700 DFC tail issue

[Lee2782]

Originally Posted by oleandro

Guys,

for your kind information I am reporting my findings with my hum issue:

First flight with KBDD blades: terrible humming
Second flight after checking all mechanical parts with Edge: humming still there but only during deloading the head.

What I have done was changing Edge for Rail 105 and moving one torque tube bearing around 10 mm to center.

Today the day of truth and: HUM GONE in all head speeds, 1850, 2000 and 2100.

What a pleasure.

I don`t know how much or if the Rails are lighter than the Edge. Maybe someone has checked.

Best,
Michael

Thanks for posting your findings Michael
I too found when putting Rail 106 blades on it fixed the hum at headspeed which you have indecated, but now i have bumped up the headspeed up to 2200 and i can hear the hum!!

If you get a chance can you up your headspeed to 2200-2250 and see if the hum starts?

[504Rone]

Originally Posted by Lee2782

Thanks for posting your findings Michael
I too found when putting Rail 106 blades on it fixed the hum at headspeed which you have indecated, but now i have bumped up the headspeed up to 2200 and i can hear the hum!!

If you get a chance can you up your headspeed to 2200-2250 and see if the hum starts?

Are you using the carbon boom?

[Lee2782]

No i installed the aluminium right from the start. i have a spare torque tube and thinking about installing that with x3 bearings to see if that will help, although i'm pretty happy flying this machine @ 2100 with no issue its just lattly reading post that the headspeed should be up around 2200-2300 for best results.

As soon as my HS gets to 2150 the hum is noticable any higher say 2200 its very noticable and than any higher than that say 2250 it is very bad!

2100 is as high as i can go and 2000 is its sweet spot! i'm pretty happy with those speeds

[EclipseSL94]

What exactly is the hum? Is it just an annoying noise or something affecting the flight performance? Sorry if it is a noobish question but I have been reading this thread and not certain what this "hum" is exactly. I am considering getting a 700 DFC along with the updated gears and tail shaft.

[beenflying]

Originally Posted by 504Rone

What changes have you made? I never had the vibs but I changed over to the black gears anyway.

I changed the TT bearing holders to some ones made by Flasher. They are firmer than the Align bearing holders, which in my opinion are too soft. This allows the TT to whip under higher loads like when using heavier blades and high torque maneuvers or hard tail maneuvers.

I also moved the rear TT bearing forward 30mm (290mm from the end joint).

I have some other even firmer bearing holders coming, which I will try as well, and report back.

Dino, can you check with Align and see if they have changed the compound of the TT bearing holder rubber. The ones provided with 700DFC, would appear to be too soft.

[Lee2782]

so bearing placement and different rubber bearing holders have made a noticable in you test? more of a difference than just changing brands of tail blades?

[johnjonfenomenon]

Oh btw I applied 3 bearings instead of the 2

[chosen69]

One of my flying buddies brought a brandnew 700DFC to the field today with all black gears and the new tailshaft and he got the humming sound at 2100 HS.
Eventhough I had not heard the humming sound before, - it was immediately clear what it was.
We changed his Align tailblades for my Edge tailblades (which I had been flying from the start and never had any sounds other than lovely bladefarts...)
- AND the hum was pretty much gone.

In my opinion there may be a combination of CG / aerodynamic / material design issues with the tail blades starting at certain headspeeds. I've been flying several pairs of the Align 105's on my 600pro without any issues, however on the 600pro the gear ratio is only 3.85. So at 2100HS the tail is only at roughly 8100rpm. That's almost 2000rpm difference to the 700DFC. While this may be a general issue, I think in many cases people would have had minor vibrations due to unrelated issues that aggrevate the situation like an out of balance motor for example.
I don't think that it is resonance frequency vibration because the sound did not match the hertz that you would expect:
The 700DFC has a 4.73 tail gear ratio (104/22~4.73). When running 2100rpm the tail turns at roughly 9930 rpm. That equals about 165 hz (9930/60~165). If you play that frequency in a tone generator, that's not what it sounded like today.
http://onlinetonegenerator.com/

I believe a good highspeed camera would probably help reveal what's really going on, especially in comparison to a setup without the hum.
Just like Dino already suggested, we had good luck today with swapping for different tailblades for now and I've been flying the DFC for many flights without any issues. In fact, it's one of the most fun heli's that I've flown.

[ghost2212]

Originally Posted by chosen69

One of my flying buddies brought a brandnew 700DFC to the field today with all black gears and the new tailshaft and he got the humming sound at 2100 HS.
Eventhough I had not heard the humming sound before, - it was immediately clear what it was.
We changed his Align tailblades for my Edge tailblades (which I had been flying from the start and never had any sounds other than lovely bladefarts...)
- AND the hum was pretty much gone.

