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#1
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Can the V-22: bring back the Rotodyne!
The problems which have been experienced by the V-22 Osprey are a
reminder of one very successful alternative: the Fairey Rotodyne. See: http://www.groenbros.com/tech/FaireyRotodyne.htm This was a large, passenger gyrodyne which had a separate lift rotor and two turboprops mounted on a short wing. For take-off and landing, gas from the turboprops was diverted to jets at the tip of the lifting rotor, providing the thrust to spin it. For level flight, the turboprops drove conventional propellers with the autorotating rotor providing about half the lift. Disadvantages compared with the V-22? Separate systems for vertical and level flight. Advantages compared with the V-22? The lift rotor and propellers were designed to be optimal for their tasks, instead of being a compromise. The autorotating ability of the big lift rotor provided a safety margin. And the whole thing was technically simple and trouble-free. It WORKED - decades ago! Its only really problem was noise from the tip-jets, but that would be far less of an issue for a military plane and they were working on that anyway. It was only cancelled due to political/industrial reasons. The company whose website contains the info listed above is proposing developing new gyrodynes by converting ewxisting fixed-wing planes - notably, the C-130 Hercules! This seems like a much lower-risk approach than tilt-rotors. Tony Williams Military gun and ammunition website: http://www.quarry.nildram.co.uk Discussion forum at: http://forums.delphiforums.com/autogun/messages/ |
#2
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Tony Williams wrote:
The problems which have been experienced by the V-22 Osprey are a reminder of one very successful alternative: the Fairey Rotodyne. See: http://www.groenbros.com/tech/FaireyRotodyne.htm This was a large, passenger gyrodyne which had a separate lift rotor and two turboprops mounted on a short wing. