FG's Cessna vs Real life.

Megaf commented 3 years ago

Hi all, so yesterday I piloted a 1977 Cessna 172N, upgraded to 172P (Engine replaced), in real life.

Important Observations

About the Cessna 172 in real life. Man, in real life, it is an absolute pleasure to fly it!
Below 90 knots, it is extremely forgiving, you can make huge inputs and the thing barely responds.
A 60 knots climb, it's extremely sharp, and your nose will be pointing to the sky. A shallow climb will be at 85 knots.
The Cessna DOES NOT ROLL TO THE LEFT ALL THE FREAKING TIME. In fact, I didn't even notice that in real life.
Seating position is way higher in real life, in FG it seems like you are hiding behind the instruments panel, in real life you can see almost the full nose of the aircraft.
Tyres don't squeak like that, like someone is raping a chicken.
It accelerates a lot quicker than it does in FG and stalls at 45 knots.
The controls are a lot less sensitive overall. I strongly advise to have a look at Octals/Joshs PA-28 on how to implement proper inputs from the joystick/yoke.

Below some photos of the aircraft I flew in.

IMG_20210618_151522_DRO IMG_20210618_151548_DRO IMG_20210618_151559_DRO

The good in FG's Cessna.

Start procedure is spot on, just like in real life.
Engine sound is ok enough.
Engine startup is alright, but the aircraft shakes too much in FG.
General dynamics are ok too.

Octal450 commented 3 years ago

@wlbragg

hold it down long enough no matter the force and it will screech

That is acceptable. I was under the impression the wheels locked immediately at a brake input of "1" from how it was described. Apologise if there was a communication barriar.

@HHS81 yes that video seems to explain it well, matches what I saw IRL. But in c172 I could produce the "severe" yawing all of the place effect with just 2 or 3 turns wheras it takes him many more. The effect is too high.

just resting the foot on the right pedal stops left roll tendency

During a typical cruise at a reduced RPM. With high RPM or climbs and especially takeoff or go arounds you need more force.

I don't recall much noticeable change in that effect with different amount of people in the plane.

@Megaf , were you correcting the left yaw effects already with rudder? If so then yes there should be almost no rolling whatsoever. Because with no rudder input at all the plane will definitely roll left unless trimmed.

Kind Regards, Josh

Megaf commented 3 years ago

@Megaf , were you correcting the left yaw effects already with rudder? If so then yes there should be almost no rolling whatsoever. Because with no rudder input at all the plane will definitely roll left unless trimmed.

@Octal450 Nope, it was rolling a lot to the left precisely because there was no rudder input/trim.

About the roll, I had an instructor, which had his foot on the rudder for a while, but he did let me control the aircraft for a while without his inputs. As shown on my video, the roll is just too exaggerated. As mentioned above, simply resting your foot on the rudder pedal should be enough to cancel it out.

This roll tendency feels better modelled in the C182S and PA-28.

HHS81 commented 3 years ago

@Megaf

@wlbragg @dany93 @tonghuix https://youtu.be/drLXaidstww

So you can clearly see the amount of right aileron I need to make the Cessna stop rolling. You can also see that a bit of right rudder will stop it rolling.

O.k.- you rotated at 45ktn- barely above stall speed- no surprise that you needed so much pedal input! Make sure to use the ASI - this uses the corrected airspeed- don´t use the HUD!

HHS81 commented 3 years ago

About the roll, I had an instructor, which had his foot on the rudder for a while, but he did let me control the aircraft for a while without his inputs. As shown on my video, the roll is just too exaggerated.

As stated above- you rotated at 45ktn- barely above stall speed- no surprise that you needed so much pedal input! Make sure to use the ASI - this uses the corrected airspeed- don´t use the HUD!

HHS81 commented 3 years ago

@HHS81 yes that video seems to explain it well, matches what I saw IRL. But in c172 I could produce the "severe" yawing all of the place effect with just 2 or 3 turns wheras it takes him many more. The effect is too high.

just resting the foot on the right pedal stops left roll tendency

During a typical cruise at a reduced RPM. With high RPM or climbs and especially takeoff or go arounds you need more force.

Thanks! That´s very helpful. Then it isn´t quite right yet on the c182s. One thing was the animation of the turn indicator. The other might be the coefficients of adverse yaw and spiral propwash. But not much changes needed. I will come up tomorrow morning with something to test for the c182s

Megaf commented 3 years ago

O.k.- you rotated at 45ktn- barely above stall speed-

@HHS81 Please... I'm not describing a one off occurrence... I have a 1+ hour flight on my YouTube channel with this happening at up to 100 kts.

don´t use the HUD!

I don't use the HUD, the HUD was there to simply demonstrate the amount of input I had to apply and how much trim I had. Also, if the HUD and the aircraft disagree about the speed and other stuff then we have a BUG. Again, this is FG's default aircraft and it should at least be 100% compatible with FG and use FG standards. Am I asking too much?

SMH...

tonghuix commented 3 years ago

For the left turning tendency, we tested Chandelle maneuver using this aircraft and compared with P3D and X-Plane. When we did Chandelle, it required nearly 3/4 of the full range of peddle movement for coordinate, and others needed 1/4 or less. In real life, it require nomally 1/3 to half of full range for coordinate.

For the adverse yaw, we tested with Steep Turn maneuver, it's a little hard to maintain minus and plus 50 feet altitude when transite from left turning to right turning, even difficult to maintain plus and minus 100 feet. I believe it's because the adverse yaw is too much, and associate with too much left turning tendency. In real life, for left steep turn, we still need a little left rudder, maybe 1/8 to 1/4, even left turning tendency helping me, for right turn, it require lots more right rudder, 1/3 to half of full range.

Elevators and ailerons are senstive, compare with other FS. But all FS are sensitive as well, compared with others this C172P is the most senstive aircraft, just a little joke/peddle movement can make huge change. We tried several landings (short field, soft field, power-off 180 accuracy and no-flap landing), at low airspeed, the airplane should reacting slaggish and less effective compared with high airspeed. However for this C172P, the yoke and peddles are still effectively control the movement. You can test this in slow flight manuver, with full flap maintain around 50 kn without altitude gain and loss (plus and minus 50ft), and without flap maintain around 55kn.

Good thing is this C172P is the most realistic one for simulating stalls and spins. All others are far more from real life.

All test using default setting, and no wind condition, standard ISA atmosphere, just moving to KDAB for take off and landings, because it is the one we most familier with.

Octal450 commented 3 years ago

@Megaf

which had his foot on the rudder for a while

That's why you no felt anything.

Kind Regards, Josh

Megaf commented 3 years ago

I flew for nearly 30 min doing the rudder myself @Octal450 There was a little left tendency but nothing like in FG.

Octal450 commented 3 years ago

nothing like in FG.

Agreed. Its too strong. I've said so for 5 years or so.

Kind Regards, Josh

wlbragg commented 3 years ago

I finally set up my peddles in Linux and have my analog brakes tied to the sim. This video demonstrates the control I have with the proper equipment, they work perfect. Small pressure on the peddles brake the aircraft without casing the wheels to lock. There is one spot I needed a sharper turn and I applied a small, brief, bit up rudder.Love the differential braking. The only thing I can think of for the keyboard braking would be to add anti-lock logic maybe or don't allow the keypress to get to 1. Don't critique my takeoff, thiswas just an example of differential braking with the right equipment. https://youtu.be/jEnmyuhFrhc

HHS81 commented 3 years ago

O.k.- you rotated at 45ktn- barely above stall speed-

@HHS81 Please... I'm not describing a one off occurrence... I have a 1+ hour flight on my YouTube channel with this happening at up to 100 kts.

don´t use the HUD!

I don't use the HUD, the HUD was there to simply demonstrate the amount of input I had to apply and how much trim I had. Also, if the HUD and the aircraft disagree about the speed and other stuff then we have a BUG. Again, this is FG's default aircraft and it should at least be 100% compatible with FG and use FG standards. Am I asking too much?

