Not very much is being heard of performances of dirigible balloons just
at present. They have shown themselves to be lacking in stanchness
and effectiveness under reasonable variations of weather. We must
have fabrics that are stronger for their weight and more impervious.
Envelopes must be so built structurally as to resist deformation at
high speeds, without having any greatly increased weight. A cheap way
of preparing pure hydrogen gas is to be desired.
Most important of all, the balloon must have a higher speed, to make it
truly dirigible. This, with sufficient steering power, will protect it
against the destructive accidents that have terminated so many balloon
careers. Here again arises the whole question of power in relation
to motor weight, though not as formidably as is the case with the
aeroplane. The required higher speeds are possible now, at the cost
merely of careful structural design, reduced radius of action, and
reduced passenger carrying capacity.
Better altitude control will be attained with better fabrics and
the use of plane fin surfaces at high speeds. The employment of a
vertically-acting propeller as a somewhat wasteful but perhaps finally
necessary measure of safety may also be regarded as probable.
[Illustration: GIRAUDON'S WHEEL AEROPLANE]