cargas em aviões introdução ita – instituto tecnológico de aeronáutica
TRANSCRIPT
Cargas em Aviões
Introdução
ITA – Instituto Tecnológico de Aeronáutica
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
cidadeaeroelasti
naturais sfreqüência
fadiga
máximas cargas
Aircraft Loads
•AIRLOADS- maneuver- gust- control deflection- component interaction- buffet
•INERTIA LOADS- due to accelerations
•POWER PLANT LOADS - thrust - torque - gyroscopic - vibration - duct pressure
•LANDING LOADS- vertical load
factor- spin-up- spring-back- one wheel- braking
•TAKEOFF LOADS- catapult
•TAXI LOADS - bumps - turns
•OTHER LOADS - towing - jacking - pressurization - crash landing
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
a) Na condição limite
b) Na condição última
1última carga
falha de carga
1limite carga
escoamento de carga
MS
MS
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
Categoria transporte – aviões especificamente destinados ao transporte regular de passageiros e de cargas.
(JAR–25 - Large Aeroplanes)
AIRWORTHINESS STANDARDSTRANSPORT CATEGORY AIRPLANES
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 g
a
W
Fna
g
WWF zza
zzza
1
g
a
W
FFna
g
WFF xxa
xxxa
Cargas de Inércia e Fator de Carga
Vôo não Nivelado
cos
cos
g
a
W
WagW
W
Fn zzza
z
sen
g
a
W
WsenagW
W
FFn xxxa
x
Cargas de Inércia e Fator de Carga
Caso Geral
W
F
W
Fn jije
j
jeF 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)
jiF
Cargas de Inércia e Fator de Carga
Vôo em Arfagem Acelerada
Cargas de Inércia e Fator de CargaFator de carga na presença de aceleração de arfagem
pppxpxi zg
WWnF
pppzpzi xg
WWnF
CGpr
x
z
pz
px
p
p rg
W
pz Wn
px Wn
pppp x
gWr
g
W
cos
pp zg
W
Cargas de Inércia e Fator de Carga
Fator de carga na presença de aceleração de arfagem
pzp
pxi
px zg
nW
Fn
pzp
pzi
pz xg
nW
Fn
pppxpxi zg
WWnF
pppzpzi xg
WWnF
Exemplo 1
Peso do piloto: 760NPeso do avião: 445.000NIy = 4,52x106 Kg.m2
5Distâncias em mm
Determinar as forças atuantes sobre o piloto:
CGp
Exemplo 1
NH
NV
NW
5
6
1041,4
10335,1
000.445
000,3445000
10335,1 6
W
Vnz
991,01045,4
1041,45
5
W
Hnx
Fatores de Carga no CG
5 Distâncias em mm
Aceleração de Arfagem
226
6
/927,0.1052,4.10186,4
0 sradmKgmN
I
MIM
y
yyy
Nm
HzVxM HVy
656 10186,405,31041,413,210335,1
mz
mx
NH
NV
mKgI
H
V
y
05,3
13,2
1041,4
10335,1
.1052,4
5
6
26
Aceleração de Arfagem
5 Distâncias em mm
Fatores de Carga e Forças no Piloto
NW
mz
mx
srad
n
n
p
p
p
x
z
760
00,1
45,9
/927,0
991,0
000,3
2
107,245,981,9
927,0000,3
Pzn
897,000,1
81,9
927,0991,0
Pxn
Forças no Piloto
NnWF pzppz 601.1107,2760
Fatores de Carga no Piloto
NnWF pxppx 682897,0760
(para trás)
(para cima)