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Sep 07, 2011, 06:12 AM
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How to set up the tail properly?


I've been flying my T-Rex 500 for over 2 years now, always in HH mode, and have no complaints about how the tail holds in that mode. I'm aware that I haven't set my tail up properly, for if I ever forget to switch to HH mode before I lift off, the heli spins uncontrollably as soon as it's light on its skids (in time for me to realise what's wrong, stop it, and switch to HH mode).

So, can someone point me to a simple guide as to how I should set things up properly, please?
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Sep 07, 2011, 06:17 AM
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Quote:
Originally Posted by abenn
I've been flying my T-Rex 500 for over 2 years now, always in HH mode, and have no complaints about how the tail holds in that mode. I'm aware that I haven't set my tail up properly, for if I ever forget to switch to HH mode before I lift off, the heli spins uncontrollably as soon as it's light on its skids (in time for me to realise what's wrong, stop it, and switch to HH mode).

So, can someone point me to a simple guide as to how I should set things up properly, please?
It's very easy. Set the gyro into rate mode and make note of which way the heli wants to spin in hover. Adjust the servo and mount on the boom whichever way forces the tail blades to counter this drift. This may take several test hovers to get right but adjust until you have the drift out as best you can mechanically while in rate mode.

Switch back into HH mode and go fly.
Sep 07, 2011, 08:57 AM
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Thanks Xrayted. What I've been doing after every crash requiring a boom replacement, is to simply adjust the servo position until the tail rotor slider looks centralised, so I'm probably not too far off.

I'll follow your instructions next time I go to the flying field.
Sep 07, 2011, 09:34 AM
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xrayted is right but I will add that you obviously keep the servo arm at 90 deg while you do it and you can use a touch of sub trim if needed to get it perfect.
Sep 07, 2011, 10:55 AM
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Quote:
Originally Posted by abenn
Thanks Xrayted. What I've been doing after every crash requiring a boom replacement, is to simply adjust the servo position until the tail rotor slider looks centralised, so I'm probably not too far off.

I'll follow your instructions next time I go to the flying field.
You will probably find that the slider ends up to the left of centre, possibly by quite a margin.

There are two schools of thought on this. Some folk, including Finless Bob, argue that we should set the slider to centre, because that gives the gyro the most resolution to work with.

What they don't seem to take into account is that when the heli is in the air, the slider will sit wherever it needs to sit, to be able to hold the tail, and the resolution is what it is, with the slider in that position. So the other school of thought, including myself and I assume Xrayted and Druss, set the slider to wherever it need to be, to be able to hold the tail, in the first place.

If your gyro has only a simple limit pot that does not set different limits for each direction, as you set it for equal movement on each side, you will not be using much of the travel on the right. But then, unless you want it to be able to piro faster in one direction than the other, you would not want to be using more limit on one side than the other in any case.

(Before someone points out that piro rate is not set by the limit pot, the maximum available piro rate is dependent on how far the slider is able to move)

Dusty
Sep 07, 2011, 11:55 AM
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I agree that wherever the slider ends up is where it ends up. The gyro would end up putting it there anyway to keep the tail straight in a hover. In forward flight it might center a bit more but in the end I'm not sure that it really matters, as long as you've set the limits so that you can reach the both ends of the tail shaft.
Sep 07, 2011, 12:03 PM
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It seems logical to me that the slider should be somewhere close to centre, so that the servo can move equally left or right. If it always ends up somewhere significantly off centre to keep the tail steady in normal mode, I wonder why the designers didn't take this into account? And, why do you say I won't be using much of the travel on the right? Surely, once the tail is trimmed to hold steady, it needs the same travel in each direction to rotate left or right, doesn't it?

I'm also puzzled, if you say that what I've been doing (centering the slider, with the servo arm and slider arm at right-angles to the pushrod) is effectively what Finless Bob advocates, how does he hold the tail steady in normal gyro mode?
Sep 07, 2011, 01:13 PM
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Quote:
Originally Posted by abenn
It seems logical to me that the slider should be somewhere close to centre, so that the servo can move equally left or right. If it always ends up somewhere significantly off centre to keep the tail steady in normal mode, I wonder why the designers didn't take this into account? And, why do you say I won't be using much of the travel on the right? Surely, once the tail is trimmed to hold steady, it needs the same travel in each direction to rotate left or right, doesn't it?

I'm also puzzled, if you say that what I've been doing (centering the slider, with the servo arm and slider arm at right-angles to the pushrod) is effectively what Finless Bob advocates, how does he hold the tail steady in normal gyro mode?
Remember that the tail doesn't need equal throw in both directions. LT yaw requires much less movement than RT does so I don't think it matters if it's centered with equal throw.

There has been much debate over the years on the subject but all I can say is I have never had an issue just setting it to where it needs to be mechanically hold the heli and be done with it. This of course as stated by others is with the servo arm at 90 degrees.
Sep 07, 2011, 01:21 PM
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Agreed, the whole idea of the tail blades is that they counter the rotation of the main blades so in a hover they will always be to one side of center. If there is no pitch at all on the tail blades in a hover (center of the slider) the heli would rotate as there is nothing countering the torque of the main blades.

When you get into 3D or FFF things change a bit because you don't do a whole lot of hovering and the tail needs to work less in FFF. In 3D you make changes so fast I don't think it really matters.

In the end, I don't think it really matters like I said, the servo easily has enough throw for the slider to travel the entire distance of the shaft regardless of which way you set it mechanically but for a beginner I think that setting the slider wherever gives a steady tail in rate mode (off center depending on head speed) is the best way.

The resolution discussion is a good one as you do have better response when the servo arm is travelling more in parallel to the tail rod and this happens when the arm is at or near 90 deg. So even with the resolution, it's still better for beginners to set it up mechanically off center to hold a hover and for experienced pilots to set it up at center.
Sep 07, 2011, 01:27 PM
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Thanks guys. I was thinking that, once it's holding steady, it needs equal force (hence, slider movement) to spin the heli clockwise or anti-clockwise. But, of course, that's not the case because of the rotational force of the main blades.

I'm going to set the slider wherever it needs to be to hold the tail reasonably steady in normal gyro mode.
Sep 07, 2011, 01:32 PM
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Quote:
Originally Posted by abenn
Thanks guys. I was thinking that, once it's holding steady, it needs equal force (hence, slider movement) to spin the heli clockwise or anti-clockwise. But, of course, that's not the case because of the rotational force of the main blades.

I'm going to set the slider wherever it needs to be to hold the tail reasonably steady in normal gyro mode.
You may even like the way it flies with the gyro in rate if you have only flown in HH before. You can fly it like a plane and the tail will follow the heli in turns with very little rudder movement. It's a different feeling so of like heli "Drifting"
Sep 07, 2011, 01:35 PM
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Quote:
Originally Posted by Xrayted
You may even like the way it flies with the gyro in rate if you have only flown in HH before. You can fly it like a plane and the tail will follow the heli in turns with very little rudder movement. It's a different feeling
This is a great way to fly scale helis as it's more realistic looking but for pod and boom flight I prefer HH myself.


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