(3) In order to insure that an accurate recording of the indicated angleof-attack is obtained, the sensing device should be located in a region where tuft surveys show that the streamlines undergo no radical change in direction up to the maximum angle contemplated. Regions well forward of the wing leading edge are desirable to keep the angular difference between true angle and indicated angle as small as possible.

(4) Means for indicating the stall warning point and the point at which the pilot is informed by the inherent flight characteristics that the airplane is stalled should be provided. This may consist of a light on the photopanel op(1) Stalls-straight flight.

erated by a switch mounted on the control wheel. In order to insure that the camera records the light image a time delay device may need to be incorporated in the light circuit in cases where camera speed is low.

(c) Configuration. Stalls should be conducted in the configurations noted in the following listings and with cowl flaps appropriate for the flight condition. Power off stalls should be conducted with the engines idling and propellers in low pitch. For power on conditions, stalls should be conducted with that power necessary to maintain level flight at a speed of 1.6 Vs, with flaps in the approach position, landing gear retracted and maximum landing weight.

May be demonstrated during stalling speed tests.

Take-off.

occurrence of the stall should be obtained. In addition to the data obtained on the photopanel shown in paragraph (b) (1) of this section, the following information should also be recorded: Weight.

C. G. position.

Ambient air temperature.
Wing flap position.

Landing gear position.

Engines, rpm and manifold pressure.

(e) Data analysis. Time histories should be plotted of the photopanel instruments. The stalling warning point (see § 4b.162-1) and the point at which "the inherent flight characteristics give a clear indication that the airplane is stalled" should be noted on the plots.

(1) Inspection of the plots will then show if the following two conditions are fulfilled:

(i) The indicated angle-of-attack increases steadily to a value measurably beyond that for maximum lift, and

(ii) The stall is evident to the pilot prior to initiation of recovery.

(2) Consideration should be given to the following points in the time-history analysis:

(i) The direction in which the elevator is moving, i. e., any nose down pitch or decrease in load factor not induced by inadvertent elevator motion,

(ii) Rudder and aileron movement with respect to uncontrollable roll,

(iii) The effect of lag in the air-speed system,

(iv) Rate of air speed change,

(v) Effect of pitching velocity or rolling velocity on indicated angle-of-attack. If possible, angle-of-attack time history should be drawn through points where pitching or rolling velocity are small. If corrections are unavoidable, the angular correction is simply tan- pd/V where p is the rolling or pitching velocity, V is the true air speed, and d is the distance from the pitch or rolling axis, as the case may be, to the sensing device. It should be noted that this correction is applicable to either true or indicated angle-of-attack.

(vi) The indicated acceleration is a function of the angle the vertical axis of the accelerometer makes with the perpendicular to the earth's surface. Therefore, bank angle will seriously affect the maximum lift point. For example, a bank of 45° without loss of lift will result

in a drop in indicated acceleration from 1.00 to .707. As a result acceleration data obtained in the region of Czmax. should be disregarded or corrected for bank angle when the bank angle exceeds nine or ten degrees.

[Supp. 24, 19 F. R. 4459, July 20, 1954] § 4b.161 Stalling; asymmetrical power.

(a) The airplane shall be safety recoverable without applying power to the inoperative engine when stalled with:

(1) The critical engine inoperative, (2) Flaps and landing gear retracted, (3) The remaining engines operating up to 75 percent of maximum continuous power, except that the power need not be greater than that at which the wings can be held level laterally with the use of maximum control travel.

(b) It shall be acceptable to throttle back the operating engines during the recovery from the stall.

§ 4b.161-1 Procedure for demonstrating stall test, asymmetrical power (FAA policies which apply to § 4b.161).

(a) Control of airplane. During this test the airplane should not become uncontrollable or lose an excessive amount of altitude when so stalled.

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

Weight-Maximum take-off.
C. G. position-Most aft.
Wing flaps-Retracted.

Landing gear-Retracted.

Operating engine (s)-Power up to 75 percent maximum continuous power, cow! flaps optional.

Critical inoperative engine-Propeller optional, feathered or windmilling, cowl flaps appropriate for flight condition. Trim speed-1.4 V81'

(c) Test procedure and required data. This test may be conducted at any optional altitude (see § 4b.100-3 (c)). See § 4b.160 (c) regarding test procedure.

(1) The speed of the airplane should be reduced from the trim condition with the wings held level until the first of the following occurs:

(i) Full rudder or aileron deflection.
(ii) 180 lbs. rudder force.

(iii) Stall is reached.

(2) If full rudder or aileron deflection, or the 180 lbs. rudder force occurs first, the power should be reduced and the test

repeated until sufficient control is available to complete the stall. The power may be reduced on the operating engine(s) before reapplying power on the operating engine or engines for the purpose of regaining level flight. The following data should be recorded at that point:

Pressure altitude.

Ambient air temperature.
Indicated air speed.

