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Thursday, April 9, 2015

Yak EXP__Tales Of The Big Dog

After writing Picking The Perfect 60" EXP I wanted a little bit of a break from writing, shooting and editing video. I was not actually planning to do another article of any sort, at least for the rest of the month, but we got so much great Yak footage yesterday that writing a little something around all that would be pretty easy. Of course, everything I plan seems to start off small and grow into a monster, so I guess we had better get started.

The Mix
As you may have read in other recent articles, I have been experimenting with a 25% spoileron mix. I have been flipping this on and off depending on what I want to do, but the Yak spends so much time in alpha that I usually leave it on all the time except for when I do my precision work.

It's been great fun and with the ailerons spoiling lift any time you pull the nose up, it's really easy to just drop her right down into 3D and start hucking. Because the spoilerons keep the lift spoiled, the wing does not start flying again as easily, and this absolutely kills any unwanted wing rock dead in it's tracks. The Yak doesn't have much to start with unless you get really sloppy with your flying, but with the mix this plane harriers about as well as the 60" Edge. In fact, I am rethinking my stance on whether the Edge is still the undisputed easiest of the 60" EXPs to fly. The Yak is right there with it, plus it might be a little more agile on top of it.

This was a warm up video, but pay attention to the elevator drops. The plane is still moving forward a bit instead of dropping like a stone. I'll explain why that is important in the next section.

The Final Tweak
All this time I thought I had the Yak pretty well dialed in. I put the battery about two inches from the wing tube and just flew it. I have about 25 flights on the plane and never moved it, simply because was so happy with it right from the beginning. The plane is so solid and dead locked in that it never occurred to me to change anything.

When shooting the first video, I noticed that with the spoileron mix that the plane was not dropping dead straight down, indicating that I might still be a little nose heavy. I did not pick this up at any other time flying the plane, including the usual roll-to-inverted and 45 degree up line tests. I probably missed this before because I had never flown the plane in anything but ripping winds. This time it was really calm with nothing to hold the plane back.

I was already so happy with the plane that I was loathe to change anything just to improve one aspect of flight, but I moved the battery thinking I could always move it back. Today's 3D airframes are not nearly as critical as the early 90s aerobatic planes that would snap into a spin and screw themselves into the ground if you got them a little tail heavy, so there was not much risk in trying.

I turned the battery around so the balance taps were forward, where they would not get caught up in my receiver and wires, and pushed it all the way back against the spar. This was a pretty big adjustment. I could have crept up on it instead, but we had clouds across the sun, which makes for most excellent video shooting conditions, and I did not want to waste any of that. This is as tail heavy as you can make the plane without adding any weight, but I have been known to do that too if need be.

I was delighted with the plane instantly. Now it came completely alive. The agility about doubled without giving up any stability at all. Now in an elevator the plane drops straight down like a rock. Completely insane.

Now check the elevator drop at about 2:20 of this video. You can clearly see how big of a difference moving the pack made. It is small adjustments like this that turns a really good airplane into a jolly damm great one.

With each succeeding pack, I became more and more confident until it was getting too crazy and we simply had to quit before I did something really stupid and killed the plane. It's been awhile since I felt totally invincible with a plane, but the Yak certain makes me feel that way.
I also think this plane is helping me improve my game all the way around. While my rollers are still a bit (ok, a lot) sloppy, at least they are starting to come around and look like sloppy rollers instead of mindless flopping around!

I think this is probably my favorite video from the day. I make a big mistake and almost killed the plane, so then I have to make up for it and the rest of the flight was pretty fair. That, and it was just simply a fun flight.

In the end, I don't think any of is are doing this for anything but fun, and this underlines how important it is to get the right plane and get it set up properly. I loved the Yak before I moved the battery, but now we have gone to the next level, so never forget that set up is everything. You can make bad plane better with a good set up, and you can turn an excellent plane into a nigthtmare (or worse) with a bad set up. 
The Big Dog
Some may wonder where all these dog differences are coming from. It took a few flights to trust the Yak's stability because it was simply too much to believe. You know, too good to be true. Once I fully understood what I had, I pushed harder and harder until the Yak reminded me of a big, friendly, obedient, giant, flying standard Poodle that happily does whatever it can to please it's master. Perhaps that's an overly enthusiastic characterization, but the videos don't lie. It is truly as easy as it looks, though admittedly it doesn't look as easy as one of Jase's Yak videos. 

I plan to do a lot more with the Yak in upcoming months, and will probably even build a 60" Russian Thunder. This has been an amazing project so far and it has really opened my eyes to a lot of things, including a different way of flying. I do believe the Yak has helped me up my game, and I really want to keep that going.
Reviewing The Equipment Set Up
My friend Dan posted one of these videos on Facebook and that generated some interest in my set up.  So, for all my facebook friends, here it is.

