Planetary gearbox for gas turbine engine

An aircraft includes first and second engines, one or more aircraft rotors associated with the first and second engines, a first epicyclic gearbox having: a) an output operatively connected at least one of the one or more aircraft rotors, and b) an input defined by a sun gear of the first epicyclic gearbox; and a second epicyclic gearbox having: a) an output operatively connected to at least one of the one or more aircraft rotors, and b) an input defined by a sun gear of the second epicyclic gearbox. Output of the first epicyclic gearbox is defined by the carrier. Output of the second epicyclic gearbox is defined by its ring gear. A multi-engine aircraft and a method of operating a multi-engine aircraft are also described.

TECHNICAL FIELD

The present disclosure relates generally to aircraft engines and, more particularly, to gearboxes used in an aircraft engine such as a gas turbine engine.

BACKGROUND

Turboprops are gas turbine engines coupled to a propeller via a reduction gearbox. One known type of reduction gearbox is a planetary gearbox. Contrary to a turbofan engine, in which bypass airflow and core exhaust airflow are used to generate thrust, a turboprop engine drives a propeller to generate forward motion. However, the rotational speed of the turbine may be too high to be directly coupled to the propeller. Accordingly, prior art reduction gearboxes exist for reducing the rotational speed of the propeller(s) relative to the turbine(s). While prior art gearbox arrangements may be suitable for their intended purposes, improvement in the aerospace industry is always desirable.

SUMMARY

In an aspect, there is provided an aircraft, comprising: first and second engines; one or more aircraft rotors associated with the first and second engines; a first epicyclic gearbox having: a) an output operatively connected at least one of the one or more aircraft rotors, and b) an input defined by a sun gear of the first epicyclic gearbox; and a second epicyclic gearbox having: a) an output operatively connected to at least one of the one or more aircraft rotors, and b) an input defined by a sun gear of the second epicyclic gearbox; and wherein: the first engine is operatively connected to the input of the first epicyclic gearbox; the second engine is operatively connected to the input of the second epicyclic gearbox; each of the first and second epicyclic gearboxes has gears carried by a carrier, and a ring gear meshed with the gears, the output of the first epicyclic gearbox is defined by the carrier of the first epicyclic gearbox, and the output of the second epicyclic gearbox is defined by the ring gear of the second epicyclic gearbox.

In some embodiments, rotation of the ring gear of the first epicyclic gearbox is blocked and rotation of the carrier of the second epicyclic gearbox is blocked.

In some embodiments, each gear of the gears of the carrier of the second epicyclic gearbox includes: a larger-radius gear meshed with the sun gear of the second epicyclic gearbox; a smaller-radius gear attached to that larger-radius gear and meshed with the ring gear of the second epicyclic gearbox, that larger-radius gear, that smaller-radius gear and the ring gear forming an interconnected set of three gears; one tooth of each gear in the interconnected set of three gears is aligned with one tooth of each of the other two gears in the interconnected set of three gears; each gear of the second epicyclic gearbox has a number of teeth; the number of teeth of all three gears of the interconnected set of three gears is one of even and odd; and the number of teeth of each of the sun gear and the ring gear of the second epicyclic gearbox is divisible by the number of gears of the carrier of the second epicyclic gearbox.

In some embodiments, in each gearbox of the first and second epicyclic gearboxes, each of the gears of the carrier of that gearbox includes: a larger-radius gear meshed with the sun gear of that gearbox, a smaller-radius gear attached to that larger-radius gear and meshed with the ring gear of that gearbox, and teeth of the larger-radius gear, the smaller-radius gear, and the ring gear are shaped such that, when rotating: a) an apex of each tooth of the teeth of the larger-radius gear passes through a top-dead-center position concurrently with an apex of a tooth of the teeth of the smaller-radius gear, and b) when in the top-dead-center position the apex of the tooth of the smaller-radius gear aligns with trough of a space between teeth of the ring gear engaged at that time by the tooth of the smaller-radius gear.

