The topic of uprating the Saturn V’s first stage engines appears to have been widely discussed, and yet there is little agreement as to how it was done.

Early Rocketdyne F-1 engines quote lower performance figures than later models, with static firing data showing increases in Isp from 260s to 263s, and in thrust from 1,500klbf to 1,522klbf. Flight data from later vehicles show marked increases as high as 265s sea level specific impulse and 1,580klbf of sea level thrust. Further digging will show varying nozzle dimensions, raising the question as to whether the earlier, lower thrust engines may have featured slightly smaller nozzle dimensions.

For example, the nozzle exit diameter had reportedly grown from 353.1cm (139in) to 364.5mm (143.5in). The latter figure has also been quoted as the nozzle exit diameter for the more capable F-1A engine. This is accompanied by an increase in external diameter from 12ft 2in (as shown in the image below) to 12ft 4in on later engines.


Often, it seems, accurate information about the Saturn V is difficult to come by. However, are these dimension changes simply figures somebody got wrong or were they actually part of a modification process?

Also, I have not found a definite throat area or diameter value for the F-1. The only figure that remains the same is the ‘16:1’ area ratio. Keeping the same area ratio would require the throat area to grow with the nozzle exit area, which would increase complexity of manufacturing even if each F-1 engine was already unique in some way. So, was throat area increased, or is it again a result of lost information as time has passed?


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