Note: Descriptions are shown in the official language in which they were submitted.
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A PROCESS AND AN INSTALLATION FOR THE CONTROL OF THE
EFFICIENCY OF THE AERODYNAMIG SURFACES OF AN AIRCRAFT
The present invention relates to the control of the
efficiency of aircraft aerodynamic surfaces. Its object is
in particular a process and an installation for the control
of the efficiency of auxiliary aerodynamic surfaces such as
the flying and stabilizing surfaces of aircrafts.
Generally, it relates to all aerodynamic surfaces to
which it can be applied, at least locally, on a portion
which is made orientable with a view to obtaining a global
determined efficiency, adapted to the various flying
conditions.
In the prior art, the dimensions of the aerodynamic
surfaces are established either for obtaining a suitable
efficiency for the most critical flying conditions of the
aircraft, or for specially optimizing some flight phases.
The result is that in normal flights, or for other flight
phases, the effect produced by said surfaces may become
excessive or penalizing and leads to a deterioration of the
qualities and performance of the flight.
The researches carried out by the Applicant in the
field of aerodynamics and the control of aircrafts stability
have led to the study and the development of a process and
an installation allowing adapting the efficiency of the
aerodynamic surfaces, particularly of auxiliary aerodynamic
surfaces which are orientable and controlled by control
means, to the various flight configurations of an aircraft.
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According to one aspect of the invention there is
provided apparatus for controlling the operation of an
aerodynamic surface on an aircraft, comprising: means
for mounting an aerodynamic surface on an aircraft to
assume variable orientation with respect thereto; means
for controlling the orientation of said surface with
respect to the aircraft; means for connecting said con-
trolling means to said surface comprising a pivot member
and linkage means pivotally connected to said pivot member
for permanently linking said controlling means to said
surface; and means for selectively blocking said pivot
member with respect to the aircraft to establish, in a
blocking condition, a steerable connection between said
controlling means and said surface to operate the same in
a controlled mode, and to disable such connection, in a
nonblocked condition thereof, to let said surface operate
in a freely floating mode.
According to another aspect of the invention there
is provided an aircraft comprising: a frame; an orient-
able aerodynamic surface mounted to said frame to assumevariable orientation with respect thereto; means including
a control member for controlling the orientation of said
surface with respect to the frame; means for connecting
said control member to said surface comprising a support
member, and a linking arm having a first point pivotally
connected to said control member, a second point pivotally
coupled to said surface and a third point pivotally con-
nected to the support member; and means for blocking said
control member with respect to the frame while allowing
said support member to move freely with respect thereto,
in a first condition of said blocking means to provide a
free floating mode of oper- ation of said surface, and for
releasing said control member and blocking said support
member with respect to the frame to provide a steering
connection between said control member and said surface to
provide a controlled operating mode of said surface in a
second condition of said blocking means.
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Accordingly the ~pplication provides a control
process and installation of the efficiency of the aerody~
namic surfaces of an aircraft, comprising orientable
aerodynamic surfaces operating according to a first opera-
ting mode consisting in controlling their orientation, oraccording to a second mode consisting in leaving them free
to assume a position of equilibrium in the stream of air,
said surfaces being connected on the one hand to actuating
means for controlling their orientation, and on the other
hand to setting means of their equilibrium position,
wherein, for passing from one to the other of said opera-
tion modes, an action is appiiea to the control of a clutch
means interposed between ~aid orientable surfaces and the
actuating means.
Thus, the invention presents the advantage of
providing the aerodynamic surfaces to which it is applied the
possibility of operating either in the "piloted mode" where
its effect is maximum and corresponding to that for which
it was designed, or in a "floating mode" where it becomes
"transparent", producing namely a zer~ or very attenuated
residual effect, or else an effect of determined magnitude.
- As will be discussed herebelow, the effect produced
in the "floating mode" may be adjusted to a desired value
which may be fixed or variable, with the aim of contribu-
ting to the general operation of the aircraft.
To this aim, in the floating mode, the equilibriumconditions of the control surface in the air stream may be
modified by any mechanical means located inside the aircraft
using for instance counterweights and/or a damping device,
or again by outer means such as a trailing-edge flap or tab
the steering of which is controlled.
The invention applies to aerodynamic surfaces of
subsonic or supersonic aircrafts or airplanes with natural
or artificial stability for all flight configurations.
