is it normal if the tail moves a lil to the right at spool up?

[finfan882002]

every time i spool up on the ground my tail moves ccw just a bit to where i have to move the rudder to compensate before i lift off......... is this normal or do i have to make some adjustments?........while in the air i dont get any drifting and its pretty stable. i have a gy401 and a 9650 servo

[pcnukem]

Hi
Yes as far as i know they do, mine always has by about 90 degrees.
Paul.

[crypto666]

mine won't move if I have everything perfect (no vibe, no wobble on a 10 second start up), which is usually never. If I do get everything perfect, it is a good indication that I am about to crash.

[michael503]

Yes, it will.

If you do not have the gyro set up mechanically to fly in rate mode, the tail will move a bit to the right as you load the head (spool up). If you set it up in rate mode with a wee bit of pitch on the tail rotor, and you center the gyro by wiggling the rudder stick, It will lift straight off, with no tail kick, however, having now done this, if you are hovering it about 12" off and hit throttle hold to float it down, you will notice the tail kick the other way. Either way you set it, it makes no discernible difference in flight.

Gyros have to move to know that they've moved.
In a standard setup with zero pitch neutral on the tail blades, a HH gyro never holds at the point its set at, but at 1-3 degrees to one side. The closer the tail gets to where its supposed to be, the less pitch the gyro tells the servo to apply, so there is a "balance" point where the tail is stable. Increasing the gain, or increasing tail authority will reduce this angle, but never eliminate it. Factors such as servo speed, tail blades, linkage slop, and the design of the gyro limit how close to "perfect" you can get.

I went through this a few years ago trying to resolve this very thing. Peeps posting that their tail was "rock solid" had me chasing wild aquatic waterfowl. There is no such thing as a tail that does not move. Some move more than others and some blow out under certain conditions, but with current gyro technology, all tails move when the load on the head changes. Its just a question of how much. I got the best performance with my 450 by raising HS and setting the tail up so the heli would hover in rate mode, although setting it up in rate mode made no difference to how it flew. The higher HS did.

A Spartan 760 will hold it better than a 401, but its still not perfect. All other things being equal, the 760 reduced the angular deflection by about half.

Hope this helps.

[markb]

every time i spool up on the ground

I have to agree with the effect michael talked about - paraphrasing: that the gyro can only sense changes... so when you change torque, it has to have some amount of change in heading in order to sense and then adjust the tail pitch to compensate... So even the best gyro will suffer a small deflection upon torque changes. However, with the good gyro's and a fast servo, its remarkably small.

But there's another factor during spinup. The motor creates full torque spinning up the main rotor long before the tail has come up to speed. So even if you have the tail blades pre-pitched with rudder or a rate-mode setup... the tail still cannot produce enough counteracting torque, because it has insufficient RPM. So if you spin up with a fair amount of torque... it'll twist the heli around even with weight on the skids, regardless of what the gyro says about it! If you spin up more gradually - with less torque - the weight on the skids will hold the heading better, until the tail gains authority.

edit: I also wanted to add... a faster tail servo coupled with your existing 401 will improve performance over what you see with the 9650. I just replaced my 9650 with a HS5084, and was very pleased. It allows a lot more gain now, and is very crisp in response. No wag in funnels, tighter in backward flight, very solid all around performance. A noticeable improvement to me.

[Cheshire_HeliCat]

Originally Posted by markb

I have to agree with the effect michael talked about - paraphrasing: that the gyro can only sense changes... so when you change torque, it has to have some amount of change in heading in order to sense and then adjust the tail pitch to compensate... So even the best gyro will suffer a small deflection upon torque changes. However, with the good gyro's and a fast servo, its remarkably small.

But there's another factor during spinup. The motor creates full torque spinning up the main rotor long before the tail has come up to speed. So even if you have the tail blades pre-pitched with rudder or a rate-mode setup... the tail still cannot produce enough counteracting torque, because it has insufficient RPM. So if you spin up with a fair amount of torque... it'll twist the heli around even with weight on the skids, regardless of what the gyro says about it! If you spin up more gradually - with less torque - the weight on the skids will hold the heading better, until the tail gains authority.

edit: I also wanted to add... a faster tail servo coupled with your existing 401 will improve performance over what you see with the 9650. I just replaced my 9650 with a HS5084, and was very pleased. It allows a lot more gain now, and is very crisp in response. No wag in funnels, tighter in backward flight, very solid all around performance. A noticeable improvement to me.

I agree with your explanation and solutions. Gradual spooling up normally cure that problem for me but sometimes I forget until the heli starts to rotate (90 degree) but normally a tough of opposite rudder shuold kill it.

A good gyro is always useful Futaba 401 is well known and reliable. I use Align GP750 and DS520 - it holds the tail rock solid.

[finfan882002]

so in other words, set it up in rate mode first and ill have better tail authority?...........also, can i replace my 9650 servo gears with the 9257 servo gears and basically have a 9257 servo performance?

[TomRex]

so in other words, set it up in rate mode first and ill have better tail authority?

No, because thats the way the formal instructions say how.
That aside. I use the soft start on my Jazz and have no rotation at startup or lift off. It' like a real heli not a toy. wee!

[michael503]

Originally Posted by finfan882002

so in other words, set it up in rate mode first and ill have better tail authority?...........also, can i replace my 9650 servo gears with the 9257 servo gears and basically have a 9257 servo performance?

It will lift off differently, but normal flight and hover will be the same. The tail will still move the same amount when you pitch pump too. If you raise your headspeed, this deflection will be less. One thing that might be different is that when I had my 401 I had a very slight tail drift. Setting the tail up mechanically solved that issue.

Do not attempt to set up in rate mode with zero gain! set your gain at 30-50% of max value for that mode, else it will be very very difficult to control.

yes, the 9650 and the 9257 are the same servo except for the case and the gears. They use the same pot, board and motor. If you have metal tail grips, consider doing the Chinese weight mod. It will take a bunch of load off the servo. If you don't know what that is, there is a whole thread here somewhere devoted to it.