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
- air scoops
- air valves
- helium valve
- gondola - holds passengers and crew
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We'll discuss each of these parts in the following sections.
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
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 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.
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).
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.
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.
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.
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.
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
- Communications - maintain radio contact with ground-support team and air traffic controllers
- 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.
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!