HPA

This thread describes the construction of a torque meter used with my 28 inch Easy Built Hellcat. This is my first torque meter for outdoor use and I don't claim it to be the best design. I have only just started using it; so cannot vouch for its resiliance. I look forward to any suggestions for improvements or alternative designs.

We will start with some photos.

The first shows that torque meter that replaces the spacer used in conjunction with a blast tube.

The dial is at the winder end of the meter. The meter is calibrated and the dial is marked in 100's of g.cm reading up to 500g.cm for the first revolution and 1000g.cm for the second.

In hindsite; oz.inches would have been more convienient units and would allow me to compare to the FAC experts meadurements.

A servo arm is glued to the back of the dial is an attachment sprocket. It is a tight fit onto the tube and allows the dial to be removed for storage in the model box.

The third photo shows the rubber end of the meter with a thick wire hook.This is needed because the loops at both ends of the meter are formed from the measurement wire. I do not trust my soldering to attach the thin measurement wire to thicker hooks. The wire is too thin to form hooks without the risk of opening out. So, a thicker wire hook is used for the attachment to the rubber motor.

Piecost -

You did some fine work in constructing your torque meter. I always advise people to wind to a predetermined launch torque in order to achieve consistently good flights.

I had the honor to fly with Herb Kothe a few times. He was a legendary rubber power free flight flier in the US. I talked to him over the phone a few years ago and he is probably into his nineties. Herb was a real gentlemen and would not hesiate to help other fliers if they asked for help.

He made his own torque meters for a vareity of different models according to the plan that you can find here:

https://www.flyingacesclub.com/PFFT/TorqueMeterKothe.pdf

Achieving good solder joints is the biggest challenge in constructing your own torque meter. Make sure that the metal surfaces are polished with Emery paper to remove any oxidized metal, and use good solder with flux. I find that the solder joint can be strengthened by wrapping very small diameter Copper wire around the joint before applying the solder. This wire can be found by removing the insulation from a standard size wire and removing one of the Copper filaments from the multi-strand Copper core. Make sure that the soldering iron hot is hot enough so that the solder flows readily onto the joint.

I am puzzled how you are able to remove the dial face of your torque meter over the hook and pointer at its front end.

Some low quality build drawings whilst I figure out how to get the pdf's off my old computer.

calgoddard,

Thanks for the details and plan from Herb. I really appreciate this kind of information and stories of great modellers of the past. I am not able to attend outdoor modelling events to talk to poeple, so my influences come internationaly from this forum, rather than from fellow Uk fliers.

Thanks for the soldering advice. I did clean the parts with abrasive, degrease with Baker's Fluid and apply flux. I used short lengths of tube rather than bind with soft wire. I was reasonavly happy with the result.

The dial slides along the full length of the tube to come off at the oppposite end.

Tim

If you want to convert Oz/in to g/cm, multiply the Oz/in by 72.
There are some fractions but less than 0.01, so for our purposes 72 is close enough (& given the differences in the actual twisting resistance of piano wire as well as differences in actual diameter of wire from nominal, 70 is probably a good enough factor