US0097.

18536B2

(12) United States Patent (10) Patent No.: US 9,718,536 B2

Danielson et al. (45) Date of Patent: Aug. 1, 2017
(54) COUNTER-ROTATING OPEN-ROTOR (56) References Cited
(CROR) U.S. PATENT DOCUMENTS
(75) Inventors: David R. Danielson, Suffield, CT (US); 2.923,361 A 2f1960 Best
Paul A. Carvalho, Hadley, MA (US); 2.948,343 A * 8, 1960 Conn et al. ..................... 416/34
Mark Raes, Andover, CT (US); Robert 4,171,183 A 10, 1979 Cornell et al.
H. Perkinson, Stonington, CT (US) 4,183,210 A 1, 1980 Snell
4,358,246 A 11, 1982 Hanson et al.
4,370,097 A 1/1983 Hanson et al.
(73) Assignee: Hamilton Sundstrand Corporation, 4,730,985 A 3, 1988 Rothman et al.
Windsor Locks, CT (US) 4,765,135 A 8, 1988 Lardellier
4,772,180 A * 9/1988 Walker et al. .................. 416/33
(*) Notice: Subject to any disclaimer, the term of this (Continued)
patent is extended or adjusted under 35
U.S.C. 154(b) by 1536 days. FOREIGN PATENT DOCUMENTS
EP 2163474 3, 2010
(21) Appl. No.: 13/109,225 GB 2175652 12, 1986

(22) Filed: May 17, 2011 (Continued)

(65) Prior Publication Data OTHER PUBLICATIONS
US 2011/0286842 A1 Nov. 24, 2011 European Search Report for European Patent Application No.
11166634.3 completed Nov. 7, 2014.
Primary Examiner — Kenneth Bomberg
Related U.S. Application Data Assistant Examiner — Jesse Prager
(60) Provisional application No. 61/345,725, filed on May (74) Attorney, Agent, or Firm — Carlson, Gaskey & Olds,
18, 2010, provisional application No. 61/345,743, P.C.
filed on May 18, 2010. (57) ABSTRACT
(51) Int. C. A method of controlling a Counter-Rotating Open-Rotor
FOID 7700 (2006.01) (CROR) includes mechanically linking a pitch change sys
B64C II/30 (2006.01) tem of a first rotor with a pitch change system of a second
B64D 27/00 (2006.01) rotor and commanding a Blade Angle (Betal commanded)
(52) U.S. C. of the first rotor such that a Blade Angle (Beta2 Actual) of
CPC ...... B64C II/306 (2013.01); B64D 2027/005 the second rotor is a function of the commanded Blade
(2013.01); Y02T 50/66 (2013.01) Angle (Betal commanded) to provide a linear relationship
(58) Field of Classification Search between an actual Blade angle (Beta1 Actual) and Beta1
CPC. B64C 11/306; Y02T 50/66; B64D 2027/005 commanded of the first rotor and a non-linear relationship
USPC ........................................... 416/1. 25, 26, 27 between Beta2 Actual and Betal commanded.
See application file for complete search history. 19 Claims, 9 Drawing Sheets
 US 9,718,536 B2
Page 2

(56) References Cited

U.S. PATENT DOCUMENTS
4,772,181 A * 9/1988 Poucher .......................... 416.33
4,842,484 A 6, 1989 Johnson
4,881,367 A 11, 1989 Flatman
4,913,623 A 4/1990 Schilling et al.
4,927,329 A 5, 1990 Kliman et al.
5,022,821 A 6, 1991 Isert
5,090,869 A * 2/1992 Wright .......................... 416,147
5, 122,034 A 6, 1992 Isert
5,152,668 A 10, 1992 Bulman et al.
5,154,580 A 10, 1992 Hora
5,156,648 A 10, 1992 Hora
5,213,471 A 5, 1993 Miller et al.
5,242,265 A 9, 1993 Hora et al.
5,299,911 A 4/1994 Moirya
5,464,324 A 11/1995 Langenberg
5,470,199 A 11/1995 Schafer et al.
5,498,135 A 3/1996 Stallard, III
6,109,871 A 8, 2000 Nelson et al.
6,295,328 B1 9, 2001 Kim et al.
