DW Foamies Yak Junior Build Thread - RC Groups
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Apr 07, 2008, 07:44 PM
I used to be all thumbs...
NumbSkull's Avatar

DW Foamies Yak Junior Build Thread

For those that haven't had the opportunity to experience what DW Foamies has to offer, then you're missing out. DW Foamies has something for just about everyone, from 28" Junior models all the way up to their 55" BAF models.

There's a handful of threads already on RCG, but not much has been said about the Junior models. DWF currently offers a Yak Jr. and a Gen-X Jr. The Yak Jr. is perfect for all out 3D both inside the gym and in your back yard, while the Gen-X Jr. is just right for practicing your pattern routine in small or limited space.

When I first saw the Yak Jr. I knew I had to have one. After talking with Mike from DWF for a few minutes, my box was on it's way with a handful of DW Foamie models. The first to go together was the Yak Jr.

When my box arrived I was pleased to see that a well packed kit CNC cut kit. All the carbon was included, and a nice ply motor mount was also included. The kit was cut extremely well and the parts are all tabbed for a key fit. I like to "dry fit" the model before I start to build it, and the model locked together nice and solid. If it weren't for hinging, I could have put some glue on the joints right then, and been done with the build.

Thanks to a low parts count, and the nice keyed fits, these kits build fast!! You can easily build one of these in an evening without breaking a sweat.
Last edited by NumbSkull; Apr 10, 2008 at 09:40 AM.
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Apr 07, 2008, 08:01 PM
I used to be all thumbs...
NumbSkull's Avatar
The first step is to clean up the edge of the foam with a bit of sand paper or an exacto. The CNC process leaves small tabs that might cause the parts to not line up just right. This takes only a minute and really helps make the models joints tight.

After the edges are clean, it's time to hinge. There are many ways to cut a bevel, Some involve sandpaper, others use exactos and straight edges. I like to just use a sharp #11 exacto, and freehand cut the bevel. In order to achieve full throws on this model, both edges of the control surface will need to be beveled. For the elevator and rudder, bevel the fuse's edge to 45 degrees, and the control surfaces edge to 10 degrees. The ailerons get 45 degrees and the wing where the ailerons attach get 10 degrees.

While you've got the exacto handy, it's time to cut the slot for the spar on the wing. Measure back 2 1/2 inches from the leading edge of the wing, and using a long ruler or straight edge, make a 24" cut down the center of the wing. I used a steal yard stick, and measured it's distance from the back side of the wing at the tips to make sure I have the spar's cut straight.

Once you have the slot cut, slide in the supplied 24" 1mm x 3mm carbon flat, and then simply cover the slit with tape on both sides. I used 1/2 inch blenderm for this. Blenderm sticks to the foam extremely well, yet it's flexible to keep from ripping should the wing flex.

Now it's time to hinge the surfaces. I again used 1/2 inch blenderm for my hinges. In the typical hinging fashion. I lined up the two surfaces with a small gap in between, and then applied a strip of tape to the top sides of the gap. Then turning the surfaces over, and letting the control surface hang over the edge of my work table, I then applied a strip of blenderm to the underside (now facing up) making sure to allow the tape to join the tape from the other side for a nice solid hinge. Small strips of tape could have been used in a few places along the surface to save weight instead of fully taping the entire hinge, however, I plan to fly this plane both inside and out, and with the way I tend to fly... the extra strength is worth the weight..
Last edited by NumbSkull; Apr 10, 2008 at 09:42 AM.
Apr 07, 2008, 08:15 PM
Xpress..'s Avatar
You will find this plane a joy to fly. Mike has taken time and built a plane that flies great, and performs above other manufacturers.

Sofar, it looks smooth.

For hingins, even just a strip ontop would have held very well. Blenderm doesn't give out easily, so you will be fine with just a strip ontop. Even on the 38" models, I've gotten away with one strip, and it has held very well.
Apr 07, 2008, 08:19 PM
I used to be all thumbs...
NumbSkull's Avatar
Now it's time to start the assembly. We begin by installing the horizontal fuse into the upper vertical fuse WITHOUT glue. Alignment is extremely simple thanks to the keyed fittings.

