Vertical/short take-off and landing - AIRCRAFT CONTROL

AIRCRAFT CONTROL

Fig. 18-18 Reaction control system.

29. The low forward speeds of V/STOL aircraft during take-off and transition do not permit the generation of adequate aerodynamic forces from the normal  flight  control  surfaces,  it  is  therefore necessary to provide one or more of the following additonal methods of controlling pitch, roll and yaw.
Reaction controls
30. This system bleeds air from the engine and ducts it through nozzles at the four extremities of the aircraft (fig. 18-18), The air supply to the nozzles is automatically cut off when the main engine swivelling propulsion nozzles are turned for normal flight or when the lift engines are shut down. The thrust of the control nozzles is varied by changing their area which varies the amount of airflow passed.
Differential engine throttling

Vertical/short take-off and landing - Lift burning systems

Lift burning systems
26. The thrust of the four nozzle lift/propulsion engine may be boosted by burning fuel in the bypass flow in the duct or plenum chamber supplying the front nozzles. This is called plenum chamber burning (P.C.B.) (fig. 18-16) and thrust of the by-pass air may be doubled by this process. This thrust capability is available for normal flight as well as take-off and landing and so can be used to increase manoeuvra- bility and give supersonic flight.

Fig. 18-16 Plenum chamber burning.

27. The thrust of a remote lift jet can also be augmented by burning fuel in a combustion chamber just upstream of the lift nozzle (fig. 18-17).  This system is commonly known as a remote augmented lift system (R.A.L.3.). The thrust boost available from the burner reduces the amount of airflow to be supplied to it and therefore reduces the size of the ducting needed to direct the air from the engine to the remote lift nozzle.

Vertical/short take-off and landing - Special engine ratings

Special engine ratings

Fig. 18-15 Thrust increases with short lift

ratings

24. Experience has shown that an engine rating  structure can be devised which provides high thrustlevels for short periods of time without reducing engine life. Operation in ground effect and the take- off and landing manoeuvres require maximum thrust for less than 15 seconds so that use of a short lift rating for that time is feasible. Fig. 18-15 shows an example of thrust permissible with a 15 second short lift rating compared to that with a 2.5 minute normal lift rating.

25. At high ambient temperatures, the engine may run into a turbine temperature limit before reaching its maximum r.p.m. and suffer a thrust loss as a result. Restoration of the thrust can be achieved by means  of  water  injection  into  the  combustion chamber (Part 17) which allows operation at a higher turbine gas temperature for a given turbine blade temperature. If desired, water injection can also be used to increase the thrust at low ambient tempera- tures.

Vertical/short take-off and landing - LIFT THRUST AUGMENTATION

LIFT THRUST AUGMENTATION
23. In many cases on V/STOL aircraft augmentation of the lift thrust is necessary to avoid an engine which is oversized for normal flight with the consequent effects of higher engine weight and fuel consumption than would be the case for a conventional aircraft- This lift thrust augmentation can be achieved in a number of different ways:
(1) Using special engine ratings.
(2) Burning in the lift nozzle gas flow.
(3) By means of an ejector system.

Vertical/short take-off and landing - Bleed air for STOL

Bleed air for STOL

Fig. 18-14 Flap blowing engine.

22. Fig. 18-14 shows one method how STOL can be achieved with a form of 'flap blowing'. The turbo- fan engine has a geared variable pitch fan and an oversized low pressure (L. P.) compressor from the exit of which air is bled and ducted to the flap system in the wing trailing edge.  The variable pitch fan enables high L.P. compressor speed and thus high bleed pressure to be maintained over a wide range of thrusts.  This  gives  excellent  control  at  greatly different aircraft flight conditions.

Vertical/short take-off and landing - Swivelling engines

Swivelling engines

Fig. 18-13 Jet lift with swivelling nozzles.

