Hello
I have a bit of an unconventional plane that I’m trying to get flying properly. It Is an university project that aims to mimic the silhouette of an eurasian goshawk. This means that it has unproportionally large wings and a really short and tiny tail (if compared to what it should be when going by tail volume coefficients). It also has a static vertical stabilizer above the tail.
For control it has an elevator and two ailerons.
Problem is, that the plane oscillates furiously while in angle controlled flight. Pitch oscillates around ±20 degrees with a period of 1-1.2 seconds or so. Amazingly it flies, but just with great oscillations.
The plane has a wingspan around 1.25m, wing area about 0.27m^2, weight 1.5 kg and max thrust also in the same region (T/W around 1). Avionics: FC - Matek F743, m10 gps with compass, RFD868EU telemetry radio, an analog airspeed sensor, ELRS 868MHz RX.
I have done 2 semi-successful flights. Before the first flight all PIDs were arduplane stock values. After first flight I modified some stuff in hopes to get it working better, but to no avail - the performance was roughly the same, maybe even worse. Things I changed between two flights:
PTCH_RATE_D 0 → 0.004
PTCH_RATE_I 0.15 → 0.05
PTCH2SRV_RMAX_DN 0 → 40
PTCH2SRV_RMAX_UP 0 → 40
PTCH2SRC_TCONS 0.5 → 1.0
I tried changing the pitch P rate during the second flight also but it did not change much. Can anyone give me some pointers of what to try for the next flight to get it flying better?
I have also tried autotune, it increased the period of oscillations but the amplitude grew larger to the point of the plane being uncontrollable and acheiving inverted flight for a few seconds.
All control surfaces are quite rigid, with no problematic slop in the linkages (I’ve flown mechanincally much worse planes with better results). Logs are available here: Pitch oscillations - Google Drive
Any help would be appreciated
Best regards
Oskar