Aircraft Electrical Load Analysis

Aircraft Electrical Load Analysis (vehicle-design/sizing/aircraft-electrical-load-analysis)

Use when you must analyze the aircraft electrical power system load at the sizing level: rolling consumer apparent power (kVA) with each duty cycle into the continuous load, discounting by the diversity factor for the coincident peak, booking the essential load at full steady power, and checking the generator rating against the single-generator-out case. This leaf implements the standard aircraft electrical load rollup in pure Python (stdlib only) and pairs with vehicle-design/sizing/battery-sizing for the traction energy storage side, which CONSUMES a load requirement but does not build the AC/DC generator and bus load rollup. It is the aircraft-side counterpart of the spacecraft EPS budget at space-systems/subsystems/power-thermal-budget. Does NOT do: traction battery/ESS sizing and mission energy (battery-sizing); power-input quality acceptance test benches (avionics/do160/power-input); generator electrical machine design; fault current and protection coordination; spacecraft EPS (space-systems).

Domain quick reference

• Consumer model: consumers = {name: (power_kva, duty)} with duty in [0, 1], the fraction of flight time the consumer draws its rated power.
• Continuous load: L_c = sum over consumers of power_kva * duty. The rollup keeps every per-consumer duty-weighted term in input order.
• Coincident peak: L_pk = DF * L_c with diversity factor DF in (0, 1]. DF of 1.0 means all loads coincide, so the peak equals the continuous load exactly.
• Essential load: L_e = sum of the FULL power_kva of the named essential consumers (conservative full-power bookkeeping; they must stay powered continuously in the failure case, duty does not discount them).
• Generator-out margin: with n generators each rated S_g the capacity left after one generator fails is (n - 1) * S_g. Margin = ((n - 1) * S_g - L_e) / ((n - 1) * S_g); verdict PASS when margin >= 0 else FAIL. For n == 1 the remaining capacity is 0.0, margin is -1.0 and the verdict is FAIL (no redundancy).
• Load fraction: L_c / installed_kva, with installed_kva = n * S_g.
• FAR 25.1355 context (referenced, not reproduced): no essential load may be lost when any one power source fails; the margin and verdict operationalize that requirement at the sizing level.

Workflow

1. List every consumer as {name: (power_kva, duty)}, powers in kVA, duty the fraction of flight time spent at rated power.
2. Roll the duty-weighted load up with continuous_load(consumers), which returns the continuous_kva and the per-consumer rollup.
3. Apply the load diversity with diversity_peak(continuous_kva, diversity_factor) to get the coincident peak the generators actually see.
4. Name the essential consumers (flight critical, they must survive a source failure) and total them at full power with essential_load(consumers, essential_names).
5. Check the redundancy with generator_out_margin(n_generators, generator_kva, essential_kva): remaining capacity, margin and verdict.
6. Report the normal operating point with load_fraction(continuous_kva, installed_kva).
7. Run the whole analysis in one call with ela_summary(consumers, diversity_factor, essential_names, n_generators, generator_kva), which returns every key above plus installed_kva.
8. Close with the deterministic checks in the contract test scripts/test_aircraft_electrical_load_analysis.py.

Worked example

Reference transport system, eight consumers (kVA, duty): avionics 4.0 / 1.0, flight-control 12.0 / 0.6, comm-nav 2.5 / 1.0, lighting 6.0 / 0.5, galley 35.0 / 0.35, anti-ice 18.0 / 0.25, hydraulic-pumps 12.0 / 0.8, fuel-boost 3.0 / 0.9. Diversity 0.85. Essential names: avionics, flight-control, comm-nav, fuel-boost. Two 60 kVA generators. Real module outputs:

• continuous_load: continuous_kva 45.75; rollup [4.0, 7.2, 2.5, 3.0, 12.25, 4.5, 9.6, 2.7].
• diversity_peak(45.75, 0.85): coincident peak 38.8875 kVA (38.89).
• essential_load: essential_kva 21.5 (4.0 + 12.0 + 2.5 + 3.0 at full power), essential_consumers the four named.
• generator_out_margin(2, 60, 21.5): remaining_kva 60.0, margin 0.641667 (64.2%), verdict PASS.
• load_fraction(45.75, 120): 0.38125 (38.1%) of the 120 kVA installed.
• ela_summary: continuous 45.75 kVA, coincident peak 38.8875 kVA, essential 21.5 kVA, remaining 60.0 kVA, margin 0.641667 PASS, load fraction 0.38125, installed 120.0 kVA.

