Hello everyone!
A few months ago I recieved an email from Lorenz, main developer of the Pixhawk research project and the PX4 autopilot. He urged me to create a small flying wing platform. Around 35 inch wing span and around 500 grams. capable of carrying a small camera like a gopro or canon s100.camera and an autopilot. I thought it sounded like an excellent idea. I could make it very portable and it could operate out of much more confined spaces then the techpod.
So I got to work. After about 4 weeks of analyzing airfoils and reiterating designs I finally came up with this wing set up.
I cut the wings out of EPP with a 4 axis hotwire CNC machine. I glued the sections together with goop and covered it with laminate material. I made some balsa elevons and vertical stabs. It came out to be 20 oz which is a little over the target weight but this is a prototype and a fully molded EPO version will be much lighter. I put a couple small holes in the bottom so it could be easily launched two finger style. hear is the video from the flight.
other than the roll trim being out a bit with it pulling to the left, the launch went very well. a little bit of left trim and it was flying flat and level. there are a couple obvious changes i need to make. one is I need to move the motor down to center with the wing. The other is to turn down the throws. It was pretty twitchy but I usually set up the first flight with a lot of throw. I put it into a few stalls and it takes a good two revolutions to recover from a spin but I think that is to be expected from a wing. I had a blast flying it and it can take a hard landing. I will be putting an apm in it and I should have much more flight performance data.
you can read more about the techwing and the techpod at hobbyuav.com
Comments
Very nice Wayne! glad to hear you have positive test flight result! That is the beauty of wings, they are relatively simple, and they provide quick production and prototyping!
@martin
It seems to fly very nicely. I will be doing more test fight in a day or two one I have the APM fully ready. It will be interesting to see the flight data.
Wayne, does the propeller axis pass above or below the CoG? Hang the aircraft from the propeller hub and see what the string(s) line up with
@Wayne
The pitching moment of a wing section is proportional to it's local lift. As the root of the wing is generating much more lift than the tip then its contribution to the pitching moment is also much greater.
Usually it's done the other way around - positive cm at the root and negative cm at the tips.
But if your approach also creates a net positive pithing moment then it's probably ok also.
So, I moved the motor closer to the CG. I was getting a lot of forward pitching especially when accelerating, like andrew talks about.
Exactly why folks run into trouble when they decide to change a designers motor on a wing with a high mount. All sorts of power related pitch weirdness. Which often ends in a moaning forum post stating that wing XYZ is rubbish because it would not fly well with an engine twice the size and three times the weight it was designed for ;-)
Nice work Wayne.
I would suggest some more thought regarding the motor mount though, since thrust will add a negative pitching moment which you're doing your best to avoid with flying wings. Can you not add some downthrust or at least make sure the thrust vector travels below the CoG?
I have considered pitch thrust vectoring for some of my theoretical wing designs since this would allow them to be trimmed for optimal drag (and lift!) in more phases of flight. If you allow significant down thrust with this you might be able to dramatically reduce stall speed under power by generating good positive pitching moment without needing to destroying your C_L by elevon reflex.
Gary, the motor mounting isn't an issue for me. I'll just have to make my own and show what I mean. :)
@Harry I think you can end up with some engine effects if people are people and decide to go against recommended. I have had several wings that mount the engine as the Techwing.
Looks really good, I like the size/form factor.
I been flying the Bomatec Q which is a small folding wing about the same size. It's great for throwing in the back of the car and tough as nails but doesn't have enough room for a camera once you've got APM and the rest of the gear in.
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