Engines, rpm and manifold pressure.
Torque pressure.

Carburetor air temperature.

Rudder force (if desirable).

(3) If stall is reached first, the same data should be recorded.

[Supp. 24, 19 F. R. 4460, July 20, 1954] § 4b.162 Stall warning.

Clear and distinctive stall warning shall be apparent to the pilot with sufficient margin to prevent inadvertent stalling of the airplane with flaps and landing gear in all normally used positions, both in straight and in turning flight. It shall be acceptable for the warning to be furnished either through the inherent aerodynamic qualities of the airplane or by a device which will give clearly distinguishable indications under all expected conditions of flight.

NOTE: A stall warning beginning at a speed 7 percent above the stalling speed is normally considered sufficient margin. Other margins may be acceptable depending upon the degree of clarity, duration, and distinctiveness of the warning and upon other characteristics of the airplane evidenced during the approach to the stall.

[Amdt. 4b-5, 16 F. R. 12220, Dec. 4, 1951] § 4b.162-1 Stall warning (FAA policies

which apply to § 4b.162).

(a) The adequacy of stall warning should depend on the relative ease with which an airplane might be inadvertently stalled following the occurrence of stall warning. For example, if unmistakable warning occurs only 2 percent above the stall speed but undue pilot effort is required to reduce the air speed to the stall, the speed margin of 2 percent may be adequate. On the other hand if conscious effort is required to avoid stalling the airplane, a positive type of warning initiated at a relatively high speed above the stall may be required.

(b) Suggested suitable stall warnings are, buffeting which may be defined as

general shaking or vibration of the airplane or elevator shake of sufficient magnitude to be unmistakable; or a stall warning instrument such as a stick shaker. A visual stall warning device which requires the attention of the crew within the cockpit is not considered acceptable by itself.

[Supp. 24, 19 F. R. 4460, July 20, 1954]

GROUND HANDLING CHARACTERISTICS

§ 4b.170 Longitudinal stability and control.

(a) There shall be no uncontrollable tendency for landplanes to nose over in any reasonably expected operating condition or when rebound occurs during the landing or take-off.

(b) Wheel brakes shall operate smoothly and shall exhibit no undue tendency to induce nosing over.

(c) When a tail-wheel landing gear is used it shall be possible during the takeoff ground run on concrete to maintain any attitude up to thrust line level at 80 percent of Vs,.

§ 4b.170-1 Procedure for demonstrating longitudinal stability and control on the ground (FAA policies which apply to § 4b.170).

Taxiing tests at velocities up to 70 percent of the stalling speed should be conducted on smooth and rough ground which may likely be encountered under normal operating conditions. Particular attention should be paid to the following:

(a) Taxiing over rough ground. There is some evidence to indicate that critical loads can be built up in taxiing over rough ground, even when the shock-absorbing system is entirely satisfactory with respect to capacity for landing purposes.

(b) Brakes. Their adequacy when maneuvering on the ground and their tendency to cause nosing-over should be investigated. Any bad tendency will normally be exaggerated when taxiing in a strong side or tail wind.

[Supp. 24, 19 F. R. 4460, July 20, 1954]

§ 4b.170-2 Longitudinal stability and control with reverse thrust (FAA policies which apply to § 4b.170). The policies outlined in § 4b.402-1 (a), (d), and (e) will apply.

[Supp. 25, 20 F. R. 2277, Apr. 8, 1955]

(a) There shall be no uncontrollable ground-looping tendency in 90° cross winds of velocity up to 0.2 Vs, at any ground speed at which the airplane is expected to operate.

(b) All landplanes shall be demonstrated to be satisfactorily controllable with no exceptional degree of skill or alertness on the part of the pilot in power-off landings at normal landing speed during which brakes or engine power are not used to maintain a straight path.

(c) Means shall be provided for directional control of the airplane during taxiing.

§ 4b.171-1

Procedure for demonstrating direction stability and control on the ground (FAA policies which apply to § 4b.171).

(a) Compliance with the requirement of § 4b.171(a) may be demonstrated during tests for the establishment of the cross wind component velocity in accordance with § 4b.173.

(b) Compliance with the requirement of § 4b.171 (b) may be demonstrated during power off landings in other tests.

(c) Compliance with the requirement of § 4b.171 (c) may be demonstrated during taxiing prior to take-off or after landing from other flight tests. [Supp. 24, 19 F. R. 4460, July 20, 1954] § 4b.171-2 Directional stability and control with reverse thrust (FAA policies which apply to § 4b.171). The policies outlined in § 4b.402-1 (a), (d), and (e) will apply. [Supp. 25, 20 F. R. 2278, Apr. 8, 1955] § 4b.171-3 Directional stability and

control with an antiskid device installed (FAA policies which apply to § 4b.170).

The policies outlined in § 4b.337-4 will apply.

[Supp. 28, 21 F. R. 2558, Apr. 19, 1956] § 4b.172 Shock absorption.

