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#11
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In article , frank may
writes Well, counter rotating props eliminate torque on twin engined airplanes & on at least some, improves the single engine performance & handling. However, your question really seems to be about contra-rotating props, which is the case of a single engine driving 2 props on a co-axial shaft, rotating opposite of each other. Same thing, it eliminates the torque & therefore makes the airplane more docile. Contra-rotating props are same shaft, same engine, like a late Seafire or Shack or Bear. Counter-rotating are separate engines, like the P-38 or F-82 or several twin engine Pipers. Then there's the case (unique AFAIK) of the Fairey Gannet. The Double Mamba engine is in fact two Mambas side by side, each driving one of the two props. One half could be shut down to allow economical loiter. As far as torque is concerned, although without a prop, don't forget the Pegasus in the Harrier. Contra-rotating shafts to balance it so that hovering is easier/possible. -- Peter Ying tong iddle-i po! |
#12
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Even by 1940, the world's air forces had discovered that there was a problem with the more-powerful engines that were coming on line: they'd drive the propeller too fast. Once the tips go trans-sonic, the prop loses efficiency. So they went from two-bladed to three-bladed props, and then to four-bladed. And they made the props longer. But there are limits to both these solutions. Thus the notion of having two sets of propellers, rotating in different directions. On prop-jets these days, you routinely see multi-bladed propellers.I'm not sure why airframe manufacturers didn't go in this direction for warplanes, but perhaps it has to do with the power output of a plane under combat conditions--that is, a seven-bladed prop will work on a transport but not on a fighter. Dunno. You're certainly right about the complexity of the counter- or contra-rotating propellers. all the best -- Dan Ford email: (put Cubdriver in subject line) The Warbird's Forum www.warbirdforum.com Expedition sailboat charters www.expeditionsail.com |
#13
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In article ,
phil hunt wrote: On 18 Sep 2004 16:05:44 +0100, ANDREW ROBERT BREEN wrote: A related issue was maintainance (this for multi-engine types): if you wanted to avoid torque effects you had to have "handed" engines, turning in different directions on each side (like the Lockheed Lightning or the De Havilland Hornet), or you put up with the torque effects and had the mainatainance/suppy gain of n identical engines. Couldn't you use identical engines, but mount them back-to-front on one wing? Tractor on one wing, pusher on the other? Could be done, I dare say, though the nacelle design would be interesting to avoid asymmetric drag or thrust.. Can't help but feel that contraprops might be easier! -- Andy Breen ~ Interplanetary Scintillation Research Group http://users.aber.ac.uk/azb/ "Time has stopped, says the Black Lion clock and eternity has begun" (Dylan Thomas) |
#14
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In article ,
Ken Duffey wrote: Andy, ANDREW ROBERT BREEN wrote: In article , Raoul wrote: I've had a questions I'd like to foist upon the collective knowledge here... I've noticed that their were many planes during the prop-to-jet transition years from about 45 to about 55 that used counter rotating propellers. I'm wondering what the perceived advantage was? Great reply................. Thank 'ee, sir... Major snip................... Not sure whether the Antonev 70 is actually in production yet, but it uses four big contraprops.. IIRC, the An-70 is not a contraprop as such - the D-27 engine is a twin-spool propfan - and the props are driven by the two shafts, not through a 'normal' contraprop gearbox. Aha.. Interesting. That said, of course, the Fairey P.24-powered Battle and then the Gannet weren't "classic" contraprops (in the gearbox-split sense), either - both having separate engines turning the two props - but the props shared an axis. I can't remember off-hand how the two engines were combined onto the contra-rotating props in the Brabazon. There were gearboxes, but where the drives joined and split I'm not at all sure.. It has 8 blades in the front row and 6 in the rear - 14 blades per engine - making a staggering total of 56 blades !!! Curved blades as well, IIRC It is extremely fuel efficient......... Didn't the unducted fans trialled about 10 years ago (on DC-9s?) have two rows of contra-rotating pusher blades? -- Andy Breen ~ Not speaking on behalf of the University of Wales.... Nieveler's law: "Any USENET thread, if sufficiently prolonged and not Godwinated, will eventually turn into a discussion about alcoholic drinks." |
#15
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In article ,
Peter Twydell wrote: Then there's the case (unique AFAIK) of the Fairey Gannet. The Double Mamba engine is in fact two Mambas side by side, each driving one of the two props. One half could be shut down to allow economical loiter. Unique in production, but didn't the Blackburn prototype offered for the same spec have the same arrangement? And before that, of course, there was the Fairey P.24 Prince engine (essentially a V12 and an inverted V12, each driving its own proellor on the same axis) - that was trialled in a Battle (which was said to have a fairly startling performance). It was offered to Republic as a powerplant for the P47, but got canned as the Min. of Supp. didn't want Fairey trying to do too many things at once. -- Andy Breen ~ Interplanetary Scintillation Research Group http://users.aber.ac.uk/azb/ "Time has stopped, says the Black Lion clock and eternity has begun" (Dylan Thomas) |
