Page images
PDF
EPUB
[blocks in formation]

We the effective weight to be used in the
drop test (pounds);

W=WM for main gear units (pounds),
equal to the static reaction on the
particular unit with the rotorcraft
in the most critical attitude; a
rational method may be used in
computing a main gear static re-
action, taking into consideration
the distance between the direction
of the main wheel reaction and
the aircraft center of gravity;
W=WN for nose gear units (pounds),

equal to the vertical component
of the static reaction which would
exist at the nose wheel, assuming
the mass of the rotorcraft acting
at the center of gravity and exert-
ing a force of 1.0g downward and
0.25g forward;
W=Wr for tail-wheel units (pounds);
(1) equal to the static weight on
the tail-wheel with the rotorcraft
resting on all wheels; (2) equal
to the vertical component of the
ground reaction which would oc-
cur at the tail-wheel assuming
the mass of the rotorcraft acting
at the center of gravity and exert-
ing a force of lg downward with
the rotorcraft in the maximum
nose-up attitude considered in the
nose-up landing conditions. (See
§ 6.246(c).)

h= specified free drop height (inches); L= ratio of assumed rotor lift to the rotorcraft weight;

d= deflection under impact of the tire
(at the approved inflation pres-
sure) plus the vertical component
of the axle travel relative to the
drop mass (inches);

n= limit inertia load factor;
n= the load factor during impact devel-

oped on the mass used in the drop
test (1. e., the acceleration dv/dt
in g's recorded in the drop test
plus 1.0).

(b) Reserve energy absorption drop test. The reserve energy absorption capacity shall be demonstrated by a drop test in which the drop height is equal to 1.5 times the drop height prescribed in paragraph (a) of this section, and the rotor lift is assumed to be not greater than 1.5 times the rotor lift used in the limit drop tests, except that the resultant inertia load factor need not exceed 1.5

times the limit inertia load factor determined in accordance with paragraph (a) of this section. In this test the landing gear shall not collapse.

NOTE: The effect of rotor lift may be considered in a manner similar to that prescribed in paragraph (a) of this section.

[21 F.R. 10291, Dec. 22, 1956, as amended by Amdt. 6-2, 22 F.R. 5568, July 16, 1957; Amdt. 6-4, 24 F.R. 7073, Sept. 1, 1959]

§ 6.240

Ski landing conditions.

The structure of a rotocraft equipped with skis shall be designed in compliance with the loading conditions set forth in paragraphs (a) through (c) of this section:

(a) Up load conditions. (1) A vertical load of Pn and a horizontal load of Pn/4 shall be applied simultaneously at the pedestal bearings, P being the maximum static weight on each ski when the rotorcraft is loaded to the maximum design weight. The limit load factor n shall be determined in accordance with § 6.230 (d).

(2) A vertical load equal to 1.33 P shall be applied at the pedestal bearings. (For P see subparagraph (1) of this paragraph.)

(b) Side load condition. A side load of 0.35 Pn shall be applied in a horizontal plane perpendicular to the center line of the rotorcraft at the pedestal bearings. (For P see subparagraph (a) (1) of this section.)

(c) Torque load condition. A torque load equal to 1.33 P (ft.-lb.) shall be applied to the ski about the vertical axis through the center line of the pedestal bearings. (For P and n see subparagraph (a) (1) of this section.)

§ 6.245 Float landing conditions.

The structure of a rotorcraft equipped with floats shall be designed in compliance with the loading conditions set forth in paragraphs (a) and (b) of this section:

[blocks in formation]

(2) The vertical load prescribed in subparagraph (1) of this paragraph shall be applied together with an aft component equal to 0.25 the vertical component.

(b) Side load condition. The vertical load in this condition equal to 0.75 the vertical load prescribed in paragraph (a) (1) of this section, divided equally between the floats, shall be applied together with a side component. The total side component shall be equal to 0.25 the total vertical load in this condition and shall be applied to one float only.

§ 6.246

Tail-wheel type landing gear ground loading conditions.

The structure of a rotorcraft equipped with landing gears arranged such that two wheels are located forward and one wheel is located aft of the center of gravity, shall be assumed to be subjected to the loading conditions in accordance with paragraphs (a) through (h) of this section.

