-
Notifications
You must be signed in to change notification settings - Fork 44
New issue
Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.
By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.
Already on GitHub? Sign in to your account
Adverse Yaw amplitude (Cnda) #1378
Comments
@dany93 to be short: low speeds, high angle attack and large aileron deflections makes a strong yaw adverse effect (https://slideplayer.com/slide/13344648/). So with cruise speed it should be very low- for at least the c182 I do know you don´t need any pedal input in turns.
I recommend: https://www.youtube.com/watch?v=ewHL8-agBWI You should also consider that the animation slip ball might not be correct in the c172p |
Hi Dany,
yes I can confirm the values.
Roskam had given two values; one is the -0.053 from "ROSKAM, J., Methods
for Estimating Stability and Control Derivatives of Conventional
Subsonic Airplanes"
and the other triple is in
"Roskam-Airplane Flight Dynamics and Automatic Flight Controls-Part
1-Appendix-B"
from where Megginson obviously took them.
NASA-CR975 gives CnDa = -0.0167 for a C182 based on theoretical
computations.
Regards,
Oliver
Am 07.07.21 um 16:23 schrieb dany93:
…
Forked from #1364 <#1364>
Let's start by what I think should be the easiest.
*Averse Yaw (Cnda)*
Megginson Roskam c172p c182s PA28
-0.0504, -0.0216, -0.0786 -0.053 -0.0216 +0.0216 to +0.0786
-0,0008676
0.2892x(-0.0015)x2
The c172p Cnda is at -0.0216, the lowest value published bt Megginson
and Roskam.
The c182 is with positive coefficients, which is 'pro'-yaw, not
adverse yaw.
The PA28 is at -0,0008676 (if I understood well), which practically
comes down to 0. No adverse yaw can be observed.
I admit that the adverse yaw effect could be decreased (despite the
values from reference publications), but I cannot believe that the
C172 is the only light aircraft giving no adverse yaw at all.
Currently I have nothing else than Megginson and Roskam, apart from
qualitative and subjective impressions by pilots (some who don't
express negative remarks, others who are in strong disagreement even
between each other).
My own observations on ultralights (a bit old and obviously
qualitative) are that the adverse yaw is easily observable, and must
be counteracted.
Adverse yaw counteracting is one of the main tasks of the rudder.
@okroth <https://github.com/okroth> wrote in this message
<#1047 (comment)>
CnDa: Megginson has -0.0504, -0.0216, -0.0786 for climb, cruise,
approach... not sure why they differ, *but the C172 does have
adverse yaw*...UIUC, Roskam, etc all use -0.053.
@okroth <https://github.com/okroth>, can you confirm that you wrote?
@tigert <https://github.com/tigert>, if you are still there, your
opinion on the amplitude?
@algefaen <https://github.com/algefaen>?
*Videos*:
Coordinated turns <https://www.youtube.com/watch?v=UV8xcm5xsuo>
Airplane Rudders! Learn to FEEL coordination in the airplane and avoid
stall spin flying accidents <https://www.youtube.com/watch?v=zdZ2Rwq86vA>
@Octal450 <https://github.com/Octal450>, @tonghuix
<https://github.com/tonghuix>
If possible please, could you make a video like the one above, showing
the (absence of?) adverse yaw on your aircraft? The important is to
start from stabilized leveled flight at a known airspeed, then
(reasonably??) rotate the yoke only, with no rudder. And observe the
temporarily opposite yaw movement prior to the desired one.
Oscillating side to side movements are interesting to observe too (see
the video).
The dashboard objects can serve as references for angular evaluations.
—
You are receiving this because you were mentioned.
Reply to this email directly, view it on GitHub
<#1378>, or unsubscribe
<https://github.com/notifications/unsubscribe-auth/ACNSRMDKBD5MP4ETXHY4JIDTWRPOHANCNFSM476YZM4Q>.
|
Isn't it merely because we don't need much aileron deflection in cruise? I admit, at least partly because Cnda (per radian of aileron deflection) might also be lower. But still far from 0. In Megginson's table (C182), -0.0216 is the value for cruise.
I'd like to observe this. Anyway, the main question is: even knowing that Cnda depends on AoA and / or airspeed, what are the values to be entered? Even if Megginson values are for 'mean' conditions (not taking every parameter in account), why are they considered as wrong in all of our conditions? On the video (I already had seen it), the adverse yaw is difficult to distinguish from the other movements. |
Hi Oliver, Nice to meet you again, and see that you are still there. Thank you for your response. Dany |
Hi,
IMHO, the CnDa should be a more or less constant parameter NOT being
dependent on AoA.