7,891,163 B2 2/2011 Richards
FOREIGN PATENT DOCUMENTS
GB 2182397 5, 1987
GB 2194649 3, 1988
* cited by examiner
U.S. Patent Aug. 1, 2017 Sheet 1 of 9 US 9,718,536 B2
U.S. Patent Aug. 1, 2017 Sheet 2 of 9 US 9,718,536 B2
U.S. Patent US 9,718,536 B2
U.S. Patent Aug. 1, 2017 Sheet 6 of 9 US 9,718,536 B2
U.S. Patent US 9,718,536 B2
 US 9,718,536 B2
1. 2
COUNTER-ROTATING OPEN-ROTOR FIG. 5 is a block diagram of one non-limiting embodi
(CROR) ment of a control system to control the counter-rotating
un-ducted rotors of the CROR propfan;
The present disclosure claims priority to U.S. Provisional FIG. 6 is a schematic representation of a control map of
Patent Application No. 61/345,725, filed May 18, 2010 and a forward rotor of the CROR propfan of FIG. 5;
U.S. Provisional Patent Application No. 61/345,743, filed FIG. 7 is a schematic representation of a control map of
May 18, 2010. an aft rotor of the CROR propfan of FIG. 5:
FIG. 8 is a schematic representation of a feedback system
BACKGROUND for an aft rotor of the CROR propfan of FIG. 5;
10 FIG. 9 is a block diagram of another non-limiting embodi
The present disclosure relates to gas turbine engines, and ment of a control system to control the counter-rotating
more particularly to Beta operation of a Counter-Rotating un-ducted rotors of the CROR propfan;
Open-Rotor (CROR). FIG. 10 is a schematic representation of a control map of
A Counter-Rotating Open-Rotor (CROR) includes a gas a forward rotor of the CROR propfan of FIG. 9;
turbine engine with counter-rotating un-ducted rotors out 15 FIG. 11 is a schematic representation of a control map of
side a nacelle structure. Propfans are also known as ultra an aft rotor of the CROR propfan of FIG. 9;
high bypass (UHB) engines and, most recently, open rotor FIG. 12 is a schematic representation of a counterweight
jet engines. The design is intended to offer the speed and system of the CROR propfan of FIG. 9;
performance of a turbofan, with the fuel economy of a FIG. 13 is a block diagram of another non-limiting
turboprop. embodiment of a control system to control the counter
CRORS may have particular challenges in terms of aero rotating un-ducted rotors of the CROR propfan;
dynamics, aeroacoustics and structural dynamics as the FIG. 14 is a schematic representation of a control map of
forward and aft rotors are outside the nacelle structure and a forward rotor of the CROR propfan of FIG. 13; and
are positioned relatively close together which may result in FIG. 15 is a schematic representation of a control map of
rotor/rotor interactions. 25 an aft rotor of the CROR propfan of FIG. 13.
SUMMARY DETAILED DESCRIPTION

A method of controlling a Counter-Rotating Open-Rotor FIG. 1 schematically illustrates a Counter-Rotating Open

(CROR) according to an exemplary aspect of the present 30 Rotor (CROR) 20. The CROR 20 generally includes a gas
disclosure includes mechanically linking a pitch change turbine engine 22 with counter-rotating un-ducted rotors 24.
system of a first rotor with a pitch change system of a second 26 outside of a nacelle structure 28 on a central longitudinal
rotor and commanding a Blade Angle (Betal commanded) engine axis A. The CROR 20 may be configured as a tractor
of the first rotor such that a Blade Angle (Beta2 Actual) of (rotors ahead of the engine in a pulling configuration), or as
the second rotor is a function of the commanded Blade 35 a pusher (shown). Although depicted as a particular archi
Angle (Betal commanded) to provide a linear relationship tecture in the disclosed non-limiting embodiment, it should
between an actual Blade angle (Beta1 Actual) and Beta 1 be understood that the concepts described herein are appli
commanded of the first rotor and a non-linear relationship cable to other architectures.
between Beta2 Actual and Betal commanded. The gas turbine engine 22 generally incorporates a com
A method of controlling a Counter-Rotating Open-Rotor 40 pressor section 30, a combustor section 32 and a turbine
(CROR) according to an exemplary aspect of the present section 34 with a power turbine 36. The power turbine 36
disclosure includes entering Beta Control and commanding provides a speed and torque output to drive a gear system 38
a Blade Angle (Beta 1 commanded) of the first rotor such that which drives the counter-rotating un-ducted rotors 24, 26.
a Blade Angle (Beta2 Actual) of the second rotor is a The sections are defined along the central longitudinal
function of the commanded Blade Angle (Beta 1 com 45 engine axis A and the gear system 38 may be located axially
manded). between the counter-rotating un-ducted rotors 24, 26.