The shock absorbing mechanism shall not produce damage to the structure

when the airplane is taxied on the roughest ground which it is reasonable to expect the airplane to encounter in normal operation.

§ 4b.172-1 Shock absorbing mechanism tests (FAA policies which apply to § 4b.172).

The shock absorbing mechanism should be checked for satisfactory operation while taxiing, taking-off and landing during other tests in the type certification program.

cross

[Supp. 24, 19 F. R. 4460, July 20, 1954] § 4b.173 Demonstrated cross wind. There shall be established a component of wind velocity at which it has been demonstrated to be safe to take off or land.

§ 4b.173-1

Cross wind demonstration (FAA policies which apply to § 4b.173).

(a) Cross wind component. A cross wind component of not less than 0.2 V.. should be established during type tests. Consequently, two results are possible:

(1) A cross wind component may be established at a value which is not marginal with the airplane's handling characteristics. This value should be included in the Operating Procedures section of the Airplane Flight Manual. The operation of the aircraft in cross winds greater than the value specified is not necessarily a hazard. Thus operation in cross winds of a greater value is entirely within the discretion of the operator.

(2) A critical cross wind component may be established at a value which is considered the maximum up to which it is safe to operate the airplane on the ground, including take-offs and landings. This value should be shown in the Operating Limitations section of the Airplane Flight Manual. Operation of the airplane in cross winds above the maximum safe value is considered hazardous and the operator should do so only on the same emergency basis that a pilot would be justified in exceeding any of the operating limitations such as air speed, engine rpm, C. G. limitations, etc.

(3) An operator may of course restrict the operation of his airplane to cross wind components of any value equal to or less than that established during the type certification tests.

(b) Configuration. This test should be conducted in the configurations that follow:

Weight-Maximum take-off and landing.
C. G. position-Most aft.
Flaps-Take-off and maximum landing posi-
tions.

(c) Test procedure and required data. At least three take-offs and landings should be made in cross wind components of 0.2 Vs, mph (or greater at applicant's option) to demonstrate satisfactory controllability and handling characteristics. The magnitude and direction of the cross wind should be established by the use of appropriate meteorological instruments.

[Supp. 24, 19 F. R. 4460, July 20, 1954] § 4b.173-2 Ground handling characteristics with reverse thrust (FAA policies which apply to § 4b.173).

The policies outlined in § 4b.402-1 (a) and (d) will apply.

[Supp. 25, 20 F. R. 2278, Apr. 8, 1955]

WATER HANDLING CHARACTERISTICS

The following wind velocities shall be established:

(a) A lateral component of wind velocity not less than 0.2Vs, at and below which it has been demonstrated that the seaplane is safe for taking off and alighting under all water conditions in which the seaplane is likely to be operated;

(b) A wind velocity at and below which it has been demonstrated that the seaplane is safe in taxiing in all directions, under all water conditions in which the seaplane is likely to be operated.

[Amdt. 4b-6, 17 F.R. 1089, Feb. 5, 1952] § 4b.181-1 Cross wind demonstration (FAA policies which apply to § 4b.181).

Policies outlined in § 4b.173-1 will apply.

[Supp. 24, 19 F. R. 4461, July 20, 1954]

§ 4b.182 Control and stability on the

water.

(a) In taking off, taxiing, and alighting, the seaplane shall not exhibit the following:

(1) Any dangerously uncontrollable porpoising, bouncing, or swinging tendency;

(2) Any

submerging of

auxiliary floats or sponsons, any immersion of wing tips, propeller blades, or other parts of the seaplane which are not designed to withstand the resulting water loads;

(3) Any spray forming which would impair the pilot's view, cause damage to the seaplane, or result in ingress of an undue quantity of water.

(b) Compliance with paragraph (a) of this section shall be shown under the following conditions:

(1) All water conditions from smooth to the most adverse condition established in accordance with § 4b.180;

(2) All wind and cross-wind velocities, water currents, and associated waves and swells which the seaplane is likely to encounter in operation on water;

(3) All speeds at which the seaplane is likely to be operated on the water;

(4) Sudden failure of the critical engine, occurring at any time while the airplane is operated on water;

(5) All seaplane weights and center of gravity positions within the range of loading conditions for which certification is sought, relevant to each condition of operation.

(c) In the water conditions of paragraph (b) of this section and the corresponding wind conditions the seaplane shall be able to drift for 5 minutes with engines inoperative, aided if necessary by a sea anchor.

[Amdt. 4b-6, 17 F. R. 1089, Feb. 5, 1952] § 4b.182-1 Procedure for demonstrating control and stability on the water (FAA policies which apply to § 4b.182).

(a) In order to check water stability, taxiing tests should be made in a cross wind determined in accordance with § 4b.181.

(b) Porpoising tendencies should be investigated and reported for extreme loading conditions.

(c) The ability to maneuver up to and while on the step should be investigated and the results reported.