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Great Planes - Yak 54 (25%)
Aircraft | Page-1 | Page-2 | Page-3 | Flight Log
Aircraft

This is a 25% sized airplane, so it will be my largest one yet. For single-wing aircraft, anything over a 80" wingspan is considered "Giant Scale". It will have a 5 HP gasoline engine.

Maiden flight coming Fall 2007 Summer 2008.
 

Quick Specs:
Wingspan: 81 inches (6 ft. - 9 in.)
Wing Area: 1138 sq. inches
Length: 68 inches
Engine: DL-50 (5.2hp - 50cc)
Servos: 164-333 oz-in @ 6V
Battery: 2 x 6.0v 2000 mAh NiMH
Radio: Futaba 6-EXAS / R138DP
Weight: 14-15 lbs.
Construct: Balsa, Lite-ply, MonoKote
Prop: Zinger 22-8 wood
Yak 54 - Stock Photo
Stock Video
 
12-15-2006 Acquired Great Planes Yak 54 (25%).
1-2007 Deciding on components and ordering some parts.
2-2007 Started building Yak 54. Installing aileron hinges.
3-2007 Installing rudder, horizontal stabilizer, and elevators.
6-2007 Installed elevator servos.
8-2007 Installed DL-50 engine.
9-2007 Installed throttle servo, ignition, and muffler.
11-2007 Put aside
3-2008 Working on final checklist to get plane finished.
 
Additional Components and Supplies

Engine: DL-50 (50cc) 5.2 hp @ 7500 rpm
Muffler: JTec DL-50 wrap-around Pitts style (custom)
Propeller: Zinger 22-8 Wood
Ignition Battery: 4.8v 2000mAh NiMH
Ignition Kill Switches:
MPi HD Switch (manual) / EMS Opto-Isolated Kill-Switch (radio)
Servos:
Elevator (2) Hitec HS-5645 MG HT 2BB Digital (164 oz-in torque @ 6V)
Ailerons (2) Hitec HS-5645 MG HT 2BB Digital
Rudder (1) Hitec HS-5955 Titanium Gear 2BB Digital (333 oz-in t. @ 6V)
Throttle (1) Futaba s3010 (90 oz-in torque @ 6V - .16 sec/60° @ 6V)
Choke (1) Futaba s3010
Radio Batteries:
Dual Setup (2) 6.0v 2000mAh NiMH / (2) EMS HD Switch w/ DSC
Servo Extensions:
(2) 24" Hobbico Pro. HD 20AWG (HCAM2721) Ailerons
(2) 24" Horizon Expert HD 20AWG (EXRA125) Elevators
(1) Horizon Expert 6" Y Harness w/ Reverser HD 20AWG (EXRA325)

Misc:
Dubro Gasoline-proof tank stopper (brown)
Brass tubing 1/8" O.D.
(5) Dubro brass fuel-line barbs 1/8" I.D.
3/32 I.D. Tygon fuel tubing (yellow)
Sullivan 2-56 Gold-N-Rod Semi-flexable Nylon Push-Rods
(2) Dubro 2-56 Ball-Links
Dubro 2-56: (1) Hex Cap Head screw, (7) Nylon Insert lock-nuts
Sullivan Giant Scale 8-32 Pull-Pull Rudder Assembly

Replaced (Substituted) Hardware
Ohio tail-wheel with 1.5" rubber wheel, Med. 10-18 lbs. (OHI120)
GraphTech carbon-fiber front landing gear #237(v.4d)

 

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Construction Details (Getting Started with Surfaces)

I basically just followed the manual, so I'm only going into detail on items that were additional or contrary to it.
 

Wings & Gluing Ailerons:

Test fit all 5 hinge points in wing with aileron all the way on (always keeping the hinge's slightly larger pin head to the wing's root side). With a small razor knife, I ended up making the top 1/16"-1/8" of some of the holes slightly squared, so that the hinges would insert down to the hinge's metal pin. Go slow and don't cut away to much where the hinge goes too far down. Operate the hinges back and forth to be sure the hinge point is installed perfectly perpendicular to the wing. Temporarily install aileron and check that it will move 2-1/2" in both directions (without binding) with about a 1/32" gap (thickness of 4-5 sheets of 24 lb. paper). The hinge gap should be the same all the way across. The hinge's metal pin should end up in the middle of the gap. The aileron's and wing's trailing edge should line up at neutral position, and there should be enough space (about 1/16") on both ends of the aileron so that it doesn't touch, rub, or bind with the wing itself.

Remove all 5 hinge points and apply petroleum jelly all around the moving hinge parts of the hinges (middle 5/16" ... so the epoxy won't stick there). Mix up some 30-minute epoxy and apply to the inside sides of the wing's 5 holes with a toothpick (down about 1-1/4"). If you get any epoxy on the outside of the wing, wipe it away with a paper towel soaked in rubbing alcohol. Apply epoxy to the 1-1/8" end of one side of the hinge and insert the hinge all the way down into hole. Repeat for other 4 hinges to complete this wing half. During the process (before glue sets), occasionally bend the hinges back and forth a little to make sure they are still perpendicular when seated. Reset all hinges to the middle. I let this dry for 2 hours.

Mix up a second batch of 30-minute epoxy. Apply to the aileron's 5 holes, and then to the second side of all 5 hinges. Reset all hinges to neutral and lay wing flat on table. Install aileron on wing, pressing all the way in place (down to 1/32" gap). Try not to scrape off the hinge point's epoxy on the way in.

Use a few pieces of masking tape to hold the wing in the middle neutral position and proper gap. Set completed wing aside to dry (with aileron pointing to ceiling).
 

 

Hinge Point Notes:

Work on one half (i.e. wing/aileron set) at a time.

The idea is to make the hinge gap as small as possible, but at the same time, allowing the surface to move all the way in both directions (even at 3D rates) without binding. The proper time to find the right gap is while you are test-fitting the parts together without glue.

Hinge points must be installed perfectly perpendicular or they will bind on themselves and eventually crack or break.

Use enough epoxy, but not so much that it pools-up on the outside of the holes (around or on the movable parts of the hinge point). The petroleum jelly might pool-up a little which is fine.

After the completed assembly dries for about 3 hours, take the tape off and operate the hinges to full deflection, and re-tape. After 8 hours, tug on the surface to make sure it is indeed glued in securely.

 

Aileron Servos

I tied the extension wire/servo wire connection together with dental floss before heat-shrink tubing. Pay close attention to the orientation of the servo. Be sure you can find the aileron's plywood mount for black control horn. For all servo and control horn screw holes use CA Hole Thread Procedure (also described in the manual). I ended up the cutting 4-40 metal control rods at 2-15/16". The rod should go all the way through the clevis barrel and extend about 1/8" on the inside before soldering. Follow manual's "Expert Tip" for a good solder joint. Be sure to use Silver Solder and not rosin-core solder (that's used for electronics). I used a hand-held hobby butane torch to get the wire hot enough to melt the silver solder. Apply light coat of 3-in-1 oil to prevent corrosion. These (and all the plane's similar) control rods will get a drop of blue Loctite on the clevis lock-nut (after final radio adjustments).

Gluing Rudder:

Follow the above directions to install the rudder. Everything is the same except make sure the rudder can deflect 4-1/2 inches in both directions (for me, basically same gap as above still worked). Use a couple of pieces of masking tape to hold in the middle neutral position, and proper gap. Let dry at least 8 hours.

Gluing Horizontal Stabilizer

Depending on where the hinge point holes were pre-drilled, you might also have a surprise after opening the slots for the horizontal stabilizer. I used the Dremel tool to carefully cut off the extra bit of hinge point so I could test-fit the h-stab. Stress this glue joint as little as possible.

Since there is not much surface area to glue the horizontal stabilizer to, I measured and cut a 1/8" thick piece of wood and epoxied in place. I put one piece in the middle, but you can also try two smaller pieces in the front and back instead.

Attach the wings and read the manual about measuring and finding the exact place to glue it in (while dry fit testing). Once I found it, I put some tiny dots on the h-stab in the front, back, top, and bottom to help me find this exact spot later. Also on my quest to make sure it's glued in really good, I opened the MonoKote on the bottom, to really coat the h-stab and mating surfaces good, and make a nice fillet of glue.

I also did the gluing a little differently. I applied a good coat of 30-minute epoxy to the exposed balsa on the top and bottom of the h-stab. Slide it into position, and try not to scrape off the epoxy on the way in. Then, move it around a bit to make sure glue transfers to the entire fuselage slot. Line it up to the tiny dot marks. Then mix up a second batch of epoxy and put in hobby syringe. From the outside, inject epoxy all around the h-stab/fuselage joint ... filling the gaps and making a nice fillet on the outside. Carefully turn plane upside down. Do the same on the inside. Be sure to get plenty along the sides, in the back, and under the additional wooden brace. You might even get creative and try to get some on the sides of the top part. Turn plane right side up.

Be sure it's still lined up to the tiny dot marks, measure with a string, and stand away and look at it like the manual says. Weight a tip of you need to. Let this dry for an 8 hours (checking periodically).

Gluing Elevators:

Follow the above directions to install the elevators. Everything is the same except make sure the rudder can deflect 3 inches in both directions (for me, basically same gap as above still worked). Use a couple of pieces of masking tape to hold in the middle neutral position, and proper gap. Let dry at least 8 hours.

 

 

 

 

 

 

 

Elevator Servos:

Basically, repeat the above aileron servo procedures (dental floss 24" extensions, CA Hole Thread Procedure for servos and control horns, find the control horn plywood mount under covering, proper soldering, etc.). I did notice that my actual elevator shape, and inner hinge point location were different from all the pictures on the box and in the manual. Others online have said the same. My solution was to install the horn directly over the hinge, with the screws straddling both sides of the hinge-point half. I cut my rods to 6-3/4" before soldering.

 

Continue to Page-2 of build...

 

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