In the early evening of October 4th 1930, to a cheer from the gathered crowd,
the largest airship of its day, the British R101 cast off from her mooring mast at Cardington
to begin her maiden international voyage from London to Karachi, then part of British India.
In the early hours of the following morning, R101 had reached the north of France,
but was suffering from bad weather, with high winds and rain hampering her progress.
Cursing at over 300 meters the airship was met with turbulent air.
One of the linen panels that covered the hull split open.
She dived into the French countryside, and burst into flames as the hydrogen that filled the airship ignited.
Forty six of the fifty four on board were killed immediately, two more died later in hospital.
What was meant to have marked the beginning of an airship network connecting the far-flung
reaches of the British Empire now burned in the French countryside,
and with it burned Britain’s airship ambitions.
The British program was cancelled and scrap metal from the wreckage was be sold to the Zeppelin Company,
who used it to build another airship, the LZ 129 Hindenburg,
an even bigger airship, whose fiery demise heralded the end of hydrogen filled, rigid hull, airships.
However, the replacement for Hydrogen – Helium –simply doesn’t produce the lift necessary
for large commercial rigid airships;
so in order to get off the ground today’s non-rigid blimps sacrifice the aerodynamic performance
gained with a rigid hull, and are limited to broadcasting whatever advertising message you like
to those watching from the ground.
But what if instead of Helium, Hydrogen was replaced with something even lighter …
… a vacuum.
First, would a vacuum airship theoretically work?
An airship floats because of the principle of buoyancy.
This is an upwards force exerted by a fluid that opposes the weight of an immersed object.
In a body of fluid, pressure increases with depth as a result of the weight of the overlying fluid
So an object immersed in a fluid, such as our atmosphere,
will have more pressure exerted on its lower side than its upper side, this net upwards force is buoyancy.
If this buoyancy force exceeds the downwards gravitational force exerted on the object,
the object will float.
For example if the density of a balloon is equal to the surrounding air, it will be neutrally boyant
just as if it were air.
If the density is increased, meaning more mass is in the same volume,
the increased mass will result in a larger gravitational force pushing downwards and the balloon will sink.
But if the density is lower, then the reduced mass will mean a reduced gravitational force
and the buoyant force will drive the balloon upwards.
A vacuum, you may be unsurprised to hear, has no mass, therefore no downwards gravitational force
It would provide the maximum possible displacement lift;
able to lift a mass equivalent to the displaced fluid.
For air that is 1.28 grams per litre.
This fact has lead many people to suggest building a vacuum airship;
including Arthur De Bausse who petitioned the United States congress for funding.
The House Committee on Ventilation and Acoustics, who after dealing with their primary jurisdiction
were being useful by considering other issues, recommended providing funding.
However, this funding was insufficient to build the craft and so De Bausse withdrew his application.
In any case, If built, it wouldn’t have flown, as the problem with a vacuum airship
isn’t its hypothetical buoyancy but the pressure itself.
The pressure that causes an airship to fly can also crush it
standard atmospheric pressure is just over one hundred thousand Pascal
the equivalent of almost six and a half tesla model 3’s sitting on every square meter of hull.
A modern blimp resists this pressure, and maintains its shape
due to the outward pressure of the lifting gas balancing this force from the atmosphere.
But a vacuum airship has no such benefit, and must resist this pressure only through structural integrity.
While it’s possible to construct an object that can withstand these forces
the weight margins on an airship are incredibly tight. The density of hydrogen is just 7% that of air
so in order to be functionally equivalent to the hydrogen filled airships of the past
the unloaded weight of a Vacuum airship cannot be increased by even 20%
beyond that of the fabric covered body of the old airships.
This, so far hasn’t been achieved
and no homogeneous material can even theoretically achieve both the strength and weight requirements.
Perhaps, in the future, a composite material can be made light and strong enough
to make such an airship possible, but don’t hold your breath
because at that point we have replaced an airship filled with a gas that could lead to a devastating explosion
with one filled with something that could lead to an equally devastating implosion.