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Saturday, February 9, 2013

The Yak Is Back

A LIVE Report
This will be much like the initial Extreme Flight 48" Laser EXP__LIVE report. You will be watching it as it happens. We will be back with construction and set up photos, and updating every chance we get. I will try to post links to this article on RC Groups whenever there is an update, but the safest way to make sure you catch it all is to check back here often. That, and please subscribe to the blog.

I have only done one previous LIVE report, so we are learning how to do this, so to speak, on the fly, pun very obviously intended, but of course.

Final Edit: This report is now finished.  For further Yak disussion, photos, video, etc, there will be a new report. This one was just to kick off the release and get some set up photo and info out there for guys putting their Yaks together.

Thanks for your patience though this process.
The Yak Is Back

Oh my and Yakkity Yak. The Yak is indeed back in the biggest, best and baddest way possible, which is as an Extreme Flight Experimental Progressive (EXP).

I was just starting to fly 3D when the original Extreme Flight 48" Yak 54 sold out for the final time. I've had a chance to fly a few since and really enjoyed them, which makes me all the more anxious to see how good one can be when given the EXP treatment. The first 48" Extreme Flight Yak 54 was a ground breaking airframe that really raised the performance bar in this size. Along with the 45" Extra 300E and Edge 540T also made by Extreme Flight, the popularity of the Yak is what put this company at the forefront of the small, high performance electric market. Extreme Flight is sort of known as "The Yak company," and the recent absence of their variant was a colossal hole in the 48" market.

Now with the advent of the EXP series, both the 45" Extra and Edge have been replaced with modern, ultra high performance 48" versions, so I think we all knew it was only a matter of time before we saw the Yak 54 EXP. The surprise was how much time, but that is what it took for "The Boss" to get the refined performance he was after, which is considerable.

As of this writing, only the red, white and blue "Russian Thunder" color scheme is available on the 48" Yak EXP, but there is also a red, white, and black version coming on the next shipment. That one is a bit reminiscent of the new 60" Extra EXP scheme, which I like a lot, so we will have one of these Yaks too as soon as they are available.

Click To Enlarge

Opening The Kit

Like all EXPs, the quality of the kit itself is top shelf. Since the debut of the 48" Laser EXP and 64" MXS EXP, the factory has been using some newer construction techniques such as recessed wings and angled motor box sides. This makes for a stronger plane, and as is the case with the recessed wings, a better looking one too.

The covering on my example had one or two edges on the control surfaces that needed a little sealing down with the trim iron, but for the most part the work was awesome, and certainly a lot better than I could have done.  Having done a lot of covering work back in the dark ages before quality ARFs, I can attest this would have been a difficult scheme to have put on the old way. I tend to be very obsessive about having my covering perfect, so it is always nice to get off to a good start like this.

All the hardware is the same stuff we have been using on all the other EXPs, so you will be right at home assembling this plane. The dual ball link hardware for the push rods means that you set it up once and you will probably never have to tinker with it again for the lifetime of the aircraft.

I especially like the lightweight Extreme Flight carbon tail wheel bracket, which could not be easier to install, maintain, or (if necessary) replace. The wheels and axles come straight out of the EXP hardware pack, and those work so well it is reassuring to have them on this plane as well.

Outside of that, it's all nuts and bolts, so everything is really pretty simple. This is actually more of a good thing that you might imagine. Complicated things can fall apart in a very spectacular and ugly way in the sky, so simple yet bulletproof is the best way as far as I can see. The Boss has come up with a good hardware pack for the EXPs. The stuff is light and strong, and I don't remember ever having a piece of it fail,  outside of ripping the tail wheel assembly off in a full speed crash. Imagine that.

In the building frenzy I simply forgot to take pictures of the hardware pack, but if you check my other 48" blog reports, all the hardware is the same great stuff.

The wheel pants are a bit weird, but remember, this is a Yak. The pants are more like little spats (for lack of a better word) that smooth out the airflow coming off the backside of the wheel. I suppose that aerodynamically they work fine, but they sure look odd. Oh, wait, what did we expect on a Russian plane?
The Build

The Yak EXP goes together very much like the Extra and Laser EXP, and I have built so many of them that this plane was nearly second nature to assemble. The Yak went together pretty much effortlessly.
As always, the best bet is going to be to check Herc's Awesome EXP Build Videos, which you can find on the Extreme Flight website. I can't cover everything here, because actually seeing how it is done on video is a lot better than reading my blabbering about it. You know, seeing it is worth a billion words and all, and Herc does a great job with his videos.

With this being a live report, I am sure I am going to miss a few things. However, The Boss has a nice little formula for cranking out and building Bad Ass airplanes, and mostly they all assemble in a similar fashion. If you have any questions, you can ask them on RC Groups Extreme Flight 48" Yak 54 EXP Tread, or send me a private message there.

Mounting the Tail
This is the one area of any build that stresses me out a bit. If you get the tail in crooked the plane is not going to fly straight.  Basically, take your time, pin it into place, and then measure it over and over. If you get it wrong, you're screwed, so don't get it wrong.

