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Groovin_DC-10

What Causes Autothrottle Hunting?

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I notice this with quite a few of my FS9 add ons.

I can eliminate this by editing the Fuel Flow Gain in the aircraft cfg from say... 0.002 to 0.6, but the downside is the engines respond extremely quick to changes on the throttle when I'm controlling it manually.

A small price to pay to eliminate the problem and something I can live with since my autothrottle hunting problems only seem to happen with some "lite" airplanes.

I'm still curious if anybody know what causes this issue?

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Hi,

Could you explain what is 'Autothrottel Hunting' ?

Sorry, but my English is not so good...

Thank you,

Bernard.

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Basically, it's caused by an unstable PID control loop.  The response characteristics of the engine to throttle inputs (i.e. delay, spool-up rate) are just a few of the factors that determine how well the PID controller (in this case the A/T) corrects a signal error, and are among the very few you can fiddle with short of changing the programming and parameterization of the feedback loop.

 

Clear as mud?

 

Regards

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Do you guys just learn to live with it, or do you edit the fuel flow gain?

 

 

Hi,
Could you explain what is 'Autothrottel Hunting' ?
Sorry, but my English is not so good...
Thank you,
Bernard.

 

It happens when you engage a/t.  If you set the speed to 250, for example, the a/t has a hard time keeping this speed.  It will constantly move up and down and if you check your speed, it will keep jumping like 251, then 250, 248, 250, and so on.  The a/t won't stabilize. 


Basically, it's caused by an unstable PID control loop.  The response characteristics of the engine to throttle inputs (i.e. delay, spool-up rate) are just a few of the factors that determine how well the PID controller (in this case the A/T) corrects a signal error, and are among the very few you can fiddle with short of changing the programming and parameterization of the feedback loop.

 

Clear as mud?

 

Regards

 

Thanks.  I'm afraid to mess with the other stuff, so I just keep it simple and edit the one line I mentioned.  It's not a big deal for me because it happens on the "lite" add ons and after I edit the cfg, it's gone.

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I don't recall having this problem with any of the jets, but it almost always occurs when I add the autothrottle to a turboprop aircraft.  I don't know how many "real" turboprops have A/T, but mine seem to like it just fine.

 

The solution that works for me is to edit the aircraft.cfg file.  Go to the [autopilot] section and locate max_throttle_rate.  This value is always set to 0.10 by default.  Start by cutting this value in half to 0.05 or less.  Then set up a flight test and experiment until you're satisfied with the result.  Each time you change the value, exit the sim, edit the .cfg file then restart the sim.

 

Let us know if this helps.

 

Regards,

JerryH

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Man, that brings back memories of yrs gone past. Never did find a solution and have never seen it in FSX. i always blamed it on the FDE in some freeware aircraft because it was rare, if ever in payware FS2004 aircraft. Tried all the "internet" fixes. maybe its surface icing trying to simulate. :)

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I don't recall having this problem with any of the jets, but it almost always occurs when I add the autothrottle to a turboprop aircraft.  I don't know how many "real" turboprops have A/T, but mine seem to like it just fine.

 

The solution that works for me is to edit the aircraft.cfg file.  Go to the [autopilot] section and locate max_throttle_rate.  This value is always set to 0.10 by default.  Start by cutting this value in half to 0.05 or less.  Then set up a flight test and experiment until you're satisfied with the result.  Each time you change the value, exit the sim, edit the .cfg file then restart the sim.

 

Let us know if this helps.

 

Regards,

JerryH

 

Hi Jerry,

Is there any downside to lowering the max throttle rate?  At the moment I'm adjusting fuel flow gain, and to get to the point where a/t hunting is minimized/eliminated, the engines react very fast to manual throttle adjustment.  This is due to the much higher fuel flow gain value.

 

Man, that brings back memories of yrs gone past. Never did find a solution and have never seen it in FSX. i always blamed it on the FDE in some freeware aircraft because it was rare, if ever in payware FS2004 aircraft. Tried all the "internet" fixes. maybe its surface icing trying to simulate. :)

 

You're right.  I've never seen this in FSX.  The add ons I own which have a/t hunting are made for both FS9 and FSX.  They perform perfectly when installed in FSX, but a/t hunting happens when installed in FS9.  Weird.

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Hi Jerry,
Is there any downside to lowering the max throttle rate? At the moment I'm adjusting fuel flow gain, and to get to the point where a/t hunting is minimized/eliminated, the engines react very fast to manual throttle adjustment. This is due to the much higher fuel flow gain value.

 

I haven't noticed any downside to lowering max_throttle_rate when applied to turboprops.  But, you can't hurt anything by trying it.  Just backup your original aircraft.cfg file (including the original value for fuel flow gain), then hack away at the max throttle rate and see what happens.

 

Is it true that you're concerned about jets rather than turboprops?

 

Regards,

JerryH

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I haven't noticed any downside to lowering max_throttle_rate when applied to turboprops.  But, you can't hurt anything by trying it.  Just backup your original aircraft.cfg file (including the original value for fuel flow gain), then hack away at the max throttle rate and see what happens.

 

Is it true that you're concerned about jets rather than turboprops?

 

Regards,

JerryH

 

I'll restore my original fuel flow gain value and try adjusting the max throttle rate. 

Yup, I fly jets 99% of the time.

 

Thanks again.

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Basically, it's caused by an unstable PID control loop.  The response characteristics of the engine to throttle inputs (i.e. delay, spool-up rate) are just a few of the factors that determine how well the PID controller (in this case the A/T) corrects a signal error, and are among the very few you can fiddle with short of changing the programming and parameterization of the feedback loop.

 

Clear as mud?

 

Regards

 

Bingo. In all honesty this is what separates the true engineers from people just trying to willy-nilly program stuff in FS. You have to write algorithms that smooth the PID controllers that command the AP channels, the A/T etc or it's going to be a jerky mess that doesn't look anything like the real life system you're trying to simulate. There's a reason the guy who does this for us here has an engineering degree and not specifically one in programming/computer science. Knowing *what* to code is far more important for stuff like this than knowing *how* to code.

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Bingo. In all honesty this is what separates the true engineers from people just trying to willy-nilly program stuff in FS. You have to write algorithms that smooth the PID controllers that command the AP channels, the A/T etc or it's going to be a jerky mess that doesn't look anything like the real life system you're trying to simulate. There's a reason the guy who does this for us here has an engineering degree and not specifically one in programming/computer science. Knowing *what* to code is far more important for stuff like this than knowing *how* to code.

 

Is there differences between FS9 and FSX when it comes to a/t programming?

Thing is, I would get a/t hunting in FS9, but the same add on won't have that problem in FSX.

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To what extent do autopilot pitch modes and autothrottle modes interfere with eachother?

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