approaching only using the OSP, horizontal visibility must be at least 1800 m, vertical visibility at least 120 m. If this meteorological minimum is not observed, it is necessary to go to alternate airfield.
Please note that the DPRM and BPRM at different ends of the band have the same frequency. In a normal situation, the radio stations at the other end should be turned off, but in the sim this is not the case, so when flying in a circle, the ARC often starts to glitch, picking up one radio station, then another.
Call by RMS
They also say "login". In general, this is the same as an ILS approach. (see also Dmitry Prosko’s article on this site)
In Russian terminology radio beacon landing system (RMS) is used as an umbrella term that includes various types of planting systems - in particular, ILS (Instrument Landing System)(as Western standard) and SP-70, SP-75, SP-80 (as domestic standards).
The principles of approaching the RMS are quite simple.
The ground part of the RMS consists of two radio beacons - localizer (LOB) And glide slope radio beacon (GRM), which emit two oblique beams (equal-signal zones) in the vertical and horizontal plane. The intersection of these zones forms the approach path. Aircraft receiving devices determine the position of the aircraft relative to this trajectory and issue control signals to PKP-1 flight control device(in other words, on the artificial horizon) and planning and navigation device PNP-1(in other words, to the course indicator).
If the frequency is set correctly, then when approaching the runway the pilot will see two moving lines on the large attitude indicator - a vertical course command arrow And horizontal glide slope command arrow, as well as two triangular indices indicating the position of the aircraft relative to the calculated trajectory.
Angle of attack
Angle of attack(the generally accepted designation is the letter of the Greek alphabet alpha) - the angle between the direction of the speed of the flow (liquid or gas) incident on the body and the characteristic longitudinal direction chosen on the body, for example, for an airplane wing this will be the chord of the wing, for an airplane - the longitudinal construction axis, for a projectile or rockets - their axis of symmetry. When considering a wing or an airplane, the angle of attack is in the normal plane, as opposed to the angle of glide.
Angle of attack aircraft - the angle between the chord of the wing and the projection of its speed V onto the OXY plane of the associated coordinate system; is considered positive if the projection of V onto the normal axis OY is negative. In flight dynamics problems, spatial control is used: (α)n is the angle between the OX axis and the direction of the aircraft speed.
Angle of attack sensors for an air-to-air missile.
Links
- Aviation: Encyclopedia. - M.: Bolshaya Russian Encyclopedia. Editor-in-Chief G.P. Svishchev. 1994.
- GOST 20058-80 "Dynamics aircraft in the atmosphere. Terms, definitions and designations."
See also
Wikimedia Foundation. 2010.
- Yo (disambiguation)
- Soyuz-29
See what “Angle of Attack” is in other dictionaries:
angle of attack Encyclopedia "Aviation"
angle of attack- Rice. 1. Angle of attack of the profile. angle of attack 1) U. a. profile angle α between the direction of the oncoming flow velocity vector and the direction of the profile chord (Fig. 1, see also Wing profile); geometric characteristic defining the mode... ... Encyclopedia "Aviation"
ANGLE OF ATTACK- (Angle of attack) the angle of inclination of the aircraft wing to the direction of air flow. On average it ranges from 1° to 14°. Samoilov K.I. Marine dictionary. M.L.: State Naval Publishing House NKVMF USSR, 1941 Angle of attack angle between cacos ... Marine Dictionary
Angle of attack- 1) U. a. profile angle (α) between the direction of the free-stream velocity vector and the direction of the profile chord (see also Wing profile); a geometric characteristic that determines the flow regime around the profile. Change in U. a. leads to change... Encyclopedia of technology
ANGLE OF ATTACK- the angle between the direction of the speed of movement of the body and the direction chosen on the body, e.g. at the wing by the chord of the wing, at the projectile, rocket, etc., by the axis of symmetry ... Big Encyclopedic Dictionary