20. This  method  consists  of  having  propulsion engines which can be mechanically swiveled closed through  at  least  90  degrees  to  provide  thrust vectoring (fig. 18-13). In addition to these propulsion engines, one or more lift engines may be installed to provide supplementary lift during the take-off and landing phase of flight.

21. The swivelling engine system can only be used with two or more engines. This then introduces the problem of safety in the event of an engine failure. So, although there is only a small weight penalty and no increase in fuel consumption, safety considera- tions tend to offset these advantages compared to some of the other powered lift systems. The normal method of providing aircraft control at low speeds is by differential throttling and vectoring of the engines which simplifies the basic engine design but makes the control system more complex.

Vertical/short take-off and landing - Remote lift systems

 Remote lift systems

Fig. 18-12 Remote lift fan.

17. Direct lift remote systems duct the by-pass air or engine exhaust air to downward facing lift nozzles remote from the engine. These nozzles may be in the front fuselage of the aircraft or in the wings.  The engine duct is blocked by means of a diverter similar to that described in para. 10.
18. The remote lift-fan (fig. 18-12) is mounted in the aircraft wing or fuselage, and is driven mechanically or by air or gas ducted into a tip turbine, The drive system is provided by the main propulsion power plant or by a separate engine.

Vertical/short take-off and landing - Lift engines

Lift engines

Fig. 18-10 A lift-jet engine.

13. The lift engine is designed to produce vertical thrust during the take-off and landing phases of V/STOL aircraft. Because the engine is not used in normal flight it must be light and have a small volume to avoid causing a large penalty on the aircraft. The lift engine may be a turbo-jet which for a given thrust gives the lowest weight and volume. Should a low jet velocity be necessary a lift fan may be employed.
14. Pure lift-jet engines have been developed with thrust/weight ratios of about 20:1 and still higher values are projected for the future. Weight is reduced by keeping the engine design simple and also by extensive use of composite materials (fig. 18-10). Because the engine is operated for only limited periods during specific flight conditions i.e. during take-off  and  landing,  the  fuel  system  can  be simplified and a total loss oil system (Part 8), in which the used lubricating oil is ejected overboard, can be used.

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Vertical/short take-off and landing - Lift/Propulsion engines

Lift/Propulsion engines
7. The lift/propulsion engine is capable of providing thrust for both normal wing borne flight and for lift. This is achieved by changing the direction of the thrust either by a deflector system consisting of one, two or four swivelling nozzles or by a device known as a switch-in deflector which redirects the exhaust gases from a rearward facing propulsion nozzle to one or two downward facing lift nozzles (fig, 18-4).

Fig. 18-4 Thrust deflector systems.

8. Thrust deflection on a single nozzle is accom- plished by connecting together sections of the jet pipe, the joint faces of which are so angled that, when the sections are counter-rotated, the nozzle moves from the horizontal to the vertical position (fig.  18-5). To avoid either a side component o! thrust or a thrust line offset from the engine axis during the  movement of the nozzle it is necessary that the first joint face is perpendicular to the axis of the jet pipe. If it is desired that the nozzle does not rotate, as may be the case if it is a variable area nozzle, a third joint  face which is perpendicular to the axis of the nozzleis required.

Vertical/short take-off and landing - METHODS OF PROVIDING POWERED LIFT

METHODS OF PROVIDING POWERED LIFT
6. Although the Pegasus engine is the only V/STOL engine in operational service in the Western World there are several possible methods of providing powered lift, such as;

Fig. 18-3 V/STOL fighter aircraft.

(1) Deflecting (or vectoring) the exhaust gases and hence the thrust of the engine.
(2)  Using specially designed engines for lift only.
(3)  Driving a lift system, which is remote from the engine, either from the engine or by a separate power unit.
(4)  Swivelling the engines.
(5)  For STOL aircraft, using bleed air from the engines to increase circulation around the wing and hence increase lift.  In  several  of  the  projected  V/STOL aircraft  a combination of two or more of these methods has been used.

