(1) The Board interprets and construes subparagraph (8) of § 4b.133 (a) as requiring the Administrator to accept for the purposes of § 4b.133 a value for the one-engine-inoperative minimum control speed which has been established in accordance with the provisions of that section with the propeller of the inoperative engine feathered: Provided, That the airplane involved is equipped with an automatic feathering device acceptable to the Administrator under § 4b.10 for demonstrating compliance with the take-off path and climb requirement of §§ 4b.116 and 4b.120 (a) and (b).

CROSS REFERENCE: For Special Civil Air Regulation applicable to turbine-powered transport category airplanes of current design, in lieu of the requirements contained in § 4b.133, see SR-422B, supra.

§ 4b.133-1 Determination of the minimum control speed, VMC (FAA policies which apply to § 4b.133).

(a) When demonstrating the minimum control speed, the applicant may choose one of three basic methods dependent on the inherent characteristics of the airplane or a combination of the methods is acceptable provided that the combination chosen does not allow the aircraft to exceed any of the limtiing factors specified in § 4b.133. These methods are:

(1) With wings level and 180 pounds rudder force, or full rudder travel causing airplane to deviate from a constant heading, or airplane stall.

(2) With the wing on the engine operating side lowered 5° and 180 pounds rudder force, or full rudder travel causing airplane to deviate from a constant heading, or airplane stall.

(3) At 0° yaw and full rudder travel causing airplane to deviate from 0° yaw, or 180 pounds rudder force, or airplane stall.

(b) When it has been found that the aircraft is limited by the 180 pounds rudder force in any of the methods in paragraph (a) of this section, a plot of force vs. air speed should be made through a suitable range of speeds to substantiate the speed chosen at Vмc.

the limits as specified in § 4b.133 at or slightly above the minimum control speed. When conducting this test it is imperative to hold all remaining factors equal so that a true comparison may be accomplished.

(d) All testing should be accomplished at the appropriate weights and powers for the range of approval desired. The minimum control speed should be determined for each take-off flap position selected for approval if the take-off flap is made variable with altitude.

(e) Civil Air Regulation Part 4b, Interpretation No. 1, interprets § 4b.133 (a) (8) as requiring the establishment of one engine inoperative minimum control speed with the propeller of the inoperative engine feathered providing that the airplane is equipped with an automatic feathering device acceptable to the Administrator under § 4b.10 for demonstrating compliance with the take-off path and climb requirements of §§ 4b.116 and 4b.120 (a) and (b). In such cases where the applicant chooses to demonstrate Vic with the propeller feathered, the value of VMC with the propeller windmilling should also be obtained and included in the Airplane Flight Manual.

(f) Configuration: This test should be conducted in the configuration that follows:

Weight-Maximum take-off. (If stall occurs prior to reaching VMC, applicant may choose to demonstrate a lower Vмc at a reduced weight.)

C. G.-Most aft.

Wing flaps-Take-off position. Landing gear-Retracted. Operating engine (s)-Take-off

manifold pressure or full throttle, cowl flaps in take-off position. Inoperative engine-Throttle closed, propeller windmilling or any other logical position, cowl flaps in take-off position.

(g) Test procedure and required data: After establishing the critical inoperative engine and the choice of method for demonstration, the tests for establishing the minimum control speed may be conducted. Using the configuration specified in § 4b.133, all engines should be adjusted for take-off power and a series of engine cuts made by moving the mixture control of the critical engine in idle cut-off position at consecutively lower air speeds until one of the limiting factors specified in § 4b.133 is experienced. When the minimum control speed is determined,

The means used for trimming the airplane shall be such that after being trimmed and without further pressure upon, or movement of, either the primary control or its corresponding trim control by the pilot or the automatic pilot, the airplane shall comply with the trim requirements of §§ 4b.141 through 4b.144. § 4b.140-1 General trim qualities (FAA policies which apply to § 4b.140).

It should be possible to trim the airplane completely for any flight condition which is reasonable to assume will be maintained steadily for any appreciable time. Compliance for unsymmetrical power should be demonstrated with "wings level" or "zero yaw" when a yawmeter is installed as a part of the required equipment.