Amongst the aerodynamic surfaces to which the invention
applies, one may particularly mention the "canard" type
con~rol surfaces, the flying surfaces and the fins.
The use of canard control surfaces exhibits a great
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interest for the operation of airplanes in very different
flying conditions :
- at lower speeds, it allows particularly increasing
the lift, or for an equal lift, it allows` improving the
S lift-drag ratio when taking off or landing;
- at higher speeds, the use of canard control sur-
faces allows increasing substantially the manoeuvrability
of the airplane, which is a quality particularly looked for
in fighter planes.
However, for some high speed flying configurations,
disadvantages appear such as for instance aerodynamic
interactions with the flying surface, leading to the
retraction of the canard control flying surfaces within
the fuselage of the airplane, or to folding them so as to
form vertical surfaces.
The invention avoids having recourse to such complex
devices. As will be explained further down, the use of
canard control surfaces to which the invention applies
allows, in s~upersonic airplanes, passing from the subsonic
condition to the supersonic condition without being penali-
zed, as is the case in the prior art, by a large increase
of the stability and by a balancing using an "off-set lift".
The tail fin of an airplane should be sized so as to
compensate for the dissymmetric moments, particularly,
eventually, that due to a disabled engine of a multi-engine
airplane. Consequently, under normal conditions, the air-
plane is very sensitive to side-slips and may exhibit an
important yawing return moment leading in practice to a
deterioration of the performance and flying qualities of
the airplane. The application of the invention to a portion
of the tape fin allows, while preserving the maximum effi-
; ciency for critical cases, limiting the efficiency of the
fin when flying under normal conditions to a value providing
the aircraft with a notable improvement of its flying
capacity when side-slipping or subjected to strong side
winds.
Various exemplary uses of a canard control surface
according to the invention are now described for illustrating
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the technical improvements brought about by the invention.
EX~MPLE 1 - Supersonic aircrafts : the longitudinal
static stability of an airplane is characterized by the
relative position of the centre of gravity relative to the
centrum or center of pressure of the aircraft. Its magnitude
is represented by the incidence return moment, the lever-
arm of which is provided by the distance from the centre of
gravity of the airplane to the aerodynamic centre. The limit
of the rear trim is generally determined by these stability
conditions in a subsonic flight;
The passage from a subsonic flight to a supersonic
flight causes the backward displacement of the aerodynamic
centre which increases the length of the hereabove mentioned
lever-arm and causes a nosedive moment which has to be
compensated for by a nose-lift moment, viz. by an "off-set
lift" of the elevator. This flight configuration is not
favourable for the fineness of the aircraft. In order to
find again a convenient flight condition, particularly
during the lo~g stretches of a supersonic flight, one is
led to apply remedies commanding the use of complex auxi-
liary means.
Said means consist generally in providing the air-
craft with a load transfer device towards the rear so as to
displace backwardly the trim of the aircraft in parallel
with the backward displacement of the aerodynamic centre.
The invention avoids having to resort to such a
device where the aircraft is provided with a canard control
surface. As a matter of fact, the application of the inven-
tion to said control surface allows compensating for the
backward displacement of the aerodynamic centre by moving
the aerodynamic centre forward, and this is obtained by
having the canard control surface passed from the subsonic
flight floating mode to the supersonic flight piloted mode.
EXAMPLE 2 - Airplanes with a controlled longitudinal
stability. In such aircrafts, the centre of gravity is behind
the aerodynamic centre, or in front but near the aerodynamic
centre, and a compensation for a lack of natura~ stability
is obtained with an automatic system supplying the return
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and damping moments which are necessary by operating the
elevator, the steering of which is function of the incidence
and pitch angular speed variations. The major disadvantage
of this operation mode resides in the fact that it is indis-
pensable to multiply, for reasons of reliability and safety,the automatic flying chains, thereby increasing notably the
cost of the electronic equipment of the airplane.
The application of the invention to the canard
control surface allows at will, and particularly when the
flight is difficult, to move the aerodynamic centre back-
wards by passing to the floating mode and to provide the
airplane with natural stabiiity conditions which restore
the possibility of controlling it.
EXAMPLE 3 - Laboratory airplanes : The canard
control surface according to the invention, which allows
displacing the aerodynamic centre of the airplane as here
above explained, provides the invention with an interesting
possibility of being applied to laboratory airplanes in
which it allows modifying the stability at will and coming
back to the initial conditions, thereby allowing adjusting
and qualifying during the flight the stability control
devices.
