125 lines
5.4 KiB
Markdown
125 lines
5.4 KiB
Markdown
# General
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Changes are marked with a comment `//KH` and their respective original value
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above the change itself. In cases where the original values were too large or
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new sections were added, the changes are enclosed in `//KH START Modified` and
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`//KH END Modified` comments.
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# Adjustments
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- Dropped idle thrust so so that aircraft doesn't start rolling when not nearly
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empty
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- Affected by `n1_and_mach_on_thrust_table`
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- Adjusted idle down on 0 mach entries only
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- Smoothed low end
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- Adjusted mach 0 curve to end at 1
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- Adjusted mach 0.25 curve to have a similar end to mach 0
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- Adjusted mach 0.74 curve to have a similar end to the surrounding
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- Spool behaviour after 90 N1
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- Affected by `corrected_n2_from_ff_table`
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- Set idle N2 FF value directly
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- Made linear until original max
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- EGT
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- Affected by `itt_peak_temperature`, `itt_tc`, `egt_peak_temperature`,
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`egt_tc`, `egt_tuning_constant`, `fuel_flow_max_itt_factor`,
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`fuel_flow_min_itt_factor`, `itt_maxcorrection`
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- At ISA, SL, 60C, EGT does not exceed 960C TO
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limit
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- Used online references to achieve idle EGT
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- Used Saudi FCOM for high altitude EGT
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- This may be unachievable
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- Disabled sim protections
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- Affected by `max_n1_protection`, `max_n2_protection`, `max_egt_protection`
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- All set to zero
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- SDK conformance
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- Affected by `fuel_flow_gain`
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- Set to zero as the SDK indicated one ought to
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- Full AND trim on climb and certain cruise conditions (aft CG, light weight)
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- Affected by `elevator_lift_coef`
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- Adjusted to increase AND trim effectiveness
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- I am unsure if this is truly a fix or my tests lead me astray
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- Adjustment is not a complete fix
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- Slat drag and approach N1
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- Affected by slat drag
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- Lowered `drag_scalar`
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# Additions
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- New ground contact model
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# Observations
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## General
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All test are done at SL (EHAM) and ISA (15C, 1013.25 hPa) unless otherwise
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noted.
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## Engines
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### General
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The defined N1 and N2 max values are too low. as per EASA TCDS, the CF6-80C2D1F
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has a N1 max of 117.5 and a N2 max of 112.5. I do not know why the lower limits
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were chosen, it may be in our interest to adjust this to the actual limits.
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This may also influence the WASM since FADEC response and thrust limit
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selection may need to be adjusted to allow values higher than currently
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possible.
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The curves that `n1_and_mach_on_thrust_table` look very strange. I do not fully
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understand how these were generated, and more importantly, why they have these
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shapes. Specifically the plateau and the bump at 25 N1 for the higher machs are
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odd. Comparisons with other addons yielded mixed results, however all of those
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curves did not have (or only in regimes unattainable during higher machs) such
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oddities.
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Also to note is the drop in thrust for 120 N1 at mach 0 and mach 0.25. This
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seems backwards to what physics would suggest, with higher RPM generating more
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thrust.
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The curves for `n2_to_n1_table` end in a rather sharp plateau. Without knowing
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how the actual CF6 behaves, this may be closer to reality than a pure
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logarithmic relation of N2 to N1 would suggest.
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`corrected_n2_from_ff_table` is an oddball. If the game is told to not use this
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table, a default logarithmic curve is used instead. The modifications done here
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do not follow this due to the WASM FADEC imposing a non linear spool behaviour
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itself. It is to note however, that the sharp upturn at the end of the original
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lead to a noticeable increase in spool rate past 90 N1, after first seemingly
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slowing down at 75 to 80 N1.
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The way the game does EGT is odd to say the least. Take the values with a hefty
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dose of salt. I could get SL static to look reasonable, but the EGT at high
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altitude remains to low. Adjusting to where high altitude looks reasonable
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will produce far too high SL temperatures, going so far as to reach above 1100
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degrees Celsius.
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### Approach N1
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A rough formula for 3° approach N1 at F35 is `GW (in metric tonnes) / 10 + 52`.
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A MLW aircraft with ~205t would hence require ~72.5 N1. The current N1 is above
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80.
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## Trim
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There have been reports of flights where the aircraft was not able to keep
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attitude with full AND trim. In essence, the APT would trim full AND, but the
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pitch kept rising. These flights were conducted with differing payloads, all of
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which set by the EFB, thus ensuring a valid CG.
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Given the MD-11 far back placement of the wing and the subsequent 1° AND vs.
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15.5° ANU trim limits, most flights would never use all of the AND trim
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authority. There seems to be some issue here.
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## Slat drag
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Users reported a strong pitch up momentum upon slat retraction, strong enough
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at times that sever trim changes were required. This ties in with the Trim
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issue noted above, where AND trim authority was not sufficient.
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I attribute this to in parts the drag the slats exhibit, the resulting slow
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speed increase suddenly shifting to a rather large speed increase hence
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requiring large trim inputs. Smoothing out the speed changes would lessen the
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effect.
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On a more personal side note, I can't see how the slats would create this
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amount of drag to begin with.
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## Approach attitude
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Approach attitude should be (as per Centurion Cargo FCOM):
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- F35, CG of 12%
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- 2.5°: Body angle of ~6.1°
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- 3.0°: Body angle of ~5.6°
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- 3.5°: Body angle of ~5.1°
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- F35, CG of 34%
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- 2.5°: Body angle of ~4.7°
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- 3.0°: Body angle of ~4.2°
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- 3.5°: Body angle of ~3.9°
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No weight is given I assumed MLW of 204.8t.
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Current attitude is ~0.5 to 1.5 degrees too low |