VTOL.2210 Structural design loads

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(a) The applicant must:

(1) determine structural design loads resulting from likely externally or internally applied pressure, force or moment which may occur in flight, ground and water operations, ground- and water-handling, and while the aircraft is parked or moored;

(2) determine the loads required by VTOL.2210(a)(1) at all critical combinations of parameters, on and within the boundaries of the structural design envelope; and

(3) the magnitude and distribution of these loads must be based on established physical principles within the structural design envelope.

MOC VTOL.2210 Structural Design Loads

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1. Loads (General)

CS 27.301(b) and (c) Amdt. 6 is accepted as a means of compliance.

Methods used to determine load intensities and distributions should be validated by flight load measurement unless the methods used for determining those loading conditions are shown to be reliable or conservative.

2. Flight Loads (General)

CS 27.321(a) Amdt. 6 is accepted as a means of compliance.

Note: more detailed MOC on flight loads to be accounted for are available in MOC VTOL.2215.

3. Design Fuel Loads

For aircraft with disposable fuel, the following is applicable:

(a) The disposable load combinations should include each fuel load in the range from zero fuel to the selected maximum fuel load.

(b) If fuel is carried in the wings or other aerodynamic elements, the maximum allowable weight of the aircraft without any fuel in this tank(s) should be established as “maximum zero wing fuel weight” or “maximum zero ‘aerodynamic element’ fuel weight”, if it is less than the maximum weight.

(c) For Category Enhanced, a structural reserve fuel condition, not exceeding the fuel necessary for compliance with VTOL.2430(b)(4), may be selected, considering the most critical fuel distribution. If a structural reserve fuel condition is selected, it should be used as the minimum fuel weight condition for showing compliance with the flight load requirements of MOC VTOL.2215 and:

(1) The structure should be designed to withstand a condition of zero fuel in the wing or aerodynamic element at limit loads corresponding to:

(i) 90 percent of the manoeuvring load factors defined in MOC VTOL.2200, and

(ii) Gust velocities equal to 85 percent of the values prescribed in MOC VTOL.2200.

(2) The durability evaluation of the structure should account for any increase in operating stresses resulting from the design condition of (c)(1).

(3) The flutter, deformation, and vibration requirements should also be met with zero fuel in the wings or aerodynamic elements.

4. Jacking loads

CS 23.507 Amdt. 4 is accepted as a means of compliance

5. Mooring loads

(a) The mooring fittings and its support structure should be analysed for the loads resulting from the maximum permissible mooring wind speed multiplied by 1.11.

(b) The wind should be considered as acting parallel to the ground in any direction to the aircraft.  Ground gust conditions should also be considered.

(c) All permissible mooring configurations, i.e. number of mooring lines and their range of angles from the aircraft fitting, should be evaluated.

(d) The maximum wind speed and gust conditions for mooring and the permissible mooring configurations should be published in the Aircraft Maintenance Manual.

6. Towing loads (towbar)

CS 23.509 Amdt. 4 is accepted as a means of compliance for towing an aircraft with the use of a towbar.

7. Towbarless towing (aircraft with wheeled landing gear)

(a) General

Towbarless towing vehicles are generally considered as ground equipment and are as such not subject to direct approval by the certifying agencies. However, these vehicles should be qualified in accordance with the applicable SAE ARP documents. It should be ensured that the nose landing gear and supporting structure is not being overloaded (by static and dynamic (including fatigue) loads) during towbarless towing operations with these vehicles. This should be ensured by the applicant, either by specific investigations as described in (b) and (c) below, or alternatively, by publishing aircraft load limitations in a towbarless towing vehicle assessment document, to allow towbarless towing vehicle manufacturers to demonstrate their vehicles will not overload the aircraft.

(b) Limit static load cases

(1) For the limit static load cases, the investigation may be conducted by rational analysis supported by test evidence.

(2) The investigation should take into account the influence on the towing loads of the tractive force of the towing vehicle including consideration of its weight and pavement roughness.

(3) The investigation should include all towbarless towing operation scenarios.

(4) Operations that are explicitly prohibited need not be addressed.

(c) Durability evaluation

(1) Durability evaluation of the impact of towbarless towing on the airframe should be conducted under the provision of VTOL.2240.

