Centus
Member
Hi guys!
I'm back at building and modifying designs lately, and came across an interesting problem while testing some mods to my "Blackwing" design.
http://flitetest.com/articles/swappable-pusher-with-canard-blackwing
Even though the plane flew really well I always thought the tall vertical stabilizer looked a little awkward, so I thought I would try replacing it with two winglets. While building the winglets I decided to not mount them vertically, but with some outward tilt, similar to the 737's blended winglets.
This modification flew well enough, but when I tried to do a barrel roll (which the previous design performed excellently), the plane nearly fell out of the sky! Here is a link to a video (including slow-motion) of this instability.
After poking around the internet the following day, I believe that the new design has developed a tendency to Dutch roll. According to wikipedia (https://en.wikipedia.org/wiki/Dutch_roll), Dutch roll is a dynamic instability mode caused by an aircraft having relatively strong roll stability and relatively weak yaw stability.
It makes sense that my changes could be causing this: adding winglets with outward cant is similar to adding polyhedral to the wing therefore increasing the roll stability. Replacing the tall vertical stabilizer with two smaller winglets mounted slightly farther forward has decreased the yaw stability.
What do you guys think?
I'm back at building and modifying designs lately, and came across an interesting problem while testing some mods to my "Blackwing" design.
http://flitetest.com/articles/swappable-pusher-with-canard-blackwing
Even though the plane flew really well I always thought the tall vertical stabilizer looked a little awkward, so I thought I would try replacing it with two winglets. While building the winglets I decided to not mount them vertically, but with some outward tilt, similar to the 737's blended winglets.
This modification flew well enough, but when I tried to do a barrel roll (which the previous design performed excellently), the plane nearly fell out of the sky! Here is a link to a video (including slow-motion) of this instability.
After poking around the internet the following day, I believe that the new design has developed a tendency to Dutch roll. According to wikipedia (https://en.wikipedia.org/wiki/Dutch_roll), Dutch roll is a dynamic instability mode caused by an aircraft having relatively strong roll stability and relatively weak yaw stability.
It makes sense that my changes could be causing this: adding winglets with outward cant is similar to adding polyhedral to the wing therefore increasing the roll stability. Replacing the tall vertical stabilizer with two smaller winglets mounted slightly farther forward has decreased the yaw stability.
What do you guys think?
