Ultrafly Sukhoi SU27 Flanker RC Aircraft

Electric Flight with the Ultrafly Sukhoi SU-27

I saw the SU27 Radio Control Plane advertised in model magazines several times, and I thought it looked really good. It's a quick-build foam kit, but it looks reasonably scale-like, and is a brushless pusher jet, which promises some pretty exciting flying. I liked the look of it so much that I showed my wife the advert, and she bought me one as a surprise birthday present!

The box is impressive, with a fantastic picture of a swarm of Russian fighter planes cruising through the clouds. Inside you find just a few polystyrene parts and a bag of plastic bits. There is also a rather nice canopy and the parts for the propulsion unit. The mystery item in the box is a bottle of glue with no label on it, that turns out to be an extremely effective foam glue.

I started work on the motor unit first, because the idea of a mini brushless motor working through a gearbox intrigued me. It was here that I hit my first two problems: The manual has plenty of pictures, but only a few words, and half of those are in Japanese. Also, it seemed that the bolts supplied to fix the motor into the gearbox were the wrong size. I puzzled over it for a while, and eventually gave up and phoned the supplier.

Sure enough, it was an error, but he assured me that this was the only mistake in the kit. I found some bolts of the right size laying around in the attic, and fixed the gearbox together. It's a small, lightweight unit, taking a 7x5 propeller on 3 Lipo cells.

Next I started gluing the larger pieces together. The manual shows you what to do, but doesn't explain what you are doing or why you are doing it. This is annoying. In fact, it gets you to stick things together in an arbitrary order. If I was building it again, I'd build the canopy last, so I could stick it on after painting the fuselage, but the manual tells you to put it on first.

The manual calls for Cyano, Epoxy and the mystery foam glue. I managed with only Cyano and the foam glue, and I have to say that this free glue is excellent. It's not long before most of the kit is together, and it begins to look impressive.

I decided to paint the fuselage because the decals supplied are quite heavy, and the finished model on the box was definitely painted. In retrospect this was a bad idea, because I couldn't get the right colour paints, and even though I used foam-safe Acrylic paint, the finish isn't particularly good on the bumpy foam surface.

There is a little bit of cutting, sanding and metal-bending to do to complete the model, and there is a serious error in one of the pictures in the manual. Luckily I didn't fall into the trap of copying the instructions and ending up with one of the pieces upside-down. The most tricky part is getting the electronics wired up. It requires a servo Y-lead and extensions to the ESC battery and motor wires. During the process I somehow stuck the soldering-iron right through one of the fins!

I bought a 2200mAh 3S1P Lipo battery from Hong Kong. It can only deliver 18 Amps, but I think that is enough for this motor. The gearbox is really noisy! Somehow the sound resonates through the fuselage and it ends up sounding more like a glow-fuel engine than a "quiet" electric.

The first flight was a bit of an adventure: I took it to a local field where I occasionally go to fly. I don't like an audience for maiden-flights. As I applied power, the motor fell off and the prop cut into the underside of the fuselage. In retrospect I should have glued the motor stick on with something more powerful than a few blobs of Cyano. So I decided to undertake a field-repair. During this the farmer who owns the field arrived in his landrover. I've never asked permission, or seen him before, so I was worried that he'd get out his 12 Bore. In fact he was very friendly, and I asked his permission to use the field for flying, and agreed that I could as long as there were no cows in it.

Next I went to do the launch, only to find that the prop was pulling the plane backwards instead of pushing it!!! I am using the RobotBirds 25 Amp speed controller, and I thought I had programmed it to spin in the right direction, but obviously not. Also, I thought I'd programmed it for a gentle cut-off, not a sudden one, but this later proved to be wrong too. I then had to try to re-program it from a vague memory of how to do so, as I'd left the instructions at home.

Eventually it was air-borne! It flies really nicely. I thought I had the ailerons and elevator at a conservative setting, but the roll rate was already very fast. My piloting skills must be improving, because I was able to fly it around until the battery ran out, and then land it with no problems at all. It flies in big loops, has plenty of power, but isn't terrifyingly fast, although I kept it on less than full throttle for most of the flight.

Now I'm just waiting for good weather so I can fly it again.

July 2006 Update

When I got home I discovered that the landing had destroyed the elevator servo. This is not surprising, as it is an all-moving tailplane, and the front edge can get caught in the long grass on a landing, ripping it down suddenly, and thus stripping the servo. I bought a more powerful metal-geared servo, and that fixed it up nicely.

There is a real art to launching this plane. The propellor is at the back, and looks lethal, and your hand is below the fuselage, gripping a little wooden thing. The skill is to keep your arm straight, extend it behind you, and lob the plane using an action a little like bowling in cricket. Bring your arm around in an arc, and release the plane at 45 degrees upwards. If you arm is always straight, you can't extend your hand out into the propellor as it leaves your grip.

I've had more trouble with the servo on the elevator, but I'm researching it more...

See the rest of my planes