Sky Flieger

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Written by Clark Salisbury
Build this easy-flying, three-channel airplane
As seen in the October 2021 issue of Model Aviation.

At a Glance

tool

Bill of Materials

(6) 3/32 x 4 x 36 balsa sheets

(12) 3/16 x 2 x 36 balsa sheets

(6) 1 x 2 x 12 balsa blocks

(1) 1/4 x 1/4 x 36 balsa strip

(4) 3/8 diameter x 36 wood dowels

(3) 5/16 diameter x 36 wood dowels

(8) 1/2 x 4 x 12 balsa blocks

(1) sheet of 1/8 aircraft or poplar plywood 12 x 24

(1) sheet of 3/16 poplar or aircraft plywood 12 x 24

(4) rolls of covering material, three colors plus clear for the windows

(2) Sullivan 5 x 1.75 wheels No. S883 or 4.75-inch diameter foam Multiplex FunCub wheels

(1) 12-inch #4-40 threaded rod

(1) package Du-Bro standard hinge (DUB116)

(4) Du-Bro ball links with hardware #4-40 (DUB2161)

(1) Du-Bro control horn (DUB237)

(1) package with a formed windshield, landing gear, and instrument panel gauges (available from the author)

(2) #8-32 x 2 machine screws

(4) #8-32 hex nuts

(4) #8-32 nylock nuts

(10) #8-32 nylon pan head x 1-inch screws

(10) #6-32 nylon pan head x 3/4-inch screws

(2) 1/16 diameter x 12-inch steel rods

Specifications

Wingspan: 71 inches

Length: 57 inches

Height: 21 inches

Weight: 4.5-plus pounds

Test-Model Details

Motor used: E-flite

Power 25 or equivalent

1,250 Kv brushless

outrunner

ESC: E-flite or equivalent 40-amp

Battery: 3S 2,100 mAh LiPo battery

Radio system: Fourchannel radio and receiver

Servos: Hitec HS-85BB

Propeller: Electric 11 × 5.5

This airplane project has been one of the most fun that I have ever completed. I was looking through my covering material and discovered that I had a lot of yellow, red, and black. It hit me that those are the colors of the German flag.

When I was 9, my dad took our family of six to Tübingen, Germany. The town had no American schools, so I had to learn German if I was going to survive the year in the country. I could converse with my teachers and friends in school, although my grammar was terrible.

Nine years later, I was called to be a missionary for The Church of Jesus Christ of Latter-day Saints in Germany, and I was happy to return and spend time in small towns near Frankfurt. I made a lot of friends in Germany during those three years, and I am still in contact with many of them. I have also returned to Germany to tour and see some of those friends, so I wanted this airplane to remind me of the Germans and how much they love model aircraft. I thought it only right to give it a German name because it has the flag colors, so I call it Sky Flieger, which means Sky Flyer.

This airplane uses the wing from a design I created six years ago called the SkyEye, but I wanted this model to be able to carry at least one pilot and a Barbie-size passenger.

It has a lot of dihedral that makes it easy to control with three channels. Rudder-only turns are beautiful. The wing loading is low and that translates to fast takeoffs from grass, even at half throttle. I also wanted to have plenty of lighting on the airplane for flying at dusk, so I used 22 white LEDs. My plans show you where to install them. Well, let’s get into building.

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Cutting Out the Parts

As seen in Figure 1, cut out all of the parts that are depicted on sheets two, three, and four of the plans. All you will need is a glue stick to glue those patterns onto either the balsa, pine, or plywood as called out. As large as this model is, you will still need to glue some parts together.

The fuselage sides are 7 inches wide, but you only have 4-inch balsa to work with, so you will have to splice the balsa together to give you an 8-inch width. Parts such as the fuselage sides and the wing ribs that require two or more to be built should be cut stacked to save some time.

Be sure to cut on an angle with your scroll saw, as shown on certain parts, such as the fuselage formers and wingtips. Notice that there are a number of holes to be drilled, and some of the holes will need to be threaded.

be sure to cut on an angle with your scroll saw
Figure 1
be sure to cut on an angle with your scroll saw
Figure 2
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Figure 3
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Figure 4
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Figure 5
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Figure 6
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Figure 7
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Figure 8
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Figure 8A
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Figure 9
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Figure 10

Building the fuselage

As shown in Figure 2, glue the plywood landing gear mount to the rear balsa floorboard. Pin these to a building board over waxed paper as they dry. My photo does not show the big slot in the landing gear mount because I cut it out later to save some weight.

Glue formers F2 and F3 to the floorboard and to the front right fuselage side panel, as shown in Figure 3. Use a square to make sure the fuselage side panel is perpendicular to the floorboard. Ensure that you have laminated F2 together for a total thickness of 3/8 inch.

