fix(a380x/flightmodel): adjust climb performance

[BlueberryKing]

Fixes #9042

Summary of Changes

Tune engine thrust and drag model to be more accurate.

• Adjust performance in .cfg files
• Update engine performance tables for vertical predictions
• Update performance tables for flight model

Screenshots (if necessary)

References

Additional context

Discord username (if different from GitHub):

Testing instructions

• Perform a full flight, ensure you get (close to) accurate predictions throughout the flight.
• Ensure that the climb, cruise, and descent performance is believable.

How to download the PR for QA

Every new commit to this PR will cause new A32NX and A380X artifacts to be created, built, and uploaded.

1. Make sure you are signed in to GitHub
2. Click on the Checks tab on the PR
3. On the left side, find and click on the PR Build tab
4. Click on either flybywire-aircraft-a320-neo or flybywire-aircraft-a380-842 download link at the bottom of the page

[chinjh93]

Tested some of the values you've amended the plane feels a bit sluggish at climb now. Gross weight of about 373tonnes and my climb was only 2000fpm during the climb from 10000feet to 15000feet with IAS 290knots on open climb. This value was more believable if the gross weight was around 500tonnes or more.

[BlueberryKing]

Tested some of the values you've amended the plane feels a bit sluggish at climb now. Gross weight of about 373tonnes and my climb was only 2000fpm during the climb from 10000feet to 15000feet with IAS 290knots on open climb. This value was more believable if the gross weight was around 500tonnes or more.

Thanks for testing! I noticed the same thing indeed, this was due to an error in my tuning method. I will continue to work on it.

[2hwk]

@BlueberryKing Let me know when you are done so we can do a formal code review

Also changelog needed.

[chinjh93]

Has the parameters been tested and merged with the supposed Another taxi thrust adjustment Cause i seem to see both pulls involve the same cfg.

[BlueberryKing]

Has the parameters been tested and merged with the supposed Another taxi thrust adjustment Cause i seem to see both pulls involve the same cfg.

My changes are now on top of the PR you mention, so they shouldn't conflict.

[donstim]

One test here and it looked very good to me. Although I don't have any data to base it on (other than comparison to the A32NX), the climb rates looked very believable. For my flight, FMS predicted FL 400 at REC MAX, and I got to FL 39.6 before the climb rate stayed below 300 fpm (one definition of REC MAX).

[flogross89]

Very cool, thank you!

[BlueberryKing]

Thank you for the reviews! I will address your comments as soon as I can.

[mattking247]

Do you need anymore data collecting on this, or just wait for an update?

[mattking247]

Quality Assurance Tester Trainee Report

Discord Username : Matt
Object of testing : #9358
Aircraft : A380X
Tier of Testing : 1
Date : 27/11/2024

Testing Process: Previous test copied with similar weights. Then a worst case max take off weight was performed to compare. Results are below.

Both Tests: LFBO departure, runway 14R. Live weather, 4 degrees. Both tests to FL 360, flown on a direct heading without any turns. Tests flown one after the other, so weather was as close to similar as possible.

Test 1 456.9 tonnes at take off (previous test repeat).

Test 1 - repeat of previous test, altitudes and climb numbers below for reference:
Flap 1 departure, initial climb until accel alt: 2700FPM

250kts - 4,000ft - 2500FPM - THR 94.3 - N1 85.1
" - 6,000ft - 2800FPM - THR 95 - N1 85.8
" - 8,000ft - 2700FPM - THR 95 - N1 86.8
" - 10,000ft - 2600FPM - THR 94.9 - N1 87.5
290kts - 12,000ft - 2300FPM - THR 93.6 - N1 87.9
" - 14,000ft - 2300FPM - THR 92.6 - N1 88.4
" - 16,000ft - 2200FPM - THR 91.7 - N1 88.9
" - 18,000ft - 2000FPM - THR 91.4 - N1 89.4
" - 20,000ft - 1800FPM - THR 91.3 - N1 89.9
" - 22,000ft - 1700FPM - THR 92.9 - N1 90
" - 24,000ft - 1700FPM - THR 94.5 - N1 90.1
" - 26,000ft - 1500FPM - THR 99 - N1 89.9
" - 28,000ft - 1200FPM - THR 99 - N1 89.5
" - 30,000ft - 900FPM - " - N1 89.4
" - 32,000ft - 600FPM - " - N1 89.2
" - 34,000ft - 500FPM - " - N1 89.0
" - 36,000ft - 500FPM - " - N1 89.0

Sadly, I did not record the time to FL360 on the previous test I ran. However, for this test it was 26.41. The results are fairly similar to the previous test.

