
An aircraft wheel fairing, commonly
called a
wheel pant or
spat or, by some
manufacturers, a
speed fairing.
A
fairing is a structure whose primary function is
to produce a smooth outline and reduce
drag.
These structures are generally light-weight shapes and covers for
gaps and spaces between parts of an
aircraft to reduce
form
drag and
interference drag,
and to improve appearance.
Types
On aircraft, fairings are commonly found on:
- engine cowlings, to reduce parasitic drag by reducing the surface area,
having a smooth surface and thus leading to laminar flow, and
having a nose cone shape, which prevents early flow separation. The inlet and the nozzle in
combination lead to an isotropic speed reduction around the cooling
fins and due to the speed-squared law to a reduction in cooling drag.
- tail cones, to reduce the
form drag of the fuselage, by recovering the pressure behind it.
For the design speed they add no friction drag.
- wheels
on fixed gear aircraft — often called "wheel pants", "speed
fairings" or in the UK
, "wheel
spats". These fairings are a trade-off
in advantages, as they increase the frontal and surface area, but
also provide a smooth surface, a faired nose and tail for laminar
flow, in an attempt to reduce the turbulence created by the round
wheel and its associated gear legs and brakes.
- wing root, to reduce interference
drag. On top and below the wing it consists of small rounded edge
to reduce the surface and such friction drag. At the leading and
trailing edge it consists of much larger taper and smooths out the
pressure differences: High pressure at the leading and trailing
edge, low pressure on top of the wing and around the fuselage.
- wing tips, which may have a complex
shape to reduce vortex generation and so also drag, especially at
low speed
- fin and rudder tips, to reduce turbulence
at the tip
- elevator and horizontal
stabilizer tips
- strut-to-wing and strut-to-fuselage
junctions
- fixed landing gear junctions
Flap track fairings
Most
jet airliners have a cruising
speed between Mach 0.8 and 0.85. For aircraft operating in the
transonic regime (about
Mach 0.8–1.2),
wave
drag can be minimized by having a
cross-sectional area which changes
smoothly along the length of the aircraft. This is known as the
area rule. On subsonic aircraft such as
jet airliners, this can be achieved by the addition of smooth pods
on the trailing edges of the wings. These pods are known as
anti-shock bodies, Küchemann
Carrots, or flap track fairings, as they enclose the mechanisms for
deploying the wing
flaps.
See also
References
- Crane, Dale: Dictionary of Aeronautical Terms, Third
Edition, page 206. Aviation Supplies & Academics Inc,
Newcastle Washington, 1997. ISBN 1-56027-287-2