Yak 54 Part Two

My first trip to the patch was blessed with a bright blue sky and very little wind. Perfect! After double-checking both airframe and radio integrity and with the engine fired up and purring nicely, it was out to the strip to let rip. After a final waggle of all the surfaces and with the camera ready, I opened the throttle and off she went. The first thing that struck me was how steady the Yak was. Yes, a tad of trim was required for straight and level flight, but otherwise she felt just right.

At a decent height I checked out the stall; even with maximum throws hauled into the elevators there was no flick or spin, just a bit of a wing-rock on the way down. The standard hover is a great manoeuvre when executed correctly, but depending on the wind it’s very hard to prevent torque rolling. With no wind at all I found that as soon as I got her upright, shed rotate. Due to the model’s size the rate of roll wasn’t so much that I couldn’t keep up with it, although stopping it with the ailerons didn’t seem to have a very positive feel. This being the case I mixed in some taileron, which improved matters considerably. After a very short time I was bringing her down to the deck where I could see exactly what was going on. Whats more, hovering at 200ft doesn’t look terribly impressive, no matter how big the model!

I couldn’t get the wings to stop rocking in upright ‘Harriers’, but inverted ones were more stable. A similar story with ‘elevators’ and ‘parachutes’, and it proved too easy to push the attitude too far when inverted, transitioning into an unintentional hover if not careful. The Yak will fly very slowly with a high angle of attack, which means you get more time to do it properly. This aspect of her capabilities put a massive grin on my face!

During straight and level inverted flight she didn’t require any elevator at all unless slowed right down, and on a straight dive from height with no power she came down vertically with no tendency to pull or tuck. This indicates that the C of G must be in a good position, although as always with this type of model, there could be a sweeter spot slightly to the rear, just waiting to be found.

Knife-edge is a breeze with that massive rudder. I experienced a very slight tuck towards the undercarriage, and although I could start mixing it out I’m still moving the C of G around to find the optimum position, which will change any mixing and maybe even make it redundant. High alpha and knife-edge parachutes needed a good deal of stick stirring, but were fairly easily achieved. Using rudder in the slowest rolls required very little deflection, and setting rates made things a whole lot smoother.

Positive and negative ‘snaps’ were slower than I’m used to with smaller models, which this makes the entry and exit a whole lot more controllable. Mind you, I struggled to keep enough inertia for more than two on a vertical up-line. A ‘blender’ is always a violent manoeuvre and even for its size, the Yak still looks like it’s going to break apart on the start of the flick. Transitioning from a vertical climb into a ‘waterfall’ proved very graceful but often resulted in a break-away to a flat spin, what with trying to keep the line straight whilst tumbling and balancing the throttle with enough down elevator to keep the manoeuvre tight.

Using my third flight mode of 15% control throws the Yak calmed down significantly for some smooth flying, and there’s an air of elegance to slow rolling circuits, ‘control line’ flat turns and the like. She goes round so well it’s not difficult to imagine a couple of wires coming out from the wing tip, especially at very low altitude.

The O.S. has proved to be the perfect match for the airframe, and in an effort to optimise its performance I’ve tried four different props. An 18 x 10″ wood was a good all-rounder and sounded great, but a Just Engines J’EN C 18 x 6″ carbon provided better static thrust and allowed the highest rpm at 8,000. I thought a Biela 20 x 6″ carbon would be optimum but found the revs too low at just 6,600rpm, with vertical pull-out performance suffering greatly. Maybe a higher nitro fuel would be the answer but I want to keep things as standard as I can on the 5% stuff I use. The last prop I tried was a new Graupner 20 x 8″ from the G Sonic range, which gave just over 7,000rpm on the floor and seemed to be the best one in the air for both 3D and smooth aerobatics. The sound from the standard exhaust wasn’t offensive and sounded more ‘gas’ than ‘glow’ most of the time. A Pitts style silencer would be prettier than the stock O.S. affair but I’ve found these to sound very tinny. Besides, there’s so much room at the front end that the standard unit doesn’t look out of place.

BRING IT ON
It’s all very well flying our toys when the sky is blue with just a whisper of wind and warm hands, but most of the time we in UK have to endure the complete opposite. I pride myself in always flying something if I’ve taken the trouble of taking it to the field, and we recently had a day of steady 25 – 30mph winds with gusts I don’t even want to imagine. Mind you, it was dry and I thought if this review was to be as detailed as possible then I had to fly in such conditions at least once.

The take-off was rather quick, and there was a little turbulence low down, but when she rose above 20 feet or so the Yak flew smooth enough. Hovering in these conditions (and even flying backwards) is too easy, but the best manoeuvre I’ve found is to get the nose high upwind and torque roll down the runway before hitting the power and fighting upwind for another go. Performing ‘the wall’ is easier with a bit of wind up the back end, jerking the tail down just as you pass yourself at low throttle. Hold the hover enough for a 180° torque roll before flipping the tail back around and flying off in the direction you came from.

I tried an ‘elevator’ from a good height but actually ended up flying backwards! I’d normally fly downwind a bit so the point of exit into a ‘Harrier’ is just about in front of me on the flightline, but on this day I had to start upwind and found it impossible to judge properly. When adding a little rudder to a ‘parachute’ it was more like doing a handbrake turn after the flick.

During the flight I lost my cap and was blown sideways a bit, so I knew the landing wasn’t going to be fun! For the first attempt I came in from height with the engine ticking over, trying to use the speed from the descent. However, low down the wings were rocking too much and so I powered out for another go. Second time around I tried to kill the engine up high, but it refused to die. On the third attempt I just flew her in normally with some airspeed, and she touched down without any fuss. I knew I should have tried that first! That one windswept flight was enough for me so I stripped her down, loaded her in the car and took the rest of the day off.

Back to the field and at the end of another calm day’s flying I checked out the Yak’s glide, which she seems to do with very minimal loss of altitude. After what seemed like a minute floating around it was time to line her up and bring her in. Again, everything was straightforward right down to the point where she stopped rolling. The only difference was that this time I had to walk the 10 feet to pick her up rather than using the engine to taxi back.

OH, YES!
I Don’t think I need to tell you this, but I absolutely love this Yak. There’s nothing I would change about it at all (except maybe experiment with an electric motor up front on a 10s Li-Po set-up).

I’ll be looking very closely at converting to electric with a 10S powerplant to satisfy my inclination to the electric side, although I’m very wary of the ‘if it ain’t broke then don’t fix it’ rule, as it works perfectly well on that lovely O.S. glow motor.