Hot air airships offer a phantastic compromise between the ease of use
common to hot air balloons and the maneuvrability of real airships.
Like balloons, hot air airships can be transported on a trailer. Their
deflation does not involve the loss of expensive helium. An expensive
hangar is thus superfluous. This does not mean that thermal airships
are cheap. A standard pressurized model costs around US$ 100,000. Without
a sponsor and commercial use such a price is out of reach for many pilots.
is a potential solution to the price barrier but experimental designs
have yet to reach the performance level of commercial hot air airships.
In most countries the legal requirements for piloting hot air airships
are similar to the ones for flying hot air balloons. In the USA
a hot air balloon pilot licence is the only requirement to fly a
thermal airship. In Switzerland and England five
additional hours on thermal airships under the supervision of
an experienced hot airship pilot are required to get
the rating (in addition to the normal hot air balloon licence of course).
However, Swiss hot air airship pilot and instructor Felix Bühlmann
recommends that prospective thermal airship pilots acquire at least 50 flight
hours in hot air balloons before attempting the transition.
There are a number of companies that manufacture hot air airships.
Thunder & Colt.
You can recognize Cameron airships by their slight "belly." Seen head on
they look somewhat like a tear drop because the gondola is attached via
load tapes to the envelope only. This construction method brings simplicity
and weight savings. Thunder & Colt and Lindstrand airships, on the
other hand, have internal suspension cables running inside the envelope
that attach the gondola to the top of the envelope. This supposedly makes
for a more stable shape and better weight distribution but also increases
the complexity of the design and its operation. Seen from the front those
airships look more or less round.
The gondola of a Cameron DP-Series airship. Note the auxiliary
electrical fan to pressurize the envelope, provide fresh air for
combustion of the propane and
to inflate the rudder and tail surfaces. The advantage of this system
is that there is an airflow even when the main engine is turned off
during precision flights in competition.
Also note the little red tank to feed the vapor pilot lights when
the main tanks are pressurized with Nitrogen.
Barely recognizable on the above picture is the König SC-430 three
cylinder two stroke engine. It is used because of its high power to
weight ratio and relative silence. Besides the König engines,
Rotax powerplants are most often used in thermal airships. So far, two
stroke engines have kept the upper hand because of their obvious
weight advantage. And since airships stay in the air even in the
event of engine failure, the reliability of two strokes has not
been a primary issue. Two stroke engines have a reputation for being
less reliable than four stroke engines, probably just because less
research time and maintenance money gets spent on them.
Recently however, some small and light four stroke engines have surfaced
and might give two stroke engines some competition in very light aviation,
including hot air airships.
Most hot air airships flying today (especially in competition) are
pressurized models. The internal pressure makes the envelope more rigid and
prevents "denting" of the nose at higher speeds. The downside of
pressurization is that the burner, located inside the envelope
cannot draw fresh air freely from the outside.
This is the Minolta CK airship piloted by Guy Moyano, 1992 World
Champion from Luxembourg. It's a Cameron DP-80. Note the windsock.
The ship is landing with its nose pointing into the wind.
Facing into the wind is especially important for inflating, landing
and deflating hot air airships because the envelope offers the smallest
resistance to the wind that way. Also, the control surfaces are most
effective when heading directly into the wind since this increases apparent
airspeed and thus the amount of air that flows over and is deflected by
the control surfaces. Despite their large surface area, the rudders of
hot airships are not very effective at low speeds.