EXPLANATION Why does the APACHE correctly roll to the left !

[CHPL]

Is there interest in a video that explains why the Apache rightly rolls to the left when the cyclic is pushed forward? 

Ask this because it is quite elaborate and the cause as I think wrong in the beta status and the flight model was found.

Edited January 17, 2023 by CHPL

[Mausar]

 

[CHPL]

@Mausar
Thanks, I know the video.

Nevertheless, there is a physical explanation for this.

Why Casmo did not make the experience in DCS and RL, he has explained.

Some things you don't do.

[Floyd1212]

If you would like to make a video to drop some knowledge bomb on all of us, go right ahead.

I think the official stance from ED is that this is currently an over-exaggerated behavior that will be toned down as the FM is refined.

[RodBorza]

8 hours ago, CHPL said:

Is there interest in a video that explains why the Apache rightly rolls to the left when the cyclic is pushed forward? 

Ask this because it is quite elaborate and the cause as I think wrong in the beta status and the flight model was found.

 

Well, I must confess that I've given much thought about it. Yes, the effect may be exaggerated due to some problems with the flight models and SCAS code, but I believe there is a reasonable explanation to this. I don't know if I am right or wrong, but it is a good nerdy exercise to think about these things.

So, here we go. When travelling forward, a helicopter suffers dissymetry of lift. For U.S. helicopters where the rotor spins counter-clockwise, the advancing blade on the right side of the helicopter is faster than the retreating blade on the left side of the helicopter. This causes a dissymetry of lift, where the right side has more lift than the left side. This should make the helicopter roll to the left, but due to the gyroscopic effect, the force is felt 90 degrees later, so, the helicopter should pitch up instead.

This dissymetry is compensated due to blade flapping, which is the freedom of movement of the blades up and down. The explanation for this is not that complicated, but takes a good amount of effort to explain it, so I recommend reading the FAA's Helicopter Flying Handbook, pages 2-19 to 2-23, where it is beautifully explained step by step. 

But in order to simplify things, blade flapping lets the blades angle of attack (AOA) to be naturally adjusted, leaving the advancing blade with less AOA, thus less lift, and the retreating blade with more AOA, thus more lift. This leads to the balancing of the lift on both sides of the helicopter disk, allowing the helicopter to fly in a controllable manner.

What I think is happening when you push the cyclic violently forward is that for some seconds, due to blade inertia, blade flapping is nulled. If blade flapping or its effects are inexistent, the helicopter has more lift on the right side than on the left side. It would cause the helicopter to pitch up and to the left, similar to what would happen in a retreating blade stall situation.

 Also, there is the effect of the tail rotor. In a U.S. built helicopter, the tail rotor pushes the tail to the right, in order to compensate for the main rotor counter-clockwise spin. So, if for some reason the main rotor pulls up, the tail rotor would help cause a left roll in the helicopter.

And, what is happening may be everything I said above or it is just a small, unforeseen error in the fly-by-wire system logic. Maybe it sees some situation it doesn't like and command a roll to the left in order to compensate for something not needing to be compensated. It has happened before in the real world, so must also happen in the virtual one.

Well, that's my two cents on the issue.

 

P.S.: I'm sorry. I didn't understand what you wrote in your first post. I thought you would like an explanation to the problem, but what you want is to make a video explaining it. Well, I would like very much to see a video explaining this phenomenon.

 

P.S.2: I tested it out in the Huey, and at high speeds, around 130 kts, the Huey does roll to the left if you push the cyclic forward violently. But the effect is not that pronounced and the Huey compensates for this command very quickly.  

Edited January 17, 2023 by RodBorza

[CHPL]

@RodBorza
You are a flight Instructor?

Thank you for your detailed explanation. I was not sure if it is really so obvious, and I am  storm tested in this regard.
Your explanation does not quite hit it, but already very close to it.
Every airplane and helicopter has its own peculiarities. This may be one of the APACHE.
Pressing the cyclic hard will cause a short but drastic change of the angle of attack. In addition, the round rotor surface becomes an oval, which also has a strong effect on the airflow. In conjunction with the gyro precision, this probably leads to a roll to the left.
If the maneuver is performed slowly and carefully, the effect is probably reduced by flapping. 
Skilled helicopter pilots are not tempted to do this because they are less hard on the controls and use the collective to sink.

However, the tail rotor moving up over the rotor head would result in a right roll. This effect should be well known to all R22 and R44 pilots, as it is explained pictorially in the Safety Course.

For all those who think angel of attack and flapping are abstract terms, a video would be the best way to illustrate and explain this. But good that I asked, why probably, so I can save myself the effort.

 

Edited January 17, 2023 by CHPL

[RodBorza]

4 hours ago, CHPL said:

@RodBorza
You are a flight Instructor?

Thank you for your detailed explanation. I was not sure if it is really so obvious, and I am  storm tested in this regard.

You are welcome. No, I'm not a flight instructor. I'm an electrical engineer with great interest in aviation, and in aviation engineering in particular. I do have a post-graduate certificate in Aircraft Flight Safety and Airworthiness, however. But what I learned in my post graduate studies is that I don't know anything and must be always learning and relearning things.

 

4 hours ago, CHPL said:

@RodBorza
Your explanation does not quite hit it, but already very close to it.
Every airplane and helicopter has its own peculiarities. This may be one of the APACHE.

Interesting. I must confess that since watching Casmo's video I was very much bugged by this. I thought on giving an explanation in a comment to his video, but I was not quite sure what was going on. Now, it seems that we are getting somewhere.

 

4 hours ago, CHPL said:

@RodBorza

Pressing the cyclic hard will cause a short but drastic change of the angle of attack. In addition, the round rotor surface becomes an oval, which also has a strong effect on the airflow. In conjunction with the gyro precision, this probably leads to a roll to the left.
If the maneuver is performed slowly and carefully, the effect is probably reduced by flapping. 
Skilled helicopter pilots are not tempted to do this because they are less hard on the controls and use the collective to sink.

 So I was not so far off. Regarding the controlled use of controls, yes, they must be done VERY gently. I made a series of tutorial videos on how to fly the Huey. They are on Brazilian Portuguese, so it may be hard to understand. Anyway, on the video below, at 6:05, I tell people to "Not be Tom Cruise". I mean, not yank at the controls like Tom Cruise does, because helicopters have very fine controls (as many real pilots state). 

I believe people are used to fast jets and when coming to helicopters are "tomcruising" the controls too much, causing strange issues.

<

Edited January 18, 2023 by RodBorza

[bradmick]

This is 100% not an actual behavior of the helicopter. There is a minimal (read that as barely noticeable) roll with forward cyclic application in the real aircraft. It’s an incorrect behavior in DCS that’s well known and been discussed to death.

Edited January 18, 2023 by bradmick

[RodBorza]

4 hours ago, CHPL said:

However, the tail rotor moving up over the rotor head would result in a right roll. This effect should be well known to all R22 and R44 pilots, as it is explained pictorially in the Safety Course.

Interesting. Is this information publicly available? Can I find it online, not being something exclusive of the manufacturer?

 

4 hours ago, CHPL said:

For all those who think angel of attack and flapping are abstract terms, a video would be the best way to illustrate and explain this. But good that I asked, why probably, so I can save myself the effort.

I still would like to see a video explaining it. It'll take your time and effort, not having too much video at the start, but could be left for those who are curious about how helos work.

 

[RodBorza]

14 minutes ago, bradmick said:

This is 100% not an actual behavior of the helicopter. There is a minimal (read that as barely noticeable) roll with forward cyclic application. It’s an incorrect behavior that’s well known and been discussed to death.

Hello Brad, 

That's understood. I imagine you (and ED) guys work hard to address this issues.

I've tested it on the Huey, and yes, it does roll to the left, but almost immediately compensates for it and keeps flying happily. Gotta love them Hueys!  

Anyway, I was just trying to understand the physics behind it, well...because helicopters are cool, ya know?

 

Edited January 18, 2023 by RodBorza

[Iron Sights]

I would say go try out the Black Shark if you want to see something different. 

[CHPL]

vor 15 Stunden schrieb bradmick:

This is 100% not an actual behavior of the helicopter. There is a minimal (read that as barely noticeable) roll with forward cyclic application in the real aircraft. It’s an incorrect behavior in DCS that’s well known and been discussed to death.

 

Hi bradmick.

I can imagine that discussions about an unfinished flight model on which you do great work get on your nerves. 

Did not want to reignite a discussion about the flight model, but only point out that it has a physical background. 

Sorry that I'm a smartass, but if I now already know something. 

Thankfully, you have confirmed the effect. 
Whether he is currently much too powerful in DCS is ultimately a question of optimization and fine-tuning and certainly not easy. To judge when this is achieved, I leave to the people who have practical experience.
However, it would be a pity if the effect, since it is already there, were to disappear completely just to avoid discussions.

[MAXsenna]

I'd love to watch a video about it.

Cheers!

Sent from my MAR-LX1A using Tapatalk

[jubuttib]

On 1/17/2023 at 8:26 PM, RodBorza said:

And, what is happening may be everything I said above or it is just a small, unforeseen error in the fly-by-wire system logic. Maybe it sees some situation it doesn't like and command a roll to the left in order to compensate for something not needing to be compensated. It has happened before in the real world, so must also happen in the virtual one.

