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About "wrong elevator position" and "pitch sensitive"


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#1 An.Petrovich

An.Petrovich
  • Posts: 565

Posted 24 August 2009 - 14:43

On a regular basis in different sections of the forum the topic of "incorrect positioning of the elevators when control column is in neutral" or comments that the aircraft have "excessive control sensitivity in the pitch axis" are being brought up. I think it's time to discuss these issues in detail.

Let's consider some facts.
Starting first with the characteristics of a PC joystick:

Fact 1.1. For all PC joysticks the forward and rearward travel are the same.

Fact 1.2. The absolute amount of PC joystick handle travel in millimeters or inches is significantly less than that found in a real aircraft, since the PC joystick is much shorter than real control column - (with the exception of a few home brews, or when compared to certain aircraft that use joystick-like control sticks, the F-16 for example).

Fact 1.3. PC joysticks without Force Feedback use a spring, so with no force applied to them by the user they will always return to the neutral/centered stick position. Only FFB sticks allow the developers to control the zero-force stick position in the software, as well as the absolute amounts of stick forces. The FFB joysticks without a spring (like MS FFB2) are more precise than the ones that, along with FFB, use a spring or rubber neck (Saitek Cyborg Evo Force or Logitech Force 3D Pro).

Fact 1.4. Joystick spring (or FFB motors) are capable of creating only a small fraction of the amount of force that a pilot would have to contend with in a real flight.

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Now on to the facts related to airplanes:

Fact 2.1. For the majority of airplanes, the upward deflection of the elevator control surface is greater than the downward deflection. As a result, the control column/stick in the cockpit has more travel aft than it has forward travel (from aerodynamic center).

Fact 2.2. For the most part, the airflow around horizontal stabilizers is complex, resulting in asymmetrical pressures on the upper surface of the elevators compared with the lower surface of the elevators. That's why, if the control column is let free or control lines are severed, the elevators will practically never end up with zero deflection, albeit close to it. The resulting elevator deflection depends on a large number of factors, related to the aerodynamics of the flow around tail surfaces of an airplane (which itself is related to many factors).

Fact 2.3. It follows from the fact 2.2 that for airplanes with a simple mechanical control linkage that the zero-force control column position rarely coincides with the geometrically neutral column position, albeit close to it. Given fact 2.1 it follows that the zero-force control column. Position is rarely going to be half-way between full-aft and full-forward control column positions, and on top of that the zero-force control column position constantly changes in flight depending on the airflow around the airplane tail surfaces (which changes with airspeed, propeller RPM, Angle of Attack, side sleep, etc).

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Fact 2.4. For each value of elevator deflection (and corresponding control column position) in flight, there is a particular value of Angle of Attack (AoA) that the airplane will settle to. This correspondence changes very little for a wide range of speeds, so we can consider it constant for any practical purpose (we are not considering supersonic flight :) ). Engine RPM is also a factor here - due to prop wash effect on the airplane surfaces - but this effect does not change anything in principle - the airplane AoA is defined by elevators deflection (and control column position).

Fact 2.5. The greater the airspeed the greater the force of lift (and G load) given the same value of AoA of the airplane.

Fact 2.6. It follows from fact 2.5, that in order to maintain level flight at constant altitude, with an increase in airspeed the AoA will have to be reduced to prevent climbing. Conversely, AoA must increase when airspeed is reduced to avoid descending. So in order to maintain constant altitude, level flight, for low airspeeds the airplane must have a high AoA, and for high speeds a low AoA.

Fact 2.7. It follows from 2.4 and 2.6 that in level flight for different airspeeds that the elevator deflection will be different in order to provide the required AoA. While some modern aircraft might do this automatically, for airplanes with only basic flight controls (like those of WWI vintage), the pilot will be required to move the control column forward as airspeed increases, and conversely, to move the control column aft as airspeed decreases. So unless the aircraft is equipped with a cockpit adjustable trim system to relieve these forces the pilot will be holding constant pressure on the controls.

Now let's analyze the above facts.

If you consider fact 1.1 and fact 2.1, it is evident that we can not make each position of the PC joystick handle correspond with the position of the control column in the real cockpit exactly, without any geometrical distortions. There are 3 simple and obvious solutions to this problem:

Solution A:

- Max aft deflection of the real aircraft control column corresponds to max aft PC joystick position.
- Max forward deflection of the real aircraft control column corresponds to the maximum forward PC joystick position.
- Between these two extremes there is direct linear dependency between the real aircraft control column and the position of the PC joystick.

This means that the neutral control column position does not coincide with the neutral PC joystick handle position, and the elevator control surfaces may be deflected somewhat when the PC joystick is centered.

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Solution B:

- Max aft deflection of the control column corresponds to max aft PC joystick deflection.
- Max forward deflection of the control column corresponds to the maximum forward PC joystick position.
- Neutral control column position corresponds to neutral PC joystick handle position.

This means that dependency between the control column position in the cockpit and PC joystick handle position is no longer linear, with a discontinuity (bend) at the neutral point.

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Solution C:

- Max aft deflection of the control column corresponds to max aft PC joystick deflection.
- Neutral control column position corresponds to the neutral PC joystick position.
- There is direct linear dependency between the control column position in the cockpit and the PC joystick position.

This means that Max forward control column position corresponds to a fraction of the full forward deflection of the PC joystick handle, and there is an unused sector of the PC joystick travel when commanding large forward deflections (deadzone at near the travel limits).

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Each of the above solutions has its own pros and cons. Since we have to pick "the least evil" solution out of those available, I will only go over the disadvantages of each.