(a) Level landing on forward gear only. The rotorcraft shall be assumed to be in the level landing attitude with only the forward wheels contacting the ground.

(1) Vertical loads shall be applied in accordance with the provisions of § 6.230.

(2) The vertical loads specified in subparagraph (1) of this paragraph shall be combined with a drag load at each wheel axle of not less than 25 percent of the respective vertical load.

(3) In the conditions of subparagraphs (1) and (2) of this paragraph, unbalanced pitching moments shall be assumed resisted by angular inertia forces.

(b) Level landing; all wheels contacting simultaneously. The rotorcraft shall be assumed to be in the level landing attitude with all wheels contacting the ground simultaneously.

(1) Vertical loads shall be applied in accordance with the provisions of § 6.230.

(2) The vertical loads specified in subparagraph (1) of this paragraph shall be combined with a drag load at each wheel axle of not less than 25 percent of the respective vertical load. Unbalanced pitching moments shall be assumed resisted by angular inertia forces.

(c) Nose-up landing condition. The rotorcraft shall be assumed to contact the ground on the rear wheel only at the maximum nose-up attitude to be ex

pected under all operational landing conditions including landings in autorotation. The conditions of this paragraph need not be applied if it can be demonstrated that the probability of landing with initial contact on the rear wheel is extremely remote. In determining the applicable ground loads, it shall be acceptable to use a rational method to account for the distance between the direction of the rear wheel ground reactions and the rotorcraft c. g.

(1) Vertical loads shall be applied in accordance with the provisions of § 6.230.

(2) The vertical loads specified in subparagraph (1) of this paragraph shall be combined with a drag load at the wheel axle of not less than 25 percent of the vertical load.

(d) One-wheel landing condition. The rotorcraft shall be assumed in the level attitude to contact the ground on one of the wheels located forward of the c. g. The vertical load shall be the same as that obtained on the one side in the condition specified in paragraph (a) (1) of this section. Unbalanced moments shall be assumed resisted by angular inertia forces.

(e) Side load landing condition. The rotorcraft shall be assumed in the landing attitudes of paragraphs (a) and (b) of this section. Side loads in combination with one-half the maximum vertical ground reactions obtained in the landing conditions of paragraphs (a) (1) and (b) (1) of this section shall be applied at each wheel. The magnitude of the side loads on the forward wheels in each case shall be 0.8 of the vertical reaction (on one side) acting inward and 0.6 of the vertical reaction (on the other side) acting outward. The magnitude of the side load on the rear wheel shall be equal to 0.8 of the vertical reaction. These loads shall be applied at the ground contact point, unless the landing gear is of the full-swiveling type in which case the loads shall be applied at the center of the axle. When a lock, steering device, or shimmy damper is provided, the swiveled wheel shall also be assumed to be in the trailing position with the side load acting at the ground contact point.

(f) Braked roll condition. The rotorcraft attitudes shall be assumed to be the same as those prescribed in paragraphs (a) and (b) of this section with the shock absorbers deflected to their static position. The limit vertical load

shall be based upon a load factor of 1.33 when the rotorcraft attitude is as specified in paragraph (b) of this section; the limit vertical load factor may be reduced to 1.0 when the attitude is as specified in paragraph (a) of this section. A drag load equal to the vertical load multiplied by a coefficient of friction of 0.8 shall be applied at the ground contact point of each wheel equipped with brakes, except that the drag load need not exceed the maximum value based on limiting brake torque.

(g) Rear wheel turning condition. The rotorcraft shall be assumed to be in the static ground attitude with the shock absorbers and tires deflected to their static position. A vertical ground reaction equal to the static load on the rear wheel in combination with a side component of equal magnitude shall be assumed. When a swivel is provided, the rear wheel shall be assumed to be swiveled 90 degrees to the rotorcraft longitudinal axis with the resultant load passing through the axle. When a lock, steering device, or shimmy damper is provided, the rear wheel shall also be assumed to be in the trailing position with the side load acting at the ground contact point.

