Fully movable aircraft stabilizer
A
stabilator
is a fully movable aircraft horizontal
stabilizer
. It serves the usual functions of longitudinal stability, control and stick force requirements
[1]
otherwise performed by the separate parts of a conventional
horizontal stabilizer
(which is fixed) and
elevator
(which is adjustable). Apart from reduced drag, particularly at high Mach numbers,
[2]
it is a useful device for changing the aircraft balance within wide limits, and for reducing stick forces.
[3]
Stabilator is a
portmanteau
of
stabilizer
and
elevator
. It is also known as an all-moving
tailplane
, all-movable tail(plane), all-moving stabilizer, all-flying tail(plane), all-flying horizontal tail, full-flying stabilizer, and slab tailplane.
[2]
General aviation
[
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]
Because it involves a moving balanced surface, a stabilator can allow the pilot to generate a given pitching moment with a lower control force. Due to the high forces involved in tail balancing loads, stabilators are designed to pivot about their
aerodynamic center
(near the tail's mean quarter-chord). This is the point at which the pitching moment is constant regardless of the angle of attack, and thus any movement of the stabilator can be made without added pilot effort. However, to be certified by the appropriate regulatory agency, an airplane must show an increasing resistance to an increasing pilot input (movement).
[
citation needed
]
To provide this resistance, stabilators on small aircraft contain an
anti-servo tab
(usually acting also as a
trim tab
) that deflects in the same direction as the stabilator,
[4]
thus providing an aerodynamic force resisting the pilot's input. General aviation aircraft with stabilators include the
Piper Cherokee
[2]
and the
Cessna 177
. The
Glaser-Dirks DG-100
glider initially used a stabilator without an anti-servo tab to increase resistance: as a result, the pitch movement of the glider is very sensitive. Later models used a conventional stabilizer and elevator.
Military
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]
All-flying tailplanes were used on many pioneer aircraft and the popular
Morane-Saulnier G
,
H
and
L
monoplanes from France as well as the early
Fokker Eindecker
monoplane and
Halberstadt D.II
biplane fighters from Germany all flew with them, although at the cost of
stability
: none of these aircraft, with the possible exception of the biplane Halberstadts, could be flown hands-off.
Stabilators were developed to achieve adequate
pitch
control in supersonic flight, and are almost universal on modern military
combat aircraft
.
[2]
The British wartime
Miles M.52
supersonic project was designed with stabilators. Though the design only flew as a scale rocket, its all-flying tail was tested on the
Miles Falcon
.
[5]
The contemporary American supersonic project, the
Bell X-1
, used separately-adjustable horizontal stabilizer and elevators allowing movement as a single surface or elevator deflection at a fixed tailplane setting.
[6]
Entering service in 1951, the
Boeing B-47 Stratojet
was the world's first purposely built jet bomber to include one piece stabilator design. A stabilator was considered for the
Boeing B-52 Stratofortress
but rejected due to the unreliability of hydraulics at the time.
[2]
The
North American F-86 Sabre
, the first U.S. Air Force aircraft which could go supersonic (although in a shallow dive) was introduced with a conventional horizontal stabilizer with elevators, which was eventually replaced with a stabilator.
When stabilators can move differentially to perform the
roll
control function of
ailerons
, as they do on many modern
fighter aircraft
they are known as
elevons
or
rolling tails
. A
canard surface
, looking like a stabilator but not stabilizing like a tailplane,
[7]
can also be mounted in front of the main
wing
in a canard configuration (
Curtiss-Wright XP-55 Ascender
).
Stabilators on military aircraft have the same problem of too light control forces (inducing overcontrol) as general aviation aircraft. Unlike light aircraft, supersonic aircraft are not fitted with anti-servo tabs, which would add unacceptable drag. In older jet fighter aircraft, a resisting force was generated within the control system, either by springs or a resisting hydraulic force, rather than by an external anti-servo tab. For example, the
North American F-100 Super Sabre
, used gearing and a variable stiffness spring attached to the control stick to provide an acceptable resistance to pilot input.
[8]
In modern fighters, control inputs are processed by computers ("
fly by wire
"), and there is no direct connection between the pilot's stick and the stabilator.
Airliners
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]
Most modern airliners do not have a stabilator. Instead they have an
adjustable horizontal stabilizer
and a separate elevator control. The movable horizontal stabilizer is adjusted to keep the pitch axis in
trim
during flight as the speed changes, or as fuel is burned and the
center of gravity
moves. These adjustments are commanded by the autopilot when it is engaged, or by the human pilot if the plane is being flown manually. Adjustable stabilizers are not the same as stabilators: a stabilator is controlled by the pilot's control yoke or stick, whereas an adjustable stabilizer is controlled by the trim system.
In the
Boeing 737
, the adjustable stabilizer trim system is powered by an electrically operated
jackscrew
.
[9]
One example of an airliner with a genuine stabilator used for flight control is the
Lockheed L-1011
.
See also
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]
References
[
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]
- ^
Roskam,
Airplane Design
, part III, Empennage layout, Longitudinal considerations
- ^
a
b
c
d
e
Abzug, Malcolm J.; Larrabee, E. Eugene (23 September 2002).
Airplane Stability and Control: A History of the Technologies that Made Aviation Possible
. Cambridge University Press. p. 78.
ISBN
978-1-107-32019-2
. Retrieved
17 October
2022
.
All-movable tail surfaces became interesting... when high Mach number theory and transonic wind-tunnel tests disclosed poor performance of ordinary flap-type controls.
- ^
Daroll Stinton,
The design of the aeroplane
, Control surfaces, p. 447 and 449 : "...for variation of tab size, gear ratio and stabilator pivot position, the stick-free neutral point can be varied almost at will.
- ^
Phillips, William Hewitt (November 1998). "6. Problems Encountered as a Result of Wartime Developments".
Journey in Aeronautical Research: A Career at NASA Langley Research Center
. NASA History Office
. Retrieved
17 October
2022
.
the tab on the all-movable tail was changed from a servo tab to a
geared unbalancing tab
. With this arrangement, the control forces were similar to those on a conventional airplane
- ^
Brown, Eric.
Wings on my Sleeve
. London: Weidenfeld & Nicolson, 2006.
ISBN
978-0-297-84565-2
.
- ^
High Speed Test Flying, Yeager, The Aeronautical Journal, December 1956, p.788
- ^
Hoerner,
Fluid dynamic lift
, about XP-55, p. 11-29, Stability Contributions : "Stabilization in any canard configuration can only be obtained from the wing."
- ^
Test Pilot, edited by Schmidt, Mach 2 Books,1997, p.50
- ^
Federal Register
. Office of the Federal Register, National Archives and Records Service, General Services Administration. July 1978. p. 32404
. Retrieved
18 October
2022
.
External links
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]