Outside of gluing the tail, you can undo almost any other mistake you can make on the build without a lot of effort. Once it's in, though, getting the stab out is a tough job, so it's better to get it right the first time.

The Boss pretty much figured out how he wanted all of this done with the  Extra EXP. Steel push rods with ball links on both ends is the best way to get a tight connection between the servo and control surface that moves smoothly with no drag. Unlike other methods of attaching a push rod to the servo arm or control arm, ball links generally do not get sloppy or develop friction and drag over time. They just stay tight and operate smoothly, which is exactly what you want them to do and exactly why the Boss includes this kind of hardware.

Also worth noting is how close the servos are to the control surfaces. While weight is a consideration, more important is that a shorter push rod is going to be stiffer and flex less. This gives you a more direct and precise command of the control surface and absolutely no chance that it is going to do anything but exactly what you demand from it.

Before we get into the linkages and set up itself, here's a little more on ball links: You can over tighten them and induce drag. You don't want drag because that can interfere with the servo centering properly.

I like to use Dubro 2mm X 12mm hardened steel allen bolts for securing my ball links. For one thing, that allows me to use one single allen driver tool for every bolt and screw on the airplane. Less importantly, though still important enough, I like the way they look.

I also like to use a 2mm aircraft locking nut that I get from Micro fasteners. I tighten this down until I start to feel a little drag on the ball link. Then I take a standard 2mm hex nut and put it on over top of the lock nut and snug it down. I back the lock nut off into the hex nut while holding it and that locks them together forever. This technique is called "jam nutting," and if you put a drop of thick CA on the few exposed threads, those are not coming off even in a nuclear Holocaust.
It sure seems like we have seen this before, doesn't it? Well, that's because we have on all of the other EXPs. This system works so well that The Boss just keeps using it. It's simple and bulletproof, and that's reason enough to do it again and again.

One thing I have been getting wrong on a lot of my previous EXPs Is putting the ball link on the wrong side of the control horn. I was using the old sport flyer technique of setting the push rod up to be completely straight when the servo is centered. In 3D, you run so much throw that you want the push rod straight at maximum deflection. This is the best geometry for getting maximum mechanical advantage out of the linkage when using full throws.

Here, so can see we use the longest servo arms that come with the Hi Tec HS65MG servo, and maxxed out the end points. This is pretty close to bevel-to-bevel, and it feels just right to me.
Again, this looks just about like any other EXP, which is awesome because I know I can trust it, something that is really important on an elevator! Since I love big elevator throws, I used a Hi Tec HS85MG with the Dubro Heavy duty arm, and the ball link bolted to the second to the outside hole. With the end points maxxed, I am getting right at 88 degrees of up elevator. On the down side, I back off the end points so the control horn doesn't hit the bottom of the stab.

Here I used one of the double sided arms that comes with the HS65MG servo, put it on straight (if it doesn't center, flip it over and use the other side), and snipped off the unused arm. Like this and with the end points maxxed out, you get just about the right amount of throw.

Rates, Expo and CG
Like always, follow the manual. The Boss puts a lot of time nd effort into developing the right set up for all the EXPs, so take advantage of that. Odds are pretty good that you might tweak one of two things to suit your own preference, but there is no better place to start than the set up from the manual. Generally I run my low aileron rates on all my EXPs just a little slower than the manual, but everything else is right out of the book,
Power System Set Up
As always, nothing less than  Extreme Flight Torque Motors and Airboss Elite ESCs will do for any of my projects. This is the Torque 2814 motor and Airboss 45, which is the same set up I use on all my 48" EXPs. The motor bolts right up to the firewall and the cooling slots on the back of the motor align perfectly with the cooling holes in the firewall. This gives the motor exceptional, unrestricted cooling airflow into the front of the motor, straight through and out the backside, then through the firewall.

Radio Installation
I have always loved how The Boss has figured everything out for us. There's a little tray for the receiver, and when mounted there the aileron servos plug in with merely a 3" extension. This cuts down on the unnecessary spaghetti, and saves the weight of longer extensions.

As you can also see, the bulkheads have nice little openings to thread the wires through. This keeps them from slapping around as badly inside the fuselage during hard maneuvering. Some people dig the sound, and some don't.  The beauty here is that you get to choose.

Of course, everyone has their own favorite method of securing their antennas. I like to use translucent plastic tubing I get from my local hobby shop. I rough them up with an Emory board and then thick CA them into place. Let these set up over night so you don't glue your antenna into the tube!


I had a pretty good idea of what to expect from the yak and I was not surprised by what I got. I liked it right away. I did one pass to check the trims and then just started flying it.  As you'll see in the video, I was completely comfortable with the plane right from the start. A lot of this is confidence in Extreme Flight and The Boss' design work, but also, like all EXPs, the Yak is a reassuring airplane to fly. It is smooth and solid and it tells you that in no uncertain terms.

