FSX Auto pilot problems

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kingsak
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FSX Auto pilot problems

Post by kingsak » 28 May 2009, 23:46

I use FSX and when I set the auto-pilot it (Altitude Hold) the a/c never holds the alt.
Instead, it exceeds the alt. and usuall goes into a stall and I'm from say FL300 down to
FL260 within seconds.
This seems to happen in just about every heavy jet, including the defaults.
AP works as far as following the plan in GPS, on "most" a/c but not all.
I have adjusted the fuel load and the payload weight but without success.
I went from FS98 to FSX and I'm ready to throw FSX away and go back to FS98!
I'm constantly having problems with the a/c doing as I set.
Any advice???
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Re: FSX Auto pilot problems

Post by DMM200 » 29 May 2009, 02:33

To be honest? That's the default FSX for you. If you really want your problems solved, you're going to have to spend some money and get some payware addons.

As for solving your current crisis, can you post a screenshot of this happening?
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Re: FSX Auto pilot problems

Post by RatherBFlyin » 29 May 2009, 02:58

To be perfectly honest, I've never had that kind of trouble with any aircraft in FSX (default or otherwise). Not sure what's causing it.

The only gripes I have with the AP in FSX are that if the AP is in altitude acquisition mode and you change the set altitude, it continues climbing (or descending) at the rate it was at when you made the change instead of going back to the set rate of climb (or descent), and that if you do any navigating by VOR's before switching to GPS, the AP always offsets the GPS course by as much as a mile to one side or the other, turning in to pass a waypoint before turning back out again.

Can you post a few screenshots of your panel? Preferably a thousand feet or so prior to reaching the set altitude, when the aircraft passes the set altitude, and again when the aircraft is near a stall? As for the altitude loss in a stall, a jet aircraft (especially a Heavy) will lose a lot of altitude in a hurry when it is stalled. Definitely not something you want to do at low altitude (as I found out the hard way a long time ago :oops: ).

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Re: FSX Auto pilot problems

Post by crash101 » 31 May 2009, 23:50

I also encountered this very same problem with all my A330 series of planes. I don't know if this will help out but when doing your Pre-flight and engine start up, skip the step where you turn on your "De-Icers" and do not turn them on at all for the entire flight. I forgot this step on 1 of my flights and found that when I engaged the de-icers I went into a stall within 5 mins.......I turned them off and the AP, gained control of the plane and set the Altitude back to FL350.......the rest of the flight went without incident.

I guess when the engines were started the de-icers were automatically turned on and I was turning them off when I thot I was turning them on. Since then, no problems with the A330 series planes.

Seemed to work for me in FS9 and FSX.

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Re: FSX Auto pilot problems

Post by kingsak » 01 Jun 2009, 16:53

I put some screen shots here:
http://onesak.tripod.com/id3.html

The only time it's this bad is when I use the heavies.
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Re: FSX Auto pilot problems

Post by jltope » 02 Jun 2009, 03:30

Hi! I'm probably wrong but it does not appear you have enough thrust engaged for the amount of fuel you have onboard. Do you suffer from this when you use the Auto Thrust and set a speed into the AP?

Most of the time when I use the Auto Thrust my engines are near peak output but I am still trying to adjust that.

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Re: FSX Auto pilot problems

Post by FJ flyer » 02 Jun 2009, 04:03

1. It looks like you need more thrust to keep your speed up.
2. Yes both those lights should be lit (One is the altitude hold and the one on the right is the Autopilot On/Off indictaor)
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Re: FSX Auto pilot problems

Post by RatherBFlyin » 02 Jun 2009, 04:31

I do have a real quick question for you. Why are you not using the auto throttle system? Southwest may not use it on their aircraft, and if that is the case I apologize, but if it is available, then by all means make use of it.

As to your autopilot settings for the climb, they appeared to be set correctly. Your thrust levels were a little low, though. The key when approaching a stall is to immediately apply full power and lower the nose to a level pitch attitude. The aircraft should have enough power to maintain a 1800 fpm climb to at least the high 20's. Tell you what, try setting your autopilot for a climb to FL350, set the engines to full power and leave them there (assuming you have the setting for aircraft damage due to stress turned off), and see at what point the airspeed begins to drop off. Let us know at what altitude the airspeed drops below 250 knots.

