T500 ESP negative collective squeal and vertical tail bounce

[Carpetbombing]

Hello, all.

I'm having two problems I can't sort out. My favorite heli is a Trex 500 ESP with the original FL head. I LOVE it, but it recently started squealing when unloading the head / negative collective, but only in IU2. Below 2,600 RPM = no squeal-y, no matter what I do. 2,600 and above = squeal during negative collective. I started out replacing the bearing blocks with the HeliOption thrusted blocks. Nice part, but no change in the noise. I had the old Align 500M motor, which is known for bad bearings, and one of the motor bearings had some play in it, so I got a good deal on an almost-new Scorpion 3026-1600 and swapped motors. No change! My Castle ESC is set to PWM:8 and timing:0 with the Scorpion. Motor gain is around 15. I don't -think- it's the motor losing synch, but at this point I have no idea. I oiled all the tail shaft bearings and swashplate; no change. All that's left is the bearings around the torque tube. It never used to do this. Anyone have a similar problem, and if so, what was the solution?

Also, on a different, flybarred Trex 500 the tail has a medium-slow rhythmic vertical bounce. It smooths out a bit at higher headspeeds - I run 2,200, 2,400 and 2,600 - but the bounce is there no matter what. I replaced the main bearing blocks and tail blades and I think it got a little better, but I'm at a loss. It's driving me nuts. I'm running a Castle governor, and have tried REALLY low governor gain and it didn't help the bounce at all, the motor just wouldn't hold speed. Again, anyone see this before, and if so, what was the solution?

Thank you for any suggestions!

[helidude71]

Vertical bounce is too hard head dampers for the used headspeed.
So, up the headspeed or use softer dampers.

The squeal could be your OWB.
Had this happen once but it's not a common problem on the 500 ESP.
More likely a shot motor bearing.

Good luck.

[Carpetbombing]

Thanks for the tips. I'll look into the dampers on the flybarred 500, I hadn't thought of that. The stock black ones are in there now. I do fly aggressively, but not full-on 3D. The only softer dampers I can find are the grey Align ones. All of the other aftermarket ones are advertised as 'hard'.

The OWB on the FBL 500 was literally brand new 15 or 20 flights ago, and I did just swap motors to a used one that was advertised as only having 4 or 5 flights on it.

I'll report back if I get a conclusive fix for either of the problems..

[Carpetbombing]

Quick update:

Helidude71, thanks for the damper tip. That fixed the vertical tail bobbing on the flybarred 500. I tried the KBDD orange progressive hard dampers, and that didn't help at all. Then I tried the Align grey 70 duro dampers. I only hovered in the front yard, but the vertical tail bob reduced down to just an imperceptible nibble. Way better than it was. I haven't thrown it around yet to see how the softer dampers feel in flight, but there are 75 duro dampers on Ebay that I can try if the grey 70's are too soft in flight. The black Align 80's were way too hard for my heli.

Now I just need to figure out the squeal on the FBL 500. Thanks!

[Relisys190]

I get a noise when inverted also. It's not quite a sqeal but more like a random chirp. I've well oiled all the bearings and I still get it randomly. More on inverted climb outs.

[Blayd]

Have you guys pulled and checked your main bearings? I swear it sounds like a slipping OWB to me, but your mains might be squealing when they have force applied in the inverted state? ( Main shaft collar pushing against the main bearing inner race???)

[Carpetbombing]

I installed new Helioption thrusted single-piece main bearing blocks. They're super smooth. That's the first thing I did to troubleshoot - no change; that wasn't the source of the squeal.

[Blayd]

OK, yeah, it was a long shot but had to ask. Still sounds like a OWB or pinion slipping. I've had brand new OWB slip in the hub. I now use green loctite on all my OWB installs. It's an absolute must on my 700.
But I think if your pinion was slipping, it would squeal even in upright orientation as well.

[PowerDyne]

Just a thought, but the squeal could be the spacer between the main and autorotation gears on the auto gear spindle. That spacer could get out of round with wear. I would try replacing that.

Also check your tail transmission block bearings. It might be the vertical shaft has play in it and might just need a shim.

One way to tell easily is if your FBL controller has a vibration log...

[gaurdian101]

I myself just changed my main block bearings and a couple other things used scorpion motor and after a week of flying I myself was getting this squealing noise also gone through the hole thing still there changed the motor again still there..... and thought since I had another set of main bearings I'd change them out and sure enough that was it even them being brand new they still gone bad really fast... just a though I'd never ever think if would be the bearing's being they new and all...

[Carpetbombing]

Solved! (mostly)

Well, the vertical tail bob on the flybarred 500 was definitely the dampers. Switching to the soft grey Align 70 duro dampers smoothed out the tail. It does fly a little softer, but not too bad. I may try some of the 75 duro dampers you can get on ebay and see if they're a good compromise between the 70 and the 80 duro Aligns.

Regarding the squeal on the flybarless 500; after swapping out just about every single bearing on the heli to troubleshoot I finally put the entire main + auto gear and one way bearing from my flybarred 500 onto the FBL one. That fixed it! Since my OWB was BRAND NEW on the FBL heli (maybe two dozen flights) I didn't think that would be the problem, but something in there was it. I'm going to try sleeve retainer on the FBL OWB and see if that fixes it. Everything is smooth and well lubed, so I don't know for sure what the deal was, but for me it was the OWB somehow. Hopefully that helps someone else troubleshooting.. I bought a new motor when that wasn't the problem. =)