Originally Posted by bearfoil
The consideration in the rulebook is for 36g's (demonstrated) in the plane of the hinges. This obviously begs the question, why is the arm at a 38 degree bias to the "plane of the Hinges". And that is the question of the day!
And that's not difficult to answer! One end of 'arm 36g' picks up the load at the hinge line, the other end transfers it to the rear spar of the V/S at a point where the spar is supported by a V/S rib. A longer arm at a smaller angle to the next spar/rib intersection would presumably be heavier.
For anyone interested in the rulebook text, I have copied the two relevant sections below. Perhaps it is of interest to note that similar criteria apply to elevator and ailerons.
regards,
HN39
Part 25 AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES
Subpart C--Structure
Sec. 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.]
Sec. 25.393 Control Surface and System Loads
Loads parallel to hinge line.
(a) Control surfaces and supporting hinge brackets must be designed for inertia loads acting parallel to the hinge line.
(b) In the absence of more rational data, the inertia loads may be assumed to be equal to KW, where--
(1) K = 24 for vertical surfaces;
(2) K = 12 for horizontal surfaces; and
(3) W = weight of the movable surfaces.