Cargas em Aviões Introdução ITA – Instituto Tecnológico de Aeronáutica Cargas em Aviões Introdução

Objetivos do Projeto Estrutural O trabalho de primeira importância para o projetista de estruturas de aviões é o de projetar uma estrutura com resistência e rigidez adequadas para as condições mais severas previstas no uso do avião, dando atenção aos seguintes pontos: minimização do peso; compatibilização das restrições aerodinâmicas com maximização do espaço interno; redução dos custos de produção; facilidade e baixo custo de manutenção; adequação na escolha dos materiais utilizados.

Requisitos Estruturais Resistência Rigidez

Aircraft Loads LANDING LOADS - vertical load factor - spin-up AIRLOADS - spring-back - one wheel - braking TAKEOFF LOADS - catapult TAXI LOADS - bumps - turns OTHER LOADS - towing - jacking - pressurization - crash landing AIRLOADS - maneuver - gust - control deflection - component interaction - buffet INERTIA LOADS - due to accelerations POWER PLANT LOADS - thrust - torque - gyroscopic - vibration - duct pressure

Cargas em Aviões Carga Limite carga máxima prevista em condições normais de operação Carga Final (ou Última) carga limite x fator de segurança

Requisitos 1) a estrutura do avião deve resistir às cargas limites sem apresentar deformação permanente prejudicial; 2) A estrutura do avião deve resistir às cargas finais sem falhas.

Implicações no Projeto * Carga Limite → escoamento * Carga Última → falha

Margens de Segurança Na condição limite b) Na condição última

Regulamentos Autoridades responsáveis pela homologação estabelecem: Exigências de aeronavegabilidade. Requisitos de segurança.

Regulamentos USA – Federal Aviation Regulations (FAR), emitidos pela Federal Aviation Agency (FAA) EUR – Joint Aviation Regulations (JAR)

FAR 23 – Airplane Categories (a). The normal category is limited to airplanes that have a seating configuration, excluding pilot seats, of nine or less, a maximum certificated takeoff weight of 12,500 pounds or less, and intended for nonacrobatic operation. Nonacrobatic operation includes: (1). Any maneuver incident to normal flying; (2). Stalls (except whip stalls); and (3). Lazy eights, chandelles, and steep turns, in which the angle of bank is not more than 60 degrees.

FAR 23 – Airplane Categories (b). The utility category is limited to airplanes that have a seating configuration, excluding pilot seats, of nine or less, a maximum certificated takeoff weight of 12,500 pounds or less, and intended for limited acrobatic operation. Airplanes certificated in the utility category may be used in any of the operations covered under paragraph (a) of this section and in limited acrobatic operations. Limited acrobatic operation includes: (1). Spins (if approved for the particular type of airplane); and (2). Lazy eights, chandelles, and steep turns, or similar maneuvers, in which the angle of bank is more than 60 degrees but not more than 90 degrees.

FAR 23 – Airplane Categories (c). The acrobatic category is limited to airplanes that have a seating configuration, excluding pilot seats, of nine or less, a maximum certificated takeoff weight of 12,500 pounds or less, and intended for use without restrictions, other than those shown to be necessary as a result of required flight tests. (d). The commuter category is limited to propeller-driven, multiengine airplanes that have a seating configuration, excluding pilot seats, of 19 or less, and a maximum certificated takeoff weight of 19,000 pounds or less. The commuter category operation is limited to any maneuver incident to normal flying, stalls (except whip stalls), and steep turns, in which the angle of bank is not more than 60 degrees.

FAR 23 – Airplane Categories (e). Except for commuter category, airplanes may be type certificated in more than one category if the requirements of each requested category are met.

FAR 25 AIRWORTHINESS STANDARDS TRANSPORT CATEGORY AIRPLANES (JAR–25 - Large Aeroplanes) Categoria transporte – aviões especificamente destinados ao transporte regular de passageiros e de cargas.