Next (still no glue) we set the wing in place. The leading and tailing edge of the wing have key slots cut into them to make alignment a snap. To set the wing in place, we slide key on the wing's leading edge into its slot on the fuse.

Still not adding glue, we will now add the vertical fuse keel to the bottom of the model. The fuse keel meets the upper fuse in two location that are precision cut for a nice tight fit. At this time, we will glue these two joints together, and no other joints.

The fuse's alignment is aided with the help of the motor mount. A ply mount is provided with the kit and has a foam back that needs to be glued to the ply mount. Simply add glue, and line up the foam and ply mount. I used Foam Safe CA applied to the depron backing, and shot the ply with a little kicker, and then stuck them together. I had planned to use a Hacker A10-15S on the model, and the Hacker has a lock nut on the back of the motor that needed a hole cut in the center of the mount to allow for clearance, so before I glued in the mount, I drilled the center of the mount for clearance. I also took this opertunity to drill pilot holes for the cross mount of the motor.

Now insert the motor mount into the recessed front of the kit. It's always best to test fit before you glue this in place. After checking fit, apply a little glue and set it in place.
Apr 07, 2008, 08:26 PM
I used to be all thumbs...
NumbSkull's Avatar
With the motor mount installed, the front of the model is nice and straight, check the rest of the model for alignment and fit, and once your happy, it's time to apply glue down the intersections of the fuse. Again, I used foam safe CA and a little kicker, just run a quick bead down the fuse, and a spritz of kicker and it's ready. The manual warns NOT to glue the leading edge of the wing to the fuse as it will cause a hard point at which the plane might break. This is great advice for all foam models, and might just save your model in a crash.

Next, the instructions suggest to install the motor. If you took the time to pre-drill the motor mount before installing it, then this step is a snap. Just set the motor up to the mount, and insert screws. I like to solder my spread controller to the motor on smaller models to save a little weight, so I did this before installing the motor. The suggested motor for this model is a Park 250. I chose a Hacker A10-15S over the 250 simply because I had one available (and I wanted to use the park 250 on the Gen-X Jr... ).
Apr 07, 2008, 08:36 PM
I used to be all thumbs...
NumbSkull's Avatar
Now it's time to install the wing struts. The kit is supplied with a few lengths of small 1mm carbon rod. Using an exacto knife and rolling the carbon under the sharp edge of the blade, score the carbon until it cuts or until you can easily break it to make four, eight inch lengths of carbon. These will be used for the wing struts.

Make a small hole near the bottom edge of the fuse at about the center cord of the wing. This will be where all four lengths of carbon will meet. I used a piece of the eight inch carbon inserted through the hole in the fuse to mark two locations on each wing, one near the leading edge, and one near the hinge. I used an exacto knife to make a very small slit for the carbon to sit in. You can also just take the carbon and press it through the depron, but sometimes it could cause the foam to tear.

Now insert all four carbon rods and glue them into place. After you glue the rods, cut two small wedges of foam, and insert and glue them into the V made where the two carbon rods for each wing join at the fuse.
Apr 07, 2008, 08:50 PM
I used to be all thumbs...
NumbSkull's Avatar
Next is the radio installation. The kit supplies all the needed carbon for the linkage, heat shrink for the joints, and well as Spider Wire for the pull pulls.

The instructions go into detail about how to create long servo arms for servos that might not have very long arms. I am using JR S185 servos on my Yak Jr. and they come with extremely long arms, so I will vary from the instructions a little here.

The kit includes depron "wedges" to be used with 1 1/2 inch lengths of carbon to create the control horns for the surfaces. Cut two of the foam wedges from the small sheet, and cut two 1 1/2 lengths of carbon using the method mentioned earlier in this thread.

Glue the carbon to the flat side of the wedge, making sure that the carbon and wedge are centered with each other. Insert and glue one of these horns into the cut out on the rudder and the other into the elevator. Make sure that these are centered with the surface, and the carbon rod is at a 90 degree angle to the surface.