Extreme Flight strongly recommends the use of Hitec 7245MH servos for the Yak, but at the time I built this plane I was scratching pennies together to make it happen. This was a turn-the-couch-upside-down-and-shake-out-the-change kind of project. I almost had to go to the field and sell pencils to make this plane happen! The plane became available at the worst possible financial moment. All the co-payments from this summer's hospital misadventure (which is being charatible) came in the week before, to the tune of about $3000 that I did not have. I had to use what I already had on the shelf.  I took the entire set up of Hitec HS5245MG servos straight out of my red MXS, with the ball links even still connected to the servo arms, and dropped them into the Yak.

Also part of the set up was a trusty Torque 4016/500 Mk II motor and Airboss 80 Elite ESC. To me, all Torque motors are interchangeable, simply because they are so bulletproof. Even one that's been beaten for three or four years is every bit as good as a new one, and the same with an Airboss ESC. This power system is the one bit of used equipment I will confidently put into a brand new plane and not even think twice about. As you can see, it works.

The beauty of coupling this power system with the HS5245MG servos is that those servos run straight off 6 volt of current delivered by the Airboss and it's on-board BEC. There is no need for a separate BEC, it's extra wiring solder joints and potential failure points.

This is a nice, simple set up. You just plug everything in and go. If you are going to hammer a plane every day, you have just got to keep things simple and tidy.

The 5245MG is the exact same size as the HS7245MH, right down to the matching mounting holes. I can drop in 7245MHs any time I please, but the plane is fly so extraordinarily well that I am loathe to change even a single thing. I am almost even afraid to clean the plane for fear of wiping off some of the magic!

Last year I had a few servo arm issues, so I switched to Hitec's PN55709 pack. These are fiber filled nylon and stay tight on the splines, assuring a solid, slop free connection. One thing I have since done differently has been to change to 2..6 X 8MM allen head bolts to secure the arms to the servos (which I get from Micro Fasteners). The arms are very solid and don't compress much, so you have to stay on top of keeping the bolts tight. You can either locktite the bolts (which makes a mess) or crank them down good with an allen driver. The Phillips head that come with the servos can round off unless you have exactly the right screwdriver, but the allens won't.

Click to Enlarge

If you follow the mechanical set up in the pictures, and set your end points at 140% (all I can get with my Futaba 7C), this will give you the exact same plane that I am flying. I run -75% (remember, Futaba is negative) on all high rates, and run the low rate from the manual. All of this is extremely simple and easy to remember, so I use it on all of my planes. I do not dink around with running different amounts of expo on different surfaces or try to get tricky. I took the set up from the manual years ago and simply learned how to fly it. I figured the guy who designed the plane has a better handle on how to set it up than I do, so the manual is the best place to start.

Set up with this equipment, there is next to no maintenance and absolutely no problems or complications. It is all extremely simple, which is a keystone to reliability. I will be able to fly this plane absolutely every day this year, beat it hard, and not worry about anything coming apart. Of course, you have to check things every so often, and I like to tighten the allen bolts on the servo arms at the beginning of every day at the field. Outside of that, all that is left to do is simply fly it.

Last Gasp for the HS5245MG?
Uhhh, no. This is still a fine medium priced servo, and as you can see, I get good performance out of them. They do have a few issues that could be better, but on balance they are about half the price of a wunder servo. For those on a budget, this remains a viable servo. It works..... just not as well as an HS7245MH.

The downside is that these servos don't have the speed, torque and laser-like centering of the more expensive Hitec HS7245MH servos. This does not make the HS5245MG a bad servo by any stretch of the imagination.  It';s just not a high dollar wunder servo.

I can get away with this on the Yak because it is not really a fast plane. The big, flat cowling is a lot of drag, and as a result it is much more fun to fly the plane around in alpha, hover and harrier it back and forth, and generally treat it like a big foamy. You don't need enough Torque to sink the Bismark for this kind of flying.

The upside is that for most pilots this is going to be enough servo for the Yak. You are going to lose a little authority in wide open snaps, tumbles and such, but then again, if you want to wind the airframe up that much you are probably better off with an MXS. while the yak does everything beautifully, I love it best for post stall flight. This is much less demanding of the servos and the HS5245MGs are still fine with this kind of flying.

Still, as you can see, the plane performs brilliantly, and you will spend about $100 less on these servos, plus another $25 less because you don't have to buy a separate BEC. With the less expensive servos you will give up some torque and speed, but I think only the guys who are really hammering the planes hard will be able to tell that kind of difference.

I am sure the plane would fly better with the Hitec 7245MH servos, but the money just wasn't there at the time I built the plane. As it is, I want to build another Yak, only this time I want it to be the 60" Russian Thunder. I will definitely pick up some HS7245MH for that plane.

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