Align Trex 700 Tail Vibration/ Hum Solution?

[TeeJayShelton]

I didn't like the bolt length with the align 106 stock blades either. The clips still allowed the grips to touch the blades but the bolts didn't make it through the nylon(only about half way). I tried them without the clips too but didn't see any improvement. I decided to put a little blue on mine. May attempt to source a longer bolt eventually.

[sammyha]

I haven't posted on here for awhile. That's because on my last test flight with the steel shims the tail separated itself from my Trex 700, in the air... That's how seriously fatal high speed flutter can be.



The bolt holding the tail grip to the hub pulled apart. The threaded part of the bolt is still in the hub. I believe it's a fatigue issue from repeated testing and the flutter not going away. I didn't ever stay in idle 2 long, but eventually it failed. Note though, it failed in idle 1!

I really had minimal damage considering pieces came off my heli and I put her in. It was away from me, about 20' out and up, and I had the steel washers in to take up the gap between the Zeal tail blades and the grips. And THAT didn't help either! It had that hum (high speed flutter) in idle 2, so I came down to idle 1 and noticed it would hum unloaded, but not hum loaded. So I was doing some real slow elevator tic tocs, just listening to it, almost like short rainbows and kinda wondering why. After about the third one, coming towards me at a 45 degree angle, one tail grip and tail blade left the heli. Watched it sail off to my left in the sunshine. I stopped the tic toc, pushed it upright and hit throttle hold. That was not a pretty sight to see against the clear blue sky, part of your tail leaving your heli! It was rotating a little and went in on the left side. Right into the snowbank from plowing my heli pad! About a five foot high pile!

So total damage was main and tail blades (one lost in the woods, one shattered from the sudden out of balance condition spinning on the shaft by itself), lost tail grip, bent tail shaft, front torque tube gears and auto gear destroyed. That's it! Had to clean out a lot of snow that was in the frame. And dry it. Minimal damage for putting a 700 size heli down.

So after rebuild, I spooled it up on the bench without the main gear. That's motor only turning. It would vibrate across the counter in idle 1. Had that hum, down the tube, coming through the braces, all the way out to the tail fin. But more vibes in the frames and landing gear. That's when I started the motor balance thread. I could not balance that big of a motor with tape. And I just could not put it back in the air with this problem.

Time for an upgrade!



Scorpian 4525-520 and cc 160 hv esc... Smooth as silk, felt like normal vibes running in idle 2, spooled up on counter without blades. Did not creep on the counter. Did not move at all.

Put my Sab 115 tails on. Spooled it up on the kitchen floor.

No high speed flutter in idle 1. Up to idle 2. Had less than before, but I could still hear something. Maybe go away with main blades on? Shit! And I just spent how much on this thing?

When I ordered parts, I had grabbed some blade clips. Oh well. Try them, right?





They fit perfectly. You can tighten the bolts and the blades move smoothly. Spooled it up in the kitchen again. Didn't hum on the kitchen floor. I had no issues with short bolts. Why not use the ones for the main grips?



Same thing, fit beautifully, look great. Blades move smooth when testing for tightness. No, I did NOT spool up a 700 in the kitchen with mains blades on!

Sooooo, outside for yet another test flight...

Never flew smoother. Not kidding. Not a hint of any sound that would make me go, well...maybe it's OK, maybe it'll stay together.

Yup, blade clips, for $6.99 plus shipping. Try them. Worked for me. Seems like different things work for people. Some sure fire things don't work for others. I think it's complicated and there are things about our helis we just don't understand. Believe me I made an effort to reason this out and trouble shoot the problem. Maybe sharing this info will help someone.

After rebuild, and looking right pretty again...



In the meantime, that Scorpian is a BEAST!

[sammyha]

More food for thought, I got to looking real close at these blade clips installed my Trex 700. I can fit a .002 thick brass shim between the grips and the blade.





