G limits. The specification (No. 7/30) for the prototype Spitfire called for the following,
5 Structural Strength
(a) The strength of the main structure when carrying the load specified in paragraph 3, plus 100 lb shall not be less than as specified hereunder ——
Load factor throughout the structure with the centre of pressure in its most forward position 9.0.
Load factor for wing structure with the centre of pressure in its most backward position in horizontal flight 6.0
Load factor in terminal nose dive 1.75
Inverted Flight
(1) Load factor at incidence corresponding to the inverted stall and with C.P. at 1/3 of chord 4.5
(2) Load factor at incidence appropriate to steady horizontal inverted flight and at the maximum speed of horizontal normal flight 4.5
(b) The alighting gear must be able to withstand an impact at a vertical velocity of 10 feet per second and at this velocity the load on the alighting gear must not exceed three times the fully loaded weight of the aircraft.
(c) When subject to the impact forces on alighting, as specified above, the load factor for the alighting gear must not be less than 1-1 /3, and for the remainder of the structure not less than 1-1/2. The load factor for the structure and the attachment fittings of the alighting gear must always be greater than that for the alighting gear itself by the margin indicated above.
(d) The maximum weight per wheel of the aircraft in pounds must not exceed 12 times the product of the wheel and tyre diameters in inches with the aircraft carrying the full load specified above.
(e) The above factors are to be determined by the approved official methods as published by the DTD and the detail requirements given in A.P.970 are also to be satisfied. With a view to minimising the risk of flutter, attention should be given to the recommendations of A.P.l 177, particularly as regards the static balance of ailerons.
(f`) The wing is to be sufficiently rigid to withstand satisfactorily any torsional or other loads which may be encountered during service operations.
(g) Ribs (both mainplane and tail unit) are required to develop, on test, factors 20% greater than those specified for the aircraft as a whole.
Many a Spitfire was lost due to overstressing.