Why is my tail chirping, whipping and just plain angry.

[Steve Graham]

So I'll post this here in case final resolution (which hopefully I'm close to) helps anyone else.

I built a new E7-SE awhile back as a replacement to and with components from my Rush that is no longer supported in the US.  My E7 had been flying very well and the only problems I had were in getting the Silverline Vbar to read the  CC Edge 160 RPM.  Never happened reliably but that is another story that I solved with a HW phase sensor.

I was really enjoying doing a lot of Buddy Boxing with friends as 1600 RPM sport flying gives me 8 minutes of flight time.  I'd done some ESC programing and forgot to reset the throttle curves in the B Box which resulted in an unplanned and less than graceful auto when I handed off control to my student.  Damage didn't seem too bad.  Very minor boom strike/dent and some links and other minor stuff here and there.  I thought I had inspected everything pretty well and replaced the things that needed it.  Flying it again it was displaying what appeared to be a very angry, chirping tail with whipping and inconsistent piros.  I spent a lot of time messing around with vbar settings to no avail.  One interesting artifact of my trouble was that at 1600 RPM the heli flew pretty well but at 1950 there was all this drama with the tail.  I checked the vibe log in the vbar and it was seeing high and extreme vibrations at the higher speeds especially.  With the blades off and the heli spooled up things didn't seem so bad but the vibes were definitely there in flight.  Watching the main shaft turn slowly with the head off there was a TINY amount of runout.  Probably less than a mm.  But I couldn't find anything else so I put a new main shaft on it.  No help.  Crap. 

Common sense told me this was mechanical and not electronic since the machine was flying well right up until the bad auto.  This morning I took the tail off and pulled the transmission.  Surprisingly even after the botched auto the tail is extremely smooth and true.  I thought maybe there was something in the torque tube transmission assembly.  There was a fair amount of lash between the tail blades and the auto rotation gear up front.  On close inspection the umbrella gears in the tranny both showed quite a bit of wear but no breakage.  I replaced both and buttoned the heli back up.  There is still just a bit of what I might call excess lash where the pin locks the straight cut metal gear on the transmission shaft but I almost feel like this is by design?

I took it out for a brief flight right before last light this evening and it SEEMS like the chirping and whipping are gone.  I will fly it again tomorrow to confirm I've got it solved.  Keeping my fingers crossed.  If this does fix my issues it begs the question.  Do worn out transmission gears create vibrations that piss off the FBL unit and create what I witnessed or do they directly screw with the mechanical functioning of the tail just through excessive lash?

[Kevin Feil]

Absolutely Steve,

 Whether it's a full scale or RC Heli, wearable items , gears, bearings, and other moving parts will wear, some quicker than others depending on flying style, climate, conditions of were your flying. A lot of factors. These Helis in my book are the best quality you can buy. However regardless of how well built they are, they require maintenance and honestly you should be inspecting them before any flights, and especially at the end of the day. Even though things may appear to be functioning normal there could be an issue just on the verge of happening.
 Also something for everyone to think about is when you are doing "Flight Training" Autos" Other maneuvers, these can also accelerate wear especially hard landing and such. (Don't want to send the wrong message, these Helis can take a ton of abuse, I'm speaking for ALL Helis) in short the more you beat on them, the more frequent your maintenance intervals should be.
 Also it's important to follow these manuals to the letter. Not correctly assembling these Helis and any Heli for that matter, can lead to premature failures of components and especially accelerated wear on the "Gear Train" .
 Great Post, hope your past this little bug and can get out and enjoy your bird..

K

[Steve Graham]

Thanks Kevin,

OK I think the worn gears on the tranny really were the cause.  I flew several flights today. Was able to do some tuning on the tail with the bluetooth android app for the vbar and the inconsistencies seem to be gone.  It's back to flying the way it was prior to the bad auto.  Both 1600 and 1950 fly well, smooth flying and hard 3D.

[Kevin Feil]

Congrats Steve! Great work in diagnosing the fault.. Glad to hear your back in the air.. If you ever need anything don't hesitate to PM me. Or call (404)809-1622 , here to help..

Best Regards,

Kevin

[Steve Graham]

Thank you sir!