Autopilot oscillation in Alt Hold mode

[Canders]

Whenever I engage A/P alt hold mode, the stab trim wheel oscillates back and forth a few degrees as it flies along. Is there a way to fix this?


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[alan CXA651]

Hi.
It should not be oscillating , but you failed to give full details , which auto pilot are you using sperry or default , what was your alt and aircraft weight , these all play a part in this problem , also what was your weather.
regards alan.

[mallcott]

As Alan suggests, wholly insufficient information for a troubleshoot.

Please either modify the original post or supply it below.

Note: It is entirely normal for the trim wheel to move as the the aircraft responds with gust alleviation and weather changes en route. It should actually be doing that with almost all aircraft in whatever sim you're flying.

Question: Why do you think it shouldn't, or is it simply that it's in your field of view and you've never noticed it before?

[Canders]

I am using the Sperry. I am cruising at 25000 ft. There are no wind gusts. This happens every time I'm in straight and level flight. I can sit there and watch the VVI go up and down +/- 200 feet. Two seconds down, then 2 seconds up. Other A2A planes I have, 172,182, T-6 don't oscillate.


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[mallcott]

I am using the Sperry. I am cruising at 25000 ft. There are no wind gusts. This happens every time I'm in straight and level flight. I can sit there and watch the VVI go up and down +/- 200 feet. Two seconds down, then 2 seconds up. Other A2A planes I have, 172,182, T-6 don't oscillate.


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And the rest of the information?

[alan CXA651]

Hi.
The connies max alt is 25000ft so it is a big ask to stay in level flight if heavy loads on the aircraft , you still failed to state the aircraft loads at the time , if aircraft at or near max loads you need to do step climbs, ie burn a lot of fuel of before you reach 25000ft , also the sperry is a very crude autopilot that needs constant trim and course corrections during flights to correct for weight and balance changes as fuel burns off and course correction for drift , also the slightest turbulance will need pilot input to correct for any alt pitch changes , i suspect you was to heavy for the alt you where flying at , this sounds like a newbie pilot error and not an aircraft fault.
regards alan.

[Canders]

Actually it does it at all weights. And I've been flying MSFS since version 2.0 so don't insult my intelligence, please. I have thousands of hours in everything from a Cessna 172 to a PMDG 747 and 777, so I have just a little experience under my belt!
So, if you want to simply say that the Sperry has a hard time, even in smooth air and all altitudes, I'll accept that.
I have enough info now to answer my question so thank you.


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[Lewis - A2A]

Hello,

whats your weather and frames during this?

Also remember previous sim experience isn't a factor with the next sim, from one to another.

thanks,
Lewis

[Canders]

Hello,

whats your weather and frames during this?

Also remember previous sim experience isn't a factor with the next sim, from one to another.

thanks,
Lewis

Hey Lewis
Weather is varying, I'm in clear air, light winds. I guess I'm trying to fly too high, FL250 and it's porposing, just like any plane will do when it's too high for its weight. I was just wondering because it's was even doing it with medium and light fuel loads.


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[Lewis - A2A]

Yes unless next to no load 25k is very high indeed for an 049 connie.

thanks,
Lewis

[AKar]

As a side question,

Note: It is entirely normal for the trim wheel to move as the the aircraft responds with gust alleviation and weather changes en route. It should actually be doing that with almost all aircraft in whatever sim you're flying.

Question: Why do you think it shouldn't, or is it simply that it's in your field of view and you've never noticed it before?

Did the original Sperry III unit actually trim the airplane? Up until recent years, auto-trim functions were relatively uncommon, except in airplanes of higher Mach numbers and all-moving trimmable horizontal stabilizers.

-Esa

[Lufthansa 380]

Does the Connie really have an alt hold mode? Could swear it's just pitch hold.

[alan CXA651]

Hi.
The standard autopilot that comes with the connie has alt hold which does a slight oscillation at max alt , but to get the sperry to hold alt , the aircraft needs to be trimmed to fly the chosen level , with a slight variation as you trim up or down , as fuel is burned , but slightest wind or turbulance or balance change , will upset its alt trim setting , so constant input required to maintain alt.
regards alan.

[Lufthansa 380]

Hi.
The standard autopilot that comes with the connie has alt hold which does a slight oscillation at max alt , but to get the sperry to hold alt , the aircraft needs to be trimmed to fly the chosen level , with a slight variation as you trim up or down , as fuel is burned , but slightest wind or turbulance or balance change , will upset its alt trim setting , so constant input required to maintain alt.
regards alan.

So in essence it doesn't have alt hold.