Mysterious tail problem

[BladesinMD]

I am having a tail issue I hope someone can help diagnose..

My 450X V2 is stock and I recently rebuilt it with about 70% new parts after a crash. I am flying smooth figure 8s (normal mode) with slight inputs, so no punching of the sticks.

The main rotor has never been smoother, but the tail has had issues since the rebuild and I have nearly lost the heli twice, skill (dumb luck) has gotten me to land with little or no damage.

So what I have starts with a slow wag evident when giving tail / collective input or encountering wind. During a hover, the tail is mostly still (but not as rock solid as it once was). I tried adjusting the gyro gain, but this did not seem to help the issue.

A much bigger issue seems to occur once the heli has a pack run through it. Sporadically, I get little or no response from the tail, usually during a right turn, then the tail will snap over. Twice now this degraded into random tail movements and loss of control. I thought maybe the tail servo, which is stock, but rebuilt, was the culprit, but the tail blades were properly angled as I examined them after my lucky landing today.

I have checked for binding and set the tail end points in the BeastX, the tail belt appears in good shape with not too much nor too little slack, the servo seems to respond properly, so I don't know where to go from here.

I have some thoughts, though I have no direct evidence to support these:

1. One-way bearing slipping after heat build up
2. Servo malfunction
3. BeastX malfunction (this is my second BeastX in this 450)
4. Tail bearing (feels smooth though)

What do you think?

[watho 46]

Hi Blades
Going on what you are saying, is the tail servo getting hot ???

Maybe try another servo, i have had tail drama's before and they are not fun, all you could try is process of elimination

hope this gives you some help or guidance

Cheers watho

[Ah Clem]

Is it the stock tail servo and, if so, how many flights are on it.

I had one get glitchy on the Blade 300 after 70 or 80 flights. I replaced the servo and the problem went away.

[Coco66]

"I get little or no response from the tail, usually during a right turn, then the tail will snap over"

I once had a slightly bent tail shaft which would cause the slider getting stuck in some circumstances giving the same symptom.

[Mike680]

Originally Posted by Coco66

"I get little or no response from the tail, usually during a right turn, then the tail will snap over"

I once had a slightly bent tail shaft which would cause the slider getting stuck in some circumstances giving the same symptom.

I had the same thing happen to me once, too. Very slightly bent tail shaft. Couldn't see any bend at all, but at certain points around the rotation, the slider would bind. So, be sure to pop off the tail rotor pushrod link at the tail end and move the slider in/out by hand while rotating the tail rotor by hand. If there's any bend at all, you'll feel it.

[BladesinMD]

Thanks for the replies.

The tail shaft is something I had not thought of. I did the test, thought I felt some binding, so I switched the shaft out. Unfortunately, the tail still has the slow wag and appears to be behaving the same. I did not do any circuits with it in fear that the tail would go crazy again - after all the time and $ rebuilding this thing, I don't want to take it out unless I am confident in the tail.

So my next plan will be to switch out the tail servo. All my servos are original. I don't know my exact flight numbers, but I would estimate around 250. Over that time I have had 3 crashes. One severe.

Any inexpensive alternative to the stock tail servo? I am mostly concerned with longevity/dependability rather than performance as my flying style does not demand much.

[watho 46]

Hi guys
I'm running KST 215s reasonably price around $30
But there is much more to chose from if you have the budget to pay for them

Cheers watho

[Heli.Maniac]

The KST 215 is a great choice for both cyclic and tail. I have setup a couple of tails with it without any issues, great speed and performance. It is quite a bit heavier than the stock servo, but it is cheap and the gears can survive some pretty hard crashes.

[NewToRC]

Totally agree. ⬆️

[BladesinMD]

Thanks for the recommendations.

I did some more testing this afternoon with the old servo on board.

And I think I may have made sense out of this all, but I will need a full flight to verify.

I had been hauling the heli to the park to fly - It would sit for maybe 10-15 mins before going up in the air, I am thinking this was not enough time to let the gyro adjust to the temperature (90s).

So today I let the heli sit outside for a good 45 minutes to adjust to temp. Then i started up with my settings unchanged, notably the Gyro, set to 74 gain. I hovered and the tail seemed a little better, but not perfect. So I upped the gain to 86, now the tail seems more stable, near perfect.

I played with the gain once before, but that was before I made other changes like the new tail shaft.

I will go ahead and try some circuits and if I get anything strange, it would seem it HAS to be the servo.

I am so gentle on the sticks, i would think my servos would last longer than the average, though I have also heard stories of servos failing during a hover, so anything is possible.

The strangest part is that before the crash/rebuild, the tail was near dead on at a gain of 70. Go figure...

[Heli.Maniac]

FWIW, I have never had to let the gyro adjust to ambient temp on a heli except for a very old Blade 400 with a Piezo gyro. Sensors have come a long way since then and are rarely affected by temp differences.

