US2978037A — Stabilizing means for helicopter aircraft

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US2978037A — Stabilizing means for helicopter aircraft; scanned drawings precede the patent heading. ·

Page 1

April 4, 1961 H. C. J. FOCKE 2,978,037
STABILIZING MEANS FOR HELICOPTER AIRCRAFT
Filed Feb. 12, 1958 4 Sheets-Sheet 1

INVENTOR
Henrich Carl JOHANN FOCKE

BY Voelomen & Pre Corere

ATTORNEYS,

Page 2

April 4, 1961 H.C. J. FOCKE 2,978,037
STABILIZING MEANS FOR HELICOPTER AIRCRAFT
Filed Feb. 12, 1958 4 Sheets-Sheet 2

46A

44a

43A

MOTOR

INVENTOR
| HeNRIcH CarL JoHann FOCKE

BY Toulmin oelomin.

ATTORNEYS

Page 3

April 4, 1961 H. GC, J. FOCKE 2,978,037
STABILIZING MEANS FOR HELICOPTER AIRCRAFT
Filed Feb. 12, 1958 4 Sheets-Sheet 3

INVENTOR

HenricH Care JoHann FOCKE

BY ToccLonein J Tonboriin.

ATTORNEYS

Page 4

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H. C. J. FOCKE 2,978,037

STABILIZING MEANS FOR HELICOPTER AIRCRAFT
Filed Feb, 12, 1958

4 Sheets-Sheet 4

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Stability Achieved By
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Approximation By Simple
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Stabilization According
7 Present Invention

HenricH Cari JoHann FOCKE

BY Toecloreioe, $ Tocelomen

ATTORNEYS

Page 5

United States Patent Office

2,978,037
Patented Apr. 4, 1961

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2,978,037
STABILIZING MEANS FOR HELICOPTER
‘AIRCRAFT

Heinrich Carl Johann Focke, Bremen, Germany, assignor
to Ministerio da Aeronautica Diretor do Material,
Aecroporto Santos-Dumont, Rio de Janeiro, Brazil

Filed Feb. 12, 1958, Ser. No. 718,939
7 Claims, (CI. 170—169.15)

‘This invention relates to improved stabilizing means
for helicopter flying machines.

This application .is.a continuation-in-part of my pend-
ing patent application Serial No. 411,501 filed February
19, 1954, now abandoned.

It is an object of my invention to provide improved
stabilizing means for helicopter flying machines which
permits to maintain a perfect dynamic stability of the
helicopter. 7

It-is a further object of the invention to provide im-
proved stabilizing. means in a helicopter flying machine
for the purpose described, which means. further permit
in a simple ‘manner to effect simultaneously both a cyclic
and a collective pitch adjustment of the blades of a multi-
blade rotor of.a flying machine, whereby. both the direc-
tion and the magnitude of the resultant. aerodynamic
forces acting on the machine are maintained constant.

Helicopter flying machines are generally provided with
a rotor or rotors each having a plurality of blades, such
as, for instance, three or four, and which blades are
pivotally connected to the‘hub of the rotor. Consequent-
ly, when the latter rotates in an air flow generated by the
movement of the airplane through the air, for instance
ia forward horizontal direction, the blades moving through
the upstream side portion of their circular path, i.e. the
blade moving forward through the. air current with the
leading edge of the blade. directed upwardly and the trail-
ing edge directed downwardly, so as to receive an upwardly
lifting force component, are tipped upward, and those
blades moving through the downstream portion, i.e. toward
the rear of the plane against the direction of flight of the

. latter, are forced downward by the action of the air upon
the blades. This results in an inclination of the axis of
the geometrical cone surface described ‘by the blades and
referred to hereinafter as the “blade cone” for the sake
of brevity.

The inclination of the blade cone axis corresponds
to an inclination of the direction of the lifting force. of
the rotor cr of the resultant of the lifting forces of the
rotors where there is more than one rotor provided with
the machine, due to the existing equality of centrifugal
forces of the several blades constituting the rotor.

Since the center of gravity of the helicopter machine
is located below the apex of the aforesaid blade cone,
the inclination of the lifting force causes the tendency
toward pendular movements of the machine which may
become so high that the weak outside damping forces of
the air available during a disturbance in the position of
equilibrium. of the machine are no longer sufficient for
maintaining the necessary dynamic stability.

