Big Dragon 3. Simple but more sophisticated than it looks.

[quorneng]

Built using thin 3mm Depron sheet, 3D printed parts and a fishing pole rear boom. This pusher also has quite sophisticated aerodynamics and construction.

!.4m span it weighs 853g with a big 4000mAh 3s in the nose.
The wing uses printed wing ribs.

The lower Depron wing skin that has a 3mm hard balsa tapered spar flange glued in.

The ribs are glued directly onto the lower skin which is hand formed to match the rib nose profile.

Note the short ribs to allow for the ailerons.
3mm Depron shear webs are added between each rib over the position of the spar flange.
Only the top skin as far as the top spar flange are glued in place.

This creates a D box structure that make the wing rigid enough to be lifted from the building board. Note the aileron has been cut out and the trailing edge portion of the wing skin taper sanded down to 1mm.
The two halves of the wing are joined.

The aileron servos are added and their wire run through the ribs. Finally the remainder of the wing top skin is added.
The result is a very light but remarkably strong and stiff wing.
It is worth noting that there are no aileron horns or linkage. Each aileron servo is buried in the wing and its arm directly glued to the inner edge of the control surface. The servo itself is the inner pivot. The outer pivot is a pin, literally!

The printed fuselage incorporates the battery box and hatch in the nose with space for the Rx behind. The wing pylon has cooling vents included within it for the ESC. The pylon includes a printed motor mount and also gives the clearance from the boom for the 11.7e prop.

In this position the motor is very well cooled. It draws 250 Watts at full power giving 130W/lb and over a 1:1 thrust to weight ratio.
Not intended to "tear about the sky" but with a power cruise duration of 1 hour it does gives long periods of gentle relaxed flying.
Video to follow.

 

[bisco]

great work, i can't wait to see it fly!

 

[Bricks]

Curious why the winglets on the V tail? Looks good a lot of effort went into this build.

 

[quorneng]

Bricks
The low angle V tail was chosen simply to keep it clear of the grass in a belly land rather than a true V. It is elevator only (it uses a single servo for both surfaces) as Big Dragon 3 is flown "bank and yank" with differential ailerons to limit adverse yaw.
After the first flight it obviously needed more fin area and placing one at the tip of the tail seemed the most effective position. It also kept them out of the prop wash!
With the prop brake on it glides really well too.