Simviation Forum - Auto throttle speed bug.

Aug 24^th, 2011 at 8:08pm

bgyuk Offline
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Does anyone else ever get the following bug?

I am crusing at assigned height then for no reason my speed will jump 20 or so kts. Like from 330 at 31000ft to 350. It overstesses my aircraft and ruins my FSpassengers ratings. Angry

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Reply #1 - Aug 24^th, 2011 at 8:19pm

DaveSims Offline
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My guess is a shift in wind speed/direction, not your auto throttle. It is an issue when using real world weather, as FS does not smoothly transition differences in winds aloft. You can go from a 40 kt tailwind to a 40 kt headwind instantly (something that does not normally happen in the real world, since it would make for a rather rough ride).

Dave

www.flymcw.com

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Reply #2 - Aug 24^th, 2011 at 9:36pm

Brett_Henderson Offline
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bgyuk wrote on Aug 24^th, 2011 at 8:08pm:

Does anyone else ever get the following bug?

I am crusing at assigned height then for no reason my speed will jump 20 or so kts. Like from 330 at 31000ft to 350. It overstesses my aircraft and ruins my FSpassengers ratings. Angry

davysims, is correct about the FSX abrupt wind-shifts..

But cruising at 330KIAS @ FL310, is part of the problem too.. that's getting real close to Mach 0.9 Shocked

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Reply #3 - Aug 25^th, 2011 at 7:02am

hyperpep111 Offline
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My problem is when I set airspeed hold to 250 KIAS it takes that as ground speed and it means that I have to control the throttle manually and that ruins the experience. Any solutions Sad

Most people think that flying a plane is dangerous, except pilots because they know how easy it is.
Arguing with a pilot is like wrestling with a pig in the mud, after a while you begin to think the pig likes it.

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Reply #4 - Aug 25^th, 2011 at 8:15am

Brett_Henderson Offline
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hyperpep111 wrote on Aug 25^th, 2011 at 7:02am:

My problem is when I set airspeed hold to 250 KIAS it takes that as ground speed and it means that I have to control the throttle manually and that ruins the experience. Any solutions Sad

I don't think there is an autopilot that references ground-speed.. I know for certain there are none in FSX.

If you mean true airspeed, I think the only way to get that to happen in FSX, is to have an autopilot that references what the airspeed indicator shows (as in, you set realism to display true airspeed).. but since there is no reason to have the airspeed indicator show anything but indicated airspeed, it's again, not something I've seen. Or, you can get an autopilot to reference something close to true airspeed, by setting it to reference a Mach number.

As for your problem with auto-throttle.. it depends on the model.. The default jets are pretty simple.. Dial in the airspeed.. make sure you engage the speed-hold.. make sure the autopilot is not set for a Mach reference, and make sure the auto-throttle is armed.

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Reply #5 - Aug 25^th, 2011 at 10:02am

bgyuk Offline
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DaveSims wrote on Aug 24^th, 2011 at 8:19pm:

My guess is a shift in wind speed/direction, not your auto throttle. It is an issue when using real world weather, as FS does not smoothly transition differences in winds aloft. You can go from a 40 kt tailwind to a 40 kt headwind instantly (something that does not normally happen in the real world, since it would make for a rather rough ride).

Yep when i think about it that must be exactly what it is, for it only happens using real world when it is set to update.

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Reply #6 - Aug 25^th, 2011 at 10:05am

bgyuk Offline
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I love YaBB 1G - SP1!

Posts: 19

Brett_Henderson wrote on Aug 24^th, 2011 at 9:36pm:

bgyuk wrote on Aug 24^th, 2011 at 8:08pm:

Does anyone else ever get the following bug?

I am crusing at assigned height then for no reason my speed will jump 20 or so kts. Like from 330 at 31000ft to 350. It overstesses my aircraft and ruins my FSpassengers ratings. Angry

davysims, is correct about the FSX abrupt wind-shifts..

But cruising at 330KIAS @ FL310, is part of the problem too.. that's getting real close to Mach 0.9 Shocked

0.86

which in fairness is only .01 above the normal 0.85 cruise speed of a 747 400. Well according to wiki anyway

.

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Reply #7 - Aug 25^th, 2011 at 10:31am

Brett_Henderson Offline
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bgyuk wrote on Aug 25^th, 2011 at 10:05am:

Brett_Henderson wrote on Aug 24^th, 2011 at 9:36pm:

bgyuk wrote on Aug 24^th, 2011 at 8:08pm:

Does anyone else ever get the following bug?

I am crusing at assigned height then for no reason my speed will jump 20 or so kts. Like from 330 at 31000ft to 350. It overstesses my aircraft and ruins my FSpassengers ratings. Angry

davysims, is correct about the FSX abrupt wind-shifts..

But cruising at 330KIAS @ FL310, is part of the problem too.. that's getting real close to Mach 0.9 Shocked

0.86

which in fairness is only .01 above the normal 0.85 cruise speed of a 747 400. Well according to wiki anyway

.

Ahhh.. 747

that gives you more MACH headroom (a 737 cruise speed is something like 0.74)

I looked at the 747 Wiki page.. Mach 0.85 is for FL350. I don't have time to research the differrence that 4,000' would make, but I'm sure it's more than a couple hundredths of Mach.. which puts cruise speed at 0.83.. and as you demonstrated.. a mere 20knot jump in indicated airspeed, (already at M0.03 over cruise speed) trips the overspeed.. Cool

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Reply #8 - Aug 26^th, 2011 at 6:58pm

Capt.Propwash Offline
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any altitude ABOVE 18,000 (FL180) do not use IAS HOLD. use the MACH HOLD. if you are setting MACH HOLD @ 0.85 @ FL350 try backing it down to mach .80 ONLY WHEN YOU RUN PASSENGERS. I have FSPassengers for FS9 and FSX as well, and for the heavies, I will not set mach above .82 for this very reason. The slightest difference in wind speed/direction will cause it to ABORT the flight due to overstressing the craft. When I fly at a slower mach speed, then I leave room for stress and the flight will not fail.

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