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3D 3DHS/Extreme Flight Family - 91" Yak 55 - Black

Discussion in 'Giant / Scale Scratch and Kit Build Threads' started by Lojik, May 17, 2015.

  1. Hi all,

    I want to document the ARF build of my 91 Yak, This is my first Yak, first large 3DHS model and first DA engine so kinda excited for this build.

    Some details below taken from the manufactures website about the model:

    Winspan: 91"
    Length: 86.5" prop to tail
    Wing Area: 1425 Sq. Inches
    Weight 17-20 lbs.

    The 91" Yak is great-looking model of the dramatic Yak-55M, a world-champion aerobatic aircraft.

    The 91" Yak has all of the features you have come to expect from a 3DHS 50-60CC ARF - Carbon wing and stab tubes, genuine Ultracote/Oracover material, premium-grade balsa and ply, molded carbon landing gear, aluminum-center lightweight wheels, spring tail-wheel, composite and aluminum reinforced landing gear mount, composite control horns with HD ball links, aluminum-reinforced motor box, pre-hinged surfaces, and wing and stab bags.

    The Yak adds some new features, including differential-drag wing tips. You can select the type of wingtip arrangement you want, for more or less yaw stability, as suits your style of flying.

    The Yak 55M has the ability to rotate in yaw with authority, giving high rotation rate to gyroscopic maneuvers - this equal wild stunts like insane pop-tops. The specially-developed fuselage profile gives excellent post-stall stability for easy harrier. The reduced girth of the fuselage and low-drag airfoil profile give the Yak a very wide speed range, making an excellent dual purpose precision and 3D hucking machine.

    Because of its large control surfaces and wide speed range, we recommend only the best servos for the Yak 55. Minimally, you will need a digital metal gear servo with at least 250 oz-inches of torque for each of the 5 servo locations. For best performance, 290 or more oz-inches of torque is recommended. The 333 oz-in Hitec 7955-TG or 7954SH are excellent choices. For the best possible performance, consider the Hitec HSB-9370TH Brushless servo.

    For this build I will putting the below into the aircraft:
    Engine: DA70 - Jtec Mufflers
    Servos: PilotRC Servos on all surfaces - I know its a little lower than recommended but I'm not a high energy guy, prefer slow and smooth so I think they will be ok
    Throttle Servo: HS5565MH or Savox alternative depends what I have on shelf
    Power Distribution: BoomaRC Power Bus 824 from AR
    Power: 2 x 2600mah BoomaRC LifePO4 Packs
    Ignition Power: Tech Aero Ultra Ibec
    Tank: Fourtitude 32oz Tank - yer i know i can go 16 but I prefer the 32 for convenience of longer flights and not to worry on fuel.
    Epoxy: Selleys Araldite for general epoxy work, Loctite Hysol 9462 for High stress areas

    Plan is to have this beast in the air in 2-3 weeks, I work long hours and can only work a little at a time, plus its winter here so not much opportunity to fly just yet

    Some Vids of the plane:

    Attached Files:

    djmoose likes this.
  2. I'll follow along, congrats on your new acquisition!
    not ruthless likes this.
  3. Well, I've started... I don't build fast, sorry, kinda work too long hours, but I am planning to get the servo's all done this weekend and maybe even start the firewall and engine mounting, some pics below, will try to get more done as I go

    So far:
    Kit is the usual 3DHS quality, gear is all usable, nothing I can see that makes me feel at unease
    The canopy decking on the fuse side is a little flimsy for my overly large man handling so I am going to glue some spruce strips in places that will stiffen that up, this isn't a mod for overall strength just more to stop unwanted splitting in the plywood due to my general clumsiness :)

    Just for personal preference and my own comfort I am going to hysol another plywood plate onto the firewall for the DA70, I know it would probably survive without it but our heavy model inspectors here are pretty strict on firewall thickness for engine size and the stock thickness is too small for a 70 twin in au, should be an easy mod, just remove the screws, trace or mark the center lines onto the new plate then hysol and screw it back in place, little bit of stock on the top and bottom and it should be sweet as for the DA70, with that much power on tap I highly doubt a few 100g's of extra strength will hurt

    I started on the control horns for all surfaces today, everything went in super smooth, only the rudder needed a tad bit of filling to get a smooth entry, everything lined up perfectly and is currently drying, will take some shots tomorrow of the completed horns

    I am going to do my trademark thing on the canopy, spray paint it :D - I will post some comparison shots when its done but will let the color be a surprise.

    Will try and keep the thread updated as I go, so far so good.

    Attached Files:

  4. toysforbigboys

    toysforbigboys 70cc twin V2

    You are going to Love this plane once you get it flying. I have one and it is a dream. With the DA70 on it, it is going to be a beast.
  5. jhelber08

    jhelber08 70cc twin V2

    Interested in this build. I was able to pick one of these up at a fly in for just a smidge above half price and its been sitting in my attic ever since. I'm tempted to put it together as I have everything but an engine and the space to keep it once its complete but right now its just sitting there waiting for my edge to bite the dust.
    toysforbigboys likes this.

  6. toysforbigboys

    toysforbigboys 70cc twin V2

    and you just got 5 new servos that you could use for the Yak.. :yesss:
  7. jhelber08

    jhelber08 70cc twin V2

    Yup!!! Those are probably going to go into my 88" edge though. I did just have a thought, and don't know why I haven't thought of it until now, but I have a 72" 3dhs extra that I could sell to purchase a DA70 and then bam, id have money for the engine and a place to put the plane...hmmm
    toysforbigboys likes this.
  8. 49dimes

    49dimes Damn I'm hungry

    That's me! Rob peter to pay Paul. Sub'd.
  9. jhelber08

    jhelber08 70cc twin V2

    Dang you for starting this thread, now I really want to sell that little 30cc and put this one together. Promised my wife no more planes this year and technically I already had it right? Technically I would be getting rid of one right and just be getting a new motor right? :angel: This guy says you don't need it but :devil: this guy says do it.
    ChickenBalls likes this.
  10. The 91" Yak is fun... do it!

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