The Zepron Micro Funfly (ZMF)
Building a Micro Funfly out of Zepron
The ZMF is an aerobatic slowflyer made out of Zepron.
The statistics are as follows:
|Zepron Micro Funfly|
|chord|| 18cm (including 3cm fullspan ailerons)|
|airfoil|| symmetric, 26mm thick|
|mass|| 150 grams|
|motor|| Potensky POT-2A with a 7.8x4.7'' folding prop|
|speed control|| Jeti JES-050 or 040|
|battery|| 7 cell NiMh, 150mAh|
|radio|| Hitec Feather receiver or GWS Pico with 2 HS-50 or HS-55 servos.|
Building the ZMF
- one sheet 60x30cm sheet of 2mm Zepron (wing)
- one sheet 60x30cm sheet of 3mm Zepron (stabilizer, fin, ailerons).
- a piece of thin balsa for the ribs
- a piece of pink foam (the insulation foam found in hardware stores for thermal insulation).
- a small piece of thick balsa (motor/battery mount)
- small piece of styrene or ABS plastic or thin plywood (control horns)
- 1mm diameter piano wire (control rods)
- a roll of Blenderm (medical sticking tape made by 3M).
- 6 minutes epoxy glue.
- a couple of self sticking velcro pads.
- 3 channel micro radio (e.g. Hitec Feather with feather receiver and two HS-55 or HS-50 servos).
- Potensky POT-2A motor or equivalent
- 7 cell NiCad (50-250mAh) or NiMh battery (150-350mAh).
I use a 7-cell 150 mAh NiMh sold at the local Radio Shack
as a replacement for 9v alkalines. I charge them at 0.3A.
Some brands don't survive that treatment, but some do.
Building the wings
The ZMF wings are made of a single sheet of 2mm Zepron folded
over 6 balsa ribs. There is no need for a spar.
Cut 6 ribs from thin balsa (see template on the right).
Hold the ribs tight together and sand them so they are all smooth and identical.
Cut a 60x30cm rectangle out of 2mm Zepron. Draw a line right in the middle of
the rectangle along the longest dimension,
then stick Blenderm tape on top of the line. This will be the exterior of the wing.
The Blenderm will prevent the sheet from breaking when we fold it.
Flip the sheet so the face with the Blenderm (exterior) is against the table.
Then trace a median line along the longest dimension as before.
Slide a cutter knife at 45 degree angle on either side of the line so as to
make a V-shape groove as shown on the picture. The groove should be
about 1mm deep (half the thickness of the foam). Make the groove is
not an absolute requirement, but it makes it easier to fold the
sheet afterwards. Align the edge of the foam sheet with the edge of the
working surface and sand the foam into a wedge as shown. This will be
the underside of the trailing edge.
Pin or tape the sheet on the table with the edge closer to you (the one
you just sanded to a wedge) flush with the edge of the working surface.
That edge will be the lower side of the wing's trailing edge.
Trace the location of the 6 ribs: the 3 ribs on either side of the wing
must be 1.5cm, 15cm, and 30cm from the centerline repectively. Glue the
six ribs using odorless CA, 6 minute epoxy, or double-sided tape.
make sure to position the ribs so that the V-groove on the sheet will
line up with the front tip of ribs when the sheet is folded.
Pin down the ribs by their "tail", with the front part sticking up
(this process is a lot simpler with a flat underside airfoil).
When the glue is set, fold the sheet while heating the bending
zone near the leading edge with a heat gun. Fold it so the upper side of
the sheet makes approximately a 90 degree angle with the table, and so that
it follows the curve of the underside of the ribs. It is helpful to slide
a wood dowel or a metal tube (or anything long and thin you can find)
under the front part of the wing to maintain the sheet in contact with
the front underside of the ribs. Glue the sheet to front of the ribs
and let it set.
Now for the fun part. Remove the pins from the ribs, except for the
outermost ones. Apply glue or double-sided tape to the top side of
the ribs and to the wedged lower trailing edge. Fold the foam sheet
using a long straight object (an aluminium square or something).
Hold down the long straight object with a weight while the
glue sets (or with your hand if you have nothing better to do).
After the glue is set, you have an aerodynamically correct,
smooth, stiff, and unwarpable wing that weighs about 30 grams.
Building the ailerons, stabilizer, and fin
To build the horizontal stabilizer: cut a 30x12cm rectangle
from 3mm Zepron. Then cut this rectangle into a 30x8 strip
(the stabilizer) and a 30x8 strip (the pitch control surface).
Cut it with the knife at a 45 degree angle so that you can
then flip the 30x4 strip upside down and hinge it to the
stabilizer with depron.
To make the hinge (this applies to the ailoron hinges as well):
Stick three strips of Blenderm (approximately 4cm each) to the
underside of the control surface (one at each end, and one in the
center). Position the control surface on top of the stabilizer
as shown in the picture.
Fold the Blenderm strips around the stabilizer.
Rotate the control surface in its normal position.
Now stick three strips of Blenderm to the top side
while maintaining the control surface as in contact
with the stabilizer. You now have a gap-free hinge.
The ailerons are cut from 2mm Zepron. Make then full-span
and 3cm wide. Cut the front side of the ailerons at an angle
so it can swing when hinged on the wing. Cut control horns
out of ABS plastic, thin plywood, or whatever material in which
you can drill 1mm holes. The hole in the horn should be approximately
15mm above the hinge (assuming you will use a 25mm servo horn).
Cut out the top of the wing to fit the aileron servo.
Connect the servo to the horns with 1mm piano wire
bent with Z-bend pliers. If you don't have Z-bend pliers,
get one immediately (Tower Hobbies
carries several models). The servo is held in place with
The vertical fin is cut from 3mm Zepron. Cut a nice-looking
shape that fits in a 13x13cm square. Glue the vertical
fin to the horizontal fin.
Building the fuselage
The fuselage is made from the 1'' thick pink foam found a
Home Depot. It is 46cm long and 4cm high at its tallest
section (right in front of the wing). Give it the shape you want,
but strenthen it with thin strips of balsa, carbon, non-stretch
adhesive tape, or other material. Without this reinforcements,
the fuselage will break at the first hard landing
(guess how I know....). With the recommended motor and
battery, the wing leading edge should be approximately
8.5cm from the front of the fuselage. Cut out the top
of the fuselage to the shape of the underside of
the wing (this is rather tricky). The wing is held
in place with rubber bands.
The motor and battery mount is a small piece of 3mm balsa
covering the front part of the fuselage. The motor is simply
Blendermed to it. The battery is held with self adhesive
velcro disks. The receiver and elevator servo are positioned
right behind the wing and held inplace with double-sided tape.
Putting it together
Zepron Micro Funfly in Flight
The ZMF flies pretty slowly and is quite easy to fly. My 12 year old
son flies it with no problem. Although it flies OK on a 7-cell 150mAh
NiMH battery, it is much more snappy with an 8 cell 300mAh NiMH. The
ZMF can do loops and rolls, but rolls are a bit slow (altitude drops
Have a look at the complete
ZMF picture and movie gallery. Unfortunately, the movies only show it flying
with a 7-cell battery, not the preferable 8-cell battery.