(2) The contribution of the towbarless towing operational loads to the fatigue load spectra for the nose landing gear and its support structure needs to be evaluated.

(3) The impact of the towbarless towing on the certified life limits of the landing gear and supporting structure should be determined.

(4) The fatigue spectra used in the evaluation should:

(i) consist of typical service loads encountered during towbarless towing operations, which cover the loading scenarios noted above for static considerations, and

(ii) be based on measured statistical data derived from simulated service operation or from applicable industry studies.

(d) Other considerations

(1) Specific combinations of towbarless towing vehicle(s) and aircraft that have been assessed as described above and have been found to be acceptable, along with any applicable towing instructions and/or limitations should be specified in the Instructions for Continued Airworthiness and in the Aircraft Flight Manual.

(2) Aircraft braking, while the aircraft is under tow, may result in loads that exceed the aircraft’s design load and may result in structural damage and/or nose gear collapse. For these reasons, the aircraft manufacturer should ensure that the appropriate information is provided in the Aircraft Maintenance Manual and in the Aircraft Flight Manual to preclude aircraft braking during normal towbarless towing. Appropriate information should also be provided in the Instructions for Continued Airworthiness to inspect the affected structure should aircraft braking occur, for example in an emergency situation.

8. Ground loads: unsymmetrical loads on multiple-wheel units

(a) Pivoting loads. CS 23.511(a) Amdt. 4 is accepted as a means of compliance

(b) Unequal tyre loads. The loads established under MOC VTOL.2220 level landing, tail-down and one-wheel landing conditions should be applied in turn, in a 60/40% distribution, to the dual wheels and tyres in each dual wheel landing gear unit.

(c) Deflated tyre loads. For the deflated tyre condition –

(1) 60% of the loads established under the MOC VTOL.2220 level landing, tail-down and one-wheel landing conditions should be applied in turn to each wheel in a landing gear unit; and

(2) 60% of the limit drag and sideloads and 100% of the limit vertical load established under the MOC VTOL.2220 sideload, lateral drift and braked roll conditions, or lesser vertical load obtained under (1), should be applied in turn to each wheel in the dual wheel landing gear unit.

VTOL.2215 Flight load conditions

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(a) Critical flight loads must be established for symmetrical and asymmetrical loading from all combinations of flight parameters and load factors at and within the boundaries of the manoeuvre and gust envelope:

(1) at each altitude within the operating limitations, where the effects of compressibility are taken into account when significant;

(2) at each mass from the design minimum mass to the design maximum mass; and

(3) at any practical but conservative distribution of disposable load within the operating limitations for each altitude and weight.

(b) Vibration and buffeting must not result in structural damage

(1) up to dive speed.

(2) within the limit flight envelope.

(c) Flight loads resulting from a likely failure of an aircraft system, component, or lift/thrust unit must be determined.

MOC VTOL.2215 Flight load conditions

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The following flight load conditions specify a set of flight conditions to be evaluated to conservatively cover the most extreme manoeuvring capability of the aircraft. They should be analysed with the aircraft in the most critical flight phases and flight configurations, in accordance with the design limitations as defined in MOC VTOL.2200. The flight load cases may be simulated or defined by combining conservative combinations of parameters, or a combination of these approaches. Full control input ranges should be considered when determining the flight load cases. The limitations imposed by the flight control system, without failure cases, may be taken into account.

Failure conditions need not be considered, except as specified in paragraph (h) of this MOC.

If automation systems, such as autopilot upper modes, or a Detect and Avoid system can generate higher control loads than pilot inputs, the corresponding loads should be taken into account.

Suddenly. For the purposes of this MOC, ‘suddenly’ is defined as the time interval for complete control input based on a rational analysis, supported by test. For conventional pilot controls, such as stick and pedal, ‘suddenly’ may be assumed as 0.2 seconds for complete control inputs.

(a) Symmetrical Flight Load Conditions: To produce these flight load conditions, the airspeeds should be set at V_D in forward, rearward and sideward flight. The normal load factor should be unity.

(b) Symmetrical pull-up and recovery: To produce these flight load conditions, with the aircraft in an initial trim condition at forward speeds:

(1) Displace the input control suddenly in order to achieve a nose up motion, to the maximum deflection as limited by the control stops;

(2) Maintain the maximum input control displacement to allow the aircraft to pitch upwards and achieve the specified positive manoeuvring load factor; and

(3) Return the  input control suddenly to that required for level flight.

