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Old 08-23-2013, 09:14 PM   #2077
XpressCS
Must. Have. Lumens..
 
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Joined: May 2012
Location: The big box California
Oddometer: 1,122
Quote:
Originally Posted by Saget View Post
For my latest project I wanted to design & build something different. Presenting the BFD, or Big F$#%ing Delta.



7' wingspan, 8-1/2 lbs with battery. 1300 sq. in., for a trainer-like wing loading of just 9.5 oz/sq-ft.



The fuselage is balsa & ply. Wings were cut from blue styrofoam insulation with spruce spars and a dowel leading edge. The wing panels plug in so I can get it in my car.



NTM Prop Drive 50-50 580 KV motor with 100 amp ESC. Notice I have the battery in the center of the fuselage, which proved to be a huge mistake. More on that later....



Under the nose is a removable hatch, giving me a place to mount a camera with an unobstructed view. That will come after a few more test flights.

And here's proof that it actually flies.




Now, about that battery location. I thought I had the CG location figured out before the first flight. I even built a 1/4 scale hand-launch glider to confirm it. I was wrong.

I was just taxiing around in the back yard getting a feel for things. I had no intention of flying it yet (which is why I don't have video, dangit). Suddenly the breeze caught it and lifted it off the ground. I immediately knew it was tail heavy, since it was about 10 feet up, pointed straight up and nearly stopped!

No room left to try a quick landing, all I could do was add throttle, shove the nose back down, and try to keep flying. It was BADLY pitch sensitive, going from straight up to straight down with the slightest elevator input. Even worse, turning would throw it into a spin. I managed to keep it pointed mostly skyward and gained some altitude, then walked across the road to the shooting range where I had more space.

After nearly spinning it in 4 or 5 times, I figured out the throttle was working against me. By throttling back to an idle I could keep it mostly under control. I was able to make some very gentle turns and get it back for a scary but uneventful landing. Not a scratch!!

The video above was the 2nd flight, with the battery all the way forward. The CG moved forward about 2 inches. Now it flies like a dream instead of a nightmare.
Awesome! Want to build me one?
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