MAX STRUCTURAL TOW vs POWER PLANT THRUST RATING

[bflyer]

HI GENTELMEN

I would appreciate your thoughts on the following subject

Is the max. structural TOW of a transport aircraft (i.e B 727) purely a function of an aircraft's landing gear design or is it a combination of landing gear structural design and power plant thrust rating?
and if so...what is the interrelation of these two components and any other components in the determination of the max structural TOW

thank you

[Intruder]

It's a matter of certification.
Many things come into the equation, including wings, landing gear, and thrust. It's not just a matter of 1-time ability, but engineering tests and studies to ensure it can be safely done for the predicted life of the airplane and its components (life cycle fatigue).

YOU may get away with an overweight takeoff or landing, but you may set up your buddy for an untimely structural failure...

[411A]

An example follows.
Lockheed L1011-1 with RR RB.211-22B engines.

Normal MTOW 440,000 pounds (later serial numbers).

However, if certain landing gear modifications and heavy wheels are fitted (and permission is obtained from Lockheed), the MTOW can be increased to 466,000 pounds.

[glhcarl]

411A,

It takes a little more than gear and wheel changes to incease the MTOW of an L-1011 to 466K. Center section fuel (1 wet bay) is required, and structural beef ups in the fuselage and wing.

The same modification that takes an L-1011 to 466K can be increased to 474K with the addition of RB-211-524's.

Add two more wet bays and the MTOW goes to 510K.

An interesting fact is that the L-1011-500's MTOW can be increased from 496K to 514K with nothing but AFM changes.

[chornedsnorkack]

Look at it this way: a plane which is overweight can fail in different ways.

It can exceed structural strength somewhere and break, whether it is landing gear that breaks, or wing, or fuselage.

Or else it may be unable to take off and climb.

An airplane where all engines have failed, or where no engines have been built to begin with, is a glider and it cannot climb or take off. But it has structural weight limits.

So, if you derate your engines, your plane at structural MTOW climbs slower. Eventually, you reach a point where the plane cannot climb steep enough to clear obstacles or certification climb limits, but still can climb at some lower weight.

The same happens if you operate the plane from a hotter or higher airport - the climb rate on structural MTOW decreases but remains adequate to a certain point, then decreases too much, so the plane becomes restricted to lower take-off weights.

It then depends on the design of the plane and engines, ambient air density as well as obstacles and runway length whether the plane can reach structural MTOW or not. But it is not exactly safe to exceed structural MTOW. A plane which has overpowered engines, low and cold conditions or long runway ahead might climb steeper and get airborne in a shorter distance, but exceeding structural MTOW might break something.

[SNS3Guppy]

I believe the question isn't about MTOW for a particular takeoff, but MGTOW at certification limits. One factor not mentioned, and far more critical than the landing gear rating (which is rated to support a static load far in excess of the certificated MGTOW or ramp weight) is wing bending moment.

The specific reasons for a specific airpalne being restricted to a specific weight rest with the manufacturer, and that's where your question must be asked.

[Mad (Flt) Scientist]

Also, some operators choose to have lower MTOWs declared for their aircraft, since landing fees can be impacted. So there may not even be a true technical reason on a specific type.