С172 flight dynamics FSX vs P3D

[ilya1502]

Hello, everyone!

Has anyone noticed that the flight dynamics in the P3D are different? I tried flying both sims on the same platform and on the same joystick+pedals, which are identically calibrated with FSUIPC, and the A2A C172 behaves differently in P3D. (And here I mean a FSX-dedicated model of A2A C172 vs a P3D-dedicated model.) The P3D version is less stable in bank, especially at low speeds. I have around 80 hours in a real Skyhawk SP. During a no-wind takeoff, I always semi-rotate early in the roll, making the aircraft run on its main wheels with the nosewheel in the air. And then at the speed of about 55 knots I gently rotate it to about 7-10 degrees nose-up. It works nicely and smoothly. This procedure works perfectly in the FSX A2A C172, but it leads to a premature lift-off in the P3D version at the airspeed around 40 knots. The aircraft just jumps into the air with a bad nose-up and tends to bank violently. I mean to say that the P3D perhaps works with the FD differently and maybe the same flight model requires additional tuning... But, anyway, has anyone noticed any differences?

Ilya

[bobsk8]

Hello, everyone!

Has anyone noticed that the flight dynamics in the P3D are different? I tried flying both sims on the same platform and on the same joystick+pedals, which are identically calibrated with FSUIPC, and the A2A C172 behaves differently in P3D. (And here I mean a FSX-dedicated model of A2A C172 vs a P3D-dedicated model.) The P3D version is less stable in bank, especially at low speeds. I have around 80 hours in a real Skyhawk SP. During a no-wind takeoff, I always semi-rotate early in the roll, making the aircraft run on its main wheels with the nosewheel in the air. And then at the speed of about 55 knots I gently rotate it to about 7-10 degrees nose-up. It works nicely and smoothly. This procedure works perfectly in the FSX A2A C172, but it leads to a premature lift-off in the P3D version at the airspeed around 40 knots. The aircraft just jumps into the air with a bad nose-up and tends to bank violently. I mean to say that the P3D perhaps works with the FD differently and maybe the same flight model requires additional tuning... But, anyway, has anyone noticed any differences?

Ilya

Sounds like you may have updated P3D, and didn't run the update for the C 172. Read this thread. https://a2asimulations.com/forum/viewto ... 07&t=55066

[Nick - A2A]

Yeah - I agree it sounds as if your 172 installation in P3D isn't updated successfully, whereas the one in FSX is. There's been quite a list of updates to the 172 flight dynamics over the past 2-3 years, so without the benefit of these the behaviour will be quite different.

Definitely worth deleting the client.wyc file as described in the thread Bob linked above, then running the Accu-Sim updater again.

Also worth checking that they're both set-up identically in terms of the maintenance hangar options; specifically that you don't have the default prop in FSX, and the 'S equivalent' prop in P3D.

Nick

[ilya1502]

Well, gentlemen, let's recap.

• 1. I must delete the file <My P3D install>\A2A\Cessna172\Update_p3d\client.wyc (In my case it is D:\FSPrepar3Dv3\A2A\Cessna172\Update_p3d\client.wyc)
  2. I must start the updater EXE, which I can download from the respective forum's thread. (I start it with Administrator rights just for sure.)
  3. When it launches it asks me, what sim I'd like to update (FSX, P3Dv1, P3Dv2 or P3Dv3). I should select P3Dv3 as it is my case.
  4. Then it successfully finds my P3D path and installs. (It is actually installing right now).

Now, I'm sure I ran this routine (except for the step #1, of course) right after I installed the A2A C172 into my sim. How could it happen that it updated improperly? How can I ensure that it is updated to the most current state?

[Nick - A2A]

To be honest Ilya, I'm not sure how the updater deals with a dual install of FSX + P3D (I only have FSX-SE at present). However, it seems quite a few of A2A's customers may inadvertently have Accu-Sim installations which aren't properly updated because of P3D updates (as Bob mentions) or because they're reinstalled from their original A2A product installer at some point.

However, deleting the client.wyc file(s) and rerunning the update should sort things out. Interested to hear if the P3D Skyhawk flight dynamic are now consistent with the FSX installation in your case...

Thanks,
Nick

[ilya1502]

Did everything as in my previous message. No changes in the aircraft behaviour

I tried with no baggage and 2 pilots in the front seats, but it still flies and handles as if it had a terrible backward center-of-gravity. By the way, I compared aircraft.cfg and air-files of P3D and FSX versions after install and all updates (TC’s function of file compare by content), and they are the same.

