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Aug 28, 2009, 11:39 PM
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motorhead's Avatar

42" EPP Yak-55 and Yak-54

If you guys have not seen the Leadfeather Yak-55 in the scratchbuilt forum you should check it out. It is an awsome light weight indoor flyer with F3P like flight.
EPP Yak55 (3 min 22 sec)

That was last winter. Now everyone is mainly flying outdoors and it only seemed natural to have a bigger one that has the same flight characteristics.
super beefy yak (5 min 14 sec)

As I finish setting up for production I want to build another one and document it here so you guys can ask questions about the build and all the info will be easily accessible.

Kit details:
All the EPP foam parts cut out.
The spar slot is precut.
The control surfaces are prebeveled
UPDATE 11-19-2010: The kits are currently being supplied with a full airfoil wing like my other 42" kits.
Reference the edge thread for the wing build:

Available in the hardware kit:
carbon spar tube
carbon tail stiffener


Needed to finish:
Paint: Airbrush, Krylon, ECT...
Glue: Welders, Hotglue, E6000, ECT...
Servos: 4 - HTX 900 , 9 gram.
Speed control: ~20 amp .
Battery: 3s, 1000 to 2000mah. Lighter is better.
Receiver: 4 channel min for dual aileron servos. (y-harness can be substituted)

Updated motor selection:
Turnigy 2410-12Y 1000kv, 10x4.7 or 11x4.7, needs prop saver and shaft shortened, mounts directly into stick mount.
Turnigy 2410-8 890kv, 10x4.7 or 11x4.7, needs prop saver and shaft shortened, mounts directly into stick mount.
2210n 1000kv, 10x4.7, needs prop saver, might be able to mount to 1" disk for stick mount with new holes.
20-22L, 10x4.7, needs prop saver and shaft reversed.

Feel free to ask questions.
I have reserved the next 4 posts to fill with the build to keep it at the front.
Below are pictures of the foam parts as they would come in the kit.
Last edited by motorhead; Jan 14, 2011 at 06:05 AM.
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Aug 28, 2009, 11:39 PM
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motorhead's Avatar
Step 1. Paint the foam parts. I went with a simple scheme but it should look good.
Step 1.5. For my kit to fit in a box the wing and wing KF doublers will be cut in half. Use Welders to glue them together.
Step 2. Glue in the spar. I used Welders and held it flat with some weights.
Step 3. Hinge ailerons and elevator with welders.
welders hinge (1 min 16 sec)

Step 4.1 I like to cut a slit about 1/2" long in the motor stick to make it easier to remove the motor if I have to later.
Step 4.2 Mark the center line of the front horizontal piece along with the motor and motor mount stick cutouts. My motor cutout is 1.25" wide x 1.5" long.
Step 4.3 Glue the motor stick into position with Welders.
Step 4.4 Glue all the horizontal parts together with welders.
Step 5. Glue (welders) in elevator stiffener. It is a 1/8" carbon tube 6" long in a v-groove that I cut in the bottom of the elevator.
Step 6. Mark the center line on the top and bottom for placement of the vertical fuselage pieces.
Step 7. Glue (3M 77) on the lower wing KF doubler. I sprayed a wet coating on the KF doubler and then pressed it onto the wing to transfer glue onto the wing with out having to deal with over spray. I took it off for a couple of minuets and then stuck it back into place.
Step 8. Use the same 3M 77 method as the KF doubler, glue the lower nose doublers onto the sides of the lower nose. Looking from the top down the left nose doubler is shorter than the right.
Step 9.1 Cut motor clearance in the front of the lower fuselage.
Step 9.2 Glue (welders) the lower fuselage onto the bottom of the horizontal assembly. The front is stiff due to the doublers. I used a strait edge to help place the back part and keep it strait.
Last edited by motorhead; Sep 07, 2009 at 02:30 PM.
Aug 28, 2009, 11:40 PM
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motorhead's Avatar
Step 10. Cut the holes for the servos but do not glue them in. I have the tail servos just behind the nose doubler and the ailerons servos are 3.5" out from the center. I have the aileron tabs sitting on top of the main wing. The top KF doubler will go over the top of them. Remember the spar is 1/2" in front of the aft side of the KF doubler. The aft of my servo is 1/4" in front of the spar so they do not hit.
Step 11. Using the wing KF glue method with 3M 77 glue on the bottom horizontal tail KF doubers.
Step 12. The left side stiffener is longer to match the different lengths of the nose doublers. Position the tail braces along the fuse. You will have to notch them for the horizontal KF doublers. To help keep from inducing a twist I like to lightly hold the braces in place and use hot glue. I put a 1/2" long swipe of glue every inch working both sides as I go from front to back. This is why the bottom of the plane is built flat on the board.
Step 13. Glue the servos in place with hot glue.
Step 14. Place the top wing KF doubler upside down behind the servos and mark the servo locations. Cut out the holes and check the KF doubler fit. I had to cut a little more out of one hole so the leading edges lined up.
Step 15. Glue the top wing KF doubler in place. After the glue tacked up I carefully aligned the KF doubler to the wing lightly pressing it into place to I could move it if needed. Once happy I placed the plane top side down on the work bench and pressed on the bottom KF doubler to lock the top one in place.
Step 16.1 Cut the motor cutout in the top vertical fuselage.
Step 16.2 Glue the upper fuselage in place with Welders. Again use a strait edge to make sure it is strait.
Step 17. Use Welders to glue the hinge for the vertical stab.
Last edited by motorhead; Sep 07, 2009 at 02:32 PM.
Aug 28, 2009, 11:41 PM
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motorhead's Avatar
Step 18. Use the 3M77 method to glue on the top horizontal tail KF doublers.
Step 19. With 1/16" ply make some control horns. These are 1.25" x .5".
Step 20. Make your pushrods.
Step 21. Mount the Motor, ESC, battery and receiver. My battery went towards the back of the nose doubler to get the CG at 4" behind the wing leading edge or at the aft edge of the wing KF doubler.
Last edited by motorhead; Jan 18, 2010 at 06:53 PM.
Aug 28, 2009, 11:42 PM
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motorhead's Avatar
Ready to fly.