[Supp. 24, 19 F. R. 4456, July 20, 1954]
§ 4b.141 Lateral and directional trim.

The airplane shall maintain lateral and directional trim under the most adverse lateral displacement of the center of gravity within the relevant operating limitations, under all normally expected conditions of operation, including operation at any speed from 1.4 Vs, to VNo or to M whichever is the lesser.

NO

[Amdt. 4b-2, 20 F. R. 5305, July 26, 1955] § 4b.141-1 Procedure for demonstrating lateral and directional trim (FAA policies which apply to § 4b.141).

(a) Configuration. This test should be conducted in the configuration that follows:

Weight-Maximum take-off and maximum landing.

C. G. position-Most forward and most aft with greatest lateral variation in useful load. Asymmetrical fuel loading should be considered.

Wing flaps-Retracted and maximum landing position.

Landing gear-Retracted and extended.
Engines Power required for level flight.
Cowl flaps-Appropriate for flight condition.

(b) Test procedure and required data. It should be possible to maintain handsoff lateral and directional trim when demonstrating compliance with § 4b.141. The following data should be recorded: Weight.

C. G. position.

Wing flap position.

Landing gear position.

Engines, rpm and manifold pressure.
Pressure altitude.

Ambient air temperature.
Trim speed at 1.4 V11·

(Additional lateral and directional trim should be demonstrated in other configurations in conjunction with tests in § 4b.150.)

[Supp. 24, 19 F.R. 4456, July 20, 1954, as amended by Supp. 32, 22 F.R. 6963, Aug. 29, 1957]

§ 4b.142 Longitudinal trim.

The airplane shall maintain longitudinal trim under the following conditions:

(a) During a climb with maximum continuous power at a speed not in excess of 1.4 Vs, with the landing gear retracted and the wing flaps both retracted and in the take-off position,

(b) During a glide with power off at a speed not in excess of 1.4 Vs, with the landing gear extended and the wing flaps both retracted and extended, with the forward center of gravity position approved for landing with the maximum landing weight, and with the most forward center of gravity position approved for landing regardless of weight,

Weight-Maximum take-off.

C. G. position-Most forward.

Wing flaps-Retracted and take-off position.
Landing gear-Retracted.

Engines Maximum continuous power.
Cowl flaps Optional.

(2) Test procedure and required data. It should be possible to maintain handsoff longitudinal trim at a speed not in excess of 1.4 V11 with the wing flaps retracted and in the take-off position. The same data specified in § 4b.141-1 (b) should be recorded.

(b) Longitudinal trim during glide, § 4b.142 (b) —(1) Configuration. This test should be conducted in the configurations that follow:

Weight-Maximum landing.

C. G. position-Most forward for maximum landing weight.

Wing flaps-Retracted and maximum landing position.

Landing gear-Extended.

Engines Power off, propellers windmilling.

(2) Test procedure and required data. It should be possible to maintain handsoff longitudinal trim at a speed not in excess of 1.4 V11 with the wing flaps retracted and extended. This test should be repeated with the most forward C. G. position for landing regardless of weight. The same data specified in § 4b.141-1 (b) should be recorded.

(c) Longitudinal trim during level flight, § 4b.142 (c)—(1) Configuration. This test should be conducted in the configuration that follows:

Weight-maximum takeoff.

C. G. position-most forward and most aft.
Wing flaps-retracted.

Landing gear-retracted and extended. Engines-power required for level flight. Cowl flaps appropriate for flight condition.

(2) Test procedure and required data. It should be possible to maintain handsoff longitudinal trim when demonstrating compliance with § 4b.142 (c).

[Supp. 24, 19 F.R. 4456, July 20, 1954, as amended by Supp. 34, 22 F.R. 6963, Aug. 29, 1957]

(2) Landing gear retracted,

(3) Wing flaps retracted.

(b) In demonstrating compliance with the lateral trim requirement of paragraph (a) of this section, the angle of bank of the airplane shall not be in excess of 5 degrees.

