Introduction


Wingspan:	68"
Wing Area:	920 sq. in.
Weight:	8-9.5 pounds
Length:	64"
Servos:	Hitec HS-5645 Digital
Transmitter:	Futaba 14MZ
Receiver:	Futaba R148DF
Battery:	2 Tanic 3650 5s packs wired in series for 10s1p
Motor:	Axi 5330/18
ESC:	Jeti 90 amp ESC
Manufacturer:	Extremeflight R/C
Available From:	Extremeflight R/C

Within the past couple of years, the Yak 54 airframe and the Extremeflight lineup have become two of the most popular in the R/C world. This review covers the electric conversion of their 68" Yak, one of their best sellers.

Here is a little info on the full scale Yak 54...."The Yak-54 is a two-seater sporting and aerobatic trainer designed for training sport pilots in aerobatic flights and for participating in aircraft aerobatic competitions. The Yak-54 is a single-engine monoplane of conventional mid-wing aerodynamic configuration with non-retractable tailwheel landing gear and tapered empennage. The aircraft is powered by the nine-cylinder M-14X engine of 360 h.p. The Yak-54 is characterized by high thrust to weight ratio and good maneuverability that provides for the full set of aerobatic maneuvers. The aircraft offers simplicity in operation and maintenance with minimum of ground equipment and could be widely used in air clubs. The cost of this aircraft is less than other aircraft of similar class with comparable flight performance."

Kit Contents

Every piece was well packed and wrapped in bubble wrap.

Included in the box was:

Lightweight built up balsa fuse and wing
Airfoiled tail surfaces
Painted carbon fiber landing gear
Carbon fiber wing tube
Painted fiberglass wheel pants
Complete hardware kit, in properly labeled packages, high quality Dubro products
Vinyl decal set
Matching painted fiberglass cowl

The hardware was very complete, high quality Dubro components. There was also an extra set of Metric hardware that the manual mentioned were included by mistake. It told me to throw some of it out but who can do that? Mine went in my spare parts box with all the other metric stuff. :)


The complete kit contents unwrapped.	The kit came with two sets of Dubro quality hardware! The manual mentioned the metric was included by mistake and to discard. I decided to keep it instead and store it in my spares box!

The labeled packages were a real plus. I've never seen an ARF do that before, it was most appreciated!

Assembly

The first thing I did, as with any ARF, was to go over everything with a covering iron. My kit did not have any major wrinkles but I noticed some after heating the covering.

CA hinges were used on everything; and properly installed, I have never had one fail. Some of the pre-cut slots were covered with covering but it was not a problem to find them as the manual gave exact measurements to where they were located! After cuttin


Servo openings cut open. There was not a pulling string in place, but none was needed due to large lightning holes.	Hinges installed, using pins to ensure they remain centered while curing.


Servo installed with a 6" extension. I made sure to use locktite on the threaded rod & nuts after I got the servo setup properly. I used the 1" aluminum arms that came with the Hitec servos and had the recommended throw on the ailerons with them.	There were 2 carbon locating dowels for each panel; here I have already roughed them up with 80 grit sandpaper prior to test fitting. I tested each dowel to ensure it reached to the next rib prior to gluing in place.

The locating dowels/antirotation pins installed in the wing.

Wing cutout...On each cutout, I left a 1/4" of covering and then folded it insidea nd ironed it down to ensure a tight seal.


Tail cutout -- I also ironed down a small edge here to keep the covering from peeling back.	After marking the stab's position on the fuselage, I "cut" the covering with soldering iron. This way there's no chance of an Xacto cutting into the wood and weakening the stab. (The stab's fit into the fuse was very tight -- great!)


Tail installed. I sealed the gaps on every surface using clear Ultracote.	Tailwheel closeup....The tailwheel was installed in the rudder before the hinges were glued by drilling a small hole in the front of the rudder for the tailwheel to stick into, then screwed to the bottom of the fuse.


I installed the provided Dubro control horns in the elevator halves and the Rudder pull-pull system. There was a small pilot hole in the hardpoints from the factory so all I had to do was drill it out the proper size and bolt the horns on.	Elevator control rod...Instead of the 4-40 all thread control rods I used 4-40 rods with a solder clevis on the end. This was just a personal preference as I like soldering control rods together. I used Dubro heavy duty control arms on the servos.


No problem getting lots of throw!	The rudder servo was mounted in the fuse and the pull-pull wires were routed out through the factory cutouts in the fuse.

Pull-Pull exits.

Motor installation

To mount the Axi 5330/18 motor, I made a mount out of some aluminum rods and sheet I got at the local hardware store a while back. There were mounts available that I could have bought, but I decided to go this route as it was a little cheaper & I had the aluminum already. The Jeti 90A ESC is rated for fourteen to thirty-two regular cells, or five to ten LiPo cells, at 90 amps and was a perfect match to the large Axi outrunner.


Finding center for the motor before drilling.	Motor mounted with 8-32 bolts from inside the firewall.


