Aircraft pitch decrease under FbW

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Opossum
Posts: 50
Joined: 23 Jul 2016, 22:33

Aircraft pitch decrease under FbW

Post by Opossum »

Hi All,

When I am flying under normal laws, without the autopilot engaged, with weather providing, even slight turbulence, I am experiencing a decreasing aircraft pitch.

This phenomenon occurs with, of course, under Active Sky for P3DV4. It is true that the turbulence produced by this software are quite strong. However, I have experienced this behavior without AS for P3DV4. Try this:

Do not start AS and fly with the P3D inbuilt weather theme “Building Storms”. Do not forget to check the P3D weather option: “Enable turbulence and thermal effects on vehicle”. Take off, fly around 2000-3000 ft, 250 kts, gears up (sorry, I wrote "gears down" before editing my post and correct this mistake :roll: ), no flaps, no autopilot.

Now, take a look at the speed tape on the PFD, the aircraft speed must varying slightly due to smooth turbulence provided by this weather theme. Use your stick to fly straight ahead, no turn so no bank, vertical speed = 0. Release the stick and take care how the aircraft pitch on PFD decreases slightly. Your vertical speed must become negative and also decreasing continuously.

Obviously, the FbW is not able to maintain a constant pitch of the aircraft when it flies through turbulence, even slight and smooth ones.

If anyone could try this short test and let me know if the same issue about the aircraft pitch occurs ? It would be a real pleasure to use the A320 FbW without autopilot and without pitch issue to perform some airport approach.

Thanks for your answers.

Best regards

P3DV4.4, ProsimA320 V1.20 used with simconnect, FSUIPC 5.15
Last edited by Opossum on 05 Mar 2019, 15:32, edited 1 time in total.
Pim
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Location: Heemstede, The Netherlands
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Re: Aircraft pitch decrease under FbW

Post by Pim »

Hi,

I just tried to duplicate your problem and here is what I see. I took off at the prescribed conditions. I tried it both at 2000 and 3000 ft and with gear up and down. I see the speed tape move +- 3 or so knots. What I see is that the plane has a tendency to sink, but very very slowly. For example when I do a pitch up of 300 ft/min then it takes about 5 minutes for the plane to be at zero pitch up. Does that match what you are experiencing?

Best regards,

--pim
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Opossum
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Joined: 23 Jul 2016, 22:33

Re: Aircraft pitch decrease under FbW

Post by Opossum »

Hi Pim,

Thank You for your answer. What are your ZFW and GW during your experiment ? Thanks to you, I have discovered that this issue depends on aircraft weight. From my side, I have the following results:

full aircraft:
ZFW = 56.8t ; GW = 70.3t ; CG = 23.1 : time from +300 ft/min to 0 ft/min = 40 s

average aircraft load:
ZFW = 52.9t ; GW = 62.2t ; cg = 24.4 : time from +300 ft/min to 0 ft/min = 1 min 50 s

light aircraft:
ZFW = 50.0t ; GW = 55.6t ; CG = 23.5 : time from +300 ft/min to 0 ft/min = 10 min 40 s

If you have completed the experiment with a lighter aircraft, could you try again with a more loaded aircraft ?

Thanks again
Pim
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Joined: 01 Jan 2011, 13:39
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Re: Aircraft pitch decrease under FbW

Post by Pim »

Hi,

The ZFW was 57.1, the GW was 64 and the CG was 25.1. I will try later to redo the experiment with a fully loaded plane. What I see from your figures is that when the plane is heavy the FbW does not assert enough thrust (and pitch) to keep the plane level.

Best regards,

--pim
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andthiel
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Location: Essen - EDLE

Re: Aircraft pitch decrease under FbW

Post by andthiel »

I don‘t have any experience with the A320. But did you think about the fact that the drag caused by „gears down“ might be the reason for this (rather normal) performance of the aircraft under the given conditions?

Just my thoughts.

Cheers, Andreas
Beechboy Andreas


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Opossum
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Joined: 23 Jul 2016, 22:33

Re: Aircraft pitch decrease under FbW

Post by Opossum »

I Andreas,

I am so sorry, it is a mistake from myself, in my first post, I must wrote "gear up" not "gear down".

I edit my post to correct this mistake.
riddler
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Joined: 19 Sep 2018, 02:30

Re: Aircraft pitch decrease under FbW

Post by riddler »

Hi Opossum,

Can you share your Fbw setting in the IOS. Also are you using a "lighter" or "real stick" in hardware settings.

Will try to reproduce your scenario and will let you know.

Thanks


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Pim
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Location: Heemstede, The Netherlands
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Re: Aircraft pitch decrease under FbW

Post by Pim »

Hi All,

Interesting conversation. I think that if the stick is in the neutral position then the flight computers should keep the plane level if it was level before. Also gear up/down should not matter.
I tried the scenario with a fully loaded plane: ZFW 58.1 t, 16.9 t fuel and CG 21.9. From 300 ft/min up it takes about 10 seconds to go level. So indeed the heavier the plane, the faster it sinks.

Best regards.

--pim
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Opossum
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Joined: 23 Jul 2016, 22:33

Re: Aircraft pitch decrease under FbW

Post by Opossum »

Hi Pim,

Thank You Pim, I am feeling less alone now. Maybe other A320 Prosim users have also observed this issue. So, other accounts are welcome. As a reminder, the decreasing pitch is effective under turbulence, even lighter ones.

I have detected this behavior since the ProsimA320 V1.06. On the changelog of this version, It could be read :

"- Fixed pitch stability issue causing slight pitch up in normal law"

Yes, before the V1.06, the issue was, in contrast to the following versions, an increasing pitch. Maybe, this could bring a clue for developers.

Best regards
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Opossum
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Joined: 23 Jul 2016, 22:33

Re: Aircraft pitch decrease under FbW

Post by Opossum »

riddler wrote: 06 Mar 2019, 15:04 Hi Opossum,

Can you share your Fbw setting in the IOS. Also are you using a "lighter" or "real stick" in hardware settings.

Will try to reproduce your scenario and will let you know.

Thanks


Sent from my iPhone using Tapatalk
Hi Riddler,

I use the lighter stick with default FbW settings in IOS (now, I feel they are well tuned). Lighter and real stick would not be taken into account when stick is on his neutral position (it is just a dynamic scale factor applied on stick generated values).

Looking forward to know your results to the suggested stability test.
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