Like Sparky Paul says  designs are developed
As a sport flyer, I'd leave it alone. But, I'm interested in the details and this model has a job to do. So, the problems are:
1) Used bullet connectors for the 4000mah Lipo. The spring tension on the male bullet weakens over time. Even when fully inserted it can lose conduction under high current loads. We noticed this in an occaisional brief loss of control and the autopilot stopped logging data after a power interruption. Will change back to Deans connectors.
2) The chord lines of the wing and stabilizer sections are set at zero incidence relative to the thrust line. At low speed there is not enough elevator control to flair the glide. The solution has been to maintain speed on landing, but a little more control won't hurt. Will increase the elevator chord by 50%.
3) The stabilizer has a tapered planform so the spanwise spar is tapered. The elevator is top hinged with tape. The taper varies the hinge radius spanwise from base to tip. That causes the tape hinge to stretch and distort over time. The cure is to center hinge the elevator. Not yet sure what to do.
4) The elevator is not an even match to the stab which leaves a ridge on the underside. Will rebuild the elevator for a better fit.
5) The motor sometimes picks up dirt on landing. Working on a cowl made from one of those little Coke cans.
6) The two graphs below show the pitch and roll angles required to automatically loiter in a circle. The center of the circle is a the lon/lat of a preprogrammed waypoint. The first record is shorter because of a power glitch.
The first graph is for a right circle. The model goes into a steep bank angle until it aligns itself with the circumference of the circle identified by the first waypoint. Once on the circumference path, the roll oscillations damp out and the pitch angle is near zero. The circle radius is 100 m. The power setting for 60kph is 40%.
The second graph is a left circle of 125 m. The model acquires the circumference of the circle but the roll oscillations do not damp out and a positive pitch angle is maintained. The power setting for 60kph is 65%.
It will take some time to understand this.
Comments welcome.
Tom
