Thankfully, the second production of the Stearman flying Wire Tensiometers is done, and they are delivered. There were 25 in this last lot.
The goal was to make the tapered leaf springs, which are the heart of the tensiometer, all so identical that a common scale with one calibration could be used. That is surely the way the government did it when they made this same model in the 30’s and 40’s.
Well it was not to be. In evaluating the bending characteristics of the springs, enough variation was found that a separate calibration and scale was required for each unit.
Since there are thirty tension data points for each scale, that meant cranking the tensiometer foot down onto the wire, making the mark and un-cranking it thirty times for 25 units or 750 cranking operations. About a third of the way through, we made a fitting for the electric driver to do the cranking, which made life a lot better.
The tensions are set on an actual flying wire with an accurate load cell in series with the wire and a turnbuckle all mounted on a strong back. The load cell reads up to 2500 lbs with a one-pound accuracy.
There are four wires that are used. The first wire is set to the lowest tension required, and then each tensiometer, in turn, is applied to the wire and the mark made on a paper blank mounted to the scale plate. The tension is verified between each tensiometer.
When all of the data points for the first wire are completed for each tensiometer, the next wire is installed, and the process completed for those points.
The scale blanks are marked with the tensiometer serial #. The blanks are then taken to Powers Manufacturing, where the entire scale for each unit was chemically etched into a stainless steel plate.
The final scale is bonded to the scale base and the etchings filled with black lacquerer.
The machining and assembly was done by Lamb Components, courtesy of Roger Lamb.
Calibration was done by the SRA staff.
The cases were made by Van & Co in Rhode Island. The materials and workmanship were outstanding. If you have any need for quality cases, call Bob at 401-722-9829