FUEL CONSUMPTION DUE TO SHAFT POWER OFF-TAKES FROM THE ENGINE

Transcription

1 FUEL CONSUMTION DUE TO SHAFT OWER OFF-TAKES FROM THE ENGINE Dieter Scholz*, Ravinka Seresinhe, Ingo Staack 3, Craig Lawson Aircraft Design and Systes Group (AERO) Haburg University of Applied Sciences Berliner Tor 9, 0099 Haburg, Gerany Departent of Aerospace Engineering, Cranfield University College Road, Cranfield, Bedfordshire, MK43 0AL, England 3 Division of Fluid and Mechatronic Systes, Linköping University Linköping, Sweden info@rofscholz.de Abstract This paper looks at fuel consuption due to shaft power off-takes fro the engine and the related increase in the aircraft s fuel consuption. It presents a review and coparison of published and unpublished data on this kind of consuption. Insight is given into the effects caused by off-takes, looking at phenoena inside the engine when shaft power is extracted. The paper presents results fro the TURBOMATCH engine siulation odel, calibrated to real world engine data. Generic equations are derived for the calculation of fuel consuption due to shaft power extraction and values are presented for different flight altitudes and Mach nubers. Main result is the shaft power factor k found to be in the order of 0.00 N/W for a typical cruise flight. This yields an aazingly high efficiency for power generation by shaft power extraction fro a turbo fan engine of ore than 70 %. INTRODUCTION. Trade-Offs Many technical options exist for the design of an aircraft syste under investigation. Safety aspects allow no coproise because certification regulations have to be closely followed. The best alternative is hence found fro trade-off studies considering syste price, aintainability, reliability, and the syste s fuel consuption. An aircraft syste consues fuel due to transportation of the syste s ass during flight (fixed or variable ass), shaft power off-takes fro the engines (by electrical generators or hydraulic pups), bleed air off- AST 03, April 3-4, Haburg, Gerany

2 Dieter Scholz, Ravinka Seresinhe, Ingo Staack, Craig Lawson takes (for the pneuatic syste), ra air off-takes (e.g. cooling air for the air conditioning syste), additional aircraft drag caused by the presents of parts sticking out into the flow field (e.g. due to drain asts or antennas) [9]. This paper liits the investigation to considering fuel consuption due to shaft power off-takes fro the engines.. Shaft ower fro the Accessory Gearbox Figure shows the principle of how shaft power is taken fro the high and/or low pressure shaft of the engine. Required is an internal gearbox that couples the engine shaft(s) to a radial driveshaft that drives an external accessory gearbox (AGB). Figure shows further that bleed air is taken fro the engine copressor. Note: Bleed air is not considered in this paper. Figure rinciple of bleed air off-takes and shaft power off-takes fro the engine accessory gearbox [7], [3] The internal gearbox is usually located between the low pressure and the high pressure copressor. In case of odern two-shaft designs, power is taken by the internal gearbox fro the high pressure shaft [4] (p. 43) i.e. the outer and shorter of the two concentric shafts. But the drive ay also take power fro each engine shaft, so as to distribute the loads onto both shafts. Aircraft systes ay in this case be driven fro the low-pressure shaft [3] (p. 67). The high-pressure shaft rotates faster than the low-pressure shaft, which ay also influence the choice of where to attach which accessory. The drive shaft runs through the air ducts of the engine (see Figure ). To liit the disruption to the airflow through the engine due to the drive shaft and the hollow fairing that encloses it, the shaft is designed as sall as possible and hence runs at high speed [3]. The accessory gearbox (AGB) is usually arranged as a curved casing (Figure ), so that the various accessories are ounted close to the engine. Separate ounting pads are provided for each accessory (Figure 3). The drive within the casing is provided by a train of spur gears. Idler gears are coonly used between the, to increase the spacing between accessories. The accessories are arranged on both sides of the driveshaft entry, in reducing order of their speed. Accessories for aircraft systes can be generators as Variable Speed Constant Frequency (VSCF) generators, Integrated Drive Generators (IDG) consisting of a Constant Speed Drive (CSD) and a generator, hydraulic variable displaceent axial piston pups, and high (e.g. for landing gear actuation) and/or low pressure copressors (e.g. for air conditioning; if not provided by the engine copressor) [3] (p. 70).