Vertical/short take-off and landing - INTRODUCTION

INTRODUCTION

Fig. 18-1 Michel Wibault's ground attack gyropter (concept) 1956

1. Vertical take-off and landing (VTOL) or short take-off and landing (STOL) are desirable character- istics for any type of aircraft, provided that the normal flight  performance  characteristics,  including payload/range, are not unreasonably impaired. Until the introduction of the gas turbine engine, with its high power/weight ratio, the only powered lift system capable of VTOL was the low disc loading rotor, ason the helicopter.
2. Early in 1941, the late Dr A. A. Griffiths, the then Chief Scientist at Rolls-Royce, envisaged the use of the jet engine as a powered lift system. However, it  was not until 1947 that a light weight jet engine, designed  by  Rolls-Royce  for  missile  propulsion, existed and had a high enough thrust/weight ratio for the first pure lift-jet engine to be developed from it.

Rolls-Royce Pegasus | Rolls-Royce RB 108

Rolls-Royce Pegasus

Rolls-Royce RB 108

The  RB108  was  the  first  engine  to  be designed specifically as a direct VTOL engine. First running in July 1955 the engine was sub- sequently thrust rated at 2340 lb, giving a thrust to weight ratio of 8.7:1. In addition to powering a variety of VTOL test rigs, the RB108 flew in a Gloster Meteor, the Short SC1 and the Marcel Dassault Balzac.

Water injection - COMBUSTION CHAMBER INJECTION

COMBUSTION CHAMBER INJECTION

Fig. 17-4 A typical combustion chamber injection system.

7. The  combustion  chamber  injection  systemshown in fig. 17-4 is a typical system for a turbo-jet engine. The coolant flows from an aircraft-mounted tank to an air-driven turbine pump that delivers it to a water flow sensing unit. The water passes from the sensing unit to each fuel spray nozzle and is sprayed from two jets onto the flame tube swirl vanes, thus cooling the air passing into the combustion zone. The water pressure between the sensing unit and the discharge jets is sensed by the fuel control system, which  automatically  resets  the  engine  speed governor to give a higher maximum engine speed.

Water injection - COMPRESSOR INLET INJECTION

Fig. 17-3 A typical compressor inlet injection system.

5. The compressor inlet injection system shown in fig. 17-3 is a typical system for a turbo-propeller engine. When the injection system is switched on, water/methanol mixture is pumped from an aircraft- mounted tank to a control unit.  The control unit meters the flow of mixture to the compressor inlet through a metering valve that is operated by a servo piston.  The servo system uses engine oil as an operating medium, and a servo valve regulates the supply of oil. The degree of servo valve opening is set by a control system that is sensitive to propeller shaft torque oil pressure and to atmospheric air pressure acting on a capsule assembly.

Water injection - INTRODUCTION

Fig. 17-1 Turbo-jet thrust restoration

1. The maximum power output of a gas turbine engine depends to a large extent upon the density or weight of the airflow passing through the engine. There is, therefore, a reduction in thrust or shaft horsepower as the atmospheric pressure decreases with altitude, and/or the ambient air temperature increases. Under these conditions, the power output can be restored or, in some instances, boosted for take-off  by  cooling  the  airflow  with  water  or water/methanol mixture (coolant). When methanol is added to the water it gives anti-freezing properties and also provides an additional source of fuel.  A  typical turbo-jet engine thrust restoration curve isshown in fig. 17-1 and a turbo-propeller engine power restoration and boost curve is shown in fig. 17-2.

2. There are two basic methods of injecting the coolant into the airflow. Some engines have the coolant sprayed directly into the compressor inlet, but the injection of coolant into the combustion chamber inlet is usually more suitable for axial flow compressor engines. This is because a more eve distribution can be obtained and a greater quantity of coolant can be satisfactorily injected.