In some embodiments, the output of the second epicyclic gearbox is operatively connected the at least one of the one or more aircraft rotors via a rotor shaft assembly; and the ring gear of the second epicyclic gearbox has a radially-inward facing surface and a radially-outward facing surface, and: includes teeth on both the radially-inward facing surface and the radially-outward facing surface, is mated with the smaller gear of each of the gears of the carrier of second epicyclic gearbox via the teeth on the radially-inward facing surface, and is connected to the rotor shaft assembly via a splined connection that includes the teeth on the radially-outward facing surface.

In some embodiments, the rotor shaft assembly includes a ring gear coupling; and the ring gear coupling has teeth mated with the teeth on the radially-outward facing surface of the ring gear of the second epicyclic gearbox and defining the splined connection.

In some embodiments, the aircraft comprises a marking provided on each of the larger-radius gears, on each of the smaller-radius gears, and on each of the ring gears, at respective locations corresponding to the top-dead-center position.

In some embodiments, the second epicyclic gearbox includes a housing; the ring gear coupling, the ring gear, the carrier, and the sun gear of the second epicyclic gearbox are disposed inside the housing; and the carrier of the second epicyclic gearbox is splined to the housing.

In some embodiments, the housing includes a rear portion and a front portion operatively connected to the rear portion to be removable from the rear portion; and the rotor shaft assembly is connected to the front portion so as to be removable relative to the rear portion together with the front portion.

In some embodiments, the first engine drives the sun gear of the first epicyclic gearbox in a given direction when the first engine operates, and the second engine drives the sun gear of the second epicyclic gearbox in the given direction when the second engine operates.

In another aspect, there is provided a multi-engine aircraft with multiple aircraft rotors, comprising: a first engine operatively connected to an input of a first epicyclic gearbox, the input of the first epicyclic gearbox defined by a sun gear thereof, the first epicyclic gearbox having an output operatively connected to a first aircraft rotor of the multiple aircraft rotors; and a second engine operatively connected to an input of a second epicyclic gearbox, the input of the second epicyclic gearbox defined by a sun gear thereof, the second epicyclic gearbox having an output operatively connected to a second aircraft rotor of the multiple aircraft rotors; and wherein each of the first and second epicyclic gearboxes has gears carried by a carrier and a ring gear meshed with the gears of that carrier, the output of the first epicyclic gearbox is defined by the carrier of the first epicyclic gearbox, and the output of the second epicyclic gearbox is defined by the ring gear of the second epicyclic gearbox.

In some embodiments, rotation of the ring gear of the first epicyclic gearbox is limited statically or variably, and rotation of the carrier of the second epicyclic gearbox is limited statically or variably.

In some embodiments, rotation of the ring gear of the first epicyclic gearbox is limited statically, and rotation of the carrier of the second epicyclic gearbox is limited statically.

In another aspect, there is provided a method of operating a multi-engine aircraft having first and second gas turbine engines, the method comprising: rotating a sun gear in a first epicyclic gearbox of the first gas turbine engine and rotating a sun gear in a second epicyclic gearbox of the second gas turbine engine, the sun gears meshed to respective gears of the carriers of the first and second epicyclic gearboxes; rotating a carrier of the first epicyclic gearbox relative to a ring gear of the first epicyclic gearbox and transmitting rotation of the carrier of the first epicyclic gearbox to a first rotor shaft of the aircraft; and rotating a ring gear of the second epicyclic gearbox relative to a carrier of the second epicyclic gearbox and transmitting rotation of the ring gear of the second epicyclic gearbox to a second rotor shaft of the aircraft.

In some embodiments, the method comprises limiting rotation of at least one of: the ring gear of the first epicyclic gearbox; and the carrier of the second epicyclic gearbox.

In some embodiments, the transmitting rotation of the ring gear of the second epicyclic gearbox to the second rotor shaft is performed via a radially-outward facing surface of the ring gear of the second epicyclic gearbox.

In some embodiments, the rotating the sun gear of the first epicyclic gearbox is in a same direction as the rotating the sun gear of the second epicyclic gearbox.

