Overview
ACDS is a browser-based aircraft conceptual sizing tool. It implements the methods used in the first phase of aircraft design — the phase before any detailed structural, aerodynamic, or propulsion analysis. The goal is a complete first-pass parameter sheet from a handful of inputs: MTOW, cruise speed, altitude, and propulsion type.
The methods are drawn from three primary references: Raymer's Aircraft Design: A Conceptual Approach, Roskam's Airplane Design series, and the classical Breguet range equation. These are standard tools in university aerospace programmes and early-stage industry sizing. They are appropriate for conceptual design — not for detailed design, certification, or structural analysis.
What ACDS computes
Methods
ISA Atmosphere
The International Standard Atmosphere (ICAO 1975) is implemented exactly, with troposphere (0–11,000 m) and stratosphere (11,000–20,000 m) layers. All atmospheric quantities — density ρ, temperature T, pressure P, and speed of sound a — are derived from first principles at the requested altitude.
Drag Polar
ACDS uses a parabolic drag polar, valid for subsonic flight below approximately Mach 0.85. Zero-lift drag CD₀ and Oswald efficiency e are either entered directly or drawn from assumptions. The Oswald factor uses the Raymer approximation.
Breguet Range Equation
Three Breguet variants are implemented — one each for propeller, jet, and electric aircraft. All include the full gravitational correction (division by g) that is often dropped in simplified treatments.
Multi-Segment Mission Profiles
The mission analysis chains multiple Breguet segments — cruise legs, loiter holds, and fixed-phase fractions — with mass continuity between segments. The fuel burned in each segment becomes the initial mass of the next. Fixed phases (start, taxi, takeoff, climb, descent, landing) use Raymer Table 3.2 historical fuel fractions.
Segments can be freely composed: multiple cruise legs at different speeds and altitudes, loiter holds with independent speed settings, and any combination of fixed phases. The total mission range is the sum of all cruise-phase Breguet contributions.
Weight Sizing Loop
MTOW is solved iteratively. Starting from a seed MTOW, ACDS estimates empty weight using Raymer's statistical regression (Table 3.1, by aircraft category), adds payload and fuel fractions, then iterates until convergence. The loop typically converges in 10–20 iterations.
Coefficients A, C1, C2, C3 are category-specific (GA single, GA twin, jet transport, military, etc.) from Raymer Table 3.1.
Constraint Diagram
The constraint diagram plots T/W vs W/S curves for cruise, climb, takeoff, and stall constraints. The feasible design space is above all curves. The optimal design point — minimum T/W at the constraint intersection — minimises installed thrust and hence engine cost and weight.
Validation
ACDS results have been checked against published data for two aircraft: the Cessna 172S (POH, Garmin G1000 version) and the Boeing 737-800. These cover opposite ends of the design space — a 1,111 kg GA trainer and a 79,016 kg jet transport.
Errors below 5% are highlighted green. Errors between 5–15% are amber — acceptable for conceptual phase. Errors above 15% indicate a known model limitation (noted).
| Aircraft | Parameter | ACDS | Actual | Error | Notes |
|---|---|---|---|---|---|
| ISA Sea Level | Temperature | 15.00 °C | 15.00 °C | 0% | ICAO 1975 exact |
| ISA 35,000 ft | Air density | 0.3796 kg/m³ | 0.3796 kg/m³ | 0% | ICAO 1975 exact |
| Cessna 172S | Stall speed V_S0 (full flap) | 52.3 mph | 50.6 mph | +3.2% | CLmax 2.1 landing config; POH gross weight |
| Cessna 172S | Stall speed V_S1 (clean) | 60.8 mph | 62.1 mph | -2.1% | CLmax 1.55 clean; within POH band |
| Cessna 172S | Range (CD₀ = 0.031) | ~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 V_S (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; excellent for conceptual phase |
| Boeing 737-800 | MTOW sizing loop | 70,013 kg | 79,016 kg | -11.4% | Statistical method ±10–15% is standard |
| Boeing 737-800 | Range — raw Breguet | 9,145 km | 5,765 km | +58.6% | Wave drag not modelled; expected overestimate for transonic |
| Boeing 737-800 | Range — mission corrected | 5,853 km | 5,765 km | +1.5% | ×0.64 factor: reserves + wave drag + climb/descent (Raymer §3.5) |
Default Assumptions
When an input is left blank, ACDS falls back to a default assumption. All assumptions are visible and editable in the Assumptions panel inside the tool. The defaults are calibrated for small-to-medium subsonic GA and UAV aircraft.
All assumptions can be changed per-session in the Assumptions tab inside ACDS. Changed values are highlighted so you always know what's an input versus a fallback.