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Bots
04-13-2011, 07:35 AM
Everything is perfectly level (swashplate etc).

When I attempted a trial hover... just as I was about to lift off the ground I noticed the heli was going to tilt off dramatically to the left side. So I quickly reduced power.

The only thing I could find a tad off was one rotor measured 1/2 degree difference in pitch than the other. So I adjusted one link and that fixed the pitch difference.

Could that have been the cause or would it be something else?

I haven't had a chance to do another spin test... I live in Canada and it went from +15 down to +3 today. So I guess an attempt is out of the question until it warms up a bit.:Slap

mulicheng
04-13-2011, 09:16 AM
Have you fully checked the swash movement without the blades spinning? Most bad tilt issues I've seen are because one of the servo directions isn't right in the CCPM mixing or something.

stephenwagner
04-13-2011, 10:33 AM
Your helicopter will naturally want to tilt to the right, here is why.
The helicopter hanges on its rotor head and produces torque in the opposite direction. To counter this torque, we use a tail rotor. Unfurtunitly, the tail rotor is mounted below the head and pushes to the helicopter to the left. The helicopter hanges on the head and the tail rotor is pushing to the left below the head causing the helicopter to tilt to the right. The only way to counter this effect is to move the tail rotor up into the same plane as the rotor head. Here is another way to look at it. Look directly down the tail boom. The tail rotor looks like it is mounted to the side of the helicopter below the rotor head pushing to the left causing the helicopter to tilt to the right. I hope this helps.

SJW

ollie2893
04-13-2011, 12:02 PM
If this is an FBL bird, then, yes, the vibrations induced by the out-of-track blades might be enough, particularly on a resonating surface, to get the aileron sensor to freak out.

Bots
04-13-2011, 12:11 PM
If this is an FBL bird, then, yes, the vibrations induced by the out-of-track blades might be enough, particularly on a resonating surface, to get the aileron sensor to freak out.

Nope, it has a fly bar.

I took the head off and used the swash plate leveler... again. I notice aileron, and pitch subtrim off by a hairs width at full pitch but couldn't iron it out. So what I did was transfer the hairs breath difference to the elevator. This is as close as I can get. Now at low, mid, and high pitch all is well... except at 3/4 pitch the elevator subtrim is now off by just a hairs width.

Hmmm. can't get it any closer. Is this normal?:dontknow

mulicheng
04-13-2011, 01:43 PM
Well, you said dramatically.. so I'd say no. But then again, it sounds to me like perhaps you haven't done this a lot.. or you wouldn't be asking if it's normal. You'll have to provide more clarification I guess.

As pointed out... all helis will slide a bit because of the tail but I wouldn't say it's "dramatic". A tiny bit of cyclic input on my takeoffs keeps them where I want them.

Bots
04-13-2011, 01:46 PM
Actually it wanted to tilt to the left... sorry I should have clarified. Will change in the original post.

ollie2893
04-13-2011, 07:03 PM
Helicopters are unconditionally unstable machines. They will do any manner of things unless proficiently controlled. Simply use the trim tabs to counter any bias to tilt left out of a hover. And let us know how much trim you needed in the end.

Nko15
04-14-2011, 07:46 AM
Helicopters are unconditionally unstable machines. They will do any manner of things unless proficiently controlled. Simply use the trim tabs to counter any bias to tilt left out of a hover. And let us know how much trim you needed in the end.


Trim:confused: Dont do that. make sure the swash is level, the CG is good, and the blade pitches are the same.... if 1 of these is off, fix them instead of trim the problem away.:...:

Bots
04-14-2011, 07:54 AM
Trim:confused: Dont do that. make sure the swash is level, the CG is good, and the blade pitches are the same.... if 1 of these is off, fix them instead of trim the problem away.:...:

Ok thanks for the advice.

WRT the swashplate... it is as close to perfect as I can get it. (See above)

The pitch is now perfect.

I'll be checking the CG soon.

Super!

ollie2893
04-14-2011, 08:46 AM
Trim:confused: Dont do that. make sure the swash is levelRead what the OP writes first before you criticize others !! He has triple-checked his swash, he says. Now what... ?!?

Trim it out in a hover and tell us how much trim you needed. I don't have any sense for your flying skills. I don't even understand whether your tilt is persistent or merely a ground effect phenomenon.

I am sure, though, that CoG will be the least of your concerns. In fact, I wonder how many here have ever balanced their CoG across aileron? (Unless you have your battery attached to the lhs only :( or fly a X-trainer)