Which is limiting Actual Wing Load or Load factor?

[Field In Sight]

If an aircraft has a limit of +3.8g and weighs 1000 kg it can sustain a load on the wings of 3800 kg.

So if the weight reduces to say 500 kg (assuming no ZFW limit) it can still sustain a load of 3800 kg but this gives a load factor of 3800/500 = 7.6g.

Do designers set the limit for the worst case scenario i.e. max weight and anything lighter just adds a little bit of safety?

FIS.

[Old Aero Guy]

Although the wing could stand more load in the example you cite, you may need to worry about other items on the airplane.
For instance, the engine still weighs the same. Pulling more than 3.8g may over stress the engine mounts.

[Intruder]

Depends on the airplane.

Military fighter airplanes have both G limits and total load limits. At high gross weights, the G limit is reduced from the "Max G."

Most civil airplanes have only a G limit published.

The long-term issue is one called "low cycle fatigue." In fighters, the number of times an airplane is stressed to X or Y Gs is significant. The greater the number of Gs, the fewer number of cycles can be safely attained over the lifetime of the airframe, and that number goes exponentially lower for each increment of higher G.

In carrier-based aircraft, arrested landings are a factor. In civil airliners, Takeoff and Landing "Cycles" are a factor.

Exceeding a set number of cycles of G, landings, or other limiting stress may not guarantee that something will break, but will increase the probability beyond the design safety factors -- and also increase the probability something will break at lower stress.

[747FOCAL]

All aircraft are certified to the 9g gust condition. :ok:

[john_tullamarine]

.. which gust condition is that ?

Good to see OAG around ... thought you must have lost interest in the site .....