International Conference on Aerospace Science and Technology 26-28 June 2008, Bangalore, India DESIGN AND DEVELOPMENT OF AN INDIGENOUS 55 HP WANKEL ENGINE K.Monickavasagom Pillai, A.J. Steve Mithran, V.K. William Grips, K. Satish Kumar, Umesh Kumar Sinha, M.N. Varadarajan, J.J. Isaac and Y.V.S.Murthy 1 National Aerospace Laboratories, Bangalore, India, kmpillai@css.nal.res.in (Council of Scientific & Industrial Research, India) 1 Aeronautical Development Establishment, Bangalore. ABSTRACT: During the last decade, a number of developmental projects have been initiated both in civil as well as military aviation, for Powered Hang Gliders for aerial spraying of pesticides, Small Aircraft, Pilot-less Target Aircrafts and Unmanned Aerial Vehicles. The requirements for all these applications are similar in that the power to weight ratio should be high, specific fuel consumption (sfc) should be low, noise and vibration levels must be low, thermal efficiency must be reasonably higher and maintenance and serviceability should be acceptable. A prominent contender that can meet all the above requirements is the Wankel engine. In recent years, they are found increasingly in roles where their compact size and quiet running is important, notably in Unmanned Aerial Vehicles (UAVs). At present, the National Aerospace Laboratories is involved in the indigenous development of Wankel engines to support the nation’s UAVs program. A 55 hp single rotor, liquid cooled, Wankel engine was designed, developed and the 1 st Proto type (PT1) was successfully tested. This paper describes the developmental work carried out on the Wankel engine and the performance validation of the engine. 1. INTRODUCTION Aerospace propulsion demands a power plant with the minimum weight possible without sacrificing on torque and power. Out of the various possible options, the Wankel engine has been actively considered for powering light aircraft and UAVs. This is because of its salient features like high power to weight ratio, good anti knock properties and smaller size when compared to a piston engine of the same class. NAL has acquired the necessary expertise in design and development of rotary combustion engine over many years due to the developmental work carried out on an air-cooled 35hp Wankel engine. Due to the expertise gained over the years, NAL was entrusted with the design and development of a 55hp liquid cooled Wankel engine for an UAV application. 2. INDIGENOUS ENGINE DESIGN 2.1 Design Methodology The brief specifications of the indigenous 55hp Wankel engine is given in Table 1. The first step in any engine design is sizing the engine i.e. deriving the basic parameters of the engine. Table 1 Brief specifications of the proposed 55 hp engine Type Single rotor Wankel engine Cycle Otto cycle Power 55 hp (41 kW) @ 8000 rpm at ISA-sea level (without exhaust muffler) Compression ratio 9.2 Housing Cooling Water-Glycol mixture Rotor cooling Air Lubrication Total loss forced lubrication system Ignition CDI system Carburettor Diaphragm type Specific fuel consumption 335 to 365 g/ kWh (0.55 to 0.60 lb/ hp h Engine weight 35.6 kg