Figure 4 shows gluing the left front side of the fuselage to the floorboard and the F2 and F3 formers, again making sure that everything is square. The upper front and rear wing mounts and F4 are also glued in place in this step. Note that it is 3/16-inch plywood and the rear edge of the fuselage side panels should only cover half the thickness of this former. The rear fuselage side panel pieces will cover the other half.

Figure 5 shows the glued-in instrument panel and the F1 motor mount. Use elastic bands to hold the side panels against these parts as they dry. This is a great time to glue in the gauges on the back side of it after you have painted the front side of the instrument panel. I painted the instrument panel dark gray, although everything else in the cabin was later painted black.

In Figure 6, the motor is screwed in place using the provided screws. This is a good time to test-fit the nose piece to see if it aligns with the motor shaft. Glue in a 1/4-inch square balsa piece, 2-3/8 inches long, in front of the motor mount on both sides as shown.

Glue in the front cowling top piece as shown in Figure 7, using T-pins to hold it in place against the fuselage side panels. Glue in former F1A, which is located just ahead of the instrument panel, and glue the battery cover attachment plate to the center of F1A.

Figure 8 shows the battery cover with the battery cover formers glued in place. Figure 8A shows the same part, with two toothpicks added to retain the front side. When it is dry, drill two 1/16-inch diameter holes in the F1 motor mount for the toothpicks to enter.

Figure 9 also shows the lower fuselage doublers pinned in place and glued. The front nose piece mount is also glued in place, along with the two inserts, which are drilled and tapped to a #6-32 thread. Those holes must line up with the holes in the pine nose piece.

In Figure 10, the drive battery box is glued together. This box only fits the E-flite LiPo battery in the bill of materials. You can glue this together around the battery itself, but leave some clearance all around the battery.

Figure 11 depicts the battery box glued in place in the front of the fuselage, directly to the back side of the F1 motor mount and F2.

The AAA battery holder for the LED lights is shown in Figure 12. It first needs to be screwed to the square plate made of 1/8-inch plywood then, as shown in Figure 12A, glue the triangular gussets to the bottom of the square plate. Glue this entire assembly to the top of the battery box that was glued into the fuselage in Figure 11. Make sure it does not interfere with the battery cover when it is put in place with the toothpicks sticking into the motor mount.

In Figure 13, the front half of the fuselage lays directly on a 48-inch straight line, which has been drawn on the building board. The front half of the fuselage should be pinned down in this step.

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Figure 13
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Figure 13A
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Figure 14
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Figure 15
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Figure 16
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Figure 17
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Figure 18
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Figure 19

I have struggled for years to make a straight fuselage. This method absolutely guarantees that you will end up with a straight fuselage.

Note that every former has a center cut at the bottom. That center cut needs to lay directly on top of the straight line that you have drawn. The formers from F4 to F7 have breakoff plates at the bottom, so these formers can lay flat on the straight line until the fuselage is done, and then the breakoff plates can be removed. The breakoff plates not only make the fuselage straight but also make the formers the right height.

Figure 14 shows the tail jig that you will need to build from scrap balsa. This jig will ensure that the horizontal stabilizer will be perfectly level when it is added later. Figure 15 shows that the straight line drawn earlier should have a perpendicular line drawn 15.5 inches rearward from the former F4. The tail jig should be pinned to the building board along this perpendicular line.

In Figure 16, former F5 is glued to the rear side panels of the fuselage. The cuts in the rear side panels need to line up exactly with the angle cuts on F5. The rear side panels have also been glued to the rear half of former F4.

In Figure 17, former F6 is glued in place, and the calipers in the photo are used as a clamp to hold the fuselage side panels to F6.

Former F8 is glued in place at the rear of the fuselage in Figure 18. A fake rear elevator is put in place with waxed paper on top of it to raise F8 to the right height. Figure 19 shows the servo mount glued to F7. A square 1/4-inch balsa place in the front helps support the servo mount. A single servo is shown, which was my intention when I first built this airplane, but I later replaced it with a double servo mount, which you have already cut out.

In Figure 20, the fuselage side panels are bent over to match up with the angle cuts on the formers. I used masking tape to hold them in position while the glue dried.

Figures 21 and 21A show the top pieces of the rear fuselage glued in place, including the front piece, which has the rear window cutout in it. Again, these pieces are held in place with pins and masking tape. After the glue has dried, the fuselage is nearly finished and can be unpinned from the building board.

