Torque Meter Tech Talk

The following are some goodies I have saved about torque meters. I lied on the "Build Your Own" page, I have read them. I must admit, though, when the formulae began, my eyes glazed. It was just more than I needed. I calibrated my meter much as described by Stan.


The Value and Use of Torque Meters - by Tony Becker

Calibrating a Torque Meter by Ken Rice via "Batsheet" via: Okie Free Flight Flyers

Calibrating a Torque Meter without (as much) math by Stan

Dennis Weatherly on Torque Meters(Postings from the Free Flight Mailing List)

The Value and Use of Torque Meters - by Tony Becker

What is a torque meter and how is it used to help indoor model builders? A torque meter is a device used to measure torque (power) in a rubber motor at any number of turns. It assists the modeler in improving duration and/or altitude of any endurance or scale model.

One of the new techniques I discovered after over 30 years of inactivity, was the need to purchase a torque meter and how to effectively use it. After having the privilege of flying indoor models In the dirigible hangers at Lakehurst, New Jersey, and winding rubber motors to capacity, winding motors today has now become more complex. With most ceiling heights of available flying sites between 20 to 60 feet high, you must control your model from climbing too fast and too high.

A torque meter is a winding stooge with a hook attached to a short piece of .012 to .016 music wire with a numbered gauge and a needle attached to a winding hook. The small diameter wire is for rubber motor sizes up to .055 and the heavier wire is for big endurance and scale models.

As you put winds into your rubber motor, you can read the torque developing. With the unusual and varying types of rubber that we buy today, a torque meter is a must. I have found variances in the rubber I am able to buy and a torque meter can show a difference of over 20% for 2000 turns. This is rubber from the same 50 foot length!

The use of the torque meter is simple. As an example, lets take a loop of .045 x .038 x 16 inch rubber motor for an EZB model. Assuming your model is adjusted, put 1000 turns in your motor and carefully observe the torque meter reading. Record the data such as the rubber size, the torque meter reading, and the turns on your flight chart (see chart which follows). Fly the model and record the time. Lets say your model climbed half-way to the ceiling (or your desired safe altitude) and landed with a time of 5 minutes. The rubber had 500 turns left. Your torque meter reading for 1000 turns was 2.5. Try another flight of 1200 turns and a torque meter reading of 3.0. If the time did not increase by at least 2 minutes, and your climb was slightly higher than the first flight, record the data on your flight chart and determine what to do next. I would suggest to either increase the size of your motor or reduce the length of your original motor. (You could also change props to one of the same diameter, but with a lower pitch). Here is where your torque meter is worth its' cost. When you wind again, put in 1000 turns. You will notice the torque meter will be over the 2.5 that you recorded on the first flight if you changed only the rubber. You should unwind until the torque meter reads 2.5. This will enable the model to again climb to the same height, but the model will fly longer and land with fewer turns. Again record all this data on your flight chart and then analyze your results. After a few flights you can determine the amount of turns, the torque meter reading you need for best results, and also develop a good concept regarding the potential of your model in any existing condition.

It is important to remember two facts;

  1. - Whenever You change the prop diameter and/or pitch, you must start over with your testing and ...

  2. - As you buy or cut rubber you will find variances in turns and torque meter readings with each motor of the same size. Is is also important to remember that you must give your motor a chance to rest after each flight. I Like to wash my motor in clear room temperature water after each flight and immediately air dry it before I re-lube it and fly.

There are a few torque meters on the market today. I have two from Jim Jones; one for motors up to .055 and the other for motors over .055. You may also buy winders with a torque meter attachment.

Good luck and better flying.

Calibrating a Torque Meter by Ken Rice

From: "Batsheet" via: Okie Free Flight Flyers

Most of the torque meter construction articles that I've seen call for calibrating the finished instrument by comparing it to a known-accurate torque meter, or by using a system of measured weights and moment arms. Neither of these is easy to do with any precision. Fortunately, there is a standard engineering formula for calculating the angular deflection of a solid shaft that works nicely for determining the dial marking instead. The simple formula is:

a = (C * T * L) / (D^4 * G)

The formula shows how many degrees that a shaft will twist, given the diameter and length of the shaft, and the amount of twisting force. The parameters for this formula are described below in both US and standard units (standard in parentheses):

a = angle of pointer deflection in degrees (degrees)
C = constant: 36.5 (584)
T = torque in inch-ounces (newton-millimeters)
L = length of the music wire torsional element in inches (millimeters)
D = diameter of the music wire torsional element in inches (millimeters)
G = torsional Modulus of Elasticity for music wire in lb/sq in (newton/sq mm)

