ETL Vibration

[Griffin]

Here's the best video I could find from inside the cockpit. Not this or any of the worse ones give you any visual ETL shake in transitions. In fact, the shaking gets worse with the increase in speed.

Starting at 4:45.

 

I asked the author of this video about the ETL vibration and here's what he answered.

Going through ETL is definitely noticeable, as with any two bladed system. It is of course louder than smaller helicopters like 206's or robbies. From experience, Multi bladed helicopters tends to be smoother through ETL. S350 series are smoother and HU500 is barely noticeable with the 5 bladed system.

The 205 is typically rougher at cruise speed than trough ETL. Although the VNE is between 110 and 120 its depending on gross weight, most operators will cruise at 100 or below due to that.

[flyer49]

I have to agree with the author of the video. The UH-1 had a ridged rotor system...this means that the rotor system acted as a rocker (when one blade went down the other went up...they were dependent of each other). You can feel and hear the vibrations...it's part of learning to control the beast. It might be slightly exaggerated in DCS but it's still there...like it or not. I also was qualified on the UH-60A and most other advanced helicopters like the AH-64 had an articulated rotor system (all blades acted independently of the other blades), this dampened the effects of ETL. This is also why these type of airframes can do aerobatic maneuvers and UH-1's can't (i.e. mast bumping).

 

As for VNE, that is when you get into "retreating blade stall". This is where forward airspeed is such that the blade moving forward is achieving greater lift than the retreating blade that is achieving less lift (stalling)....

 

EDITED: See Madcat's definition as accurate information.

Edited July 15, 2013 by flyer49

[ishtmail]

What would be pretty cool is if Belsimtek added a feature where airframe vibrations would translate into the Buttkicker vibrations. If you have Buttkicker installed, the visible vibrations in the sim turn off (or reduce significantly) and you only get shaken under your actual rear end.

[-MadCat-]

[...]

As for VNE, that is when you get into "retreating blade stall". This is where forward airspeed is such that the blade moving forward is achieving greater lift than the retreating blade that is achieving less lift (stalling). This causes your aircraft to "lean" to the left (the retreating side) and if not corrected you will barrel roll out of control and crash.

[...]

 

Physics unfortunately dictate a different effect.

Due to gyroscopic precession, forces applied to a spinning disk take effect roughly 90° out of phase.

So a retreating blade stall will tilt the rotor disk aft (not to the side) and pitch the helicopter's nose up, and thereby the effect corrects itself once you run out of forward stick travel to counteract the pitch up tendency and can't go any faster.

The vibrations with increased speed are caused by the combination of the speed of the advancing blade with the forward velocity of the system itself (the helicopter), causing vibrations starting at the tip of the advancing blade where the absolute speed is the highest.

 

Greetings

MadCat

[flyer49]

I stand corrected...I had to go back to my aerodynamics manual and look it up and you are correct.

[Griffin]

It might be slightly exaggerated in DCS but it's still there...like it or not.

I don't want to be nitpicking on your posts but just want to emphasize what I said above. I don't mind the vibrations being there at all. I'd just want the vibrations reduced to a more realistic level so you won't feel like the instrument panel is going to fly out of the window. It's almost as bad as in Ka-50 when you lose a part of a rotor blade. It would bring my concentration back to flying the helicopter instead of disorienting me big time with a fake visual effect during the most crucial part of the flight.

 

What ishtmail said there is a seriously great idea. I might really get Buttkicker one day so support for it would be awesome! And of course without the visual earthquake getting in the way.

[jay43]

This is wrong on so many levels.

 

Of course the skids will just break.

 

 

How can it be wrong when real pilots who first flew the Huey in Vietnam were on talking about.

 

And I suppose the rotors can't chop through bamboo and elephant grass shame the trees are transparent on here I would like to put that to the test.

Yes that's right the 2 pilots on Easter Sunday flying the rev to do his Easter sermon.

Only for the pilots to get a help call and using their rotor they punched a hole through the bamboo as thick as their arms they said it was.

Rescuing 30 + special forces men mixed with Vietnamese special forces men to, but I suppose that's impossible to or am I wrong.

 

Forgot to add they too were overloaded on their last run and also had to bump the Huey on its skids to get it of the ground with a run up chopping through the bamboo at the same time.

Should I be telling Discovery to check their facts lol don't make me laugh, these were and all are highly decorated pilots who for us re-live their most horrifying memories just for tv.

Edited July 15, 2013 by jay43

[flyer49]

Hi jay43...I don't think your wrong. In my Army career I knew a lot of Vietnam pilots and they love to regale you with there explotes. I did hear about the UH-1 blades being used to clear LZ of light brush and tree's. I've also heard of very unique techniques used to get a over max load into the air. The UH-1 was used and abused during war time and still stayed in the air and this is why it's such an iconic aircraft...it would take a licking and keep on ticking.

 

When I went through training, we were taught that tree strikes didn't necessarily mean we were going to crash and burn but of course it didn't do the blades a lot of good. I've heard stories of the rotor system being pretty torn up from tree strikes and small arms fire and getting crew and passengers back to safety. We were taught that when necessary do what you have to get the job done, even if that meant clearing the LZ with your blades.

Edited July 15, 2013 by flyer49

[jay43]

Hi jay43...I don't think your wrong. In my Army career I knew a lot of Vietnam pilots and they love to regale you with there explotes. I did hear about the UH-1 blades being used to clear LZ of light brush and tree's. I've also heard of very unique techniques used to get a over max load into the air.

 

When I went through training, we were taught that tree strikes didn't necessarily mean we were going to crash and burn but of course it didn't do the blades a lot of good.