A Counter-Rotating Open-Rotor (CROR) according to an With reference to FIG. 2, the gear system 38 in the
exemplary aspect of the present disclosure includes a second disclosed non-limiting embodiment is a planetary, differen
pitch change system to change a pitch of a second rotor, the tial gearbox which generally includes a Sun gear 40 driven
second pitch change system mechanically linked to a first 50 by the power turbine 36, a multiple of planet gears 42, a
pitch change system of a first rotor. planet carrier 44, and a ring gear 46 which rotate relative to
a fixed structure 48. The forward rotor 24 rotates with the
BRIEF DESCRIPTION OF THE DRAWINGS planet carrier 44 and the aft rotor 26 counter rotates with the
ring gear 46.
Various features will become apparent to those skilled in 55 The counter-rotating un-ducted rotors 24, 26 each
the art from the following detailed description of the dis includes a multiple of propeller blades 24B, 26B (one
closed non-limiting embodiment. The drawings that accom shown) which are connected with the respective planet
pany the detailed description can be briefly described as carrier 44 and ring gear 46 through a pitch change system 50.
follows: 52. The pitch change systems 50, 52 include an axially
FIG. 1 is a general perspective view an exemplary gas 60 movable forward pitch change actuator 54 and axially
turbine engine embodiment for use with a Counter-Rotating movable aft pitch change actuator 56 to pitch the rotor
Open-Rotor (CROR) propfan; blades 24B, 26B about a respective rotor blade axis B1, B2
FIG. 2 is an expanded view of the CROR propfan; to achieve the desired propeller mode such as Feather,
FIG. 3 is a schematic representation of a rotor control Forward Speed Governing, CP (coefficient of power) Bucket
position schedule: 65 “keep out Zone', and Reverse (FIG. 3).
FIG. 4 is an expanded schematic view of a transfer The pitch change systems 50, 52 may include linear
bearing for the CROR propfan; hydraulic actuation systems with metered pressures that may
 US 9,718,536 B2
3 4
be ducted to an oil transfer tube 60 which contains at least Beta Control mode is typically used after aircraft touch
four separate hydraulic passages (FIG. 4). Oil Supplied down and when the power is relatively low Such as ground
through the oil transfer tube 60 to the pitch change actuators idle, ground operations, or reverse operations.
54, 56 may flow through a four-land transfer bearing 62 With reference to FIG. 5, one non-limiting embodiment of
located at the aft end of the oil transfer tube 60. The transfer 5 a control system 80 with inputs and outputs to control the
bearing 62 provides the hydraulic connection between the counter-rotating un-ducted rotors 24, 26 of the CROR 20.
stationary and rotating hardware. Two pressures (coarse and Mechanical connections are depicted as the heavy lines from
fine pitch forward rotor) from the oil transfer tube 60 are the gas turbine engine 22 to the gear system 38 then split to
provided to the forward pitch change actuator 54, while the the counter-rotating un-ducted rotors 24, 26. The heavy
other two pressures (coarse and fine pitch—aft rotor) are 10 black line function boxes between the mechanical paths
provided to the aft pitch change actuator 56 through an aft represent the mathematical relationships due to the mechani
transfer bearing 64. cal systems.
Each of the pitch change actuators 54, 56 includes a The rotor control module 58 communicates with the pitch
dual-acting piston with differential areas sized in accordance change system 50, 52 and an engine control module 82 such
with pitch change actuator structural and performance 15 as a Full Authority Digital Electronic Control (FADEC) that
requirements. Each pitch change actuator 54, 56 includes a communicates with the gas turbine engine 22. The control
pitch change yoke 54Y. 56Y which transmits the linear force modules 58, 82 execute algorithms that are disclosed in
output of the pitch change actuator 54, 56 to a trunnion 24T, terms of functional blocks and it should be understood by
26T at the base of each rotor blade 24B, 26B. those skilled in the art with the benefit of this disclosure that
With reference to FIG. 3, a rotor control module 58 these functions may be enacted in either dedicated hardware
provides metering and control of oil Supplied to the pitch circuitry or programmed Software routines capable of execu
change system 50, 52 to change the pitch of the rotors 24, 26 tion in microprocessor based electronics control module
of the CROR 20. It should be understood that FIG. 3 is a embodiments of various configurations.
