Thermal airship
Encyclopedia
A thermal airship is an airship
that generates its lift
via the difference in density due to a temperature differential between the gas inside its envelope and the ambient air. (This is in contrast to using a gas that is lighter than air at ambient temperature, such as helium
.) Currently all thermal airships use hot air, as used in a hot air balloon
, as their lifting gas
. However, an airship that uses steam
would also qualify as a thermal airship.
-based airships. They are also routinely deflated after each flight and can be readily packed for storage and/or transport.
Hot air craft produce much less uplift per unit volume than helium
- or hydrogen
-filled craft (about 30% depending on air conditions). This necessitates lighter construction, with fewer controls and hence more difficulty in manoeuvring. This leads to:
In recent years, the steering of these ships has improved somewhat. The most successful approach has been to use higher pressure in the tail fin structures than in the rest of the envelope, or to use an internal structure (see below).
The first public flight of a hot air airship was made by Don Cameron (UK) of Cameron Balloons at the Icicle Meet in January 1973. The aircraft reportedly took 3 years to develop.
In 2006, a new type of envelope employing a tensile membrane structure
was developed by Skyacht Aircraft. This design uses an unpressurized envelope and an internal structure that uses ribs made of aluminium
to keep the envelope in shape. When not in use, the structure folds up in a manner similar to an umbrella. The structure also permits the mounting of a steerable engine/propeller on the tail of the aircraft. The tail-mounted propeller provides for vectored thrust steering, allowing tight turns.
burner is ignited and the inflation is completed using heated air.
Airship
An airship or dirigible is a type of aerostat or "lighter-than-air aircraft" that can be steered and propelled through the air using rudders and propellers or other thrust mechanisms...
that generates its lift
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
via the difference in density due to a temperature differential between the gas inside its envelope and the ambient air. (This is in contrast to using a gas that is lighter than air at ambient temperature, such as helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
.) Currently all thermal airships use hot air, as used in a hot air balloon
Hot air balloon
The hot air balloon is the oldest successful human-carrying flight technology. It is in a class of aircraft known as balloon aircraft. On November 21, 1783, in Paris, France, the first untethered manned flight was made by Jean-François Pilâtre de Rozier and François Laurent d'Arlandes in a hot air...
, as their lifting gas
Lifting gas
Because of the Archimedes' principle, a lifting gas is required for aerostats to create buoyancy. Its density is lower than that of air . Only certain lighter than air gases are suitable as lifting gases.- Hot Air :...
. However, an airship that uses steam
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...
would also qualify as a thermal airship.
Advantages/Disadvantages
Thermal airships have the advantage of being less expensive than heliumHelium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
-based airships. They are also routinely deflated after each flight and can be readily packed for storage and/or transport.
Hot air craft produce much less uplift per unit volume than helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
- or hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
-filled craft (about 30% depending on air conditions). This necessitates lighter construction, with fewer controls and hence more difficulty in manoeuvring. This leads to:
- lower airspeedsAirspeedAirspeed is the speed of an aircraft relative to the air. Among the common conventions for qualifying airspeed are: indicated airspeed , calibrated airspeed , true airspeed , equivalent airspeed and density airspeed....
- difficulty in handling on the ground if the ground wind is above 5 knots
- difficulty in steering, particularly at low airspeeds
- lack of elevator (pitch) control, causing the airship to pitch up or down in response to changes in the throttle setting (a motion called 'porpoising').
In recent years, the steering of these ships has improved somewhat. The most successful approach has been to use higher pressure in the tail fin structures than in the rest of the envelope, or to use an internal structure (see below).
History
Envelope structures
Most thermal airships are non-rigid. Some are pressurized. In some cases, the pressurized air is taken from a duct located behind the propeller. In other cases, the pressurized air comes from a separate fan.In 2006, a new type of envelope employing a tensile membrane structure
Tensile structure
A tensile structure is a construction of elements carrying only tension and no compression or bending. The term tensile should not be confused with tensegrity, which is a structural form with both tension and compression elements....
was developed by Skyacht Aircraft. This design uses an unpressurized envelope and an internal structure that uses ribs made of aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
to keep the envelope in shape. When not in use, the structure folds up in a manner similar to an umbrella. The structure also permits the mounting of a steerable engine/propeller on the tail of the aircraft. The tail-mounted propeller provides for vectored thrust steering, allowing tight turns.
Operation
Like hot air balloons, thermal airships are first inflated partially with cold (ambient temperature) air. Once the envelopes are sufficiently full, a propanePropane
Propane is a three-carbon alkane with the molecular formula , normally a gas, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as a fuel for engines, oxy-gas torches, barbecues, portable stoves, and residential central...
burner is ignited and the inflation is completed using heated air.
External links
- Hotair-Airship-Blog
- Hot air airship site
- The Flying Kettle Steam Balloon Project
- Gefa-Flug Hot Air Airships -- commercial aircraft company
- Gefa-Flug Airship-Programme
- Gefa-Flug manufactured airships
- Gefa-Flug airship in action - Youtube video
- Cameron Hot Air Airships -- commercial aircraft company
- Lindstrand Hot Air Airships -- commercial aircraft company
- Skyacht Personal Blimp -- company developing a hot air airship
- World Championship 1998 -- Sixth World Airship Championships held in Gatineau, Quebec on the 3rd of September, 1998.
- World Championship 2008 -- Eighth World Airship Championship held in Tsarskoye Selo, Russia, June 2008.
- The tree top raftRadeau des cimes
- Aerostatic tools Dany Cleyet-marrel
- ART-Airships