One % of takeoff weight is *huge*. On a B747 with MTOW of 300 tons, that is a weight saving of 3,000 kg, weight that needs not be lugged around for the couple of decades that the aircraft will be flying.

At the aircraft factory where I used to work, there were Idea Boxes everywhere where one could deposit suggestions for weight savings, every kg saved adds to improvement of fuel economy. How much depends on range and a whole lot of other factors, and can be quantified for specific aircraft.

1%. *Yuuge*.

If we make an estimate for a B747-400 flying maximum range of 12,700 km according to slide 7/14 out of [this presentation][1].

[![enter image description here][2]][2]

MTOW is given as 400,000 kg, fuel weight as 175,000 kg, this makes $W_{final}$ = MTOW - $W_{fuel}$ = 225,000 kg. With 1% saving, MTOW is reduced to 396,000 kg. Range stays the same if $\frac{W_{init}}{W_{final}}$ stays the same. So the new $W_{final}$ becomes:

$$ W_{final} = \frac{396,000}{400,000}\cdot 225,000 = 222,750 kg$$

$W_{final}$ is again MTOW - $W_{fuel}$ => 

$$W_{fuel} = MTOW - W_{final} = 396,000 - 222,750 = 173,250 kg$$

Final fuel saving is 175,000 - 173,250 = **1,750 kg**

For one long distance, maximum range flight, a reduction of 1% in TO weight saves 1,750 kg of fuel.

  [1]: https://www.slideserve.com/rhona/intro-to-aerodynamics-learning-objectives
  [2]: https://i.sstatic.net/mbfpX.png