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Calcimator

Fin Flutter Speed Calculator

Calculate the critical flutter velocity for rocket fins based on material shear modulus, fin geometry, and altitude using the NARTS approximation.

Inputs

Results

Flutter speed (m/s)

603

Flutter speed (mph)1,349
Flutter Mach number1.78
Safe max speed (m/s)482.4
Safe max speed (mph)1,079
Fin aspect ratio0.8
V Flutter (ft) S1,978.39
How to Use This Calculator
  1. Enter Root chord (mm), Tip chord (mm), and Semi-span (mm).
  2. Set Fin thickness (mm), Shear modulus (GPa), and Altitude at max speed (m).
  3. Review the Flutter speed (m/s) result.
  4. Use Flutter speed (mph) and Flutter Mach number to inform your decision.

How the result changes with Fin thickness (mm)

Fin thickness (mm)Flutter speed (m/s)
3.09880.9
115,917
2014,506.2
2722,753.8

What each input means

Root chord (mm)
Length of the fin where it attaches to the body tube.
Tip chord (mm)
Length of the fin at the outer tip. 0 for a triangular fin.
Semi-span (mm)
Distance from body tube surface to fin tip.
Fin thickness (mm)
Thickness of the fin material. Thicker fins resist flutter better.
Shear modulus (GPa)
Material shear modulus. Balsa ~0.3, plywood ~0.6, G10 fiberglass ~4.1, birch ply ~1.0, carbon fiber ~5-7.
Altitude at max speed (m)
Altitude where the rocket reaches maximum velocity (typically near burnout).

What each result means

Flutter speed (m/s)
Critical speed at which fin flutter begins. Keep max velocity below 80% of this.
Flutter speed (mph)
Flutter velocity in miles per hour.
Flutter Mach number
Flutter speed as a fraction of the speed of sound at the given altitude.
Safe max speed (m/s)
80% of flutter speed -- recommended maximum rocket velocity.
Safe max speed (mph)
Safe max speed in mph.
Fin aspect ratio
Semi-span divided by root chord. Lower AR is more flutter-resistant.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Root chord (mm) = 100, Tip chord (mm) = 50, Semi-span (mm) = 80, Fin thickness (mm) = 2.4 = 6 input(s) provided
  2. Calculate Flutter speed
    Flutter speed = a * sqrt(G / pressureTerm)
    603 = 603
  3. Calculate Flutter speed
    Flutter speed = vFlutterMs * 2.23694
    1349 = 1349
  4. Calculate Flutter Mach number
    Flutter Mach number = vFlutterMs / a
    1.778 = 1.778

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