The .002 shim just fits with a bit of drag. Notice it's enough to hold it there. The CNC aluminum grips are NOT contacting the blades!

So my thinking goes like this...
One- The blades are now separated from the CNC aluminum grips.

Two- How will the plastic blade clips hold up to the rigors of supporting the blades, both mains and tails during extreme pitch changes?

Three- There is more square inches of support with the blade clips versus the CNC aluminum grips.

Four- The blade clips are acting like dampeners? That's a good thing, right? Deaden any harmonics.

Five- They are completely captured/ supported inside the grips. Kinda answers number two, maybe.

That's what I do when it's too cold and windy to fly. I ponder stuff like this... What do you guys think? Do they insulate the tail blades from harmonics? Some guys were filing them down. I didn't, seems like they are very precisely made. The clearance is the same on the mains and tails.

[marc8090]

I can't answer all your questions, but I used the clips all of this past season and zero issues with how they hold up.

[sammyha]

That's good to hear. I got three flights on them. Feels great so far, really smooth and quiet. We don't get many good days to fly in the winter in northern Wisconsin. One flight was two degrees, the other two flights it had warmed up to twenty degrees.

[marc8090]

Off topic, but be careful flying when it's that cold. Plastic parts can be brittle.

[sammyha]

No, that's good advice. I don't bang the sticks hard when it's that cold. That was just getting in the first test flight, the one at two degrees.

[Tower]

Hi Guys (sorry for duplicate post )

Good news that Align has come out with a fix for the tail hum on the 700s with their copy of the Matt Botos 106mm Rail Blades. I am currently negotiating directly with align for free replacement blades.
If you are dealing with your local dealer or Align (Contact Lena - email her direct - see below) here is the email from Align confirming their copy of the rail blades is a fix for the 700 hum (read from the bottom up). Please feel free to cut and paste the email if you need support in your resolution process.
After suffering through the 3GX disaster (had 5 of those) it is nice to see Align stepping up and admitting when they have distributed a defective product.
Cheers


On Feb 5, 2016, at 5:57 AM, Lena <a064@ms.align.com.tw> wrote:
Dear Jeremy,

Yes, this new HQ1060A 106 Carbon Fiber Tail Blade can solve your problem. You can update your tail rotor to have a try!

BTW, please note that our office will be closed from Feb. 6thto Feb. 14th for Chinese New Year Holidays. We'll be resume operation on Feb. 15th, 2016.
So if you still have any problem, you can contact with your original shop or Align worldwide distributor for further service. http://www.align.com.tw/distributors-en/

Happy Chinese New Year!!

Thank you so much.
Best regards,

Lena Wu
Overseas Sales Team/ Align RC World
No. 345, Shui-Yuan Road, Feng Yuan, Taichung, Taiwan
TEL: + 886-4-25279117
FAX: + 886-4-25245244
Align Website．Quick Finder

Important reminder:
Align information, including telephone (+886), fax and address, products, shipping delivery from and to, also bank account are all made and located in Taiwan. If there is any change, Taiwan Align officially will make overall announcement to clear any differences. If you ever unintentionally receive mails that asking for any changes regarding to above Align company information, especially bank account number, please make sure to call your Align sales staff for double checking to prevent any misunderstanding, fraud, scam or loss.



From: Jeremy <xxxxxxxxxxxx>
Date: January 29, 2016 at 4:52:02 PM AST
To: sales@alignrcusa.com
Subject: Re: New 700 Tail Blades
Dear Sir
Can you tell me if these new blades will work as well as the rail blades we have been purchasing to eliminate hum on our 700s? I have three dominators. Two of them are hummers without the rail blades
Thanks
Jeremy xxxxx

[escsniper]

So, Rail tail blades cured the hum entirely on my first 700. On my second, they quiet it down some, but it's still there.

So I decided to order the blade clips. First problem: they don't fit with the Rail tails. Second problem: They did nothing to eliminate the hum when I reinstalled the original Align tails.

