Supersonic cruise flight of Vth generation fighters

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1 Aerospace Systems (2018) 1: ORIGINAL PAPER Supersonic cruise flight of Vth generation fighters I. Bashkirov 1 O. Ogorodnikov 1 Received: 25 September 2018 / Accepted: 30 October 2018 / Published online: 21 November 2018 Shanghai Jiao Tong University 2018 Abstract The fifth and fourth generation fighters supersonic cruise flight comparative analysis approach is proposed and demonstrated. The IVth and Vth generation supersonic cruise flight parameters difference is shown. Effective supersonic cruise flight as characteristic feature of the Vth generation is proposed together with it s criteria. Supercruise flight regime is investigated and it is shown that supercruise is not optimal from supersonic cruise range yet. Supercruise ability does not guarantee the supersonic performance advantage. Keywords Combat aircraft Supercruise Supersonic cruise flight Breguet parameter Ballistic coefficient Thrust-to-weight ratio 1 Introduction Modern stage of combat aviation development is characterized by: deep modernization of the IVth generation combat aircraft, the Vth generation putting into service, the VIth generation conceptual design start, Fig. 1. While the appearance of the VIth generation is under discussion, the Vth generation, such as Su-57 (Russia), F-22A (US) and J-20 (China), are demonstrating the typical performance the watershed between the last generations. That ones are, in the first place, low signature and supersonic cruise flight. The term low signature doesn t cause confusions among experts as well as aviation journalists, bat the Vth generation supersonic cruise flight should be précised and made clear by means of supersonic cruise flight parameters calculating analysis. B I. Bashkirov aerobig@mail.ru 1 Central Aerohydrodynamic Institute n.a. prof. N.E. Zhukovsky (TsAGI), Zhukovsky, Russia 2 The increase of the supersonic cruise flight range The terms supersonic cruise flight and supercruise with the reference to Vth generation combat aircraft went into the use at the early 90th of the last century. It was the time when the future tactical fighter F/A-22 information appeared [1]. The most issues treat the supercruise as supersonic cruise flight without afterburner. Also supercruise was defined as supersonic cruise flight at intermediate afterburning [1]. The term supercruise corresponds to the non-afterburning supersonic cruise flight for the sake of determinacy in this paper. The phrase supersonic cruise flight is one of the main requirements to the Vth generation fighter can be often met in the journalistic press. The term supersonic cruise flight with reference to the Vth generation should be précised. Indeed, any supersonic aircraft provides supersonic cruise flight- the constant speed flight at M > 1. The ratio between subsonic and supersonic cruise flight range can be considered as characteristic difference between the IVth and the Vth generations, Table 1. So, the Vth generation fighters provide ~ 1.5 times higher supersonic range than the IVth ones at comparable subsonic cruise range. The main factors of the supersonic range increase at the transition from the IVth to the Vth generation are shown in the next chapter.

122 Aerospace Systems (2018) 1:121 127 Fig. 1 Combat aircraft generations Table 1 Subsonic-to supersonic range ratio Generation IV V L max Mcr 0.8 /L max Mcr 1.

2 122 Aerospace Systems (2018) 1: Fig. 1 Combat aircraft generations Table 1 Subsonic-to supersonic range ratio Generation IV V L max Mcr 0.8 /L max Mcr Aircraft design influence on the supersonic Breguet parameter As it was shown above, increased supersonic cruise range is the characteristic feature of Vth generation fighters. The supersonic cruise range increase at the transition from the IVth to the Vth generation is conditioned by the rise of maximum Breguet parameter V(L/D)/(g c C r ) under cruise conditions at design Mach number (1): { Y G X T where Y lift, G aircraft weight, X drag, T powerplant (installed) thrust. Breguet parameter under cruise conditions (1) at aircraft design mass m des is defined by drag X (aerodynamic arrangement) and supersonic throttling characteristic Cr(T) (2): (L/D)V g c Cr(T ) (1) GV g c T Cr(T ) m des q v, (2) where q v fuel consumption per distance. g c gravity acceleration. Breguet parameter under cruise conditions (1) depends on engine operational mode (initial cruise flight altitude), it makes it possible to optimize (L/D)/ Cr ratio. Further, for the short, the engine operational mode will be defined by the supersonic throttling coefficient STC [7] (3): STC T T dry T aftb T dry. (3) STC 0, by definition, corresponds to dry mode, STC 1 afterburning. Figure 2 shows the statistical (M(L/D)/C r ) cr data of the IVth ad Vth generations as function of STC at design armament. The maximum Breguet parameter value under cruise conditions is the practical interest for the further analysis. The conditions and assumptions of the Breguet parameter optimization together with main formula (4) are presented in [5, 6]: T optim 4X 0 + T + (4X 0 2T ) 2 3T 2, (4) 6 where X 0 =qsc D0 drag at zero lift, altitude H 11 km and cruise Mach M cr, q dynamic pressure at altitude H 11 km and M cr, T * T dry Cr dry /C T r supersonic throttling characteristic indicator [6].

