ETL Vibration

[Focha]

One thing that's been bothering me is the ETL Vibration. It seems that the vibration effect somehow to some extend seems to affect the control of the aircraft. In real life you feel the vibration, but this do not influence the control of the aircraft.

 

I say this because some of the landings, when I am established on approach, when the ETL vibrations starts, the aircraft seems to randomly shake everywhere.

 

I can only speak from my real life experience, never flew an UH-1, this can be the Huey behavior, but for example in AS365 it's really smooth and you only have a lot of vibration when the blades are out of balance, still that doesn't influence the control of the aircraft and the transition from forward flight into hover is smooth and almost linear if you have no wind or headwind.

 

Best regards.

[sSkullZnBoneZz]

I have no experience as a real helicopter pilot, but based on what I've read here in the forums others who do have experience in the Huey are saying the flight model is pretty close to the real thing. Also, the difference may be that the Huey is an older airframe and there are no systems to help stabilize flight. Of course, the helicopter you have experience with may not have stabalization systems either. This is just my two cents worth, maybe someone with real life Huey experience can give you more insight...

[Robert1983NL]

I can't remember exactly what happens, but I do believe going through ETL effects helicopter attitude. Makes sense too. Maybe you don't notice it in your AS365 because you have your AFCS/SAS on :-)

[PeterP]

I noticed it too and wasn't sure to open a bug-ticket.

...(I use a FFB cyclic) I would be more pleased if this vibration would be only translated into FFB shaking instead into direct control inputs.

I had once a flight in the EC-135 and

I'm thinking about the flight stability and autopilot systems that damping a lot of the vibrations that are translated by the swash-plate to the controls.

 

Maybe it's just this - and the HU-H1 also puts this 'unwanted' feedback from the linkages directly back into cyclic input - and so it starts a unwanted 'oscillation' in your controls parameter (because the sim doesn't distinguish between FFB and input) that causes you to overreact and have to be very careful what you do while in ETL.

Edited June 5, 2013 by PeterP

[Robert1983NL]

It's not a bug. It's realism.

[PeterP]

It's not a bug. It's realism.

yes- read again what I wrote.

But it starts to be a bug when I'm not able to counteract this input from the vibrations with my controls.

[Robert1983NL]

Well, why can't you counteract it? I never noticed any problems with this.

 

Are you saying that your FFB stick moves when you go through ETL?

[Vlerkies]

Its way better than it was prior to the patch a week or so ago.

Latest patch to the beta flight model, its not easy but very doable with practice and patience.

 

 

[TimeKilla]

You can counteract it so it must just be an issue with FFB then.

[jay43]

Its way better than it was prior to the patch a week or so ago.

Latest patch to the beta flight model, its not easy but very doable with practice and patience.

 

 

 

That sir is quality gonna try that never thought of trying to land on there, I keep trying to get it down on to one of those big smoke bellowing chimneys, can't quite get the skids lined up or get the balancing point right I either fall off nose first or fall back down the chimney which is quite funny watching the huey get swallowed up by the chimney.

[Zentaos]

there shouldn't be much if any FFB response to ETL in the cyclic. The airframe should have vibrations, not the controls.

[PeterP]

You can counteract it so it must just be an issue with FFB then.

Of Course I can counteract it, but only by visual cues.

Well, why can't you counteract it? I never noticed any problems with this.

 

Are you saying that your FFB stick moves when you go through ETL?

Exactly that my point - in my initial post - there is no shaking/force added.

 

,but when looking at the mechanical linkages and used damping, I would expect a least a little shaking at the cyclic while going through ELT in the UH-1H.

 

 

 

And I interpret Focha's "issues" are that he is used to flight stabilisation - and because of the lack of controls feedback he is 'surprised' by the sudden instability.

 

Me too - and I miss the expected vibration and/or force-shift on the controls . (im not asking for oszilation/shaking that are done by the fuselage/seat - leave this to a butt-kicker or similar)

 

I have the suspicion that the ELT is translated into small controls-inputs internal of the FM-mechanics but isn't translated back into your virtual controls or FFB.