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Re: FSX Auto pilot problems

Post by kingsak » 03 Jun 2009, 01:22

Ok, this was better.
Took off 4,000 pounds from payload.
Set for FL350 full throttle and overspeed horn sounded for quite awhile but I ignored.
Finally leveled off @ FL350. At lvl. flt. full throttle N1 was 90.5%. Is that normal?
With A/T on I didn't have any big problems! :D

Added a couple of screenshots here :arrow: http://onesak.tripod.com/id3.html
Thanks 4 advise guys. I need all I can get because I don't want to screw up when flyin' on VatSim.
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Re: FSX Auto pilot problems

Post by RatherBFlyin » 03 Jun 2009, 02:18

The overspeed warning while climbing at full throttle in a 737 is normal. Nothing to be concerned about there (though you wouldn't climb that way on a normal flight).

About 90-95% N1 is normal with the throttle set to full at FL350. This is what I do on a normal climb with a 737: Below 10,000, I set the autothrottle to maintain 250 knots and climb at 2000 fpm. Above 10,000 feet I increase the autothrottle setting to 270 knots. When the airspeed starts to drop towards 250 knots, I lower the climb rate to 1000 fpm. That is usually all it takes to get up to cruising altitude, at which point I switch over to Mach hold (the "C/O" button just below the autothrottle speed setting in case you were not aware of how to make that change) and set my cruise mach speed (typically M.78 in a 737NG).

That procedure is slightly different from what you would do in the real aircraft. In a real 737NG, you would set your desired airspeed and select LVL CHG mode. This tells the autopilot to run the throttles up to maximum thrust and maintain airspeed by adjusting the rate of climb (or descent, but with the engines at idle thrust). In a lightly loaded aircraft, this yields some truly tremendous climb rates (I have seen in excess of 6000 fpm in a 737 simulator). Unfortunately the only way I am aware of getting this functionality in FS is with payware addons, like the PMDG 737's.

Now, a quick question. While you were doing the test climb with the throttles set to maximum thrust, did the aircraft actually stall at FL280? That is still somewhat unusual. Had the speed been dropping off prior to that, or was it a more sudden shift in airspeed?

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Re: FSX Auto pilot problems

Post by kingsak » 03 Jun 2009, 13:58

It did stall but I hit "Z" and got it out of the stall almost immedeiately then I turned the AP back on and was at FL350 without any further problem, except of coarse the overspd. warning, but since I had all crashes off (as it should be on VatSim) it was not a prob. just annoying. :mrgreen:
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Re: FSX Auto pilot problems

Post by RatherBFlyin » 03 Jun 2009, 14:30

Was your speed gradually decreasing as you approached FL280, or did it drop off suddenly and cause the stall?

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Re: FSX Auto pilot problems

Post by Jacob Mobley » 09 Jun 2009, 05:18

I have had so many problems with FSX's autopilot it's not even funny. I think I have a soulution for you. First off never increase the speed more than 250 knots below 11,000 feet. Once you get past 11,000 feet (this is what I do), increase speed to 350 KIAS (I realize that it is too fast to go until transition altuide, but it keeps me from stalling.) As soon as you pass FL180, increase to whatever your cruise speed is (for the default 738, I use 475 KIAS). I know it isin't realistic, but it works for me and it keeps you from stalling.

Also, when you fly with the speed hold on, make sure that your autothrottle arm switch is in the ON position. It will light up green when it is armed. then right below it, you will see two buttons that you can activate. One says N1, and the other says SPEED. Press that button after arming the AP speed hold and the autopilot will fly the desired speed. And make sure you dial in the speed before you activate the speed hold. (believe me, I've seen too many people not know what to do after arming and pressing the SPEED hold button. :D )


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Re: FSX Auto pilot problems

Post by RatherBFlyin » 09 Jun 2009, 13:20

Umm, 475 KIAS is way too fast for cruise speed. A 737NG typically cruises around M.078, which is approximately 270-280 KIAS at FL350. Are you referring to True Air Speed? True air speed is used for performance calculations, but never used by the autopilot, and never displayed on the airspeed tape/gauge. Not even sure the autopilot knows what KTAS is.

If you have your simulator set to display TAS on the airspeed indicator, that's fine. However, I would recommend changing it back to IAS. The reason I say that is because your aircraft will always stall (or overspeed for that matter) at the same IAS, regardless of altitude/temperature/pressure, but it will not always stall at the same TAS. The same applies to speed restrictions for gear/flaps/turbulence penetration, etc.