Disadvantages for Solution A:

In this case, a PC joystick in the neutral position will correspond to some value aft of the deflection of the control column in the cockpit (for example, maximum elevator deflection angles for Fokker D.VII are 30 deg. up and 18 deg. down - so the neutral PC joystick position will correspond to 6 degrees up elevator deflection). This is different from Solutions B and C, where the neutral PC joystick position corresponds to the neutral control column position in the cockpit of the real aircraft (and therefore elevator position), and in accordance with fact 2.4, the solution A will cause airplane to settle down to the higher value of AoA compared to solutions B and C. And in the light of fact 2.6, the airplane will be trimmed to a slower airspeed than that of solutions B and C. In light of fact 2.7, with solution A the virtual airplane will require more forward PC joystick deflection for level compared to solutions B and C.

Disadvantages of solutions B and C:

In the process of developing an airplane a very important characteristic is being carefully observed: the amount of control column deflection that provides 1 degree increase in Angle of Attack (or achieving 1 G load at a given airspeed), as well as the incremental amount of stick force(in pounds or kilograms) to achieve that difference. This control characteristic should meet certain established standards, to ensure controllability and comfort when flying the airplane.

If, for example, the control column forces needed were excessive, flying such an airplane would be very difficult, pilot fatigue would develop quickly, perhaps resulting in complete failure of the pilot to control the aircraft.

If the control column forces were too light, a pilot will not be able to develop fine and precise feel of the control column (because the pilot mostly "feels" the plane through control column forces, not through control column deflection angles). In such a case, the pilot's input could cause divergent oscillations in angle of attack, or in g loads - which is dangerous.

By the way, this is exactly why, (and remember fact 1.4 as well), pilots commonly perceive that PC flight simulator controls are "excessively sensitive", as compared to a real airplane. That's why my advise is to always try to pick a joystick with stiffer springs, or strong FFB mechanism, it is not only closer to the real life, but also will allow you more precise control of an airplane in a simulator.

As with stick forces, the situation is similar with control column deflection. If, in order to achieve desired change in AoA, the pilot has to deflect the control column by a large value, then the control of such a plane will be uncomfortable and sluggish - the control column travel required between aft and forward limits will end up being too large. But if that full travel is too short - the pilot will have to control the plane with minute stick movements, which will reduce the precision of control and will cause errors and oscillations (overshoots and corrections). Remembering fact 1.2, this is exactly what we observe in flight simulators.

Unfortunately, "stretching" the curve of joystick deflection vs. increase in AoA, trying to bring it closer to real control column curve is not appropriate since in this case the full deflection of joystick handle will only cover the narrow deflection sector of the real control column - and we would then be depriving the virtual pilot of the ability to command maximum G loads and perform maneuvers which the real airplane is capable of.

Hopefully it is very clear that a virtual pilot, unlike a real one, in accordance with facts 1.2 and 1.4, has a much less precise device to control the virtual airplane - a short and light joystick. This is one of the main reasons (along with g-force feel, binocular vision and other important factors) for frequently observed problems with the precise control of virtual airplanes in computer games. This is about the same as trying to drive a car with a steering wheel, the size of a coin.

This is exactly why, to achieve acceptable precision of control of a virtual airplane in the game, it is important to utilize full travel (from stop to stop) of an already short joystick, and to have the slope of Angle of Attack vs joystick handle deflection curve be as gentle as possible.

What consequences do we find in the case of Solution B?

The obvious consequence is a "discontinuity" of the curve of AoA vs. joystick deflection (in accordance with fact 2.4). The relation curve is less steep for forward stick deflections, and more steep for aft deflections (positive AoA zone). Consequently, in the range of AoA and G-loads where the most of the flying (and aiming in dogfight) is done, the airplane controls become more "touchy" or "too sensitive" as compared to Solution A. As a result, precise flying of the airplane is more difficult, and the virtual pilot will be more likely to encounter divergent oscillations. Also, a discrepancy in airplane reactions to equal deflections of a joystick will manifest, responses are "quick" when moving the PC joystick aft, and "sluggish" when pushing it forward. If you make a recording of joystick deflection vs time during a typical combat sortie it will become apparent that in case of Solution B (as opposed to A) a smaller range of joystick deflection angles was utilized (predominantly aft), and forward deflections were practically unused.

In the case of Solution C, it carries all disadvantages of Solution B, with the added problem of excessively quick control responses at negative AoA (forward stick deflections), and there is a totally unused zone of forward joystick deflections towards the limits of the PC joystick travel. This further adds to the problems that a PC joystick has already, namely the limited travel of the joystick (fact 1.2), and this solution would further reduce the useful travel of the stick.

The only advantage of Solutions B and C vs. solution A is that it is not necessary to deflect the joystick forward in a level flight at high speed, and also that when the joystick is let go, the virtual airplane's elevators will settle to the neutral position more close to the position of the real airplane elevators. However, considering facts 1.3 and 2.3, the elevators deflection with "free" control column will practically never be the same as elevators of a real plane (with control column "free"), if we are talking about a regular spring-loaded joystick. Such is the flaw of a typical joystick, which, unfortunately, was never designed to imitate the finer points of control stick forces of a real airplane control column. Exceptions to this are the force feedback joysticks (FFB), which allow developers to control the zero-force deflection angle, in accordance with control column zero-force deflection angles in the real airplane cockpit, depending on flight conditions. We do that in RoF. And the lucky owners of FFB joysticks can check it out for themselves. However, even that does not free them from problems with the zero-force stick position and the tendency of airplanes to pitch up, which the real WWI pilots had had to contend with as well. While real Fokker D.VII pilots would tie their control column to the instrument panel with a rubber band, so as to reduce the requirement of having to apply forward pressure on the stick all the time, you can try to do the same using your joystick and your monitor. :)

For the owners of regular spring loaded joysticks, due to their inherent design limitation, (central spring loading and equal travel forward and aft), it makes no sense at all to talk about solutions B and C to "fix" the supposedly incorrect zero-force deflection - it will always be incorrect, be it solution A, B or C. What's left is only complaints about less "comfortable" level flight and increased airplane tendency to pitch up.

Having analyzed all these issues, I made a decision to go with Solution A.

