Aircraft Design Projects - part 4 pot

“chap04” — 2003/3/10 — page 91 — #46 Project study: scheduled long-range business jet 91 21 550 500 450 400 12 10 8 14 20 19 18 17 16 Fig. 4.20 Trade-off study: cruise L/D ratio 46 550 500 450 400 12 10 8 14 44 42 40 38 32 34 36 1000 kg Fig. 4.21 Trade-off study: stage fuel mass 4.8.5 Economic analysis The results from the studies above can be used, together with operational data, to assess the economic viability and sensitivity to the aircraft geometrical changes. The aircraft price is related to the aircraft empty mass and engine size. The cost of fuel is proportional to fuel mass. Other operational costs are related to aircraft take-off mass. Hence, changes to the aircraft configuration will affect both aircraft selling price and operating costs. For civil aircraft designs, these two cost parameters are often selected as the principal design drivers (optimising criteria). Although the aircraft configuration “chap04” — 2003/3/10 — page 92 — #47 92 Aircraft Design Projects 127 123 119 115 111 103 107 1000 kg 8 10 12 14 400 450 500 550 Fig. 4.22 Trade-off study: aircraft max. TO mass 320 300 280 260 240 180 200 220 sq. m 8 10 12 14 400 450 500 550 Fig. 4.23 Trade-off study: wing area may not be selected at the optimum configuration for these parameters, the design team will need to know what penalty they are incurring for designs of different configuration. All of the cost calculations have been normalised to year 2005 dollars by applying an inflation index based on consumer prices. Several separate cost studies have been performed as described below. “chap04” — 2003/3/10 — page 93 — #48 Project study: scheduled long-range business jet 93 64 66 68 70 72 74 76 78 80 82 84 86 88 8 10 12 14 400 450 500 550 $m (2005) Fig. 4.24 Trade-off study: aircraft price Aircraft price Aircraft price is one component in the evaluation of total investment. This includes the cost of airframe and engine spares. For this aircraft, the total investment is about 12 per cent higher than the aircraft price. Figure 4.24 shows the variation of aircraft price for the geometrical changes con- sidered previously. At the design point the price is estimated to be $70.5 m. The carpet plot shows that this price would fall by about 5 per cent if the aspect ratio was reduced to 8, and by about 9 per cent if the configuration was moved to point 550/8. The effect of reducing wing loading progressively increases aircraft price (e.g. reducing wing loading to 400 kg/sq. m increases the price by 9 per cent). Similarly, increasing wing aspect ratio increases price (e.g. moving from 10 to 14 increases the price by over 10 per cent). Without consideration of other operating costs, the main conclusion of this study is to move the design point to lower values of both wing loading and aspect ratio. Direct operating cost (DOC) per flight There are two fundamentally different methods of estimating aircraft DOC. The tradi- tional method includes the depreciation costs of owning the aircraft. On this aircraft, this would be about 33 per cent of the total DOC. If the aircraft operator leases the aircraft, the annual cost of the aircraft is regarded as a capital expenditure. This would be considered as an indirect aircraft operating cost. In this case, the aircraft standing charges (depreciation, interest and insurance) are not included in the calculation and the resulting cost parameter is termed ‘Cash DOC’. It is important to calculate both of the DOC methods. The results of the DOC calculations are shown in Figures 4.25 and 4.26. The DOC per flight at the design point (500/10) is $72 740. This figure would be reduced by 3 per cent if the design was moved to point 550/8 and still satisfy the technical design requirements. Increasing wing area and/or aspect ratio from the design point is not seen to be advantageous. At the design point the Cash DOC is estimated to be “chap04” — 2003/3/10 — page 94 — #49 94 Aircraft Design Projects 72 70 74 76 78 80 82 8 10 12 14 400 450 500 550 $1000 Fig. 4.25 Trade-off study: DOC per flight 48 50 52 54 8 10 12 14 400 450 500 550 $1000 Fig. 4.26 Trade-off study: cash DOC per flight $49 470. In this case, curves are seen to be flatter than for the full DOC values. This results in optimum points for aspect ratio. At the design