3 AST 03, April 3-4, Haburg, Gerany Figure The location of the accessory gearbox (AGB) is usually at the lower side of the engine. As depicted, the accessories are attached to the AGB. Figure 3 Hispano-Suiza accessory gearbox and power transissions for the Rolls-Royce s Trent faily of engines powering the Airbus A /600, Airbus A330, and Boeing 777. Visible are the connection for the radial drive shaft and the ounting pads for the accessories [6].3 Exaple Flight Haburg to Toulouse with an A30 and Off-Takes To get a feel for off-takes let s look at a flight fro Haburg to Toulouse with an Airbus A30. The flight profile is given in Figure 4. The shaft power off-take is given in Table and is taken fro real flight data. However, fuel consuption is calculated for axiu shaft power extraction of 3 kw [6] for each of the two engines fro the engine deck of the V500 engine. Results are presented in Table. Maxiu shaft power extraction results in a.4 % increase in fuel consuption for this flight. Actual shaft power extraction (Table ) would give a lower increase in fuel consuption of about 0.4 %. Maxiu bleed air extraction results in a.5 % increase in fuel consuption for this flight. [] gives a higher value of 4.4 % due to bleed air extraction (for ECS) for an actual long range flight of an Airbus A330. More Electric Aircraft (Chapter ) take over also all bleed air loads as shaft power. This will result in a considerable aount of fuel consuption due to shaft power offtakes. We can conclude that fuel consuption due to shaft power off-takes is significant already for a conventional aircraft and even ore so for a More Electric Aircraft. 3

4 Dieter Scholz, Ravinka Seresinhe, Ingo Staack, Craig Lawson Figure 4 Flight profile for a flight fro Haburg to Toulouse with an Airbus A30 [] Thrust rating Table Real off-takes during the flight of Figure 4 [] Shaft power off-take [kw] Max. bleed air off-take fro fan [kg/s] Max. bleed air off-take fro H copressor [kg/s] take-off (to 500 ft) clib (to 3000 ft) cruise (in 3000 ft) descent (to 500 ft) approach Table Fuel consuption calculated fro engine deck for V500, thrust: 5000 lb [] Thrust rating Fuel [kg]: no off-takes Fuel [kg]: ax. shaft power no bleed air Fuel [kg]: no shaft power ax. bleed air Fuel [kg]: ax. shaft power ax. bleed air take-off clib cruise descent approach total fuel off-take fuel relative off-take fuel.4 %.5 % 3.8 % RESENT TRENDS Besides the introduction of new aterials and new engines, the focus in civil aviation is on ore efficient systes. These new systes and subsystes are generally ore electric replacing soe or all hydraulic and/or pneuatic systes by electric systes with the following advantages: higher engine efficiency (partly due to optiized copressor layout), better controllability and hence higher subsyste efficiency, absence of hot bleed air syste with its aintenance deanding coponents, absence of hydraulic syste with its tendency to hydraulic leakages. 4

5 AST 03, April 3-4, Haburg, Gerany But still three years after the aiden flight of the Boeing 787 the first civil transport aircraft with electrical based, bleed less subsyste design advantages and disadvantages of such a design [0] are not clear yet. One reason is that the effects of the different fors of off-takes (bleed air and shaft power off-takes) and their effect on engine fuel consuption are still not sufficiently discussed in the aviation counity. 3 SECONDARY OWER THEORY Secondary power on board an aircraft coprises of electrical power, hydraulic power, and pneuatic power. Electrical power and hydraulic power are generated fro shaft power taken fro the accessory gearbox of the aircraft s engine. The required fuel consuption for secondary power generation first of all depends on the fuel consuption of the engine for aircraft propulsion. Chapter 3. presents a generic ethod to calculate the basic thrust specific fuel consuption (SFC) of a jet engine for propulsion. Chapter 3. presents the theory to calculate fuel consuption due to shaft power off-takes which is based on the basic SFC of the engine. 3. The Engine s Specific Fuel Consuption A typical value for the thrust specific fuel consuption (SFC) of today s jet engines in cruise flight is SFC 6 g/(ns). Very advanced jet engines ay have an SFC 4 g/(ns). Note that SFC is not a constant, but rather increases with aircraft speed or Mach nuber. Data is published for the SFC in noral cruise conditions [4] [5]. If published data is not available SFC ay be calculated. Various odels exist for the estiation of jet engine s SFC. To ake this paper self sufficient one odel is selected and presented here: HERRMANN [9] provides a ethod based on TORENBEEK [] and on statistics of odern engines. SFC 5 noz G φ T ( h) T 0 cop ( + BR) G + 0. M BR M ( + BR) fan χ cop turb γ γ gasgen φ ϑ χ cop fan turb.0 χ ( χ + ϑ) φ cop turb () γ ϑ + M ; φ T TE / T( h) ; χ ϑ OAR γ γ ; gasgen 0.7M ( + 0.M inlet ) Turbine entry teperature in cruise: T TE 8000 K kn + 50 K T TO 5

