TBF-1 Avenger Torpedo Bomber Cruising Calculator Mark 1-A, Ser # 4785-43
This is an authentic original WWII-era Cruising Computer Mark 1-A designed specifically for the US Navy's Grumman Torpedo Bomber TBF-1.
The purpose of the calculator was to determine the range, in nautical miles, of the aircraft under various conditions of aircraft weight, head/tail winds, fuel quantity on board, true air speed, altitude, and throttle and supercharger blower settings.
The calculator is essentially a custom 3-panel slide-rule consisting of 4 components:
- The first component is a metal base providing attainable ranges under various aircraft weight and fuel on board, and has curled edges at top and bottom with a retention spring to grip the 3 sliding panels.
- The next two components are two hard-plastic sliding 'weight' panels each displaying 5 performance curves along air speed x-axis and fuel consumption rate (gallons per hour) y-axis for a specific aircraft weight. The 5 performance curves are for altitudes of sea level, 6000ft, 9000ft, 13000ft, and 20000ft. Each panel is specific for aircraft weight and printed on front and back sides, covering weights of 12500 and 14000 lbs on one panel, and 15000 and 16500 lbs on the other panel.
- The fourth component is a clear sliding plastic overlay panel containing lines for nautical miles per gallon fuel consumption (1.0-5.5 gal/hr) along the ground speed x-axis (adjusted for head/tail winds) and fuel gallons per hour y-axis. This allows the pilot to determine the rate of fuel consumption and thus attainable range.
On the reverse of the metal base are performance limit graphs under various conditions of pressure altitude, outside air temperature, engine RPM, and throttle and supercharge settings, plus a table of cylinder temperature limits.
The calculator measures ~11 x 7 inches. It is in exceptional condition given its age. The panels slide very stiffly. This example is serial # 4785-43 evidence of a 1943 purchase order or manufacture. It is labeled for use by the TBF-1, early Avengers manufactured by Grumman. Later Avengers, TBMs, were manufactured by the Eastern division of General Motors.
We've only ever come across five of these calculators, and have not found any additional information on them on the internet. So we believe these to be rare items, indeed.