SMH...

Please can adjust your tone down a lot? We are not here to make things just for you.

Here are people who not only flew that aircraft more than your 30minutes, but here are also people who do know the POH and other things of the real thing quite good, and tried to simulate this as good as they can.

And no, there is no bug!

Every Airspeed Indicator in an aircraft are uncorrected in the speeds they are showing. That means the ASI gauge does not always tells you the correct speed. That happens because of air compressibility error, density variations, AOA and the location of the installation. That´s why nearly every POH for a specific aircraft contains a table, which shows the corrected speeds compared to the indicated speeds. This is different for every aircraft type.

The c172p and c182s simulates this correct, that´s why you see a different speed on the HUD. It is not a bug, it is a feature of the c172p. Take a look into the POH before you judge: POH Skyhawk C172P-1982 on Page 5-9 airspeed calibration.

Rotation speed on the c172p is between 50 and 60ktn Indicated Airspeed. In your video you are rotating at <45ktn Indicated Airspeed. At this speed beta angle is high! With that you need an additional amount of right pedal to compensate. The c172p in FGFS needed already a lot of right pedal- with that high beta angle even more.

Copy that?

HHS81 commented 3 years ago

For the left turning tendency, we tested Chandelle maneuver using this aircraft and compared with P3D and X-Plane. When we did Chandelle, it required nearly 3/4 of the full range of peddle movement for coordinate, and others needed 1/4 or less. In real life, it require nomally 1/3 to half of full range for coordinate.

For the adverse yaw, we tested with Steep Turn maneuver, it's a little hard to maintain minus and plus 50 feet altitude when transite from left turning to right turning, even difficult to maintain plus and minus 100 feet. I believe it's because the adverse yaw is too much, and associate with too much left turning tendency. In real life, for left steep turn, we still need a little left rudder, maybe 1/8 to 1/4, even left turning tendency helping me, for right turn, it require lots more right rudder, 1/3 to half of full range.

At which speeds you tested that? The lower the speed the more adverse yaw effect I would expect. Or better said: the higher the speed much less adverse yaw effect should be there.

dany93 commented 3 years ago

@dany93 wrote

slightly unstable when loaded such as the CoG is at 45 inches (which might be normal). _"

@HHS81 wrote

What do you mean with "unstable"? I didn`t see anything unstable.

I checked it again. Sorry (or cheers?), that was a bad impression, unconfirmed. Not a critique, It was just just an observation to emphasize that CoG far enough behind can bring instabilities. Well known, but not verified in this case. (here, the CoG is still inside the limits).

dany93 commented 3 years ago

@Megaf wrote

if the HUD and the aircraft disagree about the speed and other stuff then we have a BUG. Again, this is FG's default aircraft and it should at least be 100% compatible with FG and use FG standards. Am I asking too much?

Prior to being so peremptory, almost aggressive, please ask or read the POH. If I remember well the airspeed needle indications have been corrected for the "Airspeed calibration" table, p. 5-9. (sorry, I personally admit I can make a mistake, that's old... I hope someone will confirm or fix me)

Confirmed. I hadn't noticed that @HHS81 already gave this response.

tonghuix commented 3 years ago

For the left turning tendency, we tested Chandelle maneuver using this aircraft and compared with P3D and X-Plane. When we did Chandelle, it required nearly 3/4 of the full range of peddle movement for coordinate, and others needed 1/4 or less. In real life, it require nomally 1/3 to half of full range for coordinate. For the adverse yaw, we tested with Steep Turn maneuver, it's a little hard to maintain minus and plus 50 feet altitude when transite from left turning to right turning, even difficult to maintain plus and minus 100 feet. I believe it's because the adverse yaw is too much, and associate with too much left turning tendency. In real life, for left steep turn, we still need a little left rudder, maybe 1/8 to 1/4, even left turning tendency helping me, for right turn, it require lots more right rudder, 1/3 to half of full range.