Pitfalls

• Discounting the essential load by duty: essential consumers must stay powered continuously in the failure case, so essential_load books the FULL power of each named consumer (the flight-control 12 kVA at duty 0.6 books 12.0, not 7.2); the generator-out margin is meaningless if the essential load is duty-weighted.
• Checking the normal operating point instead of the failure case: the rating gate is the single-generator-out margin ((n - 1) * S_g against L_e), and a single generator yields remaining 0.0, margin -1.0 and FAIL - there is no redundancy to check.
• Forgetting the diversity discount goes the other way: the coincident peak is DF * L_c (38.89 kVA in the worked example), below the raw 45.75 kVA rollup; sizing generators on the undiscounted continuous load over-sizes the system.
• Feeding a duty cycle outside [0, 1] or an unnamed essential consumer: duty 1.2 or -0.1, a power of -5, a diversity of 0 or 1.5, and essential names missing from the consumer dict all raise ValueError.
• Mixing the spacecraft context in: this leaf is the aircraft AC/DC generator and bus load rollup; the spacecraft EPS budget lives at space-systems/subsystems/power-thermal-budget, and the two should not be mixed.
• Reading the load fraction as the sizing verdict: load_fraction (L_c / installed) reports the normal operating point (38.1% in the worked example) while PASS/FAIL comes from the generator-out margin.

Verification

• continuous_load with one 10 kVA consumer at duty 1.0 returns 10 kVA and at duty 0.5 returns 5 kVA; doubling the power doubles the contribution.
• diversity_peak(45.75, 1.0) returns 45.75 exactly (identity) and factor 0.5 returns 22.875.
• essential_load of all eight consumers returns 92.5 kVA (full powers only); one flight-control consumer (12 kVA at duty 0.6) books 12.0 kVA full, not 7.2 duty weighted.
• generator_out_margin identity: essential exactly at the (n - 1) generator capacity gives margin 0.0 and verdict PASS; essential 80 with two 60 kVA generators gives margin -1/3 and verdict FAIL; a single generator gives remaining 0.0, margin -1.0, verdict FAIL.
• load_fraction(45.75, 120) = 0.38125; doubling the installed capacity halves the fraction.
• ValueError rejection of non-physical inputs: empty consumer dict; duty outside [0, 1] (1.2 or -0.1); power -5; diversity 0 or 1.5; essential name not in the dict; n_generators 0; generator_kva 0; installed_kva <= 0.
• Determinism: identical inputs give identical outputs (no RNG anywhere).
• Run the contract test offline: python3 scripts/test_aircraft_electrical_load_analysis.py (35 tests).

Related leaves

• vehicle-design/sizing/battery-sizing: traction and ESS energy storage sizing; it consumes a load requirement but does not roll up the AC/DC generator and bus load.
• vehicle-design/sizing/engine-sizing: shaft thrust and power sizing, the mechanical side of the same aircraft.
• vehicle-design/sizing/hydraulic-system-sizing: hydraulic consumers whose pump drives draw on this electrical budget.
• avionics/do160/power-input: supply power quality acceptance testing, separate from the load rollup.
• space-systems/subsystems/power-thermal-budget: the spacecraft EPS counterpart in the foreign family; do not mix the two contexts.

Behavior contract (gate 3)

Run the deterministic contract test (stdlib unittest, offline):

python3 scripts/test_aircraft_electrical_load_analysis.py

It covers the worked example (continuous load 45.75 kVA, coincident peak 38.8875 kVA, essential load 21.5 kVA, generator-out margin 0.6417 with verdict PASS, load fraction 0.38125), the diversity-1.0 and zero-margin identities, rollup ordering, full-power essential booking, summary dict keys, determinism, and ValueError rejection of every non-physical input.

Compliance

• Standards referenced, not reproduced: FAR 25.1355 (electrical system no-hazard context) is named and paraphrased only; the load rollup relations above are standard engineering methodology, summary-only per standards-map.yaml.
• compliance: STANDARDS-REF, gated: false.