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Dec 05, 2008, 11:41 PM
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EPPYak55 ... build guide, videos, free plans

One of the most durable planes I have ever built and flown is the SloFly 28...almost indestructible. One of the best flying indoor 3D kit planes I have seen and flown is the Fancy Foam Yak55M.

This plane is an attempt to get the best of both the SloFly and the FF Yak in one plane.

V1 started out as a copy of the Hobby Lobby Yak using epp. It flew, but had some issues, especially wing rock due to the change of material from depron to epp. Many, many changes later, the final version solidified. V2 maidened last night and flew very nicely.

The main changes from the HL Yak were deeper wing cord, wider profile fuselage, wider side fuselage, and a bigger rudder. By the time I was done not a single line was the same as the original.

EPP Yak55 (3 min 22 sec)

(7 min 33 sec)

Ben Fisher from 3D Hobby Shop flying the EPP Yak55 (4 min 28 sec)


Tonight Adreher did his magic using an airbrush and made a hunk of foam into a thing of beauty...thanks Adam!

VIDEO Original all 9mm epp build

Skinny Video Lighter build video

Plans of the original size Yak are in post #2

Plans for other sizes are in post #3

Build Guide

Center of gravity, cg

Kit Makers for the Yak.

Last edited by leadfeather; Jan 24, 2010 at 08:29 AM.
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Dec 05, 2008, 11:42 PM
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Plans original size (and best) 32.5"


Ken (dz1sfb) kindly generated the following plans for the EPPYak55. Thanks so much Ken!

The EZ tiled drawings have been tiled specifically to minimize and simplify joining tiles.

The non EZ files are the typical drawing types.

The plans were updated on Dec 22, 2008 with larger counter balanced ailerons, and a revised out for an easier flat build.

The plans have been modified slightly one more time, Feb 21. 2009. The aileron counterbalances have been changed slightly and the tail feather cutouts have been enlarged for more clearance.

The latest updates to the plans are from December 20, 2009. These small changes to increase the roll rate were originally done by and are available below for all the scratch builders.

As you read this thread you will see some newly coined terms. These are defined below:

The "standard" build is all 1.3#, 9mm EPP
The "skinny" build replaces some parts with 1.3#, 6mm EPP (details in plans); not as good as the "fluffy" yak.
The "super skinny" build is the milled EPP.
The "fluffy" build is 9mm 1# foam, this foam is hard to find.
The "Beefy" Yak is built with denser foam for outdoor flying.
All of these builds use the same plans.

Optional tail bracing plans:
Epp angle brace

Pilot art work:

32" cartoon Yak

22" and 36" cartoon Yak

Standard pilot

Build Guide

link to 42" EPPYak55 plans

42" EPPYak55 thread
Last edited by leadfeather; Dec 20, 2011 at 09:50 AM.
Dec 05, 2008, 11:43 PM
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Parts list and alternative size plans

Parts list for original 32.5" span size Yak

1 sheet 18 x 36 1.3# 9mm epp foam.
1/16" carbon rod for control rods.
1/32 music wire for control rod ends.
Sumo or equivalent glue
Welders glue

Here a list of hardware that can be used and the respective costs. make sure the components you chose are compatible with each other; especially motor and esc. For instance the Mag8 esc listed here will not work with the Hacker motor.

I would love to be able to find smaller/lighter stuff; especially servos; at comparable prices.

1) Cheapest, 24 gram motor, $8.95 ,

1.5) BW substitute

2) Mid $, 2204-14

3) More $,

Motor mount for 24 gram motor, Hi Model or Hobby City

Prop, $1.20, GWS 8x4 or GWS 8 x 4.3 available widely[/B]

Prop adapter if required, $1.99,

1) ESC for 24 gram motor, $11.95,
or HK supersimple $7.95

2) ESC for 2204-14, Scroll down the pageuntil you get to the motor and esc.

3) ESC for hacker,

1) cheapest Rudder and elevator Servos, $3.49 ea ,

2) mid $ servos, Eflight S60's,

3) high $ servos, Dymond D47,

Aileron servo

Reciever, $14,
Control horns 4ea, $1.25,
EZ connectors 4ea,

Fluffy foam 1 lb/cu ft: fluffy foam

Prop Saver Bands from West Michigan Parkflyers.

Parts I used on a very light 32.5" span indoor EPPYak55

Below are the Yak plans in different sizes:

Update: Indoorheli did an excellent job building a 22" Yak using 4site guts. A really outstanding build for those who want a smaller Yak for fying in really small spaces.

Also added August 24, 2009 Matt's "tabbed 36" plans"
Last edited by leadfeather; Dec 21, 2010 at 03:42 PM.
Dec 05, 2008, 11:45 PM
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Build photos (obsolete now, new flat build see build guide)

Build photos:

I did my best to design this plane to be very easy to put together. A picture is worth a thousand words so have a look at the photos showing the build sequence.

One of the things that surprised me in the development of this Yak is that the tail did not require any additional carbon or thread bracing...really simplifies the construction.

Note that the build method has been modified since this post and is detailed in the build guide linked in post #1.
Last edited by leadfeather; Sep 04, 2009 at 11:03 AM.
Dec 06, 2008, 08:28 AM
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Maiden flight

The maiden fight was a little unusual. The first flight(s) was hovering in my basement. All went well... several light crashes into walls and furniture but being built from epp, no damage to the plane. It hovered pretty good...wish I were better. I was using a 2s 360 battery.

I got brave and tried to fly a 360 around my basement. It worked, just a flat rudder turn 360. With a bit of practice I might be able to do more than one in a row. Don't try this at home kids. Mrs. Leadfeather was not home at the time.

The real maiden came Thursday evening. So far I am very happy with the flying qualities. The flight testing got cut short when a mid air collision nocke a control horn out.

The flight testing will resume today and video should be posted by the end of the day today.
Dec 06, 2008, 12:32 PM
Crash & Burn
rmgmag's Avatar
Looks really nice. I can't believe how well some people can paint!

I just started building a Slofly 28 with the hope of having a cheap fart around plane for me and my kids. I modified the profile a bit and I also changed the vertical fin and rudder to look something like my i3D. I was also toying with the idea of adding 90* braces to the fuselage sides like you did and similar to my Flash.

Other than the control rods, the wing spar, and the elevator, did you use any CF anyplace else?

Dec 06, 2008, 12:41 PM
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j2m2t2's Avatar
Next on my list to build.

My Gene Bond bluecore Yak is getting little beat up so this is a good time for this. Thanks
Dec 06, 2008, 04:30 PM
Zippy, Strong Like Bull!
Trouble Maker's Avatar
Yet another thread to subscibe to. I had the chance to see this fly today and it really looked stable and flew very well. Very light weight and durable. Another great build Dan.
Dec 06, 2008, 05:05 PM
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Flight video

Here is some video of the EppYak55 flying indoors. It still needs a bit of trimming and tuning...mostly cg, but I'm pretty happy with it. I'm especially pleased with how slow it can fly.

EPPYak55.wmv (3 min 4 sec)
Dec 06, 2008, 05:09 PM
Physics hate's my ideas
GreenAce92's Avatar
Ho! will you look at that... rolling harriers sweet! man its like a kite! lol so light!

thats awesome!
Dec 06, 2008, 05:35 PM
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Dunno what to say frankly..imo.. Mosquito like flight seems the most accurate descriptor though.
Dec 07, 2008, 07:21 AM
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Originally Posted by GreenAce92
Ho! will you look at that... rolling harriers sweet! man its like a kite! lol so light!

thats awesome!


Yep the lighter the better. With a lighter build the flight speed comes down. This makes the plane easier to fly because you have mortimeto think about which way to move the controls.

Also, with a lighter build, the required power comes way down, which allows the use of smaller battery, which in turn is one of the easiest ways to save more weight...which means you need less power etc. etc. At this point I could use a lighter motor and esc to save a little more weight.
Dec 07, 2008, 11:20 AM
Registered User
The Yak looks good! Any chance you could put up plans that are not tiled? I'm an engineer and have access to plotters that can print them full size. Thanks for a great design.
Dec 07, 2008, 12:33 PM
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Thank you, thank you, thank you.........exactly what I'm looking for
Dec 07, 2008, 01:10 PM
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Originally Posted by fxstbi
The Yak looks good! Any chance you could put up plans that are not tiled? I'm an engineer and have access to plotters that can print them full size. Thanks for a great design.

Here you go.

There will be few minor revisions to the plans but this should be fine for most builders.

The planned revisions are:

1) Reverse the aileron servo cutout so that the wires come out the back
2) Mark the cg location
3) Mark the recommended tail servo, esc and battery locations.

Right now the battery is just a bit forward of the cg. I like to have the battery right at the cg on my planes, this way I can use different size batteries with no trim changes.

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