You've
probably seen a Goodyear blimp providing TV coverage to
a sporting event, such as a football
game or golf tournament. Blimps are a type of
lighter-than-air (LTA) craft called an airship. Like a
hot
air balloon, blimps use a gas to generate lift. But
unlike a hot air balloon, blimps can move forward through the
air under their own power, like airplanes.
They can hover like helicopters,
travel in all kinds of weather and stay aloft for days. In
this edition of HowStuffWorks,
we will show you how these fascinating vehicles work.
Inside a Blimp
Blimp
History tells you how, why, where and when blimps
were first
developed.
Unlike
a balloon, a blimp has a shape and structure that enable it to
fly and maneuver. The following parts allow it to do this:
envelope - contains the helium gas
nose cone battens
forward ballonet
aft ballonet
catenary curtain
suspension cables
flight control surfaces - rudders, elevators
engines
air scoops
air valves
helium valve
gondola - holds passengers and crew
Move mouse over each part to view its
location.
We'll discuss each of these parts in the following
sections.
Envelope The
envelope is the large bag that holds the helium gas.
The envelope is generally cigar-shaped, for aerodynamic
purposes, and made of a durable, airtight, lightweight fabric
(polyester composites) that is much like the fabric of a space
suit. In fact, many envelopes are made by ILC Dover
Corporation, the company that makes spacesuits for NASA.
The envelopes can hold from 67,000 to 250,000 ft3 (1,900 to 7,093 m3) of helium, depending upon the
particular blimp. The pressure inside the envelope is low,
approximately 0.07 pounds per square inch (0.005 ATM).
Nose Cone Battens
Photo courtesy American Blimp
Corporation Nose cone battens
(gray)
The
nose cone battens are supports that radiate from the
tip of the blimp. They stiffen the front of the blimp so that
it is not damaged when it is moored to the mooring
mast. They also give the nose an aerodynamic shape, and
prevent it from pushing in as the blimp travels forward. In
addition to the battens, the mooring hooks are located
in the nose of the blimp.
Ballonets Ballonets are air-filled
bags that are located inside the envelope. The blimp has two
ballonets, one fore and one aft. The ballonets are similar to
the ballast tanks of a submarine.
Because air is heavier than helium, the ballonets are deflated
or inflated with air to make the blimp ascend or descend,
respectively. They are also used to control the trim,
or levelness, of the blimp.
Catenary Curtain and Suspension
Cables The two catenary curtains are located
inside the envelope along the length of the blimp. They are
made of fabric and sewn into the envelope, and suspension
cables attach them to the gondola. The curtains help to
support and shape the envelope and attach the gondola.
Flight Control
Surfaces The flight control surfaces are
stiff, movable parts of the blimp that are mounted to the
tail. They consist of the rudder and elevators. The
rudder is used to steer the blimp to the starboard or
port directions (yaw axis). The elevators are used to
control the angle of ascent or descent (pitch axis) of the
blimp. The flight control surfaces are operated by the pilot
as he/she flies the blimp, and can be arranged in a "+" or "x"
configuration.
Engines The two
engines on the blimp provide the thrust
necessary to move ahead. The engines are turbo-propeller airplane
engines that use gasoline
fuel and are cooled by air. The engines can generate
several hundred horsepower,
depending upon the particular blimp. They are located on
either side of the gondola. With the engines, blimps can
cruise around 30 to 70 mph (48 to 113 kph).
Photo courtesy Goodyear Tire &
Rubber Company The engines
(left) and air scoops (right)
Air Scoops The air
scoops direct exhaust air from the propellers into the
ballonets. This is how the pilots can fill the ballonets with
air while in flight. When the engines are not running,
electric fans move air into the ballonets.
Photo courtesy Goodyear Air valve of a blimp
Air Valves The pilots
must be able to vent air from the ballonets as well as add it.
This is accomplished by air valves that are located on
each ballonet. There are four valves -- two fore, two aft.