Below you can see the graph "AoA vs Joystick angle", and also graphs of joystick angle required for level flight at different airspeeds, for all 3 solutions, for Fokker D.VII in RoF.

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Nonetheless, I do understand well that there are disadvantages of Solution A, so in order to increase the gameplay comfort, I have some ideas for the future, and some that have already been implemented.

1) Level Autopilot - will allow you not to hold the joystick forward in a prolonged flight. Clearly this did not exist during WWI, so take it as our aim to help to the players in the game. To engage the Level Autopilot, it is not necessary to be in perfect level flight - small degree of bank or climb/descent is acceptable. Press
+ [A] and the airplane will establish constant barometric altitude and constant yaw, and will continue on like that regardless of air turbulence or damage received, provided that it is still in flyable condition. To disengage, it will suffice to deflect the joystick more than half it’s travel in any direction, or press
+ [A] again. This feature is available independently from difficulty settings in the game.

2) Easy controls mode (turned on by selecting "Easy piloting" in the game difficulty settings.) In this case, you will have a "virtual flight instructor" helping you to control the airplane, with a fine control stick and pedals inputs, preventing gross pilot mistakes, augmenting the flight stability, establishing horizontal level flight or coordinated turns. His actions can be observed by watching control column and pedals movements in the cockpit in response to your inputs. If you let the joystick free, the airplane will tend to continue straight flight on the current direction, if it is in physical condition to do so (depending on airspeed, engine RPM, damage received etc.).

3) Trim tabs. Strictly speaking, only a few planes of WWI had trim – (only S.E.5a had this of the airplanes included to RoF yet). However we do have plans to make trim available on all airplanes, and enable/disable it through difficulty settings menu. The trimming operation for owners of FFB joysticks will be no different from that of a real airplane - it will allow users to "trim out" stick forces in flight. For spring-loaded joystick owners, trimming will adjust the relation between elevators deflection angle and the joystick neutral (centered) position, i.e. something in-between solutions A and B. Here the partisans of Solution B (I am sure there will be ones) will win back their "lost money" :).

By the way, I am planning in the nearest future to have a poll with voting - which of the above solutions A, B or C the majority of users will want to have as a default game setting. Possibly, my choice of solution A will not turn out to be the favorite one, but now, after my explanation, at least, you will understand what are you voting for.

And finally:

4) Joystick curves settings in the game. Don't ask me "when?" :) This work is in our plans for the future, but (like trim) not in the most immediate ones. However, I will have to disillusion right now those who believe that joystick curve settings will help to cure the problems discussed here. My deep conviction is that a "dead zone" and non-linear joystick curve will just make pitch control of an airplane worse. I came to this conclusion while working on Advanced Flight Model for Su-25 of "Lock On: Flaming Cliffs". The problem is that the "dead zone" (which can be useful for roll or yaw control, if joystick has a centering problem or noisy pots/sensors) in the pitch channel just creates a disconnect between angle of Attack (AoA) and joystick deflection angle (remember fact 2.4?), and does it for a particular value of AoA at that. And as a consequence, for totally different values of G load (fact 2.5). This has nothing to do with the desire of a virtual pilot to have a level flight when joystick is let free. Simply, when controlling aircraft G loads, you will find an uncomfortable "step" in a most unexpected place (which depends on airspeed), where the airplane will stop responding with G load change to joystick deflection. This might happen during a turn, for example. Also there will be a disconnect between the required joystick deflection and achieving level flight at different airspeeds (fact 2.7).

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Non-linear joystick curves (response) also distort the relationship between Angle of Attack and joystick deflection in such a way that at moderate angles of attack the response is "soft" or "slow", but when commanding high or low AoA it becomes "abrupt" or "fast". But the moderate AoA values correspond to a particular airspeed in a level flight (for example for Fokker D.VII it is about 100km/h), and at those speeds it would be easier to maintain level flight indeed. But at speeds in excess of 150km/h the precision of control with the joystick will, to the contrary, decrease, as the plane will be "too touchy" or too sensitive to controls. And this is on top of the fact that at higher airspeeds the airplane is already more sensitive to control input even without any non-linear curves. It looks like we are improving in one area and making it worse in another. And this in no way corresponds to virtual pilot desire to correct "abrupt" reaction of the plane to the joystick inputs. All this is shown on the following figures, using Fokker D.VII as an example.

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Conclusion:

The problem of emulation of real aircraft controls in a computer game with a joystick is not new. The more exact the physics model in a flight simulator, the more the fine details and discrepancies show themselves. These details, for the most part, are known and understood by real pilots (not always though), but will surprise inexperienced virtual pilots. Games like Retaliator or F-19 had none of those problems at all, don't you remember? :) Unfortunately, ordinary spring-loaded joysticks are not adequate for this task. Force Feedback joysticks (FFB) do have an advantage here, but not without shortcomings, and not every virtual pilot has them. That's why, for the time being, we have one choice: the best out of all choices possible. I made my choice while working on Advanced Flight Model of Su-25 for "Lock On: Flaming Cliffs". This is Solution A. To help RoF users, the autopilot was made available, as well as "easy" control mode. The future measures which I presented here being trim and joystick response curves, albeit I voiced my opinion on the problems with curves (and again, it is difficult to talk about the time frame or promise anything). Also I do plan to run a poll with the question "do you prefer Solution B (or C) over Solution A". It is possible that based on the results, the preferred solution will be reconsidered. And finally, I will be glad to hear your ideas - what would be the best way given the circumstances, and what else can be thought of to make airplane control in RoF realistic and comfortable at the same time. Feel free to post your ideas in this thread. I will read them and comment when I have a free moment. If I don’t respond please don’t think I am ignoring anyone. I will certainly read everyone’s ideas and post when I can. ROF coding never ends my friends. :)

P.S. Great thanks to TX-broWright for translation this post to English!

