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ITA – Instituto Tecnológico de Aeronáutica

Part 25 § 25.473 – Landing load conditions and assumptions.

(a)(1). For the landing conditions specified in § 25.479 to 25.485 the airplane is assumed to contact the ground- (2). In the attitudes defined in § 25.479 and § 25.481; (3). With a limit descent velocity of 10 fps at the design landing weight (the maximum weight for landing conditions at maximum descent velocity); and (4). With a limit descent velocity of 6 fps at the design take-off weight (the maximum weight for landing conditions at a reduced descent velocity). (5). The prescribed descent velocities may be modified if it is shown that the airplane has design features that make it impossible to develop these velocities.

(b). Airplane lift, not exceeding airplane weight, may be assumed unless the presence of systems or procedures significantly affects the lift.

(c). The method of analysis of airplane and landing gear loads must take into account at least the following elements: (1). Landing gear dynamic characteristics. (2). Spin-up and springback. (3). Rigid body response. (4). Structural dynamic response of the airframe, if significant.

(d). The landing gear dynamic characteristics must be validated by tests as defined in Sec. 25.723(a)

(e). The coefficient of friction between the tires and the ground may be established by considering the effects of skidding velocity and tire pressure. However, this coefficient of friction need not be more than 0.8.

Part 25 § 25.479 – Level landing conditions.

(a). In the level attitude, the airplane is assumed to contact the ground at forward velocity components, ranging from VL1 to 1.25 VL2 parallel to the ground under the conditions prescribed in § 25.473 with-

(1). VL1 equal to Vso (TAS) at the appropriate landing weight and in standard sea level conditions; and

(2). VL2 equal to Vso (TAS) at the appropriate landing weight and altitudes in a hot day temperature of 41 degrees F. above standard.

(3). The effects of increased contact speed must be investigated if approval of downwind landings exceeding 10 knots is requested.

(b). For the level landing attitude for airplanes with tail wheels, the conditions specified in this section must be investigated with the airplane horizontal reference line horizontal in accordance with Figure 2 of Appendix A of this part.

(c). For the level landing attitude for airplanes with nose wheels, shown in Figure 2 of Appendix A of this part, the conditions specified in this section must be investigated assuming the following attitudes:

(1). An attitude in which the main wheels are assumed to contact the ground with the nose wheel just clear of the ground; and

(2). If reasonably attainable at the specified descent and forward velocities, an attitude in which the nose and main wheels are assumed to contact the ground simultaneously.

Part 25 § 25.479 – Level landing conditions.

(d). In addition to the loading conditions prescribed in paragraph (a) of this section, but with maximum vertical ground reactions calculated from paragraph (a), the following apply:

(1). The landing gear and directly affected attaching structure must be designed for the maximum vertical ground reaction combined with an aft acting drag component of not less than 25% of this maximum vertical ground reaction.

(2). The most severe combination of loads that are likely to arise during a lateral drift landing must be taken into account. In absence of a more rational analysis of this condition, the following must be investigated:

(i). A vertical load equal to 75% of the maximum ground reaction of §25.473 must be considered in combination with a drag and side load of 40% and 25% respectively of that vertical load.

(ii). The shock absorber and tire deflections must be assumed to be 75% of the deflection corresponding to the maximum ground reaction of §25.473(a)(2). This load case need not be considered in combination with flat tires.

(iii). The combination of vertical and drag components is considered to be acting at the wheel axle centerline.

Part 25 § 25.481– Tail-down landing conditions.

(a). In the tail-down attitude, the airplane is assumed to contact the ground at forward velocity components, ranging from V L1 to VL2 parallel to the ground under the conditions prescribed in § 25.473 with-

(1). VL1 equal to VS0 (TAS) at the appropriate landing weight and in standard sea level conditions; and

(2). VL2 equal to VS0 (TAS) at the appropriate landing weight and altitudes in a hot-day temperature of 410F. above standard.

(3). The combination of vertical and drag components considered to be acting at the main wheel axle centerline.

(b). For the tail-down landing condition for airplanes with tail wheels, the main and tail wheels are assumed to contact the ground simultaneously, in accordance with figure 3 of appendix A. Ground reaction conditions on the tail wheel are assumed to act-

(1). Vertically; and

(2). Up and aft through the axle at 45 degrees to the ground line.