[Nick - A2A]

Okay - could you just confirm if you checked which prop is installed in the FSX and P3D C172s in the maintenance hangar.

Thanks,
Nick

[ilya1502]

Yes, sure. It is a 2700 rpm prop, the 172S equivalent.

[Nick - A2A]

Maybe try switching both to the standard prop and see what you observe. The 180hp prop does seem to produce a more aggressive pitch up on take-off as discussed recently here.

Nick

[ilya1502]

Yes, I followed that discussion closely.

Well, I tried and, yes, the standard prop gives more benign behavior. I also reduced the "Simulated elevator force" number to 0 (I still struggle to understand the physical sense of this number) and it became a bit better with the 180-hp prop. The key word here is "a bit", because the change between 0 and 100 has always seemed to give me barely observable difference (more like a placebo effect). What is definitely wrong is that a real Skyhawk SP stabilizes itself at around 60 kias if the trim is set beside the "Take Off" mark and hands are off the yoke, never even close to stalling. The A2A C172 + 2700-rpm prop pitches up to an agressive stall in this case. I get the proper behavior when I roll a significant amount of nose-down trim, with the indicator roughly aligned with the "K" or "E" letter of the "TAKE OFF".

[Oracle427]

Having flown a 172N with a 180HP engine and prop STC and a 180HP 172SP but never a 172R I can say that there is a pretty big difference in the handling between the 172N and 172SP at takeoff. It will pitch up aggressively and somewhat uncomfortably for me that I will hold forward pressure and trim out to maintain Vy. It feels like it might be trimmed for something slower than Vx if I were to let it find its own trim setting. I never tried seeing what it would do at altitude and I don't have access to it anymore to test.

That said, I have no idea if an R behaves more like an N or SP or something in between.

[Nick - A2A]

[...] the change between 0 and 100 has always seemed to give me barely observable difference (more like a placebo effect).

The effect of the "simulated elevator force" slider won't really be apparent at low airspeed such as during landing. It's in cruise where it's intended to make the pitch control a little less sensitive I believe.

The discussion seems to have moved onto differences between various version of the 172 but were you able to get both your FSX and P3D version of the 172 (with standard prop) behaving the same with regards to pitch behaviour during take-off Ilya?

Thanks,
Nick

[ilya1502]

It's in cruise where it's intended to make the pitch control a little less sensitive I believe.

Yes, but how does it do it? I mean in terms of sim variables or aerodynamics, 'cause - I'm sorry for nitpicking, but I don't really grasp the meaning of the "less sensitive" here - if it does it just by changing the joystick to elevator curve slope then it is one story, if it modulates the pitch moment vs AoA curve of the airplane then it is another, and it is yet another if it does it by changing the parameters of the simulator's elevator trim. So, finally, what difference I am supposed to observe when I change the number from 0 to 100? And how big a difference?

were you able to get both your FSX and P3D version of the 172 (with standard prop) behaving the same with regards to pitch behaviour during take-off Ilya?

No, Nick, I weren't. I'll give it another try today by reinstalling the Simconnect, though I don't think it will help.

[Nick - A2A]

Yes, but how does it do it? I mean in terms of sim variables or aerodynamics, 'cause - I'm sorry for nitpicking, but I don't really grasp the meaning of the "less sensitive" here - if it does it just by changing the joystick to elevator curve slope then it is one story, if it modulates the pitch moment vs AoA curve of the airplane then it is another, and it is yet another if it does it by changing the parameters of the simulator's elevator trim. So, finally, what difference I am supposed to observe when I change the number from 0 to 100? And how big a difference?

Well - I don't know anything about A2A's code of course, but I'd say it's the joystick to elevator response curve which is being modulated based on airspeed. The easiest way to demonstrate the effect for yourself would be to establish the aircraft in level cruise and accelerate to, let's say, 110 KIAS and then try applying full fore and aft control movement* with the setting at 100% and then do the same thing with it at 0%. You should notice a significant difference, it's definitely not just a placebo effect.

Scott's explanation of this setting can be read here.

Nick

*Not recommended in the real thing!

[ilya1502]

*Not recommended in the real thing!

This is a sort of "it is prohibited to dry your pets in the microwave" type of warning

the user can adjust the elevator sensitivity based on the simulated forces on the yoke

Well, I'll try what you suggested.