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tkyler

Why artificial stability in the flightmodel is OK

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I've recently been doing some tweaking to some flight models I'm working on and I let a few folks "try" these flight models before I tweaked them.  I asked them to "yank and bank" the models and tell me what they thought.   All of them stalled the aircraft aggressively at some point while doing "high-G" turns causing the aircraft to flip over and dive.   I would casually ask, "does this feel real" and they all said no....no surprise there, I was setting them up anyhow.    I routinely go on an on about the disconnect between humans and computer hardware on a desktop flight sim and how it changes what your brain thinks is happening.  In this case, with no real G-forces and no backforce on the joysticks, the user gets no sensory resistance that they can associate with the aircraft configuration, limits and performance.  For example, say a guy jumps in a real plane and starts pulling 7 Gs.  The plane is capable of 9, but he's at the limit of his forearm muscles and G-force tolerance and just "can't go anymore".  In his mind, he's yanked the stick "all the way back agains the stops" as far as he can....his "muscle stop".  With a joystick, this doesn't exist...you just keep on yanking back until the aircrat stalls and it just doesn't feel right when the plane flips over...you expect to stay in your hard banking turn.

 

So on some of these planes I put in a tiny bit of artificial stability based on angle of attack.   Purists might say, "the real plane doesn't have these stability control mechansims and therefore should not be in the flight model  whereas I contend that your brain and body is a "stability control" system in its own right under real forces (that are not in the flight model either) that cause you to manage the  controls based on what your body is feeling, but without that in a desktop sim, you can substitute your physiological sensory feedback mechanism with x-plane's artificial stability mechanism to arrive at a happy medium on what your brain is thinking you should be experiencing.  By going this route,  one can view usage of x-plane's artificial stability as  not  "faking" a system that an aircraft does not have but rather compensating for a system that a desktop simulator does not have....flight physiology.   Every sim gives up something and its OK to step outside the box a bit to get a user closer to what they want out of the sim.  With x-plane, at the least it is within the reach of the everyman to tweak.

 

TomK

Laminar

 

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What about the planes form airbus that are controled by a joystick as well. Do these real planes have some sort of artificial stability mechanism to overcome the lack of force?

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Whatever it takes. IMO, artificial stability is fine with artificial flight. Not sure how stability works in XPlane. But as an example, in regards to joystick forces........put flaps down in a Cessna high wing; nose rises, push on yoke. Nose doesn't level enough , so push some more. Now there is a sense of airload on the flight surfaces if the siim didn't allow the nose to exactly correspond with the yoke movement. Same goes for ailerons.

 

BTW.......just yanking and banking at 3 Gs, and you'll feel it. 4 Gs and it could bother your stomach & head if you're not use to it. In this case, some built in delay to the aircrafts reactions, wouldn't hurt. It's done with r/c too. More stick is required to get the response.

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I've recently been doing some tweaking to some flight models I'm working on and I let a few folks "try" these flight models before I tweaked them.  I asked them to "yank and bank" the models and tell me what they thought.   All of them stalled the aircraft aggressively at some point while doing "high-G" turns causing the aircraft to flip over and dive.   I would casually ask, "does this feel real" and they all said no....no surprise there, I was setting them up anyhow.    I routinely go on an on about the disconnect between humans and computer hardware on a desktop flight sim and how it changes what your brain thinks is happening.  In this case, with no real G-forces and no backforce on the joysticks, the user gets no sensory resistance that they can associate with the aircraft configuration, limits and performance.  For example, say a guy jumps in a real plane and starts pulling 7 Gs.  The plane is capable of 9, but he's at the limit of his forearm muscles and G-force tolerance and just "can't go anymore".  In his mind, he's yanked the stick "all the way back agains the stops" as far as he can....his "muscle stop".  With a joystick, this doesn't exist...you just keep on yanking back until the aircrat stalls and it just doesn't feel right when the plane flips over...you expect to stay in your hard banking turn.

 

So on some of these planes I put in a tiny bit of artificial stability based on angle of attack.   Purists might say, "the real plane doesn't have these stability control mechansims and therefore should not be in the flight model  whereas I contend that your brain and body is a "stability control" system in its own right under real forces (that are not in the flight model either) that cause you to manage the  controls based on what your body is feeling, but without that in a desktop sim, you can substitute your physiological sensory feedback mechanism with x-plane's artificial stability mechanism to arrive at a happy medium on what your brain is thinking you should be experiencing.  By going this route,  one can view usage of x-plane's artificial stability as  not  "faking" a system that an aircraft does not have but rather compensating for a system that a desktop simulator does not have....flight physiology.   Every sim gives up something and its OK to step outside the box a bit to get a user closer to what they want out of the sim.  With x-plane, at the least it is within the reach of the everyman to tweak.

 

TomK

Laminar

Tom-if you are responsible for the recent added stability to the fm all I can say is Thank You!!!

 

For me it is like night and day, and has enabled me to move to xplane as my favorite sim. The feeling of being in the air is still there that xplane always excelled at but now there is the stability which allows this to be used as an excellent ifr trainer and flown with extreme precision  which is important for me.

 

I have been surprised there has not been more of a scuttle butt about this-to me it is like night and day , immediately apparent, and a huge improvement.

 

There are still a few things-I am not sure if it is instrument or fm related but for instance the ball in the turn coordinator doesn't seem to react in expected ways-for instance raise the nose as in a chandelle-the ball stays centered.

 

I for one am so grateful for these changes though, and now am a confirmed (maybe reconfirmed)  xplaner-hopefully permanently.

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I agree with Tom.  Also, the recent edits to some of the default prop aircraft that I mentioned on a former post had to do with control phase-out and custom RoGs. I do not even consider these as "artificial stability" modifications. None of the aircraft were edited in the Art Stab tab of plane maker.

 

Adding control phase-out is the way X-Plane10 offers to somehow model the effect of hinge forces, and this is perfectly acceptable for me :-)

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What about the planes form airbus that are controled by a joystick as well. Do these real planes have some sort of artificial stability mechanism to overcome the lack of force?

The "normal" and "alternate" flightcontrol laws on the Airbus aircraft have plenty of "artificial stability" built in. Deflecting the sidestick (don´t call it joystick, they hate that!) commands a certain "roll rate" or "vertical g-load". That way the response of the flightcontrol surfaces will be totally different for a given sidestick deflection at different airspeeds, but the plane will react fairly similiar at both high and low speeds. It will also (somewhat) automatically counter turbulence and configuration changes. A common joke is a phrase from the airbus manual "there is no ballooning on the airbus aircraft" (speak that with a french accent!), but in the real plane the flightcontrol computers are not fast enough to really avoid the balloon as you go from config 1 (slats only) to config 2 (slats plus second step of flaps).

 

A problem is the lack of force-feedback on these sidesticks. You can move them to the stops with easy, and since the control surfaces need a second or so to actually displace to the commanded roll-rate, it is easy to "overcontrol", since you initially miss the response that you would expect from a "full left" deflection...

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