(c). For the tail-down landing condition for airplanes with nose wheels, the airplane is assumed to be at an attitude corresponding to either the stalling angle of the maximum angle allowing clearance with the ground by each part of the airplane other than the main wheels, in accordance with figure 3 of appendix A, whichever is less.

Landing speed calculations.

tw

L

s

twL

sL

V

V

V

VVV

VVV

2

0

2hd landing

01sd landing

(tas) 25,1

(tas)

airplane stall speed for standard operation at sea level with flaps in the appropriate landing configuration

airplane stall speed for hot day operation at 41oF above standard at the maximum airport altitude for which the airplane will be certified

0 for aircraft certified for tail winds of 10 kn or less; Vtw is the tail wind when the airplane is to be certified for tail winds greater than 10 kn

0

002

02

22

2

2

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5,0

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VV

TT

TRTP

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VV

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SVCW

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hdsdL

sdhd

hdsdsdshds

hdssds

whdssL

wsdssL

1,043511,6470,61,230313.500

1,042524,0483,01,163710.000

1,039559,7518,71,00000

Thd, oRT0, oRAlt., ft 0 0TThd

Hot day atmospheric parameters

Landing speed calculations: Example.

Sw, ft2 1.951

Vtw, kn 15

0, slug/ft3 0,002378

Airplane data Condition parameters

Altitude, ft 0 13.500 0 13.500

Temperature, oR 518,7 470,6 518,7 470,6

Temperature hot day, oR 559,7 511,6 559,7 511,6

(density ratio)-0,5 = (0/)0,5 1 1,2303 1 1,2303

Landing flap, degrees 30 30 25 25

Maximum landing weight, lb 198.000 198.000 198.000 198.000

CL stall 2,779 2,779 2,630 2,630

Vs0, keas 103,8 103,8 106,7 106,7

Tail wind, ktas 15 15 15 15

VL1, ktas 103,8 127,7 106,7 131,3

VL2, ktas 107,9 133,2 110,9 136,9

Minimum landing speed, ktas 103,8 127,7 106,7 131,3

Maximum landing speed, ktas 149,8 181,5 153,6 186,1

Two point landing conditions.

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CG

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D

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Two-point level landing

Two-point tail-down landing

Two-point level landing analysis.

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Gear loads, load factors and accelerations will vary with time during the impact landing. By neglecting the engine thrust term, the resulting pitching acceleration will be conservative if the engine line of action is below the CG line. It should be noted that the aerodynamic pitching moment about the CG is assumed zero throughout the airplane oleo stroke.

Rigid airplane two-point level landing analysis.

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The load factor and pitching acceleration equations may be simplyfied if one:

a) considers VMGR and VMGL known (either obtained from drop test data or other acceptable analytical analyses);

b) assumes that the drag load acting on the main landing gear is equal to 0,25 of the maximum vertical ground reaction per FAR §25.479 (d)(1);

c) neglects the thrust term in the pitching moment equation

Airplane Wheels/gear MLW, lb VMG, lb nz

A 4 247.000 137.800 2,12

B 2 135.000 93.200 2,38

C 2 161.000 107.600 2,34

D 2 114.000 96.900 2,70

E 2 121.000 97.000 2,60

F 4 198.000 120.000 2,21

sgear wheel nose of radius rolling

sgear wheelmain of radius rolling

;

hipótese a feita é se

1

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Three-point level landing analysis.

The three-point landing conditions are usually critical for the nose gear and related support structure, and the main gear landing loads are critical for the two-point landing conditions.

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Rigid airplane three-point level landing analysis.

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The load factor and pitching acceleration equations may be simplyfied if one:

a) considers VMGR and VMGL are known (either obtained from drop test data or other acceptable analytical analyses);

b) assumes that the drag load acting on the landing gears is equal to 0,25 of the maximum vertical ground reactions per FAR §25.479 (d)(1);

c) neglects the thrust term in the pitching moment equation;

d) Assumes that Teng = D during landing.

Part 25 § 25.483 – One wheel landing conditions.

