Best of British … onboard with an Avian in the Yorkshire Dales in 2009
Avian’s new performer prove that the British hang gliding manufacturing industry is not only alive, but also kicking, says Richard Sheppard. Published in Cross Country magazine in 2002
There was a time when the British hang gliding industry ruled the world. In the mid-70s competition results invariably listed long forgotten names such as Hiway or Chargus or Wasp. And later, during the boom years of the fifth generation gliders, Airwave and Solar Wings couldn’t make enough to satisfy demand.
For several reasons, the ’90s has seen the world market enter a slow decline, leaving Avian as the UK’s only committed developer of top end, high performance hang gliders.
Avian are well known internationally for gliders such as the Amour and Java: very successful, high quality, easy handling machines that have won the hearts of many sport pilots. But with only a clutch of competition wins and without a contest ’big heater’, they have never really been perceived to be at the forefront of out-and-out performance, despite favourable plaudits for the Java competition machine from the likes of Ruhmer, Pagen and others.
In 2000, Avian came up with a totally new and serious looking racer when they launched the Cheetah 160 and 140. The planform was very different to existing high performance topless models, looking large and floaty and very curvy despite its square-cut tips.
Like previous Avian models it owed a lot to designer Steve Elkins’ own thoughts on what constitutes a high performance hang glider, helped by computer modeling which, Steve says, pointed toward the final shape for best efficiency.
Over the next two years the 160 acquitted itself well in competitions but, as with all companies striving for that elusive few percent, Avian were convinced they could improve it.
The result is the Cheetah 150, which, Elkins says, is more-or-less a new design that, in spite of retaining the familiar planform, owes little to the previous version. Avian say that it now uses 7075 tubing almost throughout and the inner leading edges have been increased in diameter to a substantial 62mm. The nose angle has also been increased, along with a new aerofoil section and pitch stability system.
DESIGN AND CONSTRUCTION
The first thing I noticed about the Cheetah was the length of its bag. A lack of currently fashionable curved composite tips makes it a good 50 cm longer than most of the competition. As I said earlier, Steve Elkins is an individualist when it comes to design and this has resulted in a refreshingly different shape to be seen in the skies.
The chord of the wing tapers only slowly for the first two thirds of the semi-span before the trailing edge curves in towards the tip. Some pilots have voiced doubts at the shape, but I remember an aerodynamicist once telling me that, in theory at least, hang glider wings were too tapered for best efficiency. Looking at the shape, the broad outer chord has a ’rightness’ that suggests good performance – we shall see…
In common with previous Avian gliders the leading edge tubes step down in size toward the tips. It has two tubular aluminium ’sprogs’ per side to keep the correct amount of minimal twist in the wing. These have a bend half-way along, enabling them to lie flat against the top surface instead of impinging on the undersurface profile.
They are suspended by a wire and simply swung into place during rigging. The outer one is angled outwards from the leading edge quite noticeably, presumably so it can be mounted onto the larger and torsionally stiffer tubing further inboard. The carbon fibre cross booms are Avian’s own design. They are rectangular in section (better than round section because they can be stronger in vertical loading for less weight) and have a pronounced downward bend near the tips to better fit within the wing profile.
One thing you won’t see these days on any comp glider worth its salt is batten elastic, and the Cheetah is no exception. The company has obviously invested a lot of time and effort in the design of the batten ends and has come up with a very neat solution. Each plastic end pivots to effectively shorten the batten.
A small spigot locates in an eyelet on the sail then the end is ’straightened out’ and clicked into place around the batten tube. It is very quick, easily adjustable and as drag-free as you’ll get. Because of the minimal amount of taper on part of the wing all battens are numbered for easy identification.
The glider will rig flat on the ground and has the now common swiveling wing-wire terminations so it can also be rigged on the A-frame without stressing the wires. I was pleased to see that all rigging is galvanized steel as opposed to stainless. Galvanized wires are more flexible, stronger and less prone to fatigue failure.
Stainless steel may look smarter but it gives no indication of imminent failure, whereas galvanized steel at least starts to produce oxides when aged, which will prompt a pilot to change them well before they are in danger of failure.
The sail is available in Dacron or – as in the review machine – Mylar composite. It is well finished and top surface is cut to match the shape formed in flight rather than using a continuous flat panel. When rigged the wing has a noticeably thin section and is fairly slack at the trailing edge with the VG off.
