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Jan 10, 2015, 04:54 PM
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Question

Pitch uneven when blades rotate


Hey Guys,

I'm having a problem with setting up my heli DFC head.
I know I've got a completely leveled out swashplate and balanced blades, but when I put the stick to full +/- pitch and turn the rotor head around with a pitch gauge on one of the blades, the pitch changes by 2deg. around one turn, i.e. At the starting point the pitch is +12 deg, but as I rotate it it decreases to 9 deg and then increases back to 12deg as I complete the rotation.

Both DFC arms are the same length, I've checked with calipers, not sure what the problem is with the blade tracking...
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Jan 10, 2015, 05:09 PM
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What makes you think your swashplate is level.
The low spot should be opposite of the high spot, indicating the slope of the swashplate.
Jan 10, 2015, 05:11 PM
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I used a swashplate leveling tool
what do you mean by low/high spot? is there supposed to be a slope on the swash?
Jan 10, 2015, 05:17 PM
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Twelve degree's is the high spot, nine is the low spot. The swash is at an angle, or your tool must be bent, or your method is not useful. Are you following your gyro manuals instructions, since it is in control.
Jan 10, 2015, 05:28 PM
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The tool is not bent, checked it out on a table and spare shaft. I'm following the manual's instructions, at one point the software assistant asks for a check on the +/- pitch of the heli by using the slider and throttle stick, it doesnt ask for blade tracking or for me to rotate the head , it's just a problem I noticed when I did rotate the head.
Jan 10, 2015, 05:38 PM
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If your swashplate is level, then the pitch will be the same all the way around. Or your head, or main shaft has something bent. How are you checking level at full pitch.
Jan 10, 2015, 05:46 PM
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I replaced the main shaft yesterday so I know it's not bent. I check if the swash is level at high and low pitch by removing the rotor head and putting the leveling tool over the shaft so it slides up and down with the shaft as I change the pitch
Jan 10, 2015, 05:47 PM
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If it helps I'm using the Naza-H and its respective software config tool.
Jan 10, 2015, 05:50 PM
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Maybe you bumped the swash putting the head back on. I would follow the manual, and go fly it.
Jan 10, 2015, 05:54 PM
Crash and learn
I feel like a fool for posting this, but does the shaft move up and down as you turn it.
Jan 10, 2015, 06:33 PM
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getsuyoubi's Avatar
Do you get the same result at zero pitch? On a flybarred head you level the swashplate at zero degrees (mid-stick), and use travel adjust at high and low stick. With flybarless heads you ONLY level the swash at mid-stick (zero degrees), and don't touch travel adjust. I guess the FBL unit somehow takes care of the situation at non-zero pitch, but don't know for sure.
Jan 10, 2015, 07:14 PM
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hmm I do not get the same result at zero pitch, i get an even pitch all around....
you might be right about the fbl unit taking care of the situation at non-zero pitch, but even then I think it's a bit odd it alters it during setup?

@Ribble what do you mean does the shaft move up and down as I turn it?
Gave the head a spin around, doesn't seem like the shaft moves up and down, it's pretty locked down. I've also tried grabbing the head (with the dfc arms attached to the swash still) and shaking it up and down gently, there's no play there.

tried following the manual, but atm it won't help that much either since I've got a tail issue that I'm trying to fix (mechanical error in the length of the tail linkage shaft causes the tail to give a LOT more pitch in one direction than the other) once that's done though I'm just going to give it a shot with training gear.
Jan 10, 2015, 08:00 PM
Crash and learn
Quote:
Originally Posted by mrpotatohead2234
@Ribble what do you mean does the shaft move up and down as I turn it?
I am learning about helicopters and like reading these posts. The pitch really does not want to change as the main rotor is turned, so something is changing the pitch. All else being square and true, then either the swashplate is moving up and down or the shaft is moving up and down as the main shaft is turned. If both blades change pitch the same (both blades are 12 degrees at the same time and both blades are 9 degrees at the same time) then it has to be the swashplate or the main shaft moving up and down relative the other.

In over my head here with an imagination that does not justify posting. Hence foolish.
Jan 10, 2015, 08:42 PM
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So my interpretation of what your saying is that the swashplate is not level at high pitch. That is normal on a helicopter. Since one of the servo's is installed reverse of others. The splines on most servo's leave the arm slightly off center. Once trimmed to center, that leaves one servo traveling slightly more, or less than the others. On a heli with a flybar that is corrected in the transmitter travel settings. On a flybarless heli the gyro's software corrects for that.
For the tail it is normal for one side to have more pitch than the other. One direction has the torque from the rotors to help it rotate, the other direction it is fighting against that torque. Just follow the manual for the gyro.
Jan 10, 2015, 10:45 PM
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What do you mean by servo is installed reverse of others? are you talking about the elevator servo? I have a trex 450, not sure if that might be relevant to servo reverse installation.
With the naza-H I don't really have the option to center the servos 90 deg, it's more like they want me to set the servo positions such that the swash is level. I might change my setup though now by lowering the swash a bit since my 0 pitch position is not when the servos are 90'd. Is this the correct setup?


ah that might explain why my heli is spinning around in circles.


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