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New rotary takes flight in India
Submitted by ekrampitzjr on Friday, May 1, 2009 - 7:15am

New rotary takes flight in India

by Edwin Krampitz, Jr. (ekrampitzjr)

1 May 2009

News of a successful new Wankel rotary engine is unusual and highly welcome—and here’s some. On 31 March 2009 India’s Nishant unmanned aerial vehicle (UAV) successfully flew with a rotary engine built entirely in India. Online reports said the engine “performed very well”, “met the requirements”, and climbed “effortlessly”. It was the maiden flight for this new engine and first for any Indian UAV using an indigenous engine. The Nishant has previously used the imported AR–801, a derivative of the old Norton motorcycle rotary, built by UAV Engines Ltd (UEL) in Britain. The new rotary, designation not given, is intended to replace the AR–801.

UAVs, also known as remotely-powered vehicles (RPVs), historically include drones. Today, however, they are highly important for reconnaissance and related duties, as with Nishant, and some can carry weapons systems. India’s Defence Research and Development Organisation (DRDO) proposed what became Nishant (= “restless” in Hindi) in 1988 as an indigenous UAV for the Indian military. After the Aeronautical Development Establishment (ADE, a branch of DRDO) began development of the craft, it first flew in 1995, went on public display at an air show in 1996, and completed 100 test flights by mid–2005.

The Indian Army began trials in 1999, including deployment during a skirmish against Pakistan-supplied guerrillas in Kashmir province that year. Despite some teething pains and developmental delays, more recent trials have been successful. The Nishant system is expected to become operational soon with the Indian Army, which has ordered 12 with three mobile launchers. Aviation Week & Space Technology began including it in the UAV chart contained in its annual aerospace industry listings in 2006.

Clearly the military desired a UAV built entirely within India for strategic reasons, so a new India-built rotary engine had to follow to replace the AR–801. ADE, the National Aerospace Laboratories (NAL), and other Indian organizations began development of that engine after feasibility studies in the late 1990s. The Propulsion Division of NAL had test-flown in 1998 what was billed as “probably the world’s first Wankel rotary engine–powered hang glider”, Altair, powered by a 35 hp UEL AR–731, so the division naturally inaugurated a Wankel testing laboratory in June 1999. Fabrication of components and development of a process to coat the rotor housing trochoid had begun by 2005. Test bed trials began shortly afterward. Program progress received brief mentions in the NAL annual reports, available online.

The maiden flight for that new engine began at an abandoned World War II runway in the village Veerapura, near Kolar, at 11:57 am local time. The Nishant climbed to an altitude of 1.8 km (1.1 miles), cruised for 35 minutes, and landed as planned in the dried-up lake Muduvadi after 40 minutes of flight. Numerous senior officers of the responsible Indian organizations witnessed the event. Note from the specifications for Nishant that follow that a mobile hydraulic system launches the UAV using rails and the craft lands by parachute; a runway is not necessary, so this UAV does not have wheels.

The new rotary has a single rotor of 324 cm³ (19.8 in³) displacement, rated at 41 kW (55 hp) at 8000 rpm. These are the engine prototype specifications:

Rotor radius, R: 71.0 mm
Rotor eccentricity, e: 11.6 mm
Rotor width, B or W: 75.2 mm
Equidistance, a: 0.5 mm
R’ = R + a = 71.5 mm
R/e or K ratio: 6.12:1

Compression ratio: 9.2:1
Rotor recess volume: 15.82 cm³
Redline in ground testing: 8100 rpm
Housing cooling: water/glycol
Rotor cooling: air
Fuel: 100LL avgas
Trochoid coating: nickel-silicon carbide composite
Engine weight as installed in Nishant: approx. 30 kg (65 lb)

Along with this successful UAV use, online reports about the flight said that the new engine was also a candidate for use in vehicles, outboard motors, and stationary industrial applications. Small Wankels for such uses have been scarce since Fichtel & Sachs ended production of its in 1975, but this new one seems thankfully imminent.

