Bathman wrote:What about the D-Motor?
I saw the D-motor, a flat-four side-valve aero-engine, at Sywell last year. Although a side-valve design might seem a backward step, provided that the combustion chamber is designed for optimal efficiency, the advantages of this "archaic" design (lightness, compactness & absence of OHV complexity) are well-suited to a power unit producing maximum bhp at a mere 2,930 rpm. The D-motor has fuel-injection, so carb-heat issues become a thing of the past. Unlike an ohv engine, a side-valve engine has zero valve overlap, which is efficient at low rpm; and whereas a dropped valve is catastrophic in an ohv engine, it is of minor consequence in a side-valve engine, which could still chug along on three cylinders back to the safety of an airfield.
I did wonder if, like the Jabiru flat-four, the D-motor might become a flat-six, light as a feather & producing perhaps 120bhp; and I see from D-motor's "news" website that they are doing just that, with a "substantial grant from a government agency". That might be a very nice power unit for the Super 2, and would be a real challenge to Rotax's stranglehold!
Personally, I remain a fan of reduction gear, to enable the prop to operate slowly and efficiently. If the D-motor (and the Jabiru units too, come to that) were to have a belt driven 3:2 reduction gear, the prop could be full-size and could extract maximum power while turning less than 2,000 rpm. As it is, both the D-motor and the Jabiru engines have to use small fast-spinning props; and even so, these engines will probably never be able to reach maximum output, which is 3,300 rpm in the Jabiru's case.
By contrast the Hewland and the Midwest units have very similar conventional reduction gearboxes (the latter's is based on the former's). The MidWest has a reduction of 2.96:1, so even when the rotary engine is turning at 6,000rpm, the prop is kept to an efficient 2,000 rpm. (By the way, if 6,000rpm seems fast, remember that it is only the central eccentric shaft that spins at these high speeds; the rotors turn at one-third of that speed, a lazy 2,000 rpm).
Bathman wrote:Was/is the airframe robust enough for instructing?
Absolutely! In the ARV's heyday, at least two flying schools used the Super2; Derby Flying Club and Bournemouth's famous Derek Davidson. Derek adored the Super2, and claims regularly to have landed the ARV without incident in crosswinds of over 30 knots! The elegant engineering gives very responsive controls without making the aircraft "twitchy".
Although built to be 60% of the weight of a Cessna 152, the ARV is remarkably rugged, having a monocoque "superplastic" alloy cockpit, conventional wings, fuselage & empennage, with GRP cowlings & wingtips. The ARV combines metal adhesive with fewer rivets, to save weight. More modern designs like the Eurostar or Tecnam Echo seem almost flimsy compared to the robust Super2.
The wonderful thing about the Super2's cabin is the shoulder-wing, which gives unrestricted visibility both above and below the wing and which obviates any need to "lift a wing" prior to turning. The Super2's seating is as spacious as a 152, which isn't saying much. If it were redesigned today, the Super2 would probably be 10% bigger, to accommodate today's broader backsides; and an increase in the minimal storage space would be welcome.
Note that the wing area of the Super 2 is a tiny 92 sq ft; and while the high wing-loading means that the aircraft is less prone to crosswinds and to buffeting in rough air, it can mean a lengthy take-off run when at maximum all-up weight. The LAA have approved a trial to fit Vortex Generators to the wings and to the tailplane, which should result in a lower stall speed, shorter ground runs and enhanced elevator response in the landing flare.
Also, the super strong main gear legs are made of spring steel and weigh a ton! A project at Liverpool John Moores University Engineering School is investigating the feasibility of lighter main legs, using a plastic composite, aluminium alloy or even titanium. As the main gear lies just behing the CG point, lighter legs would not significantly upset weight & balance.
In the UK, the all-up permissible weight of the Super2 is 499kg, or up to 527kg, if you pay extra! (How crazy is that?). I understand that Opus proposes to raise this to 599kg, on the basis that the airframe is rugged enough to cope. Apparently, they have successfully test-flown the aircraft at considerably more than 600kg MAUW (a whisper I heard was 900kg!).
Further details on:http://en.wikipedia.org/wiki/ARV_Super2http://sites.google.com/site/flyarv/Homehttp://www.opusaircraft.com/index.htmlhttps://sites.google.com/site/flyarv/su ... ay-drawing