Aircraft Conceptual Design System

ACDS is a browser-based conceptual sizing tool for fixed-wing aircraft and UAVs. Enter what you know — even just an MTOW — and the solver propagates through established aerospace engineering equations to produce a complete parameter sheet. Every output is tagged as DERIVED, ESTIMATED, or INPUT so you always know its provenance.

What it is and is not

ACDS operates at the conceptual design phase — the napkin-sketch layer before CAD, CFD, or FEA. It implements first-order engineering methods from textbook references, not high-fidelity simulation. The drag model is parabolic (valid below approximately Mach 0.85). Weight fractions are statistical regressions across historical aircraft data.

It is not a replacement for OpenVSP, SUAVE, Ansys, or certified analysis tools. Outputs should be treated as first-order estimates for design exploration and trade studies, not for flight-critical decisions.

Methodology & References

RAYMER

Aircraft Design: A Conceptual Approach

Daniel P. Raymer, AIAA Education Series

Primary reference for empty weight fraction statistical regressions (Table 3.1), Oswald efficiency factor (Eq. 12.48), and conceptual sizing methodology.

ROSKAM

Airplane Design, Parts I–VII

Jan Roskam, DARcorporation

Secondary reference for performance equations, drag buildup methods, and propulsion sizing guidelines.

BREGUET

Breguet Range Equation (1920)

Louis Breguet — implemented with full gravitational correction

Three variants implemented: piston/propeller (η/BSFC·g · L/D · ln(Wi/Wf)), turbojet (V/TSFC·g · L/D · ln(Wi/Wf)), and electric energy-balance form. Gravitational correction term g verified against published C172 range data.

ICAO

International Standard Atmosphere

ICAO Doc 7488, 1975 — troposphere + stratosphere model

Temperature, pressure, density, and speed of sound computed at any altitude from 0 to 80,000 ft. Verified against published ICAO atmosphere tables at 0, 5, 10, 20, 30, 40 km.

Validation Against Published Data

ACDS outputs were compared against published performance data for two well-documented aircraft spanning the design space — a piston GA aircraft and a transonic jet transport. All comparisons use published inputs only; no tuning to match outputs.

Aircraft	Parameter	ACDS	Published	Error	Note
ISA Sea Level	Temperature	15.00 °C	15.00 °C	0.0%	ICAO 1975 exact
ISA 35,000 ft	Density	0.3796 kg/m³	0.3796 kg/m³	0.0%	ICAO 1975 exact
Cessna 172S	Stall speed VS0 (full flap)	52.3 mph	50.6 mph	3.2%	CLmax 2.1 landing config; POH gross weight
Cessna 172S	Stall speed VS1 (clean)	60.8 mph	62.1 mph	−2.1%	CLmax 1.55 clean; within POH band
Cessna 172S	Range (CD₀=0.031, fixed gear)	~1,300 km	1,289 km	~0.8%	Fixed-gear CD₀ required; default 0.025 overestimates by 51%
Cessna 172S	Empty weight (Raymer)	680 kg	767 kg	−11.4%	Raymer Table 3.1 statistical regression; ±10% typical
Boeing 737-800	(L/D)max parabolic polar	17.8	17–19	−0.6%	Parabolic polar valid below M0.78; agrees well
Boeing 737-800	Stall speed VS (SL, MTOW)	121.5 ktas	~125 ktas	−2.8%	Landing config CLmax=2.6; within POH band
Boeing 737-800	Empty weight (Raymer)	39,071 kg	41,413 kg	−5.7%	Raymer Table 3.1; −5.7% for 79 t aircraft is excellent
Boeing 737-800	MTOW sizing loop	70,013 kg	79,016 kg	−11.4%	Statistical method ±10–15% is standard for conceptual phase
Boeing 737-800	Range — Breguet (raw)	9,145 km	5,765 km	+58.6%	⚠ Wave drag not modelled; Breguet overestimates transonic cruise
Boeing 737-800	Range — with mission correction	5,853 km	5,765 km	+1.5%	×0.64 factor: 16% reserves + wave drag + climb/descent (Raymer §3.5)

Known limitations: (1) The parabolic drag polar has no wave drag term — range is overestimated by 15–35% for transonic cruise (M > 0.78). ACDS flags this with an in-tool warning. (2) The default CD₀ = 0.025 is appropriate for retractable-gear aircraft. Fixed-gear designs (C172, Piper, most small GA) require CD₀ = 0.030–0.035; set this in the Assumptions panel. (3) All range values are single-segment Breguet — no climb/descent fuel or IFR reserves. Subtract 10–20% for mission planning. These are documented limitations standard to conceptual-phase methods (Raymer §3.3, §5.1).

Test Suite

246/246unit tests passing across all physics and solver modules

11ISA AtmosphereVerified against ICAO published tables at 6 altitudes

6Oswald EfficiencyBoundary conditions and regression curve shape

8Drag Polar & L/DCD at known CL values, LDmax calculation

6Stall SpeedC172 SL verified; zero/negative input edge cases

14Breguet RangeProp, jet, electric; gravitational correction verified; endurance unit regression

7Ground RollC172 150–500 m range; zero-thrust edge case

7Raymer Empty FractionsAll 11 categories; clamp boundaries

6Unit Conversionsmph↔m/s, ft↔m, lb/ft²↔kg/m²

4Mach NumberISA-dependent speed of sound

2Power RequiredThrust×velocity relationship

11Numerical StabilityNaN, Infinity, zero, negative inputs

14Constraint DiagramCruise/climb/takeoff curves; boundary conditions; stall limits

6Mission Fuel FractionBreguet all propulsion types; reserve factor

15Multi-Segment MissionFull mission chain; loiter; two-leg cruise; electric guard; mass monotonicity

65Airfoil GeometryNACA 4-series coordinates; section props; form factor; skin friction; wingCD0 buildup

12MTOW Sizing LoopConvergence; C172 and 737 regressions; infeasible configs

17Synthesis PipelineC172, 737, UAV end-to-end; error handling

4Physical SanityMonotonicity checks; constraint ordering

Limitations

Drag model: Parabolic polar only — valid below ~Mach 0.85. Wave drag not modelled. ACDS warns if cruise Mach exceeds 0.85.

Weight fractions: Statistical regressions from 1970s–2000s conventional aircraft. Less accurate for novel configurations (blended wing, strut-braced wing, eVTOL).

No structural analysis: Wing sizing gives area and span only. Structural weight, bending moments, and material selection are outside scope.

Propulsion: Engine sizing uses T/W ratio assumptions. No turbine thermodynamic cycle, no inlet/nozzle modelling.

Atmosphere: Troposphere + stratosphere only. No wind, turbulence, or non-standard atmosphere deviations.

Version History

v1.5 — March 2026 · Airfoil geometry layer · NACA 4-series database · Raymer §12.5 form-factor CD0 buildup · Three-view planform SVG · 246/246 tests
v1.4 — March 2026 · Multi-segment mission profiles · 181/181 tests · Chained Breguet with Raymer fixed-phase fractions
v1.3 — March 2026 · Optimal design solver · Parametric sweep · PDF export
v1.2 — March 2026 · Save/load designs · BazProp landing page
v1.1 — March 2026 · Dark mode, tooltips, About page, mobile responsive layout
v1.0 — March 2026 · Initial release · 79/79 tests · Breguet gravitational correction · ISA, Raymer, Roskam methods

ACDS is provided for educational and conceptual design purposes only.
Outputs are engineering estimates, not certified analysis.

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