The Frog Wren was originally a simple but pretty 25" span, twin fin, balsa and tissue tow line free flight glider, like this.
I wanted to make a powered 3ch version and built entirely out of Depron.
The 3.7g elevator and rudder servos are glued together as a block and mounted just behind the wing.
The control surfaces are driven by closed loop mono filament fishing line.
To operate the twin rudders the loop passes down over the top of the fuselage
out along the tail plane leading edge
Round the front of the fin, over the rudder horn to the trailing edge
Across to the other fin and back in the same way to the other servo arm.
It weighs almost nothing and yet is surprisingly free moving.
The elevator loop is just direct from the servo arm to the elevator horn.
The tiny 7g motor drives a 5x3 prop.
Initial testing showed a serious lack of directional stability so the twin fins were replaced by a big single one.
It now flew well enough to get the CofG and the main plane incidence at the best position.
The single fin was reduced in staged , then bigger, taller twin fins added along with a fixed central fin
and finally with just the taller twin fins.
Although the directional stability is now just about adequate it does fly remarkably well. With a 500mAh 2s it weighs 3.25oz.
This altimeter recording show just how well it goes.
47 minutes 30 seconds
The green line is the temperature.
It may look like I was using a 'climb and glide' technique but actually it was just the power difference of one click on the throttle stick!
Not bad from a 500mAh 2s with power on the whole time!