Case 13 / Flight-data reduction
SAAB 340B drag-polar analysis
Estimate lift and drag coefficients from eight steady-flight observations, fit a drag polar and examine the residual at each operating point.
8 steady-flight observations · coefficient reduction · least-squares fitFlight-data reduction and drag-polar identification
What does a small steady-flight dataset actually support once its units and assumptions are made explicit?
I reduced the SAAB 340B dataset using a fuel-adjusted mass estimate, consistent SI units and steady-flight force balances. The fitted drag polar separates the baseline and lift-dependent contributions to drag, with individual observations and residuals available for inspection.
Method and workflow
- 01
Trace the loading
Replace load-sheet fuel with the mean of the two recorded fuel quantities; the resulting study mass is 12,550 kg.
- 02
Normalize units
Convert EAS from knots using 1852/3600 and use sea-level reference density for dynamic pressure.
- 03
Reduce the forces
Assume steady level flight, lift equal to weight, and drag equal to summed engine thrust.
- 04
Fit and inspect
Fit CD = CD₀ + k CL² by ordinary least squares and inspect the residual of every supplied point.
Keep every observation visible.
CD = 0.02870 + 0.04612 CL². The mass trace gives 12,550 kg; EAS is converted with 1852/3600 m/s per knot. Each observation and its regression residual are shown below.
The reduction assumes steady level flight and drag equal to combined engine thrust. Measurement uncertainties are unavailable, and the fit applies to the eight supplied observations.
Inspect the reduction assumptions
- Eight observations provided for steady-flight data analysis
- Steady level flight: L = mg and D = total engine thrust
- EAS uses sea-level reference density; knots = 1852/3600 m/s
- Mass replaces load-sheet fuel with the mean of the two recorded fuel quantities
- Eight source points; ordinary least-squares CD versus CL²
- Measurement uncertainty and independent validation data are unavailable
Model assumptions and scope
- The dataset comprises eight steady-flight observations provided for analysis.
- Measurement uncertainties are unavailable. Additional operating conditions are needed to evaluate the fitted polar beyond this dataset.
- The reduction assumes steady level flight, with lift balancing weight and combined engine thrust balancing drag.
Potential extensions
Attach measurement uncertainty and test the fit on a separate recorded condition before extending its predictive use.
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