ANGLE OF ATTACK- the angle between the direction of speed of a forward moving body and the k.n. characteristic direction associated with the body, e.g. at the aircraft wing with the wing chord (see figure in the article (see CENTER OF PRESSURE)), at the projectile, rocket with their axis of symmetry. Physical... ... Physical encyclopedia
angle of attack- - [A.S. Goldberg. English-Russian energy dictionary. 2006] Topics of energy in general EN angle of attackincidence angleincidence ... Technical Translator's Guide
angle of attack- the angle between the direction of the speed of translational motion of the body and any characteristic direction chosen on the body, for example, at the wing with the chord of the wing, at the projectile, rocket, etc., the axis of symmetry. * * * ANGLE OF ATTACK ANGLE OF ATTACK, angle between... ... Encyclopedic Dictionary
angle of attack- atakos kampas statusas T sritis fizika atitikmenys: engl. angle of attack vok. Angriffswinkel, m; Anstellwinkel, m rus. angle of attack, m pranc. angle d’attaque, m … Fizikos terminų žodynas
Angle of attack- the angle between the direction of speed of a translationally moving body and some characteristic direction chosen on the body, for example, at an airplane wing by the chord of the wing, on a projectile or rocket by their axis of symmetry... Great Soviet Encyclopedia
Books
- Crew. Limit angle of attack, Andrey Yurievich Orlov. In August 1995, a Russian Il-76 aircraft carrying a cargo of ammunition made a commercial flight from Tirana to Bagram. There were seven crew members on board, all Russian citizens. Cargo…
Rod Machado
First a little theory
In a low-speed flight training class, I showed how by reducing airspeed and increasing the angle of attack of the wing, you can maintain the lift necessary for flight. You're probably wondering if there's a limit to increasing the angle of attack. After all, common sense dictates that there is a limit to everything. The ancient Egyptians always used common sense, especially when deciding what size to build pyramids (and they turned out really healthy pyramids). Wings also have limits.
The pilot's job is to utilize the four primary forces, maintain lift, and avoid stall conditions that lead to a stall. As mentioned in the previous lesson, this type of stall is not related to stopping the engine.
At a high angle of attack of the wing (about 18 degrees for most aircraft), aerodynamic vortices are formed over its upper part. These vortices disrupt the airflow from the wing, preventing lift from occurring and causing a stall. The angle at which stall occurs followed by stalling is called the critical angle of attack.
Attention! I give valuable advice. Remember this for the rest of your life. Since exceeding the critical angle of attack always leads to a stall, in order to recover from the stall, you need to reduce the angle of attack to a value that will be less than the critical one. Is everything clear? Repeat to yourself 10 times, quickly.
Stall, angle of attack and how the nose knows
To understand how a stall occurs, think of the air molecules as little race cars moving along a wing (see Figure 1-1).
Each car (and air molecule) has a goal: to overcome the curve that runs through the upper curved surface of the wing. If the wing has a small angle of attack, the curve is not very sharp and travel is not difficult (Figure 1-1).
However, look at the curve that cars and air molecules have to overcome as the angle of attack increases. When the angle of attack exceeds 18 degrees (this is called the critical angle of attack, you will soon find out why), the air molecules involved in the race are unable to overcome this turn (Figure 1-1).
The molecules form vortices, break off into the surrounding air and cease to provide a constant, high-speed, laminar air flow on the surface of the wing (Fig. 1-2). The flow stalls on the wing.
Remember, according to Jacob Bernoulli, the lower the air speed on a wing, the less lift it provides. There are still air molecules hitting the wing from below, but we already know that this lifting force is not enough to support the plane. When lift is less than gravity, bad things happen to good airplanes. The wing goes on strike and the stall begins. Left without Bernoulli, the force of gravity pulls the plane towards the ground according to its own laws.