block diagram representation of functions that may be From the gas turbine engine 22, Npt is the speed of the
enacted in either dedicated hardware circuitry or pro 25 power turbine 36 and T is the torque of the power turbine 36
grammed software routines capable of execution in a micro which is essentially the power output into the gear system
processor based electronic control environment such as rotor 38. Output from the gear system 38 is two paths because the
control module 58. The rotor control module 58 uses two planetary differential gearbox provides the two counter
primary propeller control modes for a constant speed pro rotating outputs for the counter-rotating un-ducted rotors 24.
peller system: Fixed Speed Control and Beta Control. In 30 26.
flight at high power, the CROR 20 is in fixed speed control T1 and Nr1 are torque and speed to the forward rotor 24
mode which, in technical parlance, operates as an isochro and T2 and Nr.2 are torque and speed to the aft rotor 26. The
nous governor. That is, the rotors 24, 26 are essentially the physics of the gear system 38 provide the following math
governor for the gas turbine engine power turbine 36. So the ematical relationships:
rotor control module 58 sets a fixed speed requirement and 35
then adjusts rotor blade angle to absorb whatever power the
gas turbine engine 22 outputs that the rotor blade speed will
remain fixed. Although, there may be additional selectable
rotor speeds for particular flight conditions, once that speed where:
is selected, power change is accomplished through pitch 40 Nr1 is forward rotor speed;
change of the rotor blades rather than speed change to assure Nr2 is aft rotor speed;
rotor blade frequencies are maintained in predesigned Npt is the power turbine speed;
regions and optimal performance is available. T1 is forward rotor torque;
As power is decreased, the effectiveness of the rotors 24, T2 is aft rotor torque;
26 as the governor for the power turbine 36 becomes less. 45 C is a constant from the gear system; and
That is, slop increases as pitch approaches the CP bucket K is a constant from the gear system.
where relatively large changes in rotor blade angle do not In isochronous speed governing fixed speed control, rotor
result in much change in power absorption. The CP bucket speed is measured and is desired to be held constant. The
“keep out Zone' is the region where the rotors 24, 26 cannot rotor control module 58 may increase or decrease blade
be effectively controlled through a change in rotor blade 50 angle to absorb more or less power as provided by the gas
pitch. For example, if a rotor blade pitch lower than the low turbine engine to maintain constant rotor speed. The increase
pitch stop is commanded in flight, the forward airspeed of or decrease signal is noted as BetaDOT for “rate of change
the aircraft may windmill the rotor which increases power to of Beta. For stable governing in the fixed speed control
the system such that the rotor may overspeed. Movement of mode it is desirable to measure rotor blade angle. For ground
blade angle further into the bucket in the decrease pitch 55 handling operations such as taxi and reverse operation, it is
direction will result in increasing overspeed until blade desirable to operate the system in the Beta control mode.
angle has reached the reverse region where further decreases Beta feedback is required for that purpose.
in blade angle will begin to absorb power thus reducing Due to the proximity of the forward rotor 24 to the
propeller speed which is counter-intuitive. Under certain stationary structure of the gas turbine engine 22, conven
conditions, this CP bucket “keep out Zone' may result in 60 tional technology may be used to provide speed (Nr1) and
reversed commands which overspeed the rotors. Beta feedback to the rotor control module 58. The aft rotor
The low pitch stop is the lowest blade pitch angle in the 26 is relatively remote from the stationary structure of the
fixed speed control mode below which the rotor speed can gas turbine engine 22 and signals from the aft rotor 26 must
not be effectively controlled. The low pitch stop, however, pass through at least two rotating interfaces as well as the
must be transited through to enter reverse pitch. The rotor 65 gear system 38.
control module 58 switches to the Beta Control mode where To control the blade pitch of the counter-rotating un
rotor blade pitch is directly commanded rather than speed. ducted rotors 24, 26, two feedback loops are communicated
 US 9,718,536 B2
5 6
to the rotor control module 58. A Blade Angle feedback of measurement required of the LVDT 94. It should be
signal (Beta1 Feedback) and a commanded rate of change of understood that various other measurement systems may
the blade angle signal (Beta1 DOT commanded) communi alternatively or additionally be provided.
