Leon Lasota

2025-01

ZAERO CFD-corrected unsteady aerodynamics for dynamic loads — computed subsonic and transonic aerodynamic correction factors using Euler CFD and applied W2GJ corrections to the NASTRAN DLM model for improved gust load prediction fidelity.

Challenge: Transonic W2GJ corrections showed strong frequency dependence at Mach 0.82 — the correction factor changed by 35% between 0.1 and 2.0 reduced frequency. Linear interpolation between sparse correction factor data points was inadequate and produced oscillatory gust load predictions at mid-frequencies.

Learned: Transonic W2GJ correction factors have strong reduced frequency dependence that simple linear interpolation cannot capture. Use rational function approximation (RFA) to fit the frequency dependence — RFA provides smooth interpolation in the frequency domain and is physically consistent with the unsteady aerodynamic mathematics.

2024-05

Fatigue loads spectrum development — combined PSD gust loads with maneuver loads from flight dynamics model to generate a load sequence spectrum for wing fatigue crack growth analysis. Followed CS-25.571 damage tolerance approach.

Challenge: Combining gust and maneuver loads in a fatigue spectrum requires a probabilistic model for load sequence correlation. Assuming independence between gust and maneuver loads was conservative — introduced a 15% fatigue life penalty. Required coordination with the aircraft operator for actual flight profile data to reduce conservatism.

Learned: Fatigue loads spectrum conservatism from independence assumptions can significantly impact structural weight. Investing in a realistic flight profile-based loads spectrum (even from a limited in-service data set) is worthwhile — the fatigue life extension from reducing spectrum conservatism can offset significant structural weight.

2023-10

Continuous turbulence loads analysis per CS-25.341(b) — computed design loads using the power spectral density (PSD) method with Von Karman turbulence spectrum. Combined with 1-cosine discrete gust loads for enveloping.

Challenge: PSD turbulence analysis requires integration of the load PSD over frequency — numerical integration errors at low frequencies caused by insufficient frequency resolution produced incorrect fatigue loads. Required adaptive frequency stepping that concentrated resolution at low frequencies where the Von Karman spectrum peaks.

Learned: PSD gust load integration requires careful frequency resolution, particularly at low frequencies where the Von Karman spectrum has its energy peak. Use adaptive frequency stepping with at least 5 points per decade below the first structural mode frequency — uniform frequency stepping will underresolve the low-frequency energy.

2023-03

Discrete gust analysis per CS-25.341(a) — 1-cosine gust responses for 60+ gust gradient distances across the flight envelope using NASTRAN SOL 146 frequency domain. Generated critical load conditions for structural sizing.

Challenge: CS-25.341(a) requires gust analysis at a minimum of 20 gust gradient distances (H = 9m to 107m). With 4 symmetric and 2 antisymmetric load cases per gradient distance, total analysis count was 360 runs. Manual case management was error-prone — built an automated Python case generator and result aggregator.

Learned: Dynamic gust loads analysis automation is essential for the sheer number of required cases. Invest in automated case generation, submission, and result aggregation from the start of the gust loads campaign — manual case management at this scale introduces transcription errors in the critical load condition identification.