6 Dieter Scholz, Ravinka Seresinhe, Ingo Staack, Craig Lawson OAR cop turb inlet fan noz kn kn + T TO kn kn + T ( BR) p p kn kn + T.03 kn.03 kn + T / kn T BR M BR TO TO TO TO M M BR M T(h) is the teperature at altitude, T 0 88 K, T TO is the take-off thrust of one engine and p/p 0.0 is the inlet pressure loss, the ratio of specific heats γ.4. Efficiencies are only valid for T TO > 80 kn. 3. Theory for Shaft ower Off-Takes A fuel ass flow & provides the energy per unit of tie to sustain shaft power offtakes. F, & SFC () F, SFC is the power specific fuel consuption in kg/(ws). Jet engines produce thrust T to propel an aircraft. It is custo to calculate the fuel flow of a jet engine & F based on the thrust delivered & SFC T (3) F SFC is the thrust specific fuel consuption in kg/(ns) soeties also naed SFC T. Offtakes cause a change in SFC called SFC. Therefore the fuel ass flow due to off-takes can also be expressed as with () & SFC T (4) F, SFC T SFC (5) SFC T SFC SFC SFC (6) Ai is to find a generic value describing shaft power off-takes varying only little with other paraeters. It was observed that SFC due to shaft power off-takes is roughly proportional to the SFC of the engine, SFC is rather proportional to /T than to ; i.e. the sae shaft power taken fro a large engine does not consue as uch fuel as taken fro a sall engine. 6

7 AST 03, April 3-4, Haburg, Gerany For these reasons it akes sense to define a shaft power factor k in this way: SFC SFC k T (7) SFC k SFC. (8) k has units of N/W and is deterined fro engine siulation tools (see Chapter 5) with SFC / SFC k / T. (9) It is the ai of this paper to provide generic equations with which to calculate the shaft power factor k. Data and equations are given in Chapter 4 and 5. With known k the fuel consuption the fuel ass flow can be calculated fro & k SFC (0) F, The efficiency of shaft power generation fro a jet engine is calculated with help of the heating value of jet fuel (JET A-) H N/kg & H F, k SFC H 74 % () The efficiency for shaft power off-takes with k 0.00 N/W (Table 4), SFC 6 g/(ns) (Chapter 3.) is with 74 % a uch higher value than for any other theral process! Shaft power is known fro data going along with the accessory device powered by the accessory gear box. This can be a generator, a hydraulic pup or whatever is connected. In the equations above in. This is the required input power into the accessory devices. Usually only the noinal output power out is know and the required input power has to be calculated fro in out / dev. With dev being the efficiency of the device as given in Table 3. [4] gives an efficiency of 0.7 for an IDG, [7] a value of Table 3 Efficiencies of devices connected (directly or indirectly) to an accessory gearbox [8] No Device Efficiency, dev [-] generator and Variable Frequency (VF) generator 0.83 axial piston pup electronic conversion unit gear Variable Speed Constant Frequency (VSCF) generator, consisting of and Integrated Drive Generator (IDG), consisting of, two units, and

