over the last year I have learned a bunch about the pixhawk and can tune them pretty well. There is one issue I cant solve. I have 3 planes and only got one of them to fly level it was a thing of beauty super stable flat and level…I had a motor failure with that plane and that was that.
The issue is in auto mode the planes typically fly with the right wing down about 5 degs…although I have a 3dr aero m that has the left wing down 5 deg.
First thing I did was trim the plane the best I could for level manual flight. Best I can tell with hands off it tracks a straight line for at least 150 yards does not dive, yaw or roll visually .
I use trim_auto to write the trim values as default values. I even took the plane off switched to FBWA (made sure I was not touching either control stick) Then switched back to manual and set trim_auto back to 0
It still flew with the right wing down…the plane does track a very straight line even in high winds (30mph) or calm days but it keeps that right wing down head wind, cross wind, no wind…
I measured level on the plane and compared it to the artificial horizon in mission planner. When the plane is level the horizon is level…When I tilt it 5 deg the horizon is tilted 5 deg
Thinking about this if the plane need 5 deg right roll to fly a straight line then the issue must be yaw. The plane is slipping left and to cancel this out it rolls the wings right to get its straight line.
based on the above I manually added right rudder by adjusting the linkage logic would indicate that if I add right rudder its going to cause to plane to yaw right and to keep on path the autopilot will roll the wings left (back to 0 deg was the idea) to stay on course…logic is such a liar…Well maybe a first it seemed better but the next day it was back to the same old trick.
I dont know how I got that one plane to fly level…dumb luck I guess but I spent hrs setting it up to be awesome.
So as far I can tell 95% of all pixhawk users have planes than fly with a wing down 5 deg either left of right.
The solution must be super simple but I keep overlooking it.
how can I trim my plane to fly with the wings level???
The plane paints the intended flight path with that purple line…in other words it tracks the flight plan very well…Thankfully the cross track issue is not one Im having even in high winds where I have a 29 mph 45 deg cross wind and the plane is flying with so much crab angle that I can see the entire profile at it heads towards me it still over the intended path and hitting waypoints with in about 3 meters. I consistently hit waypoints in good weather from 1 to 2 meters
In light cross winds the right wing is always down doesnt matter if the wind is on left side or right side of plane. Even in high cross wind it seems to favor the right side when flying either direction
I did radio calibration way before I got in the air
I could try the one level accel calibration.
If its got a wingtip down something is causing it want to head left and its compensating for this by adding roll to keep the plane on course. Why would adding manual rudder trim not change this??
What about transmitter trims and adding more rudder trim then using trim auto to write them as a default value? Some how there must be a way to get the autopilot to recognize an trim change…I dont know how its ignoring a manual rudder trim change via linkage adjustment.
P.S for you skywalker dudes…switch to a pusher prop like an APC 11x7ep and reverse motor direction…if you are not running a pusher prop doing so has the potential to significantly improve flight characteristics (particularly yaw wind up when power is increased and the subsequent un-winding of yaw as power is reduced. The plane will fly a straight line under chaining power conditions with significant reduced rudder compensation trim much much better with a pusher propeller.
Turn on Stick Mixing and add rudder trim, LOTS of rudder trim! This worked for most of us. The problem I then had was it was almost unflyable in Manual with that much trim, and too much for FBW. I ended up mixing in extra rudder when the mode switch is in the auto position using the Taranis.
What airplane are you flying?
I have one modified volantex ranger with a built up wing using an E201 airfoil, extended tail boom and extended nose with nose mounted motor that is on the planes center line.
I have one stock Volantex ranger
I have one Aero-m
The modded ranger performs the best and at one point I had it flying dead level…The sad thing is by moving the motor to the front the I improved stability and handling but it made a very significant reduction in efficiency it cut my flight times down from 50 min to about 30 with the same power system…I plan to move the motor back to the rear. This plane also flew perfect in manual mode.
The stock volantex ranger ex is not bad the short coupled body makes any paylod and battery placement a bit tricky and the short tail is not ideal for stability…but it does fly pretty good and is very efficient.
The aero-m (a 1900mm skywalker I think) is the worst of the lot…I dont mess with it much battery, camera, autopilot and accessory placement is horrid. its using the stock 3DR tuning which may not be aggressive enough. It wont hold a course in any wind above 7M/S. Its efficiency is good, its light, easy to hand launch, and it does its flying with the left wing down 5 deg
Thats an interesting point you bring up about stick mixing. Why would the plane need to be trimmed so far out of tolerance that its a total mess in manual mode to get it to track straight in auto mode??? If there is a yaw issue causing the plane to head off course why would the yaw correction need to be 5X (or some huge amount) of the actual error before it gets the plane to fly level in auto mode? Because of my common flying locations I cant allow the plane to fly poorly in manual / FBW mode for any reason with or without mix correction. my runway is often narrow its 26’ wide and if you make a landing at 28 feet wide you buy a new plane. If I fly mostly at 16 m/s and I can get that plane to fly level in on course in manual mode…There’s got to be a way to get it to do the same in auto mode.
I think one of the primary things I did to get that one plane to fly level was “Level adjustment” seen here level adjustment The two lines were not centered so I adjusted trim to make them centered then mechanically moved the flight surface linkage so that it flew good in manual mode…I dont know if I used trim_auto to write trim values over…I think I did not.
provide a log of the issue, and maybe someone might be able to advise further, otherwist it’s just speculation. If I’m speculating, I’d suggest looking at the motor mount to see if it’s got any anti-torque angle set on it or not. ( and maybe see if the problem goes away while in a glide ).
I often switch my props from counterclockwise to clockwise props when I run out of spares. When I do this, I switch a pair of wires to the ESC to reverse the motor and I reverse the trim on the rudder to counter the motor torque. If I do not reverse the rudder trim the plane flies with a condition similar to what you described.
It’s actually spiraling slipstream hitting the vertical stabilizer that is causing the unwanted yaw. Torque would cause an wanted rolling effect. In this case the autopilot is applying the unwanted roll in its attempt to stay on course while in a slip.
This is almost certainly the case…I came to this conclusion a long time ago when I was first trying to figure out why…I saw a picture of an F4u Corsair idling on a carrier deck the propeller tips creating a perfect spiral condensation trail around the fuse.
But If I have mechanically trimmed the rudder to compensate for this at the speed I most commonly fly what is happening to that trim in auto mode??? is the being removed in auto mode? Is it because it looks good but its really not in trim?
I uploaded a log file on google drive to help with analysis…Hopfully it works log
I had a friend watch the telem on mission planner…made some trim adjustments to elevator and aileron. Took hands off and it followed a compass heading with in a degree or 2 over a 10 to 15 second period in manual mode.
Redid trim_auto and test flew in auto mode it seemed to no longer favor one side it was a bit windy…I need more data to verify but it looks like that may have helped or eliminated the issue.