The typical behaviour of the blades of the rotor not
only causes a change in direction but also in magnitude
of the.lifting force and this is, as well as the change of
direction of.said force, harmful for the steady movement
of the aircraft. - 7 :

Such change in magnitude of the lifting force causes,
in forward. flight, an up- and downward oscillation of the

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center of gravity and thus a sinusoidal movement of the
helicopter in a vertical plane.

Thus, in order to obtain a steady flight of the helicopter,
it is necessary to compensate the effects of both the change
of direction.as well as the change of magnitude of the
resultant lifting forces,

While the compensation of the direction of the lifting
forces is achieved by cyclic pitch variation, the compen-
sation of the magnitude of the lifting forces can be real-
ized by collective pitch variation of the rotor blades of
the helicopter.

Now, I have discovered that; at the critical speeds be-
tween approximately 20 and 70 km. per hour, the rela-
tionship between the direction and the magnitude of the
lifting forces, and consequently, between the rates of col-
lective and cyclic pitch variation, can be considered con-
stant, so that the change of collective pitch variation with
the air speed is sufficient to determine the required
stabilization, if collective pitch variation and cyclic pitch
‘variation are effected simultaneously.

Various. means have already been proposed for sup-
pressing the resultant undersirable lack of dynamic stabi-
lity. Thus it has’ been suggested to convert the tilting
movement of the blade cone due to the forces due to the
air flow past the machine, i.e. the velocity of the machine
relative to the air or “relative velccity,” into a variation
of the position of an clement of the machine acting con-
trary to the high restoring moments, such as the eleva-
tor of a normal flying machine.

On the other hand, it is well known in the art, for in-
stance as described in the Patent 2,439,089 to Hodson, to
effect simultaneously a cyclic and collective adjustment
of the pitch of the blades of a helicopter multi-blade rotor
for steering purposes. This is done by a control device
comprising 2 downwardly extending rod connected by a
universal joint to the center of the propeller hub and
bearing a sleeve slidably mounted on the rod and pivot-
ably connected by a numiber of links to. the individual
propeller blades, whereby the rod coincides always with
the axis of the above-mentioned blade cone.

Furthermore, the lower end of the rod is pivotally
connected to a servo-device controlling the angular posi-
tion of a ring which is cantable relative to a plane tranis-
verse at right angle to the hub axis, and connected by
articulated arms to the blades for varying the pitch of
the latter. Separate hydraulic means are also required
for control of the flap angle of the blades relative to the
hub axis, i.e. the degree of slope of the blade cone rela-
tive to the central cone axis. :

This control is effected by raising or lowering a spheri-
cal bearing supporting the aforesaid cantable ring.

In known devices of this type, the blade cone is used
as a steering device and, if the pilot would intend to use
the same as a. stabilizing device as proposed, it would
be necessary for him to hold the steering bar or handle
rigidly in a determined neutral position. If he attempts
to do so, collective pitch variation becomes dependent
upon the movement of the aforesaid sliding sleeve on the
rod representing the axis of the blade cone without there
being provided a fixed ratio between the cyclic and the
collective pitch variations. This leads to a superimposi-
tion of the steering and stabilizing effects which has most
unpleasant effects on the pilot who is constantly under
the impression that the flying machine is uncontrolledly
carrying out manoeuvres contrary to his will. This con-
flict between intended steering and automatic control of
the machine is particularly undesirable if the machine
flies through gusty wind or gale.

Furthermore, I have proposed, for instance, in my
German Patent 950,169, to provide separate steering
means in a helicopter flying machine, independent of the
rotor head, so that the rotor itself becomes available. be-.

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2,978,087

sides its helicopter-sustaining function, exclusively for
effecting a reduction of the pendular movements and
vertical drops.

This known arrangement suffers from the drawbacks
of requiring a plurality of séparate control devices with
inherent increase in the possibility of faulty operation,
and further from the drawback that it does not permit
the craft to obtain perfect dynamic stability.

Thus, the inclination of the blade cone in the known
construction may control, by automatic variation de-
pendent on the relative velocity of the machine in air,
the angular position of the aforesaid cantable ring, there-
by producing a cyclic variation of the propeller blade
pitch. .

However, although the direction of the resultant lift-
ing force is thereby made independent of the relative
velocity, this does not apply as far as the magnitude
of the lifting force is concerned.

I provide a stabilizing system for adjusting simul-
taneously (a) collectively the pitch of the blades of a
helicopter rotor, and (b) the cyclic pitch variation of the
blade or several blades thereof, which stabilizing system
comprises a simple arrangement of an inner annular
member cantable about a fixed eccentric axis, and an
outer annular member rotatably disposed about said inner
annular member and connected by articulated linking
members to the blades of a helicopter rotor for varia-
tion of the pitch of the latter.