The most critical initial trim forward speeds should be evaluated, up to and including V_D. This flight load condition should be evaluated in both power on and power off rpm ranges, if applicable.

The intention of the symmetric pull-up and recovery manoeuvre is to achieve maximum pitch acceleration, maximum positive normal load factor and maximum aircraft nose-up angle-of attack.

(c) Symmetrical Pushover and Recovery:

To produce these flight load conditions, with the aircraft in an initial trim condition at forward speed :

(1) Displace the input control suddenly, in order to achieve a nose down motion, to the maximum deflection as limited by the control stops;

(2) Maintain the maximum input control displacement to allow the aircraft to pitch downwards and achieve the specified negative manoeuvring load factor; and

(3) Return the input control suddenly to that required for level flight.

The most critical initial trim forward speeds should be evaluated, up to and including V_D.

The intention of the symmetric pushover and recovery manoeuvre is to achieve maximum pitch acceleration, maximum negative normal load factor and maximum aircraft nose-down angle-of attack.

(d) Rolling Flight Conditions (Rolling pull-up and recovery):

To produce these flight load conditions, with the aircraft in an initial trim condition at forward speed:

(1) Displace the input control suddenly, in order to achieve a nose up and rolling moment, to the maximum deflection as limited by the control stops, or that necessary to achieve a positive load factor of not less than two-thirds that specified in paragraph (b);

(2) Maintain the control displacements to allow the aircraft to pitch, roll and achieve a positive manoeuvring load factor of at least two-thirds that specified in (b); and

(3) Return the controls suddenly to those required for level flight.

The maximum rate of roll and the load factor should occur simultaneously. The most critical initial trim forward speeds should be evaluated, up to and including V_D.

The intention of the rolling pull-up and recovery manoeuvre is to achieve maximum pitch acceleration, maximum roll acceleration with two-thirds of the maximum positive normal load factor.

(e) Yawing Conditions:

To produce these flight load conditions, with the aircraft in an initial trim condition, with zero yaw, at forward speeds and in the hover:

(1) Displace the input control suddenly, in order to achieve a yawing motion, to the maximum deflection as limited by the control stops;

(2) Maintain the input control displacement to allow the aircraft to yaw to the maximum transient sideslip angle;

(3) Allow the aircraft to attain the resulting sideslip angle; and

(4) Return the directional control suddenly to neutral.

Both right and left yaw conditions should be evaluated. The most critical initial trim forward speeds should be evaluated, from zero up to and including V_NE or V_H, whichever is less.

Yawing conditions in the hover (spot turns) should be evaluated in both in ground effect (IGE) and out of ground effect (OGE).

The intention of the yawing condition is to achieve maximum yaw acceleration and maximum aircraft sideslip angles.

(f) Gust Conditions:

(1) The aircraft should be designed to withstand, at each critical airspeed up to V_D, including hovering, the loads resulting from vertical and horizontal gusts of 9.14 metres per second (30 ft/s).

(2) The aircraft should be designed to withstand, at each critical airspeed up to V_H or V_NE,  whichever is lower, including hovering, the loads resulting from vertical and horizontal gusts of 15.24 metres per second (50 ft/s).

(3) For Category Enhanced, the aircraft should be designed to withstand, at each critical airspeed up to V_B including hovering, the loads resulting from vertical and horizontal rough air gusts of 20.12 m/s (66 ft/s)

(4) The aircraft should be designed to withstand 100% of the vertical gust condition of (0) acting on one side of the aircraft.

(5) The following assumptions should be made:

(i) For wing structures, the shape of the vertical gust is –

Where –

s = Distance penetrated into gust (ft);

= Mean geometric chord of wing (ft) if applicable, or other dimension rationally derived; and

Ude = Derived gust velocity referred to in paragraphs (1) to (3)

(ii) For other structures, and for horizontal gusts, either sharp-edged (instantaneous) gusts or sharp-edged gusts modified by an alleviation (attenuation) factor may be used for calculating aerodynamic loads for the aircraft and any installed stabilizing surfaces.