3 Aerospace Systems (2018) 1: Fig. 2 Cruise Breguet parameter vs engine throttling By substituting (4) into cruise Breguet parameter formula (5): ( ) (L/D C α L qs(p optim X 0 ) Cr T optim (Cr dry +Cr T (T optim T dry )), (5) crmax one can make sure, that cruise Breguet parameter depends on: reduced uninstalled ground afterburning thrust T 0 T 0 /(C D0 S), relative installed dry thrust at H 11 km and M cr T dry inst T dry inst /T 0. Figure 3 shows (M(L/D)/Cr) cr max as function of T dry inst i T 0 according to formula (4) and (5) based on generalized data of IVth (external store), IVth + (external/conformal store) and Vth (internal store) combat aircraft. T 0 and T dry inst increase is responsible for (M(L/D)/Cr) cr max rise. The increase of T dry inst at design T 0 (specified by subsonic performance requirements [4]) is conditioned by propulsion technology progress [9] and is the key factor at supersonic cruise range rise. It is advisable to decompose T 0 by the takeoff thrustto weight ratio G 0 /T 0 and ballistic coefficient C D0 /(G 0 /S) according (6): T 0 (T 0 /G 0 )/(C D0 /(G 0 /S)). (6) Reduced thrust T 0 tendency to rise is conditioned by G 0 /T 0 increase, Fig. 4 [5], due to take-off thrust to engine weight ratio increase 1/γ T 0 /G eng,fig.5 and by ballistic coefficient decrease, Fig. 6, because of lower zero lift drag at internal armament location. In the above discussion it was shown the quantitative difference between IVth and Vth generation fighters. Supersonic cruise flight parameters statistical analysis made it possible to derive qualitative difference between the IVth and the Vth generations. It will be presented in the next chapter. 4 Effective supersonic cruise flight Supersonic cruise flight numerical optimization (finding the maximum of (L/D)/Cr as a function of cruise flight altitude under design Mach number) is routine operation at supersonic range calculation. According experience of Breguet parameter optimization it is shown the typical shift of optimum thrust T opt from the IVth generation full reheat setting to Vth generation intermediate reheat, corresponding to ~ 30 50% of the range between dry and full reheat power setting (STC ~ ), Fig. 2. The further increase of Breguet parameter (supersonic cruise range) it should be presumed when aerodynamic arrangement and power plant will be coordinated such way, providing the coincidence of (L/D)/Cr maximum to dry power setting (minimum of supersonic installed throttle characteristic) optimum supercruise [6].

4 124 Aerospace Systems (2018) 1: Fig. 3 Cruise Breguet parameter vs supersonic relative installed dry thrust/reduced uninstalled thrust The additional condition (7) of supersonic cruise flight could be considered as a criteria of effective supersonic cruise flight : STC opt 0.5. (7) Fig. 4 Takeoff thrust-to-weight ratio So, for the sake of the Vth generation supersonic cruise flight specification it could be proposed the effective supersonic cruise flight definition as characteristic feature of Vth generation fighters. Figure 7 shows estimated relations (M(L/D)/Cr) cr f(stc) of the F-22A and J-21 (WS-10G and WS-15 engines) type examples [3, 8]. The reported relations show, that, according to criteria (7), estimated J-20 with WS-10G engine doesn t match to Vth generation club. Going to WS-15 engine would provide J-20 to be the Vth generation within assumptions and estimations of this paper. Below are the next important results of Breguet parameter optimization analysis. In particular, the Vth generation supercruise (STC 0) regime is not optimal from the point of supersonic cruise maximum range. Intermediate afterburning (STC ~ ) provides higher supersonic cruise flight range, Fig. 8:

5 Aerospace Systems (2018) 1: Fig. 5 Takeoff thrust-to-engine dry weight ratio Fig. 6 Ballistic coefficient and takeoff thrust-to-weight vs combat aircraft generation the more initial supersonic cruise flight altitude, the more specific fuel consumption coefficient Cr, bat less required thrust and, so, less fuel consumption per distance then for dry regime: less initial supersonic cruise flight altitude, less specific fuel consumption coefficient Cr, bat more required thrust and, so, more fuel consumption per distance. The other result could be as follows: the supercuise possibility (F-22A type characteristic [2]) doesn t guarantee higher supersonic performance. Figure 7 shows, that J-20 (WS 10G) type doesn t provide supercruise because of the lack of thrust, bat does provide higher maximum value of (M(L/D)/Ce) cr than that one of F-22A type because of lower

6 126 Aerospace Systems (2018) 1: Fig. 7 Effective supersonic cruise flight Fig. 8 Engine operating mode influence on supersonic range supersonic wave drag level k w C D0 M 1.6 / S wet [6]. It is because of higher aircraft slenderness p sl (9), Fig. 9: l f /d eqv p sl χ leeqv, (9) c where l f fuselage length, d eqv aircraft frontal projection area equivalent diameter (F fr pr =πd 2 eqv /4). It should be mentioned that in the case of J-20(WS-10G) type the subsonic maneuverability loss is the charge for supersonic advantage [3].

7 Aerospace Systems (2018) 1: Fig. 9 Supersonic wave drag level vs aircraft slenderness 5 Conclusions 1. The supersonic cruise range increase at turning from the IVth to the Vth generation under comparable subsonic range results from: take-off thrust to-weight T 0 /G 0 increase, supersonic relative dry thrust T dry Msps /T 0 increase, supersonic ballistic coefficient C D0 /(G 0 /S) decrease as a consequence of propulsion engineering progress and due to internal armament design. 2. The IVth generation s maximum supersonic range requires full afterburnibg operating mode. The Vth generation s maximum supersonic range corresponds to intermediate afterburning (T opt T dry )/(T aftb T dry ) ~ It is proposed the definition effective supersonic cruise flight as the Vth generation characteristic feature to distinguish the last generations supersonic cruise flight. The condition STC (T opt T dry )/(T aftb T dry ) < 0.5 is proposed to be a criteria of effective supersonic cruise flight. 3. Supercruise as supersonic cruise flight without afterburning is not optimal from the maximum range. The supercruise ability doesn t guarantee the supersonic performance advantage. References 1. Mullin SN (1992) President, Lockheed advanced development company, the evolution of the F-22 advanced tactical fighter, 1992 Wright Brothers Lecture. AIAA aircraft design systems meeting, August 24, p 7 2. Warwick G/Washington DC (2003) Ready or not.. In: Flight international, 9 15 September 2003, pp Bashkirov IG, Chabanov VA et al (2018) F-22A (USA) and J- 20 (China) flight-performance comparative analysis. In: GosNIIAS proceedings. 6(39) 4. Bashkirov IG, Irodov RD (1997) Calculation of jet aircraft parameters under design requirements, paper no World Aviation Congress, October 13 16, Anaheim 5. Bashkirov IG, Irodov RD (2016) Aircraft configuration design for supercruise. In: Bushgens GS (ed) Aerodynamics, stability and controllability of supersonic aircraft. Russian Academy of Science ( Nauka RAS), p. ISBN , Moscow, pp Bashkiorv IG (2007) Supersonic nonafterburning cruise flight: myths and realities. Aviat Sci Technol 81(2)(685): Bashkirov IG (2014) Designing for supercruise flight: supercruise from the aerodynamic designer s view point. In: AIRTEC 2014 international congress proceedings, October. Frankfurt/Main, Germany, p Bashkirov IG, Chabanov VA et al (2018) Technical appearance estimation of the F-22A (USA) and J-20 (China). In: GosNIIAS proceedings. 6(39) 9. Bashkirov IG, Ezrokhi UA (2007) The fundamentals of multirole aircraft jet engine parameters optimization. In: AeroIndia2007 international seminar proceedings February, Bangalore, India

Journal of Aeronautics & Aerospace

Journal of Aeronautics & Aerospace Engineering Journal of Aeronautics & Aerospace Engineering Ahmed Soliman M.Sherif, J Aeronaut Aerospace Eng 217, 6:1 DOI: 1.4172/2168-9792.118 Research Article Open Access