In my opinion there may be a combination of CG / aerodynamic / material design issues with the tail blades starting at certain headspeeds. I've been flying several pairs of the Align 105's on my 600pro without any issues, however on the 600pro the gear ratio is only 3.85. So at 2100HS the tail is only at roughly 8100rpm. That's almost 2000rpm difference to the 700DFC. While this may be a general issue, I think in many cases people would have had minor vibrations due to unrelated issues that aggrevate the situation like an out of balance motor for example.
I don't think that it is resonance frequency vibration because the sound did not match the hertz that you would expect:
The 700DFC has a 4.73 tail gear ratio (104/22~4.73). When running 2100rpm the tail turns at roughly 9930 rpm. That equals about 165 hz (9930/60~165). If you play that frequency in a tone generator, that's not what it sounded like today.
http://onlinetonegenerator.com/

I believe a good highspeed camera would probably help reveal what's really going on, especially in comparison to a setup without the hum.
Just like Dino already suggested, we had good luck today with swapping for different tailblades for now and I've been flying the DFC for many flights without any issues. In fact, it's one of the most fun heli's that I've flown.

Interesting that you say that, I built a friends 700 for them and had the dreaded hum at 2000RPM with the align tail blades. It was so bad that loctited bolts were coming loose and one almost hit me(I heard it hit the window behind me). As soon as we switched the tail blades to Rail it completely disappeared and he's had loads of flights since.

I'm planning on buying a 700 soon and have a GoPro capable of 240fps so maybe I'll try and get some video footage if the tail hums, with and without Rail blades which i'm planning to buy as they will be needed to fix the issue.

At the end of the day Align need to up their game, Saying that customers should switch to different tail blades than the one's included in the kit is pretty ridiculous!

[chosen69]

Originally Posted by ghost2212

At the end of the day Align need to up their game, Saying that customers should switch to different tail blades than the one's included in the kit is pretty ridiculous!

At 2100HS and a radius of roughly 14cm from center hub to blade tip, the velocity of the blade tip on the DFC is equal to 2 x pi x 14cm x 9930rpm which is about 477 ft/sec or 325mph !
On the 600pro in comparison with the 105's that's only 265mph.
If you request an engineer to design some blades for a helicopter he'll design them to the specs that you ask for. If you employ them in a different scenario (or higher rpm for that matter) you may or may not get away with it. In this case it seems they didn't.
These blades were probably not designed for that speed (as they were already around long before the 700DFC), wether we like it or not.
I'm sure we'll see some newly designed tailblades in the near future and it will all be good. Until then - swap the tailblades and fly it like you stole it...!

[beenflying]

Originally Posted by Lee2782

so bearing placement and different rubber bearing holders have made a noticable in you test? more of a difference than just changing brands of tail blades?

What I've done has now allowed me to happily run the Align blades at 1950RPM. No hum and no small tail wag, like before.

I should also point out that I'm still running the Helioption tail assembly, as well.

[latte]

I flew the whole day with align tailblades @2150rpm! No Hum. I put the stock align TT-bearingholders closer to center.

I have updated the esc to 2250rpm in idleup2, to give it a try the next time I am out flying. Dont know when that will be tho.

Super happy with both machine and Vortex.

Edit* See from my logs that rpm peaked at 2230 today

[Lee2782]

Originally Posted by latte

I flew the whole day with align tailblades @2150rpm! No Hum. I put the stock align TT-bearingholders closer to center.

I have updated the esc to 2250rpm in idleup2, to give it a try the next time I am out flying. Dont know when that will be tho.

Super happy with both machine and Vortex.

Edit* See from my logs that rpm peaked at 2230 today

So your test today was with the TT with 3 bearings? Do you have the spacing measurements?

[latte]

Originally Posted by Lee2782

So your test today was with the TT with 3 bearings? Do you have the spacing measurements?

Yes, 3 bearings in place. The middle one almost dead-center, 1-2cm off to the side. One 12cm in front of it, and one 15cm aft.

[Lee2782]

Great thanks for that I will try those distances with my spare TT which I plan on installing 3 bearings. I'm very interested to see your results when you bump up your HS to 2250

Cheers

[beenflying]

Originally Posted by latte

I flew the whole day with align tailblades @2150rpm! No Hum. I put the stock align TT-bearingholders closer to center.

I have updated the esc to 2250rpm in idleup2, to give it a try the next time I am out flying. Dont know when that will be tho.

Super happy with both machine and Vortex.

Edit* See from my logs that rpm peaked at 2230 today

Thanks for the update. Good to hear it's going well, even with the Align blades.

[johnjonfenomenon]

Originally Posted by latte

Yes, 3 bearings in place. The middle one almost dead-center, 1-2cm off to the side. One 12cm in front of it, and one 15cm aft.

This is also about how i placed my tt bearings.

[latte]

So to update, just tried 2250rpm with stock align-blades and 3 bearings a little concentrated around center of the TT.

At that headspeed, the disc gives sort of a hum of its own, but I am 99% sure there wasn't any hum. I heard no sounds that shouldnt be there, no tail-oscillations, so I just flew it like I stole it

700E DFC + 2250 + Spartan Vortex = Very easy to like!! omg I love this heli.

[DaveHolland]

I did point out the TT as a possible cause just saying

[Trulsen]

Originally Posted by latte

So to update, just tried 2250rpm with stock align-blades and 3 bearings a little concentrated around center of the TT.

At that headspeed, the disc gives sort of a hum of its own, but I am 99% sure there wasn't any hum. I heard no sounds that shouldnt be there, no tail-oscillations, so I just flew it like I stole it

700E DFC + 2250 + Spartan Vortex = Very easy to like!! omg I love this heli.

Sounds really good latte! The only changes you have done to this bird is a third torque tube bearing?:-)