Removal of Aircraft.Engine.REFERENCE_DIAMETER

[xjjiang]

Summary

Engine reference diameter never existed in GASP. This PR replaces it with a different algorithm.

Suppose AE = Engine cross-sectional area (inlet/frontal area). The current GASP algorithm computes AE as follows:

AE = 0.3×WG/1500/ENP = 0.0002×WG/ENP​, where WG is the gross weight and ENP is the number of engines.

Assume a fixed thrust-to-area relationship. Then Engine size scales with required thrust, and thrust scales with aircraft weight.

The constant (0.0002) is an empirical sizing factor. Instead of deriving constants every time, we add a new Aviary variable Aircraft.Engine.INLET_AREA_COEFFICIENT (coeff_inlet) with default 0.0002 within the range (0.0002 - 0.0006) depending on the type of aircraft:

• Lower end (~0.00035): Smaller engines, lower bypass ratio (e.g., regional jets)
• Middle (~0.0004): Typical narrow-body aircraft (most common choice)
• Upper end (~0.0005): Large, high-bypass engines (wide-body aircraft)
• BWB (0.0004 – 0.0006)
  • 0.0004 → clean, podded engines (BWB but conventional nacelles)
  • 0.00045 – 0.0005 → mild boundary layer ingestion
  • 0.0005 – 0.0006 → strong BLI / embedded engines

The above values are for references only. In Aviary, most transport aircraft use value coeff_inlet = 0.0003.

The GASP based BWB algorithm already uses the new algorithm. It still keeps coeff_inlet = 0.0002. Otherwise, it can not be compared to GASP run result.

Related Issues

• Resolves Removal of Aircraft.Engine.REFERENCE_DIAMETER #775

Backwards incompatibilities

None

New Dependencies

None