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Code of Federal Regulations
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 Sec. 25.331
Part 25 AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES |
| Subpart C--Structure | Flight Maneuver and Gust Conditions |
Sec. 25.331
General.
(a) Procedure. The analysis of symmetrical flight must include at least the conditions specified in paragraphs (b) through (d) of this section. The following procedure must be used:
(1) Enough points on the maneuvering and gust envelopes must be investigated to ensure that the maximum load for each part of the airplane structure is obtained. A conservative combined envelope may be used.
(2) The significant forces acting on the airplane must be placed in equilibrium in a rational or conservative manner. The linear inertia forces must be considered in equilibrium with thrust and all aerodynamic loads, while the angular (pitching) inertia forces must be considered in equilibrium with thrust and all aerodynamic loads, while the angular (pitching) inertia forces must be considered in equilibrium with thrust and all aerodynamic moments, including moments due to loads on components such as tail surfaces and nacelles. Critical thrust values in the range from zero to maximum continuous thrust must be considered.
(3) Where sudden displacement of a control is specified, the assumed rate of control surface displacement may not be less than the rate that could be applied by the pilot through the control system.
(4) In determining elevator angles and chordwise load distribution (in the maneuvering conditions of paragraphs (b) and (c) of this section) in turns and pullups, the effect of corresponding pitching velocities must be taken into account. [The in-trim and out-of-trim flight conditions specified in Sec. 25.255 must be considered.]
(b) Maneuvering balanced conditions. Assuming the airplane to be in equilibrium with zero pitching acceleration, the maneuvering conditions A through I on the maneuvering envelope in Sec. 25.333(b) must be investigated.
(c) Maneuvering pitching conditions. The following conditions involving pitching acceleration must be investigated:
[(1) Maximum elevator displacement at VA. The airplane is assumed to be flying in steady level flight (point A1, Sec. 25.333(b)) and, except as limited by pilot effort in accordance with Sec. 25.307(b), the pitching control is suddenly moved to obtain extreme positive pitching acceleration (nose up). The dynamic response or, at the option of the applicant, the transient rigid body response of the airplane, must be taken into account in determining the tail load. Airplane loads which occur subsequent to the normal acceleration at the center of gravity exceeding the maximum positive limit maneuvering load factor, n, need not be considered.
(2) Special control displacement. A checked maneuver, based on a rational pitching control motion vs. time profile, must be established in which the design limit load factor specified in Sec. 25.337 will not be exceeded. Unless lesser values cannot be exceeded, the airplane response must result in pitching accelerations not less than the following:
(i) A positive pitching acceleration (nose up) is assumed to be reached concurrently with the airplane load factor of 1.0 (points A to D, Sec. 25.333(b)). The positive acceleration must be equal to at least
where--
n is the positive load factor at the speed under consideration; and
V is the airplane equivalent speed in knots.
(ii) A negative pitching acceleration (nose down) is assumed to be reached concurrently with the positive maneuvering load factor (points A to D Sec. 25.333(b)). This negative pitching action must be equal to at least
where--
n is the positive load factor at the speed under consideration: and V is the airplane equivalent speed in knots.
(3) [Reserved.]]
(d) Gust conditions. The gust conditions B' through J', Sec. 25.333(c), must be investigated. The following provisions apply:
(1) The air load increment due to a specified gust must be added to the initial balancing tail load corresponding to steady level flight.
(2) The alleviating effect of wing down wash and of the airplane's motion in response to the gust may be included in computing the tail gust load increment.
(3) Instead of a rational investigation of the airplane response, the gust alleviation factor K, may be applied to the specified gust intensity for the horizontal tail.
Amdt. 25-46, Eff. 12/1/78
 Comments
Document History
Notice of Proposed Rulemaking Actions:
Notice of Airworthiness Review Program No. 2; Notice No. 75-10; Issued on 02/27/75.
Notice of Airworthiness Review Program No. 3; Notice No. 75-19; Issued on 05/13/75.
Notice of Airworthiness Review Program No. 5; Notice No. 75-23; Issued on 05/19/75.
Notice of Airworthiness Review Program No. 7; Notice No. 75-26; Issued on 06/09/75.
Notice of Airworthiness Review Program No. 8; Notice No. 75-31; Issued on 06/30/75.
Final Rule Actions:
Final Rule. Docket No. 14324, 14606, 14625, 14685, 14779; Issued on 10/10/78.
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