Of course, in slow flight, we need larger aileron movements for the same
roll rate change, but that should not change CnDa; we already have a
larger delta-aileron.
Roskam's values also are not a linear function of alpha:
cruise: alpha=0.0° CnDa= -0.0216
approach: alpha=4.0° CnDa= -0.0786
climb: alpha=5.4° CnDa= -0.0504
i.e. CnDa is larger in approach than in climb with smaller alpha, but
smallest with alpha=0...
Regards,
Oliver
Am 07.07.21 um 18:30 schrieb dany93:
…
Hi Oliver,
Nice to meet you again, and see that you are still there.
Thank you for your response.
Dany
—
You are receiving this because you were mentioned.
Reply to this email directly, view it on GitHub
<#1378 (comment)>,
or unsubscribe
<https://github.com/notifications/unsubscribe-auth/ACNSRMB7TJZAJIUXTHQ4NFDTWR6IVANCNFSM476YZM4Q>.
|
Once more, Thank You @okroth.
Your response confirms my reasoning between high AoA and cruise AoA adverse yaw, as based on my current understanding. Dany |
This subject is really hard to quantify. Part of my reluctance to get on board to make any changes is the subjectivity and the wide range of control equipment in use by users, the unknown variability in individual RL aircraft trim settings and flight control surface tuning, and the disparity between RL control feedback and simulated controls. I know with my peddles, (which are not dialed in completely), I need only slight right rudder pressure. That is what I keep hearing from multiple real life pilots. |
@HHS81 wrote
I agree, and always tried to go this way as much as I could. @HHS81 wrote
I agree too, and many seem forgetting this. Plus the return springs on our JS, which give a very different feeling than reality (without Force Feedback JS). Concerning (rudder) sensitivity |
Hi,
@HHS81 <https://github.com/HHS81> wrote
No one of us here has flight controls at home which simulates the
forces created by the airflow, mechanic and everthing else
involved, but is responsible for the "feel" of the aircraft. Or do
you use hardware which has the same travel way like the real controls?
Ahem, I do. I am building a home-cockpit that has motors being driven by
the hinge moments computed in the FDM.
I inserted an extra force-feedback system into the plane's XML file.
And yes, the controls do have the actual travel way. And the rudder
pedals are real parts.
Oliver
|
@dany93 i agree with you:
People should not be whining about small movement. If you can't get small enough the sensitivty should be adjusted, not the plane. The plane's response should be realistic. A twist rudder is bad for flying GA as you can't keep a constant input without uncomfortable. Recommend you use something even like some cheap racing pedals work. Kind Regards, |
You're right, its too low. Some typo perhaps, I will go through and re-checked it a bit. I need to do more calculation and testing later. (very sorry for slowly... health problems not much time for fgfs) Kind Regards, |
Get better Josh! |
For the video you provide, I have to say the rudder use in this perticular video is just a demostrate, it is record in steady flight situation, not a power-off stall situation. However, for the power off stall itself, requires some of rudder input indeed, of my experence about less than 1/4 of full range. I agree to test it, we need a rudder peddle, rather than just twist a stick. |
Hi Josh, Get better, I hope as soon as possible. For fgfs, there is no rush. |
Ty guys... but prob will be a while, been battling this for years. @dany93 new coeffs: https://sourceforge.net/p/flightgear/fgaddon/5900/ Now the effect is better. Please try it, it should be resolved but I admit I only could do minimal testing in a few configs (slowflight, cruise). Kind Regards, |
@tonghuix wrote
It is given as a power-off stall. Moreover, they say
But it was not the subject. My aim was to show the needed accuracy on the rudder pedals. |
@Octal450 Better. The adverse yaw effect is weak (IMO) but observable. IMO, the adverse yaw effect is still low. Hard to observe by eye, possible by @okroth wrote in this message
Your values give 25% to 41% of -0.0167. I think I observe an noticeable effect after applying a factor 3 or 4 to your values. If you wish, to make tests and tuning of this factor easier in flight, I've inserted a 'factor' in the properties, which can be changed in flight.
In pa28-aerodynamics.xml, |
Hi @dany93 I will continue to check it in various configs, what config you test at? I found the real life the effect is not as strong as in your c172 model, so I guess it also depends on what you are using for comparison. The effect is also small enough that you can comfortably fly the plane without rudder input if you HAVE to (jammed rudder or such) without the nose swinging about (I did simulated jammed surfaces training IRL) Kind Regards, |
Hi @Octal450 I use 160 or 180 hp, in the default config (the first as downloaded) in general. Not tested many configs, it was just ti give you a few indications.
