What happened to the trex 700 tail hum?

[Inkslinginmofo77]

As long as your TT is in good condition and all gears are good and boom is sound and all mechanics are good then u can reduce harmonic vibes and mums simply by using quality bearings and use the correct bearing spacing to eliminate hums. I use 5 bearings in my 800 tail and double up two sets. ____|___||_____||_________. I use this layout with good bearings and can hard feel any tail vibes. I've studied vibe analysis and spectral frequency graphing and had to become wise to the issues causing them as I use a Skookum SK-720BE and it has a built in vibe analyzer. Really helpful to eliminate issues . But it all depends on your preferences and what's acceptable to u .

[marc8090]

Originally Posted by jsbach#1

Its not a mystery, throw an extra bearing in there, smooth as silk. I've had every size trex there is all of mine have been eerie quiet.

It's not always that simple.

[marc8090]

Originally Posted by -kenny-

The tail hum itself wouldn't bother me too much. But does it result in the breaking tailshaft? Or do these two issues have nothing to do with eachother?

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It should most certainly bother you. It leads to breaking all sorts of parts besides tail shafts.

[Weule]

Originally Posted by el guapo

I want my money back. Seriously the obvious stuff has been tried.

The tail problem thread is 89 pages to date without a solid solution:
https://www.helifreak.com/showthread...445050&page=89

[Inkslinginmofo77]

Never simple is right. Any kindle of wiggle or play is gonna cause issues. If u take the time to use quality parts and locktite and make sure your TT is snug in the gear cups among many other things, u are on the right track. I've found some gear TT cups have play in them . It's best to check everything by hand and make sure to eliminate binding and stickiness and play to ensure a smooth tail. Some people aren't thorough and some are. With helis thoroughness pays off

[el guapo]

Originally Posted by Weule

The tail problem thread is 89 pages to date without a solid solution:
https://www.helifreak.com/showthread...445050&page=89

yup. but good tail blades and avoiding 2050 RPM works for me.

even OnTheSnap's 700 developed it. but a set of rail tail blades fixed it.

[Trexwilly]

I read a bunch of that thread, but never saw a clear solution either. So you ascertained that 2050 was the danger area?

[Glenn Goodlett]

Mine is fine at 2050, in fact that is where my gov is set. I have never had hum problems. I've rebuilt the tail at least 4 times due to crashing. Never a problem. However, I've seen guys that can't get rid of a horrible hum. Why? I don't know. Like most things, shit ain't as simple as you think.

[Inkslinginmofo77]

Your heli must product nasty harmonics at 2050. Like I said spool up the heli without main blades off (leave on tail blades) and feel your tail tube and locate the point that vibe SL are highest. Once u have done so remove tail rotor and position bearings towards that high vibe area. Repeat this step until all harmonics are down. Even spaced TT bearings cause bad vibes and harmonics. And if for any reason this doesn't worth them something is mechanically wrong.

[el guapo]

Originally Posted by Trexwilly

I read a bunch of that thread, but never saw a clear solution either. So you ascertained that 2050 was the danger area?

I had always been in the "I don't have it" camp, which is troubling for me because, I believe the observations. and there was a lot of them.

but one of the guys posted that on his 700E, he had tracked it down to resonance at 2050. or maybe it was 2020. I don't recall...... He said that every-time he spools up to 2150, that it would go thru resonance and then out of it as it got to head speed. I thought that was a really smart observation... I wish I remembered who that was.

I have vbar control so it was really easy to sweep thru some head speeds and I could duplicate the issue centered roughly around 2050, basically the tail rotor resonates and goes out of track. the tail blades make a raspy tone. the resonance only happened between around 2000 and 2100. and it would go away around 2150. which is where I fly. but now that I was listening for it. I was hearing it on every spool up

So, I change out the tail blades for some Rails, just like all the freaks did in the thread, and then it was immune at all head-speeds that I tested. and next time I saw OnTheSnap, I noticed his 700E had the raspy tail too , I recommended the Rail tail blades and later he told me it fixed it.

I have a few theories about the issue, but they are just theory. and for the sake of brevity, I'm filtering out some of the observations. the cupped washers are an important observation, and they should be replaced if found. anyway, I believe there is a strong correlation to the head-speed and the tail blades.

obviously, if you understand resonance, you can do one of two things. 1) remove whatever is exiting the oscillation or 2) move the natural frequency of the system to somewhere it wont cause an issue. normally moving the frequency is preferred.

and I'm wasting my flying time pounding on a keyboard later

[Inkslinginmofo77]

It depends if the vibes and the source. My sk-720BE Has a built in vibe analyzer. There's a difference between tail and tube vibes. What I was referring to was tube vibes. U can manually feel if it's stronger in the tail assembly or the tail tube.

[JohnC1988]

I had bought my trex 700 dfc a few months ago . I changed the tail to the solid shaft with black gears from the start and the main grip bolts to lynx. I still had the tail hum , it was the align 105 white tail blades. I boughta set of edge and it was all gone. Also I tried Curtis youngblood 105's also no hum .

[Inkslinginmofo77]

I'm weary of those black gears. I found that the TT fits loosely I'm the umbrella cups. I went back the the white ones. Idk if I hot a bad batch or if it's a flaw but it was hovering more play. I've heard others say the same thing. Yes quality tail blades will eliminate tail hums and some vibes. I've found that secondary parts manufacturers such as KDEdirect and Curtis Youngblood make better quality parts than stock. KDEdirect actually patented the new tail pitch slider on the aligns and align liked it so much try made a copycat and are now putting it on all helis. I got the align one and the kde one and the kde one is beefier and sturdier. So I used that one instead. Stock parts work. But the secret is in the bearings and blades. Hardware is secondary but gives your heli a more structural soundness.

[paulmedford]

I switched to the vbar gov and my tail hum went away. I maybe had too much gain on the castle gov, but either way the vbar gov took care of the weird tail noise, and so far no more tail gear stripping

[-kenny-]

Oh so now it strips tail gears aswell? Maybe i'll have to re-think getting the trex... I don't want to be flying with all these issues on my mind.

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[paulmedford]

I stripped three tail box gears, the front ones , in flight, may have been due to too high gov gain on the castle esc. But now I run the vbar gov, and so far all is well. The trex is a lovely
flying heli. You should get one. For the price it's worth it. What FBL unit do you like?

[-kenny-]

I've had a few. Microbeast, 3gx, spartan vx1 and a few vbars. I liked the spartan and the vbars the most. But i'm curious for the new gpro too, it seems to be getting some good reviews.
I'm doubting of getting another heli in the first place. And IF i'm getting one i'm going back and forth between the trex 700L dominator top (for the price) and the kds agile 7.2.

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[dchekas]

If you're stripping tail gears in flight regularly on the 700, you need to look closely at your governor gain and your tail stop gains. It's not the airframe that is the issue.

[Trexwilly]

I added zeal 105s tail hum gone!

[el guapo]

the black helical gears are strong.