What happened to the trex 700 tail hum?

[Dino Spadaccini]

It was a hit or miss on the older kits the new stuff not sure of the change but everyone seems to be happy with the kits and i am not getting any Pm lately on the tail

Dino

[Excalibur3]

Ok cool if they fixed the problem but still the parts have the same number as my 700pro than what did they fix? Was it a faulty part if so which one so we could buy the newer version of it.

Trex700ProDFCHV,Goblin 770,Goblin 570, 14SGH

[Wizza]

Originally Posted by Excalibur3

Ok cool if they fixed the problem but still the parts have the same number as my 700pro than what did they fix? Was it a faulty part if so which one so we could buy the newer version of it.

I've got a v2 700E which originally had the slower tail gears (gear ratio). Tail was not holding in tick-tocks etc, so upgraded to new faster tail (gear ratio) - still white gears but higher ratio. Then the hum came back ever so slightly, but it was there. Tried different tail blades, and helped but not a fix in my case. So grounded the 700 and stripped the tail down. Found that the rear gears (original whites) were not smooth anymore. Have rebuilt a new tail gearbox with new 6mm tail shaft, black gears and new 6mm Align tail hub. New tail gearbox received a few shims and is as smooth as silk, literally, with zero slop or play. What I have noticed is different from the old white gears, is the black gears have definite "play" on the end of the torque tube. As if the chris-cross hole in the umbrella gear is made slightly oversized. Maybe this new "play" is by design and stops transfer of vibe to the torque tube and stops resonance ??? Will be interesting to see how the end of the torque tube wears (or maybe that should be "wears out"). Time will tell. Will put the 700 back into the air this week end and see if the hum is gone. Will be testing with Rail tail blades.

[Ah Clem]

There were quite a few of them at the HeliFreak Fun Fly-I don't recall hearing one with the issue.

[el guapo]

I heard one with a really bad tail hum at the HFFF. I was going to chat with the guy after his flight, but he crashed it.

mine currently doesn't hum, but it has once

new tail blades fixed it.

[Excalibur3]

Originally Posted by el guapo

I heard one with a really bad tail hum at the HFFF. I was going to chat with the guy after his flight, but he crashed it.

mine currently doesn't hum, but it has once

new tail blades fixed it.

Same for me. I just don't understand why they won't let us know what's up. After all it is dangerous to fly if your tail is humming. And most of us did the band aid fix (rail 106's)

Trex700ProDFCHV,Goblin 770,Goblin 570, 14SGH

[el guapo]

Originally Posted by Excalibur3

Same for me. I just don't understand why they won't let us know what's up. After all it is dangerous to fly if your tail is humming. And most of us did the band aid fix (rail 106's)

Trex700ProDFCHV,Goblin 770,Goblin 570, 14SGH

the one with the bad hum had rails on it. I checked.

mine has been fine with egde, rail, zeal. It likes new blades.

I had a set of radix that developed the hum. at first it was only at certain RPM but after a few more flights the hum it was there to stay. maybe they got chipped or floppy.

my logo500 is picky about tail blades too, so its just something I accept from some helis.

[Ah Clem]

"I heard one with a really bad tail hum at the HFFF. I was going to chat with the guy after his flight, but he crashed it.

mine currently doesn't hum, but it has once new tail blades fixed it."


I missed that one, sir.

It was good to meet you in person!

[el guapo]

Originally Posted by Ah Clem

I missed that one, sir.

It was good to meet you in person!

yes it was a pleasure. it was really nice meeting you too.

[Wizza]

UPDATE - Well, I’ve had some success with my 700 tail issue, so thought that I would check back in and share my story. I’ve read about the 700 tail hum issue for long enough now to realise that there’s no single fix for this issue, and this is but one story and one fix...

As reported above a few posts, the tail hum had returned to my 700E after installing the higher ratio (front) tail gears. I wasn’t keen to go up to 115 tails, and this new ratio locked in the tail and fixed my issues there, however the hum was back. To be honest, I don’t believe the new tail gears created the hum in my case, rather I feel that it was always there only masked by the lower ratio gears, lower head speed with the Rail tail blades.

I started the week tearing down the tail on my 700 and expecting to rebuild with a new torque tube using Japanese high precision ABEC bearings. However once I removed the tail unit I realised that the gears were not meshing well nor rotating smoothly. There was no obvious sign of damage, however it was not smooth and a likely candidate for causing my 700 issue.

The previous setup was an Align V2 tail unit with the white gear, stepped down 5mm tail shaft, KDE tail pitch slider assembly, a QuickUK tail assembly and Rail 106mm tail blades.

I bought a new Align V3 tail unit with black gears, and the new 6mm tail shaft. Here I ran into my first issue, as the QuickUK tail assembly requires a 5mm tail shaft, and they do not make a 6mm tail hub as far as I am aware. So another order was placed for a new Align V2 tail assembly and an Align 6mm tail-hub.

I dry assembled the whole tail assembly first up, just to see that everything would go together smooth with no binding or issue. I ended up using a 0.1mm shim on the tail shaft, on the inside of the RHS bearing (looking from behind) so that it spaced the gears away from each other slightly and took out the side to side play in the tail shaft. This gave me a nice smooth mesh with just a hint of back lash all the way round. I also used a 0.1mm shim on both sides of the tail hub, which took out the lateral play of the tail-grips on the tail-hub.