I obviously have the c172 in mind, consciously or not. I don't know what to think... the C182 has lower adverse yaw as calculated than C172
Compared with C172
Personally, I have nothing else than that I wrote just above in this message. I'd like accurate and constructive indications from reliable C172 pilots. For the PA28, as you do your tests consciously with this issue in mind, you are probably right. |
More videos for you @dany93 . |
That's cool!
especially the first video will allow to calibrate the CnDa:
70kts, 80° aileron and then measure the plane's reaction...
If it is similar to the video, we are almost there.
Oliver
Am 15.07.21 um 02:47 schrieb Tong Hui:
…
More videos for you @dany93 <https://github.com/dany93> .
https://www.youtube.com/watch?v=zdZ2Rwq86vA
<https://www.youtube.com/watch?v=zdZ2Rwq86vA>
https://www.youtube.com/watch?v=0L4oKP5xv-8
<https://www.youtube.com/watch?v=0L4oKP5xv-8>
—
You are receiving this because you were mentioned.
Reply to this email directly, view it on GitHub
<#1378 (comment)>,
or unsubscribe
<https://github.com/notifications/unsubscribe-auth/ACNSRMF7W4FFO2FVMQBJR5DTXYV2DANCNFSM476YZM4Q>.
|
Hi dany,
one more thing: Cnp "Yaw moment from roll rate". It contributes to
adverse yaw when a roll rate is established whereas CnDa immediately
applies a yawing moment.
This coefficient is not existing (=0) in the detailed C172
I Roskam's "Flight Dynamics and ... Appendix B" it is give to
Climbing: -0.0649
Cruise: -0.0278
Approach: -0.0960
Regards,
Oliver
Am 14.07.21 um 12:15 schrieb dany93:
…
Hi @Octal450 <https://github.com/Octal450>
I use 160 or 180 hp, in the default config (the first as downloaded)
in general. Not tested many configs, it was just ti give you a few
indications.
I found the real life the effect is not as strong as in your c172
model, so I guess it also depends on what you are using for comparison
I obviously have the c172 in mind, consciously or not.
More objectively, I also have this video Coordinated turns
<https://www.youtube.com/watch?v=UV8xcm5xsuo>.
>From my memory (a bit old), flights on Ultralights.
Also, the C182 has lower adverse yaw as calculated
This message
<#1378 (comment)>
NASA-CR975 gives CnDa = -0.0167 for a C182 based on theoretical
computations.
Compared with C172
CnDa: Megginson has -0.0504, -0.0216, -0.0786 for climb, cruise,
approach... not sure why they differ, but the C172 does have
adverse yaw...UIUC, Roskam, etc all use -0.053.
Personnaly, I have nothing else than that I wrote just above in this
message.
For the C182, as you do your tests consciously with this issue in
mind, you are probably right.
—
You are receiving this because you were mentioned.
Reply to this email directly, view it on GitHub
<#1378 (comment)>,
or unsubscribe
<https://github.com/notifications/unsubscribe-auth/ACNSRMEOB625P57VV3P2ILTTXVPS5ANCNFSM476YZM4Q>.
|
Please note: These are the values for the c182 For c172p it is for cruise : -.03 |
Hi @dany93 Kind Regards, |
More C172 training flight video: Note that, due to the mount point of the camera, the pitch angle in the picture is much more lower than actural pitch angle. |
Thank you @tonghuix for your videos. Thank you Oliver @okroth and @HHS81
Close to Roskam at cruise (-0.0278). A question is: to set an AoA dependency or not? I'm looking at all of this when I can, but I have currently other problems to solve at home. |
I have added Cnp (yaw moment due to roll rate) It adds to the aileron contribution, increasing the primary adverse yaw moment. Not negligible at all, it can even be greater than the one due to ailerons. Which is the best way to get even more complaints with the published coefficients.
I hope (I think) having chosen the right properties, with bi2vel, in the product. (@okroth please ?) Please note: For Cnda and Cnp, I have inserted After many tests, I have set each tuning factor at 0.1. Surprisingly low, even if they add to each other. I don't know if that's enough, please tell me if they can be slightly greater.. Despite my reluctance, it is equivalent to setting the coefficients far from those of the published tables. I hope this is not a way to apparently fix an issue by introducing another ill-tuned feature. The easiest way to test it is by comparison from Coordinated turns (from 1:30). Testing from this video (5:00 and 6:04) can be more tricky. Please test it, tune the factors in-sim and make an agreement between all of you. From my point of view, important points are:
|
Dany,
the "bi2vel" factor is correct.
Reference: Roskam "Airplane Flight Dynamics and Automatic Flight
Controls-Part 1", page 130.