Next, cut a third wedge from the sheet. I then cut this wedge in half and cut two 3/4 inch lengths of carbon. Now glue the 3/4 inch carbon to the half wedge, lining up the side you cut with the end of the carbon so it looks like one of the pull pull horns that was has been cut in half.

Inert each of these into the holes on the ailerons with the carbon rod horn on the bottom side of the wing. I tilted these forward so that the end of the carbon rod lined up with the hinge.
Apr 07, 2008, 09:05 PM
I used to be all thumbs...
NumbSkull's Avatar
Now that we have the control horns installed, it's time to install our servos. We will begin with the aileron servo. Start by cutting a hole in the fuse keel just large enough for your servo to fit in, and clearance for your servo horn. The hole should be about 1/2 - 3/4 inch behind the leading edge of the wing.

For simplicity, it's best to attach the connecting rods to your servo before installing the servo. It's better to have the rod to long then two short. Eyeball the length of rod needed, and then add just a little more to be safe. Remember, you can always cut more off, but you cat add to it once it's been cut. (My 6th grade shop teacher would be proud of my for remembering that...).

The kit supplied some nice quality heat shrink that is just the right size for the supplied carbon rod. Since I used the horns supplied with my servos, I needed to "bridge" the gap of the heat shrink to make a tight fit, so I started by using a small bit of the heat shrink supplied with the kit, shrinking it to the carbon rod at the end that will attach to the servo. Now, using larger heat shrink (large enough to fit over the control horn on the servo, yet small enough to shrink tightly around the heat shrink on the carbon rod), I slid about 1/2 inch over the control horn, and 1/2 inch over the carbon rod (and smaller heat shrink) leaving about 1 mm gap between the servo arm and the rod. I then used my heat gun to shrink the heat shrink. Repeat for the other side of the servo arm.

Now install the aileron servo into the fuse keel. I like to glue my servos in with a tiny bit of hot glue. It's quick, and is easy to remove from the servo should I need to use it in another application.

Once you have the servo installed. Connect the servo to your rx and check it for center. Now line up your aileron, and measure and trim the carbon push rod so that it is 1mm short of meeting the carbon rod control horn on the aileron. Cut small piece of the supplied heat shrink, and slid it over the control horn rod on the aileron, and the end of the carbon push rod, making sure that the servo is centered, and the control surface is in it's neutral position. Using a heat gun could cause the foam to melt, so I like to use a hot solder iron to shrink the heat shrink. Just make sure the iron is good and hot, and then hold it near the heat shrink until it is tight. Repeat for the other side.
Apr 07, 2008, 09:16 PM
I used to be all thumbs...
NumbSkull's Avatar
Pull pull setups used to intimidate me, but I've found that often, they are easier to setup then a push rod.

You can cut servo holes for the rudder and elevator servos in the fuse, but I found that the easiest way is to just use a dot of hot glue, and glue the servo directly to the fuse. This also allows for adjustments should you need to move the servo.

Placing the servos near the tailing edge of the ailerons, making sure that they don't interfere with each other. Glue Elevator servo to the horizontal fuse and the rudder servo to the vertical fuse. You will need to cut slots in the fuse for the control horn to fit through.

Unroll the supplied Spider Wire, and cut it in half. Starting with the rudder servo, tie one end of the wire to the out hole of the servo arm. Then use a small drop of thin CA to make sure the knot will not come loose. Center up the rudder, and make two or three wraps of Spider Wire around the carbon control horn. I then used a sewing needle to thread the Spider Wire through the foam just in front of the carbon control horn on the rudder. Keeping the line tight, and the rudder centered, make a few more wraps of Spider Wire around the second side of the control horn. Do not glue these wraps until everything is nice and tight and tied off. Now tie the loose end of Spider Wire to the second side of the servo control horn. You will want the wire to be tight, but not to tight. If it is over tightened, it can buckle the hinge or worse. I tie mine so that there is no slop in the line at center, and that is usually tight enough.

