podded engine

Pod engines on a Boeing 707.

A podded engine is a jet engine in a pod, typically attached below the wing or to the tail of the aircraft. The pod itself is called a nacelle.

Almost all modern large jet airplanes use engines in pods below and in front of the wing. Placing the engines on the wing reduces the bending moment of the wing and provides the engine air undisturbed by the airframe or wing. Also the wing blocks some engine noise from reaching the aircraft cabin^{[citation needed]}.

Smaller jet airplanes in which placing the jets below the wing would cause them to be too close to the ground instead use two podded engines in the rear of the plane. This mounting location reduces asymmetric thrust should a wing-mounted engine lose power. Careful examination of such engines will show them typically mounted nose-high. These engines are mounted to face the local flow of air, and the local airflow at the airplane's tail is often descending.

As unusual counter-examples, the VFW-614 and the Hondajet place the podded engines above the wings. The Antonov An-72 and the Boeing YC-14 also place their engines above the wings, mounted very close to the wing. This placement utilizes the Coandă effect allowing a lower minimum flight speed and decreasing the amount of runway needed for takeoff and landing (i.e. STOL).

Modern jet fighters almost never use podded engines, instead typically embedding the engines within the fuselage. This was not true of earlier designs, however. The Messerschmitt Me 262, for example, used under-wing pod mounted engines. The Bell P-59 Airacomet used engines mounted in pods tucked up against the fuselage.

Advantages

• Podded engines on the wings can act as vortex generators.
• Podded engines hanging from the wing also provide wing bending relief, i.e. as the airflow bends the wings up, the weight of the podded engines resists this, allowing for a lighter structure.
• Podded engines can ease maintenance access.
• Podded engines can reduce noise within the cabin (since the engines are farther from the cabin, and for engines mounted below the wing, the wing itself acts as a noise shield).
• It is often easier to change engine models when the engine is in a pod. For example, the Boeing 747 uses engines from GE, Pratt and Whitney, and Rolls Royce, the changes being mostly isolated to the pods themselves.
• If a podded engine explodes, catches fire, or breaks free from its mounts, it is less likely to critically damage the aircraft than an engine embedded within the airframe. Although such events seldom happen to modern jet engines, this possibility helps explain why podded engines are commonly used on commercial and general aviation aircraft that may carry fare-paying passengers. Military combat jets are often occupied only by crewmembers who can bail out of the craft in an emergency, making this safety factor less crucial. ^{[citation needed]}

Disadvantages

• Podded engines can increase drag.
• A podded engine hanging low from a wing can suffer more damage from foreign objects (i.e., objects can get sucked into a low-hanging jet).
• In a water landing podded engines hanging from the wing increase the stress on the wing, by increasing the amount of drag. This can cause the wings to shear off or flip the aircraft and destroy the fuselage as happened to Ethiopian Airlines Flight 961.

Examples

A Cessna Citation uses two engines podded in the rear.

Examples of non-podded engines

The De Havilland Comet used engines embedded within the wing.

The F-16 Fighting Falcon uses a turbofan engine embedded in the fuselage.

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