WO2000059780A2

WO2000059780A2 - Flywheel peaking unit for an aircraft hydraulic system

Info

Publication number: WO2000059780A2
Application number: PCT/US2000/008652
Authority: WO
Inventors: Kerry Michael Peters
Original assignee: Hamilton Sundstrand Corporation
Priority date: 1999-04-01
Filing date: 2000-03-31
Publication date: 2000-10-12
Also published as: WO2000059780A3

Abstract

An improved aircraft (10) is provided through the use of an improved hydraulic system (12) which incorporates a flywheel peaking unit (28) that stores energy during periods when the aircraft is demanding less hydraulic power than the remainder of the hydraulic system is capable of producing, and utilizes that stored energy to augment hydraulic power being provided by the remainder of the hydraulic system when the aircraft is demanding more hydraulic power than can be produced by the remainder of the hydraulic system. The flywheel peaking unit allows use of existing Ram Air Turbines (58) on new aircraft requiring more emergency hydraulic power than previous aircraft, thereby eliminating unwanted cost and time in developing a new aircraft.

Description

FLYWHEEL PEAKING UNIT FOR AN AIRCRAFT HYDRAULIC SYSTEM

FIELD OF THE INVENTION

This invention relates to hydraulic systems, such as those used on aircraft, that are required to periodically supply hydraulic fluid for short periods of time at flowrates above a normal operating flowrate, and more particularly to aircraft hydraulic systems including a hydraulic pump driven by a Ram Air Turbine.

BACKGROUND

Most modern aircraft rely solely on hydraulic power for many purposes including moving flight control surfaces, deploying landing gear, and steering the aircraft while it is not in flight. During normal operation of the aircraft, this hydraulic power is provided by one or more hydraulic circuits on-board the aircraft which receive a flow of hydraulic fluid from pumps driven either directly or indirectly by the main propulsion engines of the aircraft.

In the event that all power is lost from the propulsion engines while the aircraft is in flight, some means of continuing to provide hydraulic power for moving flight control surfaces, deploying landing gear, and steering the aircraft safely to a stop after touch-down are required so that the aircraft may be guided to a safe landing. To provide hydraulic power after failure of the main engines, it has been common practice for many years to equip aircraft with an emergency hydraulic pump driven by a Ram Air Turbine (RAT). Normally the RAT is stowed within a RAT stowage bay in the aircraft. When it is needed, the RAT is deployed by lowering it into the air streaming past the aircraft during flight. The RAT has propeller-like blades that are caused to rotate at high speed by the air streaming past the aircraft and through the RAT. The RAT in turn drives the emergency hydraulic pump to provide sufficient hydraulic power for the aircraft to glide and maneuver for the twenty or so minutes it takes to descend and land safely from a typical airline cruising altitude of around thirty thousand feet. The demand for hydraulic power on an aircraft is intermittent in nature. The demand is high during short periods of time when flight control surfaces are being moved, when landing gear is being deployed or stowed, and when the aircraft is being maneuvered for landing, etc. These periods of high demand for hydraulic power are interspersed between more extensive periods of lower demand while the aircraft is cruising on a normal flight, and while gliding to a landing with a RAT deployed.

The intermittent nature of the demand for hydraulic power is somewhat problematic for the designers of aircraft hydraulic systems. The hydraulic system must be capable of providing all of the power required to meet the maximum demand for hydraulic power during normal operation of the aircraft with the propulsion engines running. This maximum demand is only required for short periods of several seconds, or minutes, followed by periods of many minutes of a much lower demand for hydraulic power. If the pumps driven by the engines are made large enough to meet the maximum demands for hydraulic power, they will be pumping too much flow during the longer periods of time when the demand for power is lower.

Pumping more hydraulic fluid than is required at a given moment during the flight is a waste of fuel. Furthermore, when a fluid is pressurized by a pump and then simply circulated through a hydraulic system without being utilized, the pumping energy added to the portion of the fluid which is not used for doing work will be released as unwanted heating of the hydraulic fluid when the fluid returns to the inlet pressure of the pump.