Rolls-Royce Dart | Armstrong Siddeley Viper

Rolls-Royce Dart 

Armstrong Siddeley Viper

The  Viper  was  designed  as  a  result  of experience gained with the larger Sapphire turbojet. Originally built as a 1,640 lb thrust short-life engine for target drones, it later emerged as a long life engine for the Jet Provost.  Subsequently  the  engine  was developed by Bristol Siddeley as the power plant for civil executive jets, and Rolls-Royce for present generation trainers and light strike aircraft with a maximum thrust of 4,400 lb (5,000 lb with reheat).

Turbo-Union RB199 | Metrovick F2/4 Beryl

Turbo-Union RB199 

Metrovick F2/4 Beryl

Development of the F2, the first British axial flow turbo-jet, began in f 940. After initial flight trials in the tail of an Avro Lancaster, two F2s were installed in a Gloster Meteor and first flew  on  13  November  1943.  After  early problems the F2/4 Beryl was developed which gave up to 4000 lb thrust and was used to power the Saunders Roe SR/A1 flying boat fighter.

CONTROL SYSTEM

Fig. 16-5 Simplified control system.

15. It is apparent that two functions, fuel flow and propelling nozzle area, must be co-ordinated for sat- isfactory operation of the afterburner system, These functions are related by making the nozzle area dependent upon the fuel flow at the burners or vice- versa. The pilot controls the afterburner fuel flow or the nozzle area in conjunction with a compressor delivery/jet pipe pressure sensing device (a pressure ratio control unit). When the afterburner fuel flow is increased, the nozzle area increases; when the afterburner fuel flow decreases, the nozzle area is reduced. The pressure ratio control unit ensures the pressure ratio across the turbine remains unchanged and that the engine is unaffected by the operation of afterburning, regardless of the nozzle area and fuel flow.

FUEL CONSUMPTION

FUEL CONSUMPTION

Fig. 16-9 Specific fuel consumption

comparison.

Fig. 16-10 Afterburning and its effect on the rate of climb.

23. Afterburning  always  incurs  an  increase  in specific fuel consumption and is, therefore, generally limited to periods of short duration.  Additional fuel must be added to the gas stream to obtain the required temperature ratio (para. 19). Since the temperature rise does not occur at the peak of compression, the fuel is not burnt as efficiently as in the  engine  combustion  chamber  and  a  higher specific fuel consumption must result. For example, assuming a specific fuel consumption without after- burning of 1,15 lb./hr./lb. thrust at sea level and a speed of Mach 0,9 as shown in fig. 16-9. then with 70 per cent afterburning under the same conditions of  flight,  the  consumption  will  be  increased  to

CONSTRUCTION

Burners
11. The burner system consists of several circular concentric fuel manifolds supported by struts inside the jet pipe. Fuel is supplied to the manifolds by feed pipes in the support struts and sprayed into the flame area, between the flame stabilizers, from holes in the downstream  edge  of  the  manifolds.  The  flame stabilizers are blunt nosed V-section annular rings  located  downstream  of  the  fuel  burners.  Analternative system includes an additional segmented fuel manifold mounted within the flame stabilizers. The typical burner and flame stabilizer shown in fig. 16-4 is based on the latter system.

Jet pipe

Fig. 16-4 Typical afterburning jet pipe equipment.

Thrust reversal - CONSTRUCTION AND MATERIALS

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Thrust reversal - Turbo-propeller reverse pitch system

CONSTRUCTION AND MATERIALS

Fig. 15-6 Hot stream thrust reverser installations.

20. The clamshell and bucket target doors (fig. 15- 6) described in paras. 9 and 12 form part of the jet pipe. The reverser casing is connected to the aircraft structure  or  directly  to  the  engine.  The  casing supports  the  two  reverser  doors,  the  operating mechanism and, in the case of the clamshell door system, the outlet ducts that contain the cascade vanes.  The angle and area of the gas stream are controlled by the number of vanes in each outlet duct.
21. The clamshell and bucket target doors lie flush with the casing during forward thrust operation and are hinged along the centre line of the jet pipe. They are, therefore, in line with the main gas load and this ensures that the minimum force is required to move the doors.

