flight-data-analysis

name	flight-data-analysis
description	Analyze Dynon SkyView or Garmin GDU 460 flight data CSVs. Fuel pressure stability, MAP correlation, sensor diagnostics, pump performance comparison, engine trending.
argument-hint	["path to CSV file(s) and what to analyze"]
user-invocable	true

Flight Data Analysis

Analyze flight data from Dynon SkyView or Garmin GDU 460 CSV logs.

Input

$ARGUMENTS

Context

Read reference.md in this skill directory. It contains the critical details about how N720AK's sensors work, the DIFF computation, known thresholds, current pump/regulator configuration, and the Dynon/Garmin CSV formats.

Step 1: Identify the Data

1. Determine the file format:

   • Dynon: First row is column headers, Session Time is the first column, Manifold Pressure (inHg) present
   • Garmin: First row starts with #airframe_info, column headers on row 2, data starts row 4, uses Manifold Press (inch Hg)
   • EFII System32: First row starts with #System32 config info, column headers on row 2, data starts row 3, 1 Hz sample rate. Uses MAP1/MAP2 (inHg), AFR (air-fuel ratio from wideband O2), RPM1/RPM2, FUEL FLOW (GPH), FUEL TRIM (%), INJ DUTY (%), IGNITION (timing degrees), TPS (%), IAT1/IAT2 (°F), ENGTEMP (°F), BATT1/BATT2 (V), PUMP1/PUMP2 (ON/OFF), INJ EN1/INJ EN2 (RUN/STOP), HP, TORQUE. Date format: MM/DD/YYYY, Time: HH:MM:SS. No altitude column — cross-reference with Dynon/Garmin data if altitude needed. Config metadata in row 1 includes cylinder count, MAP sensor type, HP rating, injector size, and mag positions.

2. Find flight segments by RPM transitions (RPM > 500 = engine on)

3. Report: number of flights, duration of each, date/time range, altitude range

Step 2: Load and Parse

Use uv run --with numpy --with matplotlib python3 for all analysis. Key helper:

def safe_float(row, col):
    val = row.get(col, '') or ''
    try: return float(val.strip())
    except: return None

def p_atm_inhg(alt_ft):
    """Standard atmosphere pressure in inHg from pressure altitude."""
    return 29.92 * (1 - alt_ft / 145442.0) ** 5.25588

Computing Injector Differential

The quantity we always care about is injector differential = P_fuel_absolute - MAP_absolute (in PSI). How to get it depends on the data source:

Dynon DIFF mode (current N720AK setup, post 2026-02):

• Fuel Pressure (PSI) column IS the injector differential — use directly
• No conversion needed

Dynon gauge mode (old N720AK data, pre 2026-02):

• Fuel Pressure (PSI) = gauge = P_fuel - P_atm
• inj_diff = gauge_FP + (P_atm_inHg - MAP_inHg) * 0.49115
• P_atm from pressure altitude via standard atmosphere

Garmin (always gauge):

• Fuel Press (PSI) = gauge = P_fuel - P_atm
• Same formula: inj_diff = gauge_FP + (P_atm_inHg - MAP_inHg) * 0.49115

How to tell DIFF vs gauge mode: On the ground before engine start, if FP = ~35 PSI and MAP = ambient (~24-25 inHg at KBDU), it's DIFF mode (because diff = absolute_FP - MAP ≈ 35). If FP = ~35 PSI and that equals what you'd expect for gauge (pumps on, no flow), it could be either — check once the engine starts. At ground idle (MAP ~11), DIFF mode reads ~35 PSI while gauge mode reads ~29 PSI.

Step 3: Core Analysis — Fuel Pressure vs MAP

This is the PRIMARY diagnostic. Always produce this analysis:

1. Scatter plot: Injector differential vs MAP (inHg) for all samples with RPM > 1500
2. Linear regression: slope (PSI/inHg) and r²
3. Binned averages: Mean + std dev of injector diff for each integer MAP value
4. Cruise stats: Average, std dev, and range of injector diff for MAP 18-24 inHg

Interpretation:

• A perfect regulator/pump combo produces a flat horizontal line at 35 PSI
• Negative slope = pump can't maintain pressure as fuel demand increases with power
• slope > -0.05: excellent (Walbro 392 territory)
• slope -0.05 to -0.15: acceptable (Walbro 391 territory)
• slope < -0.20: pump struggling (Walbro 393 territory)

Step 4: Time Series

Plot MAP and injector differential vs flight time on a dual-axis chart.

Look for:

• Blank/missing data: In Dynon data, empty strings mean the sensor went invalid (NOT zero). Mark these visually (orange bands). If MAP blanks, check if it's near 3.05 inHg (the min_val=1.5 PSI threshold on sensor 100434-000).
• Transients: Rapid FP drops during power changes — may explain pump cutover events
• Steady-state sag: Does FP settle at a lower value during extended cruise?

Step 5: Additional Analysis (as requested)

• CHT/EGT analysis: Spread, trends, leaning state
• Fuel burn: Total fuel flow integration, GPH averages by phase
• Pump switchover detection (Garmin only): Check Fl Pmp 1 Amps, Fl Pmp 2 Amps, FUEL PP 2 ON (discrete)
• Multi-flight comparison: Overlay binned FP-vs-MAP curves from different flights/configurations
• Before/after comparison: Compare old vs new regulator, old vs new pumps, etc.
• EFII analysis: AFR trends (target ~14.7 stoich for cruise, richer for climb/takeoff), fuel trim % (how much the ECU is correcting), injector duty cycle, ignition timing advance, MAP1 vs MAP2 correlation, pump status transitions, HP/torque estimates. EFII data has no altitude — merge with Dynon/Garmin by timestamp if altitude-dependent analysis needed.

Step 6: Generate Graphs

Always use uv run --with matplotlib --with numpy python3 and save to /tmp/ then copy to ~/Downloads/ and open them.

Standard graph set:

1. Time series (dual panel: MAP top, FP bottom, shared x-axis)
2. Scatter (injector diff vs MAP with trend line and r²)
3. Binned comparison (error bars, multiple datasets if comparing)

Step 7: Report

Provide a concise summary with:

• Flight date, duration, altitude range
• Cruise injector differential: average, std dev
• MAP slope and r²
• Any anomalies (blanking events, transients, pump switchovers)
• Comparison to baseline if applicable

Existing Script

There is also scripts/regulator_diagnostic.py which automates much of this. Run it with:

cd ~/code/rv10
uv run --with numpy --with matplotlib python3 scripts/regulator_diagnostic.py /path/to/log.csv

For Garmin data add --alt-correct. For multi-flight: pass multiple CSV paths. For altitude correction scan: --alt-scan.

The script auto-detects Dynon vs Garmin format.

Reference Data

• N88810 (Garmin, Walbro 392): ~/Downloads/log_20260308_*.csv — the gold standard baseline
• N720AK old regulator (Walbro 393): ~/Downloads/2011-01-01-N720AK-*.csv
• N720AK new regulator (Walbro 391): ~/Downloads/2026-03-16-N720AK-*.csv