It is some time now since I reviewed the Luna, an exceptional little 2-metre span moulded glider from the now defunct Slopeblasters company. Since then and every week without fail, I’ve had at least one email asking me where Luna’s can be bought. Well, they’re still in production around the world under various names but there’s no UK distributor and, sadly, would-be importers have found the model difficult to source. It may seem strange to start a review by talking about another model, but ever since the desirable Luna became so unobtainable, I’ve always referred would-be owners to the readily available Ruby from South Coast Sailplanes in Bournemouth.
Priced at around the same figure as the Luna and with a virtually identical specification, the Ruby is manufactured not in China but by the Impres Model Company in the Ukraine. Moreover, it’s clear from the website that there are links to Vladimir’s Models, whom some of the silent flight fraternity will recognise as manufacturers of high end competitive machines. South Coast Sailplanes have full UK distribution rights to the Ruby and often carry stock, though special colour combinations may have to be ordered in separately. And while we’re on the subject of availability, a fuselage for electric power can also be obtained.
On paper the attractive thing about the Ruby is the full camber MH 32 section, the two-piece, 2-metre wing and the removable cross tail. Straight off the bat I can tell you that the build quality of the Ruby far exceeds that of the Luna. With a carbon / Kevlar fuselage, carbon moulded gap seals and servo covers, the Ruby scores valuable points compared to the Luna’s all glass, and somewhat more agricultural construction. The second thing I noticed when rigging the model for the traditional ‘table top flight’ is that the bare airframe is far lighter than that of the Luna. The carbon / Kevlar fuselage helps here but so does the use of Herex in the wing skin sandwich, as opposed to the balsa used in the Luna.
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You may notice that the lines of the fin look a little out of place. It’s almost as if the Ruby uses the fuselage of another model entirely. The convex sweep of the fin front is in stark contrast to the concave edges of the wing and tailplane. Unusually, for a moulded model, the rectangular section carbon wing joiner is a permanent fixture at the root of one wing panel. Mind you, prang the model hard enough and I suspect the wing joiner will be the least of your worries. Besides, having it retained in the wing does avoid leaving it at home, and the resulting embarrassment atop the hill!
A quick online ‘Google’ reveals that, like the Luna, the Ruby is called something else over in the U.S. (Nova 2) where it’s billed as a 2-metre thermal duration model. No surprise there as the low weight ensures it’s pre-eminence in the popular American 2-metre thermal duration events. It also explains the inclusion of a nice adjustable tow hook within the kit. Not that it’s of much use for slope fliers but hey, it’s nice to have a landing skid, right?
PRE-BUILD POSERS
The absence of a slip-on nose cone means that a little more thought must to be applied to the radio installation and position of the ballast tube. There’s nothing wrong with a hatch instead of a nose cone, indeed it saves considerable weight in the airframe, however I tend to prefer the former. Two servos must be mounted under this front hatch to drive the back-end controls whilst leaving room to install the battery, receiver, switch and wiring harness to the two-piece wing. I like to use Multiplex ‘Grey’ plugs for this type of thing as the two-piece wing rules out the use of a nine pin D-connector such as one might use on a centre panel of a three piece wing or single piece unit.
The ballast tube is quite small for a model with this wing area and the impact may be quite negligible even when full. Again there’s no indication in the documentation about where it should go, so you’ll have to jiggle it around the C of G, perhaps following a period of flight testing. You’ll also have to think carefully as to how you might load it and retain the ballast within; no guidance is given on either task.
To be honest the distinct lack of tube size made me wonder if I should bother with it at all as far as the review model went, especially given the need to determine the C of G before attaching the tube permanently – I decided to leave it and see how the Ruby performed without.
I have other models for bigger wind days and reckoned that while the Ruby would make a very nice sportster and an even better light wind scratcher, she’s never going to be a competitive slope racer. Ballast may well be useful on the flat for penetration and sink avoidance, but you can manage without on the hillsides if you’re only sport flying, at least until the balance point is set right.
FIT AND FINISH
Fitting radio equipment in the wing is comparatively easy, though the servos face the other way around from the established norm. As such, the servo output shafts face the wing root instead of the tip which means that the servo wires must be routed around the body of the servo rather than flowing nicely back to the wing root connectors. Both the flaps and the ailerons are designed to be bottom driven which, due to the moulded servo covers and wing skin, means routing the linkage to the underside of the surface. Bottom driven control surfaces are fine for the ailerons, which are top hinged, but disastrous for bottom hinged flaps. You might be able to get an inordinate amount of down flap throw in this manner but I’ve never seen a bottom hinged, bottom driven flap without slop in the linkage at the neutral position. The angles are just plain wrong.
The solution is to fit overly long control horns to get trigonometry back on your side, but they look ungainly and would certainly require much more modification to the linkage covers than the routine cutting back that’s necessary. To try and minimalise the slop problem I set the horns back from the hinge line and used threaded brass inserts running straight through the control surface in the hope of later modification to top driven flaps if I felt it necessary.
