The empennage, commonly called the tail assembly, is the rear-most structure of an airplane that stabilizes the aircraft in the same way feathers stabilize an arrow. Comprising the tail cone, fixed stabilizers and movable aerodynamic surfaces, it consists of the vertical tailfin and the horizontal tailplane together with the adjoining fuselage section. By generating corrective moments around the pitch, roll and yaw axes, the empennage delivers the trim, stability and control that allow safe, steady flight.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What is the empennage in aircraft?
The empennage, known as the tail or tail assembly, is a structure at the rear of an aircraft that provides stability during flight. It consists of the entire tail assembly, which includes horizontal and vertical stabilizers, a tailfin, and a tailplane, along with the part of the fuselage to which these are attached.
The empennage is the rear part of an aircraft that comprises the tailplane, the vertical stabilizer, and the rudder. Vertical stabilizers are fixed surfaces at the rear of aircraft and they form the vertical fin, known as the tailfin. The horizontal tailplane attached to part of the fuselage carries the elevator, a movable control surface that works with the fixed surfaces at the rear of the aircraft to give pitch stability.
What are the components of an empennage?
The components of an empennage are detailed below.
- The empennage consists of a vertical stabiliser attached to the rear fuselage
- The empennage consists of two horizontal stabilisers attached to the rear fuselage
- The empennage consists of a rudder attached to the vertical stabiliser
- The empennage consists of elevators attached to the horizontal stabilisers
- The empennage consists of trim tabs attached to the rudder and elevators
Fixed aerodynamic surfaces, or stabilizers, provide longitudinal and directional stability. Control surfaces create moments as they deflect: the rudder, located on the rear edge of the fin, enables the pilot to control the airplane's left-right movement by providing yaw control around a vertical axis. The elevator supplies pitch control around the lateral axis. The tail cone streamlines the rear fuselage and encloses linkages, while the internal structure transmits loads from stabilizers to the fuselage attachment points. The empennage area is sized so that the horizontal tailplane maintains a specified combination of center-of-gravity position, flap position and airspeed. The vertical tailplane must cope with flight states like engine failure during take-off, landing and in cruise. Parked height is measured from the ground to the highest point of the tail assembly. This figure is greater than that of the vertical stabilizer alone and determines the minimum clearance needed for the aircraft to taxi under obstruction.
What materials are used in empennage?
Aircraft manufacturers select empennage materials by balancing strength, weight and fatigue resistance. Aluminum 7075 alloy is commonly used as a structural material in aviation. It equips spars, ribs, skins and the attachments that join the tail to the fuselage bulkheads. Complementary sheet-metal parts are formed from 2024 T3 aluminum, while non-critical or compound-curved sections use 6061, 5052, or 2024 Alclad sheets.
Newer empennage designs are more likely to be composite. Composites are one of the most common materials used to make empennages. They consist of reinforcing fibers like carbon fiber, fiberglass or Kevlar set in a matrix of epoxy resin. The resulting fibre-reinforced composites have a higher strength-to-weight ratio than aluminum and steel, so they reduce mass without sacrificing stiffness. For example, the dorsal fin is often built with carbon-fiber skins sandwiched over a Nomex honeycomb core, a lay-up that is optimum for thin, lightly loaded panels. The Airbus A350XWB empennage is manufactured from CRPF-carbon-fiber-reinforced plastic - proving that all-composite tails now serve on large transports.
Steel, titanium alloys and aluminum castings fulfil specialised functions. Spar-attachment castings are made from 355.0-T3 aluminum, providing hard-points for bolts. Titanium alloys retain considerable strength at temperatures up to 400-500°C (752-932°F) and offer a good fatigue-strength-to-tensile-strength ratio, so titanium fasteners and hinge fittings appear where heat or durability is pivotal. Thus, the modern empennage combines aluminum alloys, fibre-reinforced composites and selective metals to achieve an efficient, durable tail structure.
What is the function of the empennage?
The function of the empennage is to provide trim, enabling a moment around the lateral axis. The horizontal tailplane sweepback angle , which is greater than the wing, increases the critical Mach number. The vertical tailplane creates a moment around the vertical axis. The rudder allows pilots to control yaw.
What is the function of the horizontal stabilizer in the empennage?
The horizontal stabilizer, a fixed or adjustable surface located at the tail of the aircraft, creates a moment around the lateral axis and generates aerodynamic forces that counteract the aircraft's pitch tendencies. By doing so, it maintains longitudinal stability, prevents the nose from pitching up or down, and ensures equilibrium during level flight, climbs, descents, and manoeuvres.
The horizontal stabilizer provides a stable reference point for the elevator's movements, allowing smooth and controlled pitch adjustments. The elevator, a movable surface hinged to the trailing edge of the stabilizer, changes the effective shape of the stabilizer's airfoil to control the aircraft's pitch. When the aircraft is trimmed, the stabilizer is adjusted gradually with low actuating power, minimizing the control forces the pilot must apply and optimizing the longitudinal trim for cruise flight.
The horizontal stabilizer is the main active surface in the empennage accountable for maintaining proper tilt. It maintains longitudinal stability by keeping the nose position stable. When bad weather or sudden turbulence induced the nose to rear up, I utilized the horizontal stabilizer to regulate the change.
Jim GoodrichPilot, Airplane Broker and Founder of Tsunami Air
What are the types of aircraft empennage?
The types of aircraft empennage are described below.
