Low speed fore/aft oscilations

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Dreamsofwings
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Low speed fore/aft oscilations

Post Dreamsofwings »

Not sure if I am going mad here, and maybe I have just never noticed it before, but in last week or so I have noticed an oscillation that causes the aircraft to rock , possibly around the COG, when it is flying slowly eg on approach. It means that when coming in the nose is constantly rising and dipping, even with the stick held in the same position. To get a better idea please see the video below. It's more noticeable in exterior view.
Now this probably isn't a bug with the aircraft but is there anything else that might cause it. seems the same regardless of weather and I have wake turbulence off in ASP4.
Or has it always been part of the flight model and I have never noticed??….now that would be worrying :wink:
(apologies for the subscribe button...its a feature that youtube adds on anything I upload....I'm not trying to be cheap and fish for subs!!)

https://www.youtube.com/watch?v=DV8TTyz ... e=youtu.be
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Nick - A2A
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Re: Low speed fore/aft oscilations

Post Nick - A2A »

Hi Rob,

Please can you just check out the info in this topic and see if it's any help in alleviating this effect? There seems to be some weird behaviour tied in with the momentum effects that's been introduced with the most recent version of P3Dv4.

Thanks,
Nick
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Dreamsofwings
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Re: Low speed fore/aft oscilations

Post Dreamsofwings »

Hi Nick,

As ever thanks so much for such a speedy reply. The response times here on the A2A forum are incredible given that some other developers take over a week or just make like an ostrich!
Yes I had tried that in the hope it might help but no effect on it. The oscillation really kicks in when the flaps are lowered and if a bit of power is applied to adjust descent rate for example.
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Nick - A2A
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Re: Low speed fore/aft oscilations

Post Nick - A2A »

Okay, thanks Rob,

Give me a day or two and I'll see if I can systematically reproduce anything like this. Are you using ChasePlane or EZdok here by the way? Also, could you give a rough indication of the frame rate you're seeing in P3D?

Cheers,
Nick
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Dreamsofwings
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Re: Low speed fore/aft oscilations

Post Dreamsofwings »

Cheers Nick.
Using Chaseplane here.
FPS locked at 30 and getting close to that.
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Nick - A2A
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Re: Low speed fore/aft oscilations

Post Nick - A2A »

Okay, cheers! ChasePlane installed here too, so will see if I can reproduce the effect in your video.

Nick
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Dreamsofwings
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Re: Low speed fore/aft oscilations

Post Dreamsofwings »

Much appreciated Nick
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Jacques
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Re: Low speed fore/aft oscilations

Post Jacques »

Hi Rob and Nick,

To add more to the mix, I don’t have Chaseplane installed and noticed the same sort of oscillation at low speed a few days ago. I attributed it at the time to low airspeed and an impending stall. If I can, I’ll load up again today (not sure when I’m able to do so) and see what happens. Rob’s video describes what I saw, but I’d like to fly the profile again just to be certain.

-Edit- I can reproduce this by putting prop full fine and reducing throttle to the gear warning lever (or just above).

Pitch up a bit to bleed speed to just above the stall.

Lower the nose to the horizon and slowly add power

Oscillatiins begin around 105-110 MPH indicated

The rudder swings back and forth as seen from outside and by the gauge inside

You can observe it here for a while as the Spit slowly descends at ~500fpm.

Lower the nose slightly and throttle up again and it disappears around 140 mph.

Internally, while this “wiggle” is occuring, the engine sound is steady. Outside, it revs up and down in time with the “wiggle”.
Last edited by Jacques on 13 Aug 2019, 15:22, edited 1 time in total.

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Dreamsofwings
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Re: Low speed fore/aft oscilations

Post Dreamsofwings »

Thanks Jacques, at least I know I am not going mad!
have just flown without Active Sky etc running and still seeing it.
Might not be a bug, maybe just something from recent update that I've not noticed before and some pre-stall state.
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Nick - A2A
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Re: Low speed fore/aft oscilations

Post Nick - A2A »

Hello chaps,

Well, I got round to testing this with my installation, and I was able to reproduce a slightly odd pulsating effect at high power settings and low airspeed.

Initially I tested in P3Dv4.5 with ChasePlane, then I did a clean reinstall of P3D to revert back to stock P3Dv4.3, and the effect is still there. With the latter (i.e. non ChasePlane) setup it becomes much more noticeable if "visualize momentum effects" is ticked in the realism options, but the effect is still present with this option unticked.

We'll investigate this further as soon as possible. I agree that the issue may be related to a pre-stall engine torque effect, as it only becomes noticeable at slow speed and with a fairly high power settings. For example, if you're in a draggy configuration such as on approach and get a bit low and slow.

Of course, spend too long flying around like this and the coolant will start boiling off anyway. :mrgreen:

Thanks,
Nick
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Dreamsofwings
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Re: Low speed fore/aft oscilations

Post Dreamsofwings »

Hi Nick,

Many thanks for taking a look! Yay I am not going mad!

I find in mine that the oscillation is introduced even with a relatively modest power input, just a minor correction to arrest descent rate for example.

However I think we may have hit on something here.....get onto the marketing dept.

Accu-deck....or perhaps Accu-slam-a-perfectly-serviceable-aircraft-into-a-moving-surface-really-hard-and-fast-and-hope-the-string-stops-us

Yes deck landings! We can't rock the airfield to simulate the swell of the waves but by god we can rock the aircraft. This new feature gives the true gut churning experience of carrier deck landings in a WWII warbird. Marvel as the runway bobs up and down through the windscreen, thrill as you reach for the sickbag whilst holding the flightstick with your teeth, gasp as that perfect three pointer turns into Monty Python's ministry of silly walks.

For extra immersion have a couple of mates ready with buckets of salted ice cold water for when you open the canopy.

Okay I have taken this too far, I know.

If you are still reading this Nick thanks again for your help mate, it is much appreciated.

Cheers,
Rob
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Nick - A2A
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Re: Low speed fore/aft oscilations

Post Nick - A2A »

Hi Rob,

You're welcome. Alas, I don't think it's some secret Seafire code that you've found. Wouldn't something like a Seafire F Mk XV be fun though? Not convinced I'd ever manage to get one back on deck intact to be honest. :oops:

Cheers,
Nick
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Dreamsofwings
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Re: Low speed fore/aft oscilations

Post Dreamsofwings »

Yes what a challenge that would be!!

Many thanks Nick.
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whiic
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Re: Low speed fore/aft oscilations

Post whiic »

I posted this on another thread about the same bug:

The pulsating glitch is also for FSX Spitfire, MarkI and MarkII (although I tested neither with wooden prop). I don't know if it was the latest update that broke it, or the previous one since I took a long pause from flying FSX.

Pulsating happens also above stall speed, up to around even 160mph when wheels are down. When wheels are raised, you can reach stall buffeting and there's zero pulsating nonsense. Also when landing, there's less pulsating than on take-off. Also, it doesn't seem to want to accelerate with wheels down. You need to firewall the throttle lever just to get it above 120mph... before updating, the speed had a tendency to climb rapidly if you leveled off after take-off, reaching speeds too dangerous to keep wheels down, even with modest 0 to +2 psi boost (full fine pitch, MK1). Now it needs +6 and barely gets out of stall buffeting and this weird low-frequency pulsating. And when wheels are up, it behaves like it used to, even cruising nicely at -4 psi boost.

I have a suspicion that the pulsating is an engine power glitch (or propeller efficiency glitch). Engine sounds normal during take off when inside cockpit, no misfire, no fluctuation in sound or rpm gauge. This is because in-cockpit sounds and gauges are created by Accusim and uses their own audio engine. External engine sounds are based on engine power that Accusim tells FSX while audio is played by FSX. And the engine sound fluctuates in external view with the same frequency as pulsating was visible in the cockpit view.

It would appear it has nothing to do with stalling or the flight model, but the modeling of the Merlin engine (or the prop) has broken during one of the later updates (probably the very last one). Power output when wheels are down is low, erratic and pulsating at about 1 Hz frequency. This glitch is such a weird one.

I haven't yet tried other A2A planes on FSX after the newest update, so I cannot tell of more than Spitfire is affected. Non-A2A planes fly normally.

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