Here's a puzzle for you - RC Groups
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Mar 01, 2004, 02:10 AM
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nolasco's Avatar

Here's a puzzle for you

I have noticed something in my custom built Falcon that has been bugging me. It seems that it needs quite a lot of right trim. Otherwise, it wants to go to the left.

What could be causing the tendency to go left? I don't think the left side is heavier as I have a servo on the center, another on the right, and the gyro attached to it.

Some details:

MIA Two Legged Frame
DC1724 motor (Helistar)
B2 Motor direct drive with GWS 2.5x0.8 prop
BB blades
3-cell 250mah LiPoly
AUW 4.5oz.

Any ideas?

Jun Nolasco
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Mar 01, 2004, 01:47 PM
Registered User

Did you balance it?

Hows it going, I think I can give you some help with this problem. I had the same trimming problem as you did, for one thing make sure you don't put to much weight on one side, I did that with a berg 5 ch, and seperate mixer. I put it all on the left side originally and that had an effect on it. Try putting your reciever in the front tray, I put mine at an angle by using some spare fiberglass board that my frame came unassembled in. The only things i have on the side are, rightside - gyro, left side - pixie7 and gws ics50. The mixer is tucked underneath the board. If that doesn't help, you can try manually adjusting the servo arm so that it starts at a higher position. When I look at my swash plate while in netural, the right servo when looking from behind, is higher, ie: the swash plate is not level, I have the left servo higher to, so when looking behind it has a upward to the right lean. I noticed this on mario's heli when he was helping me trim my heli. After these adjustments my heli flyes with trim tabs all centered and requires almost no stick input to take off, and requires very little input to keep in hover. Try these things if you havn't its a blast to fly when you have everything perfect.
Mar 01, 2004, 11:52 PM
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nolasco's Avatar

The way I setup my Falcon, my right side should be heavier as I have nothing installed on the left side. I was expecting the heli to lean a bit to the right because of this.

Note that I have to put 40(!!!) clicks of right trim to maintain a hover. On the other hand, my 2 Piccolos do not seem to need any (at least I don't see it when looking at the swashplate) and my 5.3oz MIA Bumble Bee needs only around 10 clicks. Could it be related to the Falcon's 4.5oz AUW and/or direct drive tail?

Jun Nolasco
Mar 02, 2004, 11:06 AM
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Mario's Avatar

The heli wanting to lean to one side more than the other is a phenomenon due to the rotor torque forces. Main rotor direction and tail rotor counter torque are factors.

Things to try:

Balance the heli about the center of the main shaft under the main rotor head, as best as you can.

Diminish the main rotor blade pitch by shimming with a piece of cardstock or thin plastic, between the rotor blade and the rotor head (at the leading edgde), try this for best hover while observing minimum power draw with a watt meter. For reference use 20 watts as your target to shoot or while in hover 2ft off ground. This will change, depending on how light or heavy your RC equipment and overall weight of the heli is, but somewhere in the 20-25 watt range should be fine.

Slightly tilt the tail rotor about 3-5 degrees to the right, pilot seating in heli as reference, or "tail in", this helps a bit in particular for precision hovering and for forward flight.

Other than this trim slightly the sp aileron (Roll servo) opposite that of the heli lean as already mentioned.

Last edited by Mario; Mar 02, 2004 at 11:10 AM.
Mar 02, 2004, 04:37 PM
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nolasco's Avatar


I've already tried right-heavy, balanced, and left heavy. with no apparent difference (i.e. need lots of right trim in all cases).

I'll try tilting the tail rotor to the right next. (Why did I not think of that? Silly me after what I went through while scratch-building three R/C BD-5 pusher planes )

With regard to "tail in", did you mean tilt the tail rotor slightly toward the front? What effect does this have?

Thanks again.



Don't get me wrong. I am having a blast, especially at 4.5oz (and about to get even lighter).

I just find it strange though that my swashplate needs to tilt heavily to the right to maintain a hover. I also suspect that some binding might also be occuring when I push the stick more than just slighty to the right. I can see the main rotor RPM being affected when I apply right stick.

Maybe it's time for a ball-in-swash mod.

Jun Nolasco
Last edited by nolasco; Mar 02, 2004 at 04:46 PM.

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