Figures 22 and 22A depict the servos mounted to the mounts. They will need to be permanently mounted with the provided screws. Figure 23 shows cutting off the breakoff plates on F5, F6, and F7. In Figure 24, 5/16 × 3/32-inch balsa strips have been added to the bottom of the fuselage around each opening between the formers on the bottom of the fuselage. This makes a place to stick on the covering material. The openings on the bottom save weight at the rear of the fuselage, which is necessary to achieve the airplane’s center of gravity.

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Figure 20
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Figure 21
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Figure 21A
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Figure 22
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Figure 22A
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Figure 23
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Figure 24
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Figure 23
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Figure 26
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Figure 27

Building the Tail Feathers

In Figures 25 and 26, the construction of the horizontal stabilizer and the vertical stabilizer with the elevator and rudder attached is complete. These are done on your building board using waxed paper on top of the plans then pinning and gluing all of the pieces together. When all of the pieces are done, you will need to slot the indicated parts to accommodate the nylon hinges.

After the hinges are in place, drilling a 3/16-inch hole through the balsa and the hinge and filling the hole with epoxy will ensure that the control surfaces never separate in flight.

In Figures 27 and 28, the four LED lights have been epoxied in place. First, drill 3/16-inch diameter holes in the horizontal stabilizer at a 45° angle. The angle is so that the LEDs will point toward the vertical stabilizer and light up the tail at night.

In Figure 28, the wires are soldered to the leads of the LEDs. Groove the balsa deep enough for the wires. LEDs only work with electricity flowing in one direction, so the short lead is positive and the long lead is negative. I used yellow wires for the positive leads and black wires for the negative leads. You need to solder the yellow wires together and the black wires together. They should all end up at the AAA battery holder in front.

Wheel Pant and Seat Construction

Figures 29 and 30 show the balsa parts cut out, assembled, and glued together to form the wheel pants. Make sure that you build a left and a right wheel pant. The plywood part of the wheel pant will be closest to the center of the airplane. I have included optional cutouts on the plans sheet to lighten the wheel pants.

If you are going to use an opaque covering material on this model, go ahead and make the cutouts. It will save some weight and you won’t see the holes. If you are using a semitransparent covering material, do not make the cutouts. The holes will be visible and it will look terrible.

You will need to sand these wheel pants to round the corners. Make sure that you sand the left and right the same amount to look good later. When they are done, you can drill the 3/8-inch diameter hole in the front of each wheel pant to accommodate the LED and its holder, which will be glued in place after the covering is complete.

Figure 31 shows the seats glued together. I painted everything on the inside of the cabin black, but my wife had some nice dark gray cloth that I glued to the flat part of the seats, and it looks awesome. I also painted the instrument panel that same dark gray.

Wing Construction

Figure 32 shows the completed right wing half. I actually used the wing halves from a former model that I built six years ago. My plans only allow you to build one wing at a time, so build the right wing first. It is constructed on the building board by pinning the leading edge (LE; a 3/8-inch diameter wood dowel) to the waxed paper-covered plans. The ribs are glued to that LE one at a time, starting on the outside of the wing.

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Figure 28
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Figure 29
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Figure 30
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Figure 31
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Figure 32
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Figure 33
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Figure 34
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Figure 35
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Figure 36
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Figure 37
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Figure 38

The three outside ribs need to be notched to accommodate the 1/8 × 1 × 12.5-inch plywood piece that will be glued in place later. Although my photo shows it, do not glue in the inside rib or diagonal ribs R2 and R3 at this time. After the front dowel glue has dried, add the rear dowel against all of the ribs.

When that assembly is dry, go ahead and glue in the wingtip and the plywood strip on top. When that has dried, unpin the wing from the building board, turn it upside down, and glue in the 3/16-inch plywood strut mounts. Now repeat the entire process to build the left wing.

In Figure 33, the six LED lights are soldered into the front part of the wing. Each LED will need to be epoxied in place before soldering. Doing this step now is much easier than doing it after the wing halves have been joined. Leave plenty of wire at the inside of the wing because these wires will have to be connected and soldered inside the fuselage.

Figure 34 shows the preparation that needs to be done on your building board before the wing halves can be joined. First, draw a straight line on your building board then draw perpendicular lines spaced as shown in the photo. The outside lines should have a 2-inch piece of balsa (or any wood for that matter) pinned vertically to the building board. These spacers will provide the correct amount of dihedral to the wing.

In Figure 35, the wing halves are joined. Glue in the dihedral joiners first, with the 3/8-inch dowel pieces connecting the wing together in the front and the rear. When that has dried, glue in the inside ribs. They will need to be cut as shown on the plans to not interfere with the dihedral joiners.

Glue in diagonal ribs R2 and R3. When that is dry, glue in the front and rear balsa-block wing joiners then glue in some 5/16 × 3/32-inch balsa strips along the top of the wing center, as shown in the photo.

