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Curves in Real Planes/Jets


hassata

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You dont need a "real" pilot to understand that. It is quiete simple.

 

Even though different real aircrafts process the joystick inputs dependend on different values (it is not worth going into detail here, becuase question is "curves" ingame and believe me it would explode the topic), a ingame curve-option is mostly based on the fact allowing to balance different joystick inputs, basically a custom choice to counterbalance device properties etc etc.

 

If you wanted it realistic, the game would just recognize the joystick inputs from 0-100 linear (your pure movement) and process it according to the airframe characteristics, its input processing grid and pure flightphysics according flightsituation (like old Falcon, and it doesn´t matter in respect if fly-by-wire or not), but there is no sim in my knowing not failing in accomplishing this - i mean the PC sims.

In other words, NO, curves are just play-options, with the addition, that not one to me know sim (including this one) has not flaws, allowing to exploid your crafts performance (i gave it a shot, still the same problem like older sims have).....but this again, is another story, not worth being digged up in common interest me believes.

 

Valid question, but i would advise addressing this question directly to the makers of this (or other) sim.

 

cheers and happy x-mas

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I fly a PA-28-181 pretty regularly and can say that all control inputs are completely linear.. though there are definitely levels of deflection that you would never normally exceed, but that's a different story.

 

As the poster above me accurately described, curves are primarily designed to aid in translating large ranges of control inputs onto much smaller deflection areas (such as replicating a car's steering wheel on X-axis of an Xbox controller's analog stick.)

 

For that matter, though I could be wrong on larger aircraft (my only experience is in singles), a curve on an aircraft's control input would be generally disorienting and impractical, as it would limit accuracy by removing consistency across the input. Imagine a car's steering wheel with a section that's more or less sensitive, beyond the fact that control inputs in a car or plane do scale in intensity based on the physics of any given situation, though that (again) is an entirely separate discussion altogether.

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Depends on the aircraft. If the control surfaces that are linked to controls with cables and pulleys, the "curve" would be linear, but the effectiveness would be dependent on the airspeed. Imagine if you're flying at 100 kts and you move the stick left a certain amount, it takes a certain amount of force and it moves the left aileron up and the right aileron down a certain amount that gives you a specific roll rate. Now if you're going 300 kts, that same amount of input with move the control surfaces the same amount as before, but aerodynamically, the lift (rolling) force generated would be greater (9 times greater assuming conditions are the same as before) and the force required to move the stick would be greater also. So the only difference you would notice would be more force required to move the stick, and more sensitivity at higher airspeeds.

 

If you introduce a computer controlled/assisted system, the computer can have any type of curve desired. This can be done in many ways, but with a typical fly-by-wire system there is a curve of some sort built in and the system will see what the pilot "asks for" and will move the control surfaces to do that. In doing this, if the pilot wants a roll rate of X° per second at 100 kts, he/she moves the stick a specific amount, then if they want that same roll rate at 400 kts, he/she moves the stick that same amount, but the computer will decide how much control surface to actually use to get that same roll rate. That way the pilot doesn't have to think too hard...

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Agreed... I fly Pipers, Cessna 150, 152, 172, 177, and a lovely Citabria. Completely linear control feel. I would add that the "feel" is the magic word. In sims without the "feel" part is where a curved control axis assists. When making very small flight corrections in real world it's more of a pressure than movement applied to the yoke/stick. A very small, 10-20 percent, curve on axis helps simulate this IMHO.

 

P.S. I have screwed around in some multi's and larger a/c like King Air's before and had the same opinion.

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There are fighters that have a control schedule - while just about any FBW fighter will have that, one fighter that has no FBW but has a control schedule is the F-15. At least IIRC, the control movement is scheduled such that for x amount of travel on the stick you will get y g's out of it, so if half stick gives you 5g, it will always give you 5g (as long as the aircraft is not too slow for it).

 

More complex schedules are available for FBW aircraft, such us for example an F-22 commanding max g over 300kt, and max pitch under it, or something of the sort.

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That's really helpful-thanks guys. The curve issue was messing me up because I was looking at it the wrong way (that is, curve to better simulate reality as opposed to curve to deal with controller and sim shortcomings). Since A10 isn't FBW and doesn't have a control schedule, and since I have an accurate controller, then no dead zone and no curve is the way to go.