---

Test 2, max takeoff weight.

Next, I did a worst case scenario test with all the same test parameters, apart from this time at max take off weight.
All other variables were the same. Test was conducted immediately following the previous test.

509.4 tonnes at take off.

Test 2 - Max takeoff weight, altitude and climb numbers below for reference:
Flap 2 departure, initial climb until accel alt: 2600FPM

250kts - 4,000ft - 2500FPM - THR 93.6 - N1 84
" - 6,000ft - 2500FPM - THR 95 - N1 85.2
" - 8,000ft - 2500FPM - THR 95 - N1 86.4
" - 10,000ft - 2400FPM - THR 94.8 - N1 87.2
290kts - 12,000ft - 2200FPM - THR 93.6 - N1 87.6
" - 14,000ft - 2200FPM - THR 92.6 - N1 88.2
" - 16,000ft - 1900FPM - THR 91.7 - N1 88.7
" - 18,000ft - 1800FPM - THR 91.4 - N1 89.2
" - 20,000ft - 1800FPM - THR 91.3 - N1 89.6
" - 22,000ft - 1800FPM - THR 92.8 - N1 89.8
" - 24,000ft - 1500FPM - THR 94.5 - N1 90.1
" - 26,000ft - 1400FPM - THR 99 - N1 89.8
" - 28,000ft - 1300FPM - THR 99 - N1 89.5
" - 30,000ft - 900FPM - " - N1 89.4
" - 32,000ft - 600FPM - " - N1 89.2
" - 34,000ft - 500FPM - " - N1 88.9
" - 36,000ft - 600FPM - " - N1 89.1

As you can see, the numbers were not significantly different, and the main change in FPM came around the mid to late teens. Time to FL360 at max takeoff weight was 27.35, less than a minute more then the previous test.

For me, both of these numbers seem relatively accurate throughout the climb, but still seem to washout somewhat more than I would have thought in the 30,000ft area for the non-max TO weight test. For a max take off climb, I think these numbers seem quite accurate. As for the repeat test at 456 tonnes, maybe this lighter weight (relative to max) is where a little tweaking still needs to happen. Interested to hear the thoughts of others though. Clearly, this is all temp and conditions dependent, but at 4 deg C on take off, and clear skies both times, seems a little cooler than standard.

I am on the fence about a pass/fail. I think this new method should be implemented soon, as it is a lot more accurate than previous versions. I think the max takeoff weight climb performance seems pretty spot on to me. Maybe lighter weights is a little low on FPM climb rate in the 30,000s, but nothing much. If it needs a little tweaking later on, it is much smaller tweaks than the current climb model.

[Ueeew]

I have some bug which might help. One comment said under this topic said that the N1 is to low in Climb and Cruise. In my opinion this is true. In fact, the N1 should be higher in climb and cruise than the THR but hat isnt the case. I'm not sure if this has anything to do with the wrong engine model. I just wanted to say this in case it helps.

[BProduction222]

If I may add my 2 cents here, and some points to consider before tuning too much on the engines.

There are 2 major reasons why climb performance is currently exaggerated, especially if you are trying to compare YouTube footage with this rendition in MSFS, which in my opinion, may not require too much engine tuning.

1. Currently the Engines are not being limited by their THR %, as they normally should, but are currently being limited by N1. Which means that you will generally get a higher thrust output in the FBW A380 than you normally would.
   So to fix the first issue, the engines when set to CLB thrust must first follow the THR rating, not N1. You will then already notice a major difference in climb performance.

2. At my airline, it is common to use Derated Climb thrust for the entire climb phase, which also reduces climb performance. We use D3 for below 520t and D2 for 520t or above.

So if those two things would be properly simulated, you would notice a much more realistic representation of the climb performance of the A380.

I would recommend the next time you fly the FBW A380, look at the thrust CLB limit when taking off, and adjusting your V/S knob to match your EWD Limiting thrust with your THR %, instead of N1 %.

However if you want more data, I can try and get some footage in a level-d sim next time

[BlueberryKing]

If I may add my 2 cents here, and some points to consider before tuning too much on the engines.

There are 2 major reasons why climb performance is currently exaggerated, especially if you are trying to compare YouTube footage with this rendition in MSFS, which in my opinion, may not require too much engine tuning.

