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Is there any to tighten up the altitude hold. I realize the plane was not like today's jets, but I'm seldom sure if it's working because it porpoises so much. Anyone know of a code change to adjust this problem. It takes the fun out of flying a plane I love.

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Use the Autopilot that is part of the AC.

Once engaged and you are at your cruise altitude, engage the lever on the right hand side of the Autopilot cluster and the AC continues at your chosen altitude

cheers

Peter

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On 3/12/2020 at 5:57 AM, Winrodgers said:

Is there any to tighten up the altitude hold. I realize the plane was not like today's jets, but I'm seldom sure if it's working because it porpoises so much. Anyone know of a code change to adjust this problem. It takes the fun out of flying a plane I love.

Yes, I've found that that the alt hold porpoises a little too, but possibly not in all areas of the flight regime. Didn't notice any oscillationi until the last couple hundred miles of a long flight (Johannesburg to Manchester), after the final step climb to FL380.

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I'll look at this again.  I made a change to get more realism in another area and the AP porpoising in some conditions is the result.  There is some code to mitigate the behavior, but maybe I could find a better solution.  We'll see. 

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  • 4 weeks later...

Michael

 

I tried two flights - one with WX and one without. Without WX the airplane was rock solid at FL370. The flight with WX saw the oscillations return in ALT hold - if this info is of any help.

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I've made some changes that should bring some improvement -- I'll try to get a new version out soon.  You would think I would have a lot of time available in the current situation but in fact having my kids out of school and trying to manage their online alternative has had the opposite effect.

 

I have never noticed any instability with the altitude hold at cruise -- only during the approach phase when the aircraft is flying at 250 knots or less.  I don't use Active Sky which may be why I'm not seeing the same thing some users are.  For some years I've used Opus for weather. 

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Thanks for your response Michael.

Good luck with your "home schooling" .  Fortunately for me, my children have long left home and married.

The current times are indeed unique and come with challenges.

 

Best wishes

Trevor

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  • 2 weeks later...

I worked IRL as F/E ON DC-8 in SAS and I have not experiensed any problems with oscillation on cruise exept when flying manually....))

 

In P3D sometimes oscillation but was fixed with A/P OFF and retrimming or descent to lower altitude..

 

I attach just for info AFM DC-8-60 VOL 2 page regarding cruise and again JUST FOR INFO...!

 

Item 03 is interesting

 

DC-8.pdf

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  • 2 weeks later...

Thanks AAC47, that's interesting. The flight manual states: 

 

"For all jet aircraft flying at high altitude, the damping of
the long perlod oscillations is rather weak, causing speed
and altitude variations which may result in difficulty in
maintaining an accurate flight path, Although the aircraft
is quite stable under ail flying conditions, the autopilot
and the altitude control should be used for optimum performance."

 

Next time I encounter oscillations in level flight I'll try your technique of going to manual and retrimming. Pretty sure I tried this last time but the oscillations returned after a few seconds upon autopilot re-engagement. They weren't severe movements, about 50-100ft above and below the target. I did consider descending to a lower altitude but on that flight I wanted the better the fuel consumption at the higher flight level so I stuck with it.
 

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I have a new build ready that makes a slight improvement in this. I just need to test it a little more and package it for upload to Aerosoft. 

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  • 4 weeks later...

Hi Michael

A very interesting observation which might help you solve the oscillating problem at CRZ. Just did a flight at FL330, with AS weather, and the plane was rock solid. Then did a step climb to FL370 and the oscillating problem returned. Descended back to FL330 and the plane held the altitude perfectly again. Then went up to FL350, and the plane was rock steady at CRZ. Then went up to FL370, and the problem presented itself again. It appears that at lower altitudes (FL310-FL350) the ALT HOLD is solid but at higher altitudes (FL370-390) the problem appears. Maybe this info can help you find a solution.

On 3/16/2020 at 10:35 AM, znatusch said:

Yes, I've found that that the alt hold porpoises a little too, but possibly not in all areas of the flight regime. Didn't notice any oscillationi until the last couple hundred miles of a long flight (Johannesburg to Manchester), after the final step climb to FL380.

This quoted statement supports what I have found - the problem only appeared at a higher altitude, in this case FL380.

Regards

 

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