FSX Autopilot Porpoising When Time Accelerated

[RJP]

Hi all!

Well after recently re-installing FSX after a l-o-n-g break I also re-installed FSX 'Acceleration'.

I've now got a problem with the autopilot on numerous aircraft (inc default), porpoising when the autopilot is engaged with altitude hold selected. The problem only becomes apparent when the sim-rate is accelerated above 4x. I can be completely stable, at an appropriate level altitude and speed, set sim-rate to 4x and there's no issue, set it to any more than 4x and the ac starts porpoising over a range of +/- 1000'.

Altitudes / speeds / loads have been appropriate and I'm sure aren't the cause (& if they were I'd see the same thing at lower sim rates, only slower).

A session of googling it has come up with -lots- of people with the same issue, unfortunately though no solutions.

Does anyone know what causes the issue or, more importantly, what can be done to fix it please?

I'm currently en-route Sydney - Jo'burg (5,948nm) & at 4x I'm loosing patience

Cheers!
Richard

[TSR2]

default behaviour from what I know of it. Its the same as when an aircraft on AP goes to make a turn to the right, it starts to turn to the left first and visa versa. The porposing isn't help with higher speeds, which exaggerate it even more

[Garry Russell]

Yep a known issue

TBH 4x or any acceleration is not accurate so you can't really expect it to behave correctly.


As Ben mentions there is the reverse initial turn before the real turn bites...just one of those things.

[RJP]

Thanks, wondered if it was just 'one of those things' Didn't get it before installing FSX Acceleration so might revert to standard fsx.

Realism...... Hmm, unfortunately the realisms of real life prevent me from spending 14 1/2 hrs in front of the pc lol

Cheers
Richard

[Garry Russell]

Yah...I realise that mate...but it's never going to be A1 in acceleration.

[Tako_Kichi]

My opinion is that the 'porpoising' is due to changes in atmospheric pressure over time which is exaggerated by the time acceleration. As you travel over your route the air pressure changes which gives you a false reading on the altimeter. Normally you would hit the 'B' key periodically which would reset the altimeter's Kholsman setting to the correct pressure and the autopilot would correct the aircraft's vertical position accordingly. You don't get a chance to do that in accelerated mode but if it get's too far out of kilter the sim will adjust it for you which I believe is what happens when the aircraft seems to dive and climb for no apparent reason. It's simply reacting to the changes in air pressure but the compressed time makes it appear more violent and excessive than it would normally be in real time terms.

As to using the accelerated time function to shorten long flights there is a much better way to do it especially if you are following a flight plan or have the destination programmed into the GPS as a 'direct to' point (i.e. you are following the pink line).

Once you are established at your cruise altitude and speed and want to rapidly move down the course simply open up the 'map' view from the top menu (World/Map) and drag your aircraft icon down the line to the point where you want to start flying again, then click the <OK> button. Your aircraft will re-position itself at the selected point and you can continue your flight from there. No more porpoising, no more sitting around waiting for the world to pass under you at an exaggerated rate, just a smooth transition from Point A to Point B. Bliss!

[rohan]

... but presumably this method does not consume fuel, oil, etc. equivalent to the distance moved ? ? ?

Thanks in advance for any clarification,
regards,
Ro

[RJP]

Yah...I realise that mate...but it's never going to be A1 in acceleration.

A2 would be great, well, even 6/10 'Could try harder' would be ok

My opinion is that the 'porpoising' is due to changes in atmospheric pressure over time which is exaggerated by the time acceleration. As you travel over your route the air pressure changes which gives you a false reading on the altimeter. Normally you would hit the 'B' key periodically which would reset the altimeter's Kholsman setting to the correct pressure and the autopilot would correct the aircraft's vertical position accordingly. You don't get a chance to do that in accelerated mode but if it get's too far out of kilter the sim will adjust it for you which I believe is what happens when the aircraft seems to dive and climb for no apparent reason. It's simply reacting to the changes in air pressure but the compressed time makes it appear more violent and excessive than it would normally be in real time terms.

Hmmm, I hadn't thought of that..... Gotta admit I'm not sure it's the case, mainly because the porpoising is very rhythmic, i.e. the timing and altitude variations remain constant (up - down - up - down, as opposed to a random up - up - down - up - down - down - down - up etc), I'd have thought that with pressure changes it would be more variable? Certainly something to look into though.

When I have a bit more time I'll try to work out which ac it happens with & any that it doesnt & try to find any common differences between those it happens with & those it doesn't.

Mucho thanks gents!!

Cheers
Rich

[J0hn]

I had seen it the same way as Tako_Kichi - and also only noticed it after installing Accel (sure it wasn't there with just SP2) - my problem is that all my long flights are in Air Hauler, and slewing is disabled (it just puts your aircraft straight back to where you started from - not that I've tried it myself), so I just either put up with it or reduce the data on whichever aircraft I import to make their maximum range considerably less than it should be.

Then the routes it gives me are considerably shorter

I never use over 16x these days anyway - and max 4x in Air Hauler with the shorter 'hops', unless it's for testing fuel consumption or such-like.

[Tako_Kichi]

... but presumably this method does not consume fuel, oil, etc. equivalent to the distance moved ? ? ?

Thanks in advance for any clarification,

Correct, no fuel is used so it's no use if you are flying for a VA where you have to buy fuel.