Cyclic - can't maintain attitude?

Not berating anyone, just after the evidence (if any) here. Also, the stab / AP system in our Mi-8 may be different and have an autolevelling function or some such for all we know. So unless AlexanderT (the lead dev) pipes in, or alternatively someone proves it to be wrong, I'm sceptical and will stay that way. And that regardless of who's the claimant, RL chopper pilot or not.

Not berating anyone, just after the evidence (if any) here. Also, the stab / AP system in our Mi-8 may be different and have an autolevelling function or some such for all we know. So unless AlexanderT (the lead dev) pipes in, or alternatively someone proves it to be wrong, I'm sceptical and will stay that way. And that regardless of who's the claimant, RL chopper pilot or not.

Exactly we don't know, and any observations are mealy observations and may well be the subject of another thread and as you say there maybe other explanations. Agree :thumbup:

Oh and that other sim is a commercial flight training sim with accreditation. ;)

Mind you I did look at the graphics even compared to DCS VR and smiled a lot,.. :D

Sure is an accredited sim. Not doubting that at all. Still, the reason I'm taking all this with a huge grain of salt nowadays, is that I've heard RL pros - widebody captains and such - talk out of their a**es as much as anyone. And I've also witnessed 2 pro pilots getting into a shouting match over a mere triviality, only to be proven both wrong by a former flight engineer.

So pardon me if I'm a bit cynical here, but hey, that's just the way I swing. And if that's a hanging offence around here... well... that's just the way I swing then innit :D

Nah all good, I just want to keep a robust, respectful and open minded discussion going is all. Surely that ain't a hanging offence, right? :) :thumbup:

The Mi-8 development lead was a professional pilot with thousands of hours on the type and several RL transport chopper drivers have praised the product too, and not one of them has ever said a word about this being wrong in any way, shape or form. So I'm willing to believe they're right and you're wrong, unless you've got some tangible and unequivocal evidence supporting your claim.

I dont know if I can find any flight test data for the Mi-8/17 family.

Because this thread isnt about the Mi-8 I wont be mining the whole net for this.

Anyway, from this post:

tried the Mi-8 with the autopilot system off and the cyclic also behaves much more like you say

You might wanna look at this video:

There are some turns, I didn't look at the whole video( family weekend activities…) but if you for example look at the right turn at 18:45 to 19:24 you can see the stick going right to initiate the turn and then back to around center* and a bit back pressure to make helo turn and keep height( stick towards the camera) and when the turn is complete stick goes to the opposite direction when rolling out and then back to around center. [Edit]There's a lot of turns I think and there is another one at around the 26 minute mark that also shows the behavior [End edit]

The main thing, that the cyclic stick is used to give the helo a rolling rate when put to the right or left and that the amount of displacement from trimmed flight will set the rolling rate is very easy to proof. I guess I can find around 100 such statments on the net, including governmental sites like USA -FAA and so on. I don't know if this will be enough for anyone to believe it though.

*) As I written about before the center position of the stick depends on the main rotor turning direction but it also depends on for example the tail rotor position giving different moment to the fuselage depending on the mounting height(compare the Bell206 and AS350 with the mi-8 for example. In turns there often is a slight deviation on the stick from the trimmed position, but this is small compared to the throw needed to get the helo into or out of a banked turn.

Not berating anyone, just after the evidence (if any) here. Also, the stab / AP system in our Mi-8 may be different and have an autolevelling function or some such for all we know. So unless AlexanderT (the lead dev) pipes in, or alternatively someone proves it to be wrong, I'm sceptical and will stay that way. And that regardless of who's the claimant, RL chopper pilot or not.

I don't wanna bash another pilot helping out for fine DCS modules either.

The main thing, If I ask some of my quite experienced colleagues I think I don't get the right answer from every one about stick center during turning flight. While all of them did hear about it in basic traning, they dont remember and the like most pilots fly with the ass feeling( not like an as :) ) so they just might not exactly know where the stick is.

Im quite sure that the one helping out in most cases use a PC joystick and that it is not easy to develope the exakt right feeling with a much shorter stick.( I did a little bit of this with the Bo105 development).

