IF SOME ICE MAKE THE RUDDER TO LOSE ITS FUNCTION - VOEPASS CRASH ATR-72-500 IN BRAZIL

 ‘Not icing threw to the ground the aircraft, but the spiral descent flight in flat spin’; the VOEPASS’ aircraft ATR-72-500 performing the flight 2Z-2283 outbound Cascavel, PR airport (SBCA, ICAO code) to São Paulo Guarulhos airport (SBGU) in Brazil, on Aug 9, 2024. 

Spin recovery requirement

 Aerodynamic balance and mass balance:

aileron, elevator, and rudder tabs of ATR-72-600

SOURCE:

AIRCRAFT DESIGN

A Systems Engineering Approach

Mohammad H. Sadraey

Daniel Webster College, New Hampshire, USA

The level of acceptability relates to the ease of flight and flight safety. According to airworthiness standards, an aircraft with any level of acceptability from one to three is allowed to fly, but for the design of control surfaces, level 1 must be the objective. An aircraft with level 1 can only terminate flight phase A safely and in other phases may be run out of control. When an aircraft is in level 1, there is no failure during phases of flight. When an aircraft has one failure per 1 000 000 flights, it will be considered to be at level 1. When an aircraft has one failure per 10 000

flights, it will be considered to be at level 2. If any aircraft has one failure per 100 flights, it is considered to be at level 3. An aircraft in level 3 is recommended to be retired to avoid an accident, because any time a system or component fails, an accident may occur. The control surfaces must be designed such that the level 1 of handling qualities is achieved.

Spin Recovery

One of the most important roles of a rudder in the majority of airplanes is spin recovery.

The most significant instrument to recover aircraft from a spin is a powerful rudder. Spin is a self-sustaining (auto-rotational) spiral motion of an airplane about the vertical (z ) axis, during which the mean angle of attack of the wings is beyond the stall.

The typical range of some spin parameters is as follows:

angle of attack (α), 30–60 deg;

rate of descent (ROD), 20–100 m/s; [65 ft/s – 168 ft/s] {3900 ft/min – 10,080 ft/min}

rate of spin (Ω), 20–40 rpm;

helix angle (γ), 3–6 deg;

and helix radius (R), half of the wing span.

 The design of the rudder

The rudder is the most significant element in spin recovery to stop rotation. The primary control for spin recovery in many airplanes is a powerful rudder.

The convention for the positive rudder deflection is defined as the deflection to the

left (of the pilot). A positive rudder deflection creates a positive side force (i.e., in the positive y direction) but results in a negative yawing moment (i.e., counterclockwise).

four parameters must be determined: (i) rudder area (S R), (ii) rudder chord (CR), (iii) rudder span (bR), (iv) maximum rudder deflection (±δRmax ), and (v) location of inboard edge of the rudder (bRi).

FAR Part 25 Section 25.147 requires the following:

It must be possible, with the wings level, to yaw into the operative engine and to safely make a reasonably sudden change in heading of up to 15 deg in the direction of the critical inoperative engine. This must be shown at 1.3 VS for heading changes up to 15 deg, and with (i) the critical engine inoperative and its propeller in the minimum drag position; (ii) the power required for level flight at 1.3 VS, but not more than maximum continuous power; (iii) the most unfavorable center of gravity; (iv) landing gear retracted; (v) flaps in the approach position; and (vi) maximum landing weight.

The rudder plays different roles in different phases of flight for various aircraft. Six

major functions of a rudder are: (i) cross-wind landing, (ii) directional control for balancing asymmetric thrust on multi-engine aircraft, (iii) turn coordination, (iv) spin recovery, (v) adverse yaw, and (vi) glide slope adjustment for a glider.

Example,

Consider the maximum allowable rudder deflection is ±25 deg. Is this rudder able to satisfy the spin recovery requirement at 15 000 ft altitude? Assume the aircraft will spin at an angle of attack of 40 deg.

