I’ve become more and more fascinated recently by the function and purpose of UAV’s and Drones. Not so much the military versions, but the smaller civilian units capable of aerial photography, surveillance, support etc.
Could I use the same Flite Test techniques I’ve been using to turn out foam board parkflyers to create a stable, efficient foam board UAV?
Searching for inspiration…
I knew from the start that this was going to be a plane rather than a multirotor. I had been watching a number of documentaries on military drones to see what the really high-end stuff looked like and the simple design concept of the Reaper and Predator drones really caught my eye. These were basically just glider wings, set back on the fuselage to counter the weight of the camera equipment and sensors in the nose. The anhedral tail surfaces on the Predator are intended to assist in the prevention of prop-strike during take-off and landing – plus they look cool.
Using Sketchup to visualise the design
I’d played around with Sketchup a long time ago when it was still Google Sketchup but never really got that into it. I couldn’t get my head around using polygons to build up complex shapes. Since then the software has evolved and, along with some excellent training videos, it really is quite user friendly.
I had already sketched out a design on paper so I knew the rough dimensions. A single evening later and I had a 3D model in the computer – this was looking good!
Putting it all together
As always with these designs, once the plan is printed and cutting starts it all happens very quickly. I got the second wing cut and glued over the New Year. Full length flaperons are included with a single servo built into each wing to drive them. As with other wings like this I built the two halves separately and brought them together at the last minute, the foam providing incredible strength a rigidity even at the join.
The fuselage came together very quickly with a minimal part count. The whole thing is built up of “A” and “B” style folds with a few formers towards the rear to aid rigidity where the tail and motor will mount.
The nose section is a second piece that is a push fit over the main fuselage tube. This double thickness adds strength to the nose area to protect the expensive camera and flight control equipment that will be house there.
The tail again was very simple with the fin tabbing into the fuselage top surface and the horizontal stabilisers sitting against shaped formers in the fuselage.
A prototype is born…
In just a few hours I had gone from a Sketchup model to a full size prototype, ready for the electronics.
Some of the specs are:
- Wingspan: 72 inches (1828mm)
- Wing chord at root: 8 inches (203mm)
- Wing chord at tip: 4 inches (101mm)
- Fuselage Length: 30 inches (762mm) – without motor or camera
- Bare airframe weight: 15.8 ounces (450g)
Overall, I am very happy with the way this has transferred from paper to prototype. At 450 grams for the airframe I am not worried at all about the weight. Even from “heavy” Australian foam board this is still a light model.
UPDATE!
The following is a quote from earthsciteach on the forum (where this model has been "aired" for some time now):
The only thing that would concern me on this plane is breaking the downward point V's of the tail surfaces upon landing. Or, the nose may get slammed down when they catch on landing.
My response was that the thought of landing the thing hadn't even crossed my mind! As a result of the very useful insights and inspiration provided by the forum I have now redesigned the fuselage to have the v-tail on the top (basically I just turned the fuselage upside down!).
Currently fitting electronics so by the time this is published I should know if it flies or not...
0 comments