I figured it would be a lot like the Laser and Extra, and in a lot of ways it is. The big difference is that with the wing, stab and thrust all on one datum line, all the parts are on the same axis during rolls, snaps, spins and tumbles. In these sort of maneuvers it is very precise.

As you'll see in the video, slow and point rolls are really really crisp, and easy to get precise, in spite of the wind. It's all extremely axial, because of the central datum line.
The timing on snap maneuvers is a bit different and at first I had to be careful not to snap past where I wanted it to stop. This turned out to be more of a timing thing and after a few snap I had it figured out. The Yak seems to snap a bit more eagerly than the other EXPs, and when you hit the timing right it's pretty sweet.

The Yak is very predictable and nothing about it surprised me except it's willingness to snap roll on command. With the wing, stab and thrust all being on the same line, everything rolls, snaps, and spins  on the same axis, and while not being an enginner, I am guessing that's why the snap timing is a little different on this plane. Like I said on the blog, it's just something you adapt to.

This plane spins really nice, though I didn't try a flat spin yet.  In the typical 3D spin (with down elevator instead of up), the Yak comes down in an absolutely perfect straight line. It does that spin so nice that it's a little unnerving. I kept taking it out early because it was spinning so nice I thought it might get stuck, but it would stop instantly once I let off the sticks.

The Yak does a solid knife edge, though I am creeping up on getting them lower. I just wanted to get through the first day with the plane intact and video in the can.

Considering this plane has a big, round  fuselage and a slab sided front to the cowling, harrier was much better than I was expecting. I think I will just have to get used to holding the nose up a little higher and this plane will harrier as good as the other EXPs. It's just a matter of adapting to something different.
I'll hold off on more flying observations until I can get out on a calmer day. Today the wind was gusting from all directions, seeming all at once. Conditions were not good, but the Yak certainly handled them well enough.

Well worth noting is that I was comfortable flying the Yak hard right away. It has a very familiar feel to it, which makes sense because it's an EXP, after all.

Notable Products Used On this Project

Securing The Servo Extension Plugs
To hold my servo wire extensions together I normally use plain old heat shrink tubing, but for this project I was lucky enough to score some of Xander's Heat Shrink Servo Connector Safety Clamps. These are pre cut and fit perfectly. I like these because it saved me a step or two and it makes for a nice, neat installation ..... and by now blog readers know how I am about a nice, neat installation.
In the top picture,  you can see the servos and extensions, and the heat shrink safety clamps. In the second picture,  you can see the top connector is secured with Xander's clamps, whereas the bottom on is just plugged in and could perhaps pull apart in a violent maneuver. 
Sealing the Hinge Gap From there, I believe the most important thing you can do is seal your hinge gaps. One benefit of gap sealing is better control authority at slower speed, something you might think would be de rigueur for a slow speed sport like 3D.

Another benefit is that sealing stops the high speed bleeding of air pressure between the control and flight surfaces, which is a major contributor to catastrophic airframe failure due to high speed flutter. This is another one of these things you might imagine would be a de rigueur kind of deal for the high speed moves of an extreme aerobatic routine.

Some people like Blenderm tape, but I find that messy and it does not hold up real well. It also attracts dirt, something you don't really want clogging up your hinge line. Personally I have been using Clear Monokote for this task since the early 80s pylon racing days. It is completely invisible once installed, and will usually hold up fine for the lifetime of the aircraft.


For this project I acquired a set of Xander's pre-cut hinge gap seals, which are custom cut from clear Monokote. We knew this project was coming, so Xander cut them out and got them to me quickly.

They are the right length and width, so they just drop right it and all you do is seal them down with a trim iron. This will gratefully save me a few steps, which is critical on a time-sensitive project.

Insurance For Sloppy Builders Like Me
CA glue is wonderful stuff, but it is a bit like water in it's consistency. Even if you are an experienced builder, it is still very easy to get too much on one spot, or have it run where you don't want it to go, or just spill it and create a big mess, like gluing your shoes to the floor.

To combat this I have tried a lot of chemical CA debonders. A friend got a bottle of Golden Golden West Super Solvent for me from a local wood working store, but you can also get it at Tower Hobbies

If you do get a spill, quickly wipe up as much as you can. It is a lot easier to clean up a smeared spill than a big blob of dried CA. The solvent turns the CA into a sort of smeary gel, so it might take a few applications to get it off of covering, but the stuff does work miracles. I would be screwed without this stuff. I generally buy it five bottles at a time because the last good solvent I liked went out of business.

I've had huge spills that would have otherwise ruined an entire airplane, but cleaned it off with this solvent. If you get a big spill it's going to take some time to get it all off, but this is a lot better than having glue all over the plane.

CA fumes can leave a white film on covering, for instance, on the fuse and stab after you glue them together. One or two wipes of Golden West will usually knock that right off.

I try to build as carefully and cleanly as I can, but I still have little spills here and there, even on a good build. this stuff has saved me many, many times and I heartily recommend it.



  1. Nice blog Doc! Yak looks like it winds up good on KE spins and tumbles better than i expected a Yak to do.. WOOT

  2. Really nice blog too buddy well done!