By Tim Bailiff | email@example.com | Photos by Maggie Madril
Have you ever wanted to build a simple RC airplane that is easy to transport, doesn’t require much space to fly, and handles great?
If so, luck is on your side, because I have just the airplane for you!
Tim Bailiff launching his round airplane.
Constructed primarily of BlueCor foam, this airplane’s main airframe is made from only two pieces! It is easy to handle, flies well in the wind, and it’s very unique looking. This airplane’s wing is perfectly round and completely flat, and it’s surprisingly robust and fun to fly! Sound interesting? If so, I invite you to read on and join me in the skies above, flying a terrific, little, round airplane.
I have a lot of fun flying round airplanes. My all-time favorite round airplane design is a simple 21-inch diameter model constructed of Dow BlueCor. Airplanes this fun only appear once in a blue moon, so the original was named Blue Moon. It is very stable, yet it can do the tightest inside and outside loops that I have ever seen. It has a wide flight envelope, which enables it to fly fast or very, very slowly. Because of its light weight, it glides wonderfully. I’ve even been able to catch thermals with my Blue Moon while flying dead-stick! With all that stated, this latest version uses a slightly upgraded motor, hence the new Blue Moon 2.0.
Let’s get started on your Blue Moon 2.0. This is a super simple build, so there are no plans with this article. I have, however, included detailed instructions and plenty of construction photos on TheParkPilot.org. If I may suggest, read this article and collect your materials first. It’s guaranteed to help your project progress even faster. The materials list is as follows:
- One 2 x 4-foot sheet of Dow BlueCor or ¼-inch (6mm) Depron foam
- One 24-gram 1,700 Kv outrunner brushless motor
- 12-amp ESC
- Spektrum AR6100e receiver
- Two 3.6-gram micro servos
- Turnigy nano-tech 460 mAh battery
- Three sets of 2mm gold bullet connectors
- GWS EP-6050 propeller
- Two 14-inch long .040-inch carbon-fiber rods
- Two Du-Bro mini control horns
- Two Du-Bro mini EZ Connectors
- 2-inch wide Scotch shipping tape
- Four ¼ inch servo screws
- 1 x 1 x 1/8-inch plywood
- Two inches of .032-inch music wire
- 5-minute epoxy
There will be a few more incidental items that will be covered along the way. The transmitter that I use is a Spektrum DX7 V2, which works perfectly with the receiver listed. Any transmitter that binds with your receiver of choice is fine as well. Note that the items listed in the materials list are what I suggest; you can change things up as you see fit. However, one word of advice: Keep things light. As we all know, the lighter it is, the better it flies!
To keep things light, I chose to use Dow BlueCor, a blue construction foam underlayment. It has black printing on one side, which I made the bottom of my wing and simply left as-is. Its surface is a bit irregular, but don’t be concerned; it works out fine. BlueCor is approximately 6mm (¼ inch) thick, lightweight, and has a thin, plastic skin on both sides. It’s terrific stuff to work with. It is sold in bundles, each containing 25 2 x 4-foot folded panels. If you can’t find any in your area, you can also use 6mm thick Depron. You will notice that Depron doesn’t have a skin on it, but it still works fine.
Let’s start with the Blue Moon 2.0’s most prominent feature: its round wing. This is actually pretty easy and straightforward. You are simply going to cut out a 21-inch disc in one piece. You can use any method you’d like as long as your disc is nice and round.
Here is the method I use with good success. After determining where the center of the disc will be, I place a pushpin. I then get a length of string and tie it to the handle of a hobby knife, down near the blade. I loop the other end of the string around the head of the pushpin and tie off a loose loop so that it can easily pivot around. Adjust the string length so that the blade of the knife is exactly 10.5 inches from the center of the pushpin. Then, cut out the disc while keeping the blade vertical and the string tight. If using BlueCor, you can actually cut out two complete wings and fuselages from a single 2 x 4-foot panel with a little planning.
