has five times the lift of the present 2,000,000 cubic feet
capacity rigid, but the length of the former is only 1.7 times
greater, and therefore the weight of the structure only five
times greater (1.7); that is, the weight of the structure is
directly proportional to the total lift. Having seen that the
total lift varies as the cube of the linear dimensions while air
resistance, B.H.P.--other things being equal--vary as the square
of the linear dimensions,it follows that the ratio "weight of
machinery/total lift" decreases automatically.

In comparing the different methods of transport for efficiency,
the resistance or thrust required is compared as a percentage of
the total weight. The result obtained is known as the
"co-efficient of tractive resistance." Experiments have shown
that as the size of the airship increases, the co-efficient of
tractive resistance decreases to a marked extent; with a
proportionate increase in horse-power it is proportionally more
economical for a 10,000,000 cubic feet capacity rigid to fly at
80 miles per hour than for a 2,000,000 cubic feet capacity to fly
at 60 miles per hour.

As the ratio "weight structure/total lift" is in airships fairly
constant, it follows that the ratio "disposable lift/total lift"
increases with the dimensions.

It is therefore obvious that increased benefits are obtained by
building airships of a larger size, and that the bigger the ship
the greater will be its efficiency, providing, of course, that it
is kept within such limits that it can be handled on the ground
and manoeuvred in the air.