point, the existing value of aspect ratio is seen to be optimum. Moving to the higher wing loading (550), if feasible, would reduce Cash DOC by about 2 per cent. It is of interest to note that the design conclusions from the two DOC methods are different. This implies that the design strategy to be adopted is conditional on the accounting practices used by the operator. This is a good example of the need for the designers to understand the total operating and business environment in order to select the best aircraft configuration. “chap04” — 2003/3/10 — page 95 — #50 Project study: scheduled long-range business jet 95 Seat mile cost The cost of flying the specified stage (design range) is dependent on the payload. In the DOC calculations above, the aircraft has been assumed to be operating at full payload. This is conventional practice as it allows the maximum seats to be used in the evaluation of seat mile costs. Flying at max MTOM, the DOC per flight does not vary with passenger numbers. The seat mile cost (SMC) shown in Figures 4.27 and 4.28 (for DOC and Cash DOC respectively) are evaluated for the 80-seat executive version of the aircraft. Other versions have been evaluated at the design point and are listed in Table 4.7. Note the powerful effect of passenger numbers in reducing SMC and the substan- tial reduction in the Cash SMC method. When using values from other aircraft it is important to know the basis on which cost data has been calculated. 12.6 13.0 13.4 13.8 14.2 14.6 cents 8 10 12 14 400 450 500 550 Fig. 4.27 Trade-off study: seat-mile cost (SMC) 8.6 8.8 9.0 9.2 9.4 9.6 cents 8 10 12 14 400 450 500 550 Fig. 4.28 Trade-off study: cash SMC “chap04” — 2003/3/10 — page 96 — #51 96 Aircraft Design Projects Table 4.7 Layout Passengers SMC Cash SMC Executive only 80 12.99 8.83 Mixed class 107 9.74 6.62 Economy only 120 8.70 5.91 Charter only 150 6.85 4.68 The SMC and Cash SMC carpet plots show a similar pattern to the DOC figures. The SMC curves show an advantage to reducing aspect ratio for all values of wing loading but this advantage reduces with higher wing loadings. For the design point, a reduction of aspect ratio to 8 would be recommended. For the Cash SMC calculation, the best aspect ratio varies from 8 at low loading to 12 at the high loading. For the design point, the value of 10 is seen to be about ‘optimum’. 4.9 Initial ‘type specification’ At the end of the initial concept stage it is important to record all of the known details of the current design. This document forms the initial draft of the aircraft type spec- ification. As the design evolves over subsequent stages, this document will be amended and enlarged until it forms the definitive description of the final configuration. The initial draft will form the input data for the next stage of the design process. The sections below are typical of a professional aircraft specification. 4.9.1 General aircraft description This aircraft is designed for exclusive, business/executive, long-range routes from regional airports. Although apparently conventional in configuration, it incorporates several advanced technology features. These include natural laminar flow control, composite material and construction, enhanced passenger cabin services and com- fort standards, and three-surface control and stability. The single aisle cabin layout is arranged to accommodate four abreast seating for the baseline executive configura- tion. In other configurations it will provide five abreast economy class seating and six abreast charter operations. In these versions the increased passenger numbers reduce the range capability of the aircraft. In the baseline executive layout, space for 80 sleep- erettes at 1.1 m (44 in) pitch is available. For the other layouts, 120 economy seats at 0.8 m (32 in) pitch or 150 charter seats at 0.7 m (28 in) pitch are feasible. Toilet, galley and wardrobe provision is adjusted to suit the layout using fixed service facilities in the cabin. Emergency exits and other safety provisions meet FAR/JAR requirements. Underfloor cargo and baggage holds are positioned fore and aft of the wing/fuselage junction structure. To reduce engine operating noise intrusion into the cabin, during the long endurance flights, the engines are positioned at the rear of the fuselage, behind