In some embodiments, the method comprises transmitting rotation of the first rotor shaft to a first rotor of the aircraft, and transmitting rotation of the second rotor shaft to a second rotor of the aircraft.

In some embodiments, the first and second rotors are first and second propellers, respectively.

In some embodiments, the rotating the sun gear of the first epicyclic gearbox is performed via a turbine section of a first gas turbine engine of the aircraft; and the rotating the sun gear of the second epicyclic gearbox is performed via a turbine section of a second gas turbine engine of the aircraft.

The above are examples of possible embodiments of the present technology, and are therefore non-limiting.

DETAILED DESCRIPTION

In at least some of the figures that follow, some elements appear more than once (e.g. there may be two, three, etc. of a given part in a given embodiment). Accordingly, only a first instance of each given element is labeled, to maintain clarity of the figures.

FIG. 1illustrates a gas turbine engine10of a type preferably provided for use in subsonic flight and configured for driving a load12, such as, but not limited to, a propeller or a helicopter rotor. Depending on the intended use, the engine10may be any suitable aircraft engine. For example, the engine10may be gas turbine engine, such as a turboprop engine, or a turboshaft engine, an intermittent combustion engine such as a Wankel engine, or a combination of one or more different engine types. In the present embodiment, the engine10is a gas turbine engine, and more particularly a turboprop, and generally comprises in serial flow communication a compressor section14for pressurizing the air, a combustor16in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section18for extracting energy from the combustion gases.

The exemplary embodiment shown inFIG. 1is a “reverse-flow” engine because gases flow from the inlet17, at a rear portion of the engine10, to the exhaust outlet19, at a front portion of the engine10. This is in contrast to “through-flow” gas turbine engines in which gases flow through the core of the engine from a front portion to a rear portion. The engine10may be a reverse-flow engine (as illustrated) or a through-flow engine.

In the illustrated embodiment, the turbine section18has a high-pressure turbine18A in driving engagement with a high-pressure compressor14A. The high-pressure turbine18A and the high-pressure compressor14A are mounted on a high-pressure shaft15. The turbine18has a low-pressure turbine, also known as power turbine18B configured to drive the load12. The power turbine18B is configured to drive a low-pressure compressor14B through a low-pressure shaft22. A planetary gearbox20is configured as a reduction gearbox and operatively connects the low-pressure shaft22that is driven by the power turbine18B to a shaft24that is in driving engagement with the load12, while providing a reduction speed ratio therebetween. In the present embodiment, the load12is a rotor of an aircraft, and more particularly a propeller12, and thus the shaft24driving the aircraft rotor12is referred to as a rotor shaft.

The planetary gearbox20allows the load12to be driven at a given speed, which is different than the rotational speed of the low-pressure turbine18B. The planetary gearbox20allows both the load12and the low-pressure turbine18B to rotate at their respective optimal speed which are different. In the embodiment shown, the planetary gearbox20is axially mounted at the front end of the engine10.

Now referring toFIGS. 1-4, the planetary gearbox20may also be referred to as an epicyclic gear train, an epicyclic gearbox, etc., but is referred to herein as a planetary gearbox for clarity. The planetary gearbox20has a sun gear32mounted on a sun gear connector34which is connected to a layshaft22athat is connected the low-pressure shaft22, although other operative connections are also contemplated. For example, in an alternate embodiment, the sun gear32may be connected directly to the low-pressure shaft22. The layshaft22a, also known as a torque shaft, is may twist along its rotational axis by a certain amount. The twist of the layshaft22amay be monitored to indicate the torque that it transmits.

The planetary gearbox20further has a set of planet gears36rotatably mounted on respective shafts38. In the present embodiment, there are three planet gears36, although the planetary gearbox20may have two or more than three planet gears36. In the embodiment shown, all of the shafts38of the planet gears36are connected to a planetary gear carrier40via respective bearings or any other suitable rotational assemblies. In the illustrated embodiment, the planetary gear carrier40is rotatable about a central rotation axis (X) relative to a housing (H) of the planetary gearbox20.