If mechanically everything is sound and as it was before the rebuild, then it safe to assume that the tail servo is starting to fail on you. Unless something has changed on the heli (headspeed etc) there isn't any reason for the tail to need more gain to be dialed in imo. The only thing that I remember made a difference in the tail is keeping the tail control rod 100% straight and making sure the tail rod guides don't move around on the boom, which would cause them to mess up the rod's alignment. Unfortunately, the stock servo has a very subpar torque rating so anything that is putting extra load on it will completely ruin tail performance.

[ArchmageAU]

One thing I did not see mentioned was tail belt tension or worn belt.

Under load, you get more stress, if the tail is on the point of slipping due to tension or wear, this can also cause the problems mentioned.

[BladesinMD]

So I am back into this thread because I have tried a couple of things to no avail.

New Tail Servo (KST) installed and Heli exhibited same symptoms. Another lucky emergency landing in the grass.

I did some testing on the bench and the belts and associated gears appear very strong with no slipping under stress. I also think I would hear a change in the heli if these were slipping and RPM's of the tail dropped, and there is no change in sound at all when the problems happen.

I took the main blades off, left the tails on and spooled up in normal mode. Giving tail inputs I noticed as you give right rudder, the bottom tail pin wants to pull out of the slider's groove. In fact, it did during my test whereupon I noted marks on the plastic that showed this has happened before.

So, I replaced the tail pitch slider, lever, and linkage rod with brand new ones. Re-ran the test and it looks like the same thing is beginning to happen.

The tail shaft and boom and case are all new with new bearings. I've read about CA-ing the pins to the slider, but don't they rotate with change of pitch, tearing the pins free??

Please help as I am running out of ideas...

Thanks

[Helithunder]

Hi, you want to make sure the tail case lever is assembled correctly. The bolt should go through a bushing on the bottom then a spacer and a bushing on top then the nut. When the bolt is tight the lever should move smoothly and not deflect out out of the sliders groove. Had this issue on my blade 450x cnc tail case and this was a fix, hopes this helps.

[BladesinMD]

Thanks, Helithunder.

My tail is new, but still the plastic stock parts.

I think an aluminum upgrade may be in order to amend this issue.

[meowguy]

I don't believe that adding aluminum parts will solve this problem. Have you checked that you physically have a top and bottom bearing supporting the tail drive gear mounted in the frames behind the main gear?

The other thing that can cause this type of vibration is the main gear and tail drive (large white gears) are out of round or not completely parallel to each other.

Is drive belt too tight, too loose, does it have an extra twist in it, is it nicked or partially cut?

[BladesinMD]

Originally Posted by meowguy

I don't believe that adding aluminum parts will solve this problem. Have you checked that you physically have a top and bottom bearing supporting the tail drive gear mounted in the frames behind the main gear?

The other thing that can cause this type of vibration is the main gear and tail drive (large white gears) are out of round or not completely parallel to each other.

Is drive belt too tight, too loose, does it have an extra twist in it, is it nicked or partially cut?

Thanks, I checked all of those a while ago. It's not vibration related, rather the tail servo seems to get caught (is not binding though). The pins push outside of the groove on the bottom of the pitch slider with right rudder input under stress. I already ordered all aluminum that cannot flex so we will see how that goes.

[M3bluegsr]

Maybe on the tail pushrod, the carbon rod is moving in the link ends during flight? Don't think it's likely, but confirm servo settings in beastx after servo change.

[Gerald01]

Sorry to hear about all the trouble you're having but I believe that you're on the right track. I had issues with the plastic tail from my very first flight or attempted flight. I flipped off throttle hold and was about to lift off and the tail exploded... split right at the screws and parts flew... so, I replaced the complete case and it flew but could never get rid of the slight wag. I replaced all the plastic, complete tail with aluminum upgrades.... night and day difference... no wag, holds nice and tight and has been for about a year now. My thoughts are that plastic will flex under a load, the aluminum does not... and it looks awesome too..
Good luck

[Waxxingibbous]

hey, check the set screw to your tailhub make sure its not slipping at all(locktite) the one time my tail was barely responding and blowing out was when the set screw was gone or not secured in the groove.

next move is to check belt tension, you shouldnt be able to poke it and touch the other side of the belt. you should get about 30-40 % in when pushed/poked.

no need for alum tail, stock tail works good and the light weight components will mean more efficient tail performance
if mechanics check out, resetup tail end points and ensure whatever the tail servo is mounted on isnt moving at all, tighten as needed with locktite.

if all checks out, time to swap tail servo. after that its the beastx.
i know i said alot of whats already been noted but hopefully something i said sparks the bulb and you get it fixed. oh if the tail blades are chipped at all, swap em! beastx hates tail blades that arent perfect!