For any wing there is a critical angle of attack (it varies slightly for different aircraft). Once this angle is reached, cooperation between the wing and the wind stops. And no theories will help overcome the laws of physics and aerodynamics. The wing police are always on guard. Once the critical angle of attack is exceeded, the air molecules will no longer provide lift. It sounds serious, and it really is. Fortunately, there is ready-made solution. No, no, no need to shout to the instructor: “Take control!” Now I will ask you to plug one ear with your finger. For what? Because I’m going to say one very important thing and I don’t want it to go in one ear and out the other. So, get ready. To avoid stalling, the angle of attack should be reduced. To do this, smoothly lower the nose of the aircraft using the elevator rod (Figures 1-3A and 1-3B).
And now calm, only calm. As soon as the angle of attack becomes less than critical, air molecules will calmly flow through the top of the wing and lift will appear. It's very simple. The airplane can now continue to fly and do what airplanes normally do (Figures 1-3C and 1-3D). Please never forget this. Great, you can take your finger out of your ear.
Why do I attach such importance to this? Because in a stressful situation (and lack of lift causes stress for many pilots) you will want to do something that shouldn't be done. Pilots have a natural tendency to move the elevator rod either toward or away from them when they need to change the aircraft's pitch angle. During a stall, when the plane is falling down, you instinctively want to reject the elevator thrust towards you. You can pull this thing even up to your knees, but it won’t lead to anything good. The plane will not recover from the stall, and you, my friend, will look like a newly castrated bull.
If there is a stall on the wing, one very important thing should be done: reduce the angle of attack to a value not exceeding the critical one. Only after this will the stalling stop. Engaging full throttle also aids the recovery process as the aircraft begins to gain speed. Increasing horizontal speed helps reduce the angle of attack.
If a stall occurs on the wing, do not sit idly by. It’s not for nothing that you are called crew commander. Do something. But only something useful.
Stall at any attitude or airspeed
You should be aware that the aircraft can stall at any attitude and airspeed. Stick your finger back into your ear. The direction of the aircraft's nose (up or down) and airspeed (60 knots or 160) do not matter. An airplane can exceed its critical angle of attack at any attitude and airspeed. Figure 1-4A illustrates how this might happen.
Airplanes have inertia, which means that they tend to continue moving in the direction in which they were moving. Airplane A dives nose-down at 150 knots. (Don't try this at home!) The pilot pulled the steering wheel too vigorously, which resulted in the critical angle of attack being exceeded and stalling. Wow! Just imagine. In stall mode, the plane dives down at a speed of 150 knots! Figure 1-4B shows an airplane in level flight at 100 knots that stalled after the pilot applied too much elevator thrust.
What should you do to get out of a stall? First, you should reduce the angle of attack by moving the elevator link forward or stopping pulling the control lever towards you (do not forget that the deviation of the control link towards you may have caused a high angle of attack and subsequent stall). This will restore calm, high-speed airflow on the wing, and the aircraft will continue to fly.
Secondly (if required), you can use all available power to accelerate the aircraft and reduce the angle of attack.
When the stall stops, bring the aircraft to the required pitch angle, making sure that the flow does not stall again. A stall after recovering from a previous stall is called a secondary stall. There is nothing good about him, especially from the point of view of the instructor pilot sitting next to him. (You can understand that the instructor is dissatisfied by various witty remarks, for example: “Yes, just think! It was easier to give birth.”)
Intentionally stalling an airplane at a safe altitude can be fun, or at least educational. For most aircraft, stalling is considered a relatively calm maneuver. However, stalling a plane close to the ground is already serious, since rarely does anyone do it intentionally. During training, you will have ample time to become proficient in recovering the aircraft from a stall.
It's one thing to control an airplane in stall mode; it's another thing entirely to control your instincts. For example, a typical trap that you can (literally) fall into is associated with a high vertical rate of descent during landing. During the landing approach, the pilot may pull the rudder toward himself in an attempt to make the descent more gradual. If the critical angle of attack is exceeded, the flow will stall. And the view of the runway in the windshield will resemble the view of a supernova from low orbit.