cate with the forward rotor 24. A Blade Angle feedback With Reference to FIG. 9, another non-limiting embodi
signal (Beta2 Feedback) and a commanded rate of change of 5 ment of a control system 100 with inputs and outputs to
the blade angle signal (Beta2DOT commanded) communi control the counter-rotating un-ducted rotors 24, 26 of the
cate with the aft rotor 26. In control parlance, commanding CROR 20. In this non-limiting embodiment, the rotational
a rate such as changing a rotor blade angle at 3 degrees per speed of the aft rotor 26 is calculated (Nr.2 derived) from the
second in the positive direction, is a rate command and is mathematical functions as discussed above and the Beta2
usually given a DOT for the first derivative—so BetaDOT 10 feedback signal is eliminated.
would be rate of change of Beta. To command the aft rotor 26 for either increase pitch or
Rotor blade angle actual and rotor speed Nr1 may be decrease pitch, enough information is available because of
measured directly through, for example, dual magnetic the mathematical relationships of the gear system 38. That
sensors attached to stationary structure adjacent to the is, the power turbine output speed Npt is measured and the
forward rotor 24 for communication to the rotor control 15 rotor speed Nrl of the forward rotor is measured, then with
module 58. the mathematical relationships, the rotor speed Nr2 of the aft
The rotational speed of the aft rotor 26 is calculated (Nr.2 rotor 26 is calculated. Control of rotor speed in the speed
derived) from the mathematical functions above as fol governing mode is accomplished in the same manner as
lows—It is common and necessary for manufactures of gas described above for system FIG. 5 with the exception that
turbine engines to measure the speed of the power turbine 36 the dynamic gains used for determining Beta2 Dot must be
to provide back-up protection against accidental overspeed designed to be compatible with the least stable operating
ing and to provide underspeed governing during Beta Mode condition.
operation of the rotor system. This signal is normally Since the control system 100 does not receive the Beta2
provided to the engine control 82 for that function and feedback signal, the aft rotor 26 is prevented from entering
therefore is available to the rotor control 58. Nr.2 may then 25 Reverse pitch by the introduction of a stroke limit or hard
be calculated from the formula Nr.2=C*Npt-Nr1. That is, in stop in the actuation linkage. That is, since Beta Control for
this embodiment, the aft rotor speed is derived—not mea the aft rotor 26 is eliminated, the aft rotor 26 is prevented
sured. With Beta1, Beta1 DOT, Beta2, Beta2DOT, and the from entering a pitch below the low pitch stop (FIG. 3). Beta
rotational speed of the aft rotor 26 (Nr2) speed governing is Control operations (below the low pitch stop) such as
readily achieved to control blade angle and prevent the 30 reversing, and other Such ground operations are performed
engine 22 from over speeding and maintain power within the by the forward rotor 24 alone as the aft rotor 26 is held fixed
desired limits throughout various regimes. But this requires at the low pitch stop whenever the forward rotor 24 is
the Beta2 and Beta2DOT signals be communicated through commanded to a lower pitch than the low pitch stop.
a multiple of rotational interfaces between the aft rotor 26 Any time the control system 100 is in beta control mode,
and the rotor control module 58 which may be somewhat 35 the aft rotor 26 is on the low pitch stop and the forward rotor
complicated. 24 will alone move into the low blade angles and into
In this configuration, the aft rotor 26 is fully usable for reverse. In this configuration, the aft rotor 26 is not used for
ground and reverse operation under Beta Control in the same ground and reverse operation under Beta Control as is the
manner of the forward rotor 24 (FIGS. 6 and 7). That is, a forward rotor 24 (FIGS. 10 and 11). That is, a linear
linear relationship is provided between Beta1 Actual and 40 relationship is provided between Beta1 Actual and Beta1
Betal Commanded as well as between Beta2 Actual and commanded whereas the linear relationship between Beta2
Beta2 Commanded. This linear relationship permits a com Actual and Beta2 Commanded is cut off at the low pitch
manded negative pitch or a commanded positive pitch and stop.