I am a little curious as to why so many people have been having trouble with the autopilots in FSX, though. The only problem I have run into with it is a problem that existed with the FS9 autopilot, and it's more of an annoyance than anything else.

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Re: FSX Auto pilot problems

Post by Jacob Mobley » 10 Jun 2009, 00:21

="RatherBFlyin"]Umm, 475 KIAS is way too fast for cruise speed. A 737NG typically cruises around M.078, which is approximately 270-280 KIAS at FL350. Are you referring to True Air Speed? True air speed is used for performance calculations, but never used by the autopilot, and never displayed on the airspeed tape/gauge. Not even sure the autopilot knows what KTAS is.

If you have your simulator set to display TAS on the airspeed indicator, that's fine. However, I would recommend changing it back to IAS. The reason I say that is because your aircraft will always stall (or overspeed for that matter) at the same IAS, regardless of altitude/temperature/pressure, but it will not always stall at the same TAS. The same applies to speed restrictions for gear/flaps/turbulence penetration, etc.

I am a little curious as to why so many people have been having trouble with the autopilots in FSX, though. The only problem I have run into with it is a problem that existed with the FS9 autopilot, and it's more of an annoyance than anything else.
Umm, 475 KIAS is way too fast for cruise speed. A 737NG typically cruises around M.078, which is approximately 270-280 KIAS at FL350. Are you referring to True Air Speed? True air speed is used for performance calculations, but never used by the autopilot, and never displayed on the airspeed tape/gauge. Not even sure the autopilot knows what KTAS is.

If you have your simulator set to display TAS on the airspeed indicator, that's fine. However, I would recommend changing it back to IAS. The reason I say that is because your aircraft will always stall (or overspeed for that matter) at the same IAS, regardless of altitude/temperature/pressure, but it will not always stall at the same TAS. The same applies to speed restrictions for gear/flaps/turbulence penetration, etc.

I am a little curious as to why so many people have been having trouble with the autopilots in FSX, though. The only problem I have run into with it is a problem that existed with the FS9 autopilot, and it's more of an annoyance than anything else.

Yeah, I know it might be a little fast, but I dont't usually fly longer than 3 hours with the 737, so I don't have to worry about fuel burn. But I do like to keep my airspeed between 430-475 KIAS when above FL180. It's better than landing heavy because you didn't burn enough and flying for four hours when you are sceduled for 2 :).
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Re: FSX Auto pilot problems

Post by FJ flyer » 10 Jun 2009, 04:05

Yeah, I know it might be a little fast, but I dont't usually fly longer than 3 hours with the 737, so I don't have to worry about fuel burn. But I do like to keep my airspeed between 430-475 KIAS when above FL180. It's better than landing heavy because you didn't burn enough and flying for four hours when you are sceduled for 2 :).
Are you talking about True Air Speed (TAS) or Indicated Air Speed (IAS)?
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Re: FSX Auto pilot problems

Post by RatherBFlyin » 10 Jun 2009, 14:15

It would be impossible to fly a 737 at more than 400 KIAS during cruise, since that would be well above the aircraft's maximum speed (not to mention faster than the speed of sound). Are you positive you are not referring to KTAS? :)

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Re: FSX Auto pilot problems

Post by Jacob Mobley » 11 Jun 2009, 05:13

When I fly, I put 475 into the SPEED hold. If that's KIAS or KTAS, I don't know. That really shows me how unrealistic even Microsoft's own aircraft are if they're faster than the real thing :lol: .
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Re: FSX Auto pilot problems

Post by RatherBFlyin » 11 Jun 2009, 05:16

I am guessing that you have FS set to display KTAS instead of KIAS. Whenever I fly a 737 (default or otherwise) at M.078, the airspeed typically comes in around 270 knots and I almost never have a problem arriving late.

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Re: FSX Auto pilot problems

Post by Jacob Mobley » 11 Jun 2009, 05:19

RatherBFlyin wrote:I am guessing that you have FS set to display KTAS instead of KIAS. Whenever I fly a 737 (default or otherwise) at M.078, the airspeed typically comes in around 270 knots and I almost never have a problem arriving late.
Yeah, I think I have it set to that. I mean, it's not really that big of a deal to me, because all I care about is arriving on time, and not crashing on my approach :mrgreen: .
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