CMAD Small Wonder build pics

[KRProton]

Hi Gordon (I'm talking to Gordon, right).

Yea, it's a little C.G. stand I came up with myself. We used to include a smaller version with the Great Planes Rifle and Rifle 1M because the planes were tiny and fast and required accurate measurement of the C.G.

The strips are 1/16" plywood and the pegs are just wood dowels. The stand is stable enough, but I think when I produce these i will make the dowels a bit shorter.

Yes, it's just double-sided tape that sticks the strips to the wing where you have drawn the line for the C.G. The holes are 1/8" increments, so relocating one of the dowels one hole forward or back is a 1/16" increment.

The stand is stable enough, but I'll probably make the base larger. You can also put some weight under there.

Tim

[KRProton]

Been a long day. All finished with the plane and maidened it plus three more flights down at OJA today. But first let's continue with the rest of the build;

Somewhere along the way I mounted velcro to the receiver battery and mounted the battery to the velcro on the engine mount ring on the back of the firewall shown earlier. For now I'll use a short extension to reach the switch harness, but was in a bit of a rush to finish this so I could fly it today.

Now for the elevator pushrod. There is an indentation molded on one side of the fuselage intended to be cut out for installation of the elevator joiner with a 4-40 SHCS to serve as the torque rod for the elevator. As inconspicuous as it may be, I refuse to cut a big hole in the fuselage, so as Ray Brown alluded, I'm going to go with the "Korsen flag" apparently thought up by Craig Korsen. This method isn't for everybody because it is a bit tedious, but this is how I do it...

Drill an approximately 1/8" hole in the bottom of the fuselage directly over (under) where the head of the SHCS will be. Epoxy a 4-40 nut to the top surface of the aluminum joiner. Thread on one of the nylon torque rod horns that come with the kit to 4-40 SCHS (I purchased a bunch from McMaster-Carr), then glue another 4-40 nut near the bottom of the screw. After the epoxy hardens you're ready to test-fit the pushrod.

I'm running out of the coveted Hayes metal pin clevises, so I was going to use one of those larger DuBro clevises, but when I got it installed it was too wide to fit in the back of the narrow fuselage, so I went back to the Hayes clevis. The torque rod horn must fit tightly enough onto the clevis so that it will not flop around and will remain perpendicular as shown. Holding the fuselage vertically between my knees, I guide the assembly down through the fuselage trying to catch the bottom of the screw in the hole in the joiner. Once it lands, carefully rotate the fuselage upright (but upside-down) so you can turn the screw into the joiner with a ball end hex wrench. Later, when the servo tray is mounted with the servos and I have the wire pushrod made, I'll know where to cut the front end of the carbon pushrod. Then, I'll epoxy the pushrod wire into the carbon rod with the radio on and the elevator centered.

[KRProton]

Next I use an extended 3/32" drill bit to start the hole in the rudder pushrod exit. I would rather use a 5/32" pushrod (Like Lonnie Finch suggests), but I don't want to enlarge the hole more than intended for the 1/8" carbon pushrod. Once the 3/32" hole is drilled I use a 1/8" round wood rasp to enlarge the hole to accommodate the pushrod.

[KRProton]

This isn't the easiest way (in fact it's a difficult way) to mount guide tubes for the receiver antennas, but this is how I do it. It gives me great peace-of-mind to know I'll have a reliable, trouble-free receiver antenna setup. I've never had any radio glitches with this setup. One tube guides the antenna across the middle of the inside of the fuselage and the other guides it vertically, up toward the top of the fuselage.

I bend the tubes with a heat gun and glue them into place with Zap Goo/Shoe Goo. Later, when I install the receiver I'll guide the antennas into the tubes using hemostats.

Tim

[KRProton]

I usually mount the receiver to the "flattest" part of the fuselage behind the wing. Velcro used here too (with a layer of foam tape between the velcro and the receiver for a little cushioning).

[KRProton]

Time for the servo tray. I know this isn't an option for most people, but I have a laser-cutter, so I make my own tray. I can make one for you too for like five bucks. One reason I make my own tray is because I can, plus, I use Futaba servos for the surfaces, but a HiTec servo for the fuel cut. I also make these little rails to lock the tray into giving me more peace-of-mind. I use thin CA to glue the rails to the fuselage and shoe goo to glue the tray itself to the rails and fuselage.

One note about the servo tray installation in this model; when working with a new airplane I usually build the entire plane with the exception of gluing in the servo tray. I then put the plane on my C.G. stand and find out where the tray needs to be to get the model to balance without any additional ballast, but because there wasn't much latitude for adjustment (since I'm using the Jett round 6 0z. tank with is slightly long), but mostly because I was in a bit of a rush to get this model finished, I simply deduced that the plane was going to need about all the nose weight it could get and just mounted the tray almost as far forward as it would go. We'll see how that plays out later...

[KRProton]

Here's the rest of the servo tray installation.

