Effect of WIngbending on Spoilers

[Anand1Stress]

Hello Members,

I am sizing a spoiler for a commercial aircraft. The pressure loads derived from the maximum actuator forces are the driving factors for the sizing.

Two critical load cases, spoiler deployed and spoiler retracted conditions are considered with 3 pressure distributions. Since the spoiler is mounted on the FTE ( Fixed trailing edge) of the wing, there will be some effect on the spoiler due to the wing bending.

I can understand that at spoiler retracted (0 position), it will come in interface with the flap and FTE ribs so the up force from flap and wing bending can be considered.

My question is whether to consider the wing bending effect on spoilers at deployed condition. at deployed condition, Spoiler is not in interface with flap and FTE ribs. It will only come in contact with hinges of the FTE and these joints have a sperical bearing to give bit of rotational flexibility and an unclamped joint to give free DOF in lateral direction.

My customer insists that we combine the wing bending with spoiler pressure loads but does not give any explnantion on how and why to do this. I have had sized the FTE of other airctafts but never seen spoiler pressure loads combined with wing bending cases.

Any one with prior experience, please let me know if my thinking is correct. Already the design is oversized and I want to avoid unnecessary weight addition.

Appreciate the help.

Anand

 

[rb1957]

3pt bending can be really significant. i think the only way to avoid it is if you break the panel into two (assumng a central actuator) but that it Very uncommon.

another day in paradise, or is paradise one day closer ?

 

[tbuelna]

The pressure loads derived from the maximum actuator forces are the driving factors for the sizing.

Shouldn't your actuator be sized based on the combination of spoiler aero forces, joint frictions, and safety factors for things like jamming due to ice buildup? As opposed to sizing the spoiler based on the output capability of the actuator?

A wing structure will always be way stiffer in bending than your TE spoiler structure. And even though you are using spherical bearings at the hinge points, the radial forces acting on the spherical bearings, and the end moment frictions created, will be in proportion to the amount of bending produced in the spoiler by the wing deflection, if three or more hinge bearings are used. The only way you can isolate the spoiler from the wing bending is by using only two spherical bearings, with each having an axial translation DoF along the hinge axis, to attach the spoiler.

Even after considering the combined worst case effect of all of these aero loads and frictions, you might also need to add a FoS of 2.0 for the torque capability of your spoiler actuator.