(g) Take-off from sloping ground

(1) The aircraft should be designed for take-off from level ground and up to the maximum slope and aircraft orientation combinations permitted for operation

(2) Vertical lift/thrust should be the maximum achievable for the take-off configuration of the aircraft

(3) This condition should be evaluated in both in ground effect (IGE) and out of ground effect (OGE)

(h) Unsymmetrical loads due to lift/thrust unit failure:

(1) The aircraft should be designed for unsymmetrical loads resulting from the failure of the critical lift/thrust unit, including blade release, at speeds up to V_D including hover.

(2) The timing and magnitude of the probable pilot or automated corrective action should be conservatively estimated, considering the characteristics of the particular lift/thrust unit and aircraft combination.

(3) In the case of no corrective action being automatically performed, pilot corrective action, may be assumed to be initiated at the time maximum pitching, rolling or yawing velocity is reached, but not earlier than 2 seconds after the lift/thrust unit failure.

(4) Characterisation of the lift/thrust failure may be considered using analysis in lieu of an instantaneous loss of lift/thrust if appropriate, but should be done in a rational and conservative manner, and appropriately verified by test.

VTOL.2220 Ground and water load conditions

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The applicant must determine the structural design loads resulting from taxi, take-off, landing, and handling conditions on the applicable surface in normal and adverse attitudes and configurations.

MOC VTOL.2220 Ground and water load conditions

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1. General

(a) Loads and equilibrium. For limit ground loads –

(1) The limit ground loads obtained in this MOC should be considered to be external loads applied to the aircraft structure as if it were acting as a rigid body; and

(2) If significant, the structural dynamic response of the airframe should be taken into account considering all critical mass distributions; and

(3) In each specified landing condition, the external loads should be placed in equilibrium with linear and angular inertia loads in a rational or conservative manner.

(b) Critical centres of gravity. The critical centres of gravity within the range for which certification is requested should be selected.

2. Ground load conditions and assumptions

(a) For specified landing conditions, all weights should be considered up to the maximum weight. Total lift may be assumed to act through the centre of gravity throughout the landing impact. This lift may not exceed two-thirds of the design maximum weight.

(b) Unless otherwise prescribed, for each specified landing condition, the aircraft should be designed for a limit load factor of not less than the limit inertia load factor substantiated under MOC VTOL.2235 “Limit drop test”.

3. Tyres and shock absorbers

CS 27.475 Amdt. 6 is accepted as a means of compliance.

4. Landing conditions

(a) The following landing conditions apply depending on the configuration of the VTOL

(1) The following landing conditions apply to landing gear with two wheels aft, and one or more wheels forward, of the centre of gravity:

(i) The level landing conditions in CS 27.479 Amdt. 6 are accepted as means of compliance.

(ii) The tail-down landing conditions in CS 27.481 Amdt. 6 are accepted as means of compliance.

(iii) The one-wheel landing conditions in CS 27.483 Amdt. 6 are accepted as means of compliance.

(iv) The lateral drift landing conditions in CS 27.485 Amdt. 6 are accepted as means of compliance.

(v) The braked roll conditions in CS 27.493 Amdt. 6 are accepted as means of compliance.

(2) The ground loading conditions for landing gear with tail wheels in subparagraphs (a) to (h) of CS 27.497 Amdt. 6 are accepted as means of compliance.

(3) The ground loading conditions for landing gear with skids in CS 27.501 Amdt. 6 are accepted as means of compliance.

(b) CTOL aircraft should be designed for the additional loading conditions specified in this paragraph. In showing compliance with this paragraph, the following apply:

(1) The level landing conditions in CS 23.479(a) and (b) Amdt. 4 are accepted as a means of compliance.

(2) The tail down landing conditions in CS 23.481 Amdt. 4 are accepted as a means of compliance.

(3) The one-wheel landing conditions in CS 23.483 Amdt. 4 are accepted as a means of compliance.

(4) The sideload conditions in CS 23.485 Amdt. 4 are accepted as a means of compliance.

(5) The braked roll conditions in CS 23.493 Amdt. 4 are accepted as a means of compliance.

(6) The supplementary conditions for tail wheels in CS 23.497 Amdt. 4 are accepted as a means of compliance.

(7) The supplementary conditions for nose wheels in CS 23.499 Amdt. 4 are accepted as a means of compliance.

(8) The supplementary conditions for ski-planes in CS 23.505 Amdt. 4 are accepted as a means of compliance.