Although in other embodiments a different operative connection may be used, in the present embodiment a connector44connects the planetary gear carrier40to the rotor shaft24to transmit rotation of the planetary gear carrier40to the load12. As an example, alternatively, the planetary gear carrier40may be connected directly to the rotor shaft24. In some embodiments, the planetary gear carrier40may be a zero-twist carrier to reduce twist deflection under torque by driving the planet gears36from an axial position corresponding to a symmetry plane of the planet gears36. In a particular embodiment, the zero-twist carrier is as described in U.S. Pat. No. 6,663,530 which is incorporated herein by reference in its entirety.

Each planet gear36has a main (larger-diameter) gear46, a fore and aft (smaller-diameter) gears48disposed on opposite sides of and attached to the main gear46via any suitable construction and/or method to rotate integrally with the main gear46. The main gears46are meshed with the sun gear32. In the illustrated embodiment, the main gears46and the sun gear32are spur gears, but other types of gears may be used, such as helical gears. In the embodiment shown, a diameter50of the sun gear32is inferior to a diameter52of the main gears46to create a first rotational speed ratio to the planetary gearbox20, between the sun gear32and the main gears46of the planet gears assemblies36. In some embodiments, one or more of the planet gears36may each have only one smaller-diameter gear48.

Referring toFIGS. 2 and 3, in the present embodiment and although not necessarily in all embodiments, the planetary gearbox20has two ring gears54that are meshed with the smaller-diameter gears48of the planet gears assemblies36. In the present non-limiting embodiment, the ring gears54are disposed on each side of the main gears46, symmetrically, so that the reaction load on the bearings is equalised along their longitudinal axis. The ring gear(s)54may be spur gears and/or helical gears for example, depending on each given embodiment of the gearbox20and of the other gears of the gearbox20. Helical gears may be quieter in some applications.

In a particular embodiment, teeth of the fore gears48may be angled in an opposite way relative to teeth of the aft gears48such that the fore and aft gears48may be mirrored relative to one another. In operation, the larger-diameter gears46of such a non-limiting embodiment may tend to self-center under torque relative to the sun gear32. This may enhance the load sharing between the ring gears54. In the embodiment shown, a diameter56of the fore and aft gears48is inferior to the diameter52of the main gears46. Accordingly, a second rotational speed ratio between the planet gears36and the ring gears54is generated by the planetary gearbox20.

The planetary gearbox20may provide a rotational speed ratio between the sun gear32and the planetary gear carrier40that would require at least two conventional planetary gearboxes to achieve. In a particular embodiment, less moving parts are required which may lead to cost and weight reduction of the gas turbine engine10. Furthermore, the moving parts of such gearboxes require lubrication. By having fewer parts, less oil may be required. This may reduce the capacity of the required oil system and, because less heat is generated, the size of the required heat exchanger used to cool down the oil of the planetary gearbox20may be reduced. In a particular embodiment, a total length of the gas turbine engine10may be reduced by having the planetary gearbox20as described herein instead of at least two conventional gearboxes disposed in series in the engine10to achieve a speed reduction ratio equivalent to the planetary gearbox20.

In the illustrated embodiment, the turbine shaft22is operatively connected to the sun gear32. The rotor shaft24is connected to the connector44of the planetary gear carrier40, for instance by spline connection, and is hence operatively connected to the planetary gear carrier40. In the present embodiment, rotation of the ring gears54is limited, for example by the ring gears54being fixed to the housing (H) as shown inFIG. 2. It is understood that in the present embodiment rotation of the ring gears54is limited by being blocked (i.e. the ring gears54are non-rotational relative to the housing (H). In other embodiments, rotation of the ring gears54may be partially and/or variably limited, so as to vary the gear ratio provided by the planetary gearbox. The speed reduction ratio is defined as the rotational speed of the input (in this embodiment, the low-pressure shaft22/sun gear32) over the rotational speed of the output (in this embodiment, the rotor shaft24). In this arrangement, the shafts22and24rotate in the same direction relative to one another.