#16
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Kevin Brooks wrote:
"Ken Duffey" wrote in message ... Andy, ANDREW ROBERT BREEN wrote: In article , Raoul wrote: I've had a questions I'd like to foist upon the collective knowledge here... I've noticed that their were many planes during the prop-to-jet transition years from about 45 to about 55 that used counter rotating propellers. I'm wondering what the perceived advantage was? Great reply................. Major snip................... Not sure whether the Antonev 70 is actually in production yet, but it uses four big contraprops.. IIRC, the An-70 is not a contraprop as such - the D-27 engine is a twin-spool propfan - and the props are driven by the two shafts, not through a 'normal' contraprop gearbox. It has 8 blades in the front row and 6 in the rear - 14 blades per engine - making a staggering total of 56 blades !!! It is extremely fuel efficient......... Wait a sec. If this was such an extremely fuel efficient system, the short-haul airlines would be banging down the various manufacturers' dorrs demanding such systems--which they decidedly ain't doing. The prop fan configuration was tested here in the US a few years back (on a DC-9 airframe, IIRC), and it apparently was found wanting (how much of a problem in that regard the noise issue is I don't know). The An-70 has had a rather troubled development history (so much so that the Russians have gotten rather cold to it), and IIRC one of the major problems has been the powerplant. Brooks Ken Don't shoot the messenger - I'm only quoting what I read ............. From 'Antonov's Heavy Transports -The An-22, An-124/125 and An-70' by Yefim Gordon, Dmitriy and Sergey Komissarov - No 18 in the 'Red Star' series.......... purchased yesterday. "Four ZMKB(Muravchenko) D-27 propfane engines with a takeoff rating of 14,000 ehp and a cruise rating of 6,750 ehp designed by ZMKB Progress at Zaporozhye. The D-27 is a two-spool engine........ The engines are noted for their high fuel efficiency, the fuel burn in take-off and cruise mode being 170 g/ehp.h (0.37 lb/ehp.h) and 130 g/ehp.h (0.29 ib/ehp.h) respectively.........." I don't profess to know what that all means - I am just posting what I read. As far as the dispute between the Ukraine and Russia over the engines - again, from what I read - this has now been resolved... From Air Fleet 5/2003 - "In spite of the RusAF top brass's stance on the An-70 - (to do with structural flaws in the powerplant) - representatatives of the Russian government believe that the An-70 trials must be completed 'as sooon as possible'. According to Russian vice-premier Boris Alyoshin speaking on 15 August - 'there is no reason for saying that the programme will not be accomplished or Russia is pulling out of the programme. The commitments Russia made must be met" Ken |
#17
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In message , Peter Twydell
writes In article , frank may writes Well, counter rotating props eliminate torque on twin engined airplanes & on at least some, improves the single engine performance & handling. However, your question really seems to be about contra-rotating props, which is the case of a single engine driving 2 props on a co-axial shaft, rotating opposite of each other. Same thing, it eliminates the torque & therefore makes the airplane more docile. Contra-rotating props are same shaft, same engine, like a late Seafire or Shack or Bear. Counter-rotating are separate engines, like the P-38 or F-82 or several twin engine Pipers. Then there's the case (unique AFAIK) of the Fairey Gannet. The Double Mamba engine is in fact two Mambas side by side, each driving one of the two props. One half could be shut down to allow economical loiter. Wasn't the Gannet designed for naval officers to fly standing up? Mike -- M.J.Powell |
#18
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In article , M. J. Powell
writes In message , Peter Twydell writes In article , frank may writes Well, counter rotating props eliminate torque on twin engined airplanes & on at least some, improves the single engine performance & handling. However, your question really seems to be about contra-rotating props, which is the case of a single engine driving 2 props on a co-axial shaft, rotating opposite of each other. Same thing, it eliminates the torque & therefore makes the airplane more docile. Contra-rotating props are same shaft, same engine, like a late Seafire or Shack or Bear. Counter-rotating are separate engines, like the P-38 or F-82 or several twin engine Pipers. Then there's the case (unique AFAIK) of the Fairey Gannet. The Double Mamba engine is in fact two Mambas side by side, each driving one of the two props. One half could be shut down to allow economical loiter. Wasn't the Gannet designed for naval officers to fly standing up? It could well have been, but I bet they couldn't have done it with the same flair as Stringbag display crews do it now: White Ensign flying and the Observer and TAG saluting to the side. http://www.stringbag.flyer.co.uk/rnh...es/ls326_6.jpg is the best I can find at the moment. -- Peter Ying tong iddle-i po! |
#19