 We need to keep in mind that at 15,000 feet the RUDDER deflection demands an increase because of air density, but that deflection at that altitude must be less than 30 degrees. After all calculations we’ll get 29.11 degrees of the rudder deflection.

There is a mnemonic rule to pilots’ remembrance – PARE:

P – Power to idle

A – Ailerons on neutral

R – Rudder full opposite direction of rotation

E – Elevators forward to break the stall

For a flight instructor it has no relevance icing condition on the aircraft. The ICE & RAIN PROTECTION SYSTEM was developed to keep the plane from icing condition. 

The most interesting thing in any abnormal flight is to save the flight from the instant the abnormality has presented to the pilot, so the pilot must be prompted to manage the abnormal flight.

An airplane only gets into spiral flat spin descent flight if the RUDDER trim has lost its function to keep the plane flying in straight line (forward heading).  Any plane before takeoff must have its rudder trim set to zero deflection.

To take an airplane from a diving spiral flat spin flight, you must immediately and fully push on the pedal at the same side of the highest wing, and you must keep the ailerons on neutral.  

 

Real spiral flat spin training overview

The main difference between a normal spiral spin descent flight and a flat spiral spin descent flight is the “screw thread” shape of the descent flight.

On the flat spiral spin descent flight, the aircraft nose keeps aligning to the Earth horizon (minimum nose up) almost the entire descent flight, in other words, the nose does not point directly to terrain. The airplane makes each descent turn increasing the spiral thread diameter.  If the initial descent turn has 10 meters of radius, the last turns before colliding into the terrain will have about 20 meters of radius.

On the contrary, the normal spiral spin descent flight, the aircraft nose will fall pointing directly to terrain. The plane makes all descent turns very near to the vertical spiral axis. It starts the first turn with 10 meters of radius and at the final turn the airplane will make a turn with 10 meters of radius centered on spiral vertical axis.

Spin Recovery

One of the most important roles of a rudder in majority of airplanes is spin recovery. The most significant instrument to recover aircraft from a spin is a powerful rudder. Spin is a self-sustaining (auto-rotational) spiral motion of an airplane about vertical (z) axis, during which the mean angle of attack of the wings is beyond the stall. Almost since man first flew, spinning has caused many fatal accidents, so that most accidents were due to spin. During years 1965 to 1972, US Navy has lost an average of 2 aircraft per month and total of 169 aircraft due to spin, the list of which is headed by 44 fighter aircraft F-4s (Phantom). This statistics show the crucial role of the rudder in a spin.

Spin is a high angle of attack/low airspeed situation; the airspeed will be hovering somewhere down in the stall area. Spin has two particular specifications: 1. Fast rotation around vertical axis, 2. Fully stalled wing. Spin is usually starts after wing stalls. One of the reasons why aircraft enter into spin is that inboard of the wing stalls before outboard of the wing, in other word, lift distribution over the wing is not elliptic. Spin is recovered by a procedure which all control surfaces (elevator, aileron, and rudder) contribute; particularly the rudder in an apparently unnatural way. The rudder is the most significant element is spin recovery to stop rotation. The primary control for spin recovery in many airplanes is a powerful rudder.

The rudder must be powerful enough to oppose the spin rotation in the first place. A spin follows departures in roll, yaw and pitch from the condition of trim between the predominantly pro-spin moment due to the wings and the generally anti-spin moments due to other parts of the aircraft. If spin is not recovered, aircraft will eventually crash. The criterion for rudder design in a spinnable aircraft may be spin recovery. Acrobatic and fighter airplanes are usually spinnable, but there are some airplanes such as some transport aircraft that are spin-proof or un-spinnable.

Typical range of some spin parameters is as follows: angle of attack (α): 30 to 60 degrees; rate of descent (ROD): 20 to 100 m/sec; rate of spin (Ω): 20 to 40 rpm; helix angle (σ): 3 to 6 degrees; and helix radius (R): half of wing span. As angle of attack increases; rate of rotation increases; and helix radius decreases.