At which speeds you tested that? The lower the speed the more adverse yaw effect I would expect. Or better said: the higher the speed much less adverse yaw effect should be there.

For Chandelle, I used full thruttle, but all the way slow to nearly V1 speed, around 45-50 kn. For steep turn, it's all around Va speed, 95ktn.

P.S. Maneuver Reference https://s3.amazonaws.com/atp-program-docs/supplements/cessna-172-training-supplement.pdf

Octal450 commented 3 years ago

Gentlemen lets keep this civil and calm here please. We are must be respectful and kind each others opinions.

Again, this is FG's default aircraft and it should at least be 100% compatible with FG and use FG standards. Am I asking too much?

For the record, the difference is there for a reason. The HUD is kinda like a absolute sim values, whereas the aircraft's instruments are animated off the instrumentation values. They will not agree to due to many reasons! The HUD is not intended to be used during aircraft operation. I wouldn't be against a HUD that match the aircraft more better.

Kind Regards, Josh

wkitty42 commented 3 years ago

On 7/3/21 2:26 PM, Josh Davidson wrote:

For the record, the difference is there for a reason. The HUD is kinda like a absolute sim values, whereas the aircraft's instruments are animated off the instrumentation values. They will not agree to due to many reasons! The HUD is not intended to be used during aircraft operation. I wouldn't be against a HUD that match the aircraft more better.

unless i'm not remembering properly, the default in-sim HUD is disabled in the c172p like the route manager and for the same reasons...

Megaf commented 3 years ago

I've done some more testing. Until this test, I only had the pilot in the aircraft, without a passenger or co-pilot. This time I had the same weight on both seats. Weather is set to fair weather. The takeoff roll was at ~60 KIAS, HUD is there only to indicate my inputs. Please ignore jerky throttle movements, my throttle is not linear at all, and it has a centre notch... With the same weight on both sides, indeed the left tendency is reduced at cruise speed. I had 0 rudder trim, a slight right aileron trim (That I have no idea how it happened, and I don't know how to reset it).

https://www.youtube.com/watch?v=pGy0hIxTbTs

wkitty42 commented 3 years ago

On 7/3/21 2:46 PM, Megaf wrote:

I had 0 rudder trim, a slight right aileron trim (That I have no idea how it happened, and I don't know how to reset it).

if i'm reading FGData/keyboard.xml correctly and the craft is not overriding the key settings, it looks like CTRL-4 and CTRL-6 adjust the aileron trim left and right while CTRL-5 resets all, aileron, elevator, and rudder, trims...

  <key n="52">
   <name>4</name>
   <desc>Move aileron left (or adjust AP heading.)</desc>
   <repeatable type="bool">true</repeatable>
   <binding>
    <command>nasal</command>
    <script>
      controls.incAileron(-0.05, -1.0)
    </script>
   </binding>
   <mod-shift>
    <desc>Look left</desc>
    <binding>
     <command>property-assign</command>
     <property>/sim/current-view/goal-heading-offset-deg</property>
     <property>/sim/view/config/left-direction-deg</property>
    </binding>
   </mod-shift>
   <mod-ctrl>
     <desc>Aileron left trim</desc>
     <binding>
      <command>property-assign</command>
         <command>property-adjust</command>
         <property>/controls/flight/aileron-trim</property>
         <step type="double">-0.01</step>
     </binding>
   </mod-ctrl>
  </key>

  <key n="53">
   <name>5</name>
   <desc>Center aileron, elevator, and rudder</desc>
   <binding>
    <command>nasal</command>
    <script>controls.centerFlightControls()</script>
   </binding>
   <mod-ctrl>
     <desc>Clear all trims</desc>
       <binding>
           <command>property-assign</command>
           <property>/controls/flight/elevator-trim</property>
           <value>0</value>
       </binding>
       <binding>
           <command>property-assign</command>
           <property>/controls/flight/aileron-trim</property>
           <value>0</value>
       </binding>
       <binding>
           <command>property-assign</command>
           <property>/controls/flight/rudder-trim</property>
           <value>0</value>
       </binding>
   </mod-ctrl>
  </key>

  <key n="54">
   <name>6</name>
   <desc>Move aileron right (or adjust AP heading.)</desc>
   <repeatable type="bool">true</repeatable>
   <binding>
    <command>nasal</command>
    <script>
      controls.incAileron(0.05, 1.0)
    </script>
   </binding>
   <mod-shift>
    <desc>Look right</desc>
    <binding>
    <command>nasal</command>
    <script>
      controls.incAileron(0.05, 1.0)
    </script>
   </binding>
   <mod-shift>
    <desc>Look right</desc>
    <binding>
     <command>property-assign</command>
     <property>/sim/current-view/goal-heading-offset-deg</property>
     <property>/sim/view/config/right-direction-deg</property>
    </binding>
   </mod-shift>
      <mod-ctrl>
          <desc>Aileron right trim</desc>
          <binding>
              <command>property-assign</command>
              <command>property-adjust</command>
              <property>/controls/flight/aileron-trim</property>
              <step type="double">-0.01</step>
          </binding>
      </mod-ctrl>
  </key>

wlbragg commented 3 years ago

@Megaf why aren't you setting the trim to 0.02? That is the default to have this aircraft trimmed correctly as a permanent trimmed rudder.

While testing for a different issue I had to takeoff several times in a row. I discovered at the .02 default rudder trim, I can apply right aileron deflection as soon as I get any speed at all and keep the aircraft straight down the runway. Note, I said right aileron, opposite of what is intuitive.

wkitty42 commented 3 years ago

oops... sorry... i forgot that email replies do not support markdown code in my post above...

dany93 commented 3 years ago

@Megaf wrote

With the same weight on both sides, indeed the left tendency is reduced at cruise speed.

This is normal. I hesitated on which trim values to preset for comfort for someone who yet doesn't the aircraft. See this message

I had 0 rudder trim, a slight right aileron trim (That I have no idea how it happened, and I don't know how to reset it).

Normal too. In c172p-set.xml, I set (lines 587-588) `` <aileron-trim = 0.022 <rudder-trim = 0.02 `` Values that you would see at start with "Rudder Trim Option" OFF.

You can change this in flight via the Internal Properties (not saved). You can change this for all your future flights by setting different values in c172p-set.xml.

I have added a piece of code attached to the "hat" of my JS for the aileron trim (cheating but very comfortable).

Octal450 commented 3 years ago

unless i'm not remembering properly, the default in-sim HUD is disabled in the c172p like the route manager and for the same reasons...

Its not last time I checked.

Kind Regards, Josh

Octal450 commented 3 years ago

Note, I said right aileron, opposite of what is intuitive.

Takeoff should be corrected with rudder. Aileron in the real plane will not make much of an effect when on the ground. Ailerons should start into the wind and then go to neutral as you speed up. If you are able to stop the left turning motion with just aileron alone while on the GROUND, something is wrong.

Kind Regards, Josh

Megaf commented 3 years ago

I do not think is is, otherwise I would not have it there. It is accessible by simply pressing "'h'".

On 3 July 2021 19:31:21 GMT+01:00, waldo kitty @.***> wrote:

On 7/3/21 2:26 PM, Josh Davidson wrote:

For the record, the difference is there for a reason. The HUD is kinda like a absolute sim values, whereas the aircraft's instruments are animated off the instrumentation values. They will not agree to due to many reasons! The HUD is not intended to be used during aircraft operation. I wouldn't be against a HUD that match the aircraft more better.

unless i'm not remembering properly, the default in-sim HUD is disabled in the c172p like the route manager and for the same reasons...

-- You are receiving this because you were mentioned. Reply to this email directly or view it on GitHub: https://github.com/c172p-team/c172p/issues/1364#issuecomment-873450550

dany93 commented 3 years ago

@Megaf It seems (??) that you are responding from your e-mail. Be careful, you will not see the changes for messages which have been edited in Github.

wlbragg commented 3 years ago

If you are able to stop the left turning motion with just aileron alone while on the GROUND, something is wrong.