If you follow untrained instincts and continue to pull the elevator, the stall will only get worse. Experienced pilots are more cautious. They are aware of the possibility of stalling and skillfully combine rearward elevator deflection with throttle settings during landing in order to change the aircraft's glide path without exceeding the critical angle of attack. (The instructor will demonstrate how to properly use the elevator and throttle settings during landing.) How do pilots determine the appropriate amount of elevator input? How do they determine that the plane will not go into stall?
If the airplane had an angle of attack indicator, stall recognition would not be a problem. You would just have to be careful not to exceed the critical angle of attack for a given wing. Small aircraft are rarely equipped with angle of attack indicators, despite their usefulness. In Flight Simulator, the primary means of signaling the start of a stall is an audible alarm that starts when the aircraft exceeds its stall speed by several knots. Plus, you'll enjoy the word "Stall" appearing on the screen. In a real plane, of course, this will not happen. However, there may be a red light signal, it is almost the same.
Now that you've learned the basics of stall aerodynamics, you can move on to learning more about stall recovery.
We finish the flight, we begin stalling
Deflection of the control lever towards itself leads to exceeding the critical angle of attack of the wings and stalling the flow. Turks are formed in the air flow, and it ceases to smoothly flow around the upper part of the wing. This reduces the lifting force and the plane begins to dive (if luggage, passengers and fuel were loaded in accordance with the rules). Automatic diving is a bit like applying the Heimlich method to yourself. The angle of attack is reduced to a value not exceeding the critical one, and the aircraft is able to continue flying.
If airplanes are designed in such a way that they can recover from a stall on their own, why bother learning all this? The problem is that very often pilots do things that prevent the plane from recovering from a stall. Therefore, you should know what exactly you should not do. In addition, to recover from an accidental stall close to the ground, you need to be able to quickly restore the aircraft's attitude with minimal loss of altitude. Let's go into stall mode again and see what happens if we stop the plane from diving on its own.
What not to do when stalling
What happens if you enter a stall and prevent the airplane from regaining its attitude?
The answer is that the airplane will remain in stall mode even with the control lever pushed all the way back. No matter how much you pull this lever towards you, the plane will not begin to gain altitude. Think carefully: the airplane may not recover from the stall all the way to the ground even though the control stick is pulled all the way back. Joy is not enough, right? If you keep the control lever tilted back, the angle of attack of the wing will remain close to critical. Unfortunately, this is what some pilots do when the plane goes into stall.
What to do when stalled
That's why we taught that you don't need to pull the control stick towards you, but rather move it forward until the angle of attack of the wing is less than a critical value. The pitch angle required to restore the aircraft's attitude in space depends on several factors, so during training the negative pitch angle will be between 5 and 10 degrees. You should not point the plane too steeply nose down, as this will result in unnecessary loss of altitude and increased airspeed.
How do you know that the angle of attack has been reduced to the required value? This is something to experience in simulator training: the stall warning signal will stop sounding, the word “Stall” will disappear from the screen, the aircraft will return to flight mode, airspeed will begin to increase, and the flight controls will respond more clearly to commands. If there is an instructor on board, his voice will become less high-pitched and the whales will no longer need to beach themselves.
With a few exceptions, this is how most pilots recognize and recover from a stall. After reducing the angle of attack, you will immediately want to go to full throttle. This helps speed up the process of restoring spatial position. Be careful not to tilt the nose of the plane up. This can again lead to an increase in the angle of attack and stalling. When the airplane recovers from the stall (the warning signal stops sounding), raise the nose to the climb position and set the climb airspeed.
Stall on departure
What happens if a stall occurs at full throttle? Let's imagine that the plane has just taken off and is climbing at full throttle (as you usually do in this plane). Suddenly you notice a large bumblebee in the cockpit. You get distracted, forget about controlling the plane and try to swat the poor thing with both hands. The plane goes into stall mode, and meanwhile you jump around the cabin like a hero from a kung fu movie. What to do?