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That's really helpful-thanks guys. The curve issue was messing me up because I was looking at it the wrong way (that is, curve to better simulate reality as opposed to curve to deal with controller and sim shortcomings). Since A10 isn't FBW and doesn't have a control schedule, and since I have an accurate controller, then no dead zone and no curve is the way to go.

 

This really isnt the way to go, necessarily...

 

Your joystick has a radius of movement of less than a few inches...

 

The radius for the REAL A-10's joystick is what like a foot or so?

 

Your joystick has a MUCH smaller range of motion than the real thing, therefor each input your provide will have a MUCH greater effect on the aircraft than it would in the real thing. Keep that in mind.

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I fly a PA-28-181 pretty regularly and can say that all control inputs are completely linear.. though there are definitely levels of deflection that you would never normally exceed, but that's a different story.

 

Depends on the aircraft. If the control surfaces that are linked to controls with cables and pulleys, the "curve" would be linear, but the effectiveness would be dependent on the airspeed.

 

I'm prepared to be proven wrong, but my understanding is that the relationship between control response vs control deflection is represented by a parabolic, not linear curve.

 

However, because the relationship between control deflection and force required is also parabolic, the end result is a linear feeling. There is obviously no dead zone either.

 

In a real aircraft the transition from moving the controls through the centre from left to right, for example, is smooth which you won't have if you set the control response to linear in DCS.

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I'm prepared to be proven wrong, but my understanding is that the relationship between control response vs control deflection is represented by a parabolic, not linear curve.

 

However, because the relationship between control deflection and force required is also parabolic, the end result is a linear feeling. There is obviously no dead zone either.

 

In a real aircraft the transition from moving the controls through the centre from left to right, for example, is smooth which you won't have if you set the control response to linear in DCS.

 

 

This is for small aircraft only:

 

Think about it as a flow from the control input (stick/yoke) to the control surface. You move the stick, which pulls one end of a cable that is strung through the aircraft and the other end is directly attached to the control surface. So if you move the stick 2 inches to the left, it pulls 2 inches of cable through the system, and moves the control surface 2 inches. If you pull 4 inches, it pulls 4 inches of cable and moves the control surface 4 inches. These are just random numbers I pulled, real values depend on a particular aircraft design, but you get the idea?

 

Get some string and try it yourself, if you pull on one end of the string, the other end moves the exact same amount. You can't pull the string 1 inch and have the other end move 1 inch, then pull the same exact string another 2 inches and have the other end move 4 more inches. To do this, you would need a complicated system of pulleys and cams and whatnot, which all adds a lot of weight to an aircraft, which is a big no-no in aircraft design.

 

Higher performance and larger aircraft use assisted control systems and since they usually have a little more power available, they may have mechanical systems that allow them to have a curved response.

 

Here's a good page that discusses this, with a cool picture of a portion of an F-15's flight control linkages: http://2.bp.blogspot.com/_WX4wJ_9qjS0/TMBbv0J9TTI/AAAAAAAAAGs/q7y_L8ejCKY/s1600/F-15_Lateral_Control-1.jpg


Edited by Mobius1_MWI
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Think about it as a flow from the control input (stick/yoke) to the control surface. You move the stick, which pulls one end of a cable that is strung through the aircraft and the other end is directly attached to the control surface. So if you move the stick 2 inches to the left, it pulls 2 inches of cable through the system, and moves the control surface 2 inches. If you pull 4 inches, it pulls 4 inches of cable and moves the control surface 4 inches. These are just random numbers I pulled, real values depend on a particular aircraft design, but you get the idea?

 

Get some string and try it yourself, if you pull on one end of the string, the other end moves the exact same amount. You can't pull the string 1 inch and have the other end move 1 inch, then pull the same exact string another 2 inches and have the other end move 4 more inches. To do this, you would need a complicated system of pulleys and cams and whatnot, which all adds a lot of weight to an aircraft, which is a big no-no in aircraft design.

 

You can have all kinds of funny shaped bellcranks and pulleys that give the control surface whatever range is required by the designers. Quite often you will find an aileron goes down further than it goes up, using the same amount of stick input.

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You can have all kinds of funny shaped bellcranks and pulleys that give the control surface whatever range is required by the designers. Quite often you will find an aileron goes down further than it goes up, using the same amount of stick input.

 

+1

 

I've flown about 20 types of glider/light aircraft and this is correct. I've also worked on various control mixers and they most definitely have non-linear results (by design).

