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The powers that are: with a few exceptions in the higher-flying types that are powered by adapted aviation-extraction turbo engines, almost all drones are driven by piston engines that often find their origin in recreational ultralight aviation. But even this segment is now maturing in its new role.

The exception that confirms the rule in the turbojet engine field notably comes from the two companies Microturbo (part of Snecma) and Williams whose engines are almost ubiquitous in cruise missiles and high-speed target drones.

The widest variety comes from the traditional piston engine manufacturers (including rotary piston, if one can now include this in the traditional category). Clearly the leaders here are UEL (or UAV Engines Limited), followed by Rotax (who apparently is not too keen on being publicised as defence suppliers) with now Zanzottera, ATS and Denel emerging as engine specialists. The first three were amply described in a recent issue of this magazine (see Armada International 1/2005). We saw that Denel was working on the adaptation of a Subaru car turbocharged boxer as a possible engine for its new Bateleur Male, but what is little known is that the Seeker II also has a heavily improved engine, in this case a Limbach L550E base (see the author's photograph in the title picture). Dubbed the 'Engine Group', this power lump only retains the original crankcase and cylinders. Apart from a direct-drive alternator and carburettors tossed out in favour of injection, Denel developed its own engine management and altitude compensation systems as well as an engine health monitor. It weighs 39 kg (with propeller), yields 32 kW at 6000 rpm and has a typical specific fuel consumption of 500 grams/kW-hour

Advanced Target Systems in Abu Dhabi has been manufacturing, as the name implies, targets for some time but in a somewhat discreet manner. The company came totally out of the blue this year by displaying a rather sleek observation drone. the Yabhon-M at the Idex exhibition. Interestingly, the company also manufactures its own engines (but has also developed the drone's sophisticated autopilot and laser obstacle avoidance systems, see above). Two of these include the 35-hp, two-stroke, twin-boxer AD 500 and the 80 hp flat-four AD 1000. The first is already flying in a target drone being developed for the local armed forces. However. the company is also actively working on more refined types such as the two stroke ME684 I B4 Twin Spark, which would be used for the Yabhon's maiden flight (at time of writing planed for May/June 2005). The Yabhon should ultimately be powered by a 50 hp double-overhead camshaft three-in-line. Yet another engine is being developed; the four-in-line dohc ME998 with 140 hp.

Quite apart from the now common adoption of supercharging to improve the engines' lung capacity at higher altitudes, the manufacturers are now faced with two challenges. The first is the much-desired general preference for diesel or jet-fuel versus avgas. There is little doubt that this option will weigh seriously on future choices. The second is engine management. At varying altitudes and temperatures the performance and behaviour of an engine can be quite different. Since there is by definition no one aboard an unmanned aircraft to do the constant tweaking, this can only be carried out by telemetry. This is becoming a sharp requirement as it determines the balance between flight duration, fuel capacity requirement and payload capacity.
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Title Annotation:Complete Guide
Author:Biass, Eric H.
Publication:Armada International
Date:Jun 1, 2005
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