Primarily for general aviation discussion, but other aviation topics are also welcome.
By Bathman
#978797
Did anything any become onf the Opus Super2. Their website not changed in years
By tlyons
#983341
I'm delighted to see that the Super2 is up and running again in North Carolina. The Opus aircraft on YouTube looked pretty standard ARV, albeit with a cowling adapted to take the Rotax 912, and a Garmin 912 set into the panel. (Curiously, this Super2 still has a rather basic-looking twin blade prop, when it is known that a 3-blade Arplast EcoProp suits the airframe better).

It seems that of all the Rotax 91x's, the 100bhp 912S is probably the optimum, giving that extra bit of oomph over the 80bhp 912. A couple of guys have fitted the heavier 115 bhp 914 engine and they report amazing take-off performance. However, it has proved tricky to put a beautiful cowling around that Turbo engine; and the extra weight requires a bit more lead in the tail.

Of course, Richard Noble always felt that the Hewland engine was the optimum unit for the Super2; and perhaps it still is, since its initial problems were swiftly sorted and, decades later, many ARVs are still flying reliably with their original Hewland motors. The Hewland (an inverted three-cylinder water-cooled 75bhp 2-stroke) was beautifully made; and if it were brought up to date with fuel injection, oil-injection and 90bhp, it would probably be one of the best little aero-engines around, being smooth, compact and very light.

Just a couple of ARVs have the MidWest twin-rotor Vankel engine. This is very smooth, light and compact, and produces between 90 & 105 bhp, depending on whom you ask. The fuel-injected version is also suprisingly economical. This engine is heavier than the Hewland, but lighter than a Rotax 912. Staverton-based MidWest were bought out years ago by Austria's Diamond, who now produce only the single-rotor version, although the twin-rotor engine is still supported.

At one-time, it looked as if the MidWest could become a twin-fuel (petrol/paraffin) engine, starting on AVGAS or Mogas, and switching to AVTUR when warm. (The engine would retain spark ignition). However, this promising avenue of development was shelved by Diamond; a great pity, since an aero-engine that was small, light, compact, reliable and cheap to run would tick most of the boxes.
By tlyons
#983483
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_Super2
http://sites.google.com/site/flyarv/Home
http://www.opusaircraft.com/index.html
https://sites.google.com/site/flyarv/su ... ay-drawing
By tlyons
#983586
The proposed flat-six side-valve D-motor has really got me thinking.
http://d-motor1.vpweb.be/Recent-information.html

The Jabiru 2200 weighs 60kg and produces 85bhp; and its big brother, the 3300 weighs 81kg, and produces 120bhp (107 continuous).
The Rotax 912 weighs 60kg and produces 80bhp; and its big brother, the 914 weighs 78kg, and produces 115bhp (100 continuous).

The D-motor 4-cyl weighs 47kg and produces 80bhp; so (by analogy to the above figures) its big brother, the 6-cyl might weigh only 63kg and yet produce, say,115bhp or more.

The 6-cylinder motor might thus weigh barely more than an R912 or J2200; yet would produce nearly 50% more power.
If the price is right, it looks like the motor we've all been waiting for!
By Bathman
#983591
I was always a bit gutted I never got airbourne in one of Derby Flying Club ARV Super2 I was learning at East Midlands Flying School at the the time and it caused quite a stir that the local competition had got hold of these new wonder aircraft that were going to revolutionize the industry.

Just out of interest what the ground roll and climb out of a super2 say compared with a C150. I also heard they weren't as good when the grass was bogy compared to a C150 any truth in that?

As for the 6-cyl D-motor I really wish companies would actually get there basic product out in the market proving itself rather than spending money on further engines. Any competition to rotax is good.
By tlyons
#983664
Bathman wrote:I was always a bit gutted I never got airborne in one of Derby Flying Club's ARV Super2s ...

Derby experienced at least one engine/transmission failure with their Super2s; and they then cancelled the contract. No doubt they were justified in doing so, but Derby's action put another nail in ARV's coffin.

Bathman wrote:..what the ground roll and climb out of a Super2 say compared with a C150.

I did some of my PPL training at Derby in my own Super2, which had the more powerful MidWest engine, not the Hewland. Even when at MAUW, it was always capable of taking off with ease from Derby's rather short grass runways. A Hewland engine's power was limited, but fitting an Arplast Ecoprop will enhance any ARV's performance.

Bathman wrote: I heard they weren't as good when the grass was boggy ..

It is true that the standard tyres are a bit small; but fatter Trelleborgs fit on to the rims comfortably and transform the ARV's ability to roll on soft ground.

