Aircraft keeps rolling....!

[N1125Y 22]

18 hours ago, Janov said:

ok, lets see...

1.) Which aircraft are you flying?

2.) What airspeed and powersetting do you have when you observe the behaviour?

3.) What is your control-response and artificial stability settings (in the joystick menu)?

4.) Do you have buttons/keys set up for trimming aileron/rudder?

Cheers, Jan

 

1.) Which aircraft are you flying?

Stock 172SP

2.) What airspeed and powersetting do you have when you observe the behaviour?

Trying to adhere to the POH as much as possible  http://www.lanierflightcenter.com/wp-content/uploads/172S-POH.pdf

3.) What is your control-response and artificial stability settings (in the joystick menu)?

Never changed this, so, probably, it's set to the default

4.) Do you have buttons/keys set up for trimming aileron/rudder?

Yes for the rudder, No for the ailerons

Reg.

 

Yair

BTW

Don't know if it mean anything but reading the output from the screen seems like all is well,  when applying full forward or back pressure Yoke, numbers goes all the way up to 1.00 & -1.00

same with the roll, the Rudder is a bit off , but I guess it's the wind factor    

[jcomm 5,890]

@N1125Y,

presently in XP11.10 b5, with all of the default prop aircraft, we experience a rolling "tendency" in the same direction that the prop turns ( right for CW props, left for CCW ), that takes place at mid / high power settings, specially at positive angles of attack.

Simply takeoff with the default C172, and start your climb maintaining 76 knot IAS. You'll see that at the power settings required for that your aircraft will tend to roll right, and the ball will be off to the right, asking for right rudder, which if used to coordinate will result in further rolling moment to the right, which is not expected, I believe, in a C172...

Now, you said you were using default joystick settings, and that means Artificial Stability which is by default set at 50% for the 3 axis will be playing it's "tricks"... Since a rw C172 doesn't have it, please care to turn the Art Stab sliders all the way to the left ( NILL ).

Then, the fact that Austin has programmed the effects of airflow over trim surfaces in a more realistic way for the latest 11.10 betas, if trims are set ( fixed trim tabs, because other than pitch trim, a Cessna C172 / C182 can, at most, have rudder trim, but most don't even have that ) then as airspeed / airflow / dynamic pressure build up, the trim tabs which are set by default to counter the left turning tendencies for both the ailerons and rudder, will "start to come alive", and deflect the corresponding control surfaces. I initially though that maybe the values previously used in Plane Maker for this compensation of the left turning tendencies were now overdone, so I edited the default C172 in Plane Maker, turned to 0.000 the aileron and rudder trim tabs, and went doing some test flights...  - the right rolling tendency is still there, even if less pronounced...

Finally, since the prop axis in canted towards the right, most probably like in the real Cessnas too, also to overcome the prop effects and left turning tendencies at higher power settings and AoA, I decide to also ZERO that cant ( making it 0.000 in Plane Maker Engine properties ), and went testing again, but the right rolling tendencies are again still there...

I then decided to make the Cessna prop turn CCW, and checked for the resulting rolling moment, which reversed and becomes left-wise at the same power and AoA, used for a climb at 76 knot IAS.

Austin is now aware of it, and looking at the "problem". I sent him my ACF and test descriptions, which he replicated, and he sent me back a test version of the C172 with a 2d panel that makes testing a lot easier. 

I also told him that the only aircraft I have, and I do not own any other GA prop add-on for XP11, that does not exhibit this right rolling tendency with it's CW rotating prop, at high power settings is the VSkyLabs AA5. This aircraft rolls left at higher power settings and AoA, and if rudder is used to coordinate, "kicking the ball" with the right foot, the aircraft flies wings level, ball centered, as it is supposed to...

So, this new effect can well be due to the way the spiralling / swirling slipstream is seen interfering in the FDM with various lift / drag generation components of the aircraft, and either the problem is in the way the default props are designed, which must be fine tuned to become compatible with this new calculations, or the calculations themselves need adjustment ( ? )

Above all, Austin is working on this and other ( many other ) details of the FDM in XP11, and for me this is THE BEST NEWS I COULD ASK FOR in this cycle of X-Plane, because it means that Austin is really at it, and cooperating with experimented and knowledgeable users ( not me !, but certainly Murmur, MonrtenM, Brettt, Janov ... ) to fine tune XP11's even more sophisticated FDM. 

 

 

 

 

[Janov 2,383]

6 hours ago, N1125Y said:

1.) Which aircraft are you flying?

Stock 172SP

2.) What airspeed and powersetting do you have when you observe the behaviour?

Trying to adhere to the POH as much as possible  http://www.lanierflightcenter.com/wp-content/uploads/172S-POH.pdf

3.) What is your control-response and artificial stability settings (in the joystick menu)?

Never changed this, so, probably, it's set to the default

4.) Do you have buttons/keys set up for trimming aileron/rudder?

Yes for the rudder, No for the ailerons

Reg.

 

Yair

BTW

Don't know if it mean anything but reading the output from the screen seems like all is well,  when applying full forward or back pressure Yoke, numbers goes all the way up to 1.00 & -1.00

same with the roll, the Rudder is a bit off , but I guess it's the wind factor    

Hi,

I just tested the C-172 in X-Plane 11.10 beta 5. This is without "resaving" the aircraft, so the new flight-model changes that came with 11.10 should not be relevant. It is not recommended to save a plane in 11.10 until the author has "fixed" it for the new flightmodel, so if someone advises you to do this - don´t listen. The plane is either optimized (and therefore already "resaved" or it is not optimized, and resaving it would mess it up.

In the default C-172 (unsaved) I need these flight-control deflections to make it fly straight without rolling (remember, 1.0 is full deflection, 0.5 is half deflection, etc.):

Takeoff with full power at ca. 50kts: Rudder right by 0.16 (16% deflection)

Climbout with full power at 70kts: Aileron left by 0.04 (4% deflection)

Level flight with full power at 130kts: Very shallow left input, too small to measure.

Descent with idle power at 90kts: Aileron left by 0.005 (0.5% deflection)

So you can see that if you need "30 degrees of joystick" to keep the plane straight like you said, something isn´t right with your setup.

I invite you to do the same testflight (and setting your artificial stability to zero is good advice, articial stability is like a kids´ bikes training wheels) and post your aileron input needed to keep the plane flying straight.

Cheers, Jan

 

[jcomm 5,890]

Regarding the default C172s, you can open and save them without any problem in XP11.10 b5, as confirmed by Austin himself.

They're ready for the new features, and adapted to it.

Of course, those were also the models I was referring to in my previous message, not 3pds...

Anyway, I always make backups of the original, or use the updater to rebuild their folders if needed.

[strider1 575]

11 hours ago, jcomm said:

@N1125Y,

presently in XP11.10 b5, with all of the default prop aircraft, we experience a rolling "tendency" in the same direction that the prop turns ( right for CW props, left for CCW ), that takes place at mid / high power settings, specially at positive angles of attack.

Simply takeoff with the default C172, and start your climb maintaining 76 knot IAS. You'll see that at the power settings required for that your aircraft will tend to roll right, and the ball will be off to the right, asking for right rudder, which if used to coordinate will result in further rolling moment to the right, which is not expected, I believe, in a C172...

Now, you said you were using default joystick settings, and that means Artificial Stability which is by default set at 50% for the 3 axis will be playing it's "tricks"... Since a rw C172 doesn't have it, please care to turn the Art Stab sliders all the way to the left ( NILL ).

Then, the fact that Austin has programmed the effects of airflow over trim surfaces in a more realistic way for the latest 11.10 betas, if trims are set ( fixed trim tabs, because other than pitch trim, a Cessna C172 / C182 can, at most, have rudder trim, but most don't even have that ) then as airspeed / airflow / dynamic pressure build up, the trim tabs which are set by default to counter the left turning tendencies for both the ailerons and rudder, will "start to come alive", and deflect the corresponding control surfaces. I initially though that maybe the values previously used in Plane Maker for this compensation of the left turning tendencies were now overdone, so I edited the default C172 in Plane Maker, turned to 0.000 the aileron and rudder trim tabs, and went doing some test flights...  - the right rolling tendency is still there, even if less pronounced...

Finally, since the prop axis in canted towards the right, most probably like in the real Cessnas too, also to overcome the prop effects and left turning tendencies at higher power settings and AoA, I decide to also ZERO that cant ( making it 0.000 in Plane Maker Engine properties ), and went testing again, but the right rolling tendencies are again still there...

I then decided to make the Cessna prop turn CCW, and checked for the resulting rolling moment, which reversed and becomes left-wise at the same power and AoA, used for a climb at 76 knot IAS.

Austin is now aware of it, and looking at the "problem". I sent him my ACF and test descriptions, which he replicated, and he sent me back a test version of the C172 with a 2d panel that makes testing a lot easier. 

I also told him that the only aircraft I have, and I do not own any other GA prop add-on for XP11, that does not exhibit this right rolling tendency with it's CW rotating prop, at high power settings is the VSkyLabs AA5. This aircraft rolls left at higher power settings and AoA, and if rudder is used to coordinate, "kicking the ball" with the right foot, the aircraft flies wings level, ball centered, as it is supposed to...

So, this new effect can well be due to the way the spiralling / swirling slipstream is seen interfering in the FDM with various lift / drag generation components of the aircraft, and either the problem is in the way the default props are designed, which must be fine tuned to become compatible with this new calculations, or the calculations themselves need adjustment ( ? )

Above all, Austin is working on this and other ( many other ) details of the FDM in XP11, and for me this is THE BEST NEWS I COULD ASK FOR in this cycle of X-Plane, because it means that Austin is really at it, and cooperating with experimented and knowledgeable users ( not me !, but certainly Murmur, MonrtenM, Brettt, Janov ... ) to fine tune XP11's even more sophisticated FDM. 

 

 

 

 

"This aircraft rolls left at higher power settings and AoA, and if rudder is used to coordinate, "kicking the ball" with the right foot, the aircraft flies wings level, ball centered, as it is supposed to"     This the way the C172 should fly, I think....

Anyhow, thanks for the update ! Lets us know when Austin sends you a test version of the172 that behaves correctly !!!!

[jcomm 5,890]

I will surely try to update with any new info on this rather interesting subject.

If I just had access, right now, to a RW C172 driver and ask some stuff ....

One thing is for sure - X-Plane is now calculating in even more detail the interaction of the flows with the fuselage and wings, which is Great for a start. If fine tuned, we can end up with a really enriched version of the "props  flight dynamics"...

[N1125Y 22]

On ‎10‎/‎30‎/‎2017 at 7:44 AM, Janov said:

Hi,

I just tested the C-172 in X-Plane 11.10 beta 5. This is without "resaving" the aircraft, so the new flight-model changes that came with 11.10 should not be relevant. It is not recommended to save a plane in 11.10 until the author has "fixed" it for the new flightmodel, so if someone advises you to do this - don´t listen. The plane is either optimized (and therefore already "resaved" or it is not optimized, and resaving it would mess it up.

In the default C-172 (unsaved) I need these flight-control deflections to make it fly straight without rolling (remember, 1.0 is full deflection, 0.5 is half deflection, etc.):

Takeoff with full power at ca. 50kts: Rudder right by 0.16 (16% deflection)

Climbout with full power at 70kts: Aileron left by 0.04 (4% deflection)

Level flight with full power at 130kts: Very shallow left input, too small to measure.

Descent with idle power at 90kts: Aileron left by 0.005 (0.5% deflection)

So you can see that if you need "30 degrees of joystick" to keep the plane straight like you said, something isn´t right with your setup.

I invite you to do the same testflight (and setting your artificial stability to zero is good advice, articial stability is like a kids´ bikes training wheels) and post your aileron input needed to keep the plane flying straight.

Cheers, Jan

 

OK Jan way more clear now with the data you just provided, my figures are similar to those ( a bit off on a level with full power, but offset when trimming to about 75%) so I can assume that we are okay here

Some of the deflections are, probably, should be attributed to my aging Saitek Pro-Yoke which IMHO become less Pro & less Yoke ...... lol   

Best Reg

 

Yair.BTW 

Ground Steering/ Taxi this is a hell of an issue ..keeping engine at about 800RPM applying small Mixture, this thing is accelerating and drifting from side to side like crazy, no a pleasure at all (-:    

 

 

[olderndirt 2,295]

A little humor here.  Back in my Alaska days, I was hauling a trapper and his gear out to his line.  While loading he busied himself in the background.  All ready to go and he tells me - " Noticed these little metal thingys were bent (tabs on the left aileron, right elevator and rudder) so I straightened them for you".  He was grinning so hard, I couldn't tell him the time I'd put into getting those thingys just right.