 Basically, the rudder is not the only factor to feature an acceptable spin recovery. Two other significant factors are as follows:

1. aircraft mass distribution and aircraft moments of inertia,

2. fuselage side area and cross section.

It is very important that the inertia term be made anti-spin (negative for right spin) for recovery. When the magnitudes of pitch (Iyy) and roll (Ixx) inertia are close, the effect of inertia term is little; and hence the rudder, will be the primary control for spin recovery. But whenever the inertia term becomes quite significant, they have a considerable impact on the spin motion, and thus, the size of rudder. The application of aileron to aid recovery in generally not recommended due to its nuisance impact. In some cases, the use of ailerons while stopping a spin may suddenly cause a spin in the reverse direction.

Induced Tailplane Stall

AirAsia QZ8501 - Unbelievably Steep Climb

At 6:17 a.m. on Dec. 28, three minutes after air traffic control unsuccessfully tried to make contact and asked nearby aircraft to try to locate QZ8501, the A320 turned to the left and it began to climb from its altitude of 32,000 ft (9,750 metres), Jonan told a parliamentary hearing.

The rate of the climb increased rapidly within seconds to 6,000 ft a minute, before accelerating further to 8,400 ft a minute and finally 11,100 ft. The aircraft reached 37,600 ft just 54 seconds after it began to climb before it appeared to stall.

The aircraft began to fall at 6:18 a.m., dropping 1,500 ft in the first 6 seconds before reaching a rate of descent of 7,900 ft per minute until it reached 24,000 ft, at which point it disappeared from the radar.

UPDATED FEB 04, 2015

Georgia State University

http://hyperphysics.phy-astr.gsu.edu/hbase/orbv.html


The acceleration was 9,53 m/s²

é uma aceleração como se o avião estivesse na altitude de 90.701 m (297.576 pés). Nível de voo 3000 ou FL 3000, corresponde a 300.000 pés (trezentos mil pés). A estrutura não resistiu mesmo antes de atingir a altitude máxima prevista de 12594 m (41318 pés).

O tempo indicado pelo radar foi de 41, 4211 segundos  para subir 1600 metros, portanto, a aceleração

integral  ∮   (aceleração da Terra, aceleração no FL 320 e aceleração da aeronave resultante) foi de 9,53 m/s²

At flight level of 32,000 feet the acceleration of gravity is 9.77 m/s²

Human bodies exposed to such acceleration will immediately have the blood flowing totally to feet. Therefore, both pilots (airline pilots rarely have put their oxygen masks on above 25000 feet) will have dead faint, and passengers as well. Unless, passenger oxygen masks are deployed.

A aceleração foi de 9,53 m/s² 

No nível de voo de 32000 pés a aceleração da gravidade é de 9,77 m/s²

O corpo humano exposto a tal aceleração  de 9,53 m/s²   terá imediatamente o sangue fluindo totalmente para os pés, e por essa razão, ambos os pilotos (pilotos de linha aérea raramente colocam suas máscaras de oxigênio em altitudes acima de 25000 pés) terá desmaio profundo, e passageiros também. A menos, que as máscaras de oxigênio de passageiro sejam dispostas.

Subida Inacreditavelmente Íngreme.

Às 06:17 AM em 28 de dezembro, três minutos depois que o controle de tráfego aéreo tentou, sem sucesso, fazer contato e pediu às aeronaves nas proximidades para tentar localizar o QZ8501, o A320 curvou  à esquerda e começou a subir da sua altitude de 32000 pés (9.750 metros), Jonan disse em uma audiência parlamentar.

A razão de subida aumentou rapidamente em poucos segundos para 6000 pés por minuto, antes de acelerar adicionalmente para 8400 pés por minuto e finalmente 11100 pés [por minuto]. A aeronave atingiu 37600 ft em exatamente 54 segundos depois que ela começou subir antes dela parecesse estolar.

A aeronave começou a cair às 06:18 AM, caindo 1500 pés nos primeiros 6 segundos antes de atingir uma velocidade de descida de 7900 pés por minuto até ela   atingiu 24000 pés, ponto no qual ela desapareceu do radar.
 

