Jump to content
Sign in to follow this  
jcomm

AirfoilLabs C172...

Recommended Posts

I would agree, other than my experience with the Fresca sim (no "PC sim" and able to be used for instrument currency".

Share this post


Link to post
Share on other sites

Thx Bruce for your additional comments from RL experience flying the 172S, just like Larry.

 

That's my experience too in many flights in th R models, not as a pilot, because I only own a GPL ( now EASA :-( ) but as someone many times allowed to actually fly the aircraft by my airclub fellows.

 

I am also starting to invest on better hardware, but it's very expensive. I just ordered a GNS and Throttle Quadrant from ELITE ( Swiss ) and am witing for delivery and taxes I'll have to pay on top of the already expensive hardware, and I am planning to invest on their yoke too, because I'll be able to use it with ELITE and PSX :-)  The radio stack is still a dream.

 

ELITE provides me with that stability you mentioned Bruce, like no other FSX or X-Plane model I have tried indeed...

 

This being said, I guess that Lena probably considered I was referring to coordinated turns, and in that case she is right in what she points out because indeed if rudder is used during a tighter turn to coordinate it, and we do not use only the yoke, creating a sideslip, overbanking will occur and require outside yoke deflection.

 

Of course overbanking is my "daily" experience in gliders. At 45º+ bank I sometimes have to use almost full outside aileron in some of them!


Main Simulation Rig:

Ryzen 5600x, 32GB RAM, Nvidia RTX 3060 Ti, 1 TB & 500 GB M.2 nvme drives, Win11.

Glider pilot since October 1980...

Avid simmer since 1992...

Share this post


Link to post
Share on other sites

 

 


I moved to a certified force feedback yoke, real pitch travel length, force feedback pressure based on the aircraft IAS to mimic the real thing. All bumpiness and instabilities for nice pitch control went away.

 

Me too, and it's a world of difference. Also trimming feels real now.

 

Have given up with XPlane though. Even with such a yoke I rarely need more than 10% of travel, no matter if default or Addon plane. That's all way too twitchy.

 

Mike


1. A320 home cockpit (FSLabs, Skalarki), P3Dv5  Main PC : I7-12700K, GTX3080Ti

2. FSLabs A3xx, P3Dv5. Gigabyte Aorus 17G YC, I7-10700K, RTX 3080

Share this post


Link to post
Share on other sites

Just as a complement, and with a very well written set of "Course Notes" I strongly recommend visiting:

 

http://www.flightlab.net/Flightlab.net/Download_Course_Notes.html

 

and in line with this particular thread what is discussed regarding directional stability in this particular Note:

 

http://www.flightlab.net/Flightlab.net/Download_Course_Notes_files/4_LateralDirectional%232BA14D.pdf

 

I think that flight simulators either use the "blade" approach but really do not take into consideration all of the moments created by the various lift and drag generation surfaces, or do not model them correctly, or when using the so called "table-based" approach, use certain coefficients that are innapropriate, or the authors tune those to get some effects better modeled, causing weird behaviour on others...


Main Simulation Rig:

Ryzen 5600x, 32GB RAM, Nvidia RTX 3060 Ti, 1 TB & 500 GB M.2 nvme drives, Win11.

Glider pilot since October 1980...

Avid simmer since 1992...

Share this post


Link to post
Share on other sites

Just as a complement, and with a very well written set of "Course Notes" I strongly recommend visiting:

 

http://www.flightlab.net/Flightlab.net/Download_Course_Notes.html

 

and in line with this particular thread what is discussed regarding directional stability in this particular Note:

 

http://www.flightlab.net/Flightlab.net/Download_Course_Notes_files/4_LateralDirectional%232BA14D.pdf

 

I think that flight simulators either use the "blade" approach but really do not take into consideration all of the moments created by the various lift and drag generation surfaces, or do not model them correctly, or when using the so called "table-based" approach, use certain coefficients that are innapropriate, or the authors tune those to get some effects better modeled, causing weird behaviour on others...