FWIW you can look at Casmo's video and see what the SCAS does during these maneuvers (both in the input viewer on the top left, as well as the SCAS channels on the top right). When Casmo pushes the cyclic forward hard, the green + sign indication the SCAS' output, as well as the roll channel on the top right, both move hard to the right, trying to compensate for the roll. If the SCAS was deactivated, the Apache would roll to the left even harder than it does now.

[CHPL]

Am 18.1.2023 um 02:44 schrieb RodBorza:

Interesting. Is this information publicly available? Can I find it online, not being something exclusive of the manufacturer?

 

The insight comes from an accident report, as is unfortunately so often the case. Therefore, public and important and I also assume that it is still part of the safety tring today.
Unfortunately, it is also somewhat macabre and therefore very memorable.

Who something sensiebler should therefore Ignore it.

Spoiler

After the crash of a R22 due to a negative G situation with resulting mast bumping, the pilot was found decapitated.

However, the severed main rotor did not simply fly away, but initially split the cockpit vertically and relatively centrally, but should have missed the pilot. The vertical and not horizontal penetration could not explain the pilot's injury.

This of course led to confusion and further investigation. Thereby it was determined:
During the low G maneuver with exesive nose down attitude and thus very high tail rotor, its thrust led to a powerful roll to the right. The pilot reacted instinctively with a strong countermovement of the cyclic to the left, which was probably responsible for the mustbamping. 
The investigators finally came to the conclusion that the pilot reacted to the roll motion, which was not influenced by the control input due to the low G, by shifting his entire weight to the left. Strapped into his seat, he could only do this by lying on his left side, relatively horizontal in relation to the vertical axis of the fuselage, when the main rotor struck.

For the pilot, this did not change the sad result. However, the initially inexplicable situation eventually led to the resulting findings.

The simple sounding solution to avoid such situations: 
Avoid low G situations and do not react to rolling movements, e.g. even in the case of strong gusts. The latter is a) much more difficult than it sounds. And b) as I can say from my own experience, it causes a very very bad feeling and requires a lot of trust in the aircraft.

Even if there are upper limits for wind and gusts, specifically staggered according to flight experience, it is not recommended to test these limits.  The aircraft does its job reliably and safely, I can say that. However, how the individual reacts in the situation is written in the stars and unfortunately too often then in an accident report. 
 

Edited January 19, 2023 by CHPL

[CHPL]

vor einer Stunde schrieb jubuttib:

FWIW you can look at Casmo's video and see what the SCAS does during these maneuvers (both in the input viewer on the top left, as well as the SCAS channels on the top right). When Casmo pushes the cyclic forward hard, the green + sign indication the SCAS' output, as well as the roll channel on the top right, both move hard to the right, trying to compensate for the roll. If the SCAS was deactivated, the Apache would roll to the left even harder than it does now.

I have to admit I have not looked that closely at the APACHE and SCAS? It didn't even occur to me to check it out.

Thanks for your info. It confirms that the APACHE is doing everything right in principle and that it is ultimately a question of tuning.
But that's what the BETA is also there and even in a published version would be such discrepancies no shame. 

The exchange that has arisen here now, shows on the one hand how great the DCS community is. Not only that you always get help, many deal very intensively with the topics and the accumulated knowledge is gigantic. 

Unfortunately, and therefore I hold myself back for a long time on the German forum, some confuse knowledge with understanding and some discussion then degenerates.
Even my commercial pilot license and my time as a flight instructor do not make me an aerospace engineer. But neither does learning data and formulas by heart.

After my experiences in relation to the APACHE, also in our squadron, this has an almost religious character and other than the official views or opinions are already something like blasphemy.
Therefore the attempt to  assess the situation in advance, before I bring about my own stoning with a video. 

Edited January 19, 2023 by CHPL

[CHPL]

@RodBorza  @jubuttib @MAXsenna

Since I have already brought up the subject once, you three deserve that I take the trouble to explain to you in more detail what lies behind my educated guess.

However, I am currently working on 2 more videos on APACHE flight behavior,  in general, which I would like to complete beforehand.
It will therefore take a few weeks. 

In any case, thank you very much for being so open to the topic and the discussion. 

Edited January 19, 2023 by CHPL

[Raptor9]

As Brad stated, this is not correct behavior in the real aircraft and is being addressed.

Using the behavior of the Huey is not a worthwhile comparison. The two aircraft have very different rotor systems subject to different control behaviors under low-G conditions.

[CHPL]

vor 1 Stunde schrieb Raptor9:

As Brad stated, this is not correct behavior in the real aircraft and is being addressed.