(h) Taxiing condition. The rotorcraft and its landing gear shall be designed for loads which occur when the rotorcraft is taxied over the roughest ground which it is reasonable to expect in normal operation.

[Amdt. 6-2, 22 F.R. 5568, July 17, 1957, as amended by Amdt. 6-4, 24 F.R. 7073, Sept. 1, 1959]

[blocks in formation]

The structure of a rotorcraft equipped with skid type landing gear shall be assumed to be subjected to the loading conditions in accordance with paragraphs (a) through (d) of this section.

(a) The design weight, center of gravity and load factor shall be in accordance with the provisions of § 6.230. Structural yielding of the elastic spring member under the limit loading conditions shall be acceptable. The design ultimate loads considered for the elastic spring member need not exceed those obtained in a drop test of the skid gear from a drop height equal to 1.5 times that specified in § 6.237(a) with the assumed rotor lift not to exceed 1.5 times the rotor lift

used in the limit drop tests prescribed in § 6.237(a).

(b) The ground loads resulting from the landing conditions specified in paragraph (c) of this section shall be applied to the skid gear in its most critically deflected position for the particular landing condition being considered and a rational distribution of the ground reactions along the skid tube bottom shall be made.

(c) The following landing conditions shall be considered:

(1) Level landing; vertical reactions. The rotorcraft shall be assumed to contact the ground along the bottom of both skids. Vertical ground reactions shall be applied in accordance with the provisions of paragraphs (a) and (b) of this section.

The

(2) Level landing with drag. rotorcraft shall be assumed to contact the ground along the bottom of both skids with vertical ground reactions in combination with a horizontal drag reaction equal to 50 percent of the vertical reaction applied at the ground. The resultant ground load shall be equal to the vertical load specified in subparagraph (1) of this paragraph and shall be directed through the center of gravity of the rotorcraft.

(3) Level landing with side load. The rotorcraft shall be assumed to contact the ground along the bottom of both skids with vertical ground reactions in combination with a horizontal side reaction equal to 25 percent of the vertical ground reaction. The vertical ground reaction shall be equal to the vertical load specified in subparagraph (1) of this paragraph and shall be equally divided between the two skids. The total side load shall be applied along the length of one skid only. Unbalanced moments shall be assumed resisted by angular inertia forces. Both the inward and outward acting side loading conditions for the skid gear shall be investigated.

(4) One-skid landing condition. In the level attitude, the rotorcraft shall be assumed to contact the ground on one skid only. The vertical load shall be the same as that obtained on the one side in the condition specified in subparagraph (1) of this paragraph. Unbalanced moments shall be assumed to be resisted by angular inertia forces.

(d) Special conditions for the skid gear: (1) A ground reaction load equal to 1.33 times the maximum weight of the rotorcraft acting up and aft at an angle of 45 degrees to the horizontal shall be assumed. The load shall be distributed symmetrically between the two skids and shall be assumed concentrated at the forward end of the straight portion of the skid tube. This loading condition shall apply only to the forward end of skid tube and its attachment to the rotorcraft.

(2) A vertical ground reaction load equal to one-half the vertical load of paragraph (c) (1) of this section shall be assumed with the rotorcraft in the level attitude. This load shall be applied to the skid tube and shall be assumed concentrated at a point midway between the skid tube attachments. This loading condition shall apply only to the skid tube and its attachment to the rotorcraft.

[Amdt. 6-2, 22 F.R. 5568, July 16, 1957, as amended by Amdt. 6-4, 24 F.R. 7073, Sept. 1, 1959]

MAIN COMPONENT REQUIREMENTS § 6.250

Main rotor structure.

The requirements of paragraphs (a) through (f) of this section shall apply to the main rotor assemblies including hubs and blades.

(a) The hubs, blades, blade attachments, and blade controls which are subject to alternating stresses shall be designed to withstand repeated loading conditions. The stresses of critical parts shall be determined in flight in all attitudes appropriate to the type of rotorcraft throughout the ranges of limitations prescribed in § 6.204. The service life of such parts shall be established by the applicant on the basis of fatigue tests or by other methods found acceptable to the Administrator.

