The Super-EZ-fly Delta. Another simple KFm4 wing

by davereap | April 13, 2017 | (4) Posted in Projects


My passion is for quick and easy builds, simple powered flying models with a good performance. And for me , any KFm wing is the easiest of all wing builds to make

So here is another super easy design, its easy to build and flies extremely well.  This one is a delta wing, with a triangular shape.

 The EZ-fly Delta uses a KFm4 wing, the KFm4 is made using three layers of foam. The three layers are directly laminated with the leading edges lined up. Producing a stepped wing, with a KFm4 section.

There are a few threads, with lots of information, on the various KFm sections to be found on in the scratch build foamies forum

The basic KFm4 section looks like this, it has a main /full shape layer with partial top and bottom layers laminated on, and lined up with the leading edge,  this method produces what is referred to as a stepped wing. The steps are always left sharp and the leading edge should always be profiled.

I have made this delta design in three sizes, the smallest being a 24", then a 30" and lastly a 38" span. The 24" was made using 3mm depron, the others used 6mm depron. However all the usual thickness foams can be used, anything from 3mm up to thicker 8-9mm EPP . The 5mm $shop foam board sheets will do for all sizes

Here is a look at the finished models.



Here are the lines, with dimensions for the biggest size at a 38" span

These larger sizes, at 30" and 38", were flown on a 150W 1000kv motor, using a 9x5 prop and a suitable 3s lipo. At max the draw was only 15A. This was more than enough power and a cruise at half throttle gave a steady smooth flight. below is an old video of its first flight.

Here is the 38" sketchup file. EZ-fly delta lines in a zip. Using this file its easy to scale up or down to any chosen span.

The smaller 24" version shown below used a blue wonder type of motor, a 2730-1300kv, on 3s with an 8x4 gws prop, the model has a good vertical performance and nice slow speed handling. The slot on these models can be placed further forward but the midpoint shown works fine. Another quieter alternative is to put the prop on the front, if noise is a problem for your location then do that.



 Cut a kit of parts.  consisting of 1 main / full layer, (every thing seen above).    two front layers (seen on the drawings in pink).  and two tail fins.

Cut off the elevons, using your blade set to cut at an angle, make sure this angle cut will produce a top chamfer on the wing layer. cutting at an angle the elevons are turned over so their chamfer is now at the top, they are swapped right for left and refitted back onto the wing using a full width tape hinge.  The first picture of the KF section shows how the elevons will be re-fitted.

Laminate the KF step layers to the main layer. Profile the leading edge, Fit the tail fins , these can be fitted either vertical to the wing or angled slightly outward. They can be fitted close to the side of the slot, or further out, it makes no difference. Using vertical fins , linked rudders can be added, they will further improve slow speed handling.

Spars. either a CF rod slotted into the wing as you laminate the layers, or to keep the cost low try Pallet Strapping. Strapping is put along the step lines above and below the wing to produce a foam sandwich. This is very strong and makes the wings nice and stiff, follow the step line and cross over at the center going out forward to the leading edge profile.

The prop slot should be cut out to fit your size prop

For a motor mount a tube type is always good and is what I used on mine. The square tube is glued to the main layer so the motor sits in front of the prop slot with the propeller lined up inside the slot itself. Cutouts are made in the main layer to accept the motor. once glued the tube can be blocked over to keep it secure. see the previous finished picture. Thrust lines are all set at zero, These tubes will accept the blue wonder motors directly, and other motors are fitted to the disks provided

All that remains is to fit the gear, horns and pushrods, and to get it balanced.. the pictures show where all my gear was positioned. 


 This is another one of my super easy KF builds that fly so very well, as can be seen in the video. The prop position in the slot does make it noisier than a prop on the front, but it does protect the prop in the event of a heavy landing. Either position is however fine, so its your choice. On the KFm wing itself, I use a KFm2 from 6mm , or a KFm4 from 3mm on smaller sizes and a KFm4 all 6mm on the larger sizes. Alternatively please use your nearest equivalent , all will work fine






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The Super-EZ-fly Delta. Another simple KFm4 wing