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Use of the clock dial for propeller pitch, any historical/logical reason?


grandkodiak
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grandkodiak

Curious as to how/why the hour/minutes clock dial was used to indicate propeller pitch in some planes? It goes from 12:00 to 8:30 I believe, but it seems odd to me that the clock was used. I would think a 0-100%, low-high, forward-back, or a degree of angle would have been the natural choice. I have been unable to find anything on the web thus far that covers this quirk. The clock has 2 dials, and doesn't use a large portion of the positions available to display, and is identical to well, a clock! At 12 you might think noon, hands straight up, but then I'd think 3 oclock would be full forward and parallel to the airstream or feathered... 8:30? Just strange all around, figured maybe there was a reason for it.

 

Thanks!

Edited by grandkodiak
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  • grandkodiak changed the title to Use of the clock dial for propeller pitch, any historical/logical reason?
ITAF_Airone1989

My personal explanation: the Luftwaffe bought too many clocks 

Edited by ITAF_Airone1989
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  • 4 weeks later...
Supercharger

Very interesting question,

 

i haven't found any reference yet, why they used a "prop clock" for airscrew angle position indication. First of all blade angle position indicators are very uncommon in aviation. In my opinion the germans were the only ones who used such an indicator. One reason for this(in my opinion) was the widespread use of single lever engine/prop controls. Because without an extra prop lever (e.g. Bf 109) you have no reference what the commanded prop blade angle is. During take off, for example you can see that the "prop clock" go's to 12 o'clock what means smallest blade angle or maximum speed increase. You can be safe that the prop did what he should do during take off. I think they used a clock style indicator to unify the prop blade indication between all the different aircraft types the german airforce used at this time. Since the smallest blade angle or max speed increase is different between several types of aircraft and with this clock everybody can see without any special training that the blades has reached there smallest angle possible (12 o'clock). And with two dials you have a very accurate blade angle indication (12 hours x 60').

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