In the past, aircraft designers have dealt with the intermittent nature of the demand for hydraulic power during normal engine powered flight by reducing the size of the main pumps that provide hydraulic power during normal flight operations, and including other devices such as fluid accumulators, and/or auxiliary electric motor driven pumps in the hydraulic system. The fluid accumulators augment the flow of fluid produced by the main pumps, during short-term demands for higher rates of flow, for periods on the order of half a minute or less. Once the short term demand for higher rates of flow has past, the main pumps are once again able to meet the demands for hydraulic power, and also provide additional flow for recharging the accumulators. The electric motor driven pumps are selectively turned on during more extended periods of demand for more hydraulic power than can be produced by the main pumps, and are then selectively turned off again when the demand for hydraulic power falls to levels that can be supplied by the main pumps. In this manner, fuel is conserved, and the problem of producing unwanted heat in the hydraulic fluid as a result of pumping excess fluid is avoided. The electric motor driven pumps are thus capable of operation for extended periods of many minutes, or even continuous operation during the entire flight of the aircraft. Electric power for the electric motor driven pumps is supplied by electrical generators on board the aircraft that are driven by the main propulsion engines. Thus when engine power is lost, neither the main hydraulic pumps nor the electric motor driven auxiliary pumps are available to provide hydraulic power. As a result, it has been necessary in the past to make the emergency hydraulic pump and RAT large enough to continuously provide the maximum amount of hydraulic power that might be required during an emergency engine-out descent and landing.

In the past this has not been particularly problematic. Aircraft are typically built with multiple engines and many redundant systems. As a result, an engine-out emergency descent and landing is an extremely rare occurrence, and factors such as excess heating of hydraulic fluids that are of major concern when designing a hydraulic system for use during normal flights of several hours in duration are not of much concern in designing an emergency hydraulic system that will operate for only twenty minutes or so during an engine-out emergency descent and landing.

In general terms, the more power that a RAT is required to produce, the longer the blades have to be. In the past, if a larger emergency pump was needed, it was possible to also produce a RAT large enough to drive that larger pump by simply providing a bigger RAT with longer blades.

As aircraft have increased in size and complexity through the years, the demand for hydraulic power has also increased. New aircraft that are now being designed require such large amounts of hydraulic power that it is very difficult, if not impossible to provide a RAT large enough to drive an emergency hydraulic pump having enough capacity to meet the demands for hydraulic power during an engine- out descent and landing. This is so for two primary reasons. First, there is simply not enough space on board these new aircraft and insufficient ground clearance to stow and deploy a RAT with blades long enough to drive the emergency pump. Second, we have reached a point in time where the structural requirements that would be imposed on RAT blades and other components by continuing to increase the size of the RAT exceed the acceptable limits for currently available materials and technology. Furthermore, designing and producing a new and larger RAT and emergency pump for a new aircraft undesirably increases the cost and time required to get the new aircraft into service. It is therefore highly desirable, and essentially necessary to provide a solution to the problem of providing enough emergency hydraulic power for such new aircraft without resorting to making the RAT bigger. One potential solution is to equip an aircraft with two RATs, rather than just one. While this could potentially eliminate the structural problems associated with increasing the size of a single RAT, and allow use of an existing RAT and emergency hydraulic pump so that the increased cost and time of designing a new RAT and pump are avoided, carrying two RATs on board the aircraft would generally not be desirable. Because they are used only in emergency situations that are extremely rare, RATs and emergency hydraulic pumps spend virtually all of their lives traveling as "excess baggage" in stowage bays on the aircraft. Adding a second RAT would therefore result in undesirable increased operating cost to carry this excess baggage, and consume valuable space on the aircraft that could conceivably be otherwise utilized to increase revenue producing carrying capacity of the aircraft.

It is an object of my invention, therefore, to provide an improved aircraft and a method for operating an aircraft in which the larger demand for emergency hydraulic power imposed by modern aircraft can be met without resorting to increasing the size of the RAT or the emergency hydraulic pump, and without adding a second RAT and emergency hydraulic pump. An additional object of my invention is to provide a solution to the problems described above, in meeting the need for additional hydraulic power in an emergency mode, which also provides improvements and advantages when the aircraft is in normal, non-emergency, operation. A further object of my invention is to provide a solution that allows the use of existing RATs and emergency pumps in accomplishing the solution, thereby avoiding the need for incurring the increased cost and time required to design a new RAT and emergency pump. Yet another object of my invention is to provide a solution that is compatible with and can be readily incorporated or retrofitted into existing aircraft and aircraft hydraulic systems.