A full unmodified MH32 wing section at 8.7% permits Hitec HS85MGs to slip nicely into place for the flaps, although a good deal of case sanding might be required if you wanted to fit these to the ailerons as well. Accordingly, I used HS65s here, which still needed a tickle with the Perma-Grit block before slipping under the edges of the servo bay skin. Incidentally, whilst the ailerons are comparatively small, they’re quite up to the job asked of them in the air.
Fitting the flap servos was made considerably easier by using the wonderful Cubitt’s models (Trowbridge) GRP servo mounts, so a few quid to Pete and Joe had them in the post overnight. Sadly no frames exist for the HS65s and I had to resort to the time-honoured tradition of gluing them in place on the upper wing skin… Yuk! Wire joiners hold the tailplane in place the friction fit accuracy of the corresponding holes ensuring it’s nice and square to the wing. Rotating smoothly and without binding the internal bell-crank allows a good degree of elevator throw whilst using quite a short servo arm to maximise the torque advantage. The rudder is driven by a simple snake which, like the elevator pushrod, is factory fitted.
Some thought is required around placement of the receiver, switch (if used) and the battery pack. Access through the little hatch is limited when the servos are in place so it’s important to make sure they’re far enough back to permit removal and adjustment of whatever is being used as ballast. Finally, a dimensioned drawing of the model indicates the starting C of G. In truth the tolerance is quite wide for a model of this type so I set about balancing it up at the ‘central’ position for a fighting chance on the hillside. And so, with the Ruby ready to go – cue the British weather!
QUITE A CHALLENGE
Photographing a slope soarer for a kit review isn’t so easy. Not only do you need a dry, preferably sunny day but ideally a dry and sunny day with a northerly wind to keep the sun on your back. Oh, and another competent pilot to put the model where you need it! Remember autumn 2007? Wet wasn’t it – I think the editor was beginning to suspect I’d given up slope soaring for good! Opportunity came knocking eventually with a trip to our coastal favourite, the Great Orme in North Wales where winds were forecast to provide both high and low lift condition testing.
When I reviewed the Luna I set about debunking the idea that a good 2-metre moulded glider couldn’t be bought so cheap, so I saw no reason to approach the test flight of the Ruby any differently. To say we ‘gave it rice’ would be an understatement. With the control throws dialled up to the high-end, square cornered loops and tight turns with some level of serious wing bending abuse was the order of the day.
It’s true to say that without her ballast tube, the Ruby lacks some of the energy retention that the Luna’s higher weight provided, however it was when the lift dropped off later in the day that the Ruby really began to shine. With only lightweight Alula’s scratching around for company the Ruby soared high above. With camber dropped across the wing she remained well above the stall and totally predictable throughout the turns with no sign of wing drops even when out-turn aileron was applied against the rudder. Snap-flap added a nice feel to inverted flight and the cross tail configuration kept her on predictable headings without a hint of tail wag. Playing with differential, C of G and camber settings dialled her in nicely after half a dozen flights or so and the crow braking was found to be exceptionally good thanks to the oversize flaps dropping easily to 90 degrees as they do. The only blight of the whole model is that flap slop at neutral and the poor centring it brings to the party – a real shame.
Overall the low weight of the basic airframe and the use of camber changing flaps across the wing can produce a glide as flat as a slate layers nail bag, but it does begin to lack a little upwind penetration when the laminar blows get up. That said, in traditional moulded glider style, she’s born slippy and can generally get away with it. I suspect that this final aspect of the Ruby’s performance can be improved by removing the oversized sticker that South Coast Sailplanes plonked across the wing – just to remind you who they are in the flying shots I guess. I know from previous experience how much ‘noise’ a sticker on a wing surface can add through parasitic drag and I like to keep decals inboard on the wing where the air is already messed up a little from the fuselage. I might leave that big sticker on though as it does help orientation at distance, especially on a white model, but I’d have preferred it to be the same shade of Blue as the rest of the aircraft – fussy like that, me.
All in all she’s a lovely little bird. Packing down to practically nothing must also improve her appeal to the travelling slope flyer. The Ruby is reasonably tough, well built, fully capable and cheap with it. Fit ballast provision when you’ve had a bit of a fly, try to minimise any flap linkage slop and just go and enjoy her.
TWO MONTHS ON……..
My initial worries about the potential for sloppy flap linkages haven’t proved to be significant in any respect and I certainly haven’t been able to generate any flap flutter with the unballasted model.
The Ruby has seen plenty of flying time since the review was published and has quickly become the model I reach for when there’s little wind – it’s nice to have a model other than an Alula that can happily soar in light conditions. In fact the Ruby has been a nice suprise and really shines in light conditions and with such a low wing loading, the moulded design provides high efficiency. A nice aeroplane then.
Datafile