[KRProton]

Once the servos are mounted to the tray and the tray is glued in, time to make the switch wire. I'm on the fence whether I like the pull string setup or the nifty wire, but I'm leaning toward the wire type just because it's cool!

I made a "dummy" indicator wire to show about where the first hole for the actual wire needs to be in the fuselage. I heat a T-pin with a torch to melt a small dimple that can be seen from outside the fuselage. Drill the first hole, make your switch wire, then drill the 2nd hole and hook it up. I just use some small-diameter wire I had laying around.

[KRProton]

Now that the servos and tray are in, I finished up the elevator and rudder pushrods. The kit came with a nice fiberglass rudder control horn, but I assume it's intended for a ball link (because I would think a metal clevis pin would enlarge the hole in the fiberglass over time). So I just used one of the 4-40 flat-head screws that came with the kit to do it the typical way with a nylon control horn. I was concerned about drilling a hole through the rudder where there may be no support inside the rudder, but I felt around and pinched the bottom of the rudder in the area and it felt very solid. I marked and drilled a hole and tapped for 4-40 threads. I epoxied the screw into place.

[KRProton]

Onto the fuel tank.

I hope I'm not over complicating things. This fuel tank "wedge" system was introduced to me by Dub Jett, but I think it originated with Richard Beers. I know most probably just use foam and tape, but this way works for me. We started out with just a balsa wedge on a plywood cradle, but what happens with me is, the wedge breaks off at the notch allowing the tank to rotate. I now make the wedge out of two balsa pieces in the middle with lite-ply pieces on the outside so the wedge no longer breaks. I wrap the tank with two wraps of Kapton tape which is super tough and non-abrasive.

To determine the height of the wedge (to get the tank level), I adjust the fuselage in my cradle until the nose at the spinner is vertical as read by a bubble level. I then rest the level on the tank and raise the back end until it is level. The distance between the back of the tank and the level is the height of the back of the wedge. Time to sit down at my computer with my CAD program to draw and laser-cut the parts...

The pictures explain the rest.

[KRProton]

After the shoe goo on the wedge on the tank and on the former in the fuselage dries, I install the tank using electrical wire to pull the lines through the fuselage. I shape two wedges from soft balsa to glue between the sides of the tank at the front and the fuselage sides to prevent the tank from moving side-to-side. Finally a piece of balsa on the bottom of the tank just higher (lower) than the bottom of the wing saddle. Pressure from the wing holds the tank up into place.

[KRProton]

The aileron servo is intended to be mounted to the top of the wing placing it in the radio compartment. I am sure this system will work because everybody involved with the design of this airplane is smarter than I am, but I still wanted to mount the servo to the bottom of the wing. Mike Helsel told me how he did it, so I followed suit, only with more nicely laser-cut parts. I took some measurements and did some guess-and-by-gosh to come up with the servo location...

[KRProton]

I cut holes in the bottom of the wing for the torque rod screws, screwed them into the aluminum tubes from the top of the wing, then used 4-40 nuts and blue loctite to lock it all down.

After test-fitting the belly pan over the servo, the servo wheel was slightly touching the belly pan, so I took a little off the wheel. This worked fine.

[KRProton]

I was running out of time to be able to get this thing to fly the next day; Our electricity was out from Friday morning until late Friday afternoon, and I was hoping to maiden the plane Saturday, but I was working in a chili basement by the light of a window. But I need to leave for OJA by about 6:00am to get there by 9:00, so I was running out of time.

I needed to pot the wing to the fuselage by Friday afternoon to allow as much time as possible for the RTV silicone to dry before removing the wing Saturday to fly.

Before potting the wing though, I first checked the incidence with two Robart incidence meters to make sure both wings were the same. If necessary, I could shim the TE of one wing or the other to "zero" them out. Fortunately both wings measured the same.

I used the method I learned from Tom Scott to apply saran wrap over the wing spritzed with water (or window cleaner or whatever). I use a paper towel roll to roll out most of the fluid, then pull it tight with tape. The fluid allows the film to be stretched into place without "grabbing" the wing so it can be pulled tight.

[KRProton]

Once the saran wrap is tight, cut holes over the wing bolt holes in the wing to accommodate the wing bolts.

Some use epoxy, but I like a softer cushion between the wing and fuselage, so I use RTV silicone. I have found that clear adheres the best. If I were going to paint this fuselage I would have done this after painting.

This was the last time I was going to see the inside of the fuselage until I was going to remove the wing the next day down at OJA, so I made one last look to make sure everything was right.

Apply a generous amount avoiding the wing bolt holes. Drop the wing into place and bolt it down, but not too tight.

After the wing is potted and the RTV has dried, most cut the excess that oozed out of the wing saddle with a razor blade, but this time I cleaned it off before it dried with balsa sticks, then a paper towel square dampened with denatured alcohol. Then, when I pull the wing at the flying field the next day all I have to do is trim the excess from inside the fuselage.