 

I think it's important not to confuse static lateral stability with spiral dynamics.

 

Static lateral stability means that if the aircraft e.g. sideslips yawing the nose to the right, then it tends to roll right, and vice-versa.

 

This is the common behaviour of FSX and X-Plane aircrafts. The effect seems to be more pronounced in X-Plane aircrafts.

 

However, a positive static lateral stability is not a sufficient condition to produce also a stable spiral mode. I was surprised to learn that, apparently, even the C172 has a slightly unstable spiral mode, and if left hands off, its bank angle will (slowly) progressively increase until it's in a spiral.


"The problem with quotes on the Internet is that it is hard to verify their authenticity." [Abraham Lincoln]

Share this post


Link to post
Share on other sites

Just mentioned the site for the interesting notes available there, and not because of the dynamic nature of the spiral dive phenomenon Murmur.

 

And, in the cited document you can ( and I guess I once sent you this very same link ) find also part of the justification on how an aircraft reacts to a sideslip situation, which was exactly the one at the start of the thread - I give some yoke input, left or right, and return it to neutral, without touching the rudder.  The aircraft enters a sideslip....


Main Simulation Rig:

Ryzen 5600x, 32GB RAM, Nvidia RTX 3060 Ti, 1 TB & 500 GB M.2 nvme drives, Win11.

Glider pilot since October 1980...

Avid simmer since 1992...

Share this post


Link to post
Share on other sites

Just mentioned the site for the interesting notes available there, and not because of the dynamic nature of the spiral dive phenomenon Murmur.

 

And, in the cited document you can ( and I guess I once sent you this very same link ) find also part of the justification on how an aircraft reacts to a sideslip situation, which was exactly the one at the start of the thread - I give some yoke input, left or right, and return it to neutral, without touching the rudder.  The aircraft enters a sideslip....

 

Can you quote or give the precise point of the document you're referring to?


"The problem with quotes on the Internet is that it is hard to verify their authenticity." [Abraham Lincoln]

Share this post


Link to post
Share on other sites

There are various instances, more or less directly related to it:

 

pg. 4.1, 3rd paragraph: [...]A stable aircraft yaws toward the velocity vector, but rolls away[...]

pg. 4.5 Clp section: "An aircraft with dihedral effect rolls away from a sideslip (away from the velocity vector)"  and further down

 

"An aircraft with positive lateral stability rolls away from the sideslip (velocity vector) that results when a wing drops, and that usually means back toward level flight (although an aircraft with dihedral effect can go into a spiral dive if the bank angle is high and other moments prevail)."

 

In my real life experience aboard C172s and just as both Larry and Bruce referred, the aircraft tended to return to wings level, even faster if the roll was to the right ( positive ) and the power was in the cruise range or above ( due to prop effects ).

 

If you own the AirfoilLabs C172 you can easily check what I meant, by setting various bank angles and returning the controls to neutral, not using rudder at all, and entering sideslips ( left or right), You can then test with full power, idle power, level, climbing or descending, and see that no matter how small your initial bank is, the aircraft will continue to bank, unless opposite roll controls are input.


Main Simulation Rig:

Ryzen 5600x, 32GB RAM, Nvidia RTX 3060 Ti, 1 TB & 500 GB M.2 nvme drives, Win11.

Glider pilot since October 1980...

Avid simmer since 1992...

Share this post


Link to post
Share on other sites

There are various instances, more or less directly related to it:

 

pg. 4.1, 3rd paragraph: [...]A stable aircraft yaws toward the velocity vector, but rolls away[...]

pg. 4.5 Clp section: "An aircraft with dihedral effect rolls away from a sideslip (away from the velocity vector)"  and further down

 

"An aircraft with positive lateral stability rolls away from the sideslip (velocity vector) that results when a wing drops, and that usually means back toward level flight (although an aircraft with dihedral effect can go into a spiral dive if the bank angle is high and other moments prevail)."

 

In my real life experience aboard C172s and just as both Larry and Bruce referred, the aircraft tended to return to wings level, even faster if the roll was to the right ( positive ) and the power was in the cruise range or above ( due to prop effects ).

 

If you own the AirfoilLabs C172 you can easily check what I meant, by setting various bank angles and returning the controls to neutral, not using rudder at all, and entering sideslips ( left or right), You can then test with full power, idle power, level, climbing or descending, and see that no matter how small your initial bank is, the aircraft will continue to bank, unless opposite roll controls are input.

 

The roll moment due to sideslip is not the only factor at play. The directional (weathervane) stability, the roll moment due to yaw rate, and the yaw moment due to yaw rate, all play opposing roles in the dynamics of the long period spiral mode.

 

Now, as the academic textbook I quoted shows, apparently the C172 has a slightly unstable spiral mode.

 

This means that, on the long period, even when trimmed, if left to itself the bank angle will progressively increase. As a sidenote, this is also the behaviour of the AeroflyFS 1 C172: if you put it in a slight bank angle, it will increase its bank angle, although with a much slower rate compared to e.g. the default X-Plane C172. From the data in the academic textbook I quoted, the behaviour of the AeroflyFS 1 C172 seems quite close to the real aircraft.


"The problem with quotes on the Internet is that it is hard to verify their authenticity." [Abraham Lincoln]

Share this post


Link to post
Share on other sites

The roll moment due to sideslip is not the only factor at play. The directional (weathervane) stability, the roll moment due to yaw rate, and the yaw moment due to yaw rate, all play opposing roles in the dynamics of the long period spiral mode.

 

 

They're all mentioned in that same PDF, although in other paragraphs.

 

Two characteristics of the modern C172 that could indeed contribute to overbanking are the use of differential ailerons, which deflect up the aileron on the wing towards which the bank will occur than the one in the outer wing deflects down, causing additional drag and countering the adverse yaw, as well as the use of fries ailerons, both increasing the yaw towards the turn and hence the yaw-induced roll, but apparently and while contributing to make the 172 rather feet on floor during turns, they certainly do not contribute that much towards overbanking...

 

The dynamic instability referred to in Roskam's text probably refers to the first models of the C172, because the aircraft is actually known to be "stable" in this respect, as others in this thread confirmed too from their real life experiences.

 

BTW, the rate of roll when left at it's own will is actually superior in the AirfoilLabs C172 than in the default C172, at least in my X-plane.


Main Simulation Rig:

Ryzen 5600x, 32GB RAM, Nvidia RTX 3060 Ti, 1 TB & 500 GB M.2 nvme drives, Win11.

Glider pilot since October 1980...

Avid simmer since 1992...

Share this post


Link to post
Share on other sites

The dynamic instability referred to in Roskam's text probably refers to the first models of the C172, because the aircraft is actually known to be "stable" in this respect, as others in this thread confirmed too from their real life experiences.

 

Maybe later C172s have different lateral-directional characteristics, or maybe the explanation could be another one: let's say that the real C172 has a stronger adverse yaw, compared to the simulated one. In this case, turning the yoke without coordinating the rudder, could cause a strong sideslip and hence (after an initial banking in the direction of the yoke deflection) an almost immediate decrease of the bank angle. But this is just a short period dynamic, and it's sensed by the pilot as an apparent "stability in roll".

 

However, on the long period, the aircraft has a weak spiral instability, and hence in the long period it will slowly increase the bank angle and enter a spiral dive.

 

Mines are just hypotheses. I quote brucek:

 

I have about 200 hours in the C172S. For reasons that I will never understand, the real a/c has the issue that it is more stable in nose up/down pitch and less stable in the bank attitude than any of the sims that I have flown

 

With that said, I agree with the OP that any bank in the real thing, less than 25 degrees, will return to approximately level. That is, a sudden bank change (less then 25 degrees) will result in a rather quick return to level flight. Its's the gradual change in bank over time that makes it susceptible to graveyard spirals.

 

BTW, the rate of roll when left at it's own will is actually superior in the AirfoilLabs C172 than in the default C172, at least in my X-plane.

