Calculation of Certified MTOW
 

Can somebody please explain how an aeroplanes MTOW is calculated for certification purposes?

I don't mean the standard w&b questions to establish an aircraft's weight and C of G, as I'm comfortable with that, but how does Mr. Cessna establish that his 172 can only carry a maximum of 2300/2400lbs.

I'm supposing that it has to do with the structural strength of the airframe, but then can't quite get my head around the fact that when Mr. Douglas put water/methanol injected Wright Cyclones on the standard DC6, he increased the MTOW by 10000lbs, nor why there is a 100lb gain between the 172R and S models, even though there is only a 20hp difference in power output from the (exact same but de-rated) engine.

TIA

Duchess

The structure is only one factor in MTOM. The certification requirements also demand certain levels of performance for each category of aircraft, so putting more power in will usually result in an increased MTOM