1. Currently the Engines are not being limited by their THR %, as they normally should, but are currently being limited by N1. Which means that you will generally get a higher thrust output in the FBW A380 than you normally would.
   So to fix the first issue, the engines when set to CLB thrust must first follow the THR rating, not N1. You will then already notice a major difference in climb performance.
2. At my airline, it is common to use Derated Climb thrust for the entire climb phase, which also reduces climb performance. We use D3 for below 520t and D2 for 520t or above.

So if those two things would be properly simulated, you would notice a much more realistic representation of the climb performance of the A380.

I would recommend the next time you fly the FBW A380, look at the thrust CLB limit when taking off, and adjusting your V/S knob to match your EWD Limiting thrust with your THR %, instead of N1 %.

However if you want more data, I can try and get some footage in a level-d sim next time

Hi

Thank you for your input. The lack of a derate option does indeed contribute to the problem. That's something that we can hopefully add in the future. Regarding 1., that should only be an issue of the thrust limit. The tuning is done by comparing the thrust output (or climb gradients equivalently) for a given N1 between the sim and a reference. The thrust limit then has to be adjusted such that the correct N1 values are indeed reached during the climb at the given conditions.

And yes, indeed, the thrust limit indication is an N1 limitation rather than a THR% at the moment. This is incorrect. However, as long as it is an N1 limit that's applied to the N1 control loop, that is not much different from calculating an appropriate THR% limit and applying it to the THR% control loop, the resulting N1 is the same.

So in short, we are working on adjusting the thrust output to more realistic levels. The tuning should hopefully not take too much longer. 😄

[BProduction222]

If I may add my 2 cents here, and some points to consider before tuning too much on the engines.
There are 2 major reasons why climb performance is currently exaggerated, especially if you are trying to compare YouTube footage with this rendition in MSFS, which in my opinion, may not require too much engine tuning.

1. Currently the Engines are not being limited by their THR %, as they normally should, but are currently being limited by N1. Which means that you will generally get a higher thrust output in the FBW A380 than you normally would.
   So to fix the first issue, the engines when set to CLB thrust must first follow the THR rating, not N1. You will then already notice a major difference in climb performance.
2. At my airline, it is common to use Derated Climb thrust for the entire climb phase, which also reduces climb performance. We use D3 for below 520t and D2 for 520t or above.

So if those two things would be properly simulated, you would notice a much more realistic representation of the climb performance of the A380.
I would recommend the next time you fly the FBW A380, look at the thrust CLB limit when taking off, and adjusting your V/S knob to match your EWD Limiting thrust with your THR %, instead of N1 %.
However if you want more data, I can try and get some footage in a level-d sim next time

Hi

Thank you for your input. The lack of a derate option does indeed contribute to the problem. That's something that we can hopefully add in the future. Regarding 1., that should only be an issue of the thrust limit. The tuning is done by comparing the thrust output (or climb gradients equivalently) for a given N1 between the sim and a reference. The thrust limit then has to be adjusted such that the correct N1 values are indeed reached during the climb at the given conditions.

And yes, indeed, the thrust limit indication is an N1 limitation rather than a THR% at the moment. This is incorrect. However, as long as it is an N1 limit that's applied to the N1 control loop, that is not much different from calculating an appropriate THR% limit and applying it to the THR% control loop, the resulting N1 is the same.

So in short, we are working on adjusting the thrust output to more realistic levels. The tuning should hopefully not take too much longer. 😄

Alright, it looks like you guys have a good method to fix this issue.
I just wanted to make sure you considered those points, since a lot of people who make videos on it or stream say it is too powerful, but then don't actually limit their thrust correctly and consider derated climbs.

[G-DRAW]

Regarding taxi thrusts on the A380, in real life they use around about a maximum of 15% THR and no more that 15% THR, even at the MTOW. So according to real world A380 Pilots, they only use a small amount of thrust to get moving at very heavy weights.

[donstim]

Regarding taxi thrusts on the A380, in real life they use around about a maximum of 15% THR and no more that 15% THR, even at the MTOW. So according to real world A380 Pilots, they only use a small amount of thrust to get moving at very heavy weights.

This PR does not affect taxi thrust. Taxi thrust has already been adjusted with the assistance of IRL A380 pilots on the team. (The THR indication on the A380X is not accurately modeled yet.)

[BlueberryKing]

I have made some further adjustments to the thrust output and thrust limits. The thrust output might be a bit too high at high altitudes now, but I prefer that for this initial adjustment PR.

Feel free to give it a test!