i have a tricycle airplane that is too difficult to control on ground. Directional control is divergent outside maybe one or two degree of rudder stick throw and the amount of directional input must change simultaneously with throttle advance. What didn’t help was that I had to take off from a narrow and uneven beat-up country road to avoid people/property. I kept running off into the ditch or pirouetting in 360 deg. I know this is an easy routine for most builders, but I’ve crashed and repaired my plane too many times to continue this practice.
I’ve read about takeoff mode and tried hand launch with some success with my previous airplane but my new one is too heavy and bulky to launch reliably. Is it true that the autopilot can hold heading much better than me in manual mode on ground, if I set up a CTOL auto takeoff? The documentation also mentions takeoff in FBWA, but rudder is under manual control, so I guess it won’t help at all? Help is appreciated.
That can be true if it is tuned perfectly, but tuning the ground steering for auto-takeoff can be quite hard. There are several things that make it difficult to automate:
the proportion of control from the nose wheel and the rudder will vary as you gain speed
nose wheels are hard to make without slop in the control
while in contact with the ground there tends to be a lot of IMU noise
you need to keep pressure on the wheel for steering (ArduPilot can do this using the elevator), but if you put too much pressure then the wheel mount will tend to push sideways
So while you could do this, it generally only works well if you have a plane that has a well behaved steering system.
Cheers, Tridge
Do you use retracts or fixed gear? Do you absolutely have no way to play with the positioning of the gear? By following some standard guidelines (http://www.aerospaceweb.org/question/design/q0200.shtml) you can have a very well behaved ground tracking and steering behavior.
fixed. it’s a simple foam trainer plane. it looks like a Cessna 182 but the worksmanship is mediocre. the gears are also banged up from abuse by the previous user…steering is terrible also because I had to use a more powerful motor and a heavier propeller. I can continue to try optimizing the gain of the steering but failed attempts usually cause a lot of damage and i’m simply running out of patience unfortunately.
thanks