Edited June 5, 2013 by PeterP

[Robert1983NL]

Well, it's been like 5 years since I've flown the Huey, and I've only got 12 hours on it, but I can't imagine any of the shaking in the stick. That'd be a land immediatly situation lol. The whole aircraft shakes, not just the stick.

[Vlerkies]

Prefer to fly what I see in a sim, not ffb

[Sundowner.pl]

,but when looking at the mechanical linkages and used damping, I would expect a least a little shaking at the cyclic while going through ELT in the UH-1H.

How come? You have hydraulics and force trim in the way. Any feedback stops at the hydraulic actuators, and the force feedback makes the cyclic balanced so it can't amplify fuselage vibrations. And even helicopters that have no force feedback, but an hydraulically boosted controls - like the S-58 don't transmit any forces to the stick. A pilot from Northwest once said to me that it's "like flying a wet noodle" :smilewink: no feedback at all.

[PeterP]

Maybe it was just a brain-fart - I'm aware that there should no force linked back to the cyclic - and I'm preaching it myself on many occasions.

 

OK, - so let's scarp that FFb idea of vibration for the cyclic in the HU-1H- and this is also not what this thread is about.

 

But I'm still with Focha - something isn't right with ETL.

Edited June 5, 2013 by PeterP

[Sundowner.pl]

Yes, going through the ETL is quite violent in the sim, I can't really say anything of the real Huey on that topic though. But I've never felt anything this severe on any helicopter I was a self-loading-cargo.

 

It's up to anyone with lots of UH-1/B205 stick time to judge this.

[Focha]

As some said, "my" AS365 (wish it was mine) is stabilized with AFCS (SAS) but sometimes in training we fly it without SAS. It's not so violent going through ETL as in the sim. I flown R-22, R-44 and I fly AS350 B3, B3 is a violent machine, and even so, I can maintain it in ETL speed without all that shaking.

 

Yes, going through ETL changes the performance, and you have to adapt the controls, but in sim, even if I have my hand still, with all that violent shaking, the helicopter control behaves strangely. When I slowly translate to ETL speed, the helicopter start to shake, and sometimes even roll abruptly without input.

 

I'm not saying it is a bug, as I said never flew a Huey, but I have flown other types of helicopters, SAS stabilized and non SAS, and I never went so violently in ETL. Maybe maintenance should do blades balancing before further flights. :P

 

EDIT: The best I can do is talk with a friend that flown UH-1H and 205 in fire season. As Sundowner said, you don't have feedback in the cyclic, although you can have vibrations produced, but that doesn't have to do about the aerodynamic changes in the blades. Sometimes, in flight I look at the disk, and it's amazing how many times it flaps up and down, even though the cyclic is almost still. If you feel something in the cyclic, then probably, there is something not working as it should. At least in a hydraulic system.

 

Even in R-22, that is mechanically linked to the swashplates, you don't feel much.

 

I just feel there is a look of vibration in the transition in the sim. And if you don't quickly bleed out that speed, for example in approach, it just tends to get worse. Just my two cents.

Edited June 5, 2013 by Focha

[Vlerkies]

That sir is quality gonna try that never thought of trying to land on there, I keep trying to get it down on to one of those big smoke bellowing chimneys, can't quite get the skids lined up or get the balancing point right I either fall off nose first or fall back down the chimney which is quite funny watching the huey get swallowed up by the chimney.

:thumbup:

 

That bit intrigues me, must go looking for big smoking chimneys :pilotfly:

[PeterP]

 

EDIT: The best I can do is talk with a friend that flown UH-1H and 205 in fire season.

 

Pm'ed also a actual forum member with a lot, a lot and a lot of RL experience in the Huey to bring some light into it. Lets hope he finds the time to answer some of our questions.

 

EDIT:

He answered briefly to me :

The TL in the Huey 2 blade models is between 25-35 knots, and the vibration level in the Sim for my experience is too much. In the DCS uh1 the TL make vibration on the helicopter from high speed to low, but in the real the TL make vibration only when you are passing from low speed to high speed; only during take-off, not on landing.