the rotors 24, 26 will go to that commanded pitch. There are In one non-limiting embodiment, the aft rotor 26 is
thus no Beta restrictions on ground operation or reverse 45 physically limited to the low pitch stop by physically
operation. limiting the stroke of the aft pitch change actuator 56. That
With reference to FIG. 8, to measure the Blade Angle is, during ground operation the aft rotor 26 may be posi
feedback signal (Beta2 Feedback) from the aft rotor 26, a tioned against the low pitch stop (often referred to as the
feedback assembly 90 is connected to the aft pitch change Flight Idle Stop) and forward and reverse thrust is controlled
actuator 56. The feedback assembly 90 generally includes a 50 by a combination of engine power and beta control of the
feedback shaft 92, a LVDT 94, a sliding joint 96 and forward rotor 24.
bearings 98A, 98B. The feedback shaft 92 is held rotation As an alternate control approach, the aft rotor 26 may be
ally stationary upon bearings 98A, 98B to provide a rota positioned against a feather hard stop (FIG. 3) since use of
tionally stationary path from the aft pitch change actuator 56 the mechanical low pitch stop on the aft rotor 26 requires
to the LVDT 94. Bearings 98A permits rotation between the 55 ground thrust control based solely on blade pitch changes of
feedback shaft 92 and the forward rotor 24 while bearing the forward rotor 24. With the aft rotor 26 at a flight idle
98B permits rotation between the feedback shaft 92 and the blade angle, a relatively greater amount of reverse thrust is
aft rotor 26. required from the forward rotor 24 due to the forward thrust
The feedback assembly 90 directly monitors axial posi generated by the aft rotor 26 when reverse power is applied
tion of the aft pitch change actuator 56. Such feedback may 60 as the aft rotor 26 is limited to the low pitch stop. To
be required only below Flight Idle. The feedback shaft 92 maximize net reverse thrust, the aft rotor 26 may alterna
includes an axial stop 92S such that the feedback shaft 92 is tively be commanded to the blade angle (feathered) to
axially restrained above Flight Idle. Further axial movement minimize the forward thrust from the aft rotor 26. This may
of the aft pitch change actuator 56 above flight idle is be particularly advantageous for reverse thrust application
absorbed by the sliding joint 96 such as a spring which 65 after touchdown to minimize aircraft stopping distance.
compresses above flight idle to minimize the stroke applied While minimizing the forward thrust generated by the aft
to the LVDT 94. The stroke limitation increases the fidelity rotor 26 is advantageous from an aircraft stopping perfor
 US 9,718,536 B2
7 8
mance perspective after touchdown, minimization of the Although a linear relationship is provided between Beta1
rotational speed variation as well as minimization of the Actual and Betal commanded, a non-linear relationship
average rotation speed of the aft rotor 26 in reverse thrust between Beta2 Actual and Betal Commanded results from
operation may also be advantageous. Minimizing the Zones the control of the aft rotor 26 through the forward rotor 24.
of potential speed operation in the aft rotor 26 may be 5 The non-linear relationship between Beta2 Actual and
critical to ensuring that the aft rotor is not operated continu Beta2 Commanded may be through a scheduling function
ously at a speed that may excite any rotor blade natural provided, for example, mechanically with a cam or other
frequencies. This avoidance will minimize the potential for mechanical linkage such that the power absorption of the
fatigue damage accumulation in the rotor assemblies. rotors 24, 26 are commanded with one signal. So Beta1 is
In the unlikely event of a loss of propulsion system 10 commanded such that Betal actual is linear while Beta2 is
hydraulic pressure, counterweights 102 (FIG. 12) are a nonlinear function.
mounted to the base of each of the rotor blades 24B, 26B to Although the aft rotor 26 may be somewhat less accu
provide the force output necessary to drive the rotor blades rately controlled than the forward rotor 24, the acoustics of
24B, 26B towards increased pitch so as to provide a safe the CROR 20 may actually be improved as noise generation
failure mode through elimination of any potential engine 15 is reduced because the speeds of the rotors 24, 26 are slightly
overspeed condition. different. As the rotors 24, 26 are in series in the airflow, the
An independent electronic overspeed and low pitch stop power absorption of each rotor is different such that when
protection system, such as that disclosed in U.S. Pat. No. operated in unison the function advantageously reduces
6,422,816 B1, entitled “VARIABLE PITCH PROPELLER noise generation. In other words, one rotor 24, 26 will be
CONTROL SYSTEM,” which is assigned to the assignee of running at the commanded speed while the other rotor 26, 24
the instant disclosure and which is hereby incorporated will be somewhere close but different such that end result is
herein in its entirety, provides protection in the event of a relatively quieter CROR 20.