In an alternate embodiment, a star arrangement may be used. In a star arrangement, rotation of the planetary gear carrier40is limited and the rotor shaft24is operatively connected to the ring gears54. It is understood that limiting rotation of the planetary gear carrier40comprises completely blocking the rotation of said carrier. In this alternate embodiment, the ring gears54are both mounted and linked to the rotor shaft24. In this alternate embodiment, the rotor shaft24and the turbine shaft22rotate in opposite directions.

By having two ring gears54disposed on opposite sides of the main gears46the load is symmetrically distributed relative to a plane P, to which an axis of rotation A of the sun gear32is normal, the plane P being located half way through a thickness T of the main gears46. By symmetrically distributing the load, the planetary gearbox may be adapted to withstand higher torques and may be adapted to use plain bearings instead of heavier and more expensive rolling element bearings.

The planetary gearbox20may be used in a plurality of applications, other than gas turbine engines, in which a rotational speed ratio between two rotating components is required. In such an embodiment, an input is provided to one of the sun gear32, the planetary gear carrier40, and the ring gears54and an output is connected to another one of the sun gear32, the planetary gear carrier40, and the ring gears54. Rotation of a remaining one of the sun gear32, the planetary gear carrier40, and the ring gears54, that is not connected to the input or the output, is limited.

The planetary gearbox20is adapted to change a rotational speed of a rotating component relative to another rotating component. In the illustrated embodiment, the rotating component is the low-pressure shaft22and the other rotating component is the shaft24. In the illustrated embodiment, the shaft24is connected to the load12, but it may be connected to any other suitable component such as, but not limited to, a helicopter rotor, or an accessory of the gas turbine engine10.

To change the rotational speed of the shaft24relative to the shaft22, the planetary gearbox20first receives a torque of the low-pressure shaft22via the sun gear32. Then, the torque is transmitted to main gears46of a set of planet gears36meshed with the sun gear32. Each planet gear36comprises aft and fore gears48disposed on opposite sides of the main gear46. In the illustrated embodiment, a first rotational speed ratio is generated by having a diameter50of the sun gear32inferior to a diameter52of the main gears46.

The torque is then transmitted from the fore and aft gears48to one of the planetary gear carrier40and the ring gears54meshed with the fore and aft gears48, while another one of the planetary gear carrier40and the ring gears54is fixed so as not to rotate. A second rotational speed ratio is generated by having the diameter56of the fore and aft gears48inferior to the diameter52of the main gear46. The diameters50,52, and56may be tuned to achieve the desired reduction ratio.

Referring now toFIG. 5, another epicyclic gearbox58is shown. The gearbox58includes an input defined by a sun gear60, and an output defined by a ring gear62. A plurality of star gears64of the gearbox58carried by a carrier66operatively connect the input60to the output62. More particularly, each of the star gears64includes a larger-diameter gear64A (a.k.a. first stage gear64A) meshed to the sun gear60, and a smaller-radius gear64B (a.k.a. second stage gear64B) attached to that larger-radius gear64A (in this embodiment, but not necessarily in all embodiments, by being integral to that larger-radius gear64A) and meshed with the ring gear62. A ring gear coupling68is splined to a radially-outward facing surface62A of the ring gear62(in this embodiment, but not necessarily in all embodiments, via its free splines at each end, which engage the ring gear62and thus engage the output shaft24) to receive torque from the ring gear62and hence to be rotated by the ring gear62about a respective rotation axis (X). More particularly, and as seen inFIG. 5, the radially-outward facing surface62A of the ring gear62has radially-outwardly facing teeth which mate with radially-inwardly facing teeth defined by a radially-inwardly facing surface68B of the ring gear coupling68.