Spacing out the motor...the manual called for 3/4" in front of hte cowl to increase prop efficiency. (This is done on the full-scale yak as well!)	Another view

I soldered the JETI 90 amp ESC to the motor and mounted it on the side of the motor box with three screws.

UBEC wiring diagram...I also added a high voltage UBEC, wired to the ESC to power the radio components.


I added an air scoop to the top of the motor box to force cooling over the batteries.	The air scoop's front end.


I cut cooling air exits out the aft fuselage belly to allow air to escape.	The battery tray involved nothing more than gluing a couple hardwood pieces across the fuse and a lite ply tray cut out and epoxied to them. I also added a couple screws to make sure it wouldn't come loose.

Landing gear

I ordered a set of extended set of landing gear from TNT Landing gear, they gave plenty of clearance for the 20" prop. They were aluminum, but I used UltraCote paint and after a good cleaning with some acetone I painted them white. The wheelpants were installed with a 4-40 screw and I used some clear silicone to help hold them from rotating. The ARF's included tires were Dubro foam wheels and they were very flexible from side to side. On some landings I found that they rubbed against the wheelpant. Unfortunately these were the only wheels that would fit inside of the wheelpants...I tried to find some stronger ones but they were all too wide.


Taller gear	Wheelpant installed

Canopy mod

I modified the canopy to have 2 dowels in the front and then two 4-40 bolts in the rear. The original mount was four 4-40 bolts all the way around. I also glued in a stick of balsa across the two mounting lugs to strengthen it up.


Front dowels, notice cooling hole cut.	With canopy on and cooling scoop.

Balsa stick for strength

Cool bolts with rubber grommets included to mount canopy

Completion

The completed Yak 54 turned out beautifully. All up weight with the battery in place was right around 10lbs. I hooked the system up to a whattmeter and to my surprise the setup pulled 3,000 watts for a few seconds before settling down a little bit. Thats about 300 watts per pound! I thought that would suffice!!


The tanic packs fit nicely!	Tanic specifications. These are EXCELLENT batteries!

Flying

Every day that I took the Yak to the field, it seemed to be either cloudy or windy. Finally I got tired of it and flew anyway. The CG was perfect with the battery packs just behind the front former. The recommended CG range was from the front of the wing tube to 1/2" behind the wingtube, mine was right in the middle. I setup the control throws per the manual using the new Hangar 9 Incidence/control throw meter. The throws were setup as follows:

LowRates

Ailerons 15° both directions
Elevator 8° both directions
Rudder 15° both directions

High Rates

Ailerons 35-45° both directions
Elevator at least 45° both directions
Rudder As much as possible

Control throw meter

Taking Off and Landing

I set it on the runway and after doing a thorough range check with the throttle on and off I was ready to fly. I eased into the throttle and it took off with the expected tiny bit of rudder correction. About 1/4 throttle was all that was needed to takeoff and fly around, anything more was extra.

I did a few basic maneuvers to get a feel for the airplane and I could already tell it was a winner. The CG seemed to be a little bit noseheavy for my tastes but better that than tailheavy on a maiden flight.

Aerobatics/Special Flight Performance

This was what the Yak did best. Knife edge flight had almost no coupling and it tracked straight from one end of the runway to the other. Knife edge loops were no problem and didn't even require full rudder deflection.

Aileron rolls and point rolls were very crisp and it stopped rotating as soon as the sticks were centered. The roll rate on high rates was unbelievable, it was almost a blur it rolled so fast. The Hitec 5645 servos had plenty of power and the precise centering was very nice.

Snaps were pretty straight forward and they also stopped when I let go of the sticks, it had no tendency to over rotate. I did these on low rates most of the time.

Harriers and Elevators were equally as nice. I had some wing rocking in an Elevator but with a little spoileron mixing it went away and I was able to Elevator all the way to the runway if I wanted.


Ready to take off	Liftoff


After takeoff	Fly-by

The Yak did an awesome blender and transitioned into a inverted flat spin very nicely. The inverted flat spin could be slowed way down, and it almost seemed to hang there. This was a very violent maneuver so I made sure my wing and canopy bolts were tight.

Rolling circles could be stretched out over the whole flying field and the Yak looked very graceful while doing them.

The Axi provided more than enough power to hover. It pulled out of a hover with ease, and accelerated while doing it! With the large prop it performed torque rolls very easily. There was so much power after liftoff that I could point the nose straight up and it would accelerate while climbing!

A perfect Wall could be done and I found that a little spoileron mixing helped to keep it from snapping out.


Landing	Fly-By

Inverted

Flight Video

Downloads

Type	Name	Size
	The Yak 54 in Action	7.62 MB

Conclusion

The 68" Yak 54 is a great airplane, and I would recommend it highly. I am sorry to say that I have been informed by Chris Hinson at Extremeflight that, for now at least, these may no longer be available. However, he has lots of other great planes on his site at http://www.extremeflightrc.com for sale and they can all be converted to electric if you want them that way. I have seen the 87" version converted and it flew just as well as its gasoline counterpart. The parkflyer Yak also flies very well.