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how to calculate the torque of a balsa plane project

ByBob Womack

Torque is a crucial factor in the performance of a balsa wood airplane, especially for rubber-powered models where a wound rubber band provides propulsion. Understanding how to calculate torque can help optimize flight performance and prevent mechanical failures.

What Is Torque in a Balsa Plane?

Torque is the rotational force that twists the rubber band motor, which in turn drives the propeller. It is measured in Newton-meters (Nm) or ounce-inches (oz-in) and is determined by the force applied and the length of the lever arm.

Basic Torque Formula

T=F×rT = F \times rT=F×r

Where:

  • T = Torque (Newton-meters or ounce-inches)
  • F = Force applied (Newtons or ounces)
  • r = Length of the lever arm (meters or inches)

Step-by-Step Guide to Calculating Torque

1. Measure the Force Applied to the Rubber Motor

  • If using a torque meter, measure the force exerted when winding the rubber motor.
  • If no torque meter is available, estimate force based on the type of rubber and the number of winds.

2. Determine the Lever Arm Length

  • The lever arm in this case is the radius of the rubber motor hook to the center of the propeller shaft.
  • Measure this in inches or meters.

3. Calculate Torque

Using the formula T = F × r, multiply the force by the radius to get the torque value.

Example:

  • Force applied = 5 ounces
  • Lever arm length = 2 inches
  • Torque = 5 oz × 2 in = 10 oz-in

Optimizing Torque for Better Flight

1. Selecting the Right Rubber Band

  • A thicker, high-quality rubber band provides more torque.
  • A longer rubber band allows more winds, generating sustained power.

2. Properly Winding the Rubber Motor

  • Too few winds = Low torque, shorter flight.
  • Too many winds = Excessive torque, risk of rubber snapping or unstable flight.

3. Balancing Torque and Stability

  • High torque at launch can cause torque roll, where the plane veers sideways.
  • Use a torque meter to test different wind counts for stability.

Conclusion

Calculating torque for a balsa plane project helps optimize flight duration and stability. By measuring force, determining lever arm length, and applying the torque formula, you can fine-tune your rubber-powered plane for the best performance.

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