A preferred embodiment of my invention further com-

prises rod means for indicating the inclination of the
blade cone and for automatically converting that inclina-
tion into a simultaneous interdependent adjustment of
the collective pitch and the individual pitch variation of
the rotor blades.
. In another embodiment of the invention there is fur-
ther provided an element for measuring simultaneously
the change in the direction and, in the aforesaid ratio
thereto, the magnitude of the lifting forces, by deter-
mining the relative speed of the machine in air, and
operating means for changing the inclination of the afore-
said outer annular member about the said eccentric axis
and relative to the rotor shaft.

This air-speed measuring element may, for instance,
comprise a piston working in a cylinder which has an
open end or nozzle-like mouth piece directed toward the
air current past the machine.

A hydraulic power transmission connected to this pis-
ton then engages the aforesaid eccentrically mounted an-
nular members, in such a manner that, upon adjustment
of the position of the annular members relative to the
eccentric axis a variation of the average angle of attack
of the propeller blades (or pitch of the blade relative

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to the longitudinal blade shaft axis) is effected dependent °

on the position of the aforesaid piston in the cylinder,
ie. on the relative velocity of the machine in the air.

Thus, due to the rotary movement of the outer an-
nular‘member about the inner one when the plane in
which the latter extends, is at an oblique angle relative
to the propeller hub axis, i.e. canted about the eccentric
axis, both the cyclic pitch variation and the collective
pitch of the propeller blades are simultaneously changed.

By a suitable selection of the rate of eccentricity of
the eccentric axis, ie., its distance from the aforesaid
hub axis, the amount of collective pitch can be deter-
mined in conformity with the above mentioned ratio of
cyclic to collective pitch variation, and is preferably such
that the amount. of collective pitch variation is by 20%
larger than the effected cyclic pitch variation. The ratio
between the longest and the shortest part of the ring
diameter normal to and divided by the eccentric axis is,
therefore, in the order of 1.25.

The invention will be better understood from the de-
scription thereof following hereinafter in connection with
the accompanying drawings, in which

Figure 1 is a perspective view of a helicopter propeller
mounted on the propeller-bearing portion of a helicopter

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flying machine and comprising a mechanical stabilizing
system according to the invention;

Figure 2 is a longitudinal section view of the arrange-
ment shown in Figure 1;

Figure 3 shows in perspective and fragmentarily a
similar view as in Figure 1, in which the aforesaid
mechanical system is replaced by a hydraulic system;

Figure 4 shows, also in perspective, a hydraulic system
as in Figure 3 but in which the blade cone indicating
means are replaced by air flow measuring means.

Now describing the embodiment comprising a measur-
ing element for determining the inclination of the blade
cone, Figures 1 and 2 show the main rotor head of a
helicopter comprising a rotor having blades 1 connected
in a conventional manner pivotably to the rotor hub 2,
which is rigidly mounted on the hollow rotor shaft 3 for
rotation with the latter in a stationary shaft sleeve 30.
This sleeve is mounted on a gearbox 33 inside the bull
31 of the machine and through an opening 63 in the hull.
Hollow shaft 3 is supported by rolling contact bearing
means 32 as shown in Figure 2 (for instance, ball or
roller bearings) against the wall of the gear box 33, and
receives its rotary movement from a power shaft 34
via a gear train comprising, for instance, gears 35 and 36.

On the wail of gear box 33, or at another suitable
portion, for instance of hull 31, there is rigidly mounted
a rod 37 which extends upwardly through hollow shaft
3 coaxially with the latter. At its upper end, rod 37
bears a toggle joint 5 to which an inclinable rod 6 is
attached for displacement in any direction and inclina-
tion at an angle between the axis of rod 37 and shaft 3,
on the one hand, and a plane at right angle thereto and
passing through the toggle joint 5, on the other hand.

Rod 6 bears a sleeve 7 which is slidably displaceable
on rod 6 and is connected via articulated joints 7a to a
number of links 8 which are articulatedly connected at
8a to the blade shafts 1a.

At its upper end, shaft sleeve 30 bears a transverse
shaft 21 which is displaced by an eccentricity e from the
common center M of two concentrically disposed annular
members or rings 4 and 40, of which the outer ring 4
is mounted about the inner ring 40 for rotation there-
about by rolling on intermediary rolling contact bearings,
for instance ball bearings 22.