After you have the loose end tied to the servo, make sure everything is straight and just the way you want it, and then apply a drop of CA to the second knot at the servo, and to both sets of wrapped Spider Wire on the control horns on the rudder.

Repeat this for the Elevator....
Apr 07, 2008, 09:25 PM
I used to be all thumbs...
NumbSkull's Avatar
Using velcro, you'll want to use your battery to set your CG to about 1/4" behind the wing spar, leaving room to adjust to your preference as you get used to the plane.

For extreme 3D flight, you will set your controll throws to their max. The manual suggest at least 30 degrees of deflection on all surfaces. As you get used to the model, you can adjust these to your liking as well.
Apr 07, 2008, 09:28 PM
ClioRC's Avatar
Very nicely done,NumbSkull.Looks like a great little plane.Olin
Apr 07, 2008, 09:34 PM
I used to be all thumbs...
NumbSkull's Avatar
I equipped my Yak Jr. with a Hacker A10-15S, CC Phoenix 10 ESC, AR6100 rx, and three JR S185 servos and was able to keep the weight inside the 3.75-4.75 ounce range suggested in the manual. With a 2S 350 lipo, the plane came in right at 4.25 ounces, and had excellent performance. The winds in Kansas have kept me from flying the model outside, but we take over the gym at the local middle school twice a week during the colder months, so I've been able to put several flights on the plane in the last few weeks.

The plane is an absolute blast to fly. Over the last year or better, I've been looking for the perfect small space bird to fly in gyms and in a parking lot across from my house. During this "search", I've had the opportunity to fly many many models, everything from high wing slow fliers, to "3D" aerobatic wings, and until the Yak Jr. I've not been able to find a model that will perform like the Yak Jr. has.

It's flight characteristics are just great. The model will slow down to a crawl when you want, yet has enough power and strength to really rip when you want. Upright and inverted harriers are a snap, with very little wing rock. Knife edge flight is also a pure joy to fly. I was also surprised to see how easy this model will hover. I was expecting it to be a handful due to it's small size, however, I couldn't have been more wrong. The plane likes to settle into a nice manageable hover with no problems at all.

I cant say enough good about this model. It's very affordable at only $26.95 from DWfoamies.com. It's size is just right for smaller, more affordable gear, yet not so small that you have to buy hard to find, expensive gear to keep it light enough to fly. It has a great flight envelope, and should fit into just about any one's hanger (pun intended... ).
Apr 07, 2008, 09:35 PM
ExtremeFlight - 3DHS - Legacy
blucor basher's Avatar
Nice job, Numb! I've built a couple of the Yak juniors over the last several weeks. Love 'em. I can definitely get it into the air faster than any other foamy kit I've tried, and I love the flight performance. I have one on the 250 and 3S, and another on the Cyclon nano and 2S. Works fine either way. Hey, bring this one to SEFF, I'll fly it low for you!
Apr 07, 2008, 09:40 PM
I used to be all thumbs...
NumbSkull's Avatar
Originally Posted by Xpress..
You will find this plane a joy to fly. Mike has taken time and built a plane that flies great, and performs above other manufacturers.

Sofar, it looks smooth.

For hingins, even just a strip ontop would have held very well. Blenderm doesn't give out easily, so you will be fine with just a strip ontop. Even on the 38" models, I've gotten away with one strip, and it has held very well.
Mike does make great models. I'm going to start building the Gen-X Jr. next, and I might try the single side tape as I want to keep it as light as I can.
Apr 07, 2008, 09:41 PM
I used to be all thumbs...
NumbSkull's Avatar
Originally Posted by ClioRC
Very nicely done,NumbSkull.Looks like a great little plane.Olin

This is a great little model. I think that I'll probably just keep the model in my truck incase the wind dies down enough to fly. Spring is here in Kansas, and it wont be long before the winds calm down enough to fly. This is the perfect "lunch time" model if you ask me.
Last edited by NumbSkull; Apr 07, 2008 at 09:51 PM.

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