CALCULATORS / AERODYNAMICS AND FLIGHT SCREENING

Aerodynamic Reynolds number calculator

Characteristic Reynolds number at constant air properties.

aerodynamics-reynolds-number.napkin / editable

SCENARIO COMPARISON

Compare the numbers.

This source describes an analytical model. Its quantities and checks are the view.

Scenario	reynolds
	203039
	162431

All calculated quantities are listed with the inputs. Switch to Source to inspect the equations.

SCENARIOS / CALCULATED VALUESSAME SOURCE

Change an input to see the consequences.

model range example203038.67 ✓ passes

BASELINE INPUTS

density1.225 kg/m^3speed15 m/schord0.2 mviscosity0.0000181 Pa*s

CALCULATED

reynolds203040

Edits change the baseline source.

THE SOURCE

Edits below update the same model.

# Aerodynamic Reynolds number
# Scope: Characteristic Reynolds number at constant air properties.
# Status: illustrative worked example; engineering review pending.
# Inputs are example values. Checks are editable example requirements, not standards.

density = 1.225 kg/m^3
speed = 15 m/s
chord = 0.2 m
viscosity = 0.0000181 Pa*s

reynolds := density*speed*chord/viscosity

check model range example: reynolds >= 100000

scenario alternative: density = 0.98 kg/m^3

Calculated from your source · not saved

Baseline · Baseline

model range example203038.67 ✓ passes

alternative · alternative

model range example162430.94 ✓ passes

Illustrative first-order example. Checks are editable requirements, not design standards. The broader topic may require additional equations, data, and validation.

Formula and units

This example uses the following equations. Input names and units match the editable source above.

reynolds: reynolds = density*speed*chord/viscosity

Original worked example

These are the baseline values in the downloadable source. Edits above let you test your own values.

Given

density: 1.225 kg/m^3
speed: 15 m/s
chord: 0.2 m
viscosity: 0.0000181 Pa*s

Calculated

reynolds: 203039

Assumptions and limits

Characteristic Reynolds number at constant air properties.

The requirement checks use the limits written in this example. Passing a check does not establish that the model covers every load, material behavior, or operating condition in a real design.

Download this .napkin example ↓

Take it further with your agent

Napkin keeps the inputs, equations, checks and assumptions together in one study. Your agent sets it up; you change the numbers.

Try with Claude ↗

codex 'Use Napkin (https://napkin.engineering/mcp, or the local Napkin plugin) to build a study: Aerodynamic Reynolds number. Inputs: speed; characteristic length; fluid properties. Outputs: Reynolds number; regime context. Model scope: Coefficient-based models over an explicitly limited flight regime. Read napkin_capabilities and the current snapshot. Ask me for the values that matter, label assumptions with units, author .napkin source, validate it and apply it with napkin_source using the current revision, then open the study. Add checks for the limits I supply. Keep unsupported analyses explicit.'

Claude needs the Napkin connector; Codex needs the Napkin plugin. Set up your agent ↗

The broader study

The topic brief below describes the broader scope. The worked example above states the particular calculation it implements.

Inputs: speed, characteristic length, fluid properties
Outputs: Reynolds number, regime context
Modes: calculate, compare, sweep
Drawing: Force and flight-envelope plots

EXECUTABLE WORKED EXAMPLE · FIRST-ORDER MODEL · CHECK THE SCOPE & ASSUMPTIONS