Centric nature of the cyclic in the Gazelle.

[borchi_2b]

About the Fenestron producing a roll effect on the Gazelle I received the intel today that it does not a all in hover or slower speeds. The reason for this is the fact that it is at nearly the exact same level of the gravitational center.

The Gazele hangs low skid right to counter the drift cause by the maindisc and the Fenestron push to counter the torque. So I am not completely certain but I think I saw this mentioned in one of the descriptions here.

 

@docWilly can you maybe make a video of what you express there and the others too? It kind of gets hard to folow all the taking sometimes and understanding everybody, plus all the input fro the french side at the moment that we get. Would be cool to have something visual to check and understand wat you guys encounter or miss.

[docWilly]

@borchi:

unfortunately I am no video maker. I just referred to the post by Smokin Hole, his tests said that there´s no roll and that the controls re-centered despite trimming. My results are totally opposite: roll to the left on hover take off is always present (and always to the left) if you don´t raise the colletive too aggressiv, there´s no "real" roll-over tendency (over skids) due to lack of ground friction (I guess). You roll over if you push the cyclic unrealisticly hard left or right manually (not with trim).

 

Controls did not self-re-centering (like Smokin Hole´s) = my trimming keeps them where I put them including the modelled stick in the Gazelle. Maybe that´s also a different finding than the original post by FragBum (centric nature...).

 

The only questionable thing is (and the test itself is completely OFF anything a pilot would do IRL apart test pilots during internal tests :-)))): if I trim the stick totally to the right - then not touching it anymore....would there be a left roll on hover takeoff (conditions like in Smokin Hole´s Test) or would it be compensated (partially or totally) by trimming. I´d assume a compensation but I am no helicopter pilot (only fixed wing IRL).

 

The lack of ground friction (skids) is a different story and I believe it hard to be coded as autorotation landings on surface will be affected too (leading to a hard stop when touching the ground, right?). Many DCS modules have an "issue" with ground friction compared to RL planes. But I am fine with that and even here we have improvements compared to earlier FM versions.

 

I am one of the customers completely satisfied with the way the updates go. For me it feels right and maybe you remember my post about the interview I had with a EC135 pilot (former Army Bo105 jockey) about the effects of the fenestron in hover, slow and fast forward flight. Thus I believe Gazelle´s FM going in the right direction.

 

Thanks for listening to our discusions :-)

Edited October 27, 2017 by docWilly

[FragBum]

About the Fenestron producing a roll effect on the Gazelle I received the intel today that it does not a all in hover or slower speeds. The reason for this is the fact that it is at nearly the exact same level of the gravitational center.

The Gazele hangs low skid right to counter the drift cause by the maindisc and the Fenestron push to counter the torque. So I am not completely certain but I think I saw this mentioned in one of the descriptions here.

 

I'm re-reading Wagtendonk ch 9 again to see if I follow that. :)

 

Well I don't use trim, it just confused things a lot. Also usually don't fly with AP, Trim and Gyro and maybe I just missed a setting for the Gazelle. It's probably just as difficult to put this in a video as explain it but here you go.

 

Just centring the cyclic using the controls display here for pick up that's it just using controls display and I don't normally use the controls display. hand off only collective and torque pedals till 1:03. :helpsmilie:

 

This seems to be consistent from near MTOW to near empty flight phases and load outs.

 

 

Hopefully it's at least entertaining. :lol:

 

You may need to down load the file first sometimes my ISP is a little slow.

 

I guess I just expect that there would be some input to balance prior to pick up.

 

Also much appreciate that the Gazelle is getting some luv. :thumbup:

[borchi_2b]

ok. I tried to understand all of this during the past days and I fear one thing. The discussion is up for some time. Do to the updates that we released we need to have the people check if they see the same observations in DCS 1 .5.7 exclusivly, cause it has the latest files and if so I would like to agree to pick up the conversation from the on.

 

For me it makes no sense to talk about stuff and pushing it back and forth if we are not talking about the latest version, cauee as you can see some stuff is already fixed and it only causes confusion if people stay on an old track.

[FragBum]

Well previous was 2.1.1.x (which has had updates yes?) the cyclic behaviour seems the same in 1.5.7.x but I will try again perhaps tomorrow if that version has just been updated.

