Control Surface Inertial Loads

Question

Control Surface Inertial Loads

Miner89r (Aerospace)

(OP)

8 Jun 17 15:11

FAR 25.393 specifies that "Control surfaces and supporting hinge brackets must be designed for inertia loads acting parallel to the hinge line." A load of 12G (18G Ultimate) is given for horizontal surfaces.

I'm trying to determine if this requirement should be applied to the wing flaps. Is the wing flap considered a control surface?

Personally I think that the control surfaces would include the elevator, ailerons, and rudder however some colleagues disagree. If you believe that this requirement should be applied to the flap, is there any reason it shouldn't also be applied to the leading edge slats?

Perhaps the reasoning behind this requirement would help determine if it should apply.

IRstuff (Aerospace) · Answer 1 · 2017-06-08 15:32:19

How is that even up for argument? If you can move it and control how the plane is flying, it's a control surface.

see page 3 and 4: https://www.princeton.edu/~stengel/MAE331Lecture10...

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rb1957 (Aerospace) · Answer 2 · 2017-06-08 15:50:02

Flaps have their own requirements, 25.457, which points to 25.345.

I thought I'd seen a spanwise load, I thought it was 100g; could've been an OEM's private case, could be I'm mis-remembering ...

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

3DDave (Aerospace) · Answer 3 · 2017-06-08 15:52:12

The alternatives are that the FAA doesn't care if other moving surfaces fall off or the FAA has sections dedicated to those surfaces or that this covers all moving surfaces that control airflow. Maybe someone wants to redefine what a hinge is?

rb1957 (Aerospace) · Answer 4 · 2017-06-08 15:56:38

an aileron has an obvious hinge line (not many translating ailerons).

a flap can have a hinge line (very old designs) but most translate significantly (so not much of a hinge line).

i think the FAA thinks that different surfaces do different things. Ailerons and such are different to flaps. The consequences of failure are different too. And I guess over the years different things have happened (creating different rules).

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

3DDave (Aerospace) · Answer 5 · 2017-06-08 17:39:16

I was typing my response while you were typing yours. I did guess correctly (by covering all the bases) that the FAA had coverage for flaps. If I read it correctly, high lift devices don't have cross-flow loading requirements. I wonder how it came up for rudder and elevators.

TimMcK_Aero (Aeronautics) · Answer 6 · 2017-06-09 01:55:55

23.393 was created in Amdt 48, from a JAA suggestion contain modified version of the requirements of 23.657(c). (ctr-f "23.393")

FAR 23.657 at the time.

Tim

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Control Surface Inertial Loads