I've noticed that the Blackfoot AH seems to roll along an axis that is placed at the bottom of the fuselage of the helicopter. So when executing a right roll, the rotor head will rotate right. In actual helicopter physics, all roll and yaw movements revolve around the center of gravity, (pitch movements turn around the rotor head) that is the main pivot point of the aircraft.
- Legacy ID
Just fly it and notice. It shows more clearly in 3rd person.
In actual helicopter physics, all movements revolve around the rotor head, that is the main pivot point of the aircraft.
No, they are not... All rotational movements of a free system are always going around center of mass. Physics 101.
I wonder how many people will fall to this same fallacy again...
See my comment (http://feedback.arma3.com/view.php?id=12443#c58619) for the list of videos disproving your point.
You are absolutely correct about that CoG comment. The only thing is that (wiki quote:) For helicopters in hover, the center of mass is always directly below the rotorhead. In forward flight, the center of mass will move aft to balance the negative pitch torque produced by applying cyclic control to propel the helicopter forward; consequently a cruising helicopter flies "nose-down" in level flight. (end quote)
But still, in the blackfoot the roll axis is not placed somewhere in the middle of the aircraft where it should be, but on the bottom of its fuselage. I play massive amounts of FSX and have played some DCS, and the way these helicopters turn is completely different to the blackfoot. I've read most of the comments you've posted in the other thread, and i cant argue with you reasoning. But that doesn't mean that the roll axis on the Blackfoot is correctly placed.
Well, the Wikipedia has bad wording here
In forward flight, the center of mass will move aft to balance the negative pitch torque produced by applying cyclic control to propel the helicopter forward; consequently a cruising helicopter flies "nose-down" in level flight. (end quote) <<
By "movement of center mass" it's actually meant that since the helicopter pitches forward, the rotor center will be ahead of center mass (and, vice versa - the center of mass will become behind of rotor center)
In the blackfoot the roll axis is not placed somewhere in the middle of the aircraft where it should be, but on the bottom of its fuselage.
With that, I agree fully. The center of mass seem to be too low in many of ArmA choppers, lying close to gear. However, that still doesn't mean that, quote from your ticket:
when executing a right roll, the fuselage should tilt left alround an axis that runs through the rotor head.
Instead, the rotation should be done around *correct* center of mass, and not the arbitrary one currently present in the model. If you change the wording in your ticket, I'll happily change mo downvote to upvote.
Right. So i will adjust that. By the way ( I had to do some digging in my head, i once was educated for 4 years as an aircraft maintenance engineer and helo's were extensively taught) there is actually a play between the center of force (ie the rotor head/swash plate) and the CoG. So it's actually not JUST CoG. Helo's are a strange beast of dynamics. But i'd have to try and find my helicopter books to really see what that exactly was.
(pitch movements turn around the rotor head)
You can see that the helicopter turns around center of mass, until the backward rotor thrust makes the movement too complex to understand anything again.
"Rotating around rotor" is just an illusion, appearing because the rotor is bigger and is subconsiously taken as point of reference.
So it's actually not JUST CoG. Helo's are a strange beast of dynamics. But i'd have to try and find my helicopter books to really see what that exactly was.
Whatever "strange" they are, they still obey basic laws of physics. Human perception and intuition, on the other hand, are faulty, and don't work well in complex matters. For example, rotation + motion can easily be confused for rotation around another axis - which is what happening now ;)
there is actually a play between the center of force (ie the rotor head/swash plate) and the CoG. So it's actually not JUST CoG.
Well, I guess, helicopter technician training instructors cared not about scientific correctness, but about you getting the idea ;)
From physics point of view, there is only rigid body dynamics, which is affected by aerodynamic forces/torques. Aerodynamic is complex, yes - but once it's accounted for, it's plain old mechanics from the Newton age - CoG + mass distribution + forces distribution = movement. Everything is simple as an axe.
True, but nog JUST CoG, that's my only point here. And my original observation about the axis placement still persists. I don't want to make this an elaboration about physics, I just want an acceptable flight model. Not perfect, it's not a flight sim, just somewhat more believable.
True, but nog JUST CoG, that's my only point here.
I get what you're saying, but that's what I'm trying to tell you. It is CoG, CoG and only CoG :)
I understand that for you it's me vs. something you heard a while ago, but please understand that here I'm talking from the position of science approach, not from my own intuition. I think you agree that scientific approach has precedence over opinions. Otherwise you may as well believe in flat Earth on 4 elephants and a turtle :) And I would not be able to prove otherwise to you.
I am sorry for (possibly) mentoring and/or blunt tone, however, I just don't know how to bring my point otherwise.
As a physicist (by education) with some experience in creating aircraft simulations, I'm feeling painful when someone is promoting an incorrect point.
I kindly ask you to review the videos I've provided again - in every video you'll see proof to my point.