I did find some posts of AlexanderT and one of them referred to a experienced Mi-8 pilot but I think this was translated from russian. It would be very nice to have a talk/mess or post dialogue to someone that still flies the Mi-8. Because I think after my questions this person will need to test and try after the issue is bringed to mind.

We ha one example around one year ago where somébody claming that the DCS Huey didnt work as it should when flying with the governor off.

While we couldnt test it on a Huey one ED Forum memeber could test it on a AW139 on ground and there was the proof that I was right, concering frozen fuel flows. If I remember it wright this AW139 pilot was a bit amazed cause I think he also thought it would be the other way around.

https://forums.eagle.ru/showthread.php?t=196588&highlight=Torque&page=31

From that thread we can see that one Huey pilot(if really…?) and one AW139 pilot( I think we had some private mess and I'm quite sure he is a AW139 pilot for real) had another belief of how it worked than it actually worked.

What we learn from that thread is, if we havent really been looking active with the right awareness in the mind, we might have wrong despite actually knoving a lot about the subject.

Ummm... no. There're no grounds to claim the stabilizer we have in our Hip couldn't physically have such functionality that could level the chopper if ìt was switched on. Switched off, fine, that's another thing altogether; and FragBum's testing seems to indicate precisely that. So pardon me, but I'm still sceptical and will remain so for the time being.

Anyway, I'll just bow out now, since this indeed isn't a Hip thread. Regardless, anyone having doubts about the Mi-8 AP functionality should raise the matter on the pertinent sub-board, and I'll certainly follow the discussion there with interest myself. So bye for now and thanks for playing gents ;)

Correct me if I'm wrong, but it would entirely depend on pulling enough G in the turn for the helo not to require lateral cyclic inputs to maintain the roll. Not enough centripetal force and the helicopter will try to right itself because, you know, gravity? The mast is essentially the fulcrum for the suspended helicopter body. If that body is not flung outwards by sufficient centripetal force, it will hang down. That is why the pilot has to pull back on the cyclic to maintain enough G's that the pilot no longer requires lateral cyclic input.

Ummm... no. There're no grounds to claim the stabilizer we have in our Hip couldn't physically have such functionality that could level the chopper if ìt was switched on. Switched off, fine, that's another thing altogether; and FragBum's testing seems to indicate precisely that. So pardon me, but I'm still sceptical and will remain so for the time being.

 

Anyway, I'll just bow out now, since this indeed isn't a Hip thread. Regardless, anyone having doubts about the Mi-8 AP functionality should raise the matter on the pertinent sub-board, and I'll certainly follow the discussion there with interest myself. So bye for now and thanks for playing gents ;)

Offcourse a autopilot/stab system in a properly selected mode can return the helo to wings level.

I have flown 99% of my latest flown >3000 hrs in ATTITUDE MODE( both in Super Puma and NH90). When using ATT the reference is aircraft pitch and bank values. When releasing the stick the helo returns to the referens attitude.ä wich can be reset to what you wish with a button in cyclic. I did touch this subject in the former posts, and I also stated this:

When autopilot or stab syst in work they will have to move the stick in the same manner the pilot would have to do. Autopilot cannot change the relationship between the cyclic stick and rotor system ( Im not screaming, just trying to make one important statement be seen :)

Correct me if I'm wrong, but it would entirely depend on pulling enough G in the turn for the helo not to require lateral cyclic inputs to maintain the roll. Not enough centripetal force and the helicopter will try to right itself because, you know, gravity? The mast is essentially the fulcrum for the suspended helicopter body. If that body is not flung outwards by sufficient centripetal force, it will hang down. That is why the pilot has to pull back on the cyclic to maintain enough G's that the pilot no longer requires lateral cyclic input.

In every turn, the sum of G-forces is straight down to the floor( perpendicular to the floor).

The Huey teetering rotor is acting like the helo is hinged under the rotor in a loose joint between the rotor and the mast. It can dangle freely. It will automatically go to the position where it I described above. This is G-independent from just anove zero G to max achievable G. Less then the lower G limit will cause mast bump, and then you are dead.

If you are riding a bicycle and do a turn, in each turn you have the correct bank for having the G force straight down in the bicycle bank. If tou dont; you crash !

This means at in each clean turn with the helo the G force acts straight down, and the helo can not know whats really level according to earth. It cant. You cant either if you shut your eyes.

I did write this in the former posts also.

The pull back in cyclic is not like I read your text. It is because of two things( actually its the same but easier to understand divided to two:

- If the helo is banked only there will be no turn. The bank togheter with pull back is what makes a turn.

- If cyclic not pulled back tje helo will loose altitude. The leaning rotordisc will loose lift upwards( seen from the worlds perspective), so pull back is needed to keep altitude.

Both two statements is exactly the same as with aircrafts.

No problem here.

..

cannot change the relationship between the cyclic stick and rotor system

Never said it could. So what's this particular handbag war about then? The cockpit stick graphical presentation, a real hardware FFB stick, or a POS cheapo non-FFB HW stick most of us use? Because the only thing I objected to, was the (possibly misunderstood) part where someone claimed you couldn't return the booger wings level automatically.

No problem here

Heh :D

Never said it could. So what's this particular handbag war about then? The cockpit stick graphical presentation, a real hardware FFB stick, or a POS cheapo non-FFB HW stick most of us use? Because the only thing I objected to, was the (possibly misunderstood) part where someone claimed you couldn't return the booger wings level automatically.

Its not a war :)

When you start making statements, you should read at least a few posts back so your comment is on topic and not a statement on a completely different thing.

This is from OP:

For example, if you bank, even slightly, then it just keeps rolling until you recenter the cyclic. It feels like flying with an ancient digital joystick. Is this correct behaviour?

Yes it is, thats my point.

If the rate or sensivity is like a real SA-342: I dont know. I newer flew the Gazelle IRL and I dont have the module. But, from my experience and professional knowledge I can tell some parts about it. I did see some other recent posts in threads about people thinking that the sidewards stick position correlates to a specific bank angle, which of course is completely wrong. One of the posters claim to be a real Gazelle pilot. I can help by telling how it really works.

One problem is that people compare the SA-342 flight caracteristic with other modules which is a double fault:

-The other module will not be perfect, it will have flaws.

-The worst part: you can not really compare helos with different types of rotor systems. The teetering rotor( like Huey, Jet ranger and Robinson) will have a slow, delayed response because of the principles. The fully articled rotor( Gazelle, mi-8) will be quicker with much less lag but there is a big difference between types, because of the hinge of the rotor blade( the further out the quicker), and also how the rotor head is built. Still, they are not as quick as the rigid rotor heads( Bo105, Lynx).

I have time in all types of rotor heads. I know you cannot fly a DCS Huey and then complain about the Gazelle module based on what you learnt in the Huey. I know there is a huge( really !!) difference between a Huey and a Bo105 when it comes to characteristics.

Like this:

That is not right. Even in DCS. Deflection of cyclic places certain attitude of helicopter. If cyclic is re-centered, so would attitude.

Above post, again, wrong.

I've tried the Mi-8 with the autopilot system off and the cyclic also behaves much more like you say (and that other sim video shows) it should.

My answer:

...stab systems/autopilots they have one thing common IRL: They have to use the sticks exactly as the pilot have to. If you are using SAS or ATT mode or similar( stabilisation modes that makes the helo more easy to fly) and release the stick you will se the stick moving in the same maner you had to do to stabilize it. The stick is mechanically connected to the rotor system.

 

From you post it looks like DCS Mi-8 simulation of the stick when autopilot is on is not correct.

Ummm... no. There're no grounds to claim the stabilizer we have in our Hip couldn't physically have such functionality that could level the chopper if ìt was switched on

Here you have lost the track. We are not talking about the autopilot capabillities. Yes, in ATT mode a autopilot can( as I sad multiple times before). But the autopilot can not return the helo to wings level without using the cyclic in opposite direction. Period.

We are talking about the basic helicopter, think A/P off. Because if it was on it has to perform the same stick movements as you have to do if it is off.

cause the only thing I objected to, was the (possibly misunderstood) part where someone claimed you couldn't return the booger wings level automatically.

Yes, either you did not read everything, or I didnt write so you could understand me( English isnt my native...).

Hope this post made it less unclear ?

What the DCS community do not need is people claiming to be real pilots and posting rubbish that might ( worst case) impose the modules flight characteristics. In this matter, I think it would be better the more people having the right idea of how it works, no matter real pilot, pilot claim or not. :)

OK, you're good at posting walls and walls of text at least. Good for you. Still, I freely admitted to maybe having misunderstood about what exactly was the point of contention here, and just pointed out that the AP must be capable of returning wings level, unless you exceeded its control limits. And that was all really. Yet...

But the autopilot can not return the helo to wings level without using the cyclic in opposite direction. Period.

Umm... yes, taken into account that the AP is indeed fully capable of doing that, where exactly did I contradict that claim?

OK, pissing off here, so toodle-oo. Suggest you do likewise. And oh, in case it helps/supports/props your ego in any way, we'll just agree you won the debate.

Reference litterature /sources for what I state:

https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/helicopter_flying_handbook/media/hfh_ch09.pdf

Page 9-11, Turns.

How fast the helicopter banks depends on how much lateral cyclic pressure is applied. How far the helicopter banks (the steepness of the bank) depends on how long the cyclic is displaced. After establishing the proper bank angle, return the cyclic toward the neutral position

http://www.helitraining.co.nz/Modules/LSDocumentManager/DocumentDownload.aspx?DocumentId=22

Cyclic stick - Lateral stick controls...

Once you have attained the required bank angle the stick is laterally centralised in order to maintain that amount of bank.

https://books.google.se/books?id=VYAGAgAAQBAJ&pg=PA133&lpg=PA133&dq=control+disc+tilt+angle++bank+angle&source=bl&ots=mhdq3wLg0N&sig=ACfU3U2vOzTtu47En1qjP0T2oEVtp1dIaQ&hl=sv&sa=X&ved=2ahUKEwiU78OGu-PgAhVSxIsKHTodCqgQ6AEwDXoECAcQAQ#v=onepage&q=control%20disc%20tilt%20angle%20%20bank%20angle&f=false

S.133 ( same basics as above)

http://www.danubewings.com/helicopter-turns/

Yes, the tell the same story...

This is written by Ray W Prouty: says the same but also in detail why some helos have the stick slighty to the left or slightly to the right during sustained turn.

R.W. Prouty is very known in the subject helicopter aerodynamics. I got all his books(by my work) and I also followed his magazine articles. I dont think anyone in the bussiness have a doubt of his knowledge, or articles or books.

https://www.rotorandwing.com/2017/11/24/ray-prouty-archives-crosscoupling/

R.W.Prouty again, details about cyclic stick during turns with a little more info again then the other, page 93-94, single control turns:

https://books.google.se/books?id=rxryAgAAQBAJ&pg=PA203&lpg=PA203&dq=ray+prouty+cyclic+lateral&source=bl&ots=p-D6omsdZm&sig=ACfU3U0V2JVUyYMzPtIBRY71RkVptAZWZA&hl=sv&sa=X&ved=2ahUKEwiCv661rOTgAhXSo4sKHWrYD0MQ6AEwA3oECAQQAQ#v=onepage&q=ray%20prouty%20cyclic%20lateral&f=false

After the desired bank angle is achieved, the stick is returned to the initial trim position - or nearly so - since to hold it would result in a continous roll rate.

 

To hold a steady coordinated turn requires both pedal and lateral stick displacements. In almost all helicopters, stick must be held against the turn and pedals with the turn

I hope this is enough valid sources to be accepted.

OK, pissing off here, so toodle-oo. Suggest you do likewise. And oh, in case it helps/supports/props your ego in any way, we'll just agree you won the debate.

Well, I try the best I can to contribute to the forum. Im not going to get pissed off. I will continue, and you’re welcome to contribute with what you can. :)

Unfriendly posts etc that you may post will just be ignored from me. Its not my ego driving me, only pure interest for the matter, and thinki’n I can contribute.

I have one question though; why getting pissed and why do I feel a bit of unfriendliness?

My meaning was not to piss anyone off, although one might be if one had decided that the idea of cyclic displacement = bank angle, and nit ready to adopt any alternate reality.

And yet none of this pertains to how a helo stab / AP system may work. And that system switched off, we've certainly agreed to the basics already - because they of course hold true.

So what is it really? Non comprendo? Jag inte talar svenska eller hur? Because we're definitely talking past each other here. But never mind, since you're undoubtedly going to post yet another wall of text next :unsure:

I've tried with and without the AP but it seems impossible to hold your attitude in the Gazelle.

 

For example, if you bank, even slightly, then it just keeps rolling until you recenter the cyclic. It feels like flying with an ancient digital joystick. Is this correct behaviour?

Well, finally post ≠64 settled the question. At least for those that can accept FAA and RW Prouty as valid sources.

The Mi-8 development lead was a professional pilot with thousands of hours on the type and several RL transport chopper drivers have praised the product too, and not one of them has ever said a word about this being wrong in any way, shape or form. So I'm willing to believe they're right and you're wrong, unless you've got some tangible and unequivocal evidence supporting your claim.

Well, I might actually have :)

From what i find on the net, Mi-8MTB-1 (the export version – Mi-171B).

I could find proof of both using the same swash plate, thats a good indication of using virtually the same rotor system.

Mi-171B Flight Manual page 4-53:

https://storage35.uloz.to/Ps;Hs;fid=2408693;fide=EPJukX;hid=Rz36m6;cid=756726525;rid=111946803;up=0;uip=81.235.204.136;tm=1551743429;ut=f;aff=uloz.to;did=uloz-to;rs=0;He;ch=d9f92bea178d45d67ad7643a3a5883b9;Pe/!D22LfMug/kazan-mi-17-1b-flight-manual-full-version-pdf?bD&c=756726525&De&redirs=1

4.25.1 Turns and spirals

 

Enter a turn through co-ordinate application of the control stick and pedals and maintain selected speed and altitude by changing the main rotor collective pitch.

In entry into LH turn the helicopter shows a tendency to nose down, and In entry into RH turn the helicopter shows a tendency to nose up. Counteract these tendencies by appropriate application of the control stick.

Upon attainment of the selected bank angle indicated on the ArEigyro horizon note the position of natural horizon relative to the flight compartment glazing at this bank angle and retain this position in the course of tum.

In LH tum the helicopter shows a tendency to increase roll, in RH tum the helicopter shows a tendency to decrease roll.

Counteract the helicopter-rolling tendency by application of the control stick out of turn while In LH turn and into turn while in RH turn, and coordinate the turn by appropriate application of the directional control pedals.

Being 15 to 20° short of the selected reference object or desired heading apply the control stick and pedals In a coordinated manner out of turn to begin recovery from turn so as the bank angle is completely removed when the helicopter reaches the selected reference object or intercepts the desired heading.

Well, thats seems to validate my thoughts/claims about the mi-8 as well.

You can do whatever you wish with this information.

Source

[/img]

After this excellent contribution to the development of a better DCS I will call it day, and enjoy a good nights sleep. :)

Yes, this definitely counts as evidence. Will have to investigate this further. Thank you, although I still think we're talking past each other here.

While this thread isn't about Mi-8 at all, not even the mi-8 forum I suggest someone knowing AlexanderT ( reference from earlier post) pass this information on, and that we leave it from now in this thread.

(By the way, the description of pitching up vs down when entry a turn is also common knowledge in aerodynamics. It has to do with the blade flapping when commanding a turn. This is also the same on all helos but may be ATT hold function in an AP/SAS. Issue well covered by R.W.Prouty. Only thing bothers me, it should be the other way around on the mi-8, due to the clockwise rotor).

