Federal Aviation Administration, DOT § 25.415 (2) The minimum forces specified in fort forces up to those specified in § 25.397(c). § 25.397(b). (b) The control system must be de- (b) Balancing tabs. Balancing tabs signed for pilot forces applied in the must be designed for deflections con- same direction, using individual pilot sistent with the primary control sur- forces not less than 0.75 times those ob- face loading conditions. tained under § 25.395. (c) Servo tabs. Servo tabs must be de- signed for deflections consistent with § 25.405 Secondary control system. the primary control surface loading Secondary controls, such as wheel conditions obtainable within the pilot brake, spoiler, and tab controls, must maneuvering effort, considering pos- be designed for the maximum forces sible opposition from the trim tabs. that a pilot is likely to apply to those § 25.415 Ground gust conditions. controls. The following values may be used: (a) The control system must be de- signed as follows for control surface PILOT CONTROL FORCE LIMITS (SECONDARY loads due to ground gusts and taxiing CONTROLS) downwind: (1) The control system between the Control Limit pilot forces stops nearest the surfaces and the Miscellaneous: cockpit controls must be designed for *Crank, wheel, or lever .. ((1 + R) / 3) × 50 lbs., but not loads corresponding to the limit hinge less than 50 lbs. nor more moments H of paragraph (a)(2) of this than 150 lbs. (R=radius). (Ap- plicable to any angle within section. These loads need not exceed— 20° of plane of control). (i) The loads corresponding to the Twist ............................... 133 in.–lbs. maximum pilot loads in § 25.397(c) for Push-pull ........................ To be chosen by applicant. each pilot alone; or *Limited to flap, tab, stabilizer, spoiler, and landing gear op- (ii) 0.75 times these maximum loads eration controls. for each pilot when the pilot forces are applied in the same direction. § 25.407 Trim tab effects. (2) The control system stops nearest The effects of trim tabs on the con- the surfaces, the control system locks, trol surface design conditions must be and the parts of the systems (if any) accounted for only where the surface between these stops and locks and the loads are limited by maximum pilot ef- control surface horns, must be designed fort. In these cases, the tabs are con- for limit hinge moments H, in foot sidered to be deflected in the direction pounds, obtained from the formula, that would assist the pilot, and the de- H=.0034KV2cS, where— flections are— (a) For elevator trim tabs, those re- V=65 (wind speed in knots) K=limit hinge moment factor for ground quired to trim the airplane at any gusts derived in paragraph (b) of this sec- point within the positive portion of the tion. pertinent flight envelope in § 25.333(b), c=mean chord of the control surface aft of except as limited by the stops; and the hinge line (ft); (b) For aileron and rudder trim tabs, S=area of the control surface aft of the hinge those required to trim the airplane in line (sq ft); the critical unsymmetrical power and (b) The limit hinge moment factor K loading conditions, with appropriate for ground gusts must be derived as fol- allowance for rigging tolerances. lows: § 25.409 Tabs. Surface K Position of controls (a) Trim tabs. Trim tabs must be de- (a) Aileron ..................... 0.75 Control column locked signed to withstand loads arising from or lashed in mid-posi- all likely combinations of tab setting, tion. (b) ......do ...................... 1 1 Ailerons at full throw. primary control position, and airplane ±0.50 speed (obtainable without exceeding (c) Elevator ................... 1 1 (c) Elevator full down. the flight load conditions prescribed ±0.75 (d) ......do ...................... 1 1 (d) Elevator full up. for the airplane as a whole), when the ±0.75 effect of the tab is opposed by pilot ef- (e) Rudder .................... 0.75 (e) Rudder in neutral. 407 VerDate Mar<15>2010 14:10 Mar 01, 2011 Jkt 223043 PO 00000 Frm 00417 Fmt 8010 Sfmt 8010 Y:\SGML\223043.XXX 223043 wwoods2 on DSK1DXX6B1PROD with CFR.