 

Okay just got an update to 1.5.7.10872 does this include the latest updates?

 

Quick try seems to have the same characteristic

Edited October 27, 2017 by FragBum
Added okay...

[Gizzy]

ok. I tried to understand all of this during the past days .....

 

You'll lucky, I gave up a long time ago... you must have plenty of spare time... :)

 

Different terminology, different languages and interpretation can confuse things as does unqualified adamant posts.

 

For what it is worth 'I think' Doc Willy is alluding that if AP and Giro are off and you use the 'trim nose up / down' - 'left / right wing down / up' functions, the control indicator overlay shows the stick moving and holding to the amount allowed by that particular trim function - but of course there is no effect on the airframe, because trim is all off.

 

The trim function 'T' on the other hand does not 'hold' the cyclic in any position within the control indicator overlay as expected.

 

If this is what the Doc is saying, as he should, I would put it at the bottom of the list :)

 

As far as FM issues are concerned I only try and understand points raised by those with good RL experience... more so if it relates to the intended design & role of the Gaz - of which there are a few about :)

[Jester986]

Agreed that the fenestron should not be having much impact on the roll while picking up because it is very near the same height as the center of gravity. In my original post about that I think I meant to say it is a much greater factor in the Huey and MI-8 because of how high their tailrotors are. I'm having trouble following all of the conversation but if there were some specific helicopter aerodynamic questions I'd be happy to answer them. I'll have a harder time testing the FM now though because I switch the a TM Warthog and although its much better for jets, I find it much less friendly for helicopters than my last HOTAS.

[docWilly]

@FragBum: what I see in both of your vids is totally different to what I have in 2.1 and 1.5 (latest versions):

 

1. for me it´s impossible to take off straight without anti-torque pedals: it would start to spin to the left as expected.

2. on hover take-off I always have a intended roll to the left (slowly raised collective or ripping it off the ground - whatever you like) as expected

 

I have no modified curves or saturation (which would not matter at all if I had that), I have a perfectly centered WARTHOG HOTAS set and I fly with "realistic mode" not "easy controls" (to be set in main menue).

 

I come to the point that there´s some issue on your side within settings and not within the FM.

I wish we could go through this on teamspeak or so some day.

[FragBum]

What? Em okay another "unqualified adamant posts" here. :noexpression:

 

Both my 1.5.7 and 2.1.1 are fully patched with the latest patches.

 

I do not have Game mode or easy controls selected give me a break please!

 

 

 

I'll leave this to ponder.

 

Principle of Helicopter Flight second edition. W. J. Wagtendonk.

Aviation Supplies and Academics Inc. 2011.

 

Ch 9 p70/71 describes Translating Tendency and Rolling Tendency and asserts that this is caused by the resultant sum vector of horizontal thrust and vertical caused by the tilt of the rotor disc and thrust of the tail rotor.

 

Translating tendency causes the aircraft to want to drift rotor tilt is required to balance the aircraft CoG.

 

<edit>

Rolling Tendency is the resultant thrust vector of horizontal thrust from the main rotor and the tail rotor and causes a rotational force on the aircraft AKA roll.

 

 

It goes on to describe design methods to mitigate rolling tendency.

 

One of these methods is to raise the tail rotor to about the height of the main rotor hub!

 

The opposite to having the tail rotor at or about CoG. Because it has less to do with CoG and more to do with leverage of the vector sum of horizontal thrust from the rotor and horizontal thrust from the tail rotor acting on the aircraft.

</edit> Been thinking more on this whilst helping a friend do some work on their motor car. :D

 

 

@ Jester986. I am surprised at that statement about the Mi8 and Huey.

 

@docWilly I'd be happy to jump on to teamspeak and chat. I also don't have any curves in cyclic and collective I do on torque pedals more authority.

 

Thanks guys!

Edited October 28, 2017 by FragBum
<edit>

[FragBum]

@FragBum: what I see in both of your vids is totally different to what I have in 2.1 and 1.5 (latest versions):

 

1. for me it´s impossible to take off straight without anti-torque pedals: it would start to spin to the left as expected.

