Originally posted by PopeyeFAFL
I known that on a big airliner, the landing gear is not design for the maximum take-off weight.
In order word, the landing will occur after burning a substantial amount of fuel (therefore weight).
I vaguely remember in my aeronautic Engineering classes, that trying to design a landing gear (for a large aircraft) for the maximum take-off weight
will lead to a diverging solution.
The necessary added weight of that landing gear, if it could be design, for the extra fuel weight will required bigger engine, needed even more fuel
and aircraft mass, which will required an even stronger landing gear, so on and so forth (technical impossibility).
Could someone confirm that.
You have your terms mixed up - of course the landing gear is designed for the maximum takeoff weight, as that is the weight the landing gear has to
sustain when taking off fully loaded. Happens every day on long haul flights.
The term you are looking for is the Maximum Landing Weight.
The problem with the Maximum Landing Weight is not necessarily the landing gear - aircraft can and do land while above the MLW (even to the Maximum
Takeoff Weight) in emergencies, with no immediate problem.
The issue is the amount of stress it places on the entire airframe - landing above the MLW places much more stress on the airframe than landing below
the MLW. This shortens the life of the airframe, and can in some situations trigger an inspection of certain parts of the airframe.
Airports also do not take kindly to aircraft landing on their runways above the rated energy - more weight impacting the runway means more energy is
transferred to the runway, which means the runway needs inspecting as well.
So to answer your question - the landing gear is certainly designed to handle a landing at the MTOW, it just requires extra care and attention
afterward to ensure the airframe has not been overstressed. Theres no reason to design an aircraft to do over-heavy landings every day as they are an
emergency situation only.
Also the assertion that the perpetual weight addition will result in an ever diverging solution is wrong - there is always a 'sweet spot' to aim
For example, you know that to handle a landing at MTOW, the airframe will require strengtening which will need W amount of weight.
You know that a weight increase of W will, according to known data, result in a fuel burn increase of X.
You also know that a weight increase of W+X will, again according to known data, require a thrust increase of Y.
Your engine manufacturer will tell you that a thrust increase will require an additional weight increase of eW and an additional fuelburn of eX.
However, your engine manufacturer is already taking that into consideration when building your new engine, so instead of going round and round in
circles with regard to the engine being bigger, thus weighing more, thus requiring a bigger engine, you now just have a more powerful engine.
So now you know the sweet spot the change to your airframe will require.
[edit on 19/6/2009 by RichardPrice]