Using the behavior of the Huey is not a worthwhile comparison. The two aircraft have very different rotor systems subject to different control behaviors under low-G conditions.

@Raptor9
I think about the question of whether or not this is correct on the APACHE, we're already over that. 

It is only about a physical effect that could theoretically occur independently of the type of helicopter to explain such behavior theoretically. 
As far as the flight model of the APACHE is concerned, we have full confidence in you. 
Rod's comparison was also not a confirmation of right or wrong, he has only made his own thoughts about it.
Please do not see any criticism where there is none. 

To avoid further confusion, I consider the topic for me as closed.
 

[RodBorza]

7 hours ago, CHPL said:

@Raptor9
I think about the question of whether or not this is correct on the APACHE, we're already over that. 

It is only about a physical effect that could theoretically occur independently of the type of helicopter to explain such behavior theoretically. 
As far as the flight model of the APACHE is concerned, we have full confidence in you. 
Rod's comparison was also not a confirmation of right or wrong, he has only made his own thoughts about it.
Please do not see any criticism where there is none. 

To avoid further confusion, I consider the topic for me as closed.
 

Yep, just to reinforce our views:  what we were discussing was not to throw shade at ED or criticize the current state of the Apache. Just nerding out behind the physics of it.

Regarding the Huey, I was not trying to make a comparison.

It was just an empirical experiment. My thought was: "since American helos do have counter-clockwise spinning rotors, would the same effect show up on the Huey as well?"   

Well it does, but it is much less pronounced. 

Which is very cool.

Kudos to ED and Belsimtek for that. 

[Rogue Trooper]

I have to admit, I have never seen this.

When I need to dive for cover the collective drops first, the pedals and stick follow and their fluid positions are dictated by the direction of egress and airframe reaction to the collective drop. I always try to maintain enough collective to guarantee main blade manoeuvre authority. All 3 inputs are changing constantly whilst I move the machine to a far more advantageous defensive position. everything is wet and liquid. Every pedal input is heart thumping stuff as I drop deep into trees, roll speed and yaw are true fluidity to the machines position in safe space.

There is nothing like fighting a weapon platform into a tight safe space and hovering, always wondering did I do enough.... it is a glorious achievement when the missile passes over you.

The Apache so far, is the best for fighting a defensive position and then pushing a retaliatory firing solution. I love the wobble.

I want so much more from George. I really want more from George! 

I guess this is 8 or 9 years of DCS choppers muscle memory... but mostly KA-50 dogfighting where it is all main blade authority and fantastic pedal Authoratar!

Bone idle pedal authority is the plague of most fighter pukes in choppers..... it is also the plague of a lot of virtual chopper pilots.

I will hate the day the the Apache is sterilised to "real" ..... I will hate it!

It will be so bland and rigid, gone will be its liquidity, its exaggerated personality.

Edited January 21, 2023 by Rogue Trooper

[CHPL]

vor 16 Stunden schrieb Rogue Trooper:

I have to admit, I have never seen this.

When I need to dive for cover the collective drops first, the pedals and stick follow and their fluid positions are dictated by the direction of egress and airframe reaction to the collective drop.

 

CASMO has already mentioned this as well. In DCS, you can fly an APACHE without any basic flying skills and act as no trained pilot would. (@CASMO / sorry for hiding behind your authority here  ).

This makes it especially difficult to develop a module and to check it for correctness when it comes to things that are not known from the real aircraft. Especially not from situations you don't usually create.
The same is true when creating a campaign. The really difficult and time consuming part is to anticipate things and actions that you would never think of yourself.

To make matters worse, those players are often the ones who voice the most harsh criticism. 

But we do not want to generalize. Crowned whiners and those who can not express themselves particularly diplomatically are rather the exception. But they are hard-working writers. 

Edited January 21, 2023 by CHPL

[FalcoGer]

Is there perhaps an explanation on why the aircraft sometimes and suddenly rolls over? I don't mean the somewhat gentle and tame roll to the left during full forward stick, I mean the 360° rolls in 3 seconds out of nowhere at low speeds.

[admiki]

3 minutes ago, FalcoGer said:

Is there perhaps an explanation on why the aircraft sometimes and suddenly rolls over? I don't mean the somewhat gentle and tame roll to the left during full forward stick, I mean the 360° rolls in 3 seconds out of nowhere at low speeds.

have track file?

[FalcoGer]

2 hours ago, admiki said:

have track file?

It's very sporadic. I do mainly lengthy multiplayer session. Often enough it doesn't happen at all. Maybe once every 10 hours or so. I never really tried to reproduce the issue though.