aircraft cant hold speed

A

American398

Guest
hello everyone, i have a really weird issue with FS9, and it seems to happen with all my aircraft, Opensky(Now FreeSky Project), SGA/FFX, Project Airbus...ect, all freeware. for some reason, if i turn the aircraft in either direction the plane will have a tendency to either speed way up or slow way down, so for example im flying at mach .79 and i have a fairly sharp turn over a waypoint, the aircraft will go from .79 to like .81 for higher, or it will slow down to like .77 or even lower, so when it needs to throttle up it goes down, when it needs to throttle down it goes up, also im using the IAS hold, so its not like im flying manually and im just not doing anything lol. If anyone has a solution or something i could try, let me know, thanks.
 
FS9's autopilot/autothrottle code isn't the greatest in the world to begin with. Also, if you're flying above 18-20,000', it may help to switch over to Mach hold.
 
Also, its programmed into the airfiles for having things like induced drag when in turns, etc. The coding for FS will naturally speed you up in a turn, like a slingshot, but I believe it should be the other way around, slowing you a bit as you are going slightly sideways (very slightly) adding more area for the air to go around, which should add drag, slowing you down.

Just something that is built into FS that you have to kind of just deal with..



Bill
 
when i am flying level the speed is fine, its just when i start turning the throttles will go crazy, here is a video, now when i did this turn the throttles went way down and i lost speed like crazy, sometimes it will go the opposite way. this video isnt great quality, you will have to go full screen to see whats happening, but on the left side you can see what the speed is doing.

http://www.youtube.com/watch?v=SBDLcVmfri8
 
First off it appears you do have altitude hold and airspeed hold turned on, just noting it, which is fine.

From the video it looked like the plane behaved normally during the turn in that it slowed a little as the plane began to increase bank for the level flight turn.

In a level turn, keeping altitude, the wing lift has to be increased. Added wing lift increases drag. As your plane turned it did demonstrate that airspeed was slightly lost due to the increased lift/drag, and airspeed was regained as your plane transitioned back to wings level flight.

What was puzzling is that it appeared as if the throttle call was working backwards from what should have been called for. As the plane went into the turn the wing lift/drag increased for the level turn, the throttles should have increased slightly to compensate for the added lift/drag induced by the turn.

As the plane came out of the turn, the throttles should have slightly backed off as wing lift/drag began deminishing in the transition back to wings level flight which would offer an increase on speed due to the reduction of lift/drag, and then followed by a slight increase of throttle to hold airspeed.

It appeared throttles worked backwards. I wouldn't worry about it if your throttles work fine manually. Also the slight variation of your airspeed into tun and out of turn didn't appear very abnormal either even though you had "Hold Airspeed" turned on. I thought I did see your throttles were at full power before the turn was initiated. It may simply be that as the autopilot called for the turn that the plane needed to reduce the speed for the turn to reduce over stressing the aircrafts design manuevering speeds.

Try the same setup but at about 80% intial throttle settings and see if you come up with different results with the airspeed/throttle reactions.
 
but the strange thing is, this doesn't happen in FSX, i understand that the aircraft may have to adjust power but there is no reason it should go 30kts overspeed or 30kts or even more underspeed.
 
This got me curious enough to dig the SGA DC-10-30F out of the boneyard (where all my tubeliners, Greyhound buses and semi's reside).

Out of PANC to FL290 and then let it stabilize - m0.80 at about 75% weight. Initiated a 135* turn and sure enough.. power comes up..up.. altitude stays close to preset but speed increases to m0.84 -- repeat and it goes the other way.. power drops and speed reduces to m0.77 until on course. Pondering... so I turn OFF Real World Weather. Four test later the needles (hey its old and analog) are still glued to the preset speed, altitude and power only shifts about 2%N1 at the beginning of the turn...

I think we're on to something Orlie! Back to real world wx (wind 323/62) and yep... the same wild swings of speed/power.

Conclusion: 1) it's not messed-up airplanes. 2) it's not sleepy pilots. 3) it's just that the poor autopilot can't interpolate the wind effects nor can it anticipate well enough to smoothly transition through headwinds/crosswinds/tailwinds while in a speed/altitude mode in FS9

Have some compassion.. it's only one part of a $50 simulator.
 
srgalahad said:
This got me curious enough to dig the SGA DC-10-30F out of the boneyard (where all my tubeliners, Greyhound buses and semi's reside).

Out of PANC to FL290 and then let it stabilize - m0.80 at about 75% weight. Initiated a 135* turn and sure enough.. power comes up..up.. altitude stays close to preset but speed increases to m0.84 -- repeat and it goes the other way.. power drops and speed reduces to m0.77 until on course. Pondering... so I turn OFF Real World Weather. Four test later the needles (hey its old and analog) are still glued to the preset speed, altitude and power only shifts about 2%N1 at the beginning of the turn...

I think we're on to something Orlie! Back to real world wx (wind 323/62) and yep... the same wild swings of speed/power.

Conclusion: 1) it's not messed-up airplanes. 2) it's not sleepy pilots. 3) it's just that the poor autopilot can't interpolate the wind effects nor can it anticipate well enough to smoothly transition through headwinds/crosswinds/tailwinds while in a speed/altitude mode in FS9

Have some compassion.. it's only one part of a $50 simulator.
Click to expand...

you described your problem the exact same way as it happens in my sim, turn real world weather off and its perfect.
 
In this case, what's happening is related to momentum. I've even seen it happen without making a turn at all. I can be flying along nicely at a fast cruise, then hit a stronger headwind and sudently my overspeed warning is screaming at me. My plane isn't moving any faster, but the air moving past it is. Since airspeed is relative to air movement, it's something you can't get away from without turning off all weather.
 
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