2. on hover take-off I always have a intended roll to the left (slowly raised collective or ripping it off the ground - whatever you like) as expected

 

I have no modified curves or saturation (which would not matter at all if I had that), I have a perfectly centered WARTHOG HOTAS set and I fly with "realistic mode" not "easy controls" (to be set in main menue).

 

I come to the point that there´s some issue on your side within settings and not within the FM.

I wish we could go through this on teamspeak or so some day.

 

I m using torque pedals in those vids but at pickup I am not using cyclic I just centre it by the indicator and the Gazelle magically picks up pretty much straight up.

 

To be fair I can pickup in Huey and Mi8 hands off the cyclic but I need to carefully balance the aircraft first and not centre the cyclic. That's the point I am making.

 

More then happy to jump on to a server and teamspeak. :helpsmilie:

[FragBum]

Okay this is one of those questions that I need to ask.

 

One of the most noticeable nuances between the Gazelle and other helicopters is the centric nature of the cyclic. It's one of those things that seems odd and almost as if it is a design feature that might say make using a joystick with centre detent so much easier as all the action is around that centre. It may well be that this is the way it is however I doubt it.

 

I fly the Gazelle almost exclusively with AP off, Trim off and sometimes also the Gyro off but I'm not real sure the latter makes a difference?? Also AP on or AP off does not seem to change this attribute just the way the Gazelle handles.

 

The "feel" seems about right if I ignore the the actual position of the cyclic in that input to the cyclic does what is expected however there is no general offset in the position of the cyclic to balance the aircraft from pick up to flight the cyclic is just centred and only slight blips or movement to correct as needed. Same holds true for set down and hover.

 

Also in forward flight there is no offset in the cyclic position once you balance the aircraft it seems to move forward (or what direction you want to fly) with the cyclic bought back to the centre.

 

I have no centre detent or spring action on my cyclic just some dampers that provide some resistance to movement and hold the cyclic where I leave it, (look Ma no hands :D) in effect I do not need to use trim. Also no curves so the cyclic is fairly sensitive but does have about 250 mm extension.

 

An oddity to this behaviour is pickup or set down on an uneven surface you need to bias the position of the cyclic away from centre to get the lift vector correct as I would expect.

 

Okay here is is my original question that has not been answered, there has been many responses going off on tangents and that's fine I get that that sort of thing occurs.

 

However this is a question that as far as I can see has been raised before with no explanation as to why this is specifically a function of the Gazelle and not of other helicopters.

[Smokin Hole]

@DocWilly,

 

I doubt I made myself clear but you mistated my description of the issue somewhat. I will make a short video when I get home in a few days. Its pretty simple really. Lift into a hover hands-off to prove that the cyclic is centered. Sure, it might roll a touch but thats not the point. You’re only in hover for a few seconds. Land and force trip full left or right and lift into a hover again. Note lack of change.

[docWilly]

@ FragBum

Man I do have to apologize.....it took me soo long to get whats your point. I did not realize that you used anti-torque in your short videos. You are definitely right about the "stable into hover feature" which is not to be seen on - for example EC135 (have real life experience as I am medical doc and for this "in touch" with the rescue helicopter) nor on other light helos like the Guimbal Cabri G2 (featuring a fenestron as well).

I put in two video links - relevant is only the first minute or so - where the helicopter picks up.

 

SA341

 

Guimbal Cabri G2

 

We clearly see that a fair amount of counter-action on the stick is necessary to lift (unfortunately the SA341 translates very fast into forward flight without stick inputs).

With the Gazelle in DCS you just lift straight, hands off and after short time you will, have to correct your attitude (due to slight roll left, effect of rudder or while picking up speed)

 

 

@Smokin Hole: now I got you!!. Confirmed: trimming stick left/right does not lead to any change in rotor tilt on take-off hover and therefore no roll-over. ONLY when you push the stick MANUALLY left/right and try to get into a hover it ends in skid-over roll. That is clearly not a IRL behaviour.

 

Sorry gents that I missed your points.

 

Have a fine sunday

 

Willy

[FragBum]

@ FragBum

Man I do have to apologize.....it took me soo long to get whats your point. I did not realize that you used anti-torque in your short videos. You are definitely right about the "stable into hover feature" which is not to be seen on - for example EC135 (have real life experience as I am medical doc and for this "in touch" with the rescue helicopter) nor on other light helos like the Guimbal Cabri G2 (featuring a fenestron as well).