The whole tail assembly was silky smooth and no play or slop anywhere, so I proceeded to assemble the tail unit with Loctite for the final time, and grease the thrust bearings (which were supplied dry from factory). I then applied some Tri-flow Dry Lube on the black gears and left them overnight to dry. If you haven’t used dry lube before, make sure to shake the bottle really well before use and leave it overnight for the carrier to evaporate and dry. This leaves a waxy dry film over the gears, after the carrier has all evaporated.

I then went to fit the Rail tail blades and ran into my next issue, as they were way too tight in the Align tail grips. So a quick search in the 700 spares box found a set of new Align 105mm carbon tails in the latest design/style. Interestingly these blades fitted nicely into the Align tail grips and tensioned up nicely, not to loose and not too firm.

I also tried those new Align plastic blade clips which sit inside the grips either side of the blade root, however I found them to make the Align blades too tight a fit in the grips. So they went back in the bag and into the 700 spares box for another day.

Last week I did a live vibration analysis on the 700E with the Vbar vibration analyser and the Bluetooth link to the notebook computer, and saw 1300+ vibe at the tail. Today I did three test hovers with the new tail unit and there was no hum and only about 250 on the Vbar vibration analyser.

Also worth mentioned, that as others have found, the black umbrella gears are a loose fit on the torque tube spline and there’s a fair amount of back lash there. Time will tell how they wear, or wear out, and how the aluminium end of the torque tube lasts.

So in my case, this was a successful rebuild for my 700E and fixed my hum issue. Maybe someone else will benefit from this information. Again, there’s no one fix for this issue, and the tail gears are just another point to check when trying to chase done the dreaded 700 tail hum.

Fly safe, and cheers for now guys...

Mark R

[raptor50luvver]

I have the Dominator Top with stock blades and I have the tail hum on mine.

I had the hum on my original 700DFC but tail blade change sorted that out.

This one hums regardless unless running a lowish headpseed.

At least my Raptor E700 and Logo 690 fly without issue.

[vtown nick]

My bran new V3 Pro DFC with the new blades had a nasty hum!! I tried Zeals first on the bench, way worse!! Rails?? Noise gone, like that!! I added a small piece of packing tape to one of them dynamically checking and was able to get it more smooth. Happy heli now.

[el guapo]

I tried zeal tail blades. I bought two sets. one hummed, the other didn't.

[Excalibur3]

I'm in the process of building a new 700L top super combo and was wondering if this version has the tail hum problem as well?

Trex700ProDFCHV,Goblin 770,Goblin 570, 14SGH

[vtown nick]

Originally Posted by Excalibur3

I'm in the process of building a new 700L top super combo and was wondering if this version has the tail hum problem as well?

Trex700ProDFCHV,Goblin 770,Goblin 570, 14SGH

Hold the boom in your hand and run that puppy up through the rpm ranges with no mains. I have 1800-2000-2200 for gov and at 1800 you can feel it in the boom. 2000 you can start to hear it and the disk starts to go out of track. 2200 and you can clear as day see a gap between the tail blades they are so out of track from the vibe and if you look at the center of the hub it's a complete blurr. No wonder people break tail shafts on these.

I wish I would have done this test prior to maiden. If yours fails this test don't fly it. Balance the tail blades or get the Rails like many people suggest.

The reason this heli does this to my understanding is it is one of aligns only helis to actually have a high tail ratio so at 3D head speed the tail is spinning like mad. If the tail blades aren't a perfect match balance wise or the rotating assembly is off it will let you know!

Just like the tail on a 130x only much worse things will happen if neglected on this size.

[semperfib400]

Is somebody able to give me an explanation why the rail blades seem to "fix" the issue? Is it because they are lighter?

I wonder if it's just masking the issue and not really "fixing" it properly?

I have a set of rails on order now so I'm curious to see if I can tell a difference. I seems like I can hear a slight hum on the bench but it's no where near like in this video:

Align Trex 700 DFC Tail HUM TERMINATED (7 min 8 sec)

I just wonder how the rail blades are actually fixing it. Puzzling for sure.

[-=RAGE=-]

Originally Posted by semperfib400

Is somebody able to give me an explanation why the rail blades seem to "fix" the issue? Is it because they are lighter?

I wonder if it's just masking the issue and not really "fixing" it properly?

Yes and yes.

As I got my Rail blades, the tail hum at 2200 rpm was nearly gone.
On the workbench a did a dynamic balancig. A short piece of tape on one of the tail blades fixed the tail hum completely.
I do not know the true reason for this tail hum phenomenon.
There are several heli pilots without a tail hum. They are flying stock T-Rex 700 Combos with the stock tail blades.

[-kenny-]

I can't beleive this issue is STILL not resolved :-s way to go Align

[Ukhan24]

Originally Posted by -kenny-

I can't believe this issue is STILL not resolved :-s way to go Align

I agree I can't believe in their TOP KIT that this issue exist.

I have a Align 700N which I am running the new style Tail. I have been using the new Align Tail blades that come with the Kit. How come I don't have this tail Hum Noise?

[semperfib400]

Originally Posted by Ukhan24

I agree I can't believe in their TOP KIT that this issue exist.

I have a Align 700N which I am running the new style Tail. I have been using the new Align Tail blades that come with the Kit. How come I don't have this tail Hum Noise?

Being as yours is a Nitro I wonder if you just can't hear it? But yes I can't believe they don't have a fix for this either