Addendum #1:
Plane #1 had different lengths for the nose doublers and tail stiffeners to make room for the battery. I tried to make them the same on #2 but it allowed some additional tail twist so I have modified the plans back to having different lengths. I have revised the build info above to show this but some of the pictures may still show it incorrectly. See steps 8 & 12.

Addendum #2:
I changed from a ply motor mount disk to a plastic motor stick. See steps 4, 9 & 16.
Corrected the CG listed in step 21.

Last edited by motorhead; Jan 18, 2010 at 06:53 PM.
Aug 29, 2009, 01:48 AM
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pootman's Avatar
Cool, can't wait to see how she flies!!!
Aug 29, 2009, 06:42 AM
Righteous 87
Randidly's Avatar
Couple of questions
Is it built out of 1.3 or 1.9 EPP?
Are there going to be plans available?
How much is the kit.


Aug 29, 2009, 08:04 AM
Registered User
The link to the motor didn't work for me. What motor are you using? Watts, Kv?
Aug 29, 2009, 08:31 AM
Gravity gets me down.
helicow's Avatar
I believe the link motorhead meant to post is this:

Hacker Style Brushless Outrunner 20-22L

Motorhead - hope I did not step on your toes.

Looking forward to the build.

Aug 29, 2009, 08:44 AM
Sippin' on Kool Aid
Should be good. I have the smaller one (home build) and its awesome. I really would love a larger outdoor one
Aug 29, 2009, 09:48 AM
Registered User
motorhead's Avatar
I have fixed the link for the motor.
I am using 1.5lb EPP.
I will have plans done this next week.
Looks like the kit price will be $50.
It will be on my new web site on Monday.
Last edited by motorhead; Aug 29, 2009 at 05:18 PM.
Aug 29, 2009, 11:45 PM
Registered User
RJD1234's Avatar
MH - Does you big Yak have any tail twist? I know LF was going to look into this. I made a 36" version and added 4mm EPP in the rear fuselage area.
Aug 30, 2009, 12:05 AM
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motorhead's Avatar
With the addition of the KF to the horizontal and the angled fuse stiffeners it has virtually none. LF is interested in if the KF will help the 32" version.
Aug 30, 2009, 12:11 AM
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RJD1234's Avatar
Gotta. I will post some pics as soon as I can.
Aug 30, 2009, 01:49 AM
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jadamian75's Avatar
I am interested but would like to see a pre-painted version that comes with hardware. Or at least an option for it. Also where can welders adhesive be found.

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