STALL Is Only An Angle Of Attack Problem, It Is Not Directly A Speed Problem

 

 

 

Interpretação dos gráficos acima

No gráfico do meio à esquerda da imagem, logo que o fluxo de ar passando por cima da superfície da asa começa a se separar (curva VERMELHA) inicia-se a dimunuição da razão do Coeficiente Máximo de Sustentação (Cl_MAX) da superfície aerodinâmica. Quando o fluxo de ar se separa totalmente, a curva atinge seu ponto máximo, o qual corresponde ao AoA de Estol e ao Coeficiente Máximo de Sustentação.

Se neste exato momento os SLATS se estenderem (curva MAGENTA, vértice mais alto), observe que o ganho na segurança do voo é substancial, pois tanto o AoA de Estol quanto o Coeficiente Máximo de Sustentação aumentam significativamente.

Supondo-se que neste instante, o piloto presuma que se ele estender os FLAPS (curva VERDE), a aeronave ganharia mais segurança na situação, o gráfico demonstra exatamente ao contrário. Aqui há um engano que tem sido compartilhado pela maioria dos pilotos voando aeronave em altas altitudes, pois observe que imediatamente o AoA de Estol diminui assustadoramente (eixo dos X), e embora o Coeficiente Máximo de Sustentação diminua também, ele ainda permanece maior do que o valor para a separação total do fluxo acima da asa.

Se nesta hipotética situação, as asas ficarem contaminadas com GELO (curva ÂMBAR), o pior acontecerá, pois tanto o AoA de Estol diminui quanto o Coeficiente Máximo de Sustentação.

Se os SPEED BRAKES forem abertos nesse instante (curva MARROM ESCURO), o AoA de Estol e o Coeficiente Máximo de Sustentação farão a segurança do voo ficar mais comprometida.

No gráfico da direita, na imagem, fica bem claro que em altas altitudes, quanto menos veloz  o avião estiver voando, o Ângulo de Ataque para o Estol (AoA_STALL) e o Coeficiente de Sustentação Máximo da asa, serão maiores, pois  o Número Mach estará baixo, mas o que  mais é observado, é comandante de avião à jato voando em altas altitudes tentando aumentar o número MACH do voo através do FMS.

Este piloto não está se importando com segurança do voo, pois existe a possibilidade da aeronave entrar numa emergência, e o Coeficiente Máximo de Sustentação das asas bem como o AoA_STALL ficarem muitíssimo reduzidos quando voando nessa condição. Veja no gráfico da direita na imagem. Observe que quando o Número MACH está muito ALTO, tanto o AoA_STALL quanto o Cl_MAX estão muito reduzidos.

PITCH UP EFFECT

The shape of the wing will also determine the STALL characteristics

 You have to remember for a given MACH number a wing stalls at a given angle of attack when the MACH number increases the value of angle of attack stall decreases.

Você tem que se lembrar que para um dado número MACH uma asa estola em um dado ângulo de ataque, quando o número MACH aumenta, o valor de AoA  de estol diminui.

 

 

Fundamental to understanding angle of attack and stalls is the realization that an airplane wing can be stalled at any airspeed and any altitude. Moreover, attitude has no relationship to the aerodynamic stall. Even if the airplane is in descent with what looks like ample airspeed, the surface can be stalled. If the angle of attack is greater than the stall angle, the surface will stall.

 

Most pilots are experienced in simulator or even airplane exercises that involve approach to stall. This is a dramatically different condition than a recovery from an actual stall because the technique is not the same. The present approach to stall technique being taught for testing is focused on “powering” out of the non-stalled condition with emphasis on minimum loss of altitude. At high altitude this technique may be totally inadequate due to the lack of excess thrust. It is impossible to recover from a stalled condition without reducing the angle of attack and that will certainly mean a loss of altitude, regardless of how close the airplane is to the ground. Although the thrust vector may supplement the recovery it is not the primary control. At stall angles of attack, the drag is very high and thrust available may be marginal. Also, if the engine(s) are at idle, the acceleration could be very slow, thus extending the recovery. At high altitudes, where the available thrust will be reduced, it is even less of a benefit to the pilot. The elevator is the primary control to recover from a stalled condition, because without reducing the angle of attack, the airplane will remain in a stalled condition until ground impact, regardless of the altitude at which it started.

