Aerodynamic (or “Dynamic”) Flight – Heavier-than-air craft like airplanes and helicopters use propulsion and control surfaces (wings, rotors, etc.) to actively force their flight into the air.
Aerodynamic (or “Dynamic”) Lift – This is the lift generated by an airship’s envelope as a lifting body or wing. Modern blimps are normally flown slightly heavy, meaning that their aerostatic lift is less than their weight. Since lift must equal weight, the pilot makes up the shortfall by flying the blimp in a slight nose-up attitude to generate aerodynamic lift. If the blimp becomes light, meaning the aerostatic lift is greater than the weight (which can happen due to fuel burn), the pilot flies slightly nose-down to generate negative aerodynamic lift.
Aerostatic (or “Static”) Flight – Lighter-than-air craft such as blimps and other airships use a lifting gas that is lighter than air to become buoyant and passively rise into the air.
Aerostatic (or “Static”) Lift – This is the net upward force on an airship equal to its buoyancy minus the weight of its lifting gas. Since helium is heavier than hydrogen, a helium-filled airship will have less aerostatic lift than a hydrogen-filled one of the same volume and buoyancy.
Aerostatic (or “Static”) Heaviness and Lightness – If an airship’s aerostatic lift is less than its weight, it is statically heavy. If its aerostatic lift is greater than its weight, it statically light. If aerostatic lift equals weight, it is said to be in static equilibrium or neutrally buoyant. In flight, heaviness or lightness are counteracted with aerodynamic lift. To sit on the ground, an airship must be statically heavy; its heaviness is managed with ballast. If an airship is placed on a weighing scale, the scale measures its static heaviness, not its weight. Thus, a blimp might register 200 kg or 440 lbs on a scale.
Ballast – This is typically a heavy fluid material such as sand or water that adds additional weight which can be dumped in order to increase the upward lift or buoyancy of an airship.
Ballonet – These are air cells located within the helium cell of a non-rigid (blimp) or semi-rigid airship, that deflate and reinflate automatically to allow the helium to expand and contract in response to changes in altitude, air pressure and helium temperature. Most blimps have two ballonets, fore and aft, but small blimps may have only one. In an airship with two ballonets, they are also used to trim the airship in pitch. Adding more air to one ballonet causes the other to deflate by the same amount, which moves the helium, and therefore the center of lift, fore or aft. Ballonet operation has no effect on aerostatic lift, and they are not used to control weight or buoyancy as has been misconstrued.
Blimp – A blimp is a non-rigid airship because it relies upon the pressure of the lifting gas to hold its shape. The story goes that it got its name from a World War I era Lieutenant who mimicked the sound made when thumping on the side of the airship.
Buoyancy – This is the upward force experienced by an airship in response to displacing atmospheric air, in accordance with Archimedes’ Principle. A lifting gas does not independently create lift, but rather the denser air it displaces results in the buoyancy effect, which creates the lift.
Control Car – This is often a separate compartment that hangs below an airship where the airship’s controls are located and where the airship’s piloting crew operates.
Dirigible – Is derived from a French word that means ‘to steer’. A dirigible is essentially any lighter than air craft that can be steered or controlled.
Elevator – Elevators are the hinged sections or control surfaces on the horizontal tail fins, just as in an airplane. Elevators control pitch, the nose-up or nose-down attitude of the aircraft in flight. In an X-tail airship, the elevator and rudder functions are coupled, and the control surfaces are known as ruddervators.
Envelope – The envelope is the external covering of an airship. On a rigid or semi-rigid airship, it covers the structure and protects the interior cells and compartments. On a blimp, it encloses the lifting gas and forms the airship’s hull.
Gold Beater’s Skin – Many old airships used gold beater’s skin to create the gas impermeable cells that contained the lifting gas. Gold beater’s skin was made from specially treated cow intestines and was originally used by gold beaters who used it to beat and thus shape gold into thin sheets.
Gas Impermeable – This applies to material which gas cannot permeate or pass through.
Gondola – This is a compartment that holds passengers, crew, and/or equipment and is located beneath a balloon or airship.
Helium – Helium is the second lightest gas after hydrogen. It is one of the noble gases due to its inherent stability. This is the primary gas used in most blimps today.
Hydrogen – Hydrogen is the lightest gas of all. It is highly flammable. Many airships of the past used hydrogen as a lifting gas, however today it is more likely to be used in liquid form as rocket fuel.
Lifting Gas – Typical lifting gasses are hydrogen, helium, methane, ammonia and hot air due to the fact that they are less dense than the surrounding air and thus tend to rise. When harnessed within the envelope of an airship these gasses become lifting gasses for the purpose of lifting the airship.
Mooring Lines – These lines were dropped from the nose section of large airships and used to help reel them in toward their mooring mast.
Mooring Mast – The mooring mast is a tower-like structure whose mast connects to the nose cone of airships that have landed.
Pitch – Pitch is the nose up or nose down angle that an airship takes through the air, which is controlled by the elevators or horizontal control surfaces on the tail fins.
Pressure Height – Pressure height is the altitude at which the lifting gas has expanded to the point of filling its cell or cells. This is the airship’s operating ceiling. Climbing above this results in the automatic valving-off of lifting gas to prevent the internal pressure from rising and a loss of lift that is not recovered again in the descent.
Rudder – Rudders are the hinged sections or control surfaces on the vertical tail fins, just as in an airplane. Unlike an airplane, most airships have upper and lower fins and rudders. The rudders control yaw, the direction of the aircraft in flight. In an X-tail airship, the elevator and rudder functions are coupled, and the control surfaces are known as ruddervators.
Ruddervators – In an X-tail airship, the elevator and rudder functions are combined and serve the functions of both.
Sub-cloud Car – During World War I German zeppelins used these one man contraptions to lower hundreds of feet below the zeppelin so that a spotter could find targets while the rest of the airship remained safely hidden above the clouds. They are said to have not been very effective.
Yaw – Yaw is the horizontal left or right direction that an airship can fly. This is controlled by the rudders on the tailfins.
Zeppelin – Named after its inventor, Ferdinand Graf (Count) von Zeppelin, a Zeppelin (with a capital Z) is or was an airship manufactured by the Zeppelin company. Thus the Hindenburg and the modern, semi-rigid Zeppelin NT are both Zeppelins. However, historic rigid airships in general, even those not manufactured by Zeppelin, are often referred to as zeppelins (with a small z). Thus the British R100 and R101, and the USS Akron and Macon, are sometimes called zeppelins, although they are not Zeppelins.