Swappable Pusher with Canard: "Blackwing"

Introduction

This article describes my design for a swappable, pusher airplane with a canard wing. It is based on re-arranging components from the Bloody Wonder mkIII design by SP0NZ. This article includes pictures from the unique parts of the build process, a test flight video and plans for this airplane.

Pusher/Canard Configuration

I love the Bloody Wonder. It is simple to build, exciting to fly and very robust. I really like how the entire wing is a fold-over because it avoids the wing-tip damage that I inevitably do to my FT builds with wing-tip undercamber. Of course, while the absence of any undercamber or dihedral provide excellent maneuverability, the skill level required of the pilot is increased, as is the likelihood of tip-stall. 

The pusher/canard configuration is one way to make the venerable Bloody Wonder design even more interesting. When I do eventually crash and ruin my BW's, it is because I have nose dived into the dirt and busted a firewall or propeller or bent the powerpod. Luckily I haven't bent a propeller shaft (yet) but my nose cone shows the evidence of my many mishaps. Putting all of the valuable electronics in the back of the plane means that the $1 foam fuselage takes the hits instead. Of course moving the motor, ESC and receiver to the back of the plane will also move the CG aft which pushes the designer toward the aft-wing and canard configuration. One more benefit of the canard is that it can be designed to share the load of the main wing. For example, David's highly successful FT Viggen design has 10 degrees positive angle of attack on the canard wings (relative to the main wing). This will give the plane a very nice stall characteristic because the AoA of the canard is always 10 degrees greater than the main wing, ensuring that it will stall first and cause the airplane to nose down.

The "Blackwing"

With all of this in mind I had the idea to use the MKIII BW's wing design and fuselage, except flip the wing around and move it as far toward the back of the plane as possible. I then added canard wings that fit into slots cut into the fuselage with 10 degrees angle of attack like the Viggen. I also added a single rudder that fits into a slot cut near the back edge of the wing. I built this plane with electronics from Power Pack C, and a 2200 mAh 3S battery. To get the CG right (about 1/2" forward of the main wing leading edge) I put the battery in front of the power pod. This is nice visually and aerodynamically because it tucks into the fuselage, rather than dangling from beneath the power pod, like on the BW MKIII.  The photos below demonstrate the placement of the electronics within the power pod and the location of the battery.

Propellers

I have flown this airplane with 8x4.5, 9x6 and 10x4.5 propellers, all with good results. The video in this article is with the 8" prop which is nice, but with the 10" propeller this airplane really rips and has a very cool sound. Even with the 8" prop I like the sound of this airplane alot.

Unsuccessful Design Variants

The design presented in this article is actually my fourth. In the first iteration, the canard was a miniature version of the main wing, with split trailing edge control surfaces, actuated by one servo and meant for pitch control. 

 This thing was hooooooooorible. The canard-elevator was not big enough and too close to the CG and therefore did not provide any pitch control authority. Back to the drawing board!

The second version used a fixed canard with 10 degrees AoA and elevons on the main wing for pitch and roll control. This plane flew really well and is very similar to the final version. The CG of V2 was farther forward and the wing was attached to the fuselage with rubber bands. This was nice because the fuselage could be replaced easily, but it was a pain in the butt to get into the powerpod because the rubber bands had to be removed.

Version 3 reduced the AoA on the canard to 5 degrees. This version was pretty good and was a little faster, but the CG had to be moved aft to balance the plane which reduced the yaw stability. This plane was ruined when I crashed into a tree. The forward momentum of the fuselage stretched the rubber bands and the spinning propeller tore the elevons apart! Whoops!

With version 4 I have gone back to 10 degrees on the canards and a CG just 1/2" forward of the main wing LE. With this setup the stall characteristic is awesome: if you cut the throttle and pull all the way back on the elevator the plane will assume a slow, steady decent with a level attitude. I've ridden this mode all the way to the ground for a fairly nice landing.

Black Adams Readi-board

The namesake of this airplane is fairly obvious, and came about because I wanted to test out the black foam board from my local Dollar Tree. It sucks. The paper is not attached to the foam as well as with the standard DTFB, and it makes it weaker and more difficult to work with. It looks kind of cool but other than that, not recommended.  

Build Quirks

This thing goes together just as easily as the Bloody Wonder, except for a few small quirks. First, I only put a slot for the canard into the plans for the fuselage, not the fuselage doubler. I found it easier to build the fuselage, glue in the doublers and then use the slot in the fuse to cut out the slot in the doubler. That way you can be sure they line up perfectly.

Secondly, the canards need to be strengthed a little bit because they need to carry more load than usual for a single layer of foam. My solution for this is to cut a 2.5" length of BBQ skewer and insert it all the way into the inboard end of the canard. I inserted it about 1/2 of the chord from the leading edge and tried to follow the angle of the canard leading edge. Pictures of this process below:

Make sure that your skewer is sharp and that it is aligned with the surface correctly, otherwise it could poke through one side or the other. Its not difficult if you're careful about it and provides all the necessary strength at the root of the canard.

Flight Videos and Plans!

I really had fun designing and flying this plane, please let me know if you build it also and if you have any suggestions for improvements! Thanks for reading!

and

Blackwing Full-size Page 1

Blackwing Full-size Page 2

Thanks SP0NZ for allowing me to modify your BW MK3 plans and include them in this article!