the cabin pressure bulkhead. Several existing and some proposed new engine developments are suitable to power the aircraft. This provides commercial competitiveness and flexibility to the “chap04” — 2003/3/10 — page 97 — #52 Project study: scheduled long-range business jet 97 potential airline customers. All the engines are modern, medium-bypass (typically 6.0) turbofans offering efficient fuel economy. The modern, aerodynamically efficient, high aspect ratio wing layout provides good cruise efficiency. A lift to drag ratio in cruise of 19 is partly achieved due to the aerody- namic section profiling and the provision of natural laminar flow. Leading and trailing edge, high-lift devices provide the short field performance required for operation from regional airfields. The three-surface (canard, main wing and tail) layout offers a reduction to trim drag in cruise and improved ride comfort. Integrated flight control systems with fly-by- wire actuation to multi-redundant electric/hydraulic controllers provide high levels of reliability and safety. Aircraft manufacture combines established high-strength metallic materials with new composite construction techniques. The combination of conventional and novel structural and manufacturing practices offers reduced structural weight with confidence. 4.9.2 Aircraft geometry Principal dimensions Overall length = 43.0 m, 141 ft Overall height = 13.0 m, 42.6 ft Wing span (total) = 48.0 m, 157 ft Main wing Gross (ref.) area = 216 sq. m, 2322 sq. ft Aspect ratio = 10 Sweepback (LE) = 22 ◦ Mean chord = 4.65 m, 15.25 ft Taper ratio = 0.3 Thickness (mean) = 11% Control surfaces Horizontal tail area = 20.0 sq. m, 215 sq. ft Vertical (fin) area = 15.5 sq. m, 167 sq. ft Canard area = 7.0 sq. m, 75 sq. ft Fuselage/cabin Fuselage length = 40.0 m, 131 ft Cabin outside dia. = 3.6 m, 142 in Pass. cabin length = 22.0 m, 72 ft Landing gear Wheelbase = 18.0 m, 59 ft Track =8.25m, 27ft Engines (two) Various types, static SL thrust (each) = 160 kN, 35700 lb 4.9.3 Mass (weight) and performance statements Mass statement Aircraft empty mass 50 858 kg, 112 142 lb Aircraft operational mass 52 862 kg, 116 560 lb Aircraft max. (design) mass 108 000 kg, 238 140 lb “chap04” — 2003/3/10 — page 98 — #53 98 Aircraft Design Projects Baseline (executive) version (80 PAX) Zero fuel mass 62 462 kg, 137 729 lb Payload 9600 kg, 21 168 lb Fuel load 45 538 kg, 10 0411 lb Still air range 7200 nm Mixed-class version(107 PAX) Payload 11 380 kg, 25 093 lb Fuel 43 758 kg, 96 486 lb Still air range 6810 nm All economy version (120 PAX) Payload 12 160 kg, 26 812 lb Fuel 44 138 kg, 97 324 lb Still air range 6675 nm Charter version (150 PAX) Payload 13 450 kg, 29 657 lb Fuel 41 688 kg, 91 922 lb Still air range 6350 nm Stretched version (160 economy PAX) Payload 16 000 kg, 35 280 lb Still air range 5600 nm Performance statement (baseline version with 80 PAX and fuel): Cruise speed = M0.85 Cruise altitude = 36 000 ft Initial cruise altitude climb rate = 300 fpm Take-off distance = 1790 m (5870 ft) Balanced field length = 1720 m (5670 ft) Second segment climb gradient = 0.033 Approach speed = 125 kt Landing distance = 1594 m (5225 ft) 4.9.4 Economic and operational issues Cost statement (baseline aircraft, 2005 US dollars) Aircraft price = $62.0 M Total investmt/aircraft = $70.6 M Standing charges/yr = $6.0 M Standing charges/flt hr = $1430 DOC/fl hr = $4930 Stage cost = $71 000 Aircraft mile cost = $10.14 Seat mile cost (100% PAX) = 12.7 cents Cash DOC/flt hr = $3500 Total stage cash cost = $50 450 Aircraft cash mile cost = $7.20 Cash seat mile cost (100%) = 9.0 cents “chap04” — 2003/3/10 — page 99 — #54 Project study: scheduled long-range business jet 99 Operational statement The aircraft is capable of stretching to accommodate up to 204 charter seats. In a military role the baseline aircraft can seat 186 soldiers and in the stretched version 246 troops. In each of these versions it would be possible to fly 7000 nm (unrefuelled). Other roles for the aircraft could include: • Civil corporate jet • Freighter • Military refuelling tanker • Communication platform • Military surveillance aircraft • Military supply aircraft These versions of the aircraft have not been considered in the overall geometrical layout of the aircraft in the initial design process. A short study would be appropriate when the initial baseline study has been completed to identify any small changes to the aircraft layout to accommodate any of the above roles. 