Well, grasshopper, no kung fu techniques will help now if you don’t do one thing: reduce the angle of attack to a value not exceeding critical. Once the airplane has recovered from the stall, it can be returned to its climb position. Since the full throttle mode is already engaged, the engine control lever can be left alone.
So we had our first acquaintance with the aerial amusement park called “Stall World”. The only problem is that you didn't visit the Reality attraction. Here's what you missed.
It is easy to remember that the plane goes into stall mode if the critical angle of attack is exceeded. But remember that this can happen at any attitude, at any airspeed and at any engine power setting. It's time to confess something else.
In fact, if the airplane's nose is pointed straight down and the pilot vigorously pushes the stick away from him, the airplane will still not recover from the stall. Of course, no one would do this on a real plane (even if it's rented). Remember, this is a simulator. You can do things in it that you can’t do in a real plane. It's like traveling to a fictional country where we are not in danger. So take advantage new technology and experience what others only talk about.
It's time to learn how to get out of the stall mode. To start training, click the link Start training flight. Have a nice time!
As increases, the magnitude of the force R increases and it deflects more and more backward due to the increase in air resistance, but the angle of attack cannot constantly and with impunity increase, in the end the branch breaks off and flow stalls from the wing.
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When the flow stalls, the wing loses its load-bearing capacity and is not much different from a normal one. edged boards. In addition, the stall does not occur simultaneously on the entire wing and is accompanied by shaking with subsequent rotation of the aircraft.
Each wing has its own critical angle of attack , after which the flow stalls when exceeded. For thick profiles, kr is greater than for thin ones due to the smoother flow around the profile.
kr depends little on flight speed.
It should be understood and firmly remembered that a stall occurs due to excess of cr, the loss of speed is only a special case of achieving cr.
An aircraft can be brought to cr in a wide range of speeds, with intensive maneuvering.
After an aircraft stall, a reserve altitude is required to return to normal flight.
An aircraft stalling near the ground due to a lack of altitude leads to a ground collision.
Low-altitude stalls are the cause of 80% of all accidents among amateur pilots. There is a special device “Angle of Attack Indicator”, which is installed on all modern aircraft. It shows the current real angle of attack.
11. Total aerodynamic force r. Its components. Center of pressure.
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Rice. 12 |
Full aerodynamic force R is the resultant of all friction and pressure forces acting on a body in flight. The point of intersection of the force R with the chord is called the center of pressure (CP). The R force formula is the main aerodynamic formula of all times and peoples, however, not only the R force - but in general ALL aerodynamic forces acting on airplanes, diesel locomotives, falling bricks and cars. It is simple and ingenious and consists of three factors: 1) S - wing area 2)
3) coefficient (in our case C R - ce er) of the total aerodynamic force. |
- speed pressure
If the force R is expanded along the axes of the velocity coordinate system, we obtain 3 (three) of its components: X, Y and Z.
X - drag force;
Y - lift force.
Z - lateral force.
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Angle (beta) - sliding angle. This is the angle between the longitudinal plane of symmetry of the aircraft and the free-stream velocity vector.
The Z force occurs only when slip occurs. Without sliding, the force R is resolved only into Y and X.
12. Lift and drag.
Lifting force occurs due to flow around the wing and the formation of a pressure difference under the wing and above the wing.
Wing drag is the aerodynamic force that slows down the movement of the wing in the air and is directed in the direction opposite to the movement.
The formulas for these forces are the same, the only difference is in the coefficients.
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Y=Cy |
X=C x |
S
SThe values of these coefficients are obtained by blowing the wing in a wind tunnel.
The graph of the approximate dependence of C y on looks like:
As can be seen from the graph, Cy increases almost linearly with increasing , up to cr, that is, until the flow breaks off from the wing.