8 Dieter Scholz, Ravinka Seresinhe, Ingo Staack, Craig Lawson 4 REVIOUS WORK Little data is published on fuel consuption due to shaft power off-takes fro the engine. Data fro published and unpublished previous work is collected and presented in Table Data on Shaft ower Off-Takes SAE with [] (page ) proposes with respect to shaft power off-takes SFC 0.5 lb/(hp. h) kg/(kw. h) and SFC.5 lb/(lb. h). With (8) this converts to k 0,0099 N/W. Table 4 Suary of literature data for fuel consuption due to shaft power off-takes fro the engine in cruise flight Author / organization / engine Source Shaft power Specific Fuel Consuption SFC [kg/(kw. h)] Engine Specific Fuel Consuption SFC [kg/(n. s)] Shaft power factor k [N/W] SAE [] CF6-80C [] [4] EI T400-D6 [] [5] SCHOLZ, 4 [7] see (5): YOUNG [4] Trent [3] 0,0004 CF6-80C-A 4 [3] 0,0077 CFM-56-5C- 4 [3] 0,008 RB- 4 [] 0,008 RB-535E4 5 [4] 0,0077 Trent 77 5 [4] 0,0047 AHLEFELDER 3, 5 [] new evaluation: 3 shafts, ixed nozzle shafts, unixed nozzle 0,003 shafts, ixed nozzle 0,006 shafts, unixed nozzle 0,00308 DOLLMAYER 3 [7] LAWSON [0] BR Adour L shaft: H shaft: Average data fro engine decks, average of different altitudes and Mach nubers data generated with TURBOMATCH (Chapter 5) 3 data generated with GasTurb [8] 4 data generated at axiu cruise thrust 5 data generated at noral cruise thrust The turboprop engine EI T400-D6 for the A400M is said to have SFC 0.67 kg/(kw. h) for shaft power extraction []. For propulsion this engine has a SFC 0.3 kg/(kw. h) [5]. According to this data the engine is ore efficient in producing shaft power than propulsive power. This fact confirs results fro (). 8

9 AST 03, April 3-4, Haburg, Gerany Scholz in [7] follows a different approach in defining a shaft power factor k * copared to Chapter 3.. Equation (9) is odified to SFC / SFC k* / T TO. () This eans instead of dividing by the actual thrust T under given conditions, in () is divided by a unified thrust selected to be the sea level take-off thrust T TO (noinal thrust) of the engine. This results in easier data handling when extracting engine data. () is solved for SFC and cobined with (4) to yield & F, k * T T TO SFC. (3) The disadvantage of (3) is that the user needs to estiate thrust T under given conditions in order to calculate the fuel consuption due to shaft power off-takes. This can be done in cruise where thrust equals aircraft drag and lift equals aircraft weight with help of the glide ratio L/D of the aircraft under given conditions and the earth acceleration g 9.8 /s² L A / C g T D L / D L / D. (4) This additional step (4) is not required using (0). Figure 5 k * obtained fro plotting relative change in specific fuel consuption SFC/SFC against shaft power divided by engine take-off trust [7] 9

10 Dieter Scholz, Ravinka Seresinhe, Ingo Staack, Craig Lawson With the approach fro () and (3) SCHOLZ [7] calculates k * N/W (see Figure 5). Each data point was obtained fro engine decks as the average of SFC/SFC calculated at for all cobinations of flight altitudes of 0 ft, 0000 ft, 0000 ft, and ft at Mach nubers of 0.30, 0.60, and 0.85 at axiu continuous thrust. In each case, shaft power 00 hp kw was extracted fro the engine. The conversion fro k * to k is thrust dependent. For typical cruise conditions the conversion can be attepted roughly with * Treq * k k k 0. TTO. (5) DOLLMAYER [7] investigates shaft power extraction fro the low pressure shaft versus high pressure shaft. Fuel consuption fro the high pressure shaft sees to be up to about 5 % ore fuel intensive than fro the low pressure shaft. 4. Engine Characteristics under Shaft ower Off-Takes Shaft power extraction, no atter if taken fro the H shaft or the L shaft will reduce the speed (rp) of this shaft. This reduces the ass flow in that section of the engine and the thrust of the engines is reduced. Constant thrust regulation applied to the engine (achieved today by the Full Authority Digital Engine Control, FADEC [3]) will priarily result in an increase of fuel flow, increasing the Turbine Entry Teperature, TET. Higher pressure in the cobustion chaber and higher turbine load together with a reduced shaft speed will enlarge the angle of attack at the copressor blades and therewith slightly lift the pressure rise achieved at each stage. In this way, shaft power off-takes also result in closer operation to the surge line. With higher pressure ratio and an increase in the speed of the turbine and the copressor and their ass flow a new equilibriu develops at the original thrust level. If shaft power is taken fro the L shaft, its speed will reduce. Also the fan speed is reduced which decreases the thrust considerably. With the engine controls increasing the TET, the H shaft (in this case not affected by power off-takes) will even increase its speed and ass flow through L turbine and copressor copared to the original situation. Decreasing speed generally eans decreasing efficiency of the coponents. [7] If shaft power is taken for the H shaft, its speed will reduce and so also the ass flow through H turbine and copressor. This reduces also the ass flow through the L copressor and turbine. With the engine controls increasing the TET, the situation is rectified. [7] Low thrust ratings always ean a high relative power extraction /T and high relative specific fuel consuption. At high thrust ratings the relative power extraction /T is saller and the relative specific fuel consuption is less. Taking shaft power fro the H shaft (as is usually the case) relative specific fuel consuption at low /T is especially high. 0

