he thinks will do the trick, but it hasn’t been proven yet.
If it works like he thinks it will, he said he’ll be happy to
share the name, supplier, and every little detail about it
to help other builders.
Marvin’s development efforts are similar to those of
Dumont’s. He has constructed five different airships, trying different materials and engines on each one. Some
models hardly left the hangar door before some disaster
occurred that ended that particular design. Marvin’s
experiences with his airship No. 2 showed great promise.
Polzien No. 3 did not. No. 4 was a disaster. Polzien No. 5
is another measure of improvement, but
it is plagued with helium leaks; Dumont
had a similar problem up through his
No. 4 airship. Dumont also had a lot of
engine problems, and so has Marvin.
TRIBULATIONS THROUGH THE YEARS
When building airships, several problems have been
common throughout history. If you’re thinking about
building one, you’ll want to consider them beforehand.
Lifting gas leaks and contamination: Dumont experienced this and worked hard at fixing it. Eventually, he
was successful at flying on successive days without adding lifting gas. It is difficult to fly an airship for more
than a week without servicing the lifting gas. It is not
uncommon to have to dump the whole load and start
over. During the era of the spherical hydrogen balloon,
a filling was good for only one flight, and new gas was
used for each successive flight. For commercial airships,
the lifting gas is reprocessed to regain a reasonable lift.
Envelope materials: Envelope materials must be tough
in tensile strength and tearing, lightweight, and easily
seamed together. In addition, the material should be
non-elastic to properly work with ballonet gas pressurization cells. If an envelope is made of elastic materials,
it is difficult to compress the lifting gas to reduce lift.
The balloon simply stretches and little compression is
obtained. Marvin cited this as the biggest challenge in
building an airship. “I don’t know how many different
materials that I’ve used that are not satisfactory,” he
said. “It’s pretty much ‘by guess and by gosh.’ You can’t
believe all of the stuff I’ve got in my hangar that won’t work.”
Envelope rigging: The first necessity of a
long tubular envelope for non-rigid airships is that the envelope must be pressurized to retain its shape. The internal pressure is typically 1. 5 to 2.0 inches of water
head (about 0.06 pounds/square inch). Unfortunately
there is always a fight between leakage and pressure. The
higher the pressure, the faster the gas leaks away. The ballonet and blower is typically used to replace the pressure
due to lifting gas leakage, but in a gas tight envelope the
ballonet can compress the lifting gas to reduce lift and
control altitude. There are various ways to attach the load
to the envelope.
As have others, Marvin has attached the load directly
to the surface of the bottom of the envelope material.
This method requires tough envelope material, high
internal pressures, and methods of distributing the load
over a wide area of the envelope material. Dumont ran