SUMMARY

My invention provides such an improved aircraft through the use of an improved hydraulic system which incorporates a flywheel peaking unit that stores energy during periods when the aircraft is demanding less hydraulic power than the remainder of the hydraulic system is capable of producing, and utilizes that stored energy to augment hydraulic power being provided by the remainder of the hydraulic system when the aircraft is demanding more hydraulic power than can be produced by the remainder of the hydraulic system. According to one aspect of our invention the improved aircraft includes hydraulic system having a hydraulic pump for providing a flow of hydraulic fluid through the hydraulic system, and a flywheel peaking unit for augmenting the flow of hydraulic fluid provided by the pump.

In one embodiment of our invention, a flywheel peaking unit includes a hydraulic motor/pump operatively connected in fluid communication with the hydraulic circuit for providing or receiving a portion of the flow of hydraulic fluid in the hydraulic circuit, and flywheel means operably connected for driving or being driven by the motor/pump when the motor/pump is respectively providing or receiving that portion of the flow of hydraulic fluid. According to a second aspect of our invention, a Ram Air Turbine is utilized to drive the pump. In some embodiments of our invention, the hydraulic system includes a second pump providing a portion of its flow during normal operations for powering the flywheel peaking unit, so that is it should become necessary to deploy the RAT, the flywheel peaking unit can continue to supply a flow of fluid during the time the RAT is being deployed even if the second pump has become inoperative.

These and other aspects, advantages, and novel features of our invention will be readily apparent upon consideration of the following drawings and detailed description of preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWING

The Drawing is a schematic depiction of an aircraft according to my invention including a hydraulic system having a main hydraulic pump, an emergency hydraulic pump driven by Ram Air Turbine, and a flywheel peaking unit.

DETAILED DESCRIPTION

The drawing schematically depicts an exemplary embodiment of my invention in the form of an aircraft 10 including a hydraulic system 12.

The hydraulic system 12 includes a main pump 14 and an emergency pump 16 connected in fluid communication by a high pressure or supply circuit 18 and a low pressure or return circuit 20 of the hydraulic system 12. The hydraulic system 12 also includes one or more hydraulic loads, as indicated by box 22, connected respectively in fluid communication with the high and low pressure circuits 18,20 of the hydraulic system 12 by load inlet and outlet ports 24 and 26. For a typical aircraft 10, the hydraulic loads 20 might include, for instance, actuators for flight control surfaces or landing gear, and steering or braking system components.

The hydraulic system 12 further includes a flywheel peaking unit 28. The flywheel peaking unit includes a hydraulic motor/pump 30 operably connected in fluid communication with the supply and return circuits 18,20 of the hydraulic system 12 via fluid lines 34a, b and 36a, b and a control valve 38. The control valve 38 includes a first portion 40 for directing a flow of hydraulic fluid straight through the control valve 38 via fluid lines 34a and 34b from the high pressure supply circuit 18 to an inlet port 30a of the motor/pump 30, when the control valve 38 is in a straight-through position as shown in the drawing. In similar fashion, with the control valve 38 in the straight-through position, the first portion 40 of the control valve 38 directs a flow of hydraulic fluid from an outlet port 30b of the motor/pump 30 to the low pressure or return circuit 20 via fluid lines 36a and 36b.

The control valve 38 also includes a second portion 42 for directing a flow of hydraulic fluid in a cross-over fashion through the control valve 38 via fluid lines 36b and 34a from the outlet port 30b of the motor/pump 30 to the high pressure supply circuit 18, when the second portion 42 of the control valve 38 is shifted to the left into a cross-over position wherein the second portion 42 is moved into the position occupied by the first portion 40 of the control valve 38 as depicted in the drawing. In similar fashion, with the control valve 38 in the cross-over position, the second portion 42 of the control valve 38 directs a flow of hydraulic fluid from the low pressure return circuit 20 to the inlet port 30a of the motor/pump 30 via fluid lines 36a and 34b.