I put in two video links - relevant is only the first minute or so - where the helicopter picks up.

 

SA341

 

Guimbal Cabri G2

 

We clearly see that a fair amount of counter-action on the stick is necessary to lift (unfortunately the SA341 translates very fast into forward flight without stick inputs).

With the Gazelle in DCS you just lift straight, hands off and after short time you will, have to correct your attitude (due to slight roll left, effect of rudder or while picking up speed)

 

Willy

 

All good it's just that I'm curious about what seems to be a lack of "balancing" the Gazelle like you would for Mi8 and Huey and even R44. As Grizzy said there is language and terminology differences however I think we're getting there. :thumbup:

 

Thing is I enjoy flying the Gazelle (as you might gather by the vids I posted) and I have been enjoying the recent tweaks so I'm not out to bash the FM but I am asking what I consider to be valid question.

 

Curiously I normally don't have the controls indicator on as it's not necessary and picking up the Gazelle makes you carefully balance (position) the cyclic and "it feels" pretty much the same as the Mi8 or Huey as you pick up you put input into the cyclic to maintain balance (CoG) <and balance torque > as you lift collective and up you go.

 

It's just that it seems you don't have to account for CoG of the aircraft just electrically centre the cyclic and your good to pick up.

 

Also keep in mind I have a home made cyclic with no centre detent and only dampers to provide a fairly uniform feel (resistance to movement) and also hold the cyclic in position much the same feel as an R44 cyclic feel so it's really muscle memory. :)

 

Frag.

Edited October 29, 2017 by FragBum
<edit>

[sc_neo]

Have you guys been meeting on teamspeak already? How about having a little chat about our observations later today?

[Scarecrow84]

 

One of the most noticeable nuances between the Gazelle and other helicopters is the centric nature of the cyclic. It's one of those things that seems odd ...

Also in forward flight there is no offset in the cyclic position once you balance the aircraft it seems to move forward (or what direction you want to fly) with the cyclic bought back to the centre.

 

.

 

 

I hope the original question about the cyclic dynamics from this post doesn't get lost in the discussion...

 

 

I raised the same question a long time ago:

 

 

https://forums.eagle.ru/showthread.php?t=181563

[sc_neo]

@Scarecrow84

 

I have re-read your linked op and this threads op and i gotta say, that centric nature is not really true, at least not in the ''absolut centric'' way you seem to imply. If you pick up with no inputs whatsoever on the cyclic and only right rudder so you don't turn one inch horizontally, the Gazelle flys pretty damn straight forward, that is true. But you absolutely must put in some constant forward pitch or trim it forward to stay level. If you pitch forward to pick up speed and let go off the cyclic so it centres again, the Gazelle keeps going foward, but it climbs steadly as well. You need to trim it to stay level. Additionally, i must admit i fail to see in it in the video you linked.

 

Borchi stated earlier in this thread that the Gazelle indeed has no rolling tendency on lift off due to its design, i.e. the Fenestrom being pretty much level with the CoG.

 

I wonder two more things: if it is indeed stable in the roll axis by design, does the loadout matter (weight of weapons and fuel) and would that shift the CoG in a way that we should expect a rolling tendency on pick up? Sorry if i am beating that horse to death. Its not that i am in anyway unhappy with the fm, i simply like to really understand why the Gazelle behaves like it does.

 

Second, can somebody explain that ''new?'' roll to the left or right when sharply raising or lowering collective when flying at crusing speed? I see it gradually happening and then increasing above 60kmh ground speed. Below 60, it purely translates into yaw which you need to counter with pedal inputs. Somewhere above 60 no pedal inputs are needed anymore and torque is completely countered through airflow along the fuselage. Which combo of forces actually makes the aircraft roll at that partiuclar point then? Is it the tailrotor that produces a bit more thrust in that instant that is not being translated in to a yaw but a rolling movement because of aforementioned airflow a at cruising speed? Or is it because mainrotor vertical thrust changes not completely in sync on both sides?

Edited October 29, 2017 by sc_neo

[FragBum]

@Scarecrow84

 

I have re-read your linked op and this threads op and i gotta say, that centric nature is not really true, at least not in the ''absolut centric'' way you seem to imply. If you pick up with no inputs whatsoever on the cyclic and only right rudder so you don't turn one inch horizontally, the Gazelle flys pretty damn straight forward, that is true. But you absolutely must put in some constant forward pitch or trim it forward to stay level. If you pitch forward to pick up speed and let go off the cyclic so it centres again, the Gazelle keeps going foward, but it climbs steadly as well. You need to trim it to stay level. Additionally, i must admit i fail to see in it in the video you linked.

 

Have a look at the vids in my previous page here I have electrically centred the cyclic using the controls indicator. Once centred I use torque pedal and collective input only to pick up. If I faff about setting the cyclic to electrical centre I can get the Gazelle to pickup damn near vertically initially.

 

A previous post observe the controls indicator for the cyclic.

 

From about 12 sec in to about 1:03 there is no cyclic input I take control at that point and attempt to land if you watch the control indicator you'll see that from 1:03 point the cyclic input is small and and is centred with small inputs.

 

If your using a joy stick type control your mechanical centre may not 100% align with electrical centre and therefore bias the cyclic input slightly.

 

Keep in mind I have trim off AP off and gyro off.

 

I'll get back to some of the other stuff when I get time.

[FragBum]

Have you guys been meeting on teamspeak already? How about having a little chat about our observations later today?

 

Would love to, I'm In Australia so time zones can be a problem however keen to do so.

 

I hope the original question about the cyclic dynamics from this post doesn't get lost in the discussion...

 

 

I raised the same question a long time ago:

 

 

https://forums.eagle.ru/showthread.php?t=181563

 

Yes I don't fully understand this and make no pretence that I do however I am keen to understand and learn more. :thumbup:

Edited October 29, 2017 by FragBum
<edit>

[FragBum]

I wonder two more things: if it is indeed stable in the roll axis by design, does the loadout matter (weight of weapons and fuel) and would that shift the CoG in a way that we should expect a rolling tendency on pick up? Sorry if i am beating that horse to death. Its not that i am in anyway unhappy with the fm, i simply like to really understand why the Gazelle behaves like it does.

 

Same here as I understand it balance or CoG is a thing!

 

Some great free information here.

[FragBum]

Second, can somebody explain that ''new?'' roll to the left or right when sharply raising or lowering collective when flying at crusing speed? I see it gradually happening and then increasing above 60kmh ground speed. Below 60, it purely translates into yaw which you need to counter with pedal inputs. Somewhere above 60 no pedal inputs are needed anymore and torque is completely countered through airflow along the fuselage. Which combo of forces actually makes the aircraft roll at that partiuclar point then? Is it the tailrotor that produces a bit more thrust in that instant that is not being translated in to a yaw but a rolling movement because of aforementioned airflow a at cruising speed? Or is it because mainrotor vertical thrust changes not completely in sync on both sides?

 

 

As best I understand it the term Wagtendonk uses is Blow Back and Blow Forward (Flap Back Flap Forward)

 

Goes on to describe raising or lowering the collective causes an change in AoA simultaneously to all blades which causes the advancing blade to produce proportionately more lift than the retreating blade. Hence a roll force is applied to the aircraft.

 

Raising the collective causes the rotor disc to tilt back which implies lowering would tilt the rotor disc forward??

 

So with the Gazelle lowering the collective produces a right roll and raising the collective causes a left roll.

 

I might read over that a few more times as the application of the cyclic will also produce Blow Back and presumably Blow Forward which even implies sideways or any direction. :)

[borchi_2b]

@FragBum:

The blowback and flip forward only occures in the gazelle in relativ forward flight, according to the paper I recieved during the past days.

[sc_neo]

sorry for not getting back to you earlier. You are 9 ahead of me, i am located in Germany. I guess wednesday or thursday might work. We just need to work out who takes the morning shift :9. Or on the weekend. Cheers mate

[FragBum]

@ borchi_2b Ah ha well there is a different feel and a different amount of cyclic required when you take off and maintain sideways or backwards flight kinda makes sense. :thumbup:

Edited October 30, 2017 by FragBum

[sc_neo]

@borchi 2b ...and loadout and fuel quantity has really not enough influence on CoG, so that it does not roll on pick up?