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ITA – Instituto Tecnológico de Aeronáutica. Cargas nas Asas. Cargas em Aviões. Wing structural box loads : nomenclature and sign convention. Symmetrical maneuver analysis. Required parameters: airplane load factor, n z pitching acceleration, ; pitching velocity, ;
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ITA – Instituto Tecnológico de Aeronáutica Cargas nas Asas Cargas em Aviões
Symmetrical maneuver analysis. • Required parameters: • airplane load factor, nz • pitching acceleration, ; • pitching velocity, ; • wing reference angle of attack, aw ; • inertia parameters due to operating empty weight and fuel; • airspeed and Mach number. Wing spanwise net load distribution: lift distribution at aw = 0 lift distribution due to angle of attack lift distribution due to pitching velocity lift distribution due to aeroelastic effect of inertia (equal to zero for rigid wing) inertia load distribution lift distribution due to speedbrakes (spoilers or other symmetrical devices)
Steady-state maneuver conditions. In general, the steady-state maneuver conditions will produce the maximum wing design shear loads and bending moments for symmetrical maneuvers. Critical maneuver conditions are usually due to extreme positive and negative load factors, with spoilers acting as speed brakes, extended or retracted. Flaps-down maneuver conditions in general are not critical for wing-bending moment, but the rear spar is critical for the trailing edge flap support loads and the associated shear and torsion
Effect of speedbrakes on symmetrical flight conditions. To compensate for the loss in lift due to spoilers during positive amneuver conditions, the wing angle of attack must be incrfeased to maintain flight at a given load factor. This has the effect of increasing the wing shear and bending moment outboard of spoilers and hence will be more critical that the speadbrakes-retracted conditions. For negative maneuver conditions, the opposite will happen. Wingloads will be more critical inboard for inboard spoiler-up conditions and outboard for spoiler-retracted conditions. Speedbrakes extended must be included in the symmetrical flight 1-g load conditions for vertical gust analysis loads in a manner similar to that of the design maneuver conditions.
Abrupt unchecked pitch maneuver. • is accomplished at VA • compressibility effects diminish CNmax W = 326.000 lb ; Sw = 2.500 ft2 ; altitude = sea level
Abrupt checked maneuvers are not considered as critical wing conditions Abrupt checked pitch maneuvers. The pitching acceleration, at the time of the checked maneuver, is negative. For the portion of the wing aft of the CG, this results in a downward inertia force. For the inboard wing that may be forward of the CG, the opposite is true. The effect of pitching acceleration on the resulting wing maneuver loads thus generally increases the relief due to inertia loads. The aeroelastic effect on the resulting wing angle of attack distribution must be given consideration.
Rolling maneuver analysis. • Required parameters: • airplane load factor, nz (=2/3 nzmax and = 0) • maximum roll velocity, for the steady roll condition; • maximum roll acceleration, and related roll velocity for the roll acceleration condition Symmetrical load increments: for aircraft configurations with unsymmetrical operation of lateral control devices (unsymmetrical operation of ailerons and/or use of spoilers for lateral control), a correction must be made to maintain the design load factor during the roll.
Rolling maneuver analysis. Spanwise load distributions during rolling maneuvers:
Rolling maneuver analysis. Rolling maneuver load factors:
Yawing conditions. In general, the wing structure outboard of the side of the fuselage body is not critical for the yawing conditions and lateral gust requirements, except for the attachment of engine/nacelles located outboard on the wing, or other such external store devices, such as wing tank pods and engine pods mounted on the wings for ferry purposes. Winglets are critical for these maneuvers and must be given special considerations. The need for compatible load conditions on the wing for yawing maneuver and gust loads on nacelles can be of importance when modelling the nacelle and local wing structure by finite element analysis. Yawing maneuver and lateral gust conditions may be critical for the wing center section.
Static ground-handling and landing conditions. In general, the two-point breaked roll and the reversed braking are critical in shear and torsion for the wing box inboard of the main landing gear that is mounted on the wing. The two-point landing conditions, level and tail-down landings, are critical for main gear and related support structure on the wing. Both the spin-up and spring-back conditions should be considered in the design of this structure. Wing loads for the main landing gear ground-handling conditions are readilly computed using the applicable load factors specified for each condition. These load factors are applied to the inertia loads for the condition under investigation with the appropriate maximum or minimum fuel load at the gross weight under consideration. Wing load is assumed zero for these conditions. Wing loads for the main gear design landing conditions must include the airload and inertia loads. Load factors compatible with the main gear deseign level and tail-down landing loads may be calculated as discussed earlier. The airplane is placed in balance using the appropriate itching accelerations for the spin-up and spring-back conditions. The inertia loads due to landing impact are added to the 1-g flight condition.
Effect of fuel usage on wing loads. The effect of fuel usage must be considered in determining the spanwise distribution of net wing loads that are the sum of airloads and inertia loads. If the airplane has multiple tanks in both wing and body, then the fuel usage may have a profound effect on the resulting design loads. In the design of a modern narrow-body airplane, the placement of the wing fuel tanks was studied to optimize the load relief due to inertia such that the fuel was consumed from the center wing tanks before the outboard wing fuel was used. This required fuel pumps to be placed in the central tank to continuously maintain the fuel in the outboard tanks until the center tanks emptied. The inboard tank end rib position was selected on the basis of this optimization study.