Movement of the first and second portions 40,42 of the control valve 38 between the straight-through and cross-over positions is controlled by a force balance between spring 46 and a control pressure applied to a control pressure cavity 44 of the control valve 38. As shown in the drawing, when a predetermined control pressure is applied to the control cavity 44, the spring 46 is compressed and the control valve 38 is placed in the straight-through position. When control pressure in the control cavity 44 drops below the predetermined value the spring 46 biases the valve 38 into the cross-over position. A solenoid powered on-off valve 48 is provided to control the level of control pressure applied to the control cavity 44. The on-off valve 48 has a high pressure inlet H connected in fluid communication with the high pressure supply circuit 18 , a low pressure inlet L connected in fluid communication with the low pressure return circuit 20, and a control port C connected in fluid communication with the control pressure cavity 44 of the control valve 38. When the solenoid of the on-off valve 48 is in the ON position, the high pressure inlet H of the on-off valve 48 is connected in fluid communication with the control port C, and fluid communication between the control port C and the low pressure inlet L of the on-off valve 48 is blocked, thereby providing fluid communication between the high pressure supply circuit 18 and the control cavity 44 of the control valve 38. Conversely, when the solenoid of the on- off valve 48 is in the OFF position, the low pressure inlet L of the on-off valve 48 is connected in fluid communication with the control port C, and fluid communication between the control port C and the high pressure inlet H of the on-off valve 48 is blocked, thereby providing fluid communication between the low pressure return circuit 18 and the control cavity 44 of the control valve 38.

The flywheel peaking unit 32 further includes flywheel means 52 operably connected via a geartrain 54 for driving or being driven by the motor/pump 30 when the motor pump is respectively providing a flow of hydraulic fluid.

The aircraft 10 of the exemplary embodiment as shown in the drawing further includes primary drive means 56 operably connected to drive the main pump 14. This primary drive means 56 could be provided in a number of forms within the scope of my invention. The drive means 56 could be an engine directly coupled by drive shafts or geartrains to the main pump 14. Alternatively, drive means 56 could include an electric motor driven from a battery. Drive means 56 could also be provided by an engine indirectly coupled to the main pump 14 via an electric generator driven by the engine, wires, and an electric motor operably connected for driving the main pump 14. A pneumatic drive means 56, and many other alternatives are also within the contemplated scope of the invention.

The aircraft 10 also includes a RAT 58 operably connected to drive the emergency pump 16 when the RAT 58 is deployed in an airstream 60 flowing past the aircraft 10 when the aircraft is in motion.

In a normal preferred mode of operation of the aircraft 10, the RAT 58 is stowed on-board the aircraft 10, so that the emergency pump 16 is not being driven, and the primary drive means 56 drives the main pump 14 to produce a flow of hydraulic fluid from the main pump 14 sequentially through the high pressure supply circuit 18, the loads 22, and back via the low pressure circuit 20 to the main pump 14. The on-off valve 48 is in the ON position, thereby applying pressure from the flow of hydraulic fluid in the high pressure supply circuit 18 to the control cavity 44 of the control valve 38. The control cavity 44 and spring 46 are designed such that at a predetermined pressure within a normal operating range of the high pressure supply circuit 18, the control valve 38 will generally move to the straight through position when the on-off valve 48 is in the ON position, thereby allowing a portion of the flow of hydraulic fluid in the hydraulic circuit to pass from the high pressure supply circuit to the inlet port 30a of the motor/pump, through the motor/pump 30, and back to the low pressure return line 20.

With high pressure from the supply circuit 18 applied to the inlet port 30a of the motor/pump 30, the motor/pump functions as a motor and drives the geartrain 54 to spin-up the flywheel 52, any time the loads 22 are demanding a rate of flow of hydraulic fluid that is low enough for the main pump 14 to supply more than the flow needed by the loads 22 at that moment while maintaining a pressure in the supply circuit 18 that is greater than the predetermined pressure required to move the control valve 38 to the straight-through position. As the flywheel is accelerated by the excess portion of the flow of hydraulic fluid, energy in the fluid is extracted by the flywheel 52 and converted into kinetic energy stored in the spinning flywheel 52. Should the loads 22 temporarily require a rate of flow in excess of the rate of flow at which the main pump 14 can sustain pressure in the supply circuit 18 above the predetermined value, the pressure in the control cavity 44 will fall to a point at which the spring 46 will move the control valve 38 to the cross-over position wherein the inlet port 30a of the motor/pump 30 will be connected to the low pressure return circuit 20, and the motor/pump outlet port 30b will be connected to the high pressure supply circuit 18. The motor/pump 30 will then function as a pump, driven by the flywheel unit 32, and energy stored in the flywheel 52 will be re-converted to hydraulic power by the motor/pump 30 to augment the hydraulic power produced by the main pump 14 in meeting the intermittent needs of the loads 22. Once the intermittent needs of the loads 22 return to normal lower values, the main pump 14 will be able to once again supply a flow of hydraulic fluid in excess of what is needed by the loads 22, pressure in the supply circuit and control cavity 44 will rise above the predetermined value, the control valve 38 will return to the straight-through position, and a portion of the fluid flow in the hydraulic circuit will drive the motor/pump 30 as a motor to recharge the flywheel 52 with stored energy to be used during the next intermittently high demand for flow to the loads 22.