control system failure which may otherwise result in an It should be understood that like reference numerals
increase in rotor RPM outside of established limits or a identify corresponding or similar elements throughout the
commanded blade angle below established limits. In the 25 several drawings. It should also be understood that although
event of a complete loss of electrical power to the rotor a particular component arrangement is disclosed in the
control system, the rotors 24, 26 are driven hydraulically illustrated embodiment, other arrangements will benefit
towards high pitch (feather) to avoid overspeeds as well as herefrom.
in-flight low pitch stop violations. This may be accom Although particular step sequences are shown, described,
plished by the application of an electrical null bias in the 30 and claimed, it should be understood that steps may be
electro-hydraulic servo-valve such that with no electrical performed in any order, separated or combined unless oth
input to the valve, the porting is such that the actuators 54, erwise indicated and will still benefit from the present
56 are always hydraulically driven in the increase pitch disclosure.
direction. The foregoing description is exemplary rather than
Another non-limiting embodiment limits movement of 35 defined by the limitations within. Various non-limiting
the aft rotor 26 to the low pitch stop through a pitchlock such embodiments are disclosed herein, however, one of ordinary
as that disclosed in United States Patent Application No. skill in the art would recognize that various modifications
2007/0212220A1, entitled “CONTROLLED PROPELLER and variations in light of the above teachings will fall within
PITCH LOCK ACTUATION SYSTEM,” which is assigned the scope of the appended claims. It is therefore to be
to the assignee of the instant disclosure and which is hereby 40 understood that within the Scope of the appended claims, the
incorporated herein in its entirety. In this non-limiting disclosure may be practiced other than as specifically
embodiment multiple pitchlocks may be symmetrically described. For that reason the appended claims should be
around the forward and aft rotor actuators which lock-up and studied to determine true scope and content.
prevent unwanted travel in the decrease pitch direction upon
loss of hydraulic power. This permits reduction or elimina 45 What is claimed is:
tion of the counterweights thus resulting in reduced system 1. A method of controlling a Counter-Rotating Open
weight. Rotor (CROR) comprising:
With reference to FIG. 13, another non-limiting embodi commanding a Blade Angle (Betal commanded) of a first
ment of a control system 110 with inputs and outputs to rotor through a first pitch change system such that a
control the counter-rotating un-ducted rotors 24, 26 of the 50 Blade Angle (Beta2 Actual) of a second rotor having a
CROR 20 is schematically illustrated. In this non-limiting second pitch system mechanically linked to the first
embodiment, pitch change systems 50, 52 are mechanically pitch change system changes according to a function of
linked such as through a ball screw. The blade angle of the the Blade Angle (Beta 1 commanded) of the first rotor
forward rotor 24 (Beta1) is commanded and the blade angle to provide a linear relationship between an actual Blade
of the aft rotor 26 (Beta2) follows such that there is a 55 angle (Beta1 Actual) of the first rotor and the Blade
mechanical functional relationship B2=f(B1). The relation Angle (Beta 1 commanded), of the first rotor and a
ship is predetermined as described in United States Patent non-linear relationship between the Blade Angle (Beta2
Application No. 2010/0310369 A1 entitled “PITCH Actual) of the second rotor and the Blade Angle (Beta1
CHANGE ACTUATION SYSTEM FOR A COUNTER commanded) of the first rotor.
ROTATING PROPELLER,” which is assigned to the 60 2. The method as recited in claim 1, wherein the first rotor
assignee of the instant disclosure and which is hereby is a forward rotor and the second rotor is an aft rotor along
incorporated herein in its entirety. This configuration elimi a common axis of rotation of a pusher configuration Coun
nates the need for Nr2 and Beta2 feedback signals as well as ter-Rotating Open-Rotor.
the command signal Beta2DOT from the aft rotor 26. This 3. The method as recited in claim 1, further comprising
minimizes complexity. 65 locating a gear system which drives the first rotor and the
In this configuration, the aft rotor 26 is used for ground second rotor axially between the first rotor and the second
and reverse operation under Beta Control (FIGS. 14 and 15). rOtOr.