4.10 Study review This aircraft project has shown how, for a relatively simple aircraft, the design process is taken from the initial consideration of the operational requirements to the end of the concept design phase. The intervening stages have shown how the aircraft design evolves during this process. This showed that the initial configurational assumptions for thrust and wing loadings, based on data from existing aircraft, were found to be in error because of the unique operational performance of the aircraft. A more efficient aircraft layout was identified. Even the revised configuration was shown capable of improvement by the trade studies. For most aircraft projects, this iterative process is commonplace. The economic assessment of the aircraft indicated that the project was viable and therefore worth taking into the next stage of development. Due to time and resource restrictions in the conceptual stage, several technical aspects of the design have not been fully analysed. These include: • The stability and control analysis of the aircraft including the assessment of the effect of the three-surface control layout. • The aerodynamic analysis of the laminar flow control system and the associated structural and system requirements. • The aircraft structural analysis and the realisation of the combined conventional and composite structural framework. • The aircraft systems definition and the associated requirements for the new executive- class communication and computing facilities. • The special requirements for aircraft servicing and handling at regional airports. • The detailed trade-off studies applied to the field requirements (e.g. the definition of aerodynamic (flap design and deflection), propulsion (T /W ), structures, systems and costs). • The assessment of the overall market feasibility of the project. Each of the topics in the list above involves work that is either comparable with, or exceeds, the work that has already been done on the project. In industry, progress- ing to the next stage of aircraft development would involve a 20- to 50-fold increase “chap04” — 2003/3/10 — page 100 — #55 100 Aircraft Design Projects in technical manpower. To commit the company to this expenditure is a significant investment. A decision to proceed would only be taken after discussions with potential airline customers. If the type of operation envisaged by this project is seen to be attractive, it will stimulate competition. This may come from airframe manufacturers who could modify existing aircraft to meet the specification. It is essential that the design team of the new aircraft anticipate this threat. They will need to conduct their own studies on the modifications to the aircraft that may be used as competitors. These are studies that require substantial effort, but in completing them, the advantages of the new design can be identified. This information will be useful to the technical sales team of the new aircraft and used to counteract the threat from the ‘old-technology’, ‘modified’ existing types. References 1 Jenkinson, L. R., Simpkin, P. and Rhodes, D., Civil Jet Aircraft Design, 1999, AIAA Education Series, ISBN 1-56347-350-X. 2 Mason, W. H. et al., Low-cost Commercial Transport – Undergraduate Team Aircraft Design Competition, 1995, Virginia Tech. AIAA 95–3917. 3Howe,D.,Aircraft Conceptual Design Synthesis, 2000, Prof. Eng. Pub. Ltd, ISBN 1-86058- 301-6. 4 Fielding, J. P., Introduction to Aircraft Design, 2000, Cambridge University Press, ISBN 0-502-65722-9. 5 Hoerner, S. F., Fluid Dynamic Drag, published by the author, Bricktown, NJ, 1965. [...]... 545 A (P&W Canada) DV-25 (PS/Russian) TFE 73 1-6 0 (Allied-Sig.) CFE 738 (GE/ASE) PW 306A (P&W Canada) Adour 871 (Rolls Royce) F12 4- 1 00 (Allied-Signal) AE 3007C (AEC) – Citation MiG-AT F5/T38 MB339 Citation Yak 130 Citation Falcon 2000 DO 328 Hawk/T45 – UAV 10.20/2300 13. 54/ 3 045 14. 12/3175 15.57/3500 19.30 /43 39 19.79 /44 50 21.58 /48 52 24. 86/5590 24. 90/5600 25.35/5700 26.81/6028 28.02/6300 28.89/ 649 5 0 .45 ... 28.02/6300 28.89/ 649 5 0 .45 0.55 0. 