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"Ken Duffey" wrote in message ... Kevin Brooks wrote: "Ken Duffey" wrote in message ... Andy, ANDREW ROBERT BREEN wrote: In article , Raoul wrote: I've had a questions I'd like to foist upon the collective knowledge here... I've noticed that their were many planes during the prop-to-jet transition years from about 45 to about 55 that used counter rotating propellers. I'm wondering what the perceived advantage was? Great reply................. Major snip................... Not sure whether the Antonev 70 is actually in production yet, but it uses four big contraprops.. IIRC, the An-70 is not a contraprop as such - the D-27 engine is a twin-spool propfan - and the props are driven by the two shafts, not through a 'normal' contraprop gearbox. It has 8 blades in the front row and 6 in the rear - 14 blades per engine - making a staggering total of 56 blades !!! It is extremely fuel efficient......... Wait a sec. If this was such an extremely fuel efficient system, the short-haul airlines would be banging down the various manufacturers' dorrs demanding such systems--which they decidedly ain't doing. The prop fan configuration was tested here in the US a few years back (on a DC-9 airframe, IIRC), and it apparently was found wanting (how much of a problem in that regard the noise issue is I don't know). The An-70 has had a rather troubled development history (so much so that the Russians have gotten rather cold to it), and IIRC one of the major problems has been the powerplant. Brooks Ken Don't shoot the messenger - I'm only quoting what I read ............. From 'Antonov's Heavy Transports -The An-22, An-124/125 and An-70' by Yefim Gordon, Dmitriy and Sergey Komissarov - No 18 in the 'Red Star' series.......... purchased yesterday. "Four ZMKB(Muravchenko) D-27 propfane engines with a takeoff rating of 14,000 ehp and a cruise rating of 6,750 ehp designed by ZMKB Progress at Zaporozhye. The D-27 is a two-spool engine........ The engines are noted for their high fuel efficiency, the fuel burn in take-off and cruise mode being 170 g/ehp.h (0.37 lb/ehp.h) and 130 g/ehp.h (0.29 ib/ehp.h) respectively.........." I believe they have had not one but two accidents ('95 and '01) tied to the engines and props? From Pravda in '99 (not the best source, I'd agree--but it was saying the same thing the Russian AF folks were saying): "Vladimir Mikhailov says that the plane cannot be put into production because of its imperfect engine D-27 that is "unsafe, short-life and very expensive." Experts think it is impossible to get the engine into shape." english.pravda.ru/main/18/89/357/11829_aviation.html That does not sound like a ringing endorsement of the powerplants. I don't profess to know what that all means - I am just posting what I read. As far as the dispute between the Ukraine and Russia over the engines - again, from what I read - this has now been resolved... From Air Fleet 5/2003 - "In spite of the RusAF top brass's stance on the An-70 - (to do with structural flaws in the powerplant) - representatatives of the Russian government believe that the An-70 trials must be completed 'as sooon as possible'. According to Russian vice-premier Boris Alyoshin speaking on 15 August - 'there is no reason for saying that the programme will not be accomplished or Russia is pulling out of the programme. The commitments Russia made must be met" "Moscow, 15 June: Russia will allocate about R30m for developing the An-70 military transport aircraft in 2004, Leonid Terentyev, director-general of the Medium Transport Plane international consortium, told Interfax-Military News Agency on Tuesday [15 June]. "The Russian side will most likely earmark about R30m [indicated elsewhere by the same source as being $1 million USD)] for the An-70 development in 2004. Russia is unlikely to provide more funds in 2004," Terentyev said. He noted that the upcoming meeting of the intergovernmental Russian-Ukrainian commission was unlikely to achieve a radical breakthrough with regards to the An-70 programme." www.gateway2russia.com/st/art_242733.php That sounds like anything but a strong endorsement of the An-70 program, which Russian senior defense officials have repeatedly commented of late as not being a program they are very interested in pursuing. The Russian Air Force apparently wants nothing to do with it, preferring its cheaper Il-76's. Brooks Ken |
#20
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In message , Peter Twydell
writes In article , M. J. Powell writes In message , Peter Twydell writes In article , frank may writes Well, counter rotating props eliminate torque on twin engined airplanes & on at least some, improves the single engine performance & handling. However, your question really seems to be about contra-rotating props, which is the case of a single engine driving 2 props on a co-axial shaft, rotating opposite of each other. Same thing, it eliminates the torque & therefore makes the airplane more docile. Contra-rotating props are same shaft, same engine, like a late Seafire or Shack or Bear. Counter-rotating are separate engines, like the P-38 or F-82 or several twin engine Pipers. Then there's the case (unique AFAIK) of the Fairey Gannet. The Double Mamba engine is in fact two Mambas side by side, each driving one of the two props. One half could be shut down to allow economical loiter. Wasn't the Gannet designed for naval officers to fly standing up? It could well have been, but I bet they couldn't have done it with the same flair as Stringbag display crews do it now: White Ensign flying and the Observer and TAG saluting to the side. http://www.stringbag.flyer.co.uk/rnh...es/ls326_6.jpg is the best I can find at the moment. Lovely! Mike -- M.J.Powell |
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