The following description is given with reference
to the accompanying drawings wherein :
Fig. la is a schematic representation of an aircraft
provided with a canard control surface in a fixed or flying
condition (operating in the "piloted mode");
Fig. lb is a schematic representation similar to
that of Fig. la, where the canard control surface is in the
disengaged condition (operating in the "floating mode");
Fig. 2 shows schematically a control surface accor-
ding to the invention;
Fig. 3 is a schematic illustration of a control
surface comprising a trailing edge flap or tab;
Fig. 4a and 4b show schematically a clutch means or
control installation of an aerodynamic surface comprising
a mechanism allowing bringing it into a disengaged condition
or into a piloting condition;
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Fig. 5 illustrates an embodiment of the invention
envolving a part only of a control surface; and
Fig. 6 shows an embodiment of the invention invol-
ving the ends of the main flying surfaces of an aircraft.
In Fig. la and lb, reference numeral 1 designates
the main flying surface of an airplane, numeral 2 a canard
control surface articulated along an axis situated in a
horizontal plane and disposed transversely relative to the
longitudinal axis of the airplane. In Fig. la, control
surface 2 is under the dependençe of the control moments.
It operates in a piloted mode tP mode), viz. its setting
may be modified or maintained fixed relative to the airplane.
During the evolutions of the airplane, the control surface
2, in this condition, operates at the same incidence
variations as the flying surface 1 and partakes to the
operation of the airplane by producing in particular, on
the one hand a nose up moment originating from force F2
which varies with the incidence, and on the other hand a
forward displ~cement of the general aerodynamic centre of
the aircraft causing a decrease of the longitudinal stabi-
lity due to the position of the canard situated in the
front of the flying surface.
In Fig. lb, the control surface is made floating
(operating in the F mode), meaning that it is free in
rotation about an axis situated substantially perpendicular
to the flight direction. The rotation axis 6, visible in
Fig. 2, being in front of the aerodynamic centre Fc of the
canard, the control surface 2 takes its bearings in the
wind's eye and operates under an incidence and a lift F2
of constant and low or zero value, which remains independent
of the incidence variations of the airplane. In practice,
under such conditions, it may be considered that the
control surface does not partake to the incidence operation,
being then called "transparent", and the effects hereabove
mentioned for the P mode (nose up moment and forward dis-
placement of the aerodynamic centre) disappear. Compared
to the case of Fig. la, there is therefore an increase of
the longitudinal stability and, moreover, the aerodynamic
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interaction with the flying surfaces becomes negligible.
When operating in this F mode, apart from a low
constant influence originating in the residual force F2,
the aircraft operates as if it was not equiped with a
canard control surface or if the latter was in a retracted
position.
Fig. 2 shows schematically the means allowing
setting the trim position of the control surface 2 operating
in the F mode. This position results from the equilibrium
of the moments about the rotation axis 6, that is the
equilibrium between the moment of aerodynamic origin from
F2, the moment pertaining to the mass originating from the
excentered position of the centre of gravity of the system
relative to axis 6 and the setting moment due to the
mechanism which comprises the counterweight 4 and the
damping device 5.
The invention foresees setting the trim position
of the control surface 2 by means of a setting mechanism 4-
5 in order to,reach a configuration such that the force
produced assumes a desired value which may be fixed or
variable. A first way consists in displacing the counter-
weight 4 which may be brought nearer or further from the
rotation axis 6 by means of a motor, not shown.
Numeral 7 designates the engaging and disengaging
device for the control surface 2. This device, the control
of which is illustrated schematically at 7', provides
between the connecting rod 9 which is rigid with the
control surface 2 and the connecting rod 11 which is rigid
with the control means of the control surface an engaged
condition and a disengaged condition.
A second way for varying the trim condition of the
control surface 2 is shown in Fig. 3. The control surface 2
is provided with an auxiliary flap 3 or tab articulated on
the control surface 2 by means of a hinge the axis 6' of
which is parallel to the rotation axis 6 of the control
surface 2. The flap 3 is connected to the mobile part of a
jack 3' the body of which is rigid with the control surface
2. The jack, shown outside the control surface 2 for the
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sake of clarity, is under the dependence of known control
means establishing an appropriate piloting law. The deflec-
tion of the flap controlled by the jack 3' develops an
aerodynamic force F'3 the moment of which causes a free
pivoting of control surface 2 on its rotation axis 6 until
it reaches a position such that there is an equilibrium with
the opposed moment originating in the new force F"2 relative
to control surface 2.
