This Instructable shows how I built a VTOL (Vertical Take-off and Landing) hybrid drone, aka "Quadplane", starting with a very basic fixed-wing radio control aircraft kit and customizing it with off-the-shelf quadcopter components. The end result is a very capable multi-purpose drone, ideally suited to a range of technical applications. The hybrid or "Quadplane" concept combines the best of both worlds: Duration,speed and range of a fixed wing aircraft with the vertical flight aspects of a rotary wing aircraft. A typical quadcopter can only fly for around 15 mins and will struggle to cover more than 10Km in a single flight, whereas this quadplane can fly for nearly an hour and cover around 50Km. If a runway is available to use for launch and landing, then the rotary wing components can be removed in a few minutes for fixed-wing only flight. The reduced weight in this form gives around 80mins flight duration and 70Km range.

The drone is dual purpose in the application sense too, because it can be fitted with two sensor types, depending on the task required:

1. Stabilized video for applications in conservation, security, Search & Rescue, surveillance, etc.(see first demo video).

2. High resolution hard-mounted stills camera for photogrammetry, terrain modelling, crop monitoring in agriculture, etc. (the second video shows a typical photogrammetry/3D model application).

The aircraft I chose as the basis for this concept is called a Quanum Observer, which is available as a kit from Hobbyking (it is also sold by other retailers under the name of Volantex Ranger-Ex). This Instructable is not intended to deal with the basic steps required to build the kit into a "standard" RC model - those steps are fairly straightforward and covered in the manufacturer's instruction manual. Rather, this Instructable covers the mods required to convert the fixed wing aircraft into a hybrid quadplane, capable of autonomous flight and able to carry sensors required for technical tasks as mentioned above.

The wingspan of the aircraft is around 2m and the quadcopter frame is 1m (measured diagonal). All up weight in it's quadplane form,including batteries and camera, is around 4.8Kg. By removing the quadcopter components (ie. flying it as fixed wing only aircraft) the weight comes down to 3.7Kg, but that obviously requires a landing strip.

Here are the main components of the build, with links to the respective suppliers/manufacturers:

Volantex Ranger-Ex: http://www.banggood.com/New-Version-Volantex-Range...

Futaba 14SG radio control set: http://www.futabarc.com/systems/futk9410-14sg/

Turnigy SK3 3542 1000KV: http://www.hobbyking.co.uk/hobbyking/store/__18163...

Hobbywing 60A ESC: http://www.myrcmart.com/hobbywing-platinum-60a-v4-...

T-Motor MT4006 740KV (x4): http://www.rctigermotor.com/html/2013/Professional...

T-Motor Air 40A ESC (x4): http://www.rctigermotor.com/html/2014/esc_1223/285...

T-Motor carbon props 14 x 4.8 (x4): http://www.rctigermotor.com/html/2013/prop_0904/32...

4S 5,200mAh lipo (x2): http://www.hobbyking.co.uk/hobbyking/store/__56840...

Pixhawk flight controller: https://store.3dr.com/products/3dr-pixhawk

Carbon Fibre Square Box Section 8mm (7mm) - 1m Length (x2): http://www.easycomposites.co.uk/#!/cured-carbon-fi...

Carbon sheet at motor mount: Prepreg Carbon Fibre Flat Sheet 0.5mm: http://www.easycomposites.co.uk/#!/cured-carbon-fi...

Booms: 20mm(18mm) Woven Finish Carbon Fibre Tube - 1m Length: http://www.easycomposites.co.uk/#!/cured-carbon-fi...

20mm Tube clamps: https://www.hobbyking.com/hobbyking/store/uh_viewI...

CNC Motor Mount for DIY Multi-Rotors 20mm Tube: https://www.hobbyking.com/hobbyking/store/uh_viewI...

Hitec HS-65 servos (x6): http://www.servoshop.co.uk/index.php?pid=HITHS65MG

600mW Video transmitter: http://www.immersionrc.com/fpv-products/5-8ghz-600...

3D printed pitot holder: http://www.shapeways.com/product/NTAMX6FNG/3dr-pix...

