Swept wing design with engine cutout in the center

Finally I got time to check the difference between flying wings (swept wing design) that have a cut out in the center part of the wing  for the prop. I was surprised to find out that it was not reduced lift but additional induced drag that made the wing with a reduced depth of the wing in the center (because of forward mounted engine to meet the CG) less efficient.

Here is a comparison of two similar wing designs, one with a cutout for the engine in the center, one without:




Click on the animations for a higher resolution video.

It is interesting to observe how the drag increases significantly in the center, if there is a cutout for the engine.

The yellow surface visualizes the induced drag, the colored arrows lift.

Caipy + PX4 + Live video

TBS Caipirrinha with downward tilted camera, pitot holder and PX4 auto pilot.

I have been overhauling the ConservationDrones.org Caipy build. This build looks pretty much like the previous one but under the hood, there is not really much left from the last build except the servos, ESC, engine and the Battery.

First of all, this one features a long range live video feed while still being an autonomous vehicle if you want. The ArduPilot 2.X has been replaced with a PX4+PX4IO. The old, rather problematic analog airspeed sensor has been replaced with the swiss 4525DO digital airspeed sensor. Additionally a PCB camera has been added (60° FOV), a TBS 400mw 2.4GHz transmitter, a TBS core (for constant 5/12V power supply to the camera and video TX) as well shielded wiring for the video setup. New is also the 3D printed pitot holder which keeps the pitot tube from getting dirty during landings. The 2.4GHz r/c system has been swapped out by a 433MHz EzUHF system. At the same time I changed transmitter from Multiplex Smart-SX (which is a very nice and simple TX) to a more capable but also more complex Multiplex Royal Pro (16 Channels).

Additional I2C wire

Even if there is a lot of more electronics in this build, it is only 25g heavier than the previous one. This could partially be achieved by stripping down all electronics (no cases) keeping wiring short and the PX4 itself is pretty light compared to the Pixhawk or even APM 2.6 (one more reason to use the PX4).

The digital Airspeed sensor connects to I2C which is also used by the external compass in the 3DR gps module. The PX4IO board only offers one I2C connector. I could have used the PX4 I2C splitter but this seemed the be a bit overkill, my intention was to have a light build. To solve this, I soldered an additional wire to the underside of the I2C connector on the IO board (see left).

This is the final layout I am using, it is basically what TBS has designed with a forward moved battery, an extra hole for the PX4 + 3DR telemetry module + pitot tube holder and 3DR GPS/compass mounted into the nose. The gopro has been tilted down a little bit, I don't like having 50% of my footage showing the sky.

TBS Caipirinha with PX4+PX4IO, EzUHF 4 chan receiver, TBS Core, 3DR Telemetry module and 3DR GPS.