fix: Update landing gear drag

[donstim]

Summary of Changes

Updates landing gear drag increment to better match gear down performance data from FCOM supplementary procedures section. CONF 3 and CONF FULL drag had to be re-tuned since the published performance data for those configurations is with the landing gear down. Changing the gear drag increment means the basic flap drag for these configurations must be changed to retain the same drag level with gear down.

The gear down drag increment and the CONF 3 and FULL drag polars are also updated for the VNAV guidance algorithm.

References

The following screenshots compare the resulting A32NX climb, cruise, and descent performance with gear down to the published FCOM values. (Values are transcribed from the FCOM. Note that the FCOM includes some inappropriate flight conditions with speeds less than green dot and sometimes even less than VLS. These conditions were excluded from the comparisons.)

Additional context

I only recently became aware that landing gear down performance is provided in the supplementary procedures section of the Airbus A320 FCOM. The current landing gear drag increment is an estimate based on previous experience that seemed to match expectations pretty well. When trying to match the FCOM performance data, however, it became obvious that the gear drag increment estimate, while reasonably close, was too low.

The MSFS flight model allows one value for the gear drag increment. In actuality, the gear drag increment varies inversely with lift coefficient. You can see from the above climb performance comparisons that as the airplane climbs higher, especially at heavier weights, the A32NX takes longer to climb than the real airplane. This is probably due to the constant gear drag increment, which should be getting smaller at these higher CL conditions. Still, it works pretty well.

Discord username (if different from GitHub): donbikes#4084

Testing instructions

There should not be a substantial change to the flight characteristics of the airplane. In CONF 3 and FULL with gear down, the airplane should perform exactly as it did before. In CONF 3 and FULL with gear up, there should be slightly less drag. And with flaps up, CONF 1, 1+F, and 2, there will be a bit more drag with gear down. This will provide a bit more capability to decelerate and/or descend by dropping the gear in these configurations.

How to download the PR for QA

Every new commit to this PR will cause a new A32NX artifact 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, click on the bottom PR tab
4. Click on the A32NX download link at the bottom of the page

[crocket63]

Note that we'll use a gear drag portion (pretend gear is 10% out) to simulate gear door opened drag when gear is up and doors are opened. Would probably not change much and this is a relatively rare case when using second turn of gravity extension handle, just wanted to bring it up :)

[donstim]

Hopefully, this will be it for a while for the flight model updates.

[Hellfire-2345]

Quality Assurance Trainee Report

Discord : hellfire#7383
Object of testing: #7660
Tier of Testing : 1
Date : 6/01/2023

Testing Process:
After dropping the landing gear on approach there was a difference in the drag the
aircraft was creating to when the gear was up.
Negatives:
N/A
Testing Results:
passed
Conclusions:
aircraft behaved well

[mico975]

Quality Assurance Tester Report

Discord : mico#3145
Object of testing: #7660
Tier of Testing : 1
Date : 11/01/2023

Testing Process:
There should not be a substantial change to the flight characteristics of the airplane. In CONF 3 and FULL with gear down, the airplane should perform exactly as it did before. - OK
In CONF 3 and FULL with gear up, there should be slightly less drag. OK
And with flaps up, CONF 1, 1+F, and 2, there will be a bit more drag with gear down. - OK
This will provide a bit more capability to decelerate and/or descend by dropping the gear in these configurations. - TRUE

Negatives:
N/A

Testing Results:
Passed

Conclusions:
LGTM