RA Cores Yak 55 Review

Whether it's flown for 3D or for sport, this compact model delivers some serious fun.

Splash

Introduction

RA Cores Yak 55
Wingspan:32" (813mm)
Approximate Wing Area:230 sq in (15 sq dm)
Flying Weight w/o Battery:6.3 oz. (180g)
Length:30.25" (768.35mm)
Construction:Laser cut 9mm EPP airframe; 3mm EPP nose and tail reinforcement panels; laser cut lite ply motor mount, aileron servo bellcrank, control horns and pushrod guides; steel and carbon fiber pushrod assemblies
Servos:One Hextronik HXT900 9g / 1.6kg / .12sec analog micro for the ailerons; two Hextronik HXT500 5g / .8kg / .10sec analog micros for the rudder and elevator
Transmitter:Hitec Optic 6 Sport 2.4GHz six-channel computerized aircraft
Receiver:Hitec Minima 6S 2.4GHz six-channel micro
Battery:Mad Dog 450mAh 3S 40C lithium polymer with JST connector and JST-XH balancing lead
Motor:Hextronik 24g brushless outrunner, 1300Kv
Propeller:GWS EP-8040 8x4 electric
ESC:Turnigy 10A brushless
Minimum Skill Level/Age:Intermediate/advanced; 14+
Manufacturer/Available From:Racores.com
Price (USD):$29.95 unpainted airframe only; $59.95 painted airframe only

A remarkable number of reviews begin here with some inspiration from the blogs here at RCGroups. This one began with a blog post from one of our users who also happens to be a manufacturer.

After reading the responses to the blog and viewing some of the embedded YouTube videos, I sent a private message to "Coreman," aka Jim Reith, owner of RA Cores out of Southbridge, Massachusetts and co-developer of the RA Cores Yak 55 in conjunction with RCG member "Leadfeather." Jim makes three, fully 3D and aerobatic profiler versions of the famous Yakovlev Yak-55 single-seat aerobatic aircraft. All are of the same basic design with a compact 32" (813mm) wingspan, differing in material and setup. Guidance will come in the guise of the fantastic Hitec Optic 6 Sport radio and Hitec Minima 6 mini receiver, both supplied by Hitec RCD in Poway, California. Hitec's Suzanne Lepine is my "go-to gal" for all things Hitec and, as luck would have it, she and Jim are well acquainted! Suz even refers to Jim as "Santa" and if one looks at his photo, it's easy to see why.

Mark Grohe of 2DogRC.com in Fayetteville, North Carolina was kind enough to supply two of his terrific Mad Dog 450mAh 3S 40C lipos for a previous review; they're a perfect match to the Yak 55.

I'll be reviewing the versatile, laser cut 9mm EPP version, suitable for flight both indoors and out. Also offered are a 6mm Depron version which weighs the same as the EPP model and a super-light 6mm EPP version. A 3mm Depron version is slated for release in the fall/winter of 2014-15.

Jim even offers two different completion kits with HobbyKing-sourced components; the choice of kits depends on the model. Another really useful offering is Beacon Foam-Tac glue and believe me, there is probably nothing better for assembling a foamie than Foam-Tac. I would highly recommend ordering a bottle when ordering one of these kits.

While I can speak from experience after assembling some small models with Foam-Tac, I learned that it can actually be used to hinge control surfaces on small models such as this.

I'm looking forward to trying this procedure for the first time, so it's time to get started!

Contents

Everything arrived nicely packaged:

The basic kit comes with:

  • Laser cut airframe part sheets
  • Carbon fiber and steel pushrod assemblies
  • Laser cut lite ply components

The completion kit adds:

  • 1300Kv brushless outrunner
  • One 9g aileron servo and two 5g elevator and rudder servos
  • 10A ESC with separate JST connector
  • GWS 8x4 electric propeller

Needed to assemble and complete the model are:

  • 2.4GHz computerized aircraft radio with micro receiver
  • Beacon Foam-Tac glue or equivalent, available through RA Cores
  • Medium foam-safe CA and kicker for pushrod assembly
  • 18" (45cm) cork-backed stainless steel ruler
  • X-Acto #11 hobby knife or equivalent with several new blades
  • Two optional Du-Bro mini EZ connector sets (#845)
  • Optional E-flite 2mm gold bullet connector set (EFLA248)
  • Self-adhesive hook-and-loop fastener
  • Small tie wraps
  • Basic soldering equipment
  • Small diameter shrink wrap tubing for the solder joints on the ESC's battery lead

RA Cores might be a small operation, but you wouldn't know it by the careful packaging. The airframe parts came in their own heat sealed bag, the hardware in another and the Foam-Tac by itself. All were taped to the bottom of the box and topped with newspaper to protect the contents.

The airframe parts themselves were cleanly laser cut and bore a nicely done digital paint job. The paint is lightly applied to save weight and as such, some areas of paint on my example rubbed off during assembly. There's a way to prevent the problem as I would soon learn.

It wasn't a problem with the paint at all but rather some outdated steps in the instructions. Jim emailed me to explain that he sprays very light coats of paint in order to save weight. The problem was not in the paint but rather the CA kicker. Even a small amount on one's fingers is enough to lift it.

And so it did:

Jim is updating his printed and online manuals to instruct the builder to use contact cement instead of CA and kicker; the CA should only be used when assembling the pushrods later on.

Should one wish to have some paints on hand to touch up their own model or to spray their own scheme on an unpainted Yak, RA Cores uses and recommends high-quality Createx airbrush colors available through Dick Blick Art Materials in Galesburg, Illinois.

Also nicely done were the various laser cut lite ply parts with no excessive scorching and which were easily punched out later without delaminating.

All in all, some terrific first impressions. Time to put everything together!

Assembly

Assembly begins with cutting the airframe parts from their sheets with an X-Acto. Beveling the hinge area of the ailerons and elevator are next with the aid of a new X-Acto blade and the 18" cork-backed ruler serving as a guide. The sharp blade made quick work of the task until it started tearing into the foam. Per the instructions, that's the time to switch to a new blade.

Hinging the elevator and ailerons are next and Jim recommends using the glue hinging method. Simply put, it involves running a thin bead of contact cement along the hinge points, witing a couple of minutes for the cement to begin to set and then joining the parts together. I admit that I was skeptical, but the method works amazingly well, resulting in a far stronger hinge than I would have imagined with virtually no weight penalty. A YouTube video (without sound) explains the procedure in greater detail:

welders hinge (1 min 16 sec)

The procedure worked so well that I had to slice some of the aileron hinges in order to free them up. After a 24-hour curing period, the hinges were at maximum strength.

The carbon fiber wing spar is glued in place on both sides with contact cement and not CA and kicker as might be instructed. It's recommended that wax paper or plastic wrap be used to protect the work surface from CA and kicker, not a bad idea with the use of contact cement.

From there, the nose/motor mount, central fuselage and elevator/stab assembly are glued together with contact cement, resulting in a sort of "outline" of a plane. A small strip of carbon fiber is supplied for use as optional reinforcements at the nose once cut in half with a rotary tool and cutoff wheel.

I wanted the airframe to be as stiff as possible, so I installed the strips which later proved their worth. RA Cores recommends painting the assembly and other parts of the unpainted version at this time.

Making the assembly easy was the "tab and slot" construction, resulting in a straight, true build.

The underside of the fuselage is next along with the thin 3mm EPP tail stiffeners. The fuselage is keyed for a perfect fit, but the stiffeners are not tabbed. Rather, they're glued in place with the aid of alignment holes punched in the wing and tail. One more, the Yak was coming together nice and straight.

Before the top half of the fuse is glued in place, the 9g aileron servo needs to be prepped with its wooden bellcrank glued to one of the control arms. The alignment holes in the bellcrank are keyed to match up with the arm provided with the Hextronik servo and a bit of CA joins the bellcrank to the arm.