11 AST 03, April 3-4, Haburg, Gerany 5 ENGINE SIMULATION WITH SHAFT OWER OFF-TAKES The effect of shaft power off-takes on the engine operating point cannot be generalized because of the coplexity of a gas turbine. The location of the operating point within a wide operating range of an aircraft propulsion syste to the design point of the engine and each of its coponents need to be considered. During siulation and odel based engine perforance investigations (at a certain operating point), the liiting factors like TET, spool velocities and stall/surge argins have to be observed. For this paper the siulation based investigations are done with TURBOMATCH. 5. Introduction to TURBOMATCH The TURBOMATCH Schee has been developed at Cranfield University to analyze design point and off-design point calculations for gas turbines. The different stages of the engine are siulated by eans of pre-prograed routines referred to as bricks which are operated with the use of code words. The different stages are calculated individually and then the overall perforance is calculated and presented in the for of thrust, SFC and other key engine paraeters. The progra has pre-loaded copressor aps and turbine aps that can be chosen according to the requireent. 5. Validation of the Baseline Engine in TURBOMATCH Engine specifications are [5]: Engine Designation: RB-54-D4 Application: Boeing , Boeing By-ass Ratio, BR: 5 Copressor: L: single stage fan I: 7 stage axial flow H: 6 stage axial flow Overall ressure Ratio, OAR: 9.5 (noinal sea level conditions) Cobustion chaber: annular Turbine: L: 3 stage axial flow I: single stage axial flow H: single stage axial flow Maxiu take-off thrust rating, T TO : 5980 lbf Maxiu continuous thrust rating, T : 4730 lbf Specific Fuel Consuption, SFC: 0.39 lb/lbf/h The siulation odel could be validated as shown in Table 5. The siulation odel shows a deviation fro published data in the design point of less than 5 %.

12 Dieter Scholz, Ravinka Seresinhe, Ingo Staack, Craig Lawson Table 5 Design point siulation results Maxiu Takeoff thrust rating, T TO [N] Thrust specific fuel consuption at ax. take-off thrust ratio, T [kg/(ns)] ublished value Siulation result Deviation % % Siulation conditions The engine was siulated under the following conditions:. International standard atospheric conditions at sea level. All optional bleed air closed 3. Aircraft accessory drives unloaded, hence no shaft power extraction % intake recovery 5.3 Siulating Shaft ower Off-Takes with TURBOMATCH to yield k As discussed previously the engine perforance is penalized by extracting shaft power. For the case of the RB-54-D4 engine analyzed with TURBOMATCH, the shaft power was extracted fro the Low ressure (L) shaft. Many variables were used to create an engine perforance database with shaft power off-takes to analyze the trends. The research focused on three altitudes h: 0, 5000, and The Mach nuber M was varied fro 0 to 0.8 with an interval of 0. and the power off-take was varied between 0 kw and 600 kw in 0 steps. The net thrust was varied in the siulation by using the Turbine Entry Teperature (TET) as a handler fro 00 K to 600 K with an interval of 00 K. To study the penalties caused by the power off-takes, the SFC at each power off-take needed to be copared to the SFC at the sae condition but without any power extraction. The proble is however, that as power is extracted thrust is reduced. A true and fair coparison can only be done with the sae level of thrust. Also in real aircraft operation engine control (FADEC) would ensure thrust to be constant no atter what the power offtakes are. Engine control would allow burning ore fuel to increase the TET in order to aintain the original thrust level. Figure 6 Thrust specific fuel consuption SFC of the RB-54-D4 engine plotted against net thrust and Mach nuber (data shown here is for 0000 )