In this embodiment, the sun gear60, the ring gear62, the planet gear carrier66, and the ring gear coupling68are coaxial. Referring toFIG. 7, as shown, in this embodiment, the gears64, and more particularly in this embodiment the first stage gear64A and second stage gear64B in this embodiment, are attached to each other, for example by being electron beam (EB) welded together, or by any other suitable manufacturing/method/construction, so that one tooth of each first stage gear64A is aligned with one tooth of a corresponding second stage gear64B and with one tooth of the ring gear62(i.e. as shown inFIG. 7with respective planes at 12 o'clock, 4 o'clock, and 8 o'clock, each of which planes contains the rotation axis of the sun gear60and one tooth of each respective set of first stage gear64A, second stage gear64B and the ring gear62). Accordingly, as shown inFIG. 7, in the present embodiment the gearbox58includes three interconnected sets of three gears (i.e. each set having three interconnected gears, and the three sets sharing the ring gear62). Each set includes one of the first stage gears64A, one of the second stage gears64B, and the ring gear62, with one tooth of each of these three gears62,64A,64B being aligned with one tooth of each of the other two of these three gears62,64A,64B.

In this embodiment, and as shown inFIG. 7, this alignment is indicated by respective marks64C,64D on each of the gears62,64A,64B in respective locations contained in respective ones of the planes. The number of teeth of each of these gears62,64A,64B is one of: odd and even, whereas the number of the sun gear60and the ring gear62is divisible by the number of star gears64. In an aspect, such an arrangement provides a reduction in possible spacing error. In an aspect, while possibly absent in some embodiments, the marking may help make assembly easier. While in this embodiment this is the case, the marks64C,64D need not be positioned at top-dead-centre position (TDC) in all embodiments. In some embodiments, assembly may further be facilitated by using a slave sun gear (not shown) to mesh with the star first stage gears64A before assembly of the gearbox58. In some embodiments, teeth of the ring gear62, the larger-radius gears64A and the smaller-radius gears64B may be shaped such that when assembled and relative to the rotation axis X, the apex of each tooth of each of the smaller-radius gears64B arrives at a top-dead-centre position (TDC) (i.e. the position furthest from the rotation axis X) simultaneously with the apex of a tooth of a corresponding one of the larger-radius gears64A, and these apexes may be aligned with the apex of the trough of a space between the teeth of the ring gear engaged at that time by the top-dead-centre position (TDC) tooth of the corresponding smaller-radius gear64B.

This alignment is shown with planes P1, P2, P3that contain the rotation axis X and divide the 360-degrees about the rotation axis X into equal 120-degree parts, with one of the planes P1being aligned with the top-dead-centre position (TDC). Respective marks64C,64D may be provided on the gears62,64A,64B to help during assembly. As an example, in this embodiment markings64C,64D may be provided at locations that correspond to and indicate the top-dead-center position (TDC) and include a marking on each of the larger-radius gears64A, on each of the smaller-radius gears64B, and on the ring gear(s)62. In some embodiments, the gearbox20has a similar alignment and similar markings64C,64D. Because the alignment and markings64C,64D may be similar,FIG. 7shows the alignment and the markings64C,64D for both the gearbox20and the gearbox58.

Still referring toFIG. 5, the sun gear60, the ring gear62, the planet gear carrier66, and the ring gear coupling68may be disposed within a housing70of the gearbox58. The housing70includes a rear portion70A and a front portion70B removably connected to the rear portion70A. A rotor shaft assembly72that may include a rotor shaft72A and bearings72B supporting its rotation, may be connected to the rear portion70A so as to be removable relative to the rear portion70A together with the front portion70B. In some embodiments, such as the present, and not necessarily in all embodiments, the rotor shaft assembly72includes the ring gear62connected to the front portion70B of the two part gearbox housing70, and is a self-contained assembly unit, meaning it removes from the rear portion70A as a single assembly piece. While providing some advantages in some applications, for facilitated assembly in comparison with at least some prior art designs of similar size and application, in other embodiments, the housing70may have a different number of parts and/or different construction. For example, additional housing parts may be disposed between the front and rear portions70A,70B such that the rear portion70A would be operatively connected to the rear portion70A to be removable from the rear portion70A together with the rotor shaft assembly72, with or without the one or more of the interposed parts.