Fig. 15-7 A cold stream thrust reverser installation.

22. Both the clamshell door system and the bucket target system are subjected to high temperatures and to high gas loads.  The components of both systems,  especially  the  doors,  are  therefore constructed from heat-resisting materials and are of particularly robust construction.

23. The cold stream thrust reverser casing (fig. 15- 7) is fitted between the low pressure compressor casing and the cold stream final nozzle. Cascade vane assemblies are arranged in segments around the

Thrust reversal - Turbo-propeller reverse pitch system

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Thrust reversal - Cold stream reverser system

Turbo-propeller reverse pitch system

Fig. 15-5 A propeller pitch control system.

18. As mentioned in para. A, reverse thrust action is affected  on  turbo-propeller  powered  aircraft  by changing the pitch of the propeller blades through a hydro-mechanical pitch control system (fig. 15-5). Movement of the throttle or power control lever directs oil from the control system to the propeller mechanism to reduce the blade angle to zero, and then through to negative (reverse) pitch. During throttle lever movement, the fuel to the engine is trimmed by the throttle valve, which is interconnect- ed to the pitch control unit, so that engine power and blade angle are co-ordinated to obtain the desired amount of reverse thrust. Reverse thrust action may also be used to manoeuvre a turbo-propeller aircraft backwards after it has been brought to rest.

Thrust reversal - Cold stream reverser system

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Thrust reversal - Bucket target system

Cold stream reverser system 

Fig. 15-4 A typical fan cold stream thrust reversal system.

15. The cold stream reverser system (fig. 15-4) can be actuated by an air motor, the output of which is converted to mechanical movement by a series of flexible drives, gearboxes and screwjacks, or by a system incorporating hydraulic rams.
16. When the engine is operating in forward thrust, the cold stream final nozzle is 'open' because the cascade vanes are internally covered by the blocker doors  (flaps)  and  externally  by  the  movable (translating) cowl; the latter item also serves to reduce drag.
17. On selection of reverse thrust, the actuation system moves the translating cowl rearwards and at the same time folds the blocker doors to blank off the cold stream final nozzle, thus diverting the airflow through the cascade vanes.

Thrust reversal - Bucket target system

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Thrust reversal - Clamshell door system

Bucket target system
12. The  bucket  target  system  is  hydraulically actuated and uses bucket-type doors to reverse the hot  gas  stream.  The  thrust  reverser  doors  are actuated  by  means  of  a  conventional  pushrod system.  A single  hydraulic  powered  actuator  is connected  to  a  drive  idler,  actuating  the  doors through a pair of pushrods (one for each door). 13. The reverser doors are kept in synchronization through the drive idler. The hydraulic actuator incor- porates a mechanical lock in the stowed (actuator extended) position.
14. In the forward thrust mode (stowed) the thrust reverser doors form the convergent-divergent final nozzle for the engine.

Thrust reversal - Clamshell door system

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Thrust reversal - PRINCIPLES OF OPERATION

Clamshell door system

Fig. 15-3 A typical thrust reverser system using clamshell doors.

9. The clamshell door system is a pneumatically operated system, as shown in detail in fig. 15-3. Normal engine operation is not affected by the system,  because  the  ducts  through  which  the exhaust gases are deflected remain closed by the doors until reverse thrust is selected by the pilot. 10. On the selection of reverse thrust, the doors rotate to uncover the ducts and close the normal gas stream exit. Cascade vanes then direct the gas stream in a forward direction so that the jet thrust opposes the aircraft motion.
11. The clamshell doors are operated by pneumatic rams through levers that give the maximum load to the doors in the forward thrust position; this ensures effective sealing at the door edges, so preventing gas  leakage.  The  door  bearings  and  operating linkage operate without lubrication at temperatures of up to 600 deg. C.