13 AST 03, April 3-4, Haburg, Gerany Now instead of asking the siulation progra to control the thrust (like a FADEC) for each power off-take under investigation rather a fine no off-take grid of thrust levels was created beforehand with TURBOMATCH giving the specific fuel consuption for no off-take conditions (Figure 6). This grid was created for each of the 3 different altitudes and the 9 different Mach nubers studied in the research. For each of these 7 points 64 different TETs were used between 000 K and 600 K to generate the fine grid of 64 thrust levels. By using the appropriate point in the grid (as per altitude and Mach nuber), each of the 0 power off-take conditions with 6 different thrust levels (generated fro 6 different TETs called TET ) was atched to an equivalent thrust level in the no off-take grid (with thrust fro that TET 0 < TET yielding the best thrust fit). No atter how fine such a no offtake grid is created there will always be a sall deviation in the thrust atching. This deviation is calculated fro [T(,TET ) T( 0, TET 0 )] / T( 0, TET 0 ). Figure 7 is an illustration of the accuracy of the thrust atching. Except for very few cases the deviation in this thrust atching process was less than 7 %. Now the relative change in specific fuel consuptions in each case was calculated with SFC/SFC [SFC(,TET ) SFC( 0, TET 0 )] / SFC(, 0, TET 0 ) coparing SFC with and without power extracted at approxiately the sae thrust. In Figure 8 SFC/SFC was plotted against Mach nuber and values of relative power off-takes /T (which is the power extracted, divided by the thrust of the engine at this condition). It can be observed that SFC/SFC changes linearly with /T. Since the slope of SFC/SFC f(/t) is a constant the description can be siplified by just plotting this slope called k as defined in (7) and (9) (Figure 9). However, k is not a constant throughout the flight envelope. Figure 8 already shows that k decreases with Mach nuber. Figure 9 shows that this decrease is nonlinear. Figure 9 furtherore shows an increase of k with altitude. Figure 7 Accuracy of thrust atching of the RB-54-D4 engine with and without shaft power off-takes in the evaluation of TURBOMATCH data No equation is given to represent Figure 6 for the SFC of the RB-54-D4. Exact data was only necessary for the evaluation of the fuel consuption due to shaft power. If the reader needs an SFC value as for use in (0) he is referred to (). 3

14 Dieter Scholz, Ravinka Seresinhe, Ingo Staack, Craig Lawson Figure 8 Relative change in thrust specific fuel consuption of the RB-54-D4 engine plotted against relative power off-takes (/T) and flight Mach nuber (data is for a flight altitude of 5000 ) Figure 9 Shaft power factor k of the RB-54-D4 engine plotted against flight Mach nuber and altitude. Actual thrust T is used for this evaluation. Figure and Figure show a little ore detail and reveal that k is about constant if /T is sufficiently large. k taken as the average slope in Figure is a good average value for k as confired in Figure. For the evaluation with TURBOMATCH this also eans, data is based on an average thrust level as obtained with a TET between 00 K and 600 K. At h 0000 and M 0.8 the average thrust for which the evaluation is done is 8.7 % of take-off thrust. In other words T/T TO So the evaluation is done at a typical cruise thrust level. 4

15 AST 03, April 3-4, Haburg, Gerany k p fro Figure 9 can be represented by k h M h h M M (6) Figure 0 Shaft power factor k of the RB-54-D4 engine as function of Mach nuber and altitude. Copare with Figure 9. Data points are the average values fro TURBOMATCH for each Mach nuber and altitude obtained as in Figure. Actual thrust T is used for this evaluation. In equations: x M. Figure 0 gives an alternative -diensional representation of Figure 9. It includes further equations for the calculation of k (with x M). These equations can be cobined for an interpolation as given in (7). k with a( h) M c(h).0 0 a(h) b(h) b( h) M + c( h) 7 8 h h h (7) Since all turbo fan engines show siilar behavior (see Figure 5) and the dependency on Mach nuber and altitude causes larger changes of k than a change of engines (operating at the sae Mach nuber and altitude), (6) and (7) ay be used as an approxiation for all turbo fan engines as long as no other ore specific data is available. Equations (6) and (7) are two equivalent representations for k and yield alost the sae result. A axiu error up to about N/W copared to TURBOMATCH data has to be expected (copare also with Figure 0). 5

16 Dieter Scholz, Ravinka Seresinhe, Ingo Staack, Craig Lawson The values of k for M 0.8 and h 0000 is N/W. This copares favorable with the average k fro Table 4 which is N/W! Note: Aircraft are Mach liited at high altitudes (roughly above 6000 ) to M MO and are speed liited at lower altitudes to a speed called V MO. With large values of the speed of sound a close to the ground, flight Mach nubers at low altitudes M V / a are liited to values below M MO and even below noral cruise Mach nubers. This is the reason why the ost favorable condition (for shaft power extraction) at M 0.8 and h 0 is not a data point in the flight envelope and can not be used for flight. In addition flights at very low altitudes are not econoic anyway. 0,5 0, y 0,0048x R 0,9609 delta SFC / SFC 0,5 0, 0, /T [W/N] Figure Shaft power factor k of the RB-54-D4 engine obtained as the slope of the function SFC/SFC f(/t) with N/W. Actual thrust T is used for this evaluation. Mach nuber: 0.8 and altitude: ,0 0,00 0,008 k 0,006 0,004 0,00 0, /T [W/N] Figure Shaft power factor k of the RB-54-D4 engine. Representative values ay only be obtained for larger /T. Actual thrust T is used for this evaluation. Copare with Figure. Mach nuber: 0.8 and altitude:

17 AST 03, April 3-4, Haburg, Gerany 5.4 Siulating Shaft ower Off-Takes with TURBOMATCH to yield k * Figure 3 follows the alternative approach described in Chapter 4. with equations (), (3) and (5). Here SFC/SFC is plotted versus /T TO. Since T TO is constant for one particular engine this is basically the sae as plotting versus. The significance of plotting versus /T TO becoes only apparent once several engines are copared (like in Figure 5). Coparing Figure and 3, it can be seen that plotting versus /T gives a better regression than plotting versus /T TO. The values of k * for M 0.8 and h 0000 is N/W (Figure 3). With (5) and T/ T TO 0.87 (Chapter 5.3) : k k *. T/T TO N/W which is 38 % off fro the original value of k N/W (Chapter 5.3). 0, 0,8 0,6 y 0,066x R 0,8007 delta SFC / SFC 0,4 0, 0, 0,08 0,06 0,04 0, /T_TO [W/N] Figure 3 Shaft power factor k * fro Equation (4) of the RB-54-D4 engine obtained as the slope of the function SFC f(/t TO ) with N/W. Take-off thrust T TO is used for this evaluation. Mach nuber: 0.8 and altitude: 0000 Nevertheless, an attept is ade to extract also k * fro the data base generated with TURBOMATCH as a function of Mach nuber and altitude. The result of this is presented in Figure 4. It includes further equations for the calculation of k (with x M). k* 0,030 0,05 0,00 0,05 0,00 0,005 0, , 0, 0,3 0,4 0,5 0,6 0,7 0,8 0,9 Flight Mach Nuber k_* (0 k) k_* (5 k) k_* (0 k) Linear (k_* (0 k)) Linear (k_* (5 k)) Linear (k_* (0 k)) y -0,05x + 0,059 R 0,9978 y -0,008x + 0,08 R 0,9948 y -0,009x + 0,050 R 0,985 Figure 4 Shaft power factor k * of the RB-54-D4 engine as function of Mach nuber and altitude. Data points are the average values fro TURBOMATCH for each Mach nuber and altitude 7

18 Dieter Scholz, Ravinka Seresinhe, Ingo Staack, Craig Lawson k * a( h) M + b( h) with a(h) b(h) h h h.5 0 (8) It is interesting to note that k * is a linear function with Mach nuber (8), whereas k was represented by a quadratic function (7). The average of the values of all values k * is N/W. This copares not so favorable with the value of k * N/W fro Figure and is off by 39 %. 6 SUMMARY AND CONCLUSIONS Fuel consuption due to shaft power off-takes can be calculated with & F, k SFC. Equations for the shaft power factor k were derived fro a data set generated with the engine siulation package TURBOMATCH of Cranfield University. An equation to calculate SFC fro literature is also provided. The power extracted fro the engine is the input power taken fro the accessory gear box. This power depends on efficiency of the device. The efficiency of the device is also given in this paper. k was found to be in the order of N/W for a typical cruise flight. This yields an aazingly high efficiency for the power generation by shaft power extraction fro a turbo fan engine of ore than 70 %. More research is also necessary on bleed air off-takes. Only if bleed air off-takes are understood as well as shaft power off-takes it is possible to ake a true coparison between the conventional aircraft and the ore electric aircraft. 7 REFERENCES [] AHLEFELDER, Sebastian: Kraftstoffverbrauch durch Entnahe von Zapfluft und Wellenleistung von Strahltriebwerken. Haburg University of Applied Sciences, Departent of Autootive and Aeronautical Engineering, roject, 006 [] AIRBUS INDUSTRIE Conversation with the aircraft anufacturer [3] AIRBUS INDUSTRIE: Flight Crew Operating Manual : A30. Copany ublication [4] BRÄUNLING, Willy J.G.: Flugzeugtriebwerke. Berlin : Springer, 004 [5] CIVIL AVIATION AUTHORITY: Engine Type Certificate Data Sheet No.043 (Issue 36). London : UK CAA, October 988. URL: (03-0-8) [6] EUROEAN AVIATION SAFETY AGENCY: EASA Type Certificate Data Sheet IAE V500-A5 & - D5 Series Engines. Köln, Gerany : EASA, 5 January 03 (TCDS IM.E.069). URL: E.069_International_Aero_Engines_AG_%8IAE%9_V500--A5_and_V500-- D5_series_engines pdf (03-0-8) 8