In this embodiment, rotation of the carrier66is blocked relative to the rotation axis (X) by the carrier66being splined to the housing70B, and in this particular embodiment to the rear portion70A thereof. While the spline connection may provide some benefits such as relatively improved ease of assembly and maintenance, is contemplated that a different structure for blocking rotation of the carrier66may be used. In some embodiments, rotation of the carrier66may be limited, for example variably limited, relative to the rotation axis (X), so as to vary the overall gear ratio provided by the gearbox58.

Referring now toFIG. 8, an aircraft1is schematically shown. The aircraft has a first engine10A, which may be the engine10described above, and a second engine10B, which may be similar to the engine10described above except insofar as being equipped with the gearbox58instead of the gearbox20. Connections between the engine10B and the input and output of the gearbox58may be similar to the connections between the engine10A and the input and output of the gearbox20, and therefore these details are not repeated herein. As shown, the engines10A,10B drive respective rotors, which in this embodiment are propellers12P. In other embodiments, the rotors may be different (e.g. in cases where the aircraft is a helicopter, the rotors may be helicopter rotors). In other embodiments, the engines10A,10B may drive a single output, such as helicopter rotor(s), via a suitable transmission for example. In such embodiments, the suitable transmission may be operatively disposed between the output and the gearboxes20,58of the engines10A,10B.

In the present embodiment, when the engines10A,10B operate, the gearboxes20,58drive the propellers12P in opposite directions. For example, the propeller12P of the engine10A may be driven clockwise about the engine axis Xa of the engine10A, in which case the propeller12P of the engine10B may be driven counter-clockwise about the engine axis Xb of the engine10B. In other embodiments, the rotational directions may be reversed.

Now referring toFIG. 9, the present technology further provides a method90of operating a multi-engine aircraft1, comprising: rotating a sun gear32of a first epicyclic gearbox20and a sun gear60of a second epicyclic gearbox58, the sun gears32,60meshed to respective planetary gears36,64of the first and second epicyclic gearboxes20,58, rotating a planetary gear carrier40of the first epicyclic gearbox20relative to a ring gear54of the first epicyclic gearbox20and transmitting rotation of the planetary gear carrier40of the first epicyclic gearbox20to a first rotor shaft24A of the aircraft1; and rotating a ring gear62of the second epicyclic gearbox58relative to a carrier66of the second epicyclic gearbox58and transmitting rotation of the ring gear62of the second epicyclic gearbox58to a second rotor shaft24B of the aircraft1.

In some embodiments, the method90may include limiting rotation of at least one of: the ring gear54of the first epicyclic gearbox20; and the carrier66of the second epicyclic gearbox58. As seen above, in some embodiments, the limiting rotation of the at least one of the ring gear54of the first epicyclic gearbox20and the carrier66of the second epicyclic gearbox58includes blocking rotation of the at least one of the ring gear54of the first epicyclic gearbox20and the carrier66of the second epicyclic gearbox58.

Further, in some embodiments, the method90may include blocking rotation of the carrier66of the second epicyclic gearbox58by maintaining a splined connection (as described above for example) between the carrier66of the second epicyclic gearbox58to a housing70of the second epicyclic gearbox58. In some embodiments, the method90may include variably limiting rotation of the carrier66, for example to vary the gear ratio provided by the second epicyclic gearbox58. In some embodiments, the method90may include variably limiting rotation of the ring gear54of the first epicyclic gearbox20, for example to vary the gear ratio provided by the first epicyclic gearbox20. In some such embodiments, the rotating the sun gear32of the first epicyclic gearbox20may be in a same direction as the rotating the sun gear60of the second epicyclic gearbox58, transmitting rotation of the first rotor shaft to a first rotor of the aircraft, and transmitting rotation of the second rotor shaft to a second rotor of the aircraft, respectively.

In some such embodiments, the rotating the sun gear32of the first epicyclic gearbox20may be performed via a turbine section18of a first gas turbine engine10A of the aircraft1, and the rotating the sun gear60of the second epicyclic gearbox58is performed via a turbine section18of a second gas turbine engine10B of the aircraft1.