Outer ring 4 is connected via an articulated toggle joint
23 between links 24 and 25 to the hollow shaft 3, link
24 being pivotally connected to ring 4 at 24a, and link
25 being also pivotally connected at 25a to shaft 3.

Cuter ring 4 is furthermore connected at pivot points
26a to one end of link, rods 26 while the other end of
each of link rods 26 is pivotally connected at 27a to a
pitch control arm 27 being an integral part of blade
sleeve 28 which is rotatably mounted about blade shaft
ia and is rigidly fixed to blade 1. .

At its lower end where it is mounted on toggle joint
5, blade cone indicating rod 6 is provided with an arm
41 extending at substantially right angle from rod 6. At
its free end, this arm 41 is connected by pivot 42 toa
lever rod 43 which forms part of the stabilizing mecha-
nism according to the invention. Lever rod 43 extends
downwardly through hollow shaft 3 and is pivotally con-
nected at its lower end at 43a to one arm of a trans-
verse double arm lever 44 having its fulcrum 44a at a
nose portion 45 of casing 33. The other arm of lever
44 is pivotally connected at 46a to an upwardly extending
lever rod 46, the upper end of which is connected at 46b
to inner ring 40.

The stabilizing effect of this arrangement will be
briefly described hereinafter. When the blade cone
formed by blades 1 is slightly inclined in rearward direc-
tion in Figure 1, forward flight taking place in the direc-
tion of arrow F therein, lever 26.{R) attempts to raise
the right side of rings 4 and 40 (always as seen in Fig-
ure 1) and lever 26 (L) fries to lower the left side of

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2,978,087

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these rings. Rod 6 .will thus.be inclined toward the left,
the free end of arm 41 will be raised and pull rod 43
and end 43a of lever 44 upwardly. Consequently, the
end 46a of lever 44 will pull rod 46 downwardly, and,
since the upper end 46d of this rod is attached to the
right side of inner ring 40, it will pull this side of ring
40 as well as ring 4 downwardly, trying to turn these
rings about eccentric axis 21 and thus. counteracting at
Jeast partly the upwardly pulling effect of levers 26
(R), until a dynamic equilibrium of forces has been
established.

With respect to the movement of the rod 6 in the
embodiment of Figure 1, it is pointed out that when the
helicopter aircraft is moving in a forward direction, the
rotor blade moving forwardly with respect to the move-
ment of the vehicle will be forced upwardly, whereas the
rotor blade moving rearwardly will be forced down-
wardly. Thus, the geometric cone formed by the rotor
blades will be tilted in a rearward direction. However,
the metal shaft of the rotor blades will not. be moved,
and its axis will remain in a vertical position. The axis,
however, of the geometric cone of the rotor blades will
be tilted in a vertical plane extending longitudinally of
the helicopter. The tilting of the geometric cone of the
blades will depend upon the forward speed of the rotor.
Thus, as viewed in Figure 1, the rod 6 will indicate
the position of the axis of the geometric cone formed by
the rotary blades. Accordingly, the position of the rod
6 is responsive to the velocity of the aircraft in a
horizontal direction with respect to the ambient air.
Thus, the rod 6 indicates the relative speed of the heli-
copter.

‘The inclination of the cone formed by the biades is not
a matter of chance but is dependent upon the relative
speed of the aircraft: According to the present invention,
the position of the cone of the blades is varied so as
to bring the helicopter back to dynamic stability. The
original impulse for changing the position of the swash
ting 4, 49 by tilting around its eccentric axis 21 is derived
from ‘the tendency of the rotor blades to form the geo-
metric cone with its axis tilted rearwardly. Since the
axis of the geometric cone is clearly related to the for-
ward speed of theaircraft, the tilting of the swash ring
will result in the blade cone assuming a new position
which will also be related to forward speed. The new
position of the blade cone, however, will be different
from the position which would be assumed by the blade
cone if the tilting means of the swash plate 4, 40 were
not present.

The new position of the blade cone is thus related to
the forward speed of the aircraft: However, with any
different collective and cyclic pitch, there is another cor-
responding position of equilibrium. of the geometric cone,
This occurs because the position of the blade cone not
only depends upon forward speed of the aircraft but also
upon the pitch of the blades,

In Figure 3, the mechanical lever system of Figures 1
and 2 is replaced by ‘a hydraulic system comprising a
cylinder 50 and a piston 51 therein fastened at the lower
end of rod 43, and a cylinder 52 and piston ‘53, the
latter being fastened to the lower end of rod 46. Hy-
draulic fluid fills the cylinder spaces above and below
pistons 51 and 53 and can be shifted from cylinder 50
to 52 and back through fluid conduits 54 and 55. Thus,
if piston 51 is lowered by rod 43 it presses fluid through
conduit 55 and raises piston 53 in cylinder 52 and
together therewith also. rod 46.

