Trex-250 Tail Issue

There has been many posts and articles on the internet about the dreaded Tail Wag on the Trex-250 and even though I thought I had it fixed as stated in my old post, I was wrong as I recently found out when I finally had the time to try to trim & tune up the heli. On higher headspeed, the tail would “blow out” as soon as I pumped (increased or decrease) the pitch/throttle. Why was this happening? I guess firstly I am partly to blame for improper setup and Align is also to blame for their release of a less than troublefree helicopter. As mine was the first original super combos around and not the later SE versions, problems on the tail was bound to occur.

This time round I tried and rectified a few things. Here’s a note to myself and to you who might be interested as to what steps I have taken so far:

1) Decided to move back to the smaller DS420 servo since it was lighter and tried to eliminate the source of the tail issue rather than to over power it with a larger 520(?) servo.

2) Ensured that the servo was properly mounted on the right side of the boom clips to ensure that the “Pushrod” was straight from the servo horn to the guide to the tail control arm. My old servo location had a bend in the push rod. By having the pushrod bent and not straight, it led to an induced “flex” in the system whenever the servo tried to push the pushrod to the tail control arm. A stiffer pushrod will help even more here. Some people have switched to higher gauge wires or carbon fibre rods.

3) Reduced the Swash Mix from 60% for Aileron/Elevator/Pitch to approximately 50%. Will lower it to 45% if the problem persists. This is actually stated in the manual which I over looked. I guess too much pitch will definately overpower the gyro.

4) Bought & changed to new carbon fibre tail blades and installed them (No this didn’t seem to make a difference to the wag but then again it seems to create less “drag” as compared to the stock curved blades which I used.

5) Bought and changed to the new METAL Tail Control Arm which is much stiffer than the stock PLASTIC control arm which flexes under heavy load which again contributes to the delay and whipping action & tail wag.

6) I already have the new weighted tail blade holders & tail blade holder hub (which still led to the tail wag issue) and I also added additional weights (nut) to the tail blade screws. It helps with lessening the load but this is still not the only source of the problem.

With the above settings, I seem to have been able to increase the GYRO travel rate from +36 to about +50 (Head Holding Mode). This was with me holding the heli and reving up the motor (without the main blades of course). With the increase, I am sure the tail would have a little improvement. Will try to fly her this weekend and see if this is what’s needed to keep her steady as I do some pitch pumps. It’s a little unnerving when the tail is so soft and doesn’t hold well. That doesn’t allow you to do much on it apart from normal forward flights. Doesn’t help when I’m trying to get comfortable with backward flips.

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