![]() The wheel on the back of the calculator is used for calculating the effects of wind on cruise flight. Since the CRP-1s are made for the UK market, they can be used to perform the added conversions of Imperial to Metric units. Once the wheel is positioned to represent a certain fixed ratio (for example, pounds of fuel per hour), the rest of the wheel can be consulted to utilize that same ratio in a problem (for example, how many pounds of fuel for a 2.5-hour cruise?) This is one area where the E6B and CRP-1 are different. Throughout the wheel, unit names are marked (such as gallons, miles, kilometers, pounds, minutes, seconds, etc.) at locations that correspond to the constants that are used when going from one unit to another in various calculations. The front side of the flight computer is a logarithmic slide rule that performs multiplication and division. I must confess I have absolutely no idea as to how the slide works, but this description I found online explains how it is used: The rear of the panel is for the calculation of drift caused by wind. Tonight we have an example form the 1950s or 1960s marked up as a ‘Computer Dead Reckoning Mk 4’ and with a /|\ ownership mark: The computer is made up of two parts, an aluminium set of revolving dials: And a plastic insert panel with a graduated scale on it: The computer can be used on the front side for altitude calculations: And for Air Speed calculations: Note the words ‘Mach Speed’ etched into the aluminium indicating that this computer was indeed used and probably by the pilot of a supersonic fighter like the English Electric Lightning. ![]() ![]() Over 400,000 of the computers were made for the US during World War II and the RAF soon started developing its own versions of the little analogue computer. ![]() Tonight we are looking at an analogue computer used by navigators in the RAF to make calculations on speed, fuel consumption and the effects of wind upon a flight: The reverse of the computer allows different calculations to be made on the same instrument: This computer was first developed by a US airman called Phillip Dalton in 1937 and came into widespread use in the USAAF in 1940. ![]()
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