Und Nu?
review by Trevor Hewson

Okay, let's get that name out of the way. This model originates from Team Klaustrophobia, a German flying club specialising in indoor flight. The literal translation is 'And Now?', but I suspect that 'Now What?' or 'What Next?' might be closer to the spirit of the name. But, whatever, so what, who cares? Now, what next?

I first encountered this aeroplane at the BEFA Electric Flight Festival at Middle Wallop in June 2001, being flown by David Theunissen. Having just flown the Aerobic 020, I was impressed by the slow flying ability of the the Und Nu (I'm leaving the question mark off from here on), as well as its agility. Talking to David, he said that he had put a drawing of the model on his web site. As it happened, Flite Hook were also at the event and had 3mm Depron foam for sale, so Jim and I bought a sheet each.

Cheap and Cheerful
Now for the really good news. The Und Nu can be built from half a sheet of Depron - and everything else you need can be taken from that Pico Stik you have got tired with / grown out of / crashed (delete as applicable). Okay, I did raid the scrap box to make up a lighter fuselage stick, but apart from a few bits of wire for tail skid and pushrod and some tape for the hinges, I really can't think of any other materials used.

Getting it Together
I tried a few glues on the Depron. There are several that work but I was rather surprised to find how well cyano performed. I know that some Cyano glues melt some foams, but the two varieties I had in stock both worked well with the Depron - the better of the two was given to me by a double glazing fitter so may be particularly formulated for working with plastics.

The key part of any aeroplane is the wing and indoor models are no exception. However, whereas with other models there is much concern over planform, torsional rigidity, bending strength, surface finish and fidelity of section, for indoor models the requirements seem somewhat simpler - but every bit as important: Ooodles of wing area, plenty of camber, and of course, feather light. Accordingly the Und Nu wing has a generous chord of nearly 200mm for its 700mm span - and then you add gigantic 65mm ailerons, giving a wing aspect ratio of just over two and a half to one. As for wing section, there is a note on the drawing suggesting that a couple of Depron ribs should be cut out, about 12mm high. That's it. No particular section is given, just use a rib shape that the Depron will comfortably bend around, it's the camber that matters.

As well as helping the slow flying characteristics, the camber also gives the wing a bit more bending strength. However, this is further aided by taping a carbon rod to the wing underside to form a simple spar. This rod goes to just beyond the semi span point, and there is an optional suggestion about fitting additional ribs at this point to help to maintain the camber. I was happy with the strength/flexibility compromise on my wing so didn't fit the extra ribs. As a result, the camber decreases progressively from root to tip, which I think is aerodynamically beneficial, but I would be hard pressed to explain why.

Once the wing is done, the rest is straightforward. There are a few decisions left for the builder to make such as how to link the aileron servo and just where to mount the receiver, but nothing too taxing. Having said that, it did take me four attempts to make a battery mount which I was happy with, but that was my fault really - the drawing shows a single piece of bamboo skewer which would probably work just as well as my over-elaborate balsa contraption. The receiver was attached to the underside of the wing with double-sided tape.

Getting it airborne.
I finished the model in July so, since our next indoor meeting wasn't until the end of September, I hoped for a calm evening for a test flight. Then I got an e-mail telling me about an indoor session at Calshot Activities centre, organised by the Solent Model Flying Club. This is a splendid venue, being a converted flying boat hangar which now houses an indoor cycle track. I fitted a battery to the mark 2 battery mount, positioning it well forward and, after a cursory control check, opened the throttle and the Und Nu scooted across the floor. A touch of up was needed to get airborne and although the model handled okay, it was clearly nose heavy. A quick landing and battery adjustment and we were off again. After a couple more adjustments, with the battery now as far back as the mounting would permit, the model was much more responsive and I felt sufficiently comfortable to put it through a basic aerobatic schedule - not something I normally do on first flights - even outdoors!

In the interest of weight saving, I hadn't fitted the optional rudder control and so was delighted to find that, in contrast to the Aerobic 020, the aileron response of the Und Nu seemed to hold good down to extremely low speeds, making it very comfortable to fly in a small space. The roll response was good but the looping performance was poor due to shortage of power, so I made a note to look at the motor/prop combination again to liven things up a bit.

The one situation where the rudder is missed is of course taxiing. To my surprise and amusement, I found that the ailerons do steer the model quite positively on the ground - but in the opposite direction! This can be quite challenging when taxiing towards you, and curved take-off runs should not be attempted. I have now set up the rudder stick to operate the ailerons in reverse but, just in case I absentmindedly waggle the rudder stick when airborne, I can switch it off at the transmitter and just enable it for taxiing - well, that's the theory, anyway.

I had four flights with the Und Nu on this first outing and thoroughly enjoyed it. The enjoyment was no doubt all the greater since the total expenditure was around £1 - highly recommended!

Getting It Right
Since that indoor outing, I have had two outdoor flying sessions with the Und Nu. For the first of these, the only change was yet another battery mounting plate. By taking advantage of the more rearward battery position, this mounting plate was now able to double as a receiver mount, so, I now have only one servo to plug in when attaching the wing. This session proved that the model is as much fun outdoors as in - and that operating the ailerons in reverse from the rudder stick does work!

For the second outdoor session, I borrowed a three bladed 9inch prop from Chairman Clive to see if it would liven up the looping performance. The transformation was staggering! Inside and outside loops are now easy and the 7 cell 'Perkins' pack still lasts for more than six minutes. There was so much power that I inadvertently discovered the Und Nu's Vne characteristic, which is a sharp tuck under caused, I think by the wing tips twisting downwards. Whilst this was very disconcerting the first time it happened, once I had managed to work out that it wasn't a radio glitch or a rearward c of g problem, it just seemed to add to the fun. I don't recommend trying anything resembling a high speed low pass, though!

This model is the first I have seen whose manoeuvrability comes close to that of the IFO. And, as Jim put it, it has the advantage of almost looking like a real aeroplane. Well I will leave you to make your own mind about that, but I don't think my Eastern Airlines stickers are going to make anyone think it's a scale model, do you?!