When finished, you can use light sandpaper to touch up the edges, if necessary—however, do not round them off! Rather, keep them flat and blunt. When this wing moves through the air at a positive angle of attack, the blunt LE (leading edge) pushes the air up, actually helping to create lower pressure over the top of the wing. In other words, it creates lift! Cool, right?
The Blue Moon 2.0 flies great using just elevons. That means only two control surfaces need to be cut out of your round wing.
To begin, decide which will be the front and top of your airplane. As previously mentioned, I used the side of the BlueCor without the writing as the top. For the front and back, I decided to have any ripples in the foam run parallel to the centerline of the airplane. After you decide, lightly draw the centerline from front to back, crossing over the pushpin hole.
Now, from the rear of the wing, measure 3 inches forward. At that point, lightly draw a line perpendicular to the centerline, extending out to the edge of your wing. This will be your elevon's LE. Then, leaving a 1-inch area between the elevons, cut them out.
After they have been removed, cut the bottom of each elevon’s LE back at a 45° angle. This will allow them to fully deflect into the down position. Remove an additional 1/16 inch from the inside edge of each elevon to prevent binding. Using a 1-inch wide piece of Blenderm surgical tape, hinge the top of the elevons into place. Be sure to leave a slight gap at each hinge line to allow for free movement.
Now it’s time to add your spar. Begin by measuring 5¼ inches from the front of the disc. That’s the magic 25% CG (center of gravity) balance point that makes this airplane fly so well. At that point, lay a straightedge perpendicular to the centerline. Where the straightedge extends out past the wing, place a mark on both right and left sides. Put it on the actual edges so that you can see it when you turn the wing over. And then do just that—turn it over.
On the bottom of the wing, you will place a piece of 2-inch Scotch reinforced strapping tape between each CG mark, perpendicular to the airplane’s centerline. Try to center the tape at each mark, and then trim to fit the curve of the wing. It’s simple, strong, and very effective.
I suggest you look at the construction photos on TheParkPilot.org as you reinforce the LE of the wing.
Center 2-inch strapping tape along the wing’s blunt edge, beginning from the aft side of the tape “spar.” You can choose which side to start on. From there, run the tape around the front edge all the way to the other end of the tape spar. Take care to keep it centered on the ¼-inch (6mm) LE. Firmly press the tape against the LE, keeping it flat.
Beginning with the bottom, make vertical cuts on the tape every half inch. Once cut, carefully fold each piece back and down, pressing it firmly to the surface of the wing. Expect them to overlap slightly. Take your time and be sure to keep the LE as blunt as possible. When finished, do the same to the top. This strengthens your wing greatly and guards against everyday nicks and dings … aka hangar rash.
The simple fuselage is easily made as a single piece of foam that also incorporates the vertical fin. There is no rudder. Your finished fuselage with an attached vertical fin will be 22 inches long. If you look at the construction photos now, it will help you visualize what you will be making.
Start by cutting the straight bottom edge of the fuselage, which is 21 inches long. The front, where a plywood firewall will attach, should be cut 1 inch high, 90° to the bottom of the fuselage.
From the top of the 1-inch front, cut back 18 inches while slightly increasing the fuselage width to 1¼ inches. At the end of that cut, you will cut the vertical fin, leaving it attached to the top of the fuselage. Do this by first making a 3-inch cut angled back at 30°, and then sweep your cut up and back, finishing horizontally, 4.5 inches higher than the top of the fuselage and extending 1 inch back beyond the rear fuselage bottom cut.
From that point, cut straight down 5 inches. From the bottom of that cut, make a sweeping ¼ circle cut, forward and down, connecting to the end of the 21-inch fuselage bottom. Remember, your total length should be 22 inches. It takes a little planning, but it’s very doable.
Let’s put this bird together.