Should the aircraft 10 encounter an emergency situation in which flow from the main pump 14 is lost, due to engine failure for instance, the RAT 58 is deployed into the airstream 60, thereby allowing the RAT 58 to drive the emergency pump 16 for supplying a flow of hydraulic fluid through the hydraulic circuit 12 in the same manner as the flow from the main pump 14. Operation of the various elements of the exemplary embodiment are the same as described above with relation to operation with the main pump 14 supplying the flow of hydraulic fluid.

The particular type of motor/pump 30 preferred for use in my invention utilizes apressure activated internaly reversing swashplate to automatically reconfigure the motor/pump from a motor to a pump when the pressure diffemtial across the inlet and outlet ports 30a,b of the moto/pump 30 are reversed. Such pumps are well known in the art and readilly available from pump manufacturers. I have included check valve 60 influid line 34b of the exemplary embodiment of my invention to illustrate one means of providing a small amount of back pressure under pressure reversing conditions to facilitate rotation of the motor/pump swashplate.

The exemplary embodiment of my invention also incorporates a flow restricting orifice 60 within the control valve 38 that operates when the control valve 38 is in the straight-through position to provide a means for limiting the maximum speed at which the flywheel 52 can be driven by limiting the maximum flowratethrough the motor/pump 30 within the range of operating pressures allowable in the hydraulic system 12.

Where it is desired to turn off the flywheel peaking unit 32, during maintenance for instance, the solenoid is actuated to connect the control port C to the low pressure inlet L of the on-off valve 48. In this position, the spring 46 will drive the control valve 38 to the crossover position, and the internal construction of the motor/pump30 will prevent the flywheel 52 from spinning up in a reverse direction, thus effectively shutting down the flywheel peaking unit.32.

From the foregoing description, those having skill in the art will readily recognize that aircraft having a hydraulic system that includes a flywheel peaking unit according to my invention provide significant advances over prior aircraft and aircraft hydraulic systems. Those skilled in the art will also specifically recognize that the flywheel peaking unit of my invention is completely compatible with other devices such as accumulators and auxilliary pumps that are currently used to take advantage of the intermittent nature of the demand for hydraulic power in aircraft hydraulic systems, thus allowing my invention to be redilly practiced in new or retrofitted into existing aircraft.

During operation in either a normal or an emergency mode, the flywheel peaking unit provides an additional energy storage device with the capability of carrying a hydraulic system through a temporary demand for increased power lasting for several minutes, instead of only for a few seconds as is the case in systems that rely on fluid accumulators. As a result, pumps can be sized for a lower rate of continuous flow and pressure than in hydraulic systems without the flywheel peaking unit. Because the flywheel peaking unit does not require external power, electrical or otherwise, as did the auxiliary pumps of the past, the benefits of the flywheel peaking unit are available in both normal operation and in an engine out situation. Thus, for the first time, it is possible to take advantage of the intermittent nature of aircraft hydraulic load demands, and utilize the flywheel peaking unit to augment the capability of a RAT powered emergency pump in a manner that allows the RAT and emergency pump to be designed for less that maximum required load values. This flexibility allows existing RAT/emergency pump units to be utilized in conjunction with flywheel peaking units on new aircraft requiring higher levels of maximum hydraulic power, thereby eliminating unwanted cost and time expenditures for developing new RATs and emergency pumps, or the penalties involved in using multiple RAT powered units to achieve higher power levels.