Not necessarily, it's only effective with some decent airflow over the wings and it is not theoretically wrong to expect the behavior. What is not intuitive is the way you perceive what action your taking.

This should help explain the effect. This is a discussion about turning in the air and why you use rudder as well as aileron. But it also at least partially explains the effect I am describing that I experienced in the aircraft on the ground. This also is not taking into account the drag or friction change on the left and right gear due to the force of the pressure changes on the wings.

we lower an aileron, which changes the curve of the wing. That generates more lift, which means the wing with the lowered aileron—the outside one going into a turn—has more lift than the inside wing, so it goes up. However, because it has more lift, it also has more drag than the inside wing. That drag pulls the wing back. This is adverse yaw—yaw in the wrong direction. So, when the ailerons are deflected and the airplane is rolling into a bank, rudder is applied in the direction of the turn to counteract the greater drag on the outside wing.

wlbragg commented 3 years ago

Takeoff should be corrected with rudder. Aileron in the real plane will not make much of an effect when on the ground. Ailerons should start into the wind and then go to neutral as you speed up.

Keep in mind, I am not talking about correct procedures. I am simply describing what I experience in the sim. Quantify "not much of an effect". If your starting at .02 rudder trim, how much of this effect do you need?

wlbragg commented 3 years ago

I just tried the PA-28 and I'm not experiencing much of a difference in the left turning tendency. Some rudder input is required, same as the c172p. Also I was able to notice the aileron ground turning effect during a smaller range of speed and not as pronounced. But the PA-28 is a low wing aircraft and appears to have smaller ailerons. This stuff is quite interesting but requires a PHD to make sense of very cause and effect.

dany93 commented 3 years ago

Left-Turning Tendencies Torque effect:

As you throttle up your engine for takeoff, the right-turning direction of your engine and propeller forces the left side of your airplane down toward the runway. When the left side of the airplane is forced down onto the runway, the left tire has more friction with the ground than the right tire, making your aircraft want to turn left.

Which may explain why aileron deflection to roll rightwards, by lowering the force on the left wheel, can decrease (not cancel) the left turning tendency.

wkitty42 commented 3 years ago

one way to find out would be to reverse the engine to spin the other way and see if everything reverses...

wlbragg commented 3 years ago

@dany93 Agreed, I also said basically the same thing by deduction of what aileron deflection would be doing to the gear. As in...

This also is not taking into account the drag or friction change on the left and right gear due to the force of the pressure changes on the wings.

Which your article explains with "torque effect".

tonghuix commented 3 years ago

@dany93 there are FOUR factors which cause left turning tendency, and "torque effect" is just one of them.

dany93 commented 3 years ago

@tonghuix wrote

there are FOUR factors which cause left turning tendency, and "torque effect" is just one of them.

I obviously know this. @dany93 wrote

can decrease (not cancel) the left turning tendency.

dany93 commented 3 years ago

@wlbragg wrote

This also is not taking into account the drag or friction change on the left and right gear due to the force of the pressure changes on the wings. And this averse yaw seem

Yes! You had seen it exactly. :smiley: It's not the only contribution, but changing this one alone can have an observable effect on the total (depending on the relative amplitudes of each). [EDIT] And as you quoted it, the adverse yaw comes into the game to complicate everything when you act on the ailerons .... From my test, it seems dominant compared with the load / drag decreasing effect on the left wheel. Which means that you can do nothing against this load / drag effect from the left wheel with the ailerons, you only have the rudder. Which is the usual way. At observation in FG, the yaw change via drag friction on the left wheel due to load change seems very weak, hard to observe.

dany93 commented 3 years ago

This issue contains too many subjects, t will become unreadable. I opened a new one Adverse Yaw amplitude (Cnda) #1378.

c172p-team / c172p