Begin by using a toothpick to punch shallow holes down your wing’s centerline, just deep enough to pierce the thin skin. As you move down, stagger them on either side of the line you’ve drawn. Remember, your fuselage is only ¼-inch wide, so stay fairly close to the line. Smear a fair amount of 5-minute epoxy onto the bottom of your fuselage. Carefully place it along your wing’s centerline, directly on top of the holes you pierced. As the epoxy sets, ensure that the fuselage remains aligned and vertical.
Again using 5-minute epoxy, attach your 1 x 1 x 1/8-inch plywood firewall to the front of the fuselage. For additional support, glue in two 1-inch lengths of half-inch triangular balsa vertically behind your firewall on either side of the fuselage. Again, be sure that everything remains straight and aligned. I didn’t find it necessary to add any right- or downthrust.
Motor and ESC
The Blue Moon 2.0 uses a 24-gram 1,700 Kv brushless outrunner motor. You can use any brand you’d like as long as you watch the weight and Kv rating. Unless it’s already done, you will need to solder your 2mm connectors onto the motor leads. Use short lengths of heat-shrink tubing to insulate the solder joints and connectors. Do the same with your ESC.
Next, attach the aluminum motor mount that is provided with the motor to the plywood firewall. I used servo screws to secure mine. Insert your motor into the aluminum mount and rotate it until your motor leads are on the left. This is 1 inch behind the motor where you will place your ESC (using Velcro). It should be snug against the fuselage.
The propeller used is a GWS-EP 6050. It is held onto the propeller shaft using a propeller saver and rubber washer.
The battery used is a nano-tech 11.1-volt 3S 460 mAh LiPo. It should be attached flat on the wing using Velcro. Place it approximately ¾ inch behind the motor on the right side, pressed snuggly against the fuselage. It can be moved forward or aft to help with final balancing.
The servos I chose were two Blue Arrow 3.6-gram servos. To mount them, measure back 3¾ inches from the front of the disc. There, you will cut and remove a 1.5-inch long rectangle piece of fuselage, right where it contacts the wing. It should be just high enough for your servo to slide through when laid on its side.
Ultimately, both servos will be mounted flat on the wing with their bases touching. To facilitate this, you will need to add two hardwood servo mounts. I used 11/8-inch lengths of chopsticks (the square end). They are epoxied perpendicular to the fuselage at either end of the servo hole. When the servos are butted together, they can be screwed into either end of the wooden mounts. I suggest you drill small pilot holes as well. This mounting method is simple and allows for removal if necessary.
Now, install one Du-Bro mini EZ Connector into the last hole of each servo horn. You might have to enlarge the holes to make sure they rotate easily. The connectors should face away from the fuselage when the servo horns are mounted vertically to each servo.
For the receiver, you will need to cut another piece from the bottom of the fuselage, half an inch aft of the servos. Make this cut ¾ inch long and about half an inch high. The receiver is then slid through the hole and held in place by friction. Because receivers can vary in size, it’s best to premeasure your receiver before cutting the hole. You want a snug fit.
Control Horns and Pushrods
Install one Du-Bro mini control horn on top of each elevon, 1 inch from the fuselage. They should be positioned so that they face forward and are attached ¼ inch rear of the hinge line. Before using 5-minute epoxy to secure them, I trimmed the anchoring post of each to prevent them from sticking through the bottom of my elevons.
The two .040-inch carbon-fiber pushrods come next. Both have a 1-inch long .015-inch wire with the Z-bent end attached. I held mine in place with a half-inch length of heat-shrink tubing and a touch of thin CA glue. Note that the other end of the carbon-fiber pushrods fit nicely into the mini EZ Connectors. Use caution when securing, because overtightening the connectors will crush the carbon-fiber rods.
Next, 7 inches to the rear of the servos, install two pushrod “standoffs.” I made mine from two spare servo horns. Distance from the fuselage might vary; use whichever hole allows the pushrods to slide straight through without binding. These holes might need to be enlarged as well. I should mention that they should be slid onto the pushrods before the pushrods are attached to the control horns and EZ Connectors. The standoffs can then be positioned, slightly buried in the wing, and epoxied into place.