Regards,
Oliver
Am 20.07.21 um 16:26 schrieb dany93:
…
I have added *Cnp (yaw moment due to roll rate)*
It adds to the aileron contribution, increasing the primary adverse
yaw moment. Not negligible at all, it can even be greater than the one
due to ailerons. Which is the best way to get even more complaints
with the published coefficients.
|<function name="aero/coefficient/Cnp">
<description>Yaw_moment_due_to_roll-rate</description> <product>
<property>aero/qbar-psf</property>
<property>metrics/Sw-sqft</property>
<property>metrics/bw-ft</property> <property>aero/bi2vel</property>
<property>velocities/p-aero-rad_sec</property> <table> <independentVar
lookup="row">aero/alpha-wing-rad</independentVar> <tableData> 0
-0.0278 0.070 -0.0960 0.094 -0.0649 </tableData> </table>
<property>/controls/flight/adv-yaw-fact2</property> <!-- tuning factor
for tests in flight --> </product> </function> |
I hope (I think) having chosen the right properties, with bi2vel, in
the product. ***@***.*** <https://github.com/okroth> please ?)
The table coefficients for Cnp are those of Megginson.
*Please note*: For Cnda and Cnp, I have inserted
|/controls/flight/adv-yaw-fact1| (Cnda)
|/controls/flight/adv-yaw-fact2| (Cnp)
to allow tuning of each effect, separately, in-sim ("Set" in the
Properties).
After many tests, I have set each tuning factor at 0.1. Surprisingly
low, even if they add to each other. Despite my reluctance, it is
equivalent to setting the coefficients far from those of the published
tables. I hope this is not a way to apparently fix an issue by
introducing another ill-tuned feature.
The easiest way to test it is by comparison from Coordinated turns
<https://www.youtube.com/watch?v=UV8xcm5xsuo> (from 1:30).
Starting from leveled wings, the observation is easy enough, not too
much user dependent.
Testing from this video <https://www.youtube.com/watch?v=zdZ2Rwq86vA>
(5:00 and 6:04) can be more tricky.
The "dynamic" way (large left and right yoke movements at 70 kts) can
be very user dependent. You must revert the yoke before the expected
yaw movement begins. Otherwise, you can observe a false increase for
advert yaw, in fact due to the inertia from the normal yaw.
To convince yourself, cancel both factors: if you wait too long, you
can easily have the impression of adverse yaw.
You must also limit your yoke travel to 80% (like the video). To be
sure, I have limited my aileron JS factor to 0.8.
Please test it, tune the factors in-sim and make an agreement between
all of you.
—
You are receiving this because you were mentioned.
Reply to this email directly, view it on GitHub
<#1378 (comment)>,
or unsubscribe
<https://github.com/notifications/unsubscribe-auth/ACNSRMG2C3B7U45CTDIJKWLTYWBPVANCNFSM476YZM4Q>.
|
Forked from #1364
Let's start by what I think should be the easiest.
Averse Yaw (Cnda)
The c172p Cnda is at -0.0216, the lowest value published bt Megginson and Roskam.[EDIT 14 july 2021]
Sorry, it has Megginson's values.
[/EDIT]
The c182 is with positive coefficients, which is 'pro'-yaw, not adverse yaw.
The PA28 is at -0,0008676 (if I understood well), which practically comes down to 0. No adverse yaw can be observed.
I admit that the adverse yaw effect could be decreased (despite the values from reference publications), but I cannot believe that the C172 is the only light aircraft giving no adverse yaw at all.
Currently I have nothing else than Megginson and Roskam, apart from qualitative and subjective impressions by pilots (several who find the controls too sensitive, some who don't express negative remarks, others who are in strong disagreement even between each other).
My own observations on ultralights (a bit old and obviously qualitative) are that the adverse yaw is easily observable, and must be counteracted.
Adverse yaw counteracting is one of the main tasks of the rudder.
@okroth wrote in this message
@okroth, can you confirm that you wrote?
@tigert, if you are still there, your opinion on the amplitude?
@algefaen?
Videos:
Coordinated turns
Airplane Rudders! Learn to FEEL coordination in the airplane and avoid stall spin flying accidents
@Octal450, @tonghuix
If possible please, could you make a video like the one above, showing the (absence of?) adverse yaw on your aircraft? The important is to start from stabilized leveled flight at a known airspeed, then (reasonably??) rotate the yoke only, with no rudder. And observe the temporarily opposite yaw movement prior to the desired one.
Oscillating side to side movements are interesting to observe too (see the video).
The dashboard objects can serve as references for angular evaluations.
The text was updated successfully, but these errors were encountered: