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News: The latest PSX update (version 10.54 from 7 November 2018) is available at: http://aerowinx.com/board/index.php?topic=4191.0

Author Topic: Return to Centre During a Turn  (Read 358 times)

Raj Hoonjan

  • Join date: Sep 2010
  • Location: UK
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Return to Centre During a Turn
« on: Sat, 10 Nov 2018 14:38 »
Hi Hardy

Hope all is well with you.

Even after all these years of using PSX, I am always marvelled by the accuracy and complexity of what you have produced.

This was validated a couple of days ago when I had the opportunity to use a level-d 744 sim.  The numbers were right on the mark and I was able to fly the sim with a greater degree of confidence.  Thanks to you and all the contributors, it made for a very satisfying experience.

I did make a 'small' observation though, which I have experienced previously in other sim sessions too.

When banking the 744 in the air, PSX has a slow tendency to return to centre (with and without USB flight controls attached).  The level-d sim does not exhibit this behaviour and instead maintains the bank angle.

Just wanted to clarify what the correct behaviour is during a turn.

Thank you again and look forward to the next instalment of updates to PSX.

Cheers
Raj

Hardy Heinlin

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Re: Return to Centre During a Turn
« Reply #1 on: Sat, 10 Nov 2018 15:07 »
Hi Raj,

the 747 wings obviously incorporate a dihedral angle for roll stability.

Quote
The level-d sim does not exhibit this behaviour and instead maintains the bank angle.

Maintains the bank angle ... forever? Or just for a longer time? (It can't maintain it forever on its own without any fly-by-wire computer, which the 744 doesn't have, as we know.)


Regards,

|-|ardy
« Last edit: Sat, 10 Nov 2018 16:19 by Hardy Heinlin »

Raj Hoonjan

  • Join date: Sep 2010
  • Location: UK
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Re: Return to Centre During a Turn
« Reply #2 on: Sat, 10 Nov 2018 22:21 »
Hi Hardy,

Thank you for responding.


Maintains the bank angle ... forever? Or just for a longer time? (It can't maintain it forever on its own without any fly-by-wire computer, which the 744 doesn't have, as we know.)


Can't say for sure if the bank angle remains static forever but we did a turn for about 15-20 seconds, perhaps longer, level at 1700' and I noticed that the bank angle remained at 20 degrees.  From what I observed, I was only adjusting the pitch. If the aircraft is expected to return to centre, then perhaps it is at a slower rate.

Happy to confirm with the instructor in my company for further details.

Wondering if anyone else here has experienced the same behaviour in a sim or the real aircraft?

Cheers
Raj

United744

  • Join date: Oct 2014
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Re: Return to Centre During a Turn
« Reply #3 on: Sun, 11 Nov 2018 01:28 »
Were the ailerons definitely returned to center after the turn was established?

Dihedral demands the aircraft rolls back to wings-level with ailerons centered.

Hardy Heinlin

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Re: Return to Centre During a Turn
« Reply #4 on: Sun, 11 Nov 2018 01:56 »
And no foot on the rudder pedals?

Raj Hoonjan

  • Join date: Sep 2010
  • Location: UK
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Re: Return to Centre During a Turn
« Reply #5 on: Sun, 11 Nov 2018 13:15 »
Hi,

Were the ailerons definitely returned to center after the turn was established?


Aileron was centred after turn was established.

And no foot on the rudder pedals?

My feet were definitely not on the rudder pedals during the turn. 

I just found it interesting that I did not have to continually apply aileron to maintain the bank angle.  So perhaps the return too centre rate is slower.  Sorry I cannot be precise at the moment.

I really hope I'm not sending you on a wild goose chase here.

Kind regards
Raj

acannata

  • Join date: Dec 2011
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Re: Return to Centre During a Turn
« Reply #6 on: Sun, 11 Nov 2018 21:11 »
In Handling the big jets Davies says about 747 Classic: "Spiral stability is good at low speeds at low altitudes... a bit weaker but still positive in the cruise". Therefore, at least on the Classic, the 747 seems to have a tendency to decrease bank angle on ailerons release.

Aldo

Markus Vitzethum

  • Join date: May 2009
  • Location: Reutlingen, Germany (near EDDS)
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Re: Return to Centre During a Turn
« Reply #7 on: Sun, 11 Nov 2018 23:42 »
Interesting discussion.

I just remembered that I discussed the same issue with Stefan Keller last year, however more with respect to the 747-8i and X-Plane. Anyhow, in Lufthansa's 747-8i Level-D-Sim in Frankfurt, I specifically flew a turn to check the tendency to return to level flight from a turn.

I just quote from my email last year:

"This is one item I actually tried in the full flight sim - during a traffic pattern I banked to 30 degrees and let go off the controls and the aircraft practically kept the bank angle - the roll moment towards wing level was hardly noticeable."

and

"(I also checked with Aerowinx PSX and think that the roll moment there [better than X-Plane] matches the Lufthansa sim.)"

So, my conclusion of flying PSX directly after flying the 747-8i sim was that PSX behaves very similar to the Level-D sim when it comes to the tendency to roll the wings back to level flight (at a slow rate, that is).

Markus

Hardy Heinlin

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Re: Return to Centre During a Turn
« Reply #8 on: Mon, 12 Nov 2018 00:22 »
Raj and Markus,

I just realized you both wrote that you centered the ailerons when the bank was set and you also released the elevator -- at least Markus did it (you too, Raj?).

When you are trimmed in level flight and you start banking, without simultaneously pulling on the elevator, you will start descending. The greater the bank angle, the greater the sinkrate. The greater the bank angle, the greater the elevator effect on the turn rate. At 80° bank, the turn rate is almost solely controlled by the elevator. When you push the elevator at steep bank angles, you can even achieve a turn rate opposite to the bank direction.

In a normal turn there is a side slip component. The dihedral effect (which generates the restoring roll moment opposite to the pilot's roll input) becomes effective when there is a side slip, i.e. when the aircraft moves sideways away from the straight track (which happens in a turn). During a left side slip, the left wing of the V-shaped wing pair has a greater AOA than the other wing, and therefore the left wing gets more lift.

Now if you release the elevator, your turn rate will decrease. The turn rate may even become zero when pushing the elevator further. When the turn rate decreases, the side slip component decreases as well, and the dihedral effect decreases too.

So it's essential to know whether you tested this stuff with the elevator released, or the elevator pulled (to maintain the altitude).


|-|ardy
« Last edit: Mon, 12 Nov 2018 01:25 by Hardy Heinlin »

Raj Hoonjan

  • Join date: Sep 2010
  • Location: UK
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Re: Return to Centre During a Turn
« Reply #9 on: Thu, 15 Nov 2018 17:36 »
Hi Hardy,

Sorry for the late response.

So it's essential to know whether you tested this stuff with the elevator released, or the elevator pulled (to maintain the altitude).

I do remember adjusting the pitch during the turn but to be honest I cannot remember if there was a difference between the elevator released or the elevator pulled.  Really sorry.  I will ask around when I'm back in the office next week.

Thanks
Raj