The C y value fluctuates on most aircraft from 0 to 2. Essentially, the C y coefficient characterizes the ability of the wing to convert velocity pressure into lift. There are aircraft equipped with powerful wing mechanization to reduce landing speed and reduce take-off distance; they have higher C y values. However, a person could not achieve more than C y = 6, while C y of a large eagle, when taking off with prey from the ground, reaches a value of 14.
The coefficient C x, as well as the force X, consists mainly of 3 components. The wave - 4th component appears at M numbers close to critical M, around M = 0.8.
C x tr (friction) - occurs due to friction of air against the aircraft.
C x pressure (or vortex) - occurs due to the difference in pressure in front of the wing and behind the wing.
C xi (inductive) - arises due to the so-called flow skew. When the oncoming flow meets the inclined, lower plane of the wing, it changes the direction of movement parallel to the plane, that is, it tilts down somewhat. The lifting force is deflected back along with the flow by the same angle, since it is a derivative of the flow that has changed direction. The emerging component of the lifting force on the X axis is the inductive component.
C xi also arises due to the flow of air through the ends of the wing and due to the pressure difference under the wing and above the wing.
C xi depends on the wing aspect ratio and the angle of attack .
The shorter and wider the wing, the more intense the flow and the greater the inductive drag.
The larger , the more intense the flow occurs and X i increases. That's why sports gliders have such narrow and long wings - to reduce induced drag.
C x friction and C x pressure within the operating limits practically do not change, and the coefficient C xi depending on changes according to a parabolic law.
The landing speed of the aircraft in accordance with the requirements of airworthiness standards in order to ensure high flight safety must be at least 1.3 stall speed (or the minimum speed) established for the landing configuration of the aircraft. At the same time, during the flight testing of the aircraft, it must be demonstrated that it is possible to safely perform a landing and go-around without exceeding the permissible angle of attack at a minimum demonstration approach speed V3. p.d. type, which is assigned from the following conditions:
u.< (Vз. п. 15 км/ч при VЗ. п. ^ 200 км/ч>
Z.P.DL11P I knot p S km/h at VZ. P. ^ 200 km/h>
The maximum landing speed of the aircraft must be at least Vr3.n. + 25 km/h regardless of the aircraft's flight weight.
Over the entire range of permitted approach speeds, the aircraft must land on its main landing gear without first touching the runway surface with the nose wheels or the rear fuselage (tail gear); there must also be no nose-down or “goat-up” of the aircraft.
These conditions determine the range of acceptable pitch angles of the aircraft at the moment of landing. The landing angle of attack is determined by the pitch and inclination angles of the aircraft's flight path at the moment of landing, depending on the landing method. The change in the angle of attack and the angle of inclination of the trajectory compared to their values in the area of the aircraft gliding along the landing glide path for various landing methods can be determined by calculation or from statistical materials, which makes it possible to relate the range of permissible pitch angles at the moment of landing with the range of permissible angles of attack when approaching landing, which ensures a safe landing.
This approach allows us to determine the range of permissible angles of attack when an aircraft is landing. The actual angle of attack at this stage is mainly determined by the aerodynamic layout of the aircraft's wing in the landing configuration. The main role here is played by the maximum load-bearing properties of the wing, i.e. the maximum value of the lift coefficient Sushakh and the corresponding angle of attack, as well as the lift coefficient at zero angle of attack.
For modern transport and passenger aircraft, three landing methods are used:
Landing with full leveling and maintenance, on
in which the angle of attack of the aircraft increases to the landing angle;
Planting with full leveling without holding area;
Landing with incomplete leveling (mainly during automatic landing).
At all air stages of the landing mode, the pitch angle of the aircraft v along the fuselage construction axis, the inclination angle of the flight path b and the angle of attack a are related by the relation:
b = b + a-<р кр, (6.32)
Where<р кр -угол заклинення крыла относительно строительной оси фюзеляжа.
