Weights, with some degree of freedom, are apparently used in the roofs of tall buildings, to take out resonances triggered by wind.
Great reference Falcon, thanks...
As to the reference to weights added to the King Air wings, I do not know the details of the modification, my experience testing King Airs and Navajos with wing tip survey booms has me thinking that added weights might have more to do with altering the natural frequency of the wings, rather than a C of G change in the wing as a unit.
I would expect that this is similar to Bell Helicopter's "Noda-matic" suspension system, though I cannot find a photo of that. It works with small weights, with some freedom of motion in a vertical plane acting sort of as servo masses to the rest of the suspension system of the helicopter. It took out vibration. Eurocopter has something similar under the front cabin floor of AS350's.
I'm no expert on this subject, but I can't see how the above can hold true. How could the addition of weight in the fuselage possibly affect the wing mountings, when the wing mountings are not supporting the weight of any fuel?
Don't think about it on the ground, think about a steep turn.
Raisbeck have a number of mod kits for the King Air, and one of them increases MAUW. One thing they do in this mod, at the cost of a small increase in empty weight, is add weights to the wingtips.
Though there may be other reasons (C of G), the wing bending load into the wing fuselage joint (or across the single spar, in the case of the Hawker 800) is the main reason for stating MZFW. That is why wingtip fuel tanks are popular on some types, and indeed for many twin Cessnas, the tips are the mains, so you will always have fuel in them last.
During aircraft modification work we do, we often capitalize on this characteristic, whether a limitation or not, by adding wing mounted equipment, without increasing the gross weight of the aircraft. This had the effect of shifting payload away from the fuselage to the outboard, and reduces the loads on the wingspar/fuselage joint.
To add, because I don't yet know how to edit...I mean the landing weight, not configuration. The worst case scenario does require the CofG to be calculated with Zero Fuel. If there was no MZFW the graphs would have to extend a long way. MZFW is rarely a limitation that one will stop you flying.
My understanding is ; the more weight in the cabin and the less weight in the wings, then the more stress on the wing spar and wing roots. MZFW is a simple method of calaculating maximum permissible weight in the cabin. It could of course be simply stated as a figure in the POH, but then every aircraft has a different equipment fit and a different empty weight.
I'm no expert on this subject, but I can't see how the above can hold true. How could the addition of weight in the fuselage possibly affect the wing mountings, when the wing mountings are not supporting the weight of any fuel? Also, every Hawker 800 (for example) has an identical MZFW, and yes it is a limitation that is included in the Flight Manual, and it has zero to do with what additional equipment the owner of one Hawker may add to his aircraft.
I suspect that the answer has less to do with structural limitations and more to do with the practicality of writing the CofG limitation graphs for the landing configuration.
It's the same rationale as having a maximum weight of non lifting surfaces in a glider (which will often carry water ballast in the wings)
Flybymike is right. This is mainly an issue for planes with wet wings. It is the structural limit for the wing/fuselage joint. Adding fuel doesn't change much as it close to the center of lift.
MAC (mean aerodynamic chord) has been introduced to compare wings with complex shapes. Not all wings are like hershey-bars on PA28. MAC is the chord of a rectangular wing with the same surface, same center of pressure (lift) at a given AOA. %MAC is used to define CG in Airbusses and Boeings.
