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Calcimator

Rocket Motor Selection Calculator

Determine the right NAR motor class for your rocket based on mass, target altitude, and drag estimates using energy-based delta-V and impulse calculations.

Inputs

%
%

Results

Required total impulse (N-s)

65.75

Minimum delta-V (m/s)76.71
Estimated avg. thrust (N)32.87
Thrust-to-weight ratio6.7
Minimum safe thrust (N)24.52
Motor ClassG
How to Use This Calculator
  1. Enter Rocket mass (kg), Target altitude (m), and Drag loss estimate (%).
  2. Set Safety margin (%).
  3. Review the Required total impulse (N-s) result.
  4. Use Minimum delta-V (m/s) and Estimated avg. thrust (N) to inform your decision.

How the result changes with Rocket mass (kg)

Rocket mass (kg)Required total impulse (N-s)
5.01658.81
182,366.96
334,339.43
455,917.41

What each input means

Rocket mass (kg)
Total liftoff mass including motor, recovery system, and payload.
Target altitude (m)
Desired apogee altitude above ground level.
Drag loss estimate (%)
Percentage of impulse lost to aerodynamic drag. Typical: 20-40% for model rockets.
Safety margin (%)
Extra impulse margin for wind, temperature, and manufacturing variation.

What each result means

Required total impulse (N-s)
Total motor impulse needed to reach target altitude with drag and safety margins.
Minimum delta-V (m/s)
Minimum velocity change for a ballistic arc to target altitude (no drag).
Estimated avg. thrust (N)
Approximate average thrust assuming typical burn time for the motor class.
Thrust-to-weight ratio
Ratio of motor thrust to rocket weight. Minimum 5:1 recommended for safe launch.
Minimum safe thrust (N)
Minimum thrust for a 5:1 thrust-to-weight ratio.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Rocket mass (kg) = 0.5, Target altitude (m) = 300, Drag loss estimate (%) = 30, Safety margin (%) = 20 = 4 input(s) provided
  2. Calculate Required total impulse
    Required total impulse = rocketMassKg * deltaV * dragFactor * safetyFactor
    65.75 = 65.75
  3. Calculate Minimum delta-V
    Minimum delta-V = sqrt(2 * g * targetAltitudeM)
    76.71 = 76.71
  4. Calculate Estimated avg. thrust
    Estimated avg. thrust = totalImpulseNs / typicalBurnTime
    32.87 = 32.87

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