In the leveling and holding sections, the aircraft's flight speed gradually decreases and the angle of attack increases. The relationship between the angles of attack at the moment of landing and the village. and on glide path planning a z. items are determined by dependence
Yapos - #z. p.+A #1 + L a2, (6.33)
where and A a2 is the increment in the angle of attack in the alignment and holding sections, respectively.
Taking (6.31) and (6.32) into account, we can write
VnOC = in POS #Z. P. A C?1 "b A CI2 F KR (6.34)
where t>noc and in pos are the pitch angle and inclination angle of the aircraft trajectory at the moment of landing (touch.)
The results of calculations and statistical processing of materials from flight tests and operation of passenger aircraft show that in the leveling section the angle of attack increases by 1.5 2°, and in the holding section the angle of attack should increase to
landing and village When landing an aircraft with incomplete alignment, the angle of attack should be close to the landing angle and, as a result, the angle of attack of the aircraft when gliding along the landing glide path should be 2^2.5° less than the landing angle. The wing wedge angle fcr for modern passenger aircraft is close to 3° .
Taking into account the accepted assumptions, the relationship between the pitch angle at the moment of landing and the angle of attack during landing can be determined by the formula (bchZZ):
£>pos - #zl.+ (0.54-4*) - with pa*um leveling and complete
keeping;
v pos - a z. p. - (1.0 - g 1.5°) - with full alignment without
holding area;
Vnoc=a p. -3° - with incomplete alignment.
On modern passenger and transport aircraft, in order to reduce the required landing strip, it is advisable to land without a holding area. Then the minimum permissible angle of attack during glide path planning during landing should be selected from the condition that the nose wheel of the landing gear does not touch the runway.
To determine quantitative requirements for the angle of attack during landing, it is necessary to establish acceptable values of the pitch angle at the moment of landing. Typically, passenger and transport aircraft are configured so that the moment the nose wheel touches the runway surface corresponds to the zero pitch angle vKac n. k-0.
The contact of the runway with the rear part of the fuselage (tail support) for different aircraft occurs at different values of the pitch angle depending on the contours of the rear part of the fuselage and the height of the main landing gear. Therefore, the calculations should take into account the pitch angle at which the rear part of the fuselage touches the runway. Average tangent pitch angle
THE RUNWAY WITH THE TAIL SUPPORT CAN BE TAKEN EQUAL: Slope xv = 11
To select the recommended range of values for the angle of attack of an aircraft during landing, in which there is no initial contact with the runway by the nose wheel or the rear part of the fuselage, we use the values of the maximum and minimum pitch angles allowed in operation:
Chpah^ ^kas xv”1 And Vmn ^ $ kaskrn. k. + 1°
(a pitch angle margin of ±1° is introduced to ensure the safety of the aircraft landing). Thus, to ensure the safety of the aircraft during landing, it is necessary that the pitch angle at the moment of landing be greater than 1° and less than 10°.
Calculations show that at the moment of landing, in order to ensure a pitch angle within the permissible range of fnoc-Г-г 10°, the values of the aircraft’s angle of attack while gliding along the landing glide path must be in the following range:
www. vokb-la. spb. ru — Airplane with your own hands?!
2.5°< а з. п.<9°-при посадке самолета без участка
aging;
4°<<2’з. п.<9°-при посадке самолета с неполным выравниванием.
It is also necessary to determine the permissible angles of attack when the aircraft is approaching to land, taking into account the spread of the approach speed from the recommended values (L Vi = 15 km/h and AV^
10 km/h). Then the range of the aircraft’s angle of attack during the landing approach should be as follows:
For those aircraft configurations with pitch angle values ^cas n. to I VKac hv. DIFFER FROM THE ACCEPTED ones (0° AND 11°, RESPECTIVELY), the range of required values of the aircraft angle of attack during the approach mode can be accepted:
a h. p. min =^Cas n. k+4° (limitation from touching the runway with the nose wheels when landing the aircraft with full alignment without a holding section);
a h. p. max=tw xv_3° (limitation from touching the runway with the rear part of the fuselage);
a h. n. min = v cas n. k.~5.5° (limitation from contact with the nose wheels when landing an aircraft with incomplete alignment).