Today I Googled and YouTubed "Trex 700 hum" and came up with a few people who suggest that going from a 24T tail drive gear to a 22T gear "solves" the hum.

ANYONE HAVE EXPERIENCE WITH CHANGING THE TAIL RATIO TO SILENCE THE DREADED HUM?

[sammyha]

Why do the clips not fit in yours? Are the size of them different? They are snug in mine. I've ran Sab 115's and now have Rail 116 on mine. Any head speed I want to run too.

They can be reversed, by that I mean with the radius the same way going into the grips but flipped end for end. The hole is offset length wise. Should match the end of the grip with the hole lined up.

[escsniper]

i am not sure why they are so tight with Rail 116s... They just are

[sammyha]

Another thing, with the 22T tail drive gear would the tail have enough authority? If I run the Rail 106's, my tail kicks. Dial up the trans gain, then it bounces on stops. Flyable but not as clean.

[marc8090]

Originally Posted by escsniper

So, Rail tail blades cured the hum entirely on my first 700. On my second, they quiet it down some, but it's still there.

So I decided to order the blade clips. First problem: they don't fit with the Rail tails. Second problem: They did nothing to eliminate the hum when I reinstalled the original Align tails.

Today I Googled and YouTubed "Trex 700 hum" and came up with a few people who suggest that going from a 24T tail drive gear to a 22T gear "solves" the hum.

ANYONE HAVE EXPERIENCE WITH CHANGING THE TAIL RATIO TO SILENCE THE DREADED HUM?

It would be the other way around. The 22t gear spins the tail faster than the 24t which could result in the hum. Going to the original 24t setup (4.33 to 1) instead of 4.73 to 1 with the 22t should fix any hum issues since they only started when Align sped up the tails. You would have to change the 104t gear also. 22t is helical, 24t is straight. You will loose tail authority. Before the speed up gears the common "fix" was to use 115mm tail blades instead of 105s. Be careful though with what main blade length, head style, mast length, and dampers you use with the longer tail blades as blade to blade clearance could be an issue.

[sammyha]

You are right on marc8090 with the gearing and tail speed logic. I have the 700E DFC with the helical 104 auto/ 22T gear. With the Scorpian 4525-520 I feel it needs the Rail 116mm tail blades I'm running. Holds nice with that setup. I tried 106's, didn't like how the tail kicks on punch outs and moves around on tic tocs. So fix the hum if you can, it's a much cleaner tail with the higher speed.

[Thestructured]

I bought the plastic blade clips and it was so freaking hard to get the tail blades in (stock align blades). They require a lot of force, even without the bolt tightened, to move them at all. It's almost so tight that I feel like when the heli spools up it won't be able to center the blades in the grips. Then again, maybe there is enough centripetal force at whatever..10k rpm they spin at

[marc8090]

As snug as they may seem, they will straighten out once up to speed.

[sammyha]

I wonder what snug or tight means for each one of us. Mine are tight, they stay in without the bolts. So I tighten the nylock nuts to where I think the nuts won't come loose. But the blades move smoothly, no aluminum gouging them. Even if you use "some force to move them", whatever that means to you or me, it's very little compared to centrifugal force at 10000 rpm IMO.

[rcflyerheli]

One thought, but it does involve some expense. If you want to change the gear ratio to slow the tail down, consider going to the nitro boom/TT/pushrod. They are about 15mm longer, and give the tail more authority.

I went directly to this setup when I first built my DFC and it's been really trouble free for a couple years now.

[Stevin]

Does the 700x tail address the tail hum?


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[sammyha]

Looks like they are using the same tail assembly. That's good and bad. Keeps costs down. Easier for parts support . Easier for us ordering the right parts. Bad if they have issues with a design.
The kit includes their 106mm tail blades, basically Rail 106mm copy cats. Which if you've read the threads on this issue, fixes it in some but cases, but not all.
But, in all fairness, I don't have the new 700X, be better to hear from those who have it to see if this issue shows up.

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