- Conventional aircraft empennage: The conventional design pairs a horizontal stabilizer with a single vertical stabilizer
- T-tail aircraft empennage: A T-tail raises the tailplane to the top of the fin, keeping the elevator above prop-wash and wing wake
- Cruciform aircraft empennage: The cruciform tail gives the appearance of a cross when viewed from the front because the horizontal stabilizers are placed midway up the vertical stabilizer
- H-tail aircraft empennage: The H-tail mounts two vertical fins at the tips of the horizontal stabilizer and is common on transports and bombers
- Triple Tail aircraft empennage: The triple-tail has three vertical stabilizers
- V-tail aircraft empennage: The V-tail empennages replace the separate horizontal and vertical fins of a conventional aircraft empennage with two angled stabilizers that form a V when seen from behind, which work together as both rudder and elevator
- Inverted V-tail aircraft empennage: The inverted V-tail points the V downward
- Improved V-tail aircraft empennage: The improved V-tail refines the angles for lower drag and better control harmony
- Twin T-tail aircraft empennage: The twin T-tail duplicates the T arrangement for redundancy on very large aircraft
- Ring Tail aircraft empennage: The ring tail wraps the surfaces into a continuous loop
- Boom Mounted aircraft empennage: The boom mounted empennage place surfaces on extended booms or curved supports
- Y-tail aircraft empennage: The Y-tail adds a short vertical extension at the apex, blending V-tail simplicity with a little extra yaw stability
- Half-T aircraft empennage: The Half-T place surfaces on extended booms or curved supports
- U-tail aircraft empennage: The U-tail place surfaces on extended booms or curved supports
The conventional layout,.
How are empennage airfoils chosen?
Empennage airfoils start from symmetry or near symmetry, are tuned for low thickness and proper sweep to meet divergence goals, and finally are verified through the volume-coefficient sizing to deliver the needed authority with minimum drag and pitching moment. Horizontal tailplanes choose symmetrical or virtually symmetrical airfoils with 9%-12% relative thickness. NACA 0009 or NACA 0012 sections are frequent choices. Vertical tailplanes use symmetrical airfoils, often skinnier than the wing. Relative thickness is about 2% of MAC thinner than the wing to delay drag rise. The conventionally symmetric or virtually symmetrical shape guarantees that up and down lift, or side-force, respond identically. When an asymmetrical section is required for negative-lift duties, it is installed upside-down.
Design proceeds by first meeting control needs: the required lift-curve slope CL must be high, and a large usable angle-of-attack range is necessary so the tail behaves equally for positive and negative deflections. With required forces fixed, the airfoil is set so that, at the design driving Mach number, sweep and thickness together keep strong shocks from forming, thereby guaranteeing that a drag-divergence margin M = 0.05 is achieved. The tail is then sized with a tail-volume coefficient method. Horizontal area is set by the tail-to-wing area ratio and vertical area by the vertical-tail volume coefficient. These coefficients locate the respective moment arms.
Are empennage-mounted engines used in aircraft design?
Empennage-mounted engines are used in aircraft design, mostly on smaller regional and business jets. In some small single-engine aircraft the empennage is deliberately placed in the slipstream, and private jets still use rear-mounted engines to generate less cabin noise. Rear-mounted engines appeared on early jets like the Caravelle, VC10, DC-9, Trident, and 727, but starting in the 1970s this layout was gradually phased out on large air transports in favor of under-wing engine mounts that are easier to get at for maintenance and produce lower structural penalties.
Although rear-mounted engines give the additional benefit of lighter, more efficient wings, they bring weight-and-balance issues and require a T-tail configuration where the horizontal stabilizer is positioned above the fuselage to stay clear of engine exhaust. Concepts include U-tail, V-tail, and cross-tail arrangements, with and without engines mounted at the rear fuselage. For concepts with the engine option at the back, the engine contribution to stability was not taken into account for empennage sizing, and considerable trim changes occur with differing engine performance.
What is an advantage of a conventional empennage?
The chief advantage of a conventional empennage is its ability to provide adequate stability and control with the lowest structural weight. Because many aircraft carry their engines beneath the wings, the tail is set far aft. The resulting long lever arm makes it possible to keep tail areas small. Smaller tail surfaces cut both weight and drag, yielding a structurally compact and aerodynamically efficient layout. This light, simple arrangement is easy to manufacture and simpler to maintain, which helps explain why the conventional configuration accounts for roughly 70% of the world's airplanes and remains the most common tail design in commercial aviation.
What is a disadvantage of a T-tail empennage?
A major disadvantage of a T-tail empennage is its tendency to enter a deep stall at angles of attack far above the original stall angle. A stalled wing blankets the T-tail, causing loss of elevator authority and making recovery extremely difficult. The same high angle of attack places the horizontal surface in turbulent, banked airflow, increasing the risk of uncommanded pitch-up and further complicating spin recovery.
Structurally, the T-tail imposes heavier vertical tailplane loads, so the vertical stabilizer must be made stronger and stiffer to support the forces generated by the tailplane. This requirement makes the entire empennage heavier and adds weight that penalises fuel burn and payload. The configuration is more intricate than a conventional tail, and its location high up means maintenance crews struggle to access it.
Routine inspections are complicated because the elevator surface is hard to see from the ground, and maintaining T-tail aircraft is costly due to the difficulty of climbing up and undertaking work. Depending on how the elevators are designed, the high mounting causes airflow problems, while the long, flexible vertical fin increases the risk of flutter and requires extra structural mass to suppress vibrations.
