trim question

[phaed]

i don't have a real copter yet. i'm still using the G3 sim until i get good enough.

i've noticed that when i trim a bird out in hover, it seems out of trim in higher altitude flights, and vice-versa. is this normal on the sim? on real copters? am i just not fine tuned enough with the rudder to keep it straight and level yet during higher altitude flights?

if so, how do you pros do it? do you trim it out at higher altitudes and just fight the trim a bit in hover?

[flyinfool]

First let me say that I am nowhere near a "Pro", but the physics do not change reguardless of you skill level, some guys just make it look like the laws of physics have been changed for them.

The trims are different for forward flight than for hover, this is normal on both the sim and the real thing.
When you are just starting to fly the real heli you will want it trimmed for a steady hover in normal mode. Once you start forward flight you will want to use Idle up 1 and then you can have the trim set for straight level flight.

After you get to the point of straight level flight you will find that the trims are different for every attitude you can get into. Upright or Inverted hover, forward flight upright or inverted, backward flight upright or inverted, all need different trims. Once you get to that point you will find some happy medium that works best for you and just compensate with the sticks all of the other times.

My preference is to trim for whatever new thing that I am working on at the moment.

[Ivan]

Helis have 2 modesof flight. Hover and moving.

Without getting into all matter of physics and the hundreds of interactions at work on a heli, I will try to explain this.

In a hover the air goes straight down through the disk (not a hover on a windy day, which is actually moving). In this mode your trims are basically compensating for any variance of the CG relative to the mainshaft.

Now in forward or moving flight, the air is coming at the disk at an angle. that air is moving across the disk as well as through it. This does several interesting things. Most notably, the air affects the advancing side more than the retreating side, and causes one side of the disk to have more lift than the other. Gyroscopic precession included, this tends to make the heli want to pitch away from the flight path. This is mostly compensated for in the paddles, which act as a stabilizer. In extreme cases (I guess never on a model heli) you can get the tip of the retreating blade to stall at high flight speeds, from the retreating blade having almost no ground speed. A 60 size model heli has a tip speed of about 200mph, so you would have to get the heli well over 150 to experiance this, and that just won't happen on a model.

Other things that affect trim differences in moving flight:
the horizontal fin.
Paddles not being perfectly parallel
drag on the cabin compared to the boom
and there are probably hundreds more, helis are complex in every matter.

hope that sheds some light.

[WayneBrown]

You mean there are trims for more than throttle??
Wow! Here I just fly the sticks...

[phaed]

much appreciated fellas. that cleared so much up.

-Barre

p.s. i love this board.

[AndreMan]

Hi, I posted a similar question in the Reflex topic but it may be better here.

I am using a 9303 with Reflex and everything I try to fly starts off by trying to bank left. I can compensate with Aileron trim but should that be necessary.

I ask because I thought trim was necessary in different ways depending on what you're flying and so forth. Is there a reason everything would start by trying to move to the left?

Is there such a thing as making sure the transmitter is not sending a "left" signal when the trim reads 0?

Thanks for the help and I agree, what a tough time it would be without boards like this.

Andre

[flyinfool]

I is a normal thing for a heli with a clockwise rotor to drift left at lift off.
This is due to the thrust produced by the tail rotor while countering the tourque of the main rotor. Because of this side thrust the main rotor must be tilted slightly to the right to compensate for the side thrust.
This is not so much a trim issue as it is a correction that must be made at lift off.
After a little while you will not even realize that you are making the correction.

[AndreMan]

Thanks for the reply.

I see what you mean as I selected a heli with a counter clockwise spinning rotor and of course, it wanted to drift right.

I guess I was surprised by this as I was expecting the nose to yaw right or left but not the banking.

Anyway, thanks and back to some hover practice :)

Andre