(b) The main rotor structure shall be designed to withstand the critical flight loads prescribed in §§ 6.210 through 6.213.

(c) The main rotor structure shall be designed to withstand the limit loads prescribed in §§ 6.210 through 6.213 under conditions of autorotation necessary for normal operation. The rotor rpm used shall be such as to include the effects of altitude.

(d) The rotor blades, hubs, and flapping hinges shall be designed to withand a loading condition simulating the

force of the blade impact against its stop during operation on the ground.

(e) The rotor assembly shall be designed to withstand loadings simulating other critical conditions which might be encountered in normal operation.

(f) The rotor assembly shall be designed to withstand, at all rotational speeds including zero, the maximum torque likely to be transmitted thereto in both directions. If a torque limiting device is provided in the transmission system the design limit torque need not be greater than the torque defined by the limiting device, except that in no case shall the design limit torque be less than the limit torque specified in § 6.251 (c). The design torque shall be distributed to the rotor blades in a rational manner. § 6.250-1

Service life of main rotors

(FAA policies which apply to § 6.250 (a)).

Several methods which have been found acceptable by the Administrator for determining the service life of main rotors are outlined in Appendix A1 of this section for the guidance of the industry in complying with § 6.250 (a). [Supp. 6, 16 F. R. 8405, Apr. 19, 1951] § 6.251 Fuselage, landing gear, and rotor pylon structure.

The requirements of paragraphs (a) through (d) of this section shall apply to the fuselage, landing gear, and rotor pylon structure.

(a) The structure shall be designed to withstand the critical loads prescribed in §§ 6.210 through 6.213. It shall be permissible to represent the resultant rotor force as a single force applied at the hub attachment point. The balancing and inertia loads occurring under the accelerated flight conditions as well as the thrust from auxiliary rotors shall be considered.

(b) The structure shall be designed to withstand the applicable ground loads prescribed in §§ 6.230 through 6.245.

(c) The engine mount and adjacent fuselage structure shall be designed to withstand loads occurring in the rotorcraft under the accelerated flight and landing conditions, including the effects of engine torque loads. In the case of engines having 5 or more cylinders, the limit torque shall be obtained by multi

1 Not filled with the Office of the Federal Register.

[blocks in formation]

The requirements of paragraphs (a) through (c) of this section deal with emergency conditions of landing on land or water in which the safety of the occupants is considered, although it is accepted that parts of the rotorcraft may be damaged.

(a) The structure shall be designed to give every reasonable probability that all of the occupants, if they make proper use of the seats, belts, and other provisions made in the design (see § 6.355), will escape serious injury in the event of a minor crash landing (with wheels up if the rotorcraft is equipped with retractable landing gear) in which the occupants experience the following ultimate inertia forces relative to the surrounding structure.

(1) Upward 1.5g (downward 4.0g). (2) Forward 4.0g.

(3) Sideward 2.0g.

(b) The use of a lesser value of the downward inertia force specified in paragraph (a) of this section shall be acceptable if it is shown that the rotorcraft structure can absorb the landing loads corresponding with the design maximum weight and an ultimate descent velocity of 5 fps without exceeding the value chosen.

(c) The inertia forces specified in paragraph (a) of this section shall be applied to all items of mass which would be apt to injure the passengers or crew if such items became loose in the event of a minor crash landing, and the supporting structure shall be designed to restrain these items.

Subpart D-Design and Construction

§ 6.300 Scope.

GENERAL

The rotorcraft shall not incorporate design features or details which experience has shown to be hazardous or unreliable. The suitability of all questionable design details or parts shall be established by tests.

[blocks in formation]

The suitability and durability of all materials used in the rotorcraft structure shall be established on the basis of experience or tests and shall conform to approved specifications which will insure their having the strength and other properties assumed in the design data. § 6.302 Fabrication methods.

The methods of fabrication employed in constructing the rotorcraft structure shall be such as to produce a consistently sound structure. When a fabrication process such as gluing, spot welding, or heat treating requires close control to attain this objective, the process shall be performed in accordance with an approved process specification.

[blocks in formation]
« ՆախորդըՇարունակել »