Figure 6.41 shows the areas of recommended angles of attack for the O’Z approach. n. depending on the critical angles of attack a cr for long-haul aircraft in landing configuration. The value acr corresponds to the maximum value of the lift coefficient Sushakh* or stall Sus, and the angle of attack Yaz. p. corresponds to the value Su3.p = 0.59 SuC (Sutah) (this meets the requirement V"z.p. = 1.3 Vc).
In order to reduce the required length of the landing strip for passenger and transport aircraft, it is advisable to adopt a landing technique with incomplete alignment (the angle of inclination of the trajectory in< 0°). Оценочные расчеты показывают, что при таком методе
landing, the required runway length is reduced by 300-600 m. However, the partial-level landing method can be safely used only on aircraft in which the pitch angle at the moment of landing will be positive.
The values of vertical rates of descent at the moment of landing (touching the runway) when using the landing method with incomplete leveling must be acceptable in terms of the strength of the aircraft and ensuring the comfort of passengers and crew.
To apply the method of landing an aircraft with incomplete alignment, it is necessary that the angles of attack of the aircraft when gliding along the landing glide path should be quite large - at least 5.5° (it is taken into account here that the approach speed may be 15 km/h higher than the recommended one );
The aerodynamic layout of the wing of modern long-haul passenger aircraft must be made taking into account
the possibility of landing an aircraft with incomplete alignment, since these aircraft must use automatic landing, which is carried out with incomplete alignment 0<О.
In order for the aircraft's angles of attack during the landing approach to be within the recommended range, it is necessary to have a certain relationship between the Sushakh and SuO coefficients. The necessary relationship between these coefficients can be found from the following relationships:
SuZL.= 0.59 Sushakh
Suz. n.- CyO+ CyCt h. p.
0.59 Sushakh SuO
Suo - lift coefficient at 0;
Su is the derivative of the lift coefficient with respect to the angle of attack (usually for the aircraft under consideration it is close to 0.1/deg).
Suo = Suz. p. 0.1(5.5-i-8.0) =0.59Sushakh -(0.554-0.8)
These relationships can be used when developing the aerodynamic configuration of an aircraft in a landing configuration, and from them, in particular, it follows that from the operating conditions of the aircraft it is possible to determine the maximum load-bearing properties of the aircraft or determine the required value of the aircraft's Suo in the landing configuration
configurations; for example, with Su x = 2.5, the recommended value should not go out of the range Su x = 0> 67-g 0.92. When the Suo value leaves this range, there is a high probability of the aircraft landing on the nose wheels or on the rear fuselage, i.e. in this case, the safety of landing the aircraft is reduced.
Determining the range of permissible angles of attack when an aircraft is landing under safety conditions also makes it possible to determine the relationships between Sushakh and<2кр И СВЯЗЬ МЄЖДУ Якр И
a h. n. To find these additional connections, you can use the relation:
language P. = acre - (6.36)
here K is a coefficient that takes into account the decrease in the dependence Cy=/(a) near the Susha value; coefficient K can be approximately taken equal to K=0.9.
Transformation of formulas (6.35)’ and (6.36) allows us to find the following additional recommended relationships:
SS cr ~ (5> 5°-g 8.0) 4.55 Sushakh
Sutakh~0> 22 SS cr (1* 2~ 1.76)
Suo=0, Shkr- (1.26N-1.85)
acre=7.7Suo+(9.7° - g 14.2°)
Using these relationships, it is possible to correctly develop the aerodynamic configuration of an aircraft wing in a landing configuration.
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