For the one-gear landing conditions, the airplane is assumed to be in the level attitude and to contact the ground on one main landing gear, in accordance with Figure 4 of Appendix A of this part. In this attitude-

(a). The ground reactions must be the same as those obtained on that side under § 25.479(d)(1), and

(b). Each unbalanced external load must be reacted by airplane inertia in a rational or conservative manner.

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Maximum spin-up and spring-back conditions.

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HV

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VD

T = tempo para acelerar a roda à velocidade periférica VH

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a) T > tz

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b) T < tz (mais comum)

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Maximum spin-up and spring-back conditions.

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Part 25 § 25.485 – Side load conditions.

In addition to § 25.479(d)(2) the following conditions must be considered:

(a). For the side load condition, the airplane is assumed to be in the level attitude with only the main wheels contacting the ground, in accordance with figure 5 of appendix A.

(b). Side loads of 0.8 of the vertical reaction (on one side) acting inward and 0.6 of the vertical reaction (on the other side) acting outward must be combined with one-half of the maximum vertical ground reactions obtained in the level landing conditions. These loads are assumed to be applied at the ground contact point and to be resisted by the inertia of the airplane. The drag loads may be assumed to be zero.

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Part 25 § 25.487 – Rebound landing condition.

(a). The landing gear and its supporting structure must be investigated for the loads occurring during rebound of the airplane from the landing surface.

(b). With the landing gear fully extended and not in contact with the ground, a load factor of 20.0 must act on the unsprung weights of the landing gear. This load factor must act in the direction of motion of the unsprung weights as they reach their limiting positions in extending with relation to the sprung parts of the landing gear.

Absorção da energia do movimento vertical.

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§ 25.723 -- Shock absorption tests.(a). The analytical representation of the landing gear dynamic characteristics that is used in determining the landing loads must be validated by energy absorption tests. A range of tests must be conducted to ensure that the analytical representation is valid for the design conditions specified in Sec. 25.473.(1). The configurations subjected to energy absorption tests at limit design conditions must include at least the design landing weight or the design takeoff weight, whichever produces the greater value of landing impact energy.(2). The test attitude of the landing gear unit and the application of appropriate drag loads during the test must simulate the airplane landing conditions in a manner consistent with thedevelopment of rational or conservative limit loads.(b). The landing gear may not fail in a test, demonstrating its reserve energy absorption capacity, simulating a descent velocity of 12 f.p.s. at design landing weight, assuming airplane lift not greater than airplane weight acting during the landing impact.(c). In lieu of the tests prescribed in this section, changes in previously approved design weights and minor changes in design may be substantiated by analyses based on previous tests conducted on the same basic landing gear system that has similar energy absorption characteristics.(Amdt. 25-23, Eff. 5/8/70); (Amdt. 25-46, Eff. 12/1/78);, (Amdt. 25-72, Eff. 8/20/90), (Amdt. 25-103, Eff. 6/15/2001)§ 25.725 --Reserved.(Amdt. 25-23, Eff. 5/8/70), (Amdt. 25-103, Eff. 6/15/2001)§ 25.727 -- Reserved.(Amdt 25-23, Eff. 5/8/70), (Amdt. 25-103, Eff. 6/15/2001)

Part 25 § 25.723 – Shock absortion tests.

Ensaios de queda livre.

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potencial Energia

5,0 cinética Energia

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Peso Vd, ft/s Altura, in

Condição de projetoMLW 10 18,7

MTOW 6 6,7

Reserva de energia MLW 12 27,0

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Peso equivalente.

