hello every one , i have glider that weight about 2kg with 2 meter wing span ,
base on the log i need to improve my pid , it seems like always the pitch is up ,
the center of gravity seems ok to the plane , and it seems like i loosing alot of air speed im afraid to stall the aircraft i would like the air speed to keep at 13 meter for seconded but in flight i get some times 8 and 7 ias much lower then the target speed
any one can look at the log and tell me if i miss anything?
Must be something wrong other than pid gains, i have a similar airframe and it flies beautifully on default settings, I have never completed any tuning as it was never needed.
Is your plane climbing too steeply? During what flight mode do you observe the issue?
In fbwb, the altitude is loop controlled and elevator input moves the altitude setpoint. So the pitch attitude is just a result of whatever is needed to maintain desired altitude, if you want it to fly more nose down then you need to add more throttle or remove some weight.
Its all just pitch drag and thrust. It cant lower the nose 3-5 deg with the same amount of power applied or it would decend. You are basically just dragging the plane around on the back of the curve near the stall.
I wouldn’t read too much into the perceived error between desired pitch and actual. Even just the position you have the plane in when you calibrate level might affect the numbers.
You can have a look at the elevator position in cruise, if mechanically you have linkages set to for elevator at 0 degrees at 1500us then you can get some idea of how nose heavy you are,
A more foward c of g will result in needing more up elevator to maintain the angle of attack. This additional up elevator effectively adds to the wing loading and makes the plane fly even heavier but does add to the longitudinal stability. Ie moving weight forward won’t make it fly faster with the same power or make it fly level with a lower pitch attitude.
Have a look at the elevator servo pwm position while on level cruise then when you land put it in manual and see what it looks like when you get to that position. You should have something between neutral and maybe 25% up elevator depending upon your power setting when you checked it in the air. If its down at all then you are tail heavy and will be unstable and need c of g adjustment.
7m/s is not out of the question but my 2.4m powered glider flies mostly between 10 and 20. It would slow down to 7 but that would be on the slow end of the envelope.
Tail heavy unless its not built straight, you’re lucky you havent put it in the ground.
The c of g of an aircraft is supposed to be in front of the centre of lift then the tail pushes slightly down to compensate for the nose being heavier, this way they have longitudinal stability because when the craft slows down the tail creates less pressure to oppose the nose weight and the aircraft naturally pitches down which increases speed. Its an aerodynaic loop. If you have tail heavy it is inherently unstable.
How does this thing fly in manual through the speed range and if you fly with all surfaces centred what does the aircraft do in level flight?
How does the c of g compare to the range specified in the manual for the airframe, (some of the chinese foamies have specs which cannot always be trusted, they make them to look good not fly good)
There’s a huge temptation to just throw a fc in an aircraft and expect the controller to sort out all the issues with the way it flies. Every airframe should be a well balanced, well setup craft Before the auto modes are tried, then the tuning needed is very minimal.
believe me that i did all the test before go to fly, the cg of the aircraft is like in the manual 45-60mm from wing cord , maybe its not enough but its in that range , i will try in the next day to make it more front heavy and see how it effects