One option I chose to do was the use of Du-Bro #845 micro EZ connectors at the bellcrank in lieu of the Z-bend used later during the pushrod assembly sequence. I did this after the servo and upper fuselage were installed, but I would install the EZ connectors first if I had it to do again. RA Cores suggests their use as an option as well.

Installing the upper fuselage, wooden motor mount, foam motor mount doublers, wooden aileron control horns and 3mm foam nose doublers complete the basic airframe less the rudder.

All the assembly to this halfway point was as simple as could be, aided by a clearly written manual and online photos.

Let's go to the home stretch!

Completion

It should be noted that one of the wooden control horns is not like the others and it's not easy to see why until one looks closer.

The manual is clear on this; the "oddball" has a slightly different outline designed to clear the CF spar of the elevator. All may glued in place with CA and kicker per the early manuals or with contact cement.

From here, the pushrods are assembled. They consist of .032 wire with Z-bends, some small pieces of shrink wrap tubing and carbon fiber rods. The CF aileron pushrods are cut to length with the cut off pieces saved for use as additional stabilizers for the tail in the same manner as the strips at the nose. A V-bend may be bent in one of the wires per the manual as a means of adjusting the pushrod, but since I opted for the EZ connectors, I cut off the Z-bends at one end so that I could insert the wires into the connectors.

The pushrods are assembled on the model, the shrink wrap tubing used as sleeves and both ends glued with CA. No need to shrink the tubing.

My optional method with the EZ connectors allowed me to remove the pushrod once I constructed it and to use a heat gun to shrink the tubing. Nice, strong and almost infinitely adjustable.

The rudder is beveled and hinged in the same manner as the ailerons and elevator at this time and the control horn glued in place; I was an old hand at glue hinges by now and the rudder turned out fine. I installed the cut off bits of carbon fiber as additional stiffening at the tail, again as an option per the manual and which really proved their worth later on.

Installing the rudder and elevator servos, building the pushrods with their wooden standoffs and final installation of the radio system, propeller and battery complete the Yak 55. Since I wanted to be able to either remove the motor or to easily swap wires in order to change direction, I soldered a set of E-flite 2mm bullet connectors to the motor and ESC before I installed the radio equipment. While I had the soldering iron out, I took a moment to solder the JST battery connector in place.

RA Cores gives a CG of on or slightly behind the wing spar. Fore and aft adjustment of the Mad Dog battery allowed for perfect balance on the spar. I wanted 100% control throw per Jim's recommendation, but doing so requires about 50% exponential per the manual when starting out.

Nothing left to do but to fly this baby.

Flying

With my friend Ken Alan behind his HD video camera at the grass covered parade grounds of Southwest Community Church in Indian Wells, the Yak 55 was ready to rock.

It launched effortlessly from my hand, but the ailerons were very twitchy in one direction. A quick landing later, the problem was found to be a tiny bit of foam preventing it from deflecting under load. Thanks to a hobby knife borrowed from another R/C pilot, the "field surgery" was a success.

Here's the Yak at the field just before its maiden flights:

Once back in the air and trimmed, the Yak was a fantastic flyer, able to take any manuever I cared to try. The 3mm foam tail stiffeners and additional carbon fiber reinforcement worked perfectly; there was no visible bending of the nose or tail whatsoever during rolls and turns.

I admit that I'm not the greatest 3D flyer in the world, but the Yak made me look like a real pro when I went to hang it on the prop. Had I adjusted the CG rearward a bit more, I would have done even better. Lots of rudder meant fantastic flat spins and the flat airfoils meant equally fantastic inverted flight, not to mention knife edge flight. Simply flying around the pattern with other models was a lot of fun. It isn't the fastest ship imaginable, but it's no slouch, either.

The power dropped off noticeably after about five minutes of near full throttle flight, so in it came. Landing was effortless and the O-ring used to attach the GWS prop did its job well by allowing the prop to deflect upon touchdown without breaking.

In went another battery for another five minutes of fun which was over all too soon.