Connect and Program
After you have all of your electronics in place, position your battery so that your airplane balances on the 25% CG marks. Bind your equipment, and then go into your transmitter’s menu and choose the “Delta” or “Elevon” setting. Adjust as necessary until both control surfaces move properly. I suggest you center your trim and mechanically set your elevators to be ¼ inch up. If you’d like, you can also set your dual rates at 100% and 70%. Now test your motor. Should it spin in the wrong direction, it’s a simple matter to swap two of the motor leads and try again. Good job.
This section is optional. I chose to cover my radio equipment with a cowling. I think it helps streamline the airplane and looks cool!
I made my cowling in two “mirrored” pieces. Each attaches to the fuselage with a single servo screw pressed through the top of the cowling and screwed into a 1-inch piece of (square) chopstick. The chopstick was glued perpendicularly in the top part of the fuselage.
Each cowling piece used a 9-inch “rib-shaped” former on the inside and a 7-inch rib former on the outside. The ribs were made of BlueCor and trimmed as necessary to allow for the equipment. The top sheeting was made from 2mm Depron foam and trimmed to allow for the pushrods to exit. Each cowling was 2 inches wide and covered with blue packaging tape.
Make It Your Own
Here is where you get to make your Blue Moon 2.0 your own. I chose to trim mine with blue packaging tape that I purchased online.
Are you ready for some fun? This is what your careful work is all about. Because your Blue Moon 2.0 does not have landing gear, I suggest you fly over grass. Set your dual-rate switch to 70% and make sure your CG is correct. One final system check and you are set to go.
To launch, face into the wind while holding your airplane by the top of the fuselage. Advance your throttle to full and, with the nose raised about 30°, give your airplane a gentle, underhand push forward. It’s really just that easy!
Although your Blue Moon 2.0 can perform an unlimited vertical climb, for this first flight, just allow it to gently climb out. Once it is at a comfortable altitude, throttle back and try a few shallow turns. You’ll find your Blue Moon 2.0 is a solid flyer. It’s very stable, but also agile.
Once you feel comfortable with your new airplane, flip your dual-rate switch to 100% and advance the throttle to full. It’s time to “ring out” your round airplane. Try a few inside and outside loops. I bet you’ve never seen an airplane fly tighter loops—in either direction! Rolls are a breeze as well.
When it’s time to land, try something fun. Gain a little more altitude, and then cut the power all together. You will be astounded at how well your flat, round, airfoil-less airplane will glide. On a warm day, you might even be able to find some lift. It’s truly amazing. You will find that your airplane is easy to control even as you guide it down to a perfect landing at your feet!
In the Pilots' Lounge
Once you have landed, expect a few questions from your fellow pilots. No doubt they’ve all seen how much fun you’ve just had. Explain how easy it was to build and how nice it is to fly. Encourage them to build one themselves. Pilots won’t find a less expensive way to have this much fun!
Until next time, stay safe and stay well my friends. Fun stuff …
The two round wings and fuselage/fin pieces were cut from Dow BlueCor.
The two round wings and fuselage/fin pieces were cut from Dow BlueCor.
The fuselage and vertical fin are cut out as a single piece.
The elevons are cut from the rear of the round wing.
The elevons are hinged with Blenderm tape to the back of the wing.
The underside of the wing, showing spars made from 2-inch-wide shipping tape.
Two angles that show the fuselage glued to the centerline of the wing.
If you make one, you might as well make two!
This photo shows the position of the electronics, including the battery.
The optional two-piece cowling used to streamline and cover the electronics.
The pushrod “standoff” made from a spare servo horn.
Any 24-gram, 1,700 Kv motor is perfect for the Blue Moon 2.0.