Code of Federal Regulations

Title 14 - Aeronautics and Space
Volume: 1Date: 2024-01-01Original Date: 2024-01-01Title: Section 25.397 - Control system loads.Context: Title 14 - Aeronautics and Space. CHAPTER I - FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION. SUBCHAPTER C - AIRCRAFT. PART 25 - AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES. Subpart C - Structure. - Control Surface and System Loads.
Code of Federal Regulations / Title 14 - Aeronautics and Space / Vol. 1 / 2024-01-01246
§ 25.397 Control system loads. (a) General. The maximum and minimum pilot forces, specified in paragraph (c) of this section, are assumed to act at the appropriate control grips or pads (in a manner simulating flight conditions) and to be reacted at the attachment of the control system to the control surface horn. (b) Pilot effort effects. In the control surface flight loading condition, the air loads on movable surfaces and the corresponding deflections need not exceed those that would result in flight from the application of any pilot force within the ranges specified in paragraph (c) of this section. Two-thirds of the maximum values specified for the aileron and elevator may be used if control surface hinge moments are based on reliable data. In applying this criterion, the effects of servo mechanisms, tabs, and automatic pilot systems, must be considered. (c) Limit pilot forces and torques. The limit pilot forces and torques are as follows:
ControlMaximum forces or torquesMinimum forces or torques
Aileron:
Stick 100 lbs 40 lbs.
Wheel  1 80 D in.-lbs  2 40 D in.-lbs.
Elevator:
Stick 250 lbs 100 lbs.
Wheel (symmetrical) 300 lbs 100 lbs.
Wheel (unsymmetrical)  3 100 lbs.
Rudder 300 lbs 130 lbs.
1  The critical parts of the aileron control system must be designed for a single tangential force with a limit value equal to 1.25 times the couple force determined from these criteria.
2   D = wheel diameter (inches).
3  The unsymmetrical forces must be applied at one of the normal handgrip points on the periphery of the control wheel.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-38, 41 FR 55466, Dec. 20, 1976; Amdt. 25-72, 55 FR 29776, July 20, 1990]