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(a). The airplane, although it may be damaged in emergency landing conditions on land or water, must be designed as prescribed in this section to protect each occupant under those conditions.(b). The structure must be designed to give each occupant every reasonable chance of escaping serious injury in a minor crash landing when- (1). Proper use is made of seats, belts, and all other safety design provisions; (2). The wheels are retracted (where applicable); and (3). The occupant experiences the following ultimate inertia forces acting separately relative to the surrounding structure: (i). Upward, 3.0g. (ii). Forward, 9.0g. (iii). Sideward, 3.0g on the airframe; and 4.0g on the seats and their attachments. (iv). Downward, 6.0g. (v). Rearward, 1.5g.(c). For equipment, cargo in the passenger compartments and any other large masses, the following apply: (1). Except as provided in subparagraph (2) of this paragraph, these items must be positioned so that if they break loose they will be unlikely to: (i). Cause direct injury to occupants; (ii). Penetrate fuel tanks or lines or cause fire or explosion hazard by damage to adjacent systems; or (iii). Nullify any of the escape facilities provided for use after an emergency landing. (2). When such positioning is not practical (e.g. fuselage mounted engines or auxiliary power units) each such item of mass shall be restrained under all loads up to those specified in paragraph (b)(3) of this section. The local attachments for these items should be designed to withstand 1.33 times the specified loads if these items are subject to severe wear and tear through frequent removal (e.g. quick change interior items).(d). Seats and items of mass (and their supporting structure) must not deform under any loads up to those specified in paragraph (b)(3) of this section in any manner that would impede subsequent rapid evacuation of occupants.

Part 25 § 25.561 – Emergency landing conditions - General.

(a). The seat and restraint system in the airplane must be designed as prescribed in this section to protect each occupant during an emergency landing condition when-(1). Proper use is made of seats, safety belts, and shoulder harnesses provided for in the design; and(2). The occupant is exposed to loads resulting from the conditions prescribed in this section.(b). Each seat type design approved for crew or passenger occupancy during takeoff and landing must successfully complete dynamic tests or be demonstrated by rational analysis based on dynamic tests of a similar type seat, in accordance with each of the following emergency landing conditions. The tests must be conducted with an occupant simulated by a 170-pound anthropomorphic test dummy, as defined by 49 CFR part 572, subpart B, or its equivalent, sitting in the normal upright position.(1). A change in downward vertical velocity ( V) of not less than 35 feet per second, with the airplane's longitudinal axis canted downward 30 degrees with respect to the horizontal plane and with the wings level. Peak floor deceleration must occur in not more than 0.08 seconds after impact and must reach a minimum of 14g.(2). A change in forward longitudinal velocity ( V) of not less than 44 feet per second, with the airplane's longitudinal axis horizontal and yawed 10 degrees either right or left, whichever would cause the greatest likelihood of the upper torso restraint system (where installed) moving off the occupant's shoulder, and with the wings level. Peak floor deceleration must occur in not more than 0.09 second after impact and must reach a minimum of 16g. Where floor rails or floor fittings are used to attach the seating devices to the test fixture, the rails or fittings must be misaligned with respect to the adjacent set of rails or fittings by at least 10 degrees vertically (i.e., out of parallel) with one rolled 10 degrees.

Part 25 § 25.562 – Emergency landing dynamic conditions.

(c). The following performance measures must not be exceeded during the dynamic tests conducted in accordance with paragraph (b) of this section:(1). Where upper torso straps are used for crewmembers, tension loads in individual straps must not exceed 1,750 pounds. If dual straps are used for restraining the upper torso, the total strap tension loads must not exceed 2,000 pounds.(2). The maximum compressive load measured between the pelvis and the lumbar column of the anthropomorphic dummy must not exceed 1,500 pounds.(3). The upper torso restraint straps (where installed) must remain on the occupant's shoulder during the impact.(4). The lap safety belt must remain on the occupant's pelvis during the impact.(5). Each occupant must be protected from serious head injury under the conditions prescribed in paragraph (b) of this section. Where head contact with seats or other structure can occur, protection must be provided so that the head impact does not exceed a Head Injury Criterion (HIC) of 1,000 units. The level of HIC is defined by the equation:

Where t1 is the initial integration time, t2 is the final integration time, and a(t) is the total acceleration vs. time curve for the head strike, and where (t) is in seconds, and (a) is in units of gravity (g).(6). Where leg injuries may result from contact with seats or other structure, protection must be provided to prevent axially compressive loads exceeding 2,250 pounds in each femur.(7). The seat must remain attached at all points of attachment, although the structure may have yielded.(8). Seats must not yield under the tests specified in paragraphs (b)(1) and (b)(2) of this section to the extent they would impede rapid evacuation of the airplane occupants.

Part 25 § 25.562 – Emergency landing dynamic conditions.