The eagle-eyed will note that R, e, and a are the same as those of the old Fichtel & Sachs KM–914 and KM–24 snowmobile engines and the Norton, Alvis, and UEL rotaries developed from those designs. However, the rotor width for the Indian rotary is different from all of these: it is the widest of all. (But a new prototype derived in Israel from the UEL units would have an even greater width if it sees production.) Since NAL had to devise a coating technique for the trochoid and special aluminum alloys for castings, help or tooling from UEL or anyone else seems unlikely, particularly since this is a competing application and probably proceeded in some secrecy. Instead, with all the experience using the AR–801 in the Nishant, NAL likely decided to use the UEL rotor dimensions for quicker validation of sealing materials and machining techniques.

Here are the available specifications for Nishant:

Length: 4.63 m (15.2 ft)
Wingspan: 6.57 m (21.6 ft)
Empty weight: 380 kg (840 lb)
Payload: 45 kg (100 lb)
Maximum speed: 185 km/h (115 mph)
Cruise speed: varies; up to 150 km/h (95 mph)
Flight duration: 4½ hours
Range: 160 km (100 mi)
Ceiling: 3600 m (11,800 ft)
Launch: mobile hydro-pneumatic launcher system with truck-mounted rails; launch velocity 45 m/s, duration 0.6 sec, using 100 kW power
Landing: by parachute, with inflatable underbelly bags for protection

Some references:

“Altair takes off!: NAL builds a powered hang glider”, National Aerospace Laboratories website, 12 March 1998, The hang glider, powered by the AR–731, flew on 26 February 1998.

“DRDO Nishant”, the dreaded :) This site gives what appears to be the incorrect date of 5 April for the flight reported here; see comments after “Nishant UAV flies with indigenous Wankel engine”. I have attempted to confirm the specs for Nishant elsewhere and am satisfied that those given here are at least close.

“Laboratory for testing Wankel rotary engines and structural ceramic components inaugurated”, National Aerospace Laboratories Information Pasteboard online archives, page IP 352, 7–13 June 1999, .

NAL Annual Report, various years, National Aerospace Laboratories website, home page . Brief mentions of Wankel engine program status in chapter 1, “Report of the Director”, and chapter 13, “Propulsion Division”, in most of these reports from the 2002–2003 edition onward.

“Nishant UAV flies with indigenous Wankel engine”, Frontier India Strategic and Defence website, 6 April 2009, . Numerous other Indian sites covered the event. But note that others give conflicting dates for the launch, some placing it on 4 or 5 April. However, the Frontier India site cites Indian defense sources for the 31 March date and is the only one to give the time of launch. One other Indian site posted a stock picture of the old NSU-Wankel DKM 54, not of the new engine, to accompany its report!

K. Monickavasagom Pillai, K. Sivasankaram, and B. R. Pai, “Thermodynamic analysis of Wankel engine”, Proceedings of the Sixth National Conference on Air Breathing Engines and Aerospace Propulsion (6th NCABE), Bangalore, India, 11–12 January 2002, paper B5.4 (not available online; obtained from one of the authors). Validation for use of indigenous rotary in Nishant. Some sources give an incorrect year of 2003, but NCABE is held in even-numbered years and I confirmed that 2002 is correct.

K. Monickavasagom Pillai et al., “Design and development of an indigenous 55 hp Wankel engine”, Proceedings of the International Conference on Aerospace Science and Technology (INCAST), Bangalore, India, 26–28 June 2008, paper INCAST 2008–109, . Testing of prototype rotary designated PT1 for Nishant.

V. Sarveswaran, Y. V. S. Murthy, and V. Ganesan, “Altitude performance comparison of a Wankel engine with carburetor and fuel injection”, Society of Automotive Engineers/SAE International, SAE paper 2003–28–0017 (also SAE India paper 0301017), 2003, . Fuel injection was better than carburetion for higher power output and higher revs. Clearly pertains to testing for the new rotary.

“Unmanned aerial vehicles and drones” chart, Aviation Week & Space Technology, annual Aerospace Source Book issue, various years. Appears in January of each year. Oddly, Nishant first appeared in the chart only in 2006, more than 10 years after its first test flight and several years after first public display.

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