Zupair Zulu

The Zulu is a very light EPP flying wing, weighing in at just 10oz all up, on a wingspan of 48in. This light weight is achieved partly by a much thinner wing section than some foamies, necessitating mini servos. Also, carbon ribbons are used to give the wing its bending strength so obviating the need to strap the wing with reinforced tape. Instead, the wing is covered with lightweight laminating film.

The model is designed as a slow aerobat for light winds, although other versions of the Zulu have since been produced, aiming to cover everything from thermal soaring with the XL version and dynamic soaring with the DS version. At the time of writing (May 2015), a moulded version is also in development.

The wing panels each have carbon ribbon spars set in them, top and bottom, and a further length of carbon is provided, to be inserted after the panels have been joined. Once this was done, I opted to sort out the servo fixing and rout out the channels for the servo wires.

The advertised kit contents include pushrods. However, my kit had no pushrods but did have a set of four horns (two for elevons, two for drooperons). Initially I was quite happy with this but, when I compared the supplied horns with the drawings in the instructions, there was a significant mismatch.

Since the instructions were out of date in other respects (e.g. detailing how to round off the wing tips and chamfer the hinge lines - both now done at the factory), my first thought was that the drawings of the horns were out of date too. However, after posting a query on the Zulu thread on RCGroups and then e-mailing Zach, the designer, it transpired that the horns in my kit were of an earlier pattern and in this case the instructions did indeed show the later versions.

Zach was very helpful in clarifying the relative movement needed in the elevons and drooperons so I re-shaped the drooperon horn to eliminate the differential effect and fitted the elevon horn as is. The difference in length of the two horns was then accommodated by attaching the front and rear pushrods to different positions on the servo arm.

Somewhere in the process of sorting all this out, an accident befell one of the elevons. These are very vulnerable until covered, tapering away to nothing at the trailing edge. As you can see, I managed to take quite a bite out of it. Maybe this is why the instructions suggest covering the wing so early in the proceedings! After pondering the damage for a while, I mixed a little RC Modeler's Glue with some lightweight filler, in the hope that it would act as a plasticiser. Fortunately the idea worked and the result was much better than I dared expect. So much so, that I didn't feel the need to contrive a colour scheme to cover the damaged area.

After a good sanding down, the wing was covered with the laminating film. This was a new experience for me and it went much better than I feared, in fact I would say that it is easier to apply than normal covering film. I did manage to create quite a twist in one of the elevons but it was easy to get out by re-applying the heat. I used the lighter grade of film so time will tell how durable it is.

Since I am the kiss of death to any process involving paint, I contracted out the spraying of the fin and pod, so all that remained was to add some bits and pieces of trim and film to aid visibility, attach the fin and pod, install the battery and receiver and check the balance. With a 3s 800mah LiPo battery and 5v regulator, no ballast was needed.

I'll report back later when the Zulu has flown.

May 2018
Well, three years on, I can report that the Zulu is everything I hoped it would be. It flies in the merest breath of breeze, turns on a sixpence and, by virtue of the drooperons, seems to be every bit as efficient either way up. When others are scratchng around with thermal soarers, the Zulu can do close-in aerobatics, secure in the knowledge that, if the last little bit of lift does disappear, the shoulder of the slope can usually be reached very quickly. It will handle a reasonably breeze too but when it gets really windy it makes sense to reach for something a bit heavier.