Thus, the inclination of rings 4 and 49 about eccentric
axis 21 is varied in synchronism with the swinging move-
ments of rod 6 about toggle joint 5 in the vertical longi-
tudinal center plane of the flying machine, or parallel to
this plane, if the helicopter is equipped with two rotors.
This variation of the angular position of the ring effects
a cyclic pitch variation of the propeller blades in the

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sense of a correction of the angle by which the propeller
blades are tipped by the air flow attacking at the blade
surfaces,

The entire gear box 33 together with the rotor arrange-
ment borne by the same is pivotably mounted by means
of pins 60 and 61 in bearings 62, and can be tilted about
Pins 60, 61 by a known steering device (not shown) which.
can be operated by the pilot to achieve a desired rolling
motion of the helicopter. “Directional and elevational
steering is effected by control means mounted in other
parts of the helicopter. Consequently the blade pitch
arrangement of the main rotor head is reserved entirely
for stabilizing the machine,

Furthermore, the influence of the air currents in a
direction other than the longitudinal (forward). direc-
tion of the flying machine, can also be utilized for the
correction of the direction of the resulting lifting force.

Figure 4 illustrates an embodiment comprising means
by which the direction as well as the magnitude of the
resulting lifting force may be corrected in accordance
with the forces of air flow (and, therefore, in conformity
with the relative velocity of the machine in the air) so
as to reduce-the pendular movements and vertical drops
of the machine.

Like numerals in this Figure 4 indicate the same parts
as in the other figures. The means for measuring rela-
tive velocity comprise a cylinder 13 facing with an open
nozzle-like end 13a the air flow past the helicopter flying
in the direction of arrow F.

Conduit 16 connects cylinder 13. with cylinder 17 in
which piston 14 is raised or lowered depending on the
strength of the air current entering cylinder 13 through
nozzle 13a, Cylinder 17 communicates freely with the
outside at its upper end 17a.

Piston rod 15 which is connected to piston 14 protrudes
from the open end cylinder 17 and has its upper end
‘connected to the inner ring 40 at pivot 15a. In this ar-
rangement the displacements of piston 14 in cylinder 17
under the air flow entering the cylinder 13, effect a
dowaward canting movement of the right hand side of
tings 40 and 4 (in Figure 4) about eccentric axis 21,
thus causing simultaneously a ‘collective variation of the
medium ‘angle of attack of the air flow on the propeller
blades 1, and also a cyclic variation in the adjustment of
these blades, both variations being. dependent on the
relative velocity as measured. The greater the measured
relative velocity, the greater the downward tilting of the
rings 46 and 4 to counteract effects of the velocity.

it will be understood that the various constructions
shown in the drawings, are only given by.way of example
and. are not restrictive, since obviously, various alterna-
tive embediments are possible within the scope of the
appended claims.

What I claim is:

1. In a helicopter aircraft having at least one rotor
having a plurality of blades mounted on a hub, the im-
provement of stabilizing means for stabilizing the aircraft
by influencing the cyclic and collective pitch adjustment
of, said blades in response to the horizontal speed of the
aircraft relative to the air, said stabilizing means com-
prising in combination, eccentrically cantable annular
means having a canting axis, said canting axis arranged
eccentrically of the center of said annular means and
spaced from the rotary axis of the hub at a right angle
thereto, air speed responsive méans responsive to the ve-
locity of the aircraft relative to the air during substan-
tially horizontal movement of the aircraft and comprising
a member capable of adopting varying positions relative
to said hub in accordance with the horizontal speed of the
aircraft, means for connecting said air speed responsive
means to. said eccentrically cantable annular means: to
transmit changes of position of said responsive means
into a canting movement of said annular means around
said eccentrically arranged canting axis, and link mem-

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. 2,978,037

7

bers extending from said annular means to said blades for
converting the canting action of said annular means to
the cyclic and collective variations of the pitch of said
blades, the ratio of a given cyclic pitch variation to the
corresponding collective pitch variation being determined
by the eccentricity of said eccentrically arranged axis
from the center of said annular means.

