CS 25.511 Ground load: unsymmetrical loads on multiple-wheel units

(a)General. Multiple-wheel landing gear units are assumed to be subjected to the limit ground loads prescribed in this Subpart under sub-paragraphs (b) through (f) of this paragraph. In addition –

(1)A tandem strut gear arrangement is a multiple-wheel unit; and

(2)In determining the total load on a gear unit with respect to the provisions of sub-paragraphs (b) through (f) of this paragraph, the transverse shift in the load centroid, due to unsymmetrical load distribution on the wheels, may be neglected.

(b)Distribution of limit loads to wheels; tyres inflated. The distribution of the limit loads among the wheels of the landing gear must be established for each landing, taxying, and ground handling condition, taking into account the effects of the following factors:

(1)The number of wheels and their physical arrangements. For truck type landing gear units, the effects of any see-saw motion of the truck during the landing impact must be considered in determining the maximum design loads for the fore and aft wheel pairs.

(2)Any differentials in tyre diameters resulting from a combination of manufacturing tolerances, tyre growth, and tyre wear. A maximum tyre-diameter differential equal to two-thirds of the most unfavourable combination of diameter variations that is obtained when taking into account manufacturing tolerances, tyre growth and tyre wear, may be assumed.

(3)Any unequal tyre inflation pressure, assuming the maximum variation to be ±5% of the nominal tyre inflation pressure.

(4)A runway crown of zero and a runway crown having a convex upward shape that may be approximated by a slope of 1·5% with the horizontal. Runway crown effects must be considered with the nose gear unit on either slope of the crown.

(5)The aeroplane attitude.

(6)Any structural deflections.

(c)Deflated tyres. The effect of deflated tyres on the structure must be considered with respect to the loading conditions specified in sub-paragraphs (d) through (f) of this paragraph, taking into account the physical arrangement of the gear components. In addition –

(1)The deflation of any one tyre for each multiple wheel landing gear unit, and the deflation of any two critical tyres for each landing gear unit using four or more wheels per unit, must be considered; and

(2)The ground reactions must be applied to the wheels with inflated tyres except that, for multiple-wheel gear units with more than one shock strut, a rational distribution of the ground reactions between the deflated and inflated tyres, accounting for the differences in shock strut extensions resulting from a deflated tyre, may be used.

(d)Landing conditions. For one and for two deflated tyres, the applied load to each gear unit is assumed to be 60% and 50%, respectively, of the limit load applied to each gear for each of the prescribed landing conditions. However, for the drift landing condition of CS 25.485, 100% of the vertical load must be applied.

(e)Taxying and ground handling conditions. For one and for two deflated tyres –

(1)The applied side or drag load factor, or both factors, at the centre of gravity must be the most critical value up to 50% and 40%, respectively, of the limit side or drag load factors, or both factors, corresponding to the most severe condition resulting from consideration of the prescribed taxying and ground handling conditions.

(2)For the braked roll conditions of CS 25.493(a) and (b)(2), the drag loads on each inflated tyre may not be less than those at each tyre for the symmetrical load distribution with no deflated tyres;

(3)The vertical load factor at the centre of gravity must be 60% and 50% respectively, of the factor with no deflated tyres, except that it may not be less than 1 g; and

(4)Pivoting need not be considered.

(f)Towing conditions. For one and for two deflated tyres, the towing load, FTOW, must be 60% and 50% respectively, of the load prescribed.