 

Probably the real C172 has a slower spiral instability than that exhibited by X-Plane default or Airfoillabs C172s. The AeroflyFS 1 C172 has a weak and slow spiral instability.

 


"The problem with quotes on the Internet is that it is hard to verify their authenticity." [Abraham Lincoln]

Share this post


Link to post
Share on other sites

Been testing with ELITE v8.6 C172 models and idle to low power settings if banked more than 15º they'll also enter a slow progressively increasing bank, becoming a spiral dive.  

 

With power at mid to low ranges, that happens only when banking left due to prop effects.

 

There is a slight difference though between models R and S in ELITE, even at idle.  Both also slowly go towards overbanking if left control-free, on left banks with engine out of idle.

 

With a bit more than 10 º bank the aircraft slowly enter that same situation, even at idle power settings.


Main Simulation Rig:

Ryzen 5600x, 32GB RAM, Nvidia RTX 3060 Ti, 1 TB & 500 GB M.2 nvme drives, Win11.

Glider pilot since October 1980...

Avid simmer since 1992...

Share this post


Link to post
Share on other sites

Ok, just a last update on this topic...

 

1) During a short ( 2hr ) install / uninstall of FSX:SE, I tested the A2A stuff ( c172 and c182 ) and they're for sure the ones that correspond more to what real world c172 pilots reported here - they rapidlty return to wings level in powered flights through the right.

 

2) In ELITE the behavior is actually more like in FSLabs C172, although for slight bank angles the aicraft returns to wings level ...

 

3) Yesterday, to the dismay of my passenger, I decided to perform some aerodynamics stability tests on my PW6 glider :-)

Guys / Lena in particular, it surely enters a spiral dive from a banked situations after which controls are returned to neutral ( difficult to guarantee in a glider ) and left at their own... The overbanking is simply tremendous! Incredible!

 

Then when I landed I talked to three different fellow pilots ( all Airbus captains who also like to fly for real, I mean, like to fly gliders... ) and are seasoned flight instructor too... All of the three told me that either overbanking and resultant entry into spiral dives were the usual outcome on most of the GAs they fly, with the exception of twins, or at least the aircraft tends to stay at the bank angle it was left at...

 

Well...


Main Simulation Rig:

Ryzen 5600x, 32GB RAM, Nvidia RTX 3060 Ti, 1 TB & 500 GB M.2 nvme drives, Win11.

Glider pilot since October 1980...

Avid simmer since 1992...

Share this post


Link to post
Share on other sites

What are you saying now, José , that the the flight model in Elite and FSLabs C172 is correct (2) and that what most rw pilots report (1) is due to them reacting to the plane going instable - a bit like someone driving a car keeping it in the middle of the road, without thinking too much about the constant tiny corrections they make ?

Share this post


Link to post
Share on other sites

I'm saying I'm a bit confused :-)

 

In the PW6-U glider I flew yesterday, for sure banking and returning stick to neutral, hands off, will enter overbanking situ and end in a spiral dive, real fast...

 

In ELITE, if bank is bellow 15º and to the right, engine running at cruise settings, it'll recover. Same with low poer settings on a left bank, but with more power the aircraft will continue to bank.

 

In the Airfoilabs C172 it will always continue to bank, right or left, with or without power.


Main Simulation Rig:

Ryzen 5600x, 32GB RAM, Nvidia RTX 3060 Ti, 1 TB & 500 GB M.2 nvme drives, Win11.

Glider pilot since October 1980...

Avid simmer since 1992...

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

  • Tom Allensworth,
    Founder of AVSIM Online


  • Flight Simulation's Premier Resource!

    AVSIM is a free service to the flight simulation community. AVSIM is staffed completely by volunteers and all funds donated to AVSIM go directly back to supporting the community. Your donation here helps to pay our bandwidth costs, emergency funding, and other general costs that crop up from time to time. Thank you for your support!

    Click here for more information and to see all donations year to date.
×
×
  • Create New...