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# Landing Gear vs Max Take-Off Weight.

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posted on Jun, 18 2009 @ 09:54 PM
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.

P.S.: I'm not taking about small aircraft nor the fact that it will be silly to design it for max take-off weight, just the diverging aspect of such solution.

posted on Jun, 19 2009 @ 10:57 AM

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.

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]

posted on Jun, 19 2009 @ 11:09 AM
Military aircraft also have this issue and in particularly with carrier based aircraft the 'bring home weight" is a real issue.

If I recall correctly, the max load out of 6 Pheonix missiles for the F-14 resulted in a configuration that was unable to land unless it dropped some ordinance.

For the A380 its 839,950lb www.aviationpast.com...
For the 747-8 its 682.000 lbs

www.boeing.com...

The above link is interesting it also lists a max Taxi weight which is 3000 pounds more than the MTOW

posted on Jun, 22 2009 @ 06:41 AM

Originally posted by FredT
The above link is interesting it also lists a max Taxi weight which is 3000 pounds more than the MTOW

Yes, that fuel will be burnt off during taxiing, and the aircraft should be down to MTOW when set for takeoff.

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