74 1.00 0.98 0 .44 0.60 0 .42 0.37 0.39 0.78 0.81 0.33 203 /44 7 2 84/ 627 302/666 310/6 84 – 347 /765 45 0/992 42 1/929 601/1325 47 3/1 043 602/1328 49 9/1100 717/1581 1600 13 (b) Trend line (?) 140 0 Engine weight (lb) 9 11 (Adour) 1200 500 kg 12 (a) Trend line: eng wt (tb) = 50 + 0.175 thrust 1000 10 7 8 800 3 600 6 2 250 kg 10 40 0 1000 4 2000 1 20 3000 40 00 30 KN 5000 6000 7000 Engine... mass statement for the aircraft can be compiled: Component Wing Fuselage Horizontal tail Fin Undercarriage Total Useful Load kg/lb %M TO 392/6 64 6.9 518/1 142 9.1 65/ 143 ) 1.7 34/ 75) → 237/523 4. 2 1 246 /2 747 21.8 577/1272 288/635 865/1907 15.2 1200/2 646 21.0 3311/7300 58.0 900/19 84 15.8 136/300 1360/3000 2396/5283 42 .0 MAXIMUM TAKE-OFF MASS∗ Note: aircraft design take-off mass 5707/125 84 6000/13230 Total... that modern aircraft lie along the 40 per cent SLS thrust line As might be expected the manoeuvre and performance of these aircraft are similar The new supersonic aircraft are above this line and older aircraft substantially below This reflects the “chap05” — 2003/3/10 — page 109 — #9 109 110 Aircraft Design Projects 12 000 40 % Total thrust (lb) 10 000 30% 8000 6000 20% 40 00 2000 0 0 2000 40 00 6000 8000... USA Daewoo (KTX-1) South Korea Dassault-Breguet/Dornier, Alpha Jet International Denel (MB326M) South Africa Fuji (T3/T5) Japan HAI (Kiran 1A/MK2) India Israel Aircraft (TC2/TC7) Israel Kawasaki (T4) Japan Lockheed Aircraft (IA63) Argentina MAPO (MIG-AT) Russia Mitsubishi (T2) Japan NAMC (K8) China Northrop-Grumman (T38) USA PAC Pakistan Polskie (WSK PZL M-93V, I-22) Poland Raytheon-Beechcroft (T1/JPATS)... Rhein-Flugg (Fantrainer) Germany SAAB (SK 60W) Sweden Samsung/Lockheed (KTX-2) South Korea Socata (TB30/TB31) France UTVA (Soko G4) Serbia Yakovlev (Yak 130) Russia (Yak/Aeromacci) (Y130) International The list above is a ‘mixed-bag’ of aircraft including propeller types, derivatives of existing non-training aircraft, and some purely national projects It is necessary to review the collection to select aircraft. .. instrument flying and formation “chap05” — 2003/3/10 — page 105 — #5 105 106 Aircraft Design Projects Selection Elementary or basic training Basic of intermediate training Advanced training Conversion or lead-in experience Jet/fast jet trainer aircraft Tprop/jet trainer aircraft Piston-powered trainer aircraft Piston/tprop trainer aircraft Increasing complexity leading to operational posting Fig 5.2 Airforce... single-seat aircraft (see later comment), ground-based instructor console(s) and a modern communication and data linking facility (Figure 5.8) Removing the instructor “chap05” — 2003/3/10 — page 110 — #10 Project study: military training system Table 5.1 Engine (Manufacturer) Used on Thrust SLS (kN/lb) SFC (@ SLS) (–/hr) Eng mass (kg/lb) FJ4 4- 2 A (Williams/RR) JT15D (P&W Can) Larzac 0 4- C20 (TM/Snec.) J8 5-2 1... (m/s) Fig 5.12 Aircraft turn performance “chap05” — 2003/3/10 — page 120 — #20 350 40 0 Project study: military training system 100 Specific excess power 50 n=1 0 n=2 –50 n=3 –100 Point A (V = 140 m/s, n = 4. 2g) n =4 –150 n=5 –200 –250 n=6 –300 0 50 100 150 200 250 300 350 40 0 Speed (m/s) Fig 5.13 Specific excess power at SL 40 20 Specific excess power 0 n=1 –20 40 –60 n=2 –80 –100 –120 – 140 n=3 –160 –180... 0.015 CD 40 ◦ flap = 0.030 Lift co-efficients are as quoted earlier (i.e take-off 1.7 and landing 2.1) Take-off estimation In the early part of the conceptual design process simplified take-off calculations can be done using Nicolai’s (reference 4) simplified take-off parameter (this includes W /S, T /W , Clmax ) As we require only the ground run to be estimated, the take-off distance attributed to the . calculated. 12.6 13.0 13 .4 13.8 14. 2 14. 6 cents 8 10 12 14 400 45 0 500 550 Fig. 4. 27 Trade-off study: seat-mile cost (SMC) 8.6 8.8 9.0 9.2 9 .4 9.6 cents 8 10 12 14 400 45 0 500 550 Fig. 4. 28 Trade-off study:. Projects 72 70 74 76 78 80 82 8 10 12 14 400 45 0 500 550 $1000 Fig. 4. 25 Trade-off study: DOC per flight 48 50 52 54 8 10 12 14 400 45 0 500 550 $1000 Fig. 4. 26 Trade-off study: cash DOC per flight $49 47 0. In this case,. below. “chap 04 — 2003/3/10 — page 93 — #48 Project study: scheduled long-range business jet 93 64 66 68 70 72 74 76 78 80 82 84 86 88 8 10 12 14 400 45 0 500 550 $m (2005) Fig. 4. 24 Trade-off study: aircraft