Trex 700n DFC tail

[Ian.M]

Hi all,
I have just been reading info about my Trex 700n DFC on various heli sites and have come across some disturbing news, it would appear that my brand new 3 times hovered heli is in danger of the tail snapping off with the resulting consequences. Can this really be true? should I ground this heli until upgrades can be bought? It would also seem that this is a common problem with the DFC but Align take no responsibility.
Does anyone have any advice or have come across this already? I guess this heli is down until I can find out for sure.

Ian.

[raptorheli2]

yes it is true and sadly there is no official fix. just a way to reduce the chances of it is about the best you can do.

in simple terms you need the new tail hub/gear set and a pair of rail tail blades is what most report to work ok.

coolice is the one to ask though as he has finger on pulse a lot more than me re align.

cheers

[rapidgaz]

think its more so on the e version, not had any bother with mine yet, but i do have the upgrades, just not fitted yet. are you running high head speeds

[moonmanflyer]

The new black gears are avaliable that i believe solve this possible issue, mine is arriving in the next day or 2

[rapidgaz]

and no buzzing an the tail running about a 2000 HS

[tonystevens]

Should be ok to fly but if you hear a buzz or humm from the tail then you need to look at it further. As for align not taking responsibility theres a guy on HF thats taken the matter up with align and they have fixed his heli for him so that parts not nesseccarily true

[j2tgw]

Hi Ian
My wife bought me same heli for xmas .And third flight the tail let go
Not to much damage .But if you look back the Align section on the forum you will read
the help and the fix for your heli
I have done all the mods and the heli is brill now
Cheers Tom !!

[Ian.M]

Thanks for all the replies,
this kind of confirms my fears, not impressed after spending all that money and time.
Does anybody know of any suppliers with a stock of the required parts?

[electricsceadu]

as i don't fly align i don't keep up with the faults they have
but the black gears hold up to the hammering a top uk pilot gives them
now i know why they changed the gears

[rapidgaz]

H70G005XXT Torque Tube Rear Drive Gear Set

[raptorheli2]

i have put new hubs/gears and rail tails on my 700e and dfc-n. it costs about 35 quid per heli to do the upgrade.

the problem you may have is stock, not sure who has any of this. try Raj at align-trex and see how it goes.

this is the parts you need along with rail tail blades.

H70G005XXT Torque Tube Rear Drive Gear Set

cheers

[Ian.M]

i have put new hubs/gears and rail tails on my 700e and dfc-n. it costs about 35 quid per heli to do the upgrade.

the problem you may have is stock, not sure who has any of this. try Raj at align-trex and see how it goes.

this is the parts you need along with rail tail blades.

H70G005XXT Torque Tube Rear Drive Gear Set

cheers

Thanks for the info, will try tomorrow but web sites seem all out of stock

[coolice]

Hey.

As already stated both the E & N can fall foul to this hum/buzz vibration from the tail, I know of one 700N DFC which failed on it's first flight when the buzz developed and didn't stop. The E is more prone as it runs a higher tail rotor rpm, but the 700N has a longer boom by some 20mm and so if the vibes set in it can be worse than on an E I am sure.

It appears the problem is that a tail(s) blade goes out of track at certain rpm's and induces a vibration, this can then break off the stepped down end of the tail output shaft inflight which isn't good. Why this problems never been seen before I don't know, as the shaft is the same one from the original 700N which has been out years.
The new tail components strengthen the tail shaft so that should the buzz/hum develope it's not going to break off, Align also noticed a problem with the standard washers holding the tail blade grips on in that they were too thin and cupped due to the centrifugal forces pulling on the grips.

So far a known fix, combined with the upgrade tail parts, is what Raptorheli2 has fitted and that is Rail tail blades. It appears lighter tail blades help alleviate the problem, Duncan Osbourn has tried SAB tails and also fixed the problem.
On my own 700E DFC, using the original tail parts I removed the tiny amount of buzzing I had on the odd occasion. However after now fitting the new parts I'm told it can be heard again and so I will be trying Rails soon to.
Just today and I noticed it while fitting my new parts, the umbrella gear which press fits into the tail gearbox housing, is over sized a fair amount. One forum member on another site has questioned if this increased interference fit has brought about his buzzing, as he to did not have it on the older parts.
On assembly and I would suggest trying to do the same, is I spun the new black umbrella gear in a drill and wet & dryed the shaft on which the bearings sit to reduce it's size a little. When I measured old and new parts there was an increase in diameter of approx 0.14mm, the old white gear is a tight fit in the bearings, so any bigger and it's even worse.

Another trick with the tail is to run your tail blades quite loose, I get the pee taken out of me for my floppy tails, but this allows them to lead/lag much easier and originally helped stop the problems.

Also the tail boom, fit the all metal one instead of the carbon skinned one. It's not so pretty but appears to be much stiffer.
.

[Ian.M]

Hey.

As already stated both the E & N can fall foul to this hum/buzz vibration from the tail, I know of one 700N DFC which failed on it's first flight when the buzz developed and didn't stop. The E is more prone as it runs a higher tail rotor rpm, but the 700N has a longer boom by some 20mm and so if the vibes set in it can be worse than on an E I am sure.

It appears the problem is that a tail(s) blade goes out of track at certain rpm's and induces a vibration, this can then break off the stepped down end of the tail output shaft inflight which isn't good. Why this problems never been seen before I don't know, as the shaft is the same one from the original 700N which has been out years.
The new tail components strengthen the tail shaft so that should the buzz/hum develope it's not going to break off, Align also noticed a problem with the standard washers holding the tail blade grips on in that they were too thin and cupped due to the centrifugal forces pulling on the grips.

So far a known fix, combined with the upgrade tail parts, is what Raptorheli2 has fitted and that is Rail tail blades. It appears lighter tail blades help alleviate the problem, Duncan Osbourn has tried SAB tails and also fixed the problem.
On my own 700E DFC, using the original tail parts I removed the tiny amount of buzzing I had on the odd occasion. However after now fitting the new parts I'm told it can be heard again and so I will be trying Rails soon to.
Just today and I noticed it while fitting my new parts, the umbrella gear which press fits into the tail gearbox housing, is over sized a fair amount. One forum member on another site has questioned if this increased interference fit has brought about his buzzing, as he to did not have it on the older parts.
On assembly and I would suggest trying to do the same, is I spun the new black umbrella gear in a drill and wet & dryed the shaft on which the bearings sit to reduce it's size a little. When I measured old and new parts there was an increase in diameter of approx 0.14mm, the old white gear is a tight fit in the bearings, so any bigger and it's even worse.

Another trick with the tail is to run your tail blades quite loose, I get the pee taken out of me for my floppy tails, but this allows them to lead/lag much easier and originally helped stop the problems.

Also the tail boom, fit the all metal one instead of the carbon skinned one. It's not so pretty but appears to be much stiffer.
.

Thanks for all the help,
I think if I fit the upgrades and setup the tail box and blades in the way you suggest I have a good chance of avoiding the problem,

Thanks,
Ian.

[moonmanflyer]

also a problem that has been from the original 700 and never sorted, check your tail gearbox alignment, make sure it at dead vertical, i find on most 700 booms, the slot at the front needs minor trimming to get the boom and tail gearbox at the correct angle, this can cause a bad buzz