Source: https://guthlabs.ai/docs/instruments/airfoil-lift-to-drag-polar-plotter/

instrument / verified-clean

# Airfoil Lift-to-Drag Polar Plotter

The current ledger marks this instrument verified clean within the source-bound verification corpus.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Inspectable records

[01**Overview**Purpose and lifecycle](<https://guthlabs.ai/docs/instruments/airfoil-lift-to-drag-polar-plotter/>)[02**Mechanism**Method and assumptions](<https://guthlabs.ai/docs/instruments/airfoil-lift-to-drag-polar-plotter/mechanism/>)[03**Implementation**Binding and validation](<https://guthlabs.ai/docs/instruments/airfoil-lift-to-drag-polar-plotter/implementation/>)[04**Qualification**Evidence and errata](<https://guthlabs.ai/docs/instruments/airfoil-lift-to-drag-polar-plotter/qualification/>)

## Ledger state

The current ledger marks this instrument verified clean within the source-bound verification corpus.

**Area**: Thermodynamics, Fluids & Aero

**Tranche**: tranche-7

**Evidence ID**: t7-101

**Ledger rows**: 1

No ledger note is attached.

## Review findings

The core equations are standard, but the specification needs an explicit Cd-versus-α input schema, a definition of whether supplied Cd is total or profile drag, validation constraints for AR/e/Cd, and a stated interpolation and maximum-selection policy. Verdict is NEEDS_REVIEW because the current input description is insufficient to uniquely compute the advertised polar, maximum L/D, and induced-drag breakdown.

### Formula and scope findings

- L/D = Cl/Cd is the standard coefficient ratio when Cl and Cd use the same reference area and Cd is the total drag coefficient.

- Cdi = Cl²/(πeAR) is the standard finite-wing induced-drag model for subsonic flow under the assumed Oswald-efficiency and finite-wing approximation.

- The input description says Cl versus α data, but a polar and L/D require corresponding Cd data as well; Cd cannot be recovered from Cl versus α alone without an additional drag model.

- Induced-drag breakdown is ambiguous if the supplied Cd already includes induced drag: the implementation must report Cdp = Cd - Cdi and must not add Cdi to Cd a second time.

- The formula is not a complete high-lift, stall, compressibility, ground-effect, or separated-flow model; the stated elliptical-lift simplification is appropriate only within its intended finite-wing regime.

- The maximum L/D algorithm must specify whether it searches only supplied rows, interpolates between rows, or fits/extrapolates a model. Extrapolation beyond the supplied polar is not justified without an explicit model.

### Unit assumptions

- Cl, Cd, Cdi, and Cdp are dimensionless coefficients based on the same reference area.

- Aspect ratio AR is dimensionless and uses the same wing geometry as the supplied coefficients.

- Oswald efficiency e is dimensionless; the normal physical constraint is 0 < e <= 1, although effective fitted values may sometimes be outside that range and should be flagged.

- Angle of attack α is assumed to be in degrees in the lookup rows below; α units affect plotting and interpolation labels but do not enter the displayed drag formula directly.

- Cd must be the total drag coefficient for L/D = Cl/Cd and for calculating Cdp = Cd - Cdi.

- π is the mathematical constant 3.141592653589793.

## Boundary hardening

**BREAK_CLAIMED** · SELF_FLAGGED

The zero-Cd input produces an undefined L/D result and should be rejected or explicitly flagged. The branch and sign-convention probes also demonstrate outputs that can change materially depending on dataset regime and reporting convention.

## Errata and corrections

No applied erratum is attached to this unique-name record.

## Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

````
{
  "inputs": {
    "alpha_deg": 4,
    "Cl": 0.5,
    "Cd": 0.025,
    "aspect_ratio": 6,
    "Oswald_efficiency": 0.8
  },
  "expected_outputs": {
    "L_over_D": 20,
    "Cdi": 0.01657864094,
    "Cdp": 0.00842135906,
    "max_L_over_D_in_supplied_rows": 20,
    "max_L_over_D_alpha_deg": 4
  },
  "reference_data": {
    "polar_rows": [
      {
        "alpha_deg": 4,
        "Cl": 0.5,
        "Cd": 0.025,
        "source_convention": "widely tabulated standard value (NACA 0012 benchmark polar convention)"
      }
    ],
    "pi": 3.141592653589793,
    "pi_source_convention": "mathematical constant"
  },
  "working": "L/D = Cl/Cd = 0.5 / 0.025 = 20.0. Cl² = 0.5² = 0.25. πeAR = 3.141592653589793 × 0.8 × 6.0 = 15.0796447366. Cdi = 0.25 / 15.0796447366 = 0.01657864094. Cdp = Cd - Cdi = 0.025 - 0.01657864094 = 0.00842135906. With one supplied row, its L/D of 20.0 is the row maximum."
}
````

## Related workflows

No source-defined multi-instrument workflow membership is recorded.

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json · VERIFIED_CLEAN`

- `evidence-tranche7/tranche7-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`