@antigoon78 Moderator "MadDogX" just a while ago informed us about new function in game (1.02 version) what you can test in editor. You can change Center of Mass (CoM) altitude as you like:
I found next settings a good start (giving just about 30s with each listed helicopter):
For AH-9 Pawnee between (too high input what causes very rapid helicopter movements)
ah9 setCenterOfMass [[0,0,1.4],0];
ah9 setCenterOfMass [[0,0,1.6],0];
mi48 setCenterOfMass [[0,0,3.9],0];
ah99 setCenterOfMass [[0,0,2.5],0];
uh80 setCenterOfMass [[0,0,2.8],0];
po30 setCenterOfMass [[0,0,1.9],0];
And if you find your maintenance crew books (I btw happen to have own operator handbook for Apache D model) you can find out that your memory did serve you that rotating axis is above the fuselag in most cases.
As you said, helicopters are strange beasts as their physics doesn't follow the basic logic what can be found from physics books but because they combine them very curious manner it can make even experienced physics teacher not to know how they actually behave. That's why there are totally own lines for aviation engineers to study helicopters flight modeling as it is radically different from airplanes. And for people who wants to be helicopter pilots it is totally own requirements from previous flight experience and licenses.
And I believe you mean differences like these from DCS and other simulators when compared to ARMA 3:
The ARMA 3 default CoM is just way too low on every helicopter. When you raise them with couple meters you get much more realistic flight experience even with the ARMA 3's very simple flight modeling.
To teach some people the physics of helicopter flight modeling could take a year
but they still wouldn't learn if they are not ready to forgot helicopters don't behave like airplanes or follow basic laws of physics as is because rotating rotor etc.
And as a reminder, in helicopters (and airplanes etc) Center of Mass is always somewhere in fuselag and below main rotor. But Center of Gravity (CoG) does shift and can even exist outside of fuselag few meters. And when it comes to helicopters, Center of Mass can even be located above the main rotor and flight characteristics would not change. The difference between helicopters and fixed wings are so dramatic that someone needs to forget almost all about physics to learn how helicopters behave. It is no wonder why it toke much longer to finally get helicopters flying from first prototypes as the rotating rotor was just too complex by its physics.
"Whatever "strange" they are, they still obey basic laws of physics. Human perception and intuition, on the other hand, are faulty, and don't work well in complex matters. For example, rotation + motion can easily be confused for rotation around another axis - which is what happening now ;)"
First of all, there is no intuition. Second, the perception is correct even with helicopter when you fly it, when you are as passanger and when you are watching it. Once you just accept that helicopters don't fly like fixed wings and helicopters are not freely flying objects but like big swings. Just imagine a long string from main rotor up to air from where the helicopter is hanging and combined it with tens of tons weight rotating, high speeds and dozens of other laws applied different ways in different positions and maneuvers and you start understanding why helicopters don't rotate around center of mass and it is just illusion to believe they always do.
I've looked around, couldn't find my books on helicopters. I also, like Fri13 seemed to remember that there is that play between CoG, CoM and the place where all driving forces originate (being the rotor head). I just wish i had the books to prove my memory right.
@Fri13: I'm not arguing with demagogues.
And as a reminder, in helicopters (and airplanes etc) Center of Mass is always somewhere in fuselag and below main rotor. But Center of Gravity (CoG) does shift [...]
...Illiterate demagogues who don't know shit about physics yet argue.
@antigoon78: Well, if the videos don't convince you, I give up. There's a lot of materials around, but, well - if you don't want to believe me, I won't be able to force you.
"...Illiterate demagogues who don't know shit about physics yet argue."
Say a person who doesn't know that Center of Mass and Center of Gravity are not same thing and can exist in different positions. :D
You have been given examples from engineers, examples from simulators and you don't believe, even your own linked videos agrees what people have been trying to say that rotating axis is too low and those videos are against you but you just don't see that.
Now with a added code the CoM can be moved up and what happens? Suddenly ARMA 3 helicopter flight modeling starts behave closer to reality by look and feel and gives at some manner a same kind feedback as top simulators.
Yet you are still arguing it is wrong and it shouldn't be so, even when it gives correct results in this game what is thing what is wanted by many with limitations of game engine.
Of course if developers could apply dozens of laws to flight modeling, results would be helicopters rotate around rotor main head in most cases, and you would not yet to be happy at all because you don't want to believe that helicopters don't fly like fixed wings.
I'm afraid the vids don't convince me. I actually see exactly my point, although it seems to pivot around a lower point, at the moment that the rotor is tilted the lifting force also provides horizontal motion, so it seems to move around a lower point. Again, as much as it is applicable to my perception it is to yours. Your quote: 'Human perception and intuition, on the other hand, are faulty,' And what you see in a video is the same as I do, but with different interpretation. At this moment wel could both be right or wrong.
Just as a reminder, a helicopter is actually suspended instead of lifted. All forces that induce motion originate at the point of suspension. So I say it's still not just CoG / CoM. Look at this little picture.