 

As soon as possible I will make a video with the gopro hero (a cam) attached on my helmet for examine the ETL.

Some info: he has ~2000 Flighthours on the Huey, 300 of them with NVG and about 300 on war theatre. Edited June 28, 2013 by PeterP

[hassata]

From a recent show with in-cockpit footage of a Huey engaged in fast-rope spec-op training, sim ETL does seem much to violent.

[Suchacz]

Amount of shaking when going out from ETL depends on your collective setting. Try to use HIGE collective setting, you'll find shaking not so violent. Also mind that your tail rotor is going out of ETL too and it needs corrective input.

 

Note> I have zero IRL helo experience, so I can't compare. Just adding my 0.02$ :smilewink:

Edited June 6, 2013 by Suchacz

[genbrien]

For me the problem is not getting out of ETL, but entering it.

[PreAmp]

I'd like to add my own 2cts on the subject...

 

In 1991 I was on internship on a naval helicopterbase operating with Westland UH-14D Lynx helicopters.

 

I remember that a helicopter had had all of its main- and tailrotor blades replaced during a big overhaul. Because of this they had to do a frequency analysis with the machine.

To do this some 3d accelerometers were attached, as well as camera's, all of which were connected to some hardware analyzer.

 

Then they started the helicopter up, but couldn't get to normal rotor RPM before getting too much vibrations... The analyzer then gave advice on how to change some settings on the rotorblades (put some small balancing weight on this rotorblade, increase the basic pitch of that rotorblade, turn that bolt tighter on that rotorblade...) all for main and tail rotorblades.

 

This was done 3 times before they could finally get to normal RPM and start flying the helicopter (at which point I was no longer allowed on board unfortunately...)

Then they repeated the process in the air at different speeds and altitudes, untill they had the most optimum settings. Needless to say it took them all day to get there!

 

A helicopter is a very complex machine with a LOT of rotating parts (main rotor, tail rotor, engines, various gearboxes, pumps, generators, etc.). All those parts are rotating in different directions, different frequencies and in different locations from the main center of gravity.

Because of this there will always be complex vibration patterns. Helicopters are set up in such a way that you'll have the least vibrations in the speedrange closest to their operational needs. For some helicopters it will be in cruise flight, for others while hovering.

 

I know this doesn't answer you question, but I hope it will shed some light on the subject at hand...

[heloguy]

I'd like to add my own 2cts on the subject...

 

In 1991 I was on internship on a naval helicopterbase operating with Westland UH-14D Lynx helicopters.

 

I remember that a helicopter had had all of its main- and tailrotor blades replaced during a big overhaul. Because of this they had to do a frequency analysis with the machine.

To do this some 3d accelerometers were attached, as well as camera's, all of which were connected to some hardware analyzer.

 

Then they started the helicopter up, but couldn't get to normal rotor RPM before getting too much vibrations... The analyzer then gave advice on how to change some settings on the rotorblades (put some small balancing weight on this rotorblade, increase the basic pitch of that rotorblade, turn that bolt tighter on that rotorblade...) all for main and tail rotorblades.

 

This was done 3 times before they could finally get to normal RPM and start flying the helicopter (at which point I was no longer allowed on board unfortunately...)

Then they repeated the process in the air at different speeds and altitudes, untill they had the most optimum settings. Needless to say it took them all day to get there!

 

A helicopter is a very complex machine with a LOT of rotating parts (main rotor, tail rotor, engines, various gearboxes, pumps, generators, etc.). All those parts are rotating in different directions, different frequencies and in different locations from the main center of gravity.

Because of this there will always be complex vibration patterns. Helicopters are set up in such a way that you'll have the least vibrations in the speedrange closest to their operational needs. For some helicopters it will be in cruise flight, for others while hovering.

 

I know this doesn't answer you question, but I hope it will shed some light on the subject at hand...

 

Only one day for a track and balance?! That's a good day...