(c) The ski landing conditions in CS 27.505 Amdt.6 are accepted as a means of compliance.

5. Taxiing Condition

(a) CS 27.235 Amdt. 6 is accepted as a means of compliance.

(b) In addition, for aircraft with conventional take-off and landing (CTOL) capability the aircraft should be designed to withstand the loads that would occur when take-offs and landings are performed on unpaved runways having the roughest surface that may be expected in normal operation.

VTOL.2225 Component loading conditions

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(a) The applicant must determine the loads acting upon all relevant structural components, including rotor assemblies, in response to:

(1) interaction of systems and structures;

(2) structural design loads;

(3) flight load conditions;

(4) ground and water load conditions; and

(5) limit input torque from lift/thrust units at any rotational speed.

(b) Reserved.

MOC VTOL.2225 Component Loading Conditions

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1. Engine Torque

(a) For turbine engines, CS 27.361(a) Amdt. 6 is accepted as a means of compliance.

(b) For reciprocating engines, CS 27.361(b) Amdt. 6 is accepted as a means of compliance.

(c) For electrical engines, the limit torque should not be less than the highest of:

(1) The torque imposed by sudden engine stoppage due to malfunction or structural failure (such as rotor jamming), and

(2) The mean torque multiplied by one of the following factors:

(i) 1.25 for engines for which torque oscillations as a function of time are shown to be negligible, i.e. in the same range as a turbine engine

(ii)  for engines for which torque oscillations as a function of time cannot be considered as negligible. expresses the amplitude of the torque oscillations around a mean value as shown below:

2. Unsymmetrical loads for horizontal aerodynamic surfaces

(a) CS 27.427 Amdt. 6 is accepted as a means of compliance for horizontal aerodynamic surfaces that do not have installed lift/thrust units.

(b) In case of a load distribution deviation from CS 27.427 (b) Amdt. 6 and for designs with lift/thrust units installed on the horizontal aerodynamic surface, the applicant is expected to provide the rationale justifying that the selected load distribution conservatively addresses the limit flight load conditions of MOC VTOL.2215. Combinations of unsymmetrical loads, within the design envelope, should be considered including those resulting from asymmetric wing slip-stream effects, lift/thrust unit asymmetric thrust, propeller or lift/thrust unit wake effects and unsymmetrical control surface forces, as applicable. Dedicated flight load and/or wind tunnel measurements should be performed to confirm the suitability of the proposed criteria.

3. Outboard fins or winglets

(a) If outboard fins or winglets are included on the horizontal surfaces or wings, the horizontal surfaces or wings should be designed for their maximum load in combination with loads induced by the fins or winglets and moment or forces exerted on horizontal surfaces or wings by the fins or winglets.

(b) The endplate effects of outboard fins or winglets should be taken into account in applying the flight conditions of MOC VTOL.2215 to the vertical surfaces.

(c) If outboard fins or winglets extend above and below the horizontal surface, the critical vertical surface loading (the maximum load per unit area as determined under MOC VTOL.2215) should be applied as follows:

(1) For configurations where there is no possible influence of the lift/thrust unit wake on the outboard fin or winglet:

(iii) The part of the vertical surfaces above the horizontal surface, with 80% of that loading applied to the part below the horizontal surface; and

(iv) The part of the vertical surfaces below the horizontal surface, with 80% of that loading applied to the part above the horizontal surface;

(2) For configurations with possible influence of the lift/thrust unit wake on the outboard fin or winglet a conservative loading distribution should be determined, supported by flight load and/or wind tunnel measurement.

4. Special Devices

CS 23.459 Amdt. 4 is accepted as a means of compliance.

VTOL.2230 Limit and ultimate loads

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(a) Unless special or other factors of safety are necessary to meet the requirements of this Subpart, the applicant must determine:

(1) the limit loads, which are equal to the structural design loads;

(2) the ultimate loads, which are equal to the limit loads multiplied by a 1.5 factor of safety, unless otherwise provided.

(b) Some strength specifications are specified in terms of ultimate loads only, when permanent detrimental deformation is acceptable.

MOC VTOL.2230 Limit and ultimate loads

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The combination of CS 27.301(a) Amdt. 6 and CS 27.303 Amdt. 6 is accepted as a means of compliance.