how and who came up with this rule? Is there any science behind it? ++++++++++++++++++++
No science at all, only BS. Most netters already know this, but just in case ...... If the aircraft weighs 900lb, then 1G (gravity) is 900lbs. The rated load factor of 7G means the relevant part of the structure was tested /calculated to withstand seven times static weight - it can thus handle 7x900=6,300lb - that is what 7G means. You can literally put 6300lbs* of sand bags on the wing (properly spread out to represent the load) to establish the -G limit - or load the inverted airplane to establish the positive load factor. The structural strength does not change if we make it heavier, so the tested or calculated capability is still 6300lbs. If we add another 100lbs of structure, fuel, cargo, passenger etc., the MAUW will be 1000lbs and the G capability will be 6300/1000=6.3G (not 7-1=6G) If we add 400lbs (increase the MAUW to 1300lbs), then 6300/1300=4.85G (not 7-4=3G) Apply this rationale to a Cherokee typical MAUW of maybe 2000lbs and a load factor of +5.6G 2000x5.6=11,200. Apply the BS rule (1G /100lbs) 2100lbs reduces the LF to +4.6G?? The truth: 11200/2100=5.33G When we talk about load factors it is important to know: The aircraft has a CALCULATED load factor of +7G / -7G? Or, the aircraft has a DEMONSTRATED load factor of .......? Tested (loaded) to +7G with no permanent structural damage /distortion? Or, tested to destruction, i.e. failed (or permanent damage) at +7G (often referred to as the ultimate load factor). Everything in /on the airplane is subjected to G forces, not only the wing. A fuel tank could pop out the bottom of a wing if the mountings are not capable of restraining the load of the tank plus fuel at X times its static weight. Counter-balance weights (elevator) were discussed on the net recently - they must also be able to withstand any G loads that the airplane may be subjected to. We generally see G loads as pilot induced - steep turns, pull-ups etc. The discomfort of G forces will keep the pilot aware of the effects - may even cause him/her to black-out. (The blood trying to get to your brain is also subjected to the same G load (acceleration). G loads caused by turbulence scare me, they are invariably unexpected and can be very harsh. They are instantaneous, leaving no time to take any compensating action. That is why store bought airplanes have a placarded manoeuvring speed (* not strictly true - some of the wing weight will be excluded) Have a great weekend Steve J