Helium Valve The pressure
of the helium in the envelope is adjusted by changing the
amount of air in the ballonets. Normally, blimp pilots do not
have to add or remove helium from the envelope. However, there
is a helium valve on the envelope that can be used to
vent helium should the helium pressure exceed its maximum safe
limit. The valve can be opened manually or automatically.
Gondola The
gondola holds the passengers and crew. It is enclosed,
and holds two pilots and up to 12 crew, depending upon the
type of blimp (Goodyear's Eagle and Stars & Stripes each
hold two pilots and six passengers). Some gondolas have
specialized equipment, such as a camera, attached to them.
Photo courtesy American Blimp
Co. Blimp gondola with an
attached camera (round object in
front)
Photo courtesy American Blimp
Co. Forward view inside of
gondola, showing pilot seats/controls (front) and
passenger
seats
The control panels used by the pilots include the
following:
Propeller controls - monitor and regulate speed
(throttle), blade angle (blade pitch) and direction of the
engine (forward, reverse)
Fuel mixture/heat - monitor and regulate the
fuel-to-air ratio of the engine and the temperature of the
mix to prevent icing at higher altitudes
Envelope pressure controls - monitor and regulate
the helium pressure in the envelope and the air pressure in
the ballonets by opening and closing the air scoops and
valves
Flight surface controls - control the rudder
(left/right movement) and the elevators (up/down movement)
Navigation equipment - compasses,
airspeed indicators, radio beacon equipment, GPS, etc.
(Some blimps also have weather radar, and
are instrument-rated for night-flying.)
Blimp pilots
are FAA-certified
for lighter-than-air (LTA) craft. Goodyear's
pilots undergo a comprehensive training program prior to FAA
certification. In addition to piloting, Goodyear's pilots also
serve as ground-support crew, including electronics
technicians, mechanics, riggers and administrative personnel.
A ground crew follows the blimp wherever it goes, bringing
several support vehicles, including a bus that serves as the
administrative office, a tractor-trailer that serves as an
electrical/mechanical shop, and a van that is the command
car/utility vehicle.
Night Signs Some blimps
(like Goodyear) are equipped with electric lights for
nighttime advertising. In the Goodyear blimp, the night signs
consist of a matrix of red, green and blue light-emitting
diodes (LEDs). The intensities of the LEDs can be adjusted
to create various colors. The messages are programmed in with
a small laptop
computer that is carried aboard.
Now that we have seen all of the parts of a blimp, let's
look at how it flies!
How a Blimp Flies Airships are called
lighter-than-air (LTA) craft because to generate lift,
they use gases that are lighter than air. The most common gas
in use today is helium, which has a lifting capacity of 0.064
lb/ft3 (1.02 kg/m3). Hydrogen was commonly used in the
early days of airships because it was even lighter, with a
lifting capacity of 0.070 lb/ft3 (1.1 kg/m3). However, the Hindenburg
disaster ended the use of hydrogen in airships because
hydrogen burns so easily. Helium, on the other hand, is not
flammable.
While these lifting capacities might not seem like much,
airships carry incredibly large volumes of gas -- up to
hundreds of thousands of cubic feet (thousands of cubic
meters). With this much lifting power, airships can carry
heavy loads easily.
Click on the button to see how a blimp ascends and
descends.
A blimp or airship controls its buoyancy in the air
much like a submarine
does in the water. The ballonets act like ballast tanks
holding "heavy" air. When the blimp takes off, the pilot vents
air from the ballonets through the air valves. The helium
makes the blimp positively buoyant in the surrounding
air, so the blimp rises. The pilot throttles the engine and
adjusts the elevators to angle the blimp into the wind. The
cone shape of the blimp also helps to generate lift.
As the blimp rises, outside air pressure decreases and the
helium in the envelope expands. The pilots then pump air into
the ballonets to maintain pressure against the helium. Adding
air makes the blimp heavier, so to maintain a steady cruising
altitude, the pilots must balance the air-pressure with the
helium-pressure to create neutral buoyancy. To level
the blimp in flight, the air pressures between the fore and
aft ballonets are adjusted. Blimps can cruise at altitudes of
anywhere from 1,000 to 7,000 ft (305 to 2135 m). The engines
provide forward and reverse thrust
while the rudder is used to steer.