It may be seen that the invention not only allows
producing a force usable for piloting with the assitance of
a canard control surface operating in the floating mode, as
is possible to produce with the assistance of a control
surface of the prior art operating in the piloted mode, but
it offers the extra advantage according to which the control
surface of the invention which preserves substantially the
same incidence in the air stream for all the incidences of
the airplane does not modify the stability conditions of the
airplane and eliminates the risk known as "stall" of the
canard control surfaces of the prior art when the airplane
flies at a great incidence.
Advantageously, the flap 3 is provided with a
connecting rod 30 for controlling its position and which
may be made rigid with the airplane when there is a break
down of the flap control means, so that it is always possible
to control the steering of the flap.
Fig. 4a and 4b show schematically an embodiment of
the mechanism allowing the passage from the P mode to the F
mode and reverselyin the most general case where the control
surface 2 in the P mode may also be piloted under the action
of a control 11.
The mechanism comprises substantially two pairs of
symmetrically operating jacks (12,12'), (13,13') associated
to a connecting rod system 8, 9, 10, 11. The connecting rod
8 is attached to the rotation axis 6 of the control surface
;~ 35 2, as is shown in Fig. 2. The connecting rod 10 comprises
at each of its ends a block 14, 14' on which is exerted the
effort originating in the jacks. For the sake of clarity
of the drawings, only the elements which are essential for
a good understanding of the invention have been shown, and
the jacks are represented by their mobile elements.
According to Fig. 4a, the operation in the F mode
is provided by maintaining the block 14' i~n a fixed position
under the action of jacks 13 and 13' and by freeing block
14 by a symmetrical backward displacement of the jacks 12
and 12'. The control surface 2 is then free to move under
the action of the aerodynamic force F'2. Its equilibrium
position is determined as explained hereabove.
The passage to the P mode operation is obtained
(Fig. 4b) by actuating the symmetrical movement towards each
other of jacks 12 and 12' which, in their movement, bring
back and maintain block 14 in the neutral position shown in
the Figure. The control surface 2 is then locked. In the
case where the control surface should also be piloted, the
bringing together of the jacks 12 and 12' causes simultane-
ously the symmetrical backward movement of jacks 13 and 13'
and the piloting action applied on connecting rod 11 allows
steering the control surface 2 to the desired incidence.
In Fig. 5, the invention is applied to a portion
only 15' of the rear vertical fin 15 of an airplane, by
means of a device not shown which can be of the type as that
mentioned with reference to Fig. 3a and 3b. The end 15' of
the control surface rotatably mounted about an axis a-a'
substantially transverse to the longitudinal axis of the
airplane is adapted for operating in the P mode or in the
F mode, whereas the portion 15 of the control surface is
fixed or under the piloting control. The advantage brought
about by this alternative of the invention is that it is
possible to size the whole assembly of the control surface
and to choose the operation mode which is best adapted to
each of the flight configurations of an airplane. Thus, it
is possible to reduce the influence of side winds and to
improve a side-slip flight or a flight with a cross wind.
Moreover, according to the invention, the piloting of the
control surface 15 in a disengaged condition by inner
control means provides the extra possibility of a yaw
piloting.
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In Fig. 6, the invention is applied to a portion
only of the main flying surface 1 of an aircraft. The ends
2 of each wing 11, 12 are rotatably mounted on said wings
along an axis b-b' substantially transverse to the longi-
tudinal axis of the airplane.
Auxiliary flaps 3 comprising steering control means
are articulated onto the surfaces 2 along an axis parallel
to the flying surface trailing edge.
The surface 2 may operate in the ~ mode or in the
F mode due to a device not shown but which may be of the
type described with reference to Fig. 4a, 4b. Said device
provides the engagement conditions in which the surfaces
contribute to producing the total aerodynamic effect of
the flying surface 1, or the disengaged condition in which
the surfaces which take their bearings in the stream of
air allow reducing the aerodynamic surface and the lift
gradient so as to reduce for example the sensitiveness of
the airplane to turbulences.
Moreover, according to the invention, the piloting
of surfaces 2 via the flaps 3 allows preserving the totality
of the roll control capacity of the airplane.
According to the object aimed at, the invention can
be applied, on the same airplane, to one only of the sur-
faces of an appropriate type, or on the contrary simultane-
ously to several surfaces of different types.
