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Old 02-13-2018, 12:09 AM   #11
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Quote:
Originally Posted by JG3~Siggi View Post
Otherwise known as a manual pitch control?
Not in the P-51D.
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Old 02-13-2018, 09:17 PM   #12
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Quote:
Originally Posted by Art-J View Post
Still, the RPM gauge in cockpit is engine one, not the prop
I really don't think so. I have yet to come across one plane that indicates engine and not propeller RPM.
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Old 02-14-2018, 04:57 AM   #13
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I can read the P-51 manual online, and it seems to indicate that the Tachometer is engine RPM, not prop RPM. The generator that drives the tach is geared to the engine and it talks about adjusting indicated engine RPM via the prop control, see page 54 of this link: https://books.google.com/books?id=Sf...ometer&f=false
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Old 02-14-2018, 07:03 AM   #14
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Originally Posted by sobek View Post
I really don't think so. I have yet to come across one plane that indicates engine and not propeller RPM.
That's easy to settle.

A Mustang propeller has 1.7 m radius. It's circumference is (2*π*r) 10.676 meters. Which means that if 3000 was the prop RPM, then its wingtips would travel at 32028 meters per minute, which gives 1921 km/h. Nearly twice the speed of sound.

There were some supersonic propellers in the history of human flight, but not on WWII airplanes.

P-51 has a reduction gear with a ratio of 0.479 to 1, which slows the prop wingtips to a more manageable 920 km/h at takeoff.
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Old 02-14-2018, 11:35 AM   #15
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Quote:
Originally Posted by pmiceli View Post
I have over 6000 hours in piston engine types (about 50 different types) and I have never encountered an engine RPM lever. That may be what it indirectly does but that is not what ANYONE actually calls the thing.

Including the people who built the Mustang

This is showing a P51 B/C cockpit rather than the D
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Old 02-14-2018, 12:33 PM   #16
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Originally Posted by muehlema View Post
This is showing a P51 B/C cockpit rather than the D
And? What's your conclusion?
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Old 02-14-2018, 01:21 PM   #17
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Originally Posted by sobek View Post
I really don't think so. I have yet to come across one plane that indicates engine and not propeller RPM.
And I have yet to come across one that indicates prop RPM . I'm interested in piston-engined planes, though, don't remember how things are in turboprops - can bbrz comment?
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Old 02-14-2018, 03:27 PM   #18
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With turboprops the situation is a bit different and it depends if it's a free turbine or fixed turbine engine.

Free turbine turboprops usually have separate propeller levers and hence separate gauges for engine and propeller RPM.

Fixed turbine engines, without separate propeller controls, usually only have engine RPM indicated. (engine/prop RPM is controlled with the condition or speed lever)

In both cases engine RPM is always indicated in %.

Last edited by bbrz; 02-14-2018 at 03:31 PM.
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Old 02-14-2018, 07:02 PM   #19
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And usually only a secondary indicator to the pilot, as rpm remains constant though the flight, or has fixed values for ground, Takeoff, climb and cruise.
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Old 02-14-2018, 09:00 PM   #20
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Quote:
Originally Posted by Art-J View Post
And I have yet to come across one that indicates prop RPM .
Interesting, i would not have thought that the Merlin is such a slow running engine, but given the displacement, it does make sense.
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