Wire SizeG
less than .032 (.81)
12,000,000 (82 740)
.011-.062 (.84-1.6)
11,850,000 (81 700)
.063-.125 (1.6-3.2)
11,750,000 (81 010)
.126-.250 (3.2-6.4)
11,600,000 (79 980)

For example, one of my meters (for two to six strands of 1/4" rubber) uses a increments of 10 in-oz each, I used the formula like this:

a = (36.5 * 10 * 12)/(0.062**4 * 11,850,000) = 25 degrees

The dial face was drawn with 25 degrees between each 10 in-oz marking. Carefully verifying this calibration with weights showed it to be correct.

I've also verified the suitability of the formula by comparing it to published torque meter designs, such as Cezar Banks' indoor instrument that was reprinted in the July '83 Bat Sheet.

Working from the plan measurements, the formula accurately calculates the exact calibration of the dials as shown on the plan.

The formula can be used handily in reverse for designing a torque meter. You can insert the desired amount of dial deflection, and calculate the diameter or length of the music wire needed to do the job.

The three most important things in model building are: Keep it light, don't build it heavy, and it shouldn't weigh much.

Terry Rimert

Calibrating without as much Math

As an alternate...

Get a light weight stick 17 " x 3/16 ". Drill a hole sized for the wire at the center and balance just like a prop. Now fasten to the wire near the indicator arm. Adjust so the indicator is pointing to zero. Now go out 1" on the stick and hang 1 oz weight. the pointer will move to the 1 in oz torque position, move weight out to 2 " and pointer will move to 2 in oz torque position, etc out to 8 ". You will need about 8 for a P-30 or small 24 " wing span rubber plane. Use .032 wire and make length from connecting point to outside case (1/4 " tube) to indicator 14 ".

Also see Ross's Rubber powered plane book. He uses 6 " tube length. but 14" is about right from removing the blast tube.


From: "Dennis Weatherly"
Date: Tue, 5 Nov 1996 13:36:35 -0700
To: Free Flight Mailing List
Subject: Torque meters

On Nov 5, 2:02pm, Alan Monteath wrote:
>I am flying P-30 and Old Time Rubber classes and I would like to improve (or
>at least be more consistent) at the competitions. Currently I don't use a
>torque meter, but I think this would help greatly. The question is, how
>many different torque meters do I need & where do I get plans for them?

There have been a couple of designs published if the NFFS digest. Somewhere in my stuff I have the formula for calibrating one just by knowing the diameter and length of the music wire element that makes up the torque meter. I'll see if I can find my notes.

My P-30 and coupe share one torque meter, my Wakefield has another. I have a special one I built for indoor use that has two meters in one "box", one for EZB and one for Pennyplane.

Let's see if I can do this in ASCII art:

ascii art

hmmm, kinda rough but you might get the idea. The music wire winding hook is free to twist inside the brass tube but is fastened to the tube down near the rubber hook. The dial face is fastened to the brass tube at the other end. The pointer is fastened to the music wire winding hook near the winder and just in front of the dial face. As you wind the motor the music wire twists, which is displayed by the pointer moving across the dial face. I'll try to find a better drawing that could go on a web page.

BTW, I make these torque meters long enough that they also work as the extension inside my blast tube.


Dennis Weatherly
Wilsonville, Oregon U.S.A.


From: "Dennis Weatherly"
Date: Tue, 5 Nov 1996 08:30:16 -0700
To: Free Flight Mailing List
Subject: Re: [FFML] Re: How much energy in a wound-up

On Nov 5, 1:36pm, Mike Dodds - GT-X Technical Author wrote:

>Am I just imagining it or is it fact that when winding a motor the rate of >increase in tension on the winder seems to be fairly constant until a point >shortly before the rubber breaks, when the tension increases significantly.

You have just discovered the fundamental technique used while winding with a torque meter. You'll see an initial rapid rise in torque, then a long period of little change, then another rapid rise just before the motor breaks. By watching how far into this second "peak" you wind the motor you can control the initial climb of a model.

Flying EZB, winding with a torque meter and taking notes taught me a _huge_ amount about how rubber motors perform. It has helped me in every phase of rubber power FF since. -- Dennis Weatherly
Wilsonville, Oregon U.S.A.


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