2. Jn a helicopter aircraft having at least one propeller
having a plurality of blades mounted on a hub and means
for cyclically and collectively varying the pitch of the
blades, the stabilizing means as claimed in claim 1 where-
said air speed responsive means comprise a cylinder and
a piston movable therein, a pitot tube located in the air
flow. with its open end facing forward in the direction
of movement of the aircraft, said cylinder being con-
nected to said pitot tube, and means for adjusting the
position of said annular means about said eccentric axis
by transmitting changes in the position of said piston in
said cylinder to said annular means.

3. In a helicopter aircraft having at least one propeller
having a plurality of blades mounted on a hub and means
for cyclically and collectively varying the pitch of the
blades, the stabilizing means as claimed in claim 1 where-
in said air speed responsive means comprise a cylinder
and a piston movable therein, a pitet tube located in the
air flow with its open end facing forward in the direction
of movement of the aircraft, said cylinder being con-
nected to said pitot tube, and means for connecting said
piston to said annular means to vary the inclination of
said annular means about said eccentric axis relative
to said hub so as to-effect simultaneously collective and
cyclic pitch variations of the rotor blades in a pre-
determined ratio,

4. In a helicopter aircraft having at least one rotor
having a plurality of blades mounted on a hub, and means
for. cyclically and collectively varying the pitch of said
blades, the stabilizing means as described in claim 1,
wherein said measuring means comprise a tiltable rod,
a sleeve longitudinally displaceably arranged on said rod,
articulated means. for connecting said sleeve to said
blades, a stationary column mounted inside said hub, a
toggle joint at.the top of said column and having the
lower ead of said tiltable rod connected thereto, said
rod having a laterally extending arm at its lower end,
and a lever system engaging said arm and transmitting an
inclination of said tiltable rod to said cantable annular
means.

5. In a helicopter aircraft having at least one propeller
having a plurality of blades mounted on a hub, and means
for cyclically and collectively varying the pitch of said
blades, the improvement of stabilizing means for stabi-
lizing the aircraft by influencing the cyclic and collective
pitch adjustment of said blades in response to the hori-
zontal speed of the aircraft relative to the air, said

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stabilizing means comprising, in combination, eccen-
trically cantable annular ring having a canting axis ar-
ranged eccentrically to the center of said annular ring
and transverse to said hub outside the rotary axis of said
hub and at.a right angle to the same; air speed responsive
means including means having varying positions rela-
tive to fixed aircraft structure according to the speed of
the aircraft; connecting means from said air speed re-
sponsive means to said eccentrically cantable annular
ring for transmitting said changes of position of said air
speed responsive means into a canting movement of said
ring around said eccentrically arranged axis, and further
connecting means comprising lever joint members from
said eccentrically cantable ring to said blades for trans-
mitting and canting action of said ring into the cyclic
and collective variation of the pitch of said blades depend-
ing upon the position of said blades relative to said
eccentric axis in said hub.

6. In a helicopter aircraft having at least one propeller
having a plurality of blades mounted on a hub, and means
for cyclically and collectively varying the pitch of said
blades, the stabilizing means as described in claim 5,
wherein said air speed responsive means comprise a cyl-
inder and a piston movable therein; said eccentrically
cantable ring being connected to said piston; and a pitot
tube located in the air flow with its open end facing
forward in the direction of movement of the aircraft, said
cylinder being connected to said pitot tube.

7. In a helicopter aircraft having at least one propeller
having a plurality of blades mounted on a hub, and means
for cyclically and collectively varying the pitch of said
blades, the improvement of stabilizing means for stabi-
lizing the aircraft by influencing the cyclic and collective
pitch adjustment of said blades in response to the hori-
zontal speed of the aircraft relative to the air, said stabi-
lizing means comprising an annular ring pivotally mount-
ed upon an axis eccentric to the center of said annular ring,
air speed responsive means responsive to the horizontal
speed of the aircraft relative to the air, means inter-
connecting said air speed responsive means and said an-
nular ring for pivoting said ring in response to horizontal
air speed, and means interconnecting said ring and the
propeller blades fcr transmitting the tilting of said annu-
Jar ring into the cyclic and collective variation of the
position of said blades depending upon the position of
said blades relative to said eccentric axis.

References Cited in the file of this patent
UNITED STATES PATENTS

2,389,170 Stalker Nov. 20, 1945
2,425,651 Stalker . — Aug. 12, 1947
2,439,089 Hodson - Apr. 6, 1948
2,611,441 = Slechta ~. ~ Sept. 23, 1952