Here's a build of the popular Leadfeather Yak 55, scaled
from 32" to a 28" wingpan and made with heavier 1.9# EPP foam.
This plane is optimized for streamer combat, with really good speed,
agility and durability. The total cost of foam and parts can come
in under
$70. See the parts list
below.
The build guide at racores.com is a good reference to use. The guide is written for the lighter 32" Yaks,
but the build steps are very similar. The "wedge shaped tail
stiffeners" and "small foam quarter circles" referenced in the
racores.com build guide are not used and not needed with the heavier
28" version of the Yak.
The plans for the original 32" Yak can be found on rcgroups, and there is a build
guide posted. I modified the layout to scale it down to a 28" wingspan, "EPPYak55-28_multiPage.pdf",
and it can be
printed on standard 8.5"x11" letter-sized sheets. When printing,
set "Page Scaling" to "None". I've also posted a "full" version, "EPPYak55-28_full.pdf".
To cut out the foam I printed the paper sheets, taped sheets together as
needed, attached sheets to the foam with double-sided tape, and then cut
through with an exacto knife. I used a metal ruler for the
straight lines and free-handed the curves, following the printed lines
on the sheets. Foam-Tac is good for gluing the foam pieces together.
A 7.0mm x 1.2mm carbon strip is mounted in the wing, and a
5.0mm x 0.6mm carbon strip is mounted in the elevator. The easiest way I've found is to slice through foam,
insert the strip, and then glue with thin CA and accelerator.
Pieces of 5.0mm x 0.6mm carbon strip can be
mounted to the leading edges of the wing for reinforcement, attached
with epoxy and blenderm tape. Short pieces can also be mounted
between the wing and the fuse, as shown in this picture.
I used blenderm tape for hinging the control surfaces. Hinges can
also be done with Foam-Tac or Welders glue, as described in the racores.com build guide.
For decoration, most any kind of paint can be used, or even magic
markers. I painted with Testors All Purpose Spray Enamel (in the
small can). One thing to be careful of is not to apply too much
paint, as it will add weight to the airframe.
A strip of blenderm tape along the bottom of the fuse helps to protect
it. Putting double-stick tape on the leading edges of the wing
can make it easier to catch streamers. Quick field repairs can be
made with blenderm or packing tape. Tears in the foam can be
repaired permanently and cleanly with Foam-Tac (giving it a few hours
to set if the two sides can't be air dried for 5-10 minutes before
pressing together). Using CA to repair EPP results in "hard
spots" in the foam.
A nice plywood firewall for mounting the motor is available from RA Cores: Large Plywood Firewall.
(Various other accessories are also available there). Gluing the
plywood firewall to the foam with epoxy works well. The screws
that come with the servos can be used to attach the motor to the
firewall. Be sure that the grub screws on the cylinder of the
motor mount are not too loose, or the motor may come out in flight; but
also beware of tightening them too much or the motor may bind up.
Installing them firmly with some blue threadlock is a good way to do it.
Pushrods can be made using carbon-fiber rods and music wire:
One thing that can help is to make the heat shrink a bit "short" on
each end so the CA can get in between the music wire and the carbon
rod. Music wire with a .040" diameter will also work. Using
Dubro
Mini E/Z Connectors on the servo control horns makes it easier to
adjust the lengths.
Here's a video of indoor combat taken with a FlyCamOne2 mounted
above cockpit area of my Leadfeather Yak. First part is a bit of
flying with rear-facing camera, then front-facing during streamer
combat, with a couple of crashes. Edited using VirtualDub.