Sincerely,
Neoqb Lead Engineer.

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#2 congo

congo
  • Posts: 98

Posted 24 August 2009 - 15:09

An.P

I'll agree with everything you have stated except for Fact 1.2. Take a conventional joystick and add 18 to 24 inches and then measure the travel. Stick travel should be thought of in terms of angles and not inches of travel. That is why rigging protractors are an integral part of aircraft rigging. BTW the original F-16 side controller had no travel whatsoever but the pilots did not like this feature so travel was added albeit a very small amount.

Congo
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#3 ZaltysZ

ZaltysZ
  • Posts: 1638

Posted 24 August 2009 - 15:31

Imagine the stick as radius of circle. Lets assume we have fixed travel angle α. The longer is the radius, the larger will be the length of arc, despite the fixed travel angle. So if you have long stick, then you will have to move it more centimeters (inches? what is that? :) ) to get the same deflection angle, than short stick.
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#4 HotDog

HotDog
  • Posts: 57

Posted 24 August 2009 - 15:35

Thanks for your long and extremely well presented explanation. You certainly have given the problem a LOT of thought. :)
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#5 An.Petrovich

An.Petrovich
  • Posts: 565

Posted 24 August 2009 - 15:39

An.P

I'll agree with everything you have stated except for Fact 1.2. Take a conventional joystick and add 18 to 24 inches and then measure the travel. Stick travel should be thought of in terms of angles and not inches of travel. That is why rigging protractors are an integral part of aircraft rigging.

We can measure the travel in degrees or in inches - there is no difference (engineers often use both ways). The main fact is: you move your hand more or less. If you move your hand a bit - you can't sense the aeroplane perfectly, because you like a jeweler. :)

That's why pilots usually did not like F-16 side controller (I know about a feature of this stick, of course :) ). BTW, this example show us that pilot mostly "feels" the plane through control column forces, not through control column deflection angles.
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#6 J2_squid

J2_squid
  • Posts: 3815

Posted 24 August 2009 - 15:41

Thanks for that post An.Petrovich!

I think I understand the issue now. As for the solution, I can see there isnt one without drawbacks.

I actually like the controls as they are now. For me personally, I dont notice having to push forward all the time, ive simply gotten used to it.

Id rather not see a leveling autopilot or autotrim system as this to me seems unrealistic.

That said, giving people the option to alter response curves would he helpful for those that can't stand the current inputs needed. That and a trim system for the SE5a (As the real plane had one).

I think then everyone should be happy, for the purerists they can leave things as they are, for the people that find it uncomfortable the can edit out the amount of force using the curves.
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#7 An.Petrovich

An.Petrovich
  • Posts: 565

Posted 24 August 2009 - 15:48

Welcome to the club, guys! ;) :D
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#8 Jughead_Jones

Jughead_Jones
  • Posts: 170

Posted 24 August 2009 - 15:56

An, very thougth out presentation and exellent english!! ;) Also I mispelled your name in a previous post and just wanted to apologize quicky. You have cleared up everything I wanted to know and given the playerbase a well needed thought out proccess on the flight models future heading.

I know that Neoqb wanted the most realistic approach but we all are virtual pilots and use virtual sticks of many different makeups. To please all users 100% why did your developers not just create a completely linear and equal forward and aft control system? I know it is not the way these birds were desighned but did Neoqb not see this snowball effect of issues coming from the current system? Also while I could not agree with you more about curve altering, in other games such as WW2 OL you can go into a global file and just alter the values of the entire axis band. So instead of curving an axis line you could just extend or shrink it without loosing the linear path it follows, or its center. I know moving the throw bands is the same thing but this way both sides of the axis are moved equally. Could this be possible in this application?

Last I very much look forward to the trim option and hope it can come to life in a decent time frame. This while not realistic in regards to all the planes ingame will definately help the playerbase out on a monumental level. Thank you again for your time in this very clear post and GL! :D
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#9 MattM

MattM
  • Posts: 2595

Posted 24 August 2009 - 17:07

Thanks for the explanation.

I would still prefer solution B.

So instead of curving an axis line you could just extend or shrink it without loosing the linear path it follows, or its center. I know moving the throw bands is the same thing but this way both sides of the axis are moved equally. Could this be possible in this application?
That's exactly what i would like to see.
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#10 congo

congo
  • Posts: 98

Posted 24 August 2009 - 17:33

An.P

I'll agree with everything you have stated except for Fact 1.2. Take a conventional joystick and add 18 to 24 inches and then measure the travel. Stick travel should be thought of in terms of angles and not inches of travel. That is why rigging protractors are an integral part of aircraft rigging.

We can measure the travel in degrees or in inches - there is no difference (engineers often use both ways). The main fact is: you move your hand more or less. If you move your hand a bit - you can't sense the aeroplane perfectly, because you like a jeweler. :)

That's why pilots usually did not like F-16 side controller (I know about a feature of this stick, of course :) ). BTW, this example show us that pilot mostly "feels" the plane through control column forces, not through control column deflection angles.


An.P

You missed my point, I think if you look at the deflection angle of a conventional joystick and that of an actual aircraft control column there is not that much difference. And I would still argue the inches of travel statement. That is like saying If the pilots preference is to grip the stick at any other place but the top he will have less control column travel and this is simply not true. He will get the same amount of column and surface deflection no matter where he holds the stick. You are right in the respect that aircraft are flown by feel. If you refer to your drawing above and look at the angular travel they are pretty close.
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#11 congo

congo
  • Posts: 98

Posted 24 August 2009 - 17:38

An.P

I'll agree with everything you have stated except for Fact 1.2. Take a conventional joystick and add 18 to 24 inches and then measure the travel. Stick travel should be thought of in terms of angles and not inches of travel. That is why rigging protractors are an integral part of aircraft rigging.

We can measure the travel in degrees or in inches - there is no difference (engineers often use both ways). The main fact is: you move your hand more or less. If you move your hand a bit - you can't sense the aeroplane perfectly, because you like a jeweler. :)

That's why pilots usually did not like F-16 side controller (I know about a feature of this stick, of course :) ). BTW, this example show us that pilot mostly "feels" the plane through control column forces, not through control column deflection angles.


An.P

You missed my point, I think if you look at the deflection angle of a conventional joystick and that of an actual aircraft control column there is not that much difference. And I would still argue the inches of travel statement. That is like saying If the pilots preference is to grip the stick at any other place but the top he will have less control column travel and this is simply not true. He will get the same amount of column and surface deflection no matter where he holds the stick. You are right in the respect that aircraft are flown by feel. If you refer to your drawing above and look at the angular travel they are pretty close. Here is your drawing with the joystick imposed over the control stick

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  • Attached File  2.jpg   17.05KB   818 downloads

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#12 =IRFC=AirBiscuit

=IRFC=AirBiscuit
  • Posts: 2455
  • LocationNaples, FL USA

Posted 24 August 2009 - 18:00

All I have to say is that it is so fantastic to finally be hearing directly from neoqb's engineers. Faith in the future of ROF: restored.
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=IRFC=Air Biscuit

http://quetoo.org


#13 NickM

NickM
  • Posts: 1625

Posted 24 August 2009 - 18:40

4) Joystick curves settings in the game. Don't ask me "when?" :) This work is in our plans for the future, but (like trim) not in the most immediate ones. However, I will have to disillusion right now those who believe that joystick curve settings will help to cure the problems discussed here. My deep conviction is that a "dead zone" and non-linear joystick curve will just make pitch control of an airplane worse.

Firstly, thank you very much for such a good post. You have clearly though long and hard about a difficult subject. However, with regards to curves and deadzones, and with all due respect, I think you are wrong. Here's why:

As you have shown, there simply is no good solution for simulating control of an aircraft using a spring-centred joystick. It just cannot be done. So rather than try to do it anyway and force players to live with the very odd results, why not just accept the limitations and use a stick-response model that is designed to capture the "essential feel" of the aircraft within these limitations?

A good example of this is the way the stick is used in IL-2. As I understand it (please correct me if I am wrong), the full deflection is (supposedly) set to correspond to a force applied to the stick of 50 lbs, rather than assuming a direct mechanical linkage to the controls. The control surface deflection for a given stick movement at high speed may thus be smaller than the deflection for the same stick movement at low speed. This is so that the behaviour of aircraft at very high speeds can be captured - e.g., the Bf-109 had notoriously heavy pitch control response at high speed, "stick set in concrete", etc. If the player can just pull the stick fully back and have the elevator hit the stops with maximum deflection at high speed, then in the game he has super-human strength and in real life would probably have broken the controls. I doubt if any pilot in real life could achieve full up elevator deflection at 350+ knots in a Bf-109. So IL-2 cheats by reducing the control surface deflection that corresponds to stick fully back. It is a cheat, but it works and the alternatives are worse.

In RoF what are we trying to achieve? We want the essential handling characteristics of the aircraft to be preserved. Real-life pilots had to push the stick forward to hold the aircraft level at high speed, so we want that to be in the game. But real-life pilots could also use small pressures on the controls to make small adjustments to attitude, so we also want that to be in the game. In fact, this is absolutely ESSENTIAL if we are to be able to aim accurately. However, as currently implemented in RoF, the aircraft are too sensitive to small movements of the stick and small adjustments to attitude are very hard to achieve. The nose oscillates all over the place when trying to make small changes in attitude. It is harder to make small changes in attitude in RoF than it is in a real aircraft. This means the game is not more accurate but less accurate.

Having the ability to set response curves and deadzones may be un-physical, but it is essential if we are going to be able to make small attitude changes AND get full control-surface deflections for manoeuvers. IL-2's way of using stick response curves and combining force applied plus control surface deflections is a compromise, but it is a good compromise and works extremely well. I would recommend something similar for RoF.

Do we want to have to push the stick forward to fly level at full throttle? Yes. Do we want to be able to make small changes in attitude for gunnery? Yes. As far as I can see, this can only be achieved by using response curves and deadzones. In fact, if we can't do these things then the sim just becomes frustrating and people will stop playing it.

I hope you will not take this as negative criticism. It is meant to be a useful opinion and nothing more. I am actually very impressed with the quality of the work done in RoF and think it is probably the best PC flight sim ever made. I enjoy it tremendously.

Incidentally, I don't know if you fly gliders as well as powered aircraft, but the glider I fly, a Club Libelle, is famous for having almost no control forces at all. Even pushing up to Vne I can still move the stick with two fingers on the column and the rudder feels almost as free as on the ground. Not a clever design!

Finally, please do add the trim control to the SE5a - it's a beautiful 3D model but a real handful to fly at the moment without trim. I'll buy you a beer as soon as it's done.

Cheers,

Nick
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#14 MattM

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Posted 24 August 2009 - 18:55

I think NickM is 100% correct, great post.

I think most (not all, i know that) joystick control software that comes with the joystick already allows dead zones and response curve to be configurated. So i think it would be enough for most people to just add solution B as an option to the current system. That basically all i would ask for.
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#15 NickM

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Posted 24 August 2009 - 19:05

I think most (not all, i know that) joystick control software that comes with the joystick already allows dead zones and response curve to be configurated.

Yep - just my wretched Sidewinder 2 that doesn't. I think I'll have to buy a CH stick and throttle to get some decent software control. Microsoft gave up on their sticks ages ago. I've not found anything to set curves for the Sidewinder under XP.

Cheers,

Nick

PS. I actually use a Sidewinder stick, CH pedals and an X45 throttle. I can at least run the CH software to set curves for the rudder, but I've just got a new PC and am still downloading all the necessary flight sim stuff.
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#16 WWBrian

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Posted 24 August 2009 - 19:23

An.Petrovich,

Thank you for explaining this so clearly and specifcally. Not only does it answer user's previous questions and concerns regarding input and sensitivity, it should eliminate any future concerns as well.