[Amdt. 4b-6, 17 F. R. 1089, Feb. 5, 1952] § 4b.143-1 Procedure for demonstrating longitudinal, directional, and lateral trim (FAA policies which apply to § 4b.143).

(a) Configuration. This test should be conducted in the configuration that follows:

Weight-Maximum take-off.

C. G. position-Most forward.
Wing flaps-Retracted.
Landing gear-Retracted.

Cowl flaps-Appropriate for flight condition. Operating engine(s)—Maximum continuous power.

Critical inoperative engine-Throttle closed on engine most critical for trim, propeller feathered.

(b) Test procedure and required data. It should be possible to maintain handsoff longitudinal, directional, and lateral trim during climb at a speed of 1.4 Vs1. In addition to the data specified in § 4b.141-1 (b), the position of the critical inoperative engine and its corresponding propeller should be recorded.

[Supp. 24, 19 F. R. 4457, July 20, 1954]

§ 4b.144 Trim for airplanes with four or more engines.

The airplane shall maintain trim in rectilinear flight at the climb speed, configuration, and power used in establishing the rates of climb in § 4b.121, with the most unfavorable center of gravity position, and at the weight at which the two-engine-inoperative climb is equal to at least 0.01 V., at an altitude of 5,000 feet.

2

The airplane shall be longitudinally, directionally, and laterally stable in accordance with §§ 4b.151 through 4b.157. Suitable stability and control "feel" (static stability) shall be required in other conditions normally encountered in service if flight tests show such stability to be necessary for safe operation. § 4b.150-1 General stability requirements (FAA policies which apply to § 4b.150).

If an airplane design is encountered in which critical stability conditions may exist other than those prescribed in §§ 4b.151 through 4b.157 they should be investigated.

[Supp. 24, 19 F.R. 4457, July 20, 1954] § 4b.151

Static longitudinal stability.

In the conditions outlined in §§ 4b.152 through 4b.155, the characteristics of the elevator control forces and friction shall comply with the following:

(a) A pull shall be required to obtain and maintain speeds below the specified trim speed, and a push shall be required to obtain and maintain speeds above the specified trim speed. This criterion shall apply at any speed which can be obtained without excessive control force and within the limits of elevator control power except that such speeds need not be greater than the appropriate operating limit speed or need not be less than the minimum speed in steady unstalled flight.

(b) The air speed shall return to within 10 percent of the original trim speed when the control force is slowly released from any speed within the limits defined in paragraph (a) of this section.

(c) The stable slope of stick force curve versus speed shall be such that any substantial change in speed is clearly perceptible to the pilot through a resulting change in stick force.

[15 F.R. 3543, June 8, 1950, as amended by Amdt. 4b-11, 24 F.R. 7068, Sept. 1, 1959] § 4b.151-1 Procedure for demonstrating static longitudinal stability (FAA policies which apply to § 4b.151). (a) Once the airplane has been trimmed, it should tend to maintain the trim speed so that a conscious effort is required by the pilot to depart from that speed. A forward pressure on the control column should be necessary to increase the air speed and the reverse for a decrease in the air speed. These forces should be such that departures in speed in either direction from the trim speed would require control column pressure that increases approximately proportionately as the speed departs from the trim speed.

(b) It should be possible to make such changes in speed as may be required to perform a maneuver without the necessity of readjusting the trim in order to relieve very high control forces which would otherwise be necessary. Figure 3 has been prepared to indicate what should be required in the way of static longitudinal stability qualities.

(c) When conducting the stability tests specified in §§ 4b.152 through 4b.155, the elevator control force required to hold a given stabilized air speed should be measured at air speeds within the range specified by the requirements to define the curve of elevator control force versus air speed. The elevator control force should be measured at intervals of 20 mph in the region where the force indicates definite stability, and at 10 mph intervals when any change in stability becomes apparent. An elevator control force indicator should be installed in the airplane in order to obtain this data. During these tests the airplane should return to an air speed within 10 percent of the original trim speed when the control is released slowly from speeds above and below the trim speed.

[Supp. 24, 19 F. R 4457, July 20, 1954]