Those skilled in the art of designing emergency RAT powered hydraulic systems will certainly appreciate that by utilizing the flywheel peaking unit during normal operation of the aircraft with the main pump in the manner described above, the flywheel peaking unit will provide an additional advantage, should the main pump or its drive means fail, by maintaining a flow of hydraulic fluid while the RAT is being deployed and is being driven up to speed by the air streaming past the aircraft. There is thus less droop or interruption in the flow of hydraulic fluid to potentially flight critical components than with prior hydraulic systems. Those skilled in the art will further recognize that although we have described the invention herein with respect to certain specific embodiments and applications thereof, many other embodiments and applications are possible within the scope of our invention as described in the appended claims. For example, although the exemplary embodiment illustrated in the drawing utilized both a main and a RAT powered emergency pump in the same hydraulic circuit, the advantages provided by my invention can also be realized in a hydraulic system including only the RAT powered emergency pump, or alternatively, in hydraulic systems that do not include the RAT powered emergency pump. The particular arrangements of control valves, plumbing, and the on-off valve were selected for illustrative purposes. Other arrangements may be utilized to greater or lesser advantage in other applications of my invention.

I also wish to expressly point out that although I have used the terms "Ram Air Turbine" and "RAT" throughout the preceding descriptions to describe an air driven device powering one of the pumps of the embodiments described, I intend that the terms "Ram Air Turbine" and "RAT" be construed broadly to include other types of air driven turbines such as Vortex Turbines that might also be used with equal efficacy on an aircraft according to my invention.

It is understood, therefore, that the spirit and scope of the appended claims should not be limited to the specific embodiments described and depicted herein.

Claims

I claim: 1. An aircraft having a hydraulic system comprising: a) a first hydraulic pump for providing a flow of hydraulic fluid through said hydraulic system; and b) a flywheel peaking unit for augmenting said flow of hydraulic fluid provided by said first pump.

2. The aircraft of claim 1 wherein said flywheel peaking unit includes: a) a hydraulic motor/pump operatively connected in fluid communication with said hydraulic circuit for providing or receiving a portion of said flow of hydraulic fluid through said hydraulic circuit ; and b) flywheel means operably connected for driving or being driven by said motor/pump when said motor pump is respectively providing or receiving said portion of said flow of hydraulic fluid.

3. The aircraft of claim 2 wherein said flywheel peaking unit further includes: c) geartrain means operably connected between said motor/pump and said flywheel whereby said flywheel means may drive or be driven by said motor/pump.

4. The aircraft of claim 2 wherein said flywheel peaking unit further includes: d) control valve means operably coupling said motor/pump in fluid communication with said hydraulic system in such a manner that said portion of said flow of fluid through said hydraulic circuit will continue to flow in one direction through said motor/pump regardless of whether or not said first pump is producing said portion of said flow of hydraulic fluid through said hydraulic system.

5. The aircraft of claim 1 wherein said aircraft further includes Ram Air Turbine means operably connected for driving said first pump.

6. The aircraft of claim 1 wherein said aircraft further includes a drive means operably connected for driving said first pump.

7. The aircraft of claim 6 wherein said drive menas includes an engine.

8. The aircraft of claim 7 wherein said engine provides propulsion of said aircraft along a flightpath.

9. The aircraft of claim I, wherein said hydraulic system further includes: c) a second pump operably connected for providing a portion of said flow of hydraulic fluid; d) a Ram Air Turbine operably connected for driving said first pump; and e) drive means operably connected for driving said second pump.

10. The aircraft of claim 9, wherein said drive means includes an engine.

11. The aircraft of claim 10, wherein said engine is a propulsion engine for propelling said aircraft along a flightpath.

11. A method of operating an aircraft comprising the steps of: a) converting energy in a flow of air past the aircraft into hydraulic power; b) storing a portion of said energy in a flywheel peaking unit 1 operably connected to drive or be driven by said flow of

-2 hydraulic fluid; and

3 c) returning a portion of said portion of energy stored in said

-4 flywheel peaking unit to said flow of hydraulic fluid.

1 12. In an aircraft including a hydraulic circuit having both an emergency

2 powered by a Ram Air Turbine and another pump for imparting energy to and

3 providing a flow of hydraulic fluid in said hydraulic circuit, a method for

4 operating said aircraft comprising the steps of:

5 a) prior to deploying said Ram Air Turbine, storing a portion of said

6 energy in said flow of hydraulic fluid in a flywheel peaking unit;

7 and

8 b) returning a portion of said portion of energy stored in said

9 flywheel peaking unit to said flow of hydraulic fluid during a time

10 when said Ram Air Turbine is being deployed, to thereby lessen

11 a droop in or preclude a loss of said flow of hydraulic fluid while

12 the Ram Air Turbine is being deployed.