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Author Topic: Multi-Speed Propeller AirScrews.....  (Read 678 times)

Offline xylstra

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Multi-Speed Propeller AirScrews.....
« on: October 30, 2018, 08:34:42 pm »
Multi-Speed Propeller Airscrews No!! I didn't say Variable-Pitch; in other words you change speed in flight just like changing gear in a car before driving up a hill.
I am attempting an in-depth research into the history of this topic and would like to receive as much information as possible. So far it seems to be almost entirely a U.S./British-centric affair and has left me puzzled as to what the rest of the world was up to while all this was going on e.g. France, Italy, Germany, Russia, Japan, etc?  ... where are their M-S Propeller projects?
   Perhaps, someone can fill me in on these two intriguing ROLLS-ROYCE excursions into the topic:
   (i) The WW1-era 'Eagle' Mark XV V-12, 2-speed propeller (penned by the great A.J. Rowledge no less, of NAPIER 'Lion' fame) one-off prototype. Does anyone have photographs, drawings, test reports, magazine articles, etc?
...... and (ii), a mere generation later its ' namesake, the 'Eagle' H.24 sleeve-valve. It seems that a 2-speed propeller reduction gear-box was mooted but no details to report. As above, does anyone have more information?
       All constructive replies gratefully received.                            Cheers.

Offline Piper106

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Re: Multi-Speed Propeller AirScrews.....
« Reply #1 on: October 31, 2018, 04:57:02 pm »
In addition to the engines mentioned above, the 24 cylinder Lycoming H-2470-5 and -7 engines. and the Lycoming 36 cylinder R-7775-3 engine were scheduled to have this feature.

Variable pitch propellers were not yet available for the WWI era Eagle, the two speed propeller drive likely was a way to get decent thrust from the propeller during both the take-off roll / climb as well as when at altitude flying at high speed. 

For the late WW2 Eagle, a single speed reduction gear is forced to turn the propeller (relatively) slowly when flying at high speed and high altitude to avoid the exceeding sonic velocity at the tips of the blades.  When taking off or climbing (low airspeed at low altitude) since the blades are turning slowly, the blades have to take to be adjusted to an angle that is too steep to efficiently convert HP to thrust.  The two speed reduction gearbox allows a second higher rotation speed that allows a lower more efficient blade angle during take-off and climb.

Offline AeroFranz

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Re: Multi-Speed Propeller AirScrews.....
« Reply #2 on: November 01, 2018, 08:35:20 am »
Karem's optimum speed tilt-rotor uses a two-speed gearbox.
It's aimed at solving the mismatch in operating conditions of rotors in hover and high speed flight.
All modern aircraft have four dimensions: span, length, height and politics.   TSR.2 got the first three right - Sir Sydney Camm

Offline xylstra

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Re: Multi-Speed Propeller AirScrews.....
« Reply #3 on: November 02, 2018, 05:15:32 pm »
Hi "Piper 106" Thanks for your reply. First a correction: the latter Lycoming you mentioned should be: XR-7755-3. I was well aware of the 2-speed reduction gear for this and have a sectioned drawing of this unit though the H-2470-5 & -7 seems to have a lot of "missing" information, specifically drawings on its 2-speed reducer. Bit of a shame but who knows what turns up in old filing cabinets these days after the "old man kicks it"!
     Yes, the WW1 'Eagle' was reported to have demonstrated superior take-off/climb/altitude cruise performance but these comments are from an authoritative source but un-accompanied by an original test report 9same tail-end comment, as above).
     Yes, the H-24 'Eagle' would have had the 2-speeder for the reasons you state as with all the other mega-piston engines (last of the dinosaurs!) being worked on (oops, wound up!) at that time. Try googling the (very) little known STUDEBAKER XH-9350 - the numerical code should give you a hint as to the size of this monster!
                                                                     Cheers, and thanks again.