I've got a bixler and have installed an APM1.4 with v2.40, GPS, magnetometer, xbee and everything is working great but in stable mode it climbs at like a 20 degree angle. In manual it's ok. I'm sure this is because when I did the manual level (I'm not using the auto level at each boot) I just put it on the ground and made sure the wings were level but apparently the pitch is not level by just sitting it on level ground.
How should I level it before pressing the leveling command in the planner? It seems I would need to raise the tail up about an inch off the ground but is that normally necessary? I know the elevator trim is ok because in manual mode it's all trimmed out but when I switch to stable it thinks it's pitched down so gives some up elevator.
So what is the proper way to find the level point?
The COG I have at the spars but tried it a little forward and a little back but had the same problem. I thought it was a balancing problem but it's just that when you put the plane on level ground and do the level command, it is not really level so the APM is just going to give up up elevator thinking that it's not level. I think the only solution is to raise the tail about an inch and then do the level command because with it sitting on level ground, it actually must be pitching up a bit but the APM will think that is level.
Manual mode is fine so I know it's not a COG problem. It's APM that is trying to level it but to a wrong level.
Like I said, use the servo push rod slots as your guide to what is level. The bottom of the plane is not level, as you have observed, the tail needs to be higher. Imagine if you put landing gear on it, the tail would be higher than the front. The servo push rods should be level, and the wing will have a ~3 degree AOI to level, which contributes to its slow flyer characteristics. In other words, don't level off the bottom of the plane, and don't level off the wing.
If you were to hang it from the CG points, or balance it from those points, you should actually get the same results.... if properly balanced, the servo push rod slots will be level with the ground.... this is the attitude the aircraft wants to maintain in flight for level flight. You an also look at the rear horizontal stabilizer, as this is either level or within 1 degree +/- of level
Do you think it would make a big difference if make my COG 60mm vs 70mm because at any of those points I can get the servo line to be horizontal but I'm imagining that too far forward or too far back will cause this problem even though I can get the line to be horizontal.
It is almost always better to be too far forward, rather than too far back.
Well I thought I had this figured out but it doesn't seem to be flying right. What is happening is this.
In manual mode I have all surfaces level but it still wants to climb in manual or stable mode. I can find a speed where it sort of levels but really it climbs up a little which slows it down and then it levels or starts to descend a little (picking up speed of course) which increases lift and it goes up again and over and over. If I give it more than 50% throttle, it climbs and climbs.
My balance point is right below the spars which I measure at 71mm from the leading edge. It balances there and the servo rod line down the side of the fuselage seems level. Actually looking at the spars with a light behind them shows the COG line I marked is exactly on the bad edge of the fiber tube so not exactly center with the spar.
My 2200 nanotech 3S is as far forward as it can go and I also have a 2" foam nose stuck to the nose in case of impact. I don't have any of the washers that come glued in. Removed them all.
Is my COG wrong or do I need to put a heavier battery in? I eventually want to put an FPV setup in the cockpit so I know that will way it down but first I want to get it trimmed to fly normal. I know with my skywalker I never had this difficulty. I used the servo wires as the balance point and it always flew level. This thing just seems to want to go to the moon :)
So I'm guessing that if it's climbing in manual mode and all the surfaces are correct then it must be nose light right?
This may be an obvious question, but is your APM mounted in a horizontal position inside the fuselage?