 US 9,718,536 B2
9 10
4. A Counter-Rotating Open-Rotor (CROR) comprising: along a common axis of rotation of a pusher configuration
a first rotor; Counter-Rotating Open-Rotor.
a first pitch change system to change a pitch of said first 12. The Counter-Rotating Open-Rotor (CROR) as recited
rotor; in claim 4, wherein the Blade Angle (Beta2 Actual) of the
a second rotor; 5 second rotor is controllable by the control system free of a
a second pitch change system to change a pitch of said feedback signal from the second rotor and free of a com
second rotor, said second pitch change system mand signal to the second rotor.
mechanically linked to said first pitch change system; 13. The Counter-Rotating Open-Rotor (CROR) as recited
and
a control system in communication with the pitch change 10
in claim 4, wherein the non-linear functional relationship
system of the first rotor and configured to command a between the Blade Angle (Beta1 commanded) of said first
Blade Angle (Betal commanded) of the first rotor, rotor and the Blade Angle (Beta2 Actual) of said second
wherein the control system is configured to calculate rotor is caused by the mechanical linkage between the first
the Blade Angle (Beta2 Actual) of the second rotor pitch change system and the second pitch change system.
based on a functional non-linear relationship between 15 14. The Counter-Rotating Open Rotor (CROR) as recited
the Blade Angle (Beta2 Actual) of the second rotor and in claim 13, wherein the first pitch change system includes
the Blade Angle (Betal commanded) of the first rotor. an axially movable forward pitch change actuator and the
5. The Counter-Rotating Open-Rotor (CROR) as recited second pitch change system includes a second axially mov
in claim 4 wherein said first rotor is an forward rotor in a able pitch change actuator.
CROR pusher configuration. 15. The Counter-Rotating Open Rotor (CROR) as recited
6. The Counter-Rotating Open-Rotor (CROR) as recited in claim 14, further comprising an oil transfer tube config
in claim 5 further comprising a gear system which drives ured to supply oil to the first pitch change actuator and the
said first rotor and said second rotor, said gear system axially second pitch change actuator through a four-land transfer
between said first rotor and said second rotor. bearing located at an aft end of the transfer tube.
7. The Counter-Rotating Open-Rotor (CROR) as recited 25 16. The Counter-Rotating Open Rotor (CROR) as recited
in claim 4 further comprising a gear system which drives in claim 15, wherein the first pitch change actuator includes
said first rotor and said second rotor, said gear system axially a first pitch yoke configured to transmit a linear force output
between said first rotor and said second rotor. from the first pitch change actuator to a first trunnion at a
8. The Counter-Rotating Open-Rotor (CROR) as recited base of the first rotor, and the second pitch change actuator
in claim 4, wherein the control system comprises a rotor 30 includes a second pitch yoke configured to transmit a linear
control module operable to command the Blade Angle force output from the second pitch change actuator to a
second trunnion at a base of the second rotor.
(Betal commanded) of said first rotor such that the Blade 17. The Counter-Rotating Open Rotor (CROR) as recited
Angle (Beta2 Actual) of said second rotor is a function of in claim 8, wherein the control system further comprises an
said Blade Angle (Betal commanded) of the first rotor. engine control module in communication with the rotor
9. The method as recited in claim 1, wherein the com 35
manding is performed through a control system in commu control module and in communication with a gas turbine
nication with the pitch change system of the first rotor and engine, wherein the engine control module is configured to
configured to calculate the Blade Angle (Beta2 Actual) of communicate a power turbine speed of the gas turbine
the second rotor based on the non-linear functional relation engine to the rotor control module.
ship between the Blade Angle (Beta2 Actual) of the second 40 18. The Counter-Rotating Open Rotor (CROR) as recited
rotor and the Blade Angle (Beta1 commanded) of the first in claim 8, wherein the first pitch change system is mechani
rOtOr. cally linked to the second pitch change system with a ball
SCCW.
10. The method as recited in claim 9, wherein the Blade
Angle (Beta2 Actual) of the second rotor is controllable by 19. The method as recited in claim 9, wherein the non
the control system free of a feedback signal from the second 45 linear functional relationship is caused by the mechanical
rotor and free of a command signal to the second rotor. linkage between the first pitch change system and the second
11. The method as recited in claim 10, wherein the first pitch change system.
rotor is a forward rotor and the second rotor is an aft rotor k k k k k