Aerobatics and Special Flight Performance

If one can imagine it, the Yak 55 can do it:

  • Rolls
  • Loops, both inside and outside, not to mention Cuban Eights which I didn't try and Immelmanns which I did
  • Inverted flight
  • 3D
  • Knife edge
  • Split esses

Is This For a Beginner?

Sorry, but no. Although this model may be quickly and easily assembled, it absolutely requires a minimum of intermediate flying skill. This is no trainer; the Yak will not right itself and will easily fly in attitudes from which a beginner might not recover.

However, its light weight, relatively slow flying speeds and general ease of flight make it an excellent choice for someone looking to develop or perfect aerobatic maneuvers.

Flight Video Gallery

Here am I putting the Yak through its paces. This was as enjoyable a session of aerobatic flying as I can recall:

RA Cores Yak 55 - Reviewed for RCGroups.com (1 min 50 sec)

RA Cores has an entire YouTube channel dedicated to the Yak 55, found here.

Conclusion

The RA Cores Yak 55 is a winner, pure and simple. It's made right here in the USA, technical support is a close as an email to Jim Reith and assembly was fast, easy and fun. I even learned something:

Glue hinges are cool!

Two thumbs up just as high as I can give. The Yak 55 is already a favorite and it will be joining me for a lot of future flights over beautiful Indian Wells.

I cannot thank Jim Reith of RA Cores enough for supplying a sample of his fine work and for his technical assistance. Few of the vendors I'm privileged to work with here at RCGroups are as pleasant, friendly and helpful as Suzanne Lepine over at Hitec RCD. Those same kudos go to Mark Grohe of 2DogRC.com for cheerfully providing the flight batteries. No review is complete without RCG admin Angela Haglund acting as the conduit between we reviewers and you, our audience of R/C enthusiasts.

Thanks for visiting!

Pluses and Minuses

So many pluses:

  • Fantastic flight characteristics
  • Well made and well designed; quality is on par with the major manufacturers
  • Power system is a perfect match for the airframe
  • Several versions are available for both outdoor and indoor flying
  • Excellent instruction manual
  • Fun to assemble as well as to fly
  • Made in the USA

The only minus:

  • Outdated instructions directing the builder to use CA and kicker instead of contact cement in a number of steps; this has since been addressed
Last edited by DismayingObservation; Aug 16, 2014 at 04:37 PM..
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Aug 25, 2014, 09:55 AM
RIP Azarr - "Old age is not for sissies"
Azarr's Avatar
comments deleted - PM'd instead.

Azarr
Aug 25, 2014, 12:48 PM
Pronoun trouble...
DismayingObservation's Avatar
I have a correction to make and I thank Azarr for pointing it out.

Jim correctly pointed out that Leadfeather did the development along with input from RCGroups members. It would seem that I didn't make that clear and I thank Azarr once again for the help.
Aug 25, 2014, 07:36 PM
Kit Manufacturer
coreman's Avatar
Quote:
Originally Posted by DismayingObservation View Post
I have a correction to make and I thank Azarr for pointing it out.

Jim correctly pointed out that Leadfeather did the development along with input from RCGroups members. It would seem that I didn't make that clear and I thank Azarr once again for the help.
Yes, this is Dan/Leadfeather's design. I did a few tweaks to the kit as part of the packaging and assembling but the flight performance is thanks to leadfeather's wonderful design

The tweaks I added include: (step numbers for our online version of the instructions are at the end)

1) Nose doublers made of 3mm EPP to reinforce the nose where it gets beat up on landings (step 22)
2) 3mm EPP reinforcements to keep the tail from twisting (this is a suggestion that surfaced in the Yak build thread (step 16)
3) a pseudo tail wheel to prevent landings from snagging the rudder and tearing the hinges (visible in step 28)
4> quarter round EPP gussets reinforcing a plywood motor mount (step 21)

These steps were added over time having seen the places typically damaged and improves the durability
Latest blog entry: BluFO review by Jim T Graham


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