 

Effective stall recovery requires a deliberate and smooth reduction in wing angle of attack. The elevator is the primary pitch control in all flight conditions, not thrust.

   Fundamental para a compreensão de ângulo de ataque e estois (perda de sustentação) é a compreensão de que uma asa de avião pode ser estolada em qualquer velocidade e altitude. Além disso, atitude não tem relação com o estol aerodinâmico. Mesmo se o avião estiver em descida com o que se parece uma velocidade ampla, a superfície pode ser estolada. Se o ângulo de ataque for maior que o ângulo de estol, a superfície irá estolar.

   A maioria dos pilotos são experientes em simulador ou mesmo exercícios no avião que envolvem a aproximação do estol. Esta é uma condição dramaticamente diferente do que uma recuperação de um estol real, porque a técnica não é a mesma.  A presente abordagem para a técnica de estol sendo ensinada para teste está focada em "potenciação" fora a condição de não-estolado com ênfase na perda mínima de altitude. Em altitude elevada, esta técnica pode ser totalmente inadequada devido à falta de excesso de potência. É impossível se recuperar de uma condição estolado sem reduzir o ângulo de ataque e isso certamente significará uma perda de altitude, independente de quão perto o avião está do solo.

  Embora o vetor potência possa completar a recuperação ele não é o controle principal. Em ângulos de ataque de estol, o arrasto é muito alto e a potência disponível pode ser marginal. Além disso, se os motores estiverem em idle, a aceleração poderia ser muito lenta, assim, prolongando a recuperação. Em altas altitudes, onde a potência disponível será reduzida, ela é mesmo menos que uma vantagem para o piloto. O elevador é o controle principal para se recuperar de uma condição de estol, porque sem reduzir o ângulo de ataque, o avião permanecerá em uma condição estolada até o impacto com o solo, independente da altitude na qual ele  iniciou.

    Recuperação efetiva de estol exige uma redução deliberada e suave no ângulo de ataque da asa. O elevador é o controle principal do pitch  em todas as condições de voo, e não a potência.

 

Pilot Tips

Dicas de Piloto
1 - The amber bands limits do not provide an indication of sufficient thrust to maintain the current and airspeed.

1 - As faixas âmbar de limites não fornecem uma indicação de potência suficiente para manter a potência atual e a velocidade aerodinâmica.
2 - The amber bands does not give any indication of thrust limits.

2 - As faixas âmbar não dão qualquer indicação de limites de potência.
3 - The minimum maneuver speed indication does not guarantee the ability to maintain level flight at that speed

3 - A indicação de velocidade  mínima de manobra não garante a capacidade para manter o vôo nivelado nessa velocidade
4 - Flying near maximum altitude will result in reduced bank angle capability; therefore, autopilot or crew inputs must be kept below buffet thresholds.

4 - Voando perto da altitude máxima resultará em capacidade de ângulo de inclinação lateral reduzido; Portanto, as entradas de dados do piloto automático ou da tripulação devem ser mantidas abaixo dos limiares de buffet.  [Agitação aerodinâmica de uma estrutura de aeronave por fluxos separados de camadas de ar em torno das superfícies]

 5 - The use of LNAV will ensure bank angle is limited to respect buffet and thrust margins. The use of other automation modes, or hand flying, may cause a bank angles that result in buffeting.

5 - O uso de LNAV assegurará que o ângulo de inclinação lateral está limitado a respeitar a agitação (vibração que precede o estol) da estrutura da aeronave e às margens de potência. O uso de outros modos de automação, ou voando manualmente, pode causar ângulos de inclinação lateral que resultam em  agitação aerodinâmica da estrutura da aeronave.