To descend, the pilots fill the ballonets with air. This
increases the density of the blimp, making it negatively
buoyant so that it descends. Again, the elevators are
adjusted to control the angle of descent.
When not in use, blimps are moored to a mooring mast that
is either out in the open or in a hangar. To move the blimp
into or out of its hangar, a tractor tows the mooring mast
with the blimp attached to it.
Photo courtesy Goodyear Tire & Rubber
Company The Spirit of
Goodyear coming out of its hangar at Wingfoot Lake
Airship Base outside of Akron,
Ohio
Uses of Blimps and Airships
Photo courtesy Goodyear Blimp covering a Cleveland Browns football
game
Because
gas provides the lift in an airship or blimp, rather than a
wing with an engine as in an airplane, airships can fly and
hover without expending fuel or energy. Furthermore, airships
can stay aloft anywhere from hours to days -- much longer than
airplanes or helicopters.
These properties make blimps ideal for such uses as covering
sporting events, advertising and some research, like scouting
for whales.
Recently, there has been renewed interest in using rigid
airships for lifting and/or transporting heavy cargo loads,
like ships, tanks and oil rigs, for military and civilian
purposes. Modern airships, such as the Zeppelin
NT and CargoLifter,
use lightweight, carbon-composite frames that allow them to be
huge, light and structurally sound. In addition to hauling
cargo, airships may once again be used for tourism. So, the
sight of a large airship moving across the sky may become more
common in the near future.
Blimp History In 1783, two French brothers,
Jacques Etienne and Joseph Michel Montgolfier, invented the hot-air
balloon and sent one to an altitude of 6,000 ft (1,800 m).
Later that year, the French physicist Jean Pilatre de Rozier
made the first manned balloon flight. While balloons could
travel to high elevations, they could not travel on their own
propulsion and were at the mercy of the prevailing winds. The
shape of the balloon was determined by the pressure of the air
or gas (such as hydrogen or helium).
Types of Airships
All airships have solid gondolas, engine-powered
propellers and solid tailfins.
Rigid - usually long (greater than 360
ft/120 m) and cigar-shaped with an internal metal
frame and gas-filled bags. Example: Hindenburg
Semi-rigid - pressurized gas balloon
(envelope) attached to a lower metal keel. Examples:
Norge, Italia
Non-rigid (blimp) - large gas-filled
envelopes. Examples: Goodyear, MetLife, Fuji
In 1852, Henri Giffard built the first powered airship,
which consisted of a 143-ft (44-m) long, cigar-shaped,
gas-filled bag with a propeller, powered by a 3-horsepower
(2.2-kW) steam
engine. Later, in 1900, Count Ferdinand von Zeppelin of
Germany invented the first rigid airship.
Photo courtesy Goodyear Goodyear's original fleet of blimps in
1930
The
rigid airship had a metal framework -- 420 ft (123 m)
in length, 28 ft (12 m) in diameter -- containing
hydrogen-gas-filled rubber bags. The first Zeppelin had tail
fins and rudders, and was powered by internal
combustion engines. It carried five people to an altitude
of 1,300 ft (396 m) and flew a distance of 3.75 mi (6 km).
Several models of Zeppelins were built in the early 1900s.
These vehicles were used for military and civilian purposes,
including transatlantic travel. The most famous Zeppelin was
the Hindenburg, which was destroyed by a fire in 1937
while landing at Lakehurst, New Jersey. See Fall
of the Hindenburg to learn about the ship and the crash.
In 1925, Goodyear Tire & Rubber Company began building
airships of the blimp design. These aircraft were used for
advertising and military purposes (such as surveillance and
anti-submarine warfare) throughout World War II. In 1962, the
U.S. military stopped using blimps in their operations. Today,
blimps are used mainly for advertising, TV coverage,
tourism and some research purposes. However, the airship is
coming back.
For more information on airships and related topics, check
out the links on the next page.