 

At last someone believes me trying to find that episode at the moment and when I do i'll link it.

 

Those guys were lucky to they got a lot of vibration on the way back to their main base they were so low on fuel that when they landed the Huey just shut itself down and then in the morning they inspected the rotors and the last 2 foot of each blade was shredded the outer skin had been peeled off exposing the honey comb aluminium fins that was some luck or what.

[metheluckydonut]

Those guys were lucky to they got a lot of vibration on the way back to their main base they were so low on fuel that when they landed the Huey just shut itself down and then in the morning they inspected the rotors and the last 2 foot of each blade was shredded the outer skin had been peeled off exposing the honey comb aluminium fins that was some luck or what.

 

I think I saw that one too.

But again DISCOVERY CHANNEL

[flyer49]

I flew UH-1's during the eighties and we still had the Vietnam era airframes in our unit. I remember one mission where we were doing the pre-flight I asked one of the older more experienced pilots what all the small 4" x 4" patches were. They were everywhere, on the deck, in the tail boom...everywhere. His response were...they were small arms fire patches received during firefights in Veitnam. Most of our air frames had the patches and I always had respect for the staying power of the UH-1 because of this.

[jay43]

I remember now might not have been Discovery I was watching when I saw the one about the pilots bouncing her on the skids to get airborne.

 

It was summit like the birth of airborne operations or the birth of the helicopter summit like that.

I also remember the crew chiefs talking about how the Vietnamese environment would eat up parts mainly the tail blades and main blades as they got destroyed or rather sand blasted during landings, normal swap out was 2000hrs in Vietnam it was just 1000hrs before they were changed.

[Heggis]

Was it this one? Around 28min mark.

 

http://www.youtube.com/watch?v=Qk8XF7TvPq4

Edited July 15, 2013 by Heggis

[flyer49]

Wow...that was awesome...makes me want to fly my DCS Huey. Thanks for the link.

[SUBS17]

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.

 

I've been in UH1s(not as pilot lol), theres a reason why I nicknamed it the flying eggbeater lol.:D

[jay43]

Was it this one? Around 28min mark.

 

http://www.youtube.com/watch?v=Qk8XF7TvPq4

 

 

Could be but doesn't work my end protected by copyright laws.

[hansangb]

That was pretty interesting. What I don't understand though is...if you have to cut your way into the LZ, then don't you have to tear up the bamboo on your way out? I mean, you can't just take off vertically (perpendicular) to the ground, no? Even in the video, the pilots talk about needing 50 yards or so to take off (for ETL reasons)

[Zentaos]

Not to change the subject ;) but... As I have become more practiced with the sim, I really appreciate the ETL vibration. I don't think the devs should tone it down, I've come to rely on riding the burble for approach. I don't find it too violent, nor do I feel like it has any impact on control.

[hansangb]

Not to change the subject ;) but... As I have become more practiced with the sim, I really appreciate the ETL vibration. I don't think the devs should tone it down, I've come to rely on riding the burble for approach. I don't find it too violent, nor do I feel like it has any impact on control.

 

Agreed. Lacking the physical sensation, it's hard enough to gauge what's going. The shaking really helps me to quickly flip the cyclic forward to get out of VRS. Perhaps they can set it as an option - violent/non-violent ETL vibration! :)

[jimcarrel]

That was pretty interesting. What I don't understand though is...if you have to cut your way into the LZ, then don't you have to tear up the bamboo on your way out? I mean, you can't just take off vertically (perpendicular) to the ground, no? Even in the video, the pilots talk about needing 50 yards or so to take off (for ETL reasons)

 

The last Huey with the possible 22 on board was second in line, that chopper flew from his LZ thru through the 1st Huey's LZ, after 4 previous trips into the LZ, there was no way that the Zone was Less than the 40 or 50 yards needed for transitional lift. Also, you saw them in person re-telling you the event. So it must have worked.

 

It was a tremendous piece of work, I would have been taking swings at the field commander also. (and smiling at him). Pretty upside down to get a major ass-chewing for helping save about a hundred people, even if it was an unarmed VIP chopper.

Edited July 17, 2013 by jimcarrel

[GunfighterSIX]

If you’re talking about the vibration you feel during landing then you are talking about transverse flow not ELT. Each aircraft handles it differently. Even among the different Blackhawks I have in my unit some a worse in the transverse flow shudders than others. Blade tracking and balance might play a part in it I will have to ask a maintenance test pilot next time I get a chance

[hansangb]

The last Huey with the possible 22 on board was second in line, that chopper flew from his LZ thru through the 1st Huey's LZ, after 4 previous trips into the LZ, there was no way that the Zone was Less than the 40 or 50 yards needed for transitional lift. Also, you saw them in person re-telling you the event. So it must have worked.

 

It was a tremendous piece of work, I would have been taking swings at the field commander also. (and smiling at him). Pretty upside down to get a major ass-chewing for helping save about a hundred people, even if it was an unarmed VIP chopper.

 

 

No doubt. It was pretty fascinating. I did feel for that "one guy" they left behind though...Imagine how that guy must have felt.

[SUBS17]

One note about the vibration is that it can effect the graphics card and cause overheat which can lead to a CTD on my PC. I found this after flying 50nm with a shaky 110knots in the UH1 I started getting the first signs of my graphics card starting to play up.

[zaelu]

The graphic card doesn't care about what's rendering... I doubt that little animation eats so much power.

 

What I observed is that looking at the dashboard tends to eat a bit more FPS... understandable since is the most complicated thing in that pit.

 

So if you have overheat you have anyway but especially when you put the GPU to work a bit more (lower FPS being a sign of it). Solutions would be... better heat control in PC case.

[Griffin]