19 AST 03, April 3-4, Haburg, Gerany [7] DOLLMAYER, Jürgen: Methode zur rognose des Einflusses von Flugzeugsysteen auf die Missionskraftstoffasse. Aachen : Shaker, 007. ISBN: [8] KURZKE, Joachi: GasTurb 8.0, 998 Software [9] HERRMANN, Steffen: Untersuchung des Einflusses der Motorenzahl auf die Wirtschaftlichkeit eines Verkehrsflugzeuges unter Berücksichtigung eines optialen Bypassverhältnisses. Berlin, Technical University, Institute for Aerospace Sciences, Departent of Aircraft and Lightweight Design, Thesis, 00 [0] LAWSON, Craig: The Effects of Systes ower Off-Takes on Jet Engine Design and erforance. Cranfield University, AVD Lecture Notes, 0 (AVD 0439/) [] LEHLE, Wilfried: Konzeption und Entwicklung von Flugzeugkliatisierungsanlagen. raxis- Seinar Luftfahrt, Haburg University of Applied Sciences, June 006. Lecture for HAW Haburg, DGLR, VDI. URL: Download fro URL: (03-0-8) [] ROLLS-ROYCE: erforance Specification and Installation Notes RB--. Derby, UK : Rolls-Royce, 968 [3] ROLLS-ROYCE: The Jet Engine. Derby, UK : Rolls-Royce, 986. ISBN [4] ROUX, Élodie: Modèles Moteur : Réacteurs double flux civils et réacteurs ilitaires à faible taux de dilution avec C. In : Thèse : our une Approche Analytique de la Dynaique du Vol, SupAéro, Toulouse, 00. URL: (03-0-3) [5] ROUX, Élodie: Turboshaft, Turboprop & ropfan. Blagnac : Éditions Élodie Roux, 0. ISBN [6] SAFRAN: Hispano-Suiza teas up with Rolls-Royce on the Trent engine faily. URL: (03-0-6) [7] SCHOLZ, Dieter: Entwicklung eines CAE- Werkzeuges zu Entwurf von Flugsteuerungs-und Hydrauliksysteen. Fortschritt-Berichte VDI, Reihe 0, No. 6, Düsseldorf : VDI, 997. Download fro: URL: [8] SCHOLZ, Dieter: Direct Operating Costs of Systes with Bi-directional Hydraulic - Electric ower Conversion Units (HECU) & Direct Operating Cost Coparison : IDG versus VSCF Generator. Neu Wulstorf : Applied Science, 998 (Report 4-98) [9] SCHOLZ, Dieter: DOCsys - A Method to Evaluate Aircraft Systes. In: Schitt, D. (Ed.): Bewertung von Flugzeugen (Workshop: DGLR Fachausschuß S - Luftfahrtsystee, München, 6./7. Oktober 998). Bonn : Deutsche Gesellschaft für Luft- und Raufahrt, 998. Download fro: URL: [0] SLINGERLAND, Ronald; ZANDSTRA, Sijen: Bleed Air versus Electric ower Off-takes fro a Turbofan Gas Turbine over the Flight Cycle (7th AIAA Aviation Technology, Integration and Operations Conference, ATIO, 8 0 Septeber 007, Belfast Northern Ireland), AIAA, 007 [] SOCIETY OF AUTOMOTICE ENGINEERS: Aerospace Inforation Report 68/8 : Aircraft Fuel Weight enalty due to Air Conditioning. Warrendale, USA : SAE, 989 [] TORENBEEK, Egbert: Synthesis of Subsonic Airplane Design. Dordrecht, NL : Kluver, 990 [3] WILSON, R. A. L.: The Introduction of Lainar Flow to the Design and Optiisation of Transport Aircraft. Cranfield University, UK, h.d. Thesis 997 [4] YOUNG, T.M.: Investigations into the Operational Effectiveness of Hybrid Lainar Flow Control Aircraft. Cranfield University, UK, h.d. Thesis, 00 9