GoPro camera and suitable 3 axis gimbal

Wiring, connectors, glue, stock wood

Step 1: Flight Controller Mounting

To convert a normal radio control aircraft into a drone capable of autonomous flight requires a flight controller/autopilot. This also controls the transition between fixed wing and rotary wing modes - something that would not be possible by human-only control. This aircraft uses a 3DR Pixhawk flight controller and is loaded with the latest firmware version (3.6.0) which has "quadplane" support. Some very clever code, indeed, from the APM software developers!

The flight controller mounting rails are screwed to the bottom of the fuselage. One cannot use glue, as the polypropylene material does not bond well. The mounting must be absolutely level in relation to the wing seat. If not, then the aircraft will not fly well. The second photo shows how one can use a mobile phone with a bubble level app to achieve this. Note that both roll and pitch axes need to be leveled in relation to the seat of the wing.

Step 2: Control Surface Hardware Mounting Points

These photos show small plywood discs recessed into the control surfaces to act as mounting points for the control horns (these are on both sides of the control surface). Raw foam is never good for mounting control horns as they will come loose at some point. The first photo also shows how I used dual elevator servos recessed into the stabilizer and then covered the servos with thin carbon sheet to tidy things up and reinforce the area where the foam was removed.

Arguably, the mods described in this step are not necessary for this aircraft, however, when lifting expensive cameras and flying near people and property, the last thing one needs is a control linkage or servo failure.

Step 3: Camera Mount and Battery Tray Modifications

This step illustrates the modifications required to carry a hard-mounted stills camera (Sony RX100 in this case). The first and second photos show the three main components in this mod and are all made from plywood and balsa: 1.Wedge-shaped battery mount

2.Camera holder

3.Rear stopper.

The fourth photo shows the lipo batteries in place which sit partially above the camera. The fifth photo shows the fuselage underside with hole created for the camera lens. This hole is also used for the gimbal attachment when using the stabilized video camera option. For the hard-mounted still camera option shown in these photos, a "Stratosnapper" trigger is used which allows GPS-controlled camera firing via Pixhawk flight controller.

Step 4: Canopy Modifications

In order to accommodate the camera and batteries, the canopy requires some modifications since the foam canopy "floor" which comes with the kit is too deep (the first photo shows how the batteries sit proud of the fusealge). The second photo shows how I used balsa rails to create a frame and the batteries can then protrude into the canopy space.

Step 5: GPS and Pitot Tube Mounting

These photos show the positions of the GPS unit and pitot tube holder. The latter is from Shapeways and fits the 3DR pitot tube perfectly.

Step 6: Quadcopter Components: Boom Mounts

This photos shows the underside of the wing (left panel) and how I milled out some foam to accommodate the carbon fibre sheet which covers the quadcopter boom mounts, wiring and plug points.

Step 7: Quadcopter Components: Carbon Reinforcement Spars

This photo shows the the 8mm x 8mm square carbon fibre spars which are recessed into grooves in the lower surface of the wing. The grooves are actually 11mm deep so that 3mm is left to run the motor wiring along the spars and everything is flush. The spars run full length between the left and right boom mounts which gives the wing the required strength.

Step 8: Quadcopter Components: Boom Mounting Lugs

The first photo in this step shows the mounting lugs made from glass fibre sheet which are screwed to the aluminium boom clamps with blind nuts (this allows the clamps to be removed for fixed-wing only flight, if a runway is available). The second photo shows how the mounting lugs are glued to the 8mm x 8mm carbon spars in the wing.

Step 9: Quadcopter Components: Wiring Terminals

These photos show the quadcopter motor wiring and plugs which are mounted in the wing.

Step 10: Quadcopter Components: Wiring

The first 2 photos in this step show the quadcopter motor wiring and how it is laid long the 8 x 8mm carbon spars and then closed up with tape. The third photo shows how the boom mounting hardware and wiring is tidied up with carbon sheet. In the fourth photo, the Quadcopter boom is in place with motor wiring plugged in.

Step 11: Parameter Settings and Flight Testing

One will need to install quadplane-enabled firmware and then do some PID tuning to get the aircraft to fly properly. I have attached a file to show the parameters on my Pixhawk which I have settled on after around 20 flights.

This aircraft is huge fun to fly. The transition between fixed and rotary wing is absolutely amazing!