Bathman wrote:As for the 6-cyl D-motor, I wish companies would actually get their basic product out in the market proving itself rather than spending money on further engines. Any competition to Rotax is good.

Up to a point, Lord Copper! It is clear that the D-motors could be world beaters, and if government funding is there to develop the range, why not do so? It is very easy to make a 6 out of a 4, when almost all that is needed is a longer crankshaft and crankcase. The 4-cylinder will be ideal for microlights; but the 6-cylinder is the engine that I reckon will sweep the board.
By ozplane
#983695
What fuel(s) does the D-Motor run on? That will be the key for the future if/when avgas continues to rise.
By tlyons
#983708
ozplane wrote:What fuel(s) does the D-Motor run on? That will be the key for the future if/when avgas continues to rise.

Presumably it will run on both Avgas & Mogas. Whether it could be developed into a petrol/paraffin engine burning Avtur when warm remains to be seen. Paraffin engines run hotter than petrol; but the D-Motor is water-cooled and lubrication appears to be dry-sump, so with a larger radiator & oil-tank there could be scope for a dual-fuel future.
By tlyons
#984541
A side-valve motor has poor breathing at high rpm, but the simple valve gear offers no mechanical obstacle to high revs; so (in theory at least), provided the D-Motor's crankcase & internals are up to it, there seems no reason why it might not benefit in future from an induction boost via a turbocharger or supercharger. After, all the engine is so light to begin with, the extra weight of a charger would not signify much.

Just imagine: a flat-six turbocharged D-motor weighing perhaps 75kg and producing 140bhp!
By Bathman
#984543
"Also, the super strong main gear legs are made of spring steel and weigh a ton!"

What about the nose leg from the photos it looks a little unconventional but how strong is it?
By tlyons
#984551
Bathman wrote:"Also, the super strong main gear legs are made of spring steel and weigh a ton!"
What about the nose leg from the photos it looks a little unconventional but how strong is it?

The leading link noseleg is "Forth Bridge" strong but it's really heavy; no doubt it too would benefit from weight reduction.
If it were made mainly from, say, titanium or composites, that would be a significant help.

(I note that the bungee trailing link doesn't give much on landing in this video; perhaps its just good piloting!)


The ARV's shoulder-wing is wonderful and gives superb visibility, but to retain the CG in the right place, the ARV's wings had to be swept forward. Weight & balance was perfect in the original Hewland Super2, but all the alternative engines that have been fitted (i.e: 912, 912S, 914, Jabiru & MidWest) are heavier than the Hewland. So, to maintain weight & balance a newly-engined Super2 must have a lump of lead in the tail. The Midwest is the lightest of these replacement engines, but it partly wastes that advantage by needing the radiator just abaft the prop, rather than underslung amidships. The single ARV that has been fitted with a Jabiru 2200 is aircooled and needs no radiator; I would be interested to see how the owner addressed the CG issue.

In sum: anything that helps to maintain an ARV's correct CG without lumps of lead must be good, and there are two candidates:
(1) a lightweight titanium noseleg; and
(2) a D-Motor!
By Doober2004
FLYER Club Member  FLYER Club Member
#984680
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.


Is there any more info available of this? Can I get to see the drawings? When will the VGs be fitted/tested?
By tlyons
#984696
Doober2004 wrote:
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.

Is there any more info available on this? Can I get to see the drawings? When will the VGs be fitted/tested?

Francis Donaldson of the LAA has written to authorise VG trials, subject to some fairly strict conditions, such as engaging an approved test pilot. I haven't done any drawings yet; but the VGs will be attached in the standard way, in oblique pairs along a line 10% of the chord back from the wing's leading edge, and in oblique pairs just ahead of the elevator on the underside of the tailplane.

Q: Why 10% of the chord back from the wing's leading edge?
A: Because that's the norm that is known generally to work, although the testing procedure might involve trying them a bit further forward & a bit further back.

The LAA are very professional in promoting the highest safety standards; but even so, it does seem that the test requirements are slightly OTT. After-market VGs have a 100% record of doing the job properly without any detrimental side effects, apart from (some say) a small drop in cruise speed. Others argue that when flying at speed, the wing's angle of attack is at a minimum, and so the VGs are virtually out of the airflow, with little or no effect upon either lift or drag. The excellent history of VGs is such that it should surely be sufficient for the LAA to say, "Fit them as directed, and see how you like them, and tell us if there is anything to report".

I'll be doing the tests as soon as I get the aircraft re-permitted.The VGs I purchased are plastic "Landshorter" items from the USA:
See: http://www.landshorter.com/index.html & http://en.wikipedia.org/wiki/Vortex_generator