Very well written document An.Petrovich!

Thank You!
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#17 congo

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Posted 24 August 2009 - 19:47

If the control column forces were too light, a pilot will not be able to develop fine and precise feel of the control column (because the pilot mostly "feels" the plane through control column forces, not through control column deflection angles). In such a case, the pilot's input could cause divergent oscillations in angle of attack, or in g loads - which is dangerous.



Depends on the aircraft and its use a good example is the North American T-28 which through the use of servo tabs the crew chiefs could either boost or de-boost stick forces. This aircraft could be made to handle like a DC-3 or an F-100. Same for aerobatic aircraft like the Extra 300 which is quite light on the controls. This aircraft uses aerodynamic spades on the ailerons and a pretty effective aerodynamic balance on the elevator. I would say that the folks that fly these have pretty precise control over their aircraft. Personally since I have trim wheels on my JS I dont have a preference for any particular solution I am just adding food for thought.
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#18 King_Richard

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Posted 24 August 2009 - 19:58

how about doing something along the lines like dcs black shark does. just set up two buttons for us where one of them remembers our stick position when hit the button and than that becomes the new center for our joysticks and than we can reset it when we get into combat.
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#19 ZaltysZ

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Posted 24 August 2009 - 20:29

A good example of this is the way the stick is used in IL-2. As I understand it (please correct me if I am wrong), the full deflection is (supposedly) set to correspond to a force applied to the stick of 50 lbs, rather than assuming a direct mechanical linkage to the controls.

Yes, 50lbs. This has its own complications. Planes with heavy elevator are in some way under modeled, because in real life you can use both hands to pull the stick if need arises, in game this is not possible. However it is better this way than having UFOs.

However, with regards to curves and deadzones, and with all due respect, I think you are wrong.

4) Joystick curves settings in the game. Don't ask me "when?" :) This work is in our plans for the future, but (like trim) not in the most immediate ones. However, I will have to disillusion right now those who believe that joystick curve settings will help to cure the problems discussed here. My deep conviction is that a "dead zone" and non-linear joystick curve will just make pitch control of an airplane worse.

In fact there is illusion which should be gotten rid of. Joystick curved response will only make bad things to happen. Remember that straight attitude position is not constant, it changes with speed and power setting, in other words straight attitude position is floating. How will you apply the curves? Normally people like to soften response at the center and then gradually increase it for greater deflection angles, however because of floating straight attitude position your softened joystick response zone will coincide with it only at certain speed and/or power, so at in any other speed and/or power your softened response zone will be shifted from straight attitude position and this is where bad things begin. Firstly, the response will be hard to predict; secondly straight attitude position can miss softened zone by large margin and you will get sensitive positive input and very slow negative one or vise versa. Of course you can try to increase softened response zone so, that it will include all common straight attitude positions, but after that your plane will be very unresponsive and you will be flying like wounded.

The above is true for direct linkage controls, but it is slightly different for applied power response controls (like in IL2). With the later, joystick response curves work well if straight attitude position coincides with zero force position. If not, you will get almost the same problems as with direct linkage controls.

As you can see, joystick response curves won't be cure for stability problems (well, in fact it will be, but only at certain speed and power).
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#20 Bleddyn

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Posted 24 August 2009 - 21:39

Thank you for the post An.Petrovich.

You will always have people who think the way neoqb has handled this is the best way possible, and others who want it done differently. At least with your post nobody can claim it is "broken". Hopefully future conversations on the matter will reflect that.
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#21 Sensenmann

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Posted 24 August 2009 - 22:00

The problem as I see it seems to be tied to the fact that some people believe that neutral controls should create level flight: this is not the case. As others have stated and as anyone with any time piloting time (real or simulated) should know, different power states require different attitudes for level flight. That attitude is maintained by control surface configuration whether by direct input or trim settings.

The problem with the current control curves (or lack there of) is that we have an inbalance of control surface range for motion of the controls. Using An's stated ranges for the Fokker (18 degrees below, 30 degrees above) and the current use of Option A we get neutral input giving 6 degrees of deflection above and an average of 1 degree of deflection per 4.17% of control range. For control surfaces to be in a neutral position we need to hold the stick forward 25%!

As I stated earlier, having to use varied input to maintain level flight is just a matter of fact. But to have to use 25% forward input to neutralize the controls, regardless of power level or intended attitude, is awkward at best. We are accustomed to neutral input to equate to neutral controls (in the absence of trimming).

Where Option A gives us even input acorss the controls range (4.17% at the controller = 1 degree at the control surface) but an offset neutral position, Option B gives us an offset sensitivity in exchange for neutral controls. This is not good either as we now have 5.56% control input forward and 3.33% control input rearward resulting in the same 1 degree of control surface deflection. The result would be detrimental to our gunnery as we now have to double forward input in comparison to rearward input when trying to draw a bead on our kill.

Option C seems to be the best candidate as we get an even 3.33% input equating to 1 degree of deflection on either side of neutral. Only thing is we only get 60% of the forward range before we hit a dead zone. I am not certain how this would affect anyone, but suspect it might frustrate some as the controls would be "non-responsive" in this dead zone.

Perhaps there should be an option D where we get the linear response in the rearward direction, neutral is neutral and then we get a curved response for forward input to fill in the full range of motion while smoothing out the sensitivity. The result would be a loss of sensitivity across the forward range but it would be gradual enough not to be a problem.

Below (hopefully) is a graph showing all three original Options and my proposed fourth one. Also there should be a spreadsheet with more detailed information on the figures I am using.

Attached Files


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#22 Sensenmann

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Posted 24 August 2009 - 22:05

Bah! Didn't get my spreadsheet attachment. Let me try again…
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#23 TJTAS

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Posted 24 August 2009 - 22:11

I don't mind the current system, I think it could be improved but i can live with it.

What worries me a little bit is the system getting changed by popular demand to something i don't get on with.

Maybe what we need is an option in the control setup for methods A,B,C,D or a customizable approach of our own. I think An.Petrovitch's wonderful description in this first post should be included.
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#24 Sensenmann

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Posted 24 August 2009 - 22:12

Nope. That didn't work either. :roll:
Here, made a jpeg out of the data…

Attached Files

  • Attached File  data.jpg   167.64KB   1160 downloads

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#25 TX-EcoDragon

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Posted 24 August 2009 - 22:25

Sensenmann, my feeling on the best compromise agrees with yours.

If there were a way to have option A, but to have correct trimspeeds for the aircraft, that would be ideal of course, but as we see here, it's not that simple. Having deadzone at the maximal limits of joystick travel in the nose down direction is not going to present obvious performance issues as this control input will be used rarely, during aggressive evasions and during certain maneuvers for short durations where full input is commanded.

Auto level feature is not the same as correct trimspeed behaviors, and can not be used to allow for constant rate climbs or descents etc as should be possible in real aircraft.

I have an FFB joystick on the way to test the current trimspeeds assuming the stick is centered where Petrovich has configured it to center.
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#26 TX-EcoDragon

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Posted 24 August 2009 - 22:37

Same for aerobatic aircraft like the Extra 300 which is quite light on the controls. This aircraft uses aerodynamic spades on the ailerons and a pretty effective aerodynamic balance on the elevator. I would say that the folks that fly these have pretty precise control over their aircraft.
Quite right that these aircraft allow for extreme precision, but it comes only after a fair amount of practice as it requires the pilot to dial in their muscle memory because aerodynamic center has almost no associated feel (breakout force), and these aircraft respond so fast that using visual cues is not going to allow for fast enough reactions. Mastering something like a max rate four point hesitation roll in the Extra will be much harder than the same maneuver in the Pitts. The Extra makes the maneuver less physically demanding, but it's harder to do with the same standard of precision for a pilot new to the airplane without progressive stick force increases with G loading, and without a tangible aerodynamic center.

[quote="congo"Personally since I have trim wheels on my JS I dont have a preference for any particular solution I am just adding food for thought.

As do I, and this gives us something like option C. . .which I think is a reasonable compromise, and apparently so do you as you don't seem to be having trouble with a shifted axis and the associated issues.
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#27 Tanner

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Posted 24 August 2009 - 23:12

Dumb question:

How did it work in the actual planes??

Given the simple nature of the controls on these planes, one presumes that, disregarding stick forces, there is a pretty much linear relationship between the column deflection and control surface deflection. Presumably if there was little downward deflection possible on the elevators, then most of the range of the column's movement was fairly useless in the forward direction. If that is the way it was, then that is the way it was. Why not merely use a direct linear relationship that captures the real way the controls were on the plane rather than modeling a response curve? I realize the throw of the controls between the PC and the plane are significantly different, but I would rather have something that was accurate, rather than degrees of motion in the controller that simply were not present in the plane.
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#28 congo

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Posted 25 August 2009 - 00:04

Same for aerobatic aircraft like the Extra 300 which is quite light on the controls. This aircraft uses aerodynamic spades on the ailerons and a pretty effective aerodynamic balance on the elevator. I would say that the folks that fly these have pretty precise control over their aircraft.
Quite right that these aircraft allow for extreme precision, but it comes only after a fair amount of practice as it requires the pilot to dial in their muscle memory because aerodynamic center has almost no associated feel (breakout force), and these aircraft respond so fast that using visual cues is not going to allow for fast enough reactions. Mastering something like a max rate four point hesitation roll in the Extra will be much harder than the same maneuver in the Pitts. The Extra makes the maneuver less physically demanding, but it's harder to do with the same standard of precision for a pilot new to the airplane without progressive stick force increases with G loading, and without a tangible aerodynamic center.

[quote="congo"Personally since I have trim wheels on my JS I dont have a preference for any particular solution I am just adding food for thought.
As do I, and this gives us something like option C. . .which I think is a reasonable compromise, and apparently so do you as you don't seem to be having trouble with a shifted axis and the associated issues.


Eco,

I agree with all you said just pointing out that extremely light stick forces do not translate into dangerous uncontrollable aircraft. Yes most will over control the first time they get their hands on something like a Extra or even a Jet Ranger for that matter. BTW is that your S2 in the background? Nice looking bird!
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#29 congo

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Posted 25 August 2009 - 00:10

but it comes only after a fair amount of practice

Thats true of all things in aviation. Watch a new mechanic safety wire and then watch someone who has done it for thirty years or so. Watch a first solo approach and land and then watch someone with beacoup hours. Sullenbergers landing on the Hudson is a perfect example of practice and training coming into play at a most critical time.
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#30 NickM

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Posted 25 August 2009 - 06:24

In fact there is illusion which should be gotten rid of. Joystick curved response will only make bad things to happen. Remember that straight attitude position is not constant, it changes with speed and power setting, in other words straight attitude position is floating. How will you apply the curves? Normally people like to soften response at the center and then gradually increase it for greater deflection angles, however because of floating straight attitude position your softened joystick response zone will coincide with it only at certain speed and/or power, so at in any other speed and/or power your softened response zone will be shifted from straight attitude position and this is where bad things begin.

OK - agreed that stick sensitivity curves are going too be difficult or impossible to apply for elevator. Of course, that still leaves a question as to where it is best to place the elevator for the neutral stick position. The current model we have that, e.g., places the SE5a elevator strongly deflected upwards at (spring) centred stick is, IMO, not a good compromise because it means the player experiences flight characteristics (strong hands-off pitch up at anything above modest speeds) that the real aircraft did not have. In fact, with the SE5a, the real pilot also had trim, which is unaccountably missing from our SE5a.

More importantly, this is only a problem with elevator control. There is no reason why we should not have response curves for rudder and aileron. In order to aim the guns, rudder control is usually vital. At the moment, the nose often ends up oscillating in yaw because of the linear scaling of input means the player cannot produce the equivalent of the real pilot's gentle pressure on the rudder. This makes aiming with twist rudders much harder than it needs to be.

I will think about it more, but today I think the best solution is to set "PC stick centred" to correspond to the elevator position at normal cruise, to have response curves for rudder (and aileron) and to give aircraft trim if they had it in real life. It's perplexing to me that the game has gone to such lengths to consider stick responses, but ommitted something as basic as trim from aircraft that had it in real life.

I suppose I come back to my original point - we should be trying to capture the flavour of these aircraft's handling, rather than trying to reproduce control surface deflections for a given stick movement.

Fascinating problem, anyway, and I am very impressed that An. has taken the time to discuss it at length.

Cheers,

Nick
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#31 J2_squid

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Posted 25 August 2009 - 08:58

I don't mind the current system, I think it could be improved but i can live with it.

What worries me a little bit is the system getting changed by popular demand to something i don't get on with.

Agreed, As I mentioned I dont notice the forward inputs anymore. Ive a feeling that there is no easy solution, if we change things we will just have to learn to fly again.

A trim option for all aircraft, if provided should be selectable from the difficulty options and not default for all the aircraft. That way we can pick and choose as our preference. I would expect that the "full real" servers will enforce the original flight model though.

If a plane has trim in real life (SE5a) then all the better. Im happy given An's explination that ROF is doing what its ment to (Give us the most realistic FM possible).

Just my 10p
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#32 congo

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Posted 25 August 2009 - 12:44

BTW, this example show us that pilot mostly "feels" the plane through control column forces, not through control column deflection angles.

An,

This is quite an interesting statement as there is no mechanical linkage between the stick and the control surfaces. Anything the pilot feels is artificially induced. What the pilot actually feels is G loading on his derriere.

Congo.
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#33 An.Petrovich

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Posted 25 August 2009 - 14:32

As you have shown, there simply is no good solution for simulating control of an aircraft using a spring-centred joystick. It just cannot be done. So rather than try to do it anyway and force players to live with the very odd results, why not just accept the limitations and use a stick-response model that is designed to capture the "essential feel" of the aircraft within these limitations?

A good example of this is the way the stick is used in IL-2. As I understand it (please correct me if I am wrong), the full deflection is (supposedly) set to correspond to a force applied to the stick of 50 lbs, rather than assuming a direct mechanical linkage to the controls.

Hi NickM,
Thank you for your post!
Of course, I was thinking about this type of control. But I found there some mistakes, wich make the control unnatural. I offer everybody here to discuss this matter and find disadvantages for this type of control yourself. :) And I'll certainly take part into discussion if it need.

BTW, in RoF you can see limitation of movement control stick from the force neutral at high airspeed. So, there is a combination of "direct mechanical linkage" control mode (for normal airspeed) and "force control" mode (for high airspeed).
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#34 An.Petrovich

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Posted 25 August 2009 - 14:53

congo,

Please, re-check the first post in this thread, and re-watch the first picture (I've edited it) for clear understanding the fact 1.2.
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#35 awreaper

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Posted 25 August 2009 - 16:35

My question would be why is this such an issue in ROF while other flight sims do not suffer from this? I know this flight model is new but I do not believe it is so far advanced from say FSX. I fired up FSX with your DR1 model. At neutral stick the elevators are neutral. I would think it would always be best to have the control surfaces at neutral with neutral stick and then deflect as necessary up and down. To me this is like having your car steering wheel offset 45 degrees so that you have to have the wheel turned to go straight.
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#36 congo

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Posted 25 August 2009 - 16:50

congo,

Please, re-check the first post in this thread, and re-watch the first picture (I've edited it) for clear understanding the fact 1.2.

An,

That is not very clear as your measurement of the throw of the joystick is measured in a different area than the throw of the aircraft control. Measure at the exact point on each and you will see they are close to the same.

Congo
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#37 congo

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Posted 25 August 2009 - 16:54

There is only a slight variation in the range of these two control devices on just has a longer arm than the other. You are trying to show the great difference in thes two input devices by using two different standards of measurement when in essence their angular travel is almost identical. Thats why my original staement about inches of travel leads to erroneous assumptions. The longer arm of an aircraft control stick is to locate it between the pilots legs where it should be and to slightly lessen the forces the pilot will feel because of the added momment.

Attached Files


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#38 congo

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  • Posts: 98

Posted 25 August 2009 - 18:25

An.

Just one example of how an aircraft can have a neutral stick position and asymetrical movement on the elevator where neutral stick translates to neutral elevator.

Attached Files


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#39 Tanner

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Posted 25 August 2009 - 19:16

Right, thanks for that. That's what I was thinking as well. So my question is still, "How is it implemented on the actual planes?" That's what I want. I don't care if I have to hold the stick forward if that is what the real pilots actually had to do.
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#40 An.Petrovich

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Posted 25 August 2009 - 20:18

You are trying to show the great difference in thes two input devices by using two different standards of measurement

Congo, this "different standards of measurement" (handle travel in millimeters) is using by professional air-engineers, btw. ;) I had been working for Sukhoi Design Bureau for some years and I am intimately familiar with this matter, trust me. :)

And I'm not trying to show the great difference in these two input devices. I'm trying to show the great difference in precision of your feeling the stick position (on your hands). If you need to increase the AoA of 1° - you have to move your hand of 10 millimeters, or 1 millimeter (f.e.) - what way is better for precision AoA control?

If you are sure there is no difference - try to control the aeroplane accurately with a stick, the size of a small male pin (match, vesta, etc.) ;)
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