I got caught with an ill-handling Yak because I didn't catch a distorted horizontal
stabilizer. The result was an ill-handling plane.
Text, photos and video by Tom Hintz
Flight video by Clark Ponthier
Posted – 8-22-201
When I started FlyingRC.net I promised to continue my “warts and all” philosophy of running my web sites. Of course, I hoped to not make mistakes but living in the real world means reality over powers ego every time. In this Review, you get to see what happened when I failed to check things over as I know I should. The result was nearly killing a brand-new airplane.
Back when we stick built our planes, we routinely checked everything, including the control surfaces, for twists and warps because we recognized our ability to make mistakes. Now that other people are building the airframes I (and many of you) seem to believe that paying them to build the planes means they will not make a mistake, ever. Unfortunately, those plane builders live in the same real world we do and an occasional mistake is inevitable. In this case, I failed to check the elevators, one of which had a small twist in it. On a high-performance airframe such as the QQ YAK 54 35CC ARF, that twist had a pronounced effect on the handling.
This is where too many people invoke the “make lots of noise and manufacturers give you free stuff” aberration of customer service. I could not get myself to be that small. As I would find out, contacting Flex Innovations about the issue had them shipping new stabs and elevators to me without a bunch of questions or argument.
Note: The first flights were done before we identified the twisted elevator. During the first flights, I convinced myself that I had an engine thrust line problem. Of course, my aerodynamic prowess meant that assumption had a huge chance of being wrong.
When the QQ YAK 54 35CC ARF lifted off for the first time it nosed up as the airspeed increased. I could push the nose back down but it turned up again making it obvious that I had a problem. I struggled through a few flights trying to trim the bad handling out. When those adjustments failed to produce the change I was looking for finally decided to contact Flex Innovations. Quique Somenzini called me saying that he suspected a problem at the stabs. As dumb as it sounds, I was not convinced that Quique (world-renowned RC plane designer) was right. Like I said, way dumb on my part.
I have the good fortune to know a guy who actually understands the use of incidence meters and what they are telling him. He was nice enough to meet me at the field with his gear and he confirmed the twisted stab diagnosis.
I emailed Flex Innovations, falling on my proverbial sword admitting that Quique was correct, the problem was in the stabs. To their credit they immediately shipped a new set of stabs to mas they had offered to do the week before, without a bunch of questions. Even more surprising was that they had the stabs in stock!
The good news is that the new stabs did cure the QQ YAK 54 35CC ARF handling problems. The bad news is that a few of the initial attempts at maiden flights ended with landings that were rougher than I like (or thought) but the QQ YAK 54 35CC ARF seemed to be none the worse for wear.
It was hard to see the twist in the stab
but it was there and Flex Innovations sent a new
stab assembly.
After a few trim flights with the new stabs I again took off to refine the trim further when a couple minutes into the flight a friend saw the right wheel fall off. We would see later that the axle itself had come off, probably from the early rough landings. I found the tallest patch of field grass and tried to belly flop the QQ YAK 54 35CC ARF into that to reduce the shock of that now bare main gear digging in when it touched down. A strong weed snagged an elevator and the QQ YAK 54 35CC ARF was unceremoniously slapped down tearing the gear out of the fuselage.
I was undecided on the way home if I was going to continue with the QQ YAK 54 35CC ARF project. However, I realized that were it not for a few bad decisions on
my part most of this drama would have been avoided. I checked the Flex Innovations site and again, they had the fuselage and rudder assemblies in stock and way cheaper than I anticipated. The fuse was selling for $179.99 (8-14-2017)! I ordered the new parts and went to work stripping the components from the damaged fuse.
I must admit being a little apprehensive about putting the QQ YAK 54 35CC ARF in the air again but those fears would be quickly replaced with a smile. The QQ YAK 54 35CC ARF lifted off the grass, I nosed it up a little to clear the trees and let go of the sticks. It had a little sink and a little right aileron. A few clicks of correction and it was generally flying hands off at speed. Keep in mind that I do not have the Aura 8 Control System in the QQ YAK 54 35CC ARF yet. I am following Flex Innovations suggestions on getting the plane set up with the trims neutral before installing the Aura 8 Control System. This flight control system (as well as many others) “sees” trims as stick movements. The Aura 8 Control System has full trim capabilities and we will look at that in a coming Review focused on the Aura 8 Control System.
In a moment of glee, I hammered the aileron stick and discovered that the QQ YAK 54 35CC ARF has a very quick roll rate but stops that roll dead when you let go of the stick. It is also very responsive to the elevator. I love using the rudder and the QQ YAK 54 35CC ARF listens to rudder commands very smoothly with surprisingly little counter aileron needed.
I am a touch and go fanatic so began doing a bunch of those with the QQ YAK 54 35CC ARF and the brand new DA35. The rudder is so smooth and predictable that I felt comfortable using it very close to the ground to counter cross winds and to slide the QQ YAK 54 35CC ARF into alignment with the runway without banking the wings. The QQ YAK 54 35CC ARF has no tendencies to rock the wings aggressively when rudder is introduced.
With the new stab the Yak was way more
fun to fly.
Knife edge flight is ridiculously simple. If there is any coupling I can’t see it. The QQ YAK 54 35CC ARF tracks nicely in knife edge flight as it does in virtually any direction you point it. The included side force generators appear to be very effective and help holding a knife edge track at lower speeds than expected easy.
I did not get into aerobatics with the QQ YAK 54 35CC ARF just yet in large part because the brand new DA35 that was literally on its 4th, 5th and 6th flights and is still a touch rich. I was content to practice touch and goes and refine the trim setup. The QQ YAK 54 35CC ARF is fun to fly even without tearing holes in the sky – for the time being…
When I put the QQ YAK 54 35CC ARF on a 45-degree up-line it has a virtually no variation, up or down. That generally means that the CG is correct. However, the QQ YAK 54 35CC ARF seems to want to establish a slight nose up (and I do mean slight…) attitude as it settles in for a landing. The design and weight of the QQ YAK 54 35CC ARF means the controls remain responsive right up to where it falls out of the sky. A couple clicks of power lets it settle in to the runway gently.
I am going to move the CG forward just a little more as an experiment than to fix anything. I want to see if the QQ YAK 54 35CC ARF landing attitude changes at all. At this point any changes I make are going to be very small because the QQ YAK 54 35CC ARF is flying very well. I just want to be sure I have it as perfect as I can mechanically so the trims are neutral when I install the Aura 8 Control System.
The QQ YAK 54 35CC ARF turns out to be a great airplane despite my early mistakes that nearly killed it. This was one of the more difficult maiden projects I have done but nearly all that falls on me for not checking the components in the first place. The folks at Flex Innovations were ready to make it good if I would have listened to them the first time around. You can put good money on my listening to whatever Quique Somenzini has to say about an airplane!
In the coming weeks, I will be installing the Aura 8 Control System and we will look at that as well as using the free software to set it up. The Aura 8 Control System has provisions for all the trims we normally dial in through the transmitter. Letting the Aura 8 Control System handle all that gives it a totally clean signal that does not compromise its efficiency. This should be interesting. Stay tuned!
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