FAR 25 Subpart C – Structure

§ 25.301 - Loads. (a). Strength requirements are specified in terms of limit loads (the maximum loads to be expected in service) and ultimate loads (limit loads multiplied by prescribed factors of safety). Unless otherwise provided, prescribed loads are limit loads. (b). Unless otherwise provided, the specified air, ground, and water loads must be placed in equilibrium with inertia forces, considering each item of mass in the airplane. These loads must be distributed to conservatively approximate or closely represent actual conditions. Methods used to determine load intensities and distribution must be validated by flight load measurement unless the methods used for determining those loading conditions are shown to be reliable. (c). If deflections under load would significantly change the distribution of external or internal loads, this redistribution must be taken into account.

§ 25.303 - Factor of safety. Unless otherwise specified, a factor of safety of 1.5 must be applied to the prescribed limit load which are considered external loads on the structure. When a loading condition is prescribed in terms of ultimate loads, a factor of safety need not be applied unless otherwise specified.

§ 25.305 - Strength and deformation. (a). The structure must be able to support limit loads without any detrimental permanent deformation. At any load up to limit loads, the deformation may not interfere with safe operation. (b). The structure must be able to support ultimate loads without failure for at least 3 seconds. However, when proof of strength is shown by dynamic tests simulating actual load conditions, the 3-second limit does not apply. Static tests conducted to ultimate load must include the ultimate deflections and ultimate deformation induced by the loading. When analytical methods are used to show compliance with the ultimate load strength requirements, it must be shown that- (1). The effects of deformation are not significant; (2). The deformations involved are fully accounted for in the analysis; or (3). The methods and assumptions used are sufficient to cover the effects of these deformations.

§ 25.305 - Strength and deformation. (c). Where structural flexibility is such that any rate of load application likely to occur in the operating conditions might produce transient stresses appreciably higher than those corresponding to static loads, the effects of this rate of application must be considered. (d). Reserved (e). The airplane must be designed to withstand any vibration and buffeting that might occur in any likely operating condition up to VD/MD, including stall and probable inadvertent excursions beyond the boundaries of the buffet onset envelope. This must be shown by analysis, flight tests, or other tests found necessary by the Administrator. (f). Unless shown to be extremely improbable, the airplane must be designed to withstand any forced structural vibration resulting from any failure, malfunction or adverse condition in the flight control system. These must be considered limit loads and must be investigated at airspeeds up to VC/MC.

§ 25.307 - Proof of structure. (a). Compliance with the strength and deformation requirements of this subpart must be shown for each critical loading condition. Structural analysis may be used only if the structure conforms to that for which experience has shown this method to be reliable. The Administrator may require ultimate load tests in cases where limit load tests may be inadequate. (b). [Reserved] (c). [Reserved] (d). When static or dynamic tests are used to show compliance with the requirements of § 25.305(b) for flight structures, appropriate material correction factors must be applied to the test results, unless the structure, or part thereof, being tested has features such that a number of elements contribute to the total strength of the structure and the failure of one element results in the redistribution of the load through alternate load paths.

Critical Conditions – L1011

Critical Conditions – Typical Fighter

Eixos de Referência Eixos do avião: utilizados na análise estrutural.

Cargas de Inércia e Fator de Carga Vôo Nivelado

Cargas de Inércia e Fator de Carga Vôo não Nivelado

Cargas de Inércia e Fator de Carga Caso Geral Somatório das forças externas na direção j (excluídas todas e quaisquer forças de inércia) Somatório das forças de inércia na direção j (incluídas as componentes do peso)

Cargas de Inércia e Fator de Carga Vôo em Arfagem Acelerada

Cargas de Inércia e Fator de Carga Fator de carga na presença de aceleração de arfagem CG

Cargas de Inércia e Fator de Carga Fator de carga na presença de aceleração de arfagem

Exemplo 1 Determinar as forças atuantes sobre o piloto: 5 Distâncias em mm p CG Peso do piloto: 760N Peso do avião: 445.000N Iy = 4,52x106 Kg.m2

Exemplo 1 5 Distâncias em mm Fatores de Carga no CG

Aceleração de Arfagem Aceleração de Arfagem 5 Distâncias em mm

Fatores de Carga e Forças no Piloto Fatores de Carga no Piloto Forças no Piloto (para trás) (para cima)