RIGGING
The glider rigs easily with no idiosyncrasies. The two sprogs simply swing out before the undersurface is zipped up, meaning there’s no scrambling about under the sail trying to locate spigots or pegs. It uses 12 upper surface and three undersurface battens per side and I found it easiest to locate and tension the top ones before applying the cross boom tensioner.
As I mentioned, you need to sort the battens by their number rather than length but this is probably quicker than the ’picking straws’ method anyway.
The tip battens are retained on a hook on the leading edge tube but that is the only locating work you need to do during the rig. The sail tensions up very easily, the webbing strap locates on an undercut retainer and is secured with a split ring. The front wires attach simply and easily with a swan neck catch.
FLYING
The glider felt well balanced on the ground and take off was nothing more than a formality. Once in the air I felt instantly in tune with the handling. The bottom bar is quite far forward at trim speed making a fast cruise comfortable and easy to maintain.
Gone are the days when you had to fly on the edge of the stall if you wanted to be top of the stack – with a glider like the Cheetah there seems to be hardly any difference in sink rate for quite a speed range.
Pitch felt solid with plenty of pressure throughout its range. Pushing the bar out and holding it there eventually resulted in the nose dropping softly without a sign of wing dropping. Continuing to hold the bar out resulted in a sort of mushy stalled descent that vanished the instant the bar was let back in.
With VG off roll control was light, responsive and well co-ordinated with pitch, making repeated rhythmic wingovers a delight to perform, especially as the wing seemed to retain so much energy. Thermaling the Cheetah in the mild blobs over Lords Seat, a 1200 ft site in the UK’s Peak District, was a pleasure.
It felt extremely well balanced with little or no high-siding required. Sink rate appeared to be excellent and I found that it climbed best if flown on the fast side rather than pushing out too much, which also made the flying much smoother and less tiring even if it did go against my initial instincts.
One outstanding aspect of this glider was the glide at medium speeds with full VG on. I didn’t have another hot glider to compare against but using the paragliders on the ridge as markers (it was blowing around 25km/h on take off) I was very impressed that I could glide out for over a kilometer very quickly and loose little height in the process.
It seemed to have a very broad usable speed range with little effect on sink rate up to about 60km/h according to an average gained from my GPS.
With the VG cord straining in its cleat and with the bar at my knees it felt very quick and there was still plenty of pitch pressure. But I did have some difficulty in holding a straight line if knocked off course by turbulence. Try as I might, I could not control this without slowing down in order to damp out the oscillations.
At lesser speeds it was sweet and straight but as usual, roll control with a tight wing was very slow and stiff. On the other hand, glide still seemed pretty respectable with the sail slack and I spent a lot of time whizzing here there and everywhere in this configuration.
This is where modern, clean hang gliders win out – reduction in parasitic drag means best glide not only improves but also happens at a higher speed so it’s a kind of double whammy – to match the best glide of a kingposted glider you are probably flying 10 or 15% faster.
Slow down and you’ll not only out-glide it, you’ll still also be going slightly quicker. Landings were no problem, the wing showing a large and controllable flair window with very good low speed handling.
SUMMARY
I really enjoyed flying this glider. It is extremely well made and I think the shape is beautiful. It gave me lots of confidence, both with its out-and-out performance and (apart from those balls out high-speed wobbles) in its general flying characteristics.
Avian are to be congratulated on producing a distinctive wing that isn’t a clone of the current popular designs, has full BHPA C of A certification and yet remains one that offers pilots a potentially world beating performance.
It would be great to see more pilots dong well on this glider to carry on from Steve Elkin’s and Ron Richardson’s recent second and third placing in the British Nationals – and maybe resume Britain’s tradition as a front runner in those international results sheets!
Cheetah 150 Specifications
Top Surface battens 25
Undersurface battens 6
Span 10.27m
Centre Cord 1.87m
Aspect Ratio 7.6
Area approx 150 ft2
Double Surface 95%
Nose angle 130-133 degrees
Pilot Weight Range 70 – 100kg
Glider Weight 35kg
Packed Length 5.8m
Easy short packed length 4.6m
More difficult short pack 4m
C of A status BHPA pending
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