Thrust reversal - PRINCIPLES OF OPERATION

want to read about : Thrust reversal - INTRODUCTIONPRINCIPLES OF OPERATION

Fig. 15-2 Methods of thrust reversal.

6. There are several methods of obtaining reverse thrust on turbo-jet engines; three of these are shown in  fig.  15-2  and  explained  in  the  following paragraphs.
7. One method uses clamshell-type deflector doors to reverse the exhaust gas stream and a second uses a target system with external type doors to do the same thing.  The third method used on fan engines utilizes blocker doors to reverse the cold stream airflow.
8. Methods of reverse thrust selection and the safety  features  incorporated  in  each  system described are basically the same. A reverse thrust lever in the crew compartment is used to select reverse thrust; the lever cannot be moved to the reverse thrust position unless the engine is running at a low power setting, and the engine cannot be opened up to a high power setting if the reverser fails to move into the full reverse thrust position. Should the operating pressure fall or fail, a mechanical lock holds the reverser in the forward thrust position; this lock  cannot  be  removed  until  the  pressure  is restored. Operation of the thrust reverser system is indicated in the crew compartment by a series of lights.

Thrust reversal - INTRODUCTION

INTRODUCTION

Fig. 15-1 Comparative landing runs with and without thrust reversal.

1. Modern aircraft brakes are very efficient but on wet, icy or snow covered runways this efficiency may  be reduced by the loss of adhesion between the aircraft tyre and the runway thus creating a need for an additional method of bringing the aircraft to rest within the required distance.
2. A simple and effective way to reduce the aircraft landing run on both dry and slippery runways is to reverse the direction of the exhaust gas stream, thus using engine power as a deceleration force. Thrust reversal has been used to reduce airspeed in flight but it is not commonly used on modern aircraft. The difference in landing distances between an aircraft without reverse thrust and one using reverse thrust is illustrated in fig. 15-1.
3. On high by-pass ratio (fan) engines, reverse thrust action is achieved by reversing the fan (cold stream) airflow. It is not necessary to reverse the exhaust gas flow (hot stream) as the majority of the engine thrust is derived from the fan.

Rolls - Royce Gem 2 | Armstrong Siddeley Python

Rolls - Royce Gem 2

Armstrong Siddeley Python

The Python was developed from the  ASX  axial-flow turbo-jet which first ran in April 1943 and was producing 2800 lb thrust by 1944. With the addition of a propeller gearbox the engine produced 3600 shp plus 1100 lb thrust and was known as the  ASP. Renamed the Python it entered service as the power plant for  the  Westland  Wyvern  S4  turbo-prop fighter.

Rolls-Royce RB211-524D4D | Bristol ProteusRolls-Royce RB211-524D4D

Rolls-Royce RB211-524D4D

Bristol Proteus

Work began in September 1944 on the 4000 e.h.p. Proteus turbo-prop originally intended to  power  the  Bristol  Brabazon  2  and Saunders-Poe Princess. The Proteus first ran in January 1947 and was later used to power the  Bristol  Britannia  at  4445  e.h.p.  A development  of  this  engine,  the  Marine Proteus, is used to power various patrol boats, hovercraft and hydrofoils.

CANARD PLANE PROJECT

Aim :- To build a RC(Remote Controlled) Canard
Plane.
What is canard plane? 
Canard is an airframe configuration of fixed wing aircraft in which the forward surface is smaller than the rearward, the former being known as the "canard", while the latter is the main wing. In contrast a conventional aircraft has a small horizontal stabilizer behind the main wing.
Canard designs fall into two main classes:-
a) Lifting canard:- In this configuration, the weight of the aircraft is shared between the main wing and the canard wing
b) Control canard:- most of the weight of the aircraft is carried by the main wing and the canard wing is used primarily for longitudinal control during maneuvering. The pros and cons of the canard versus conventional configurations are numerous and complex, and it is impossible to say which is superior without considering a specific design application.

Various Parameters involved in the design of Canard Plane:-