I am always happy to make things from cheap parts, especially when you add up all the money I spend on my hobbies. Building radio control airplanes from BlueCor (Fan Fold) foam board keeps cost down.
In addition to being low cost, Fan Fold airplanes are fast to build and easy to repair. This build should take less than two hours, and sans electronics, cost under $5.00. Compare this to commercial kits, which start at $40.00 for a box of foam. Forty Dollars is not a bad price, very good in my book, but you can build eight wings for the same price.
If you have read my post on my interest in Flying Wings, then you will know that this is the second wing I have built in the last thirty days. I said they were cheap.
This wing uses a Kline-Fogelman Airfoil and the design comes from a discussion on RCGroups.com that was started by Tony65x55′s. This is different than the first wing I built, which used an asymmetrical airfoil.
What makes the Kline-Fogelman Airfoil so different is that it has a step under the wing which creates low pressure under the wing. This goes against the norm of airfoil design, which strives to create the low pressure on the top of the wing to produce lift.
In the Kline-Fogelman airfoil, the step is located at 40 to 50% of chord.
The low pressure area works similar to the steps on a hull of a boat, it pushes the wing upward. This wing has great characteristics at all speeds, it is very easy to land, and requires no elevon reflex to stay level in flight.
One of my flying club members, who flies the Unicorn, was impressed at how stable, yet responsive the wing was. The landings are soft and slow, not at all the high speed landing he is used to.
To build the wing you will need a few things:
- BlueCor foam sheet (2×4 piece x 1/4 thick)
- Spruce spars – (3 pieces, 1/4 or 3/8 square stock by 3 feet long)
- Duct Tape (lightweight is better)
- Zip Ties (4 small to medium size)
- Pins (6 T-Pins or Map Pins)
Tools you will need:
- Cutting knife/Razor (Xacto or other hobby knife is fine)
- Straight Edge, Triangle, or t-square
- Foam Safe CA Glue or 5 Minute Epoxy.
For the Radio Control you will need:
- R/C Radio that support delta wing or elevon mixing
- 2 Mini Servos
- Lightweight Receiver (park flyer type is fine, I use the Spektrum DX6 Radio & Receiver)
- Motor (I used a brushless UltraFly Frio 10 with speed Apollo 12 controller)
- Propeller (I used GWS 8×6 electric prop)
- Battery – LiPo (I used 3Cell ElectriFly Lipo)
- Lay out the 2′ x 4′ FanFold on a flat surface, make sure you foam is flat and wrinkle free. The Dimple side can be the top of the wing, and the side with the manufacture can be the underside. It doesn’t matter really, it is just aesthetics. Using a t-square, triangle and straight edge, draw out the pattern from the plans.Cut out the foam using a very sharp blade, and use a good straight edge. Be careful, no blood on the foam please.Once all the pieces are cut, use the folding instructions. Make sure you bevel one edge at 45 degrees to make the fold easier later. Tape the two pieces together before folding and glue the spruce spars before folding.If you are not planning on going fast with this wing, the layout of the cross spar is fine, otherwise it should be further back. I noticed some flex and flutter at very high speeds. After the wing folded during a flight, I corrected the problem with the addition of a second spar. If I had placed the initial spar further back initially it would have been fine. FoamingINMI has posted some great photos of what the build should look like at this point.When you are ready to make the fold, put the Foam Safe CA glue on the spruce spar and put CA activator on the other surface. Then when the two touch you have instant set. If you are not sure of this, leave out the activator, make the fold, and put some weights to hold in place until the glue sets.The elevons are cut from the same foam and are attached with the duct tape. Make sure they are flat and the wing is flat when you attach. Note that you will need to bevel the side of the elevon so it can swing downward and upward.The fins are attached with a few pins and foam safe CA. The fins should extend down below the step about a half inch. They help keep the air from “spilling off the wing” as well as provide stabaility.
The motor was mounted on another piece of spruce, or you could use a piece balsa plywood depending on the motor and the mount needed. I used some CA and zip ties to keep it in place.
The servos are mounted with zip ties. Reinforce anywhere you put a zip tie through the foam with some tape. Put the tape first, then make the hole.
For the elevons, I used control horns I had around, but you could use popsicle sticks and 5 minute epoxy.
The speed control, receiver, and battery are all Velcro’ed on to the center of the wing. The Velcro easily lets you move the battery forward or aft to adjust center of gravity. The Kline-Fogelman airfoil has a very forgiving, wide center of gravity, which makes it easy to balance.
Add some more tape to the center front of the wing, help reduce impact damage on any nose in landings. Not too much, careful of the weight. I also added tape fore to aft on the sides of the velcro. This added some strength as I saw a few stress cracks after the first flights.
You are about ready to fly. Make sure you put the prop on in the right direction. Give it a go. If it lumps around, then the center of gravity is off, make your adjustments accordingly. The motor I am using is 2.13 oz, and I have the battery about 1.75 inches form the nose, and the balance is great.
This wing is can move, it will surprise you. With the 3 cell LiPo battery and an 8×6 prop on that brushless motor, she really picks up speed.
On about my 10th flight I was going full speed in a loop and the plane began to flutter, it then folded and fell to earth from about 150 feet. I shut the motor very quickly, and it did a slow spiral down. The damage was minimal and easily fixed. The spruce spar going across the wing came loose and the plane folded along stress cracks on the left side of the velcro. I re-glued, added some tape, and added the second spar. It flies fine, has a little flutter but nothing to be concerned about now.
It flies well in heavy and light winds. I had it out with winds gusting over 25 mph, and there was no problem flying it. Just watch turns against the wind, then you get pushed around a bit.
Enjoy your $4.99 wing.