[Edit]

I actually accidently found a flight test with mi-171V made by the Polish armed forces.( google search from yesterday was still on my phone)

http://yadda.icm.edu.pl/yadda/element/bwmeta1.element.baztech-article-BUJ5-0041-0038/c/httpwww_bg_utp_edu_plartjok42011jok42011317.pdf

Of i terrest for this matter vi have fig.7 in page 323.

This picture shows the swash plate position for the mi-171 in different kinds of turns at 3000m an different speeds.

Negative values normally to the left so this tell us that the stick is virtually centered in right turns at speed 205km/h but at left turns the stick is to the right. Stick to the right is valid for left turns at all speeds, and for right turns at lower speeds stick will be to the right:

This values are taken by using some of the tests that you need to do to certify a large rotorcraft according to FAR29.

Only a fool will say these tests ”aren’t true”.

We've touched on blow back and cyclic position in forward flight* some time ago in this thread, I read that document re the US evaluation of the Gazelle and found it interesting .

The other "difference" is for doing level turns and accordingly the requirement for adding more power to maintain altitude and speed seems not all the helis are the same and it doesn't seem to be the Gazelle that is odd, but I'm not a pilot.

W. J. Wagtendonk goes into some detail here.

*Yeah I do reverse circuits in Gazelle/Huey/Mi-8 meh. :P:D

We've touched on blow back and cyclic position in forward flight* some time ago in this thread, I read that document re the US evaluation of the Gazelle and found it interesting .

 

The other "difference" is for doing level turns and accordingly the requirement for adding more power to maintain altitude and speed seems not all the helis are the same and it doesn't seem to be the Gazelle that is odd, but I'm not a pilot

Yes, stick forward in forward flight is valid for all real helos. (Fact, not opinion)

”Adding power” is the same for all aircrafts. If you find a difference in litterature, it will be because how they express the issue.

This is how it works. (Facts, not opinion):

If you are to keep the same airspeed and altitude you need to add power in a turn. Easiest eay to understand this is that a turn will increase the G force. Small bank doesnt give that much G-force, but indeed there is.

G = 1/(cos bank). For a 30 degree bank the G-force will be 1.15. Thats 15% more lift needed, and if you keep the power and altitude the speed will go down.

But, because in many cases, the exact speed is not important you can just leave the set power and perform your turn. This is how I do the must of my turns.

When learning to fly you need to learn this though, and for Fixed Wing in slower speed regime you might find yourself in a smoking hole in the ground if you dont apply power and try to keep the altitude without adding power :cry:

W. J. Wagtendonk: heard of but I havent read his book.

Cool name BTW :)

Yes, stick forward in forward flight is valid for all real helos. (Fact, not opinion)

 

”Adding power” is the same for all aircrafts. If you find a difference in litterature, it will be because how they express the issue.

 

This is how it works. (Facts, not opinion):

If you are to keep the same airspeed and altitude you need to add power in a turn. Easiest eay to understand this is that a turn will increase the G force. Small bank doesnt give that much G-force, but indeed there is.

G = 1/(cos bank). For a 30 degree bank the G-force will be 1.15. Thats 15% more lift needed, and if you keep the power and altitude the speed will go down.

 

But, because in many cases, the exact speed is not important you can just leave the set power and perform your turn. This is how I do the must of my turns.

When learning to fly you need to learn this though, and for Fixed Wing in slower speed regime you might find yourself in a smoking hole in the ground if you dont apply power and try to keep the altitude without adding power :cry:

 

W. J. Wagtendonk: heard of but I havent read his book.

Cool name BTW :)

W. J. Wagtendonk "Principles of Helicopter Flight" is basically the standard literature for civil helicopter students today.

In addition you also need it due to the total rotor thrustvector is tilted relative to gravity, some of the thrust is used for the altering of direction (component pointing to the center of the turn arc) and hence less thrust fighting the gravity (component pointing straight up).

Right, but in the same way wrong. Thats because the G-force and formula I referred to is actually

the calculation to maintain the same lift vertical to the earth. Your description is another way to describe the same as G= 1/(cos bank angle). So it is not ’in addition’ :)