 

As robmlufc said, you often get asymmetric aileron deflection. Typically the upwards deflecting aileron deflects more because that increases the drag on the downwards rolling wing, reducing adverse yaw. Also the upwards deflecting aileron's leading edge often protrudes into the airflow (by careful placement of the hinge point) to further increase drag.

 

For a given (downward) aileron deflection there will be a force generated. The resultant lift is likely to be a square function relative to airspeed. The upwards deflecting aileron will have a different amount of negative lift (that is a very, very gross approximation), and the magnitude of that will vary by its own function. The combination of the two will generate roll. And that will be non-linear relative to airspeed, and also stick deflection.

 

It complex enough that getting a linear relationship to anything at all would be very unlikely, or a designer genius.

 

There can also be dead zones in a control circuit, depending on the design. A 20ft push rod is going to expand and contract with temperature (which might go from +60degC sitting on the ground to -40degC at 45,000ft). So there must be some play in the system to take that into account.

 

I immediately changed my curves in pitch and roll (to around +15 from memory) because it didnt "feel" right with my Cougar. Slight movements of the stick should result is slow roll and pitch rates. Still tweaking though.

 

Brad

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You can have all kinds of funny shaped bellcranks and pulleys that give the control surface whatever range is required by the designers. Quite often you will find an aileron goes down further than it goes up, using the same amount of stick input.

I agree with that, it's a matter whether there's a parabolic (or otherwise) curve built in.

 

I've flown Cessnas, Pipers, and a Yak-52 and they are all mechanically actuated and all have seemingly linear responses through the full range of controls in flight.

 

The only experience I have in anything else is several hours in an F-16 sim and that is definitely not a linear control curve.

 

EDIT: Just realized I'm on my other account. I had to register the other one, "Mobuis1_MWI" to get access to the beta forum. Sorry for any confusion.


Edited by Mobius1

Stupid thermals...

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I realize its all subjective, but what are you guys inputting for curves in DCS? RL pilots with WHs, especially.

I would say use whatever you feel comfortable with. It's one of those things that you can't exactly replicate with the WH because the stick throws are different between it and the actual jet. I'm not at my computer right now so I can't see the values, but I have it set to the low-mid range of curvature so I have fairly precise control with larger stick movements towards the center, then large control movements out to the outside since the only time you would throw the stick to the limiters would be when you really need all the performance you can get.

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Stupid thermals...

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I realize its all subjective, but what are you guys inputting for curves in DCS? RL pilots with WHs, especially.

 

I don't have a WH stick (yet), but on my X52 I have a slight curvature set to aid precision in the lower end of the deflection spectrum. IRL I always have so much more travel on the stick than with a simulator stick that a linear linkage is no problem for precision, but I find that to get the same level of control on a sim stick I want a bit of curvature. 15-20 I think is where I have it set.

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They still are no joke tho. :P

Been meaning to try out some paragliding sometime. Have a friend that does it with a motored backpack, and if you get one that runs on regular 95 Octane you could go cross-country and refuel at regular gas stations... :D

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They still are no joke tho. :P

Been meaning to try out some paragliding sometime. Have a friend that does it with a motored backpack, and if you get one that runs on regular 95 Octane you could go cross-country and refuel at regular gas stations... :D

 

I have never flown a paramotor, I dont like motorized paragliding. It should pure be flying with sun's cheap energy:)

 

For paramotors, going cross country is not a big issue. Because of the engine type, you have to mix some lubricant to gasoline. You can carry some lubricants within your backpack, land near a gas station, fill up and keep flying.

 

The world record for paramotors is I guess around 1.300km or something...

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I realize its all subjective, but what are you guys inputting for curves in DCS? RL pilots with WHs, especially.

 

I'm not RL pilot but I do pay attention to as realistic as possible attitude. After experimenting I found TM WH X/Y (roll/pitch) curvatures to set at 15/15 (no deadzones) and Saitek Rudder Pro curvature set to 25 (2 deadzone due to loss of precision) and toe brakes to user curvature/inverted (otherwise You encounter partly blocked wheel brakes problems, not with user curvature though). These settings allows precise flight control (Note: TM WH has to be fixed/corrected first to get rid off 'bump' movements and x/y shafts plays!) as well as good feeling while performing evasive/max performance limits mvr.

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