At this point, you can cover the wing with the material that you have chosen. I covered the bottom of the wing with yellow transparent material and partly with opaque yellow. I covered the top with red to go along with the colors of the German flag. The top center is covered with yellow opaque material.

When you cover the wing, do the top first. The wing will curve upward. This helps provide more effective dihedral, which lends to steady, stable, forward flight. Make sure that the amount of curvature is equal on both sides. You might have to add more heat to one side to achieve this.

Make absolutely sure that the wing does not have negative washout. My wing had no washout at all, and my model flew perfectly. If you do have some washout, make sure that the rear outside of the wing is higher than the front of the wing and that the washout is equal on both sides.

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Figure 39
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Figure 40

Finishing the Airplane

Although not shown, the wing struts need to be completed. Insert 1-1/8-inch long pieces of #4-40 threaded rod into each hole at both ends of the wing struts and epoxy them in place. The struts should be covered with yellow if you are following my color scheme.

Figure 36 shows the battery box cross support glued in place. Note that it is cut in parts, and that one side has a hole to accommodate the ESC wire. At this point, your receiver needs to be wired in, with servos attached and the ESC in place. Do not install the propeller yet for safety. Check your radio transmitter and make sure that all of the servos go in the direction that you want them to for rudder and elevator control.

I had elevator control as forward, backward, and side motion on the right stick that controls the rudder. Make sure that the left stick pushes forward to activate the throttle. Take the leads on your AAA battery holder (for your LEDs) and lengthen them so that they can go back into the cabin area approximately 6 inches to later solder all of your LED wires together.

Figure 37 shows the seat support box glued together. I later painted this black. In Figure 38, the seat support box is in the cabin and the seats are sitting on top of it. Note that 1/4-inch square balsa strips need to be glued to reinforce the top of the fuselage above the cabin windows.

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The front-facing landing lights are epoxied to the front LED plywood mount in Figure 39. Add the wire leads to these, and then glue in the entire assembly to the front bottom of former F2 in the fuselage.

Figure 40 shows the front bottom of the fuselage glued in place. Before that is glued in, make sure that you have first glued in the 3/16-inch balsa fuselage doublers at the bottom of the side panels. Note the dark hole in the front of the bottom of the fuselage. After everything has dried, glue in the balsa and plywood air scoop. It would be best to glue the entire air scoop assembly together first.

Before covering the fuselage, sand the entire fuselage assembly. Install the nose piece so that it can be sanded to the same radius as the fuselage. Don’t sand the corners too much or they will not remain intact. Be careful how you handle the fuselage when you are sanding. Hold it where there is a former to back it up.

When you cover the fuselage, leave the bottom and the windows open so that you can solder all of your LED wiring together after the wheel pants and wing halves have been added. The wing halves will require match drilling #8-32 through the top of the wing in four places so that it can be attached with the nylon screws.

Paint and glue on the tail skid made of 3/16-inch plywood. I painted mine black. Install all of the connecting hardware for the wheel pants, the windshield, etc., as called out on the first sheet of the plans.

Hook up the servos to the control surfaces using the nylon control horns and bending the 1/16-inch steel rod between the servo arm and the control horn. I usually have to bend the connector rods several times to get the length right. Your elevator travel should leave roughly 1/4-inch of clearance to the rudder. The rudder should travel at least 15° in both directions.

Flying the Airplane

After building this airplane, it will be hard to push yourself to fly it because you have put so much hard work into its construction. It was tough for me; however, the real joy comes from watching this model fly. The tail skid actually helps this airplane take off straight if you are flying from grass because it tends to drag through the blades of grass, keeping it straight.

I needed no rudder correction on the maiden flight. I gently eased the throttle forward and it took off in roughly 25 feet, although I was only at approximately 2/3 throttle. Let the model climb out for a couple of seconds then start your turn. Your first turn won’t require any elevator input. When you are flying level, a little up-elevator needs to be added with rudder to make a level turn.

The airplane makes pretty, smooth turns. I brought the throttle back even more for cruising to half throttle or less. This airplane is just a joy to fly. My maiden flight was on a perfectly calm day, which made for graceful flying.

My wife’s video of those maiden flights is very smooth. At my home in Utah, at a 4,600-foot elevation, the airplane still has plenty of power. I recommend flying in a large area. Because the airplane is large, it is deceptively fast.

I did not design this airplane to be aerobatic, so I cannot comment on its ability to do loops. It probably will, but I haven’t yet tried any. Complete dead-stick landings are fun. The airplane tracks as though it is on rails when you pull the throttle all the way back and let it turn into a glider. Again, all of that dihedral makes this possible. I did both maiden flight landings dead stick, just for the fun of it.

Have fun!

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