Empennage

The empennage of a Boeing 747-200

The empennage (/ˌɑːmpˈnɑːʒ/ or /ˈɛmpnɪ/), also known as the tail or tail assembly, provides stability for aircraft, in a way similar to the feathers on an arrow.[1][2][3] The term derives from the French language word empenner which means "to feather an arrow".[4] Most aircraft feature an empennage incorporating vertical and horizontal stabilising surfaces which stabilise the flight dynamics of yaw and pitch,[1][2] as well as housing control surfaces.

In spite of effective control surfaces, many early aircraft that lacked a stabilising empennage were virtually unflyable. Even so-called "tailless aircraft" usually have a tail fin (vertical stabiliser). Heavier-than-air aircraft without any kind of empennage (such as the Northrop B-2) are rare.

Structure

Structurally, the empennage consists of the entire tail assembly, including the tailfin, the tailplane and the part of the fuselage to which these are attached.[1][2] On an airliner this would be all the flying and control surfaces behind the rear pressure bulkhead.

The front (usually fixed) section of the tailplane is called the tailplane or horizontal stabiliser and is used to provide pitch stability. The rear section is called the elevator, and is usually hinged to the horizontal stabiliser. The elevator is a movable aerofoil that controls changes in pitch, the up-and-down motion of the aircraft's nose. Some aircraft employ an all-moving stabiliser and elevators in one unit, known as a stabilator or "full-flying stabiliser".[1][2]

The vertical tail structure (or fin) has a fixed front section called the vertical stabiliser, used to restrict side-to-side motion of the aircraft (yawing). The rear section of the vertical fin is the rudder, a movable aerofoil that is used to turn the aircraft's nose to one side or the other. When used in combination with the ailerons, the result is a banking turn, often referred to as a "coordinated turn".[1][2]

Some aircraft are fitted with a tail assembly that is hinged to pivot in two axes forward of the fin and stabiliser, in an arrangement referred to as a movable tail. The entire empennage is rotated vertically to actuate the horizontal stabiliser, and sideways to actuate the fin.[5]

The aircraft's cockpit voice recorder, flight data recorder and emergency locator transmitter (ELT) are often located in the empennage, because the aft of the aircraft provides better protection for these in most aircraft crashes.

Trim

In some aircraft trim devices are provided to eliminate the need for the pilot to maintain constant pressure on the elevator or rudder controls.[5][6]

The trim device may be:

Multi-engined aircraft often have trim tabs on the rudder to reduce the pilot effort required to keep the aircraft straight in situations of asymmetrical thrust, such as single engine operations.[7]

Tail configurations

Aircraft empennage designs may be classified broadly according to the fin and tailplane configurations.

The overall shapes of individual tail surfaces (tailplane planforms, fin profiles) are similar to wing planforms.

Tailplanes

Main article: tailplane

The tailplane comprises the tail-mounted fixed horizontal stabiliser and movable elevator. Besides its planform, it is characterised by:

Some locations have been given special names:

" "
Fuselage mounted
" "
Cruciform
" "
T-tail
" "
Flying tailplane

Fins

The fin comprises the fixed vertical stabiliser and rudder. Besides its profile, it is characterised by:

Twin fins may be mounted at various points:

" "
Tailplane mounted
" "
Twin tail boom
" "
Wing mounted

Unusual fin configurations include:

" "
Triple fins
" "
Ventral fin

V and X tails

An alternative to the fin-and-tailplane approach is provided by the V-tail and X-tail designs. Here, the tail surfaces are set at diagonal angles, with each surface contributing to both pitch and yaw. The control surfaces, sometimes called ruddervators, act differentially to provide yaw control (in place of the rudder) and act together to provide pitch control (in place of the elevator).[1]

" "
V-tail
" "
Inverted V-tail
" "
X-tail
" "
Pelikan tail

Box kite tails

Some of the earliest aircraft combined horizontal and vertical stabilisers in a box kite design, such as the 1910 Bristol Boxkite.

Tailless

Main article: Tailless aircraft

A tailless aircraft (often tail-less) traditionally has all its horizontal control surfaces on its main wing surface. It has no horizontal stabiliser - either tailplane or canard foreplane (nor does it have a second wing in tandem arrangement). A 'tailless' type usually still has a vertical stabilising fin (vertical stabiliser) and control surface (rudder). However, NASA adopted the 'tailless' description for the novel X-36 research aircraft which has a canard foreplane but no vertical fin.

The most successful tailless configuration has been the tailless delta, especially for combat aircraft.

See also

References

  1. 1 2 3 4 5 6 Crane, Dale: Dictionary of Aeronautical Terms, third edition, page 194. Aviation Supplies & Academics, 1997. ISBN 1-56027-287-2
  2. 1 2 3 4 5 Aviation Publishers Co. Limited, From the Ground Up, page 10 (27th revised edition) ISBN 0-9690054-9-0
  3. Air Transport Association (10 November 2011). "ATA Airline Handbook Chapter 5: How Aircraft Fly". Archived from the original on 10 November 2011. Retrieved 5 March 2013.
  4. "Empennage". Oxford Dictionaries Online. Oxford Dictionaries. Retrieved 5 March 2013.
  5. 1 2 3 4 5 6 7 Aviation Publishers Co. Limited, From the Ground Up, page 14 (27th revised edition) ISBN 0-9690054-9-0
  6. 1 2 Reichmann, Helmet: Flying Sailplanes, page 26. Thompson Publications, 1980.
  7. 1 2 Transport Canada: Flight Training Manual 4th Edition, page 12. Gage Educational Publishing Company, 1994. ISBN 0-7715-5115-0
  8. Crane, Dale: Dictionary of Aeronautical Terms, third edition, page 524. Aviation Supplies & Academics, 1997. ISBN 1-56027-287-2
  9. Anderson, John D., Introduction to Flight, 5th ed, p 517
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