Updated May 18, 2012

A couple months ago I flew a Chris Klick designed Zephr II and was very impressed with its performance and gentle flying characteristics. I had wanted to try a KFm4 airfoil and had some scrap Depron so the Mini Depron Zephr II was born. Chris has named it the Mini Dep Zep. It is one fine flying wing.

This platform has great flying qualities, is easy to build, inexpensive ($40 total cost) and easy to transport. Beginners to experienced flyers enjoy flying this wing. Formation flying with multiple wings has become common place at our field; the plane feels like it is on rails.

I’ve built two versions, a 2S and a 3S. The 2S configuration is just a joy to fly with plenty of performance and the 3S is speedy with out of site vertical performance, including vertical takeoffs.

I’m tired of building these wings, 11 as of today. This build log, with step by step instructions, allows new wing want-to-bes to build their own. The most important action is to get your Chinese parts ordered. There is nothing worse than a wing owner waiting on the China mail to arrive.

Flying the 2S and 3S versions.

Mini Zephr II: 24" and 28" Flying Wings flown by Otto Dieffenbach (2 min 30 sec)

Vertical Takeoffs with the 3S version.

KFm4 24" Mini Zephr II Flying Wing Vertical Takeoff flown by Otto Dieffenbach (0 min 48 sec)

Seven wings at play.

Flying Wing Meet Up (3 min 43 sec)

2S versions at play.

Mini Depron Zephr II (Mini Dep Zep) KFm4 Wings at Play by Otto Dieffenbach (3 min 31 sec)

Mini Zephr II Parts List

AX 1806N, 2500kv motor (HK) $9
Exceed RC Proton 10A Brushless Speed Controller ESC (hobbypartz) $12
2 HXT900 (HK) or T-Pro SG-90 (hobbypartz) $3
SPECTRUM AR6100 E, clone parkflyer receiver (targethobby) $4
Female JST connector (red)
3- ½” 2-56 screws
E-Flite 3mm prop adapter

2S setup (quick with 6 min flying time):
APC LP05145E prop 5.1 x 4.5
GENS ACE LIPO 800mAh 20C 7.4V lipo battery pack (hobbypartz) $4.50

3S setup (really quick but 3 min flying time):
APC LP04541E prop 4.5 x 4.1
GENS ACE LIPO 450mAh 25C 11.1 V lipo battery pack (hobbypartz) $4.35

Other:

5 or 6mm Depron or Model Plane Foam sheet
1/8” Plywood (plus access to a scroll saw)
9" long, 1/8" dia. carbon tube spar
music wire
clear boxing tape

Using the drawing as a reference, layout the design on a large sheet of paper. The back of wrapping paper works well. Make a set of patterns and cut the parts from a sheet of 6mm Depron. If you have a 39" x 27" sheet, you can cut 3 complete sets of parts.

Glue the leading edge, upper and lower pieces, together. Run a bead of foam safe CA along the leading edge and join the pieces using scrap Depron as a spacer/separator on the rear edge. Put a weight on top to hold straight and run some CA accelerator along the leading edges.

For each wing half, insert the rear wing piece into the rear slot formed by the upper and lower front pieces. The overlap should be 3/8". Tack glue at each end and confrim alignment of the pieces at the ends. Run a bead of CA down the joint on both sides of the wing half. Apply some CA accelerator.

On a flat surface, draw a 14" x 14" square. Use this square to trim/sand the centerline and tips to insure they are parallel.

Using a very sharp knife, trim the top and bottom of the leading edges. Use a 150 grit sanding block to complete shaping of the leading edge.

Using a straight edge, cut the elevons from the wing panels. Bevel the front of the elevon at 45 degrees with the knife and sanding block. Be careful to make a right and left wing panel.

I use clear box packing tape to protect the leading edge and to hinge the elevons. I run a length of tape around the leading edge and seal with a covering iron on medium heat setting. I run a length of tape on the top of the elevon hinge line. I then fold the elevon over and run a length of tape along the bottom. I then use the covering iron to seal the tape. As a durability option, I recommend 5 mil New Stuff, for the leading edge. If you use New Stuff back to the step the structure becomes quite rigid.

Before I attach the tip plates, I draw a centerline on one side for alignment with the wing and wrap/seal tape to the bottom edge to protect the Depron on landings. Make sure you make a right and left tip. Attach the tips to the wing halfs with CA.

The servos are now installed. Their bases are located 2 1/4" from the centerline, as far forward as possible. I cut out the servo outline in the top Depron and rout into the lower Depron with a 1/8" drill bit in my Dremel being careful not to go through the bottom. I thread the servo wire between the leading edge top and bottom and glue the servo inplace with CA or Gorilla Glue.

From 1/8" ply, you now cut the center backbone and motor mount. For the 1806 motor, a quarter makes a perfect circle pattern for the motor mount. If you are using the 2S or 3S batteries specified, the motor mount location shown on the drawing is correct. For heavier batteries you will want to move the motor to the rear. Take a wing half and butt the center section to the ply and trace the wing outline. Now trace the battery outline flush to the bottom of the leading edge location. Now draw the skid bottom line allowing a quarter inch from the battery for strength. I extend this line straight to the bottom of the motor mount as shown in the more recent pictures with the orange color scheme. Flyers have been breaking the backbone on full speed dives into the ground. Draw the backbone support for the motor mount at the proper location. Using a scroll saw, cut the pieces and sand. Drill a 1/8" hole at the loaction for the carbon spar. CA glue the motor mount to the backbone. Note the upper backbone is for a heavier battery setup, 3s 1000mah. That backbone is 1" longer for balance.

Stuff the excess servo lead into the wing hollow leaving about 2". Make a knotch in the wing for the lead to exit at the backbone joint. Fit the backbone to the wing half and make the motor cutout. With CA, glue the backbone to one wing half. Let dry. Note, the last two pictures show the heavier battery setup. The servos will be located in the rear wing piece for balance. Before joining the other wing half, install the carbon spar through the backbone and into this wing panel. Cut a 1/8" grove in the bottom surface for the spar and glue with CA or a small bead of Gorilla Glue.

Using the same process as in Step 11, join the other wing half. I use a lot of CA, hold the joint firmly together and touch with accelerator. At this point, add a 9" carbon spar running from outside one servo to the outside of the other in the lower step (picture with orange color scheme). The spar should intersect the V joint of the lower step. This will make your wing more durable and the Depron less prone to cracking.

I frabricate my own control horns but you can get some from most hobby shops. The Parkzone horns work well. I center each servo, make a linkage with Z bends in both ends, attach the link to the servo arm and the control horn. I then glue the horn to the elevon with 3mm of up elevon in each elevon at neutral. If you want an adjustable link, feel free to use one instead. Throws should be 7mm up and down in both elevons.

Using double sided foam tape, mount your ESC and receiver as shown. Make sure that you make the top and bottom of your wing different in appearance. I use duct tape and pin stripping.

Check your CG; it should be 4.75" from the wing's point. Check your lateral balance and correct with small nails, if required.

I have done enough of these wings to know that the motor torque and elevon correction creates a little nose left yaw. I glue a little 1/4" x 1/4" Depron square under the right wing panel, 1" from the tip, on the top of the wing's step.