Flight 1: Flew perfectly off the ground and required very little trim adjustment. I flew it round at about half throttle, like a trainer, and did a stall test. About 4 minutes into the flight the left aileron suddenly flew off, which totally took me surprise, but I was able to land the plane immediately and very gently. The aileron looked as though it had been wrenched off very hard, since the fibre hinges had been ripped off with the surrounding balsa.

Flight 2: With aileron repaired, I flew the plane again a few weeks later. The plane needed retrimming, then suddenly again at about the four minute mark the plane wallowed a bit, so I landed it immediately (again very gently) and found that one of the elevator push-rods had come detached, even though I had checked that it was really tightened down hard just a few minutes early.

Flight 3: With everything double checked, I expected third time lucky. Again, I flew the plane round at about half throttle, only going to full throttle for one or two verticals ending in stall turns. I did a few gentle loops and rolls, I think still on low rates. Again at about the four minute mark (!), I was flying the plane straight and level at about half throttle when all hell broke loose. An aileron stripped off and various other apparent debris (one piece was a wheel spat that when retrieved appeared to have been wrenched hard off the plane!). Yet again I was able to make a gentle emergency landing. I was lucky to get it down because one aileron was missing, both aileron servos were completely stripped (i.e., I had landed on rudder and elevator only without knowing it), and the port wing with the missing aileron was cracked right across the chord just outboard of the wing tube, and the opposite wing was also slightly cracked. I must have cut the power just before the wing failed completely. In this last incident there was a loud fluttering noise, so this was a clear case of flutter, probably of the ailerons, but possibly also the wings. The entire destructive episode could not have lasted more than one or two seconds, but the damage it did in that time was incredible.

I stripped the covering off both wings, and the more seriously damaged one practically fell apart in my hands. It is clear what the problem is: although the Katana wings look very well made (from the outside) they are very weak. The main spar is notched half way through at every rib, creating a very weak point where the wing tube ends. Also, the way the instructions tell one to set up the aileron servos with long servo arms and the pushrod connected to the second innermost hole on the aileron horn. Is mechanically very weak for such a large control surface with such big throws. This combined with the weakness of the wing was undoubtedly the cause of the flutter. Also, the rear spar that takes the aileron hinges is only about a quarter of an inch thick, which is not really enough for holding the hinges securely.

So the problem is not one of equipment or manufacture, but bad design. I would say this is the reason Hangar 9 have withdrawn this model. The Funtana much have a much stronger wing construction, because mine has survived vigorous aerobatics over three years without falling apart.

I am rebuilding the wings at the moment, including carbon fibre bracing spars, and adding blocks for the hinge mounts . Already the wing is probably about ten times stronger than the original.

For all of you who have Katana 50's, I would suggest that you might strip the covering off the wings and beef them up as I have done, before the plane breaks up on you.