TREX700N DFC - Tail shear possible issue

[tonystevens]

having just read Ians post ive just checked my grip bolt washers and they are now conical after only half a dozen flights!

Not that ive noticed a buzzing but ill be changing them for some stronger ones
Nice one Ian

[anjki]

There seems to be many variables Tony,and no set rules to this hum.
All these fixes seem to have fixed problems or helped in differnt ways.Differnt models have shown differnt hums and fixes.Its hard for anyone to say what the root cause is,but i believe a beefier hub with a straight cut shaft will deal with these higher tail speeds that we are now seeing.
I for one will continue to spank my 700 with confidence .

andy k

[raptorheli2]

ahhh, it is like i've never been away from align, welcome home. :-)

cheers

[tonystevens]

I for one will continue to spank my 700 with confidence .

andy k

Im with you there, all ive gained by changing the washers is a slop free tail lol

[dszabo]

Hi All

Not posted in a very long time

Just thought I would let any of you with the new trex700 dfc than there may be a problem with the tail shaft or to be careful about over tightening the grub screws, mine sheared today and the blades, hub etc flew off never to be found.

Apparently there are other people that have had the same issue, so it might be a good idea to check yours (exactly how one goes about 'checking' I don't know)



ATB
Gareth

[ATTACH=CONFIG]52106[/ATTACH]

I had the exact same problem on my 700E DFC failed on maiden flight, I reported this problem back to Robbie UK who sorted my repairs FOC, but it looks like the problem is still there.

http://www.rcheliaddict.co.uk/t-rex-...bo-owners.html

[coolice]

having just read Ians post ive just checked my grip bolt washers and they are now conical after only half a dozen flights!

Not that ive noticed a buzzing but ill be changing them for some stronger ones
Nice one Ian

Hey Tony.

You're welcome buddy. Mine had quite a few more flights on it when I looked.

To date there has been many ideas and changes tested, but I think its come down to one thing and that is the excess slop in the tail blade grips on the hub. This causes the tail blades to almost flutter when tail command is given and the blades deflect. Removing the slop cures the problem.
The one size tail shaft from an engineering point of view makes sense, but it's not the fix nor is the stronger gears, they are just more tolerant to vibrations causing the turned hub portion to break off.
My concern if you like is that should the vibration not be removed a tougher shaft would only cause the problem to manifest itself somewhere else on the airframe.

Another option mentioned by Colin was to switch to trailing edge tail blade control, which brought back memories of the early Raptors where people performed the main blade grip flip to remove the blade flutter in flight.
.

[jwatts007]

I dont think it is the slop in the blade grips other helis have more play on the shaft and never have a problem...as for the washers bending how knaff is that but it just goes too show that there is no play there when in flight...I reckon its just pot luck whether you get a good shaft or a rubbish one...nice too see they have come out with a fix but that is no consultation too those who have crashed there new models...this new part should have been in these kits....

[anjki]

This isnt the only model i have had, that has had this problem.I believe we have just reached the critical speed of our tails now were vibes can show themselfs.
I have spent hours on the bench over the last couple of years spinning up models and messing with tails because of vibes and resonance (how sad am i!).
Logos are the same,i have had these try to explode when spooled up on the bench!,the cure could be as simple as turning the hub around and re fixing to the shaft with a new grub screw,sometimes new blades would stop it and othertimes a piece of tape on a blade could cure it.
I have also seen it on 2 raptor g4s,now these are both high end quality models,and i have never found a true answer to the problem but have learnt that when i here the hum,to investigate further.On all my models that have developed this hum, i have always cured it by trying a few of the sugested cures.

I have flown over the last few years many variations of align 700s,some electric and some nitro, 100s an 100s of flights.What i can say is it has been the most bullet proof tail i have ever flown untill the gear ratio was increased.
I still believe we have reached the limits of our tail speeds and that by beefing them up,and with regular maintanance we will see an end to this problem.

A recent test i did on the bench with my nitro tail assembly,fixed into an electric airframe for testing showed me that out of 3 tail shafts i tried(all new),1 would show the hum.On closer inspection,all 3 shafts ran true when measured on the straight part of the shaft in a dial indicator.When i measured it at the step,The 1 that showed the vibe was definatly showing runout.This would have meant my hub would have not sat central to the shaft. Could this be the problem we are seeing? Certainly in this instance the new shaft thats coming will eliminate this problem that i have seen.

It will be interesting to follow this over the next few weeks as the new items from align are released.

cheers
andy k

[Delarado]

Thats interesting Andy, so potentially your saying we have an issue in that the step down on the shaft is not actually machined central on the shaft? This would certainly contribute to this issue and having a shaft with no step would probably make it better!

[anjki]

Carl
Yes,In this instance the new shaft will cure the hum.

It would be good if anybody else could investigate further with a dial indicator.

andy k

[Delarado]

I will have a look at mine later tonight if i get chance and report back. I dont think I have the hum.

[aww]

Has any one seen this:- ALIGN New Torque Tube Drive Gear Set Crash test! - YouTube
Anthony

[jasoncook]

Hi All, my mate had the same break on the shaft on his 700N just at the point where it got smaller. We concluded the tail assemble or tail blades were out of balance and caused a stress crack then it sheared. I have only seen this on 700 models where the shaft gets thinner must be resonance.

[raptorheli2]

I was amazed to see align still using this step down on their shaft. You would never have this issue if that was not there. Instead of them trying to economise and have the 600/700 tail interchangeable they should design a new hub to cater for the thicker shaft for the 700 only IMO.

I know Alan is at align this week for product demos/testing so if your reading dude, please make a hub to suit 700 only.

Cheers

[ChrisB]

Sounds like they are obviously designing a beefed up tail shaft and hub,never ever had a problem with the current tail myself,I know obviously others have,as mentioned above I have also had issues with Mikado tail hubs so it's not just Align.

The problem will get resolved,a fix will be available and it will add to what's already proven to me to be a bullet proof range of helis,unlike other brands I have owned.