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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.
I’ve managed to fix my tail wag issue on my T-Rex 250. Thought I’d share it with those of you who are looking for a solution.
I basically did the following:
1) I made my own “chinese weights” for the tail by using the nut ends of EZ Connectors and putting them through longer screws used to secure the tail blades. With the Nuts as added weight, it perfectly balanced the tennis raquet effect of the unweighted tail grips. After making adjustment, I was able to move the tail pitch slider (with or without the tail blades) easily without much force and when I let go of the pushrod, it would stay in place instead of move back to the center. The basically cures the high-torque needed to move the original tail slider due to design flaws.
2) I substituted the Align DS420 with a DS520 servo. I’m not sure if the 520 is needed after my fix above since I made the changes at the same time but the 520 definitely packs a bigger punch in terms of torque delivered to the tail slider.
As a result of the above changes, My GYRO Sensitivity which was previously at 60% is now up to 70%. I am probably also able to move it up to 75% without getting much wag but since I have changed my pinion from 15T to 16T now, I had to dial it back a little to prevent tail wag.
The Heli now feels locked in. I have yet to test full collective climb outs but I have a feeling the tail will hold this time round. Here’s to having more enjoyable flights rather than an expensive paper weight 🙂
I’ve also ordered a set of new tail grips from Align which comes with the counter weights. I’ll put them on to see if they perform as well as my mod but I doubt it since I’ve seen a video on YouTube which shows that the weights on the new tail grips are still not heavy enough to counter the tennis raquet effect. We shall see…
UPDATE – 4 July 2009 : I’ve installed the new tail grips from Align (which comes with the larger screw heads – thus new allen screwdriver is needed), and true enough, the weights on them does not make a big enough difference. As such I decided to put on my mod onto the tail which seems to even improve it more. Pls refer to the pictures below to see how I’ve done it.
Basically the new tail from Align and the weighted nuts did the job of curing the tail issue. When spooled up, I can move the tail freely with hand and if I leave it at any spot, it does not move or spring back to any position. Having said that, I’ve left the DS520 on the tail because that seems to deliver more power than the DS420 which in my opinion is a little on the weak side. Good Luck Guys
My latest addition to my fleet is Align’s newest micro helicopter, the TREX 250. This little baby captured my interest the first time I laid eyes on it… or rather the first time I laid eyes on the box. My next encounter with it was by reading an article on RC HELI magazine which featured the new comer. What got me interested was that the combo kit came with almost everything that you would need to get this heli up and flying except for a radio, receiver and battery. Apart from those three items, it came with everything like its very own digital servos, 3 for the cyclics and 1 for the rudder and it also comes with a high quality gyro fit even for larger birds.
The build of this heli was done over a span of 2 weeks although I believe you can actually get it done in 1 night since most of the heli was already pre-built. I took my time because I had to order LIPO batteries for it. For those of you who are short sighted and have fat fingers, do be warned… the screws and parts are really really minute! Don’t drop any screws or you’ll spend the rest of the night looking for them! Having said that… the instructions that came with the kit was pretty well written and laid out. Oh might I also add the quality of this kit is unbelievably good with its machined metal heads, carbon fibre parts and basically smooth operations of the tail drive and all head linkages.
I have just managed to fly this baby last Thursday / Friday but found that the GWS receiver which I used was prone to interference (which almost cost me to lose the chopper a few times). I have since changed it to a ‘spare’ 8CH corona receiver which seems to be doing very well.
I was also hit by the dreaded tail wag issue when gain was only set at 51% (head-holding) or 49% (non-head hold). Needless to say, the tail held terribly. I was so sure that I used the correct ‘+’ (plus) shaped horn measured at 5mm but still I decided to try to change it to the ‘o’ shaped horn which seemed to have the mounting point just slightly closer to the center than the ‘+’ shaped horn. Unbelivably, that cured the problem! So if you guys are having tail wag problems, make sure you use the right horn with the Align DS420 servo and Gyro! 5mm is the magic number. you might even want to try 4mm if there’s such a mount point! My rates are not at 65% there abouts and the tail holds like a dream. I have also set my gyro to have a delay of close to 100% since a 0% delay seemed to give me a slight wag. I think the servo might be a little too quick for the tail and gyro to keep up!
Alright that’s all I have to report for now. Btw I’m using a Zippy 1000 mAH battery that’s rated at 25C. It was a little tight for the canopy but that was cured by drilling two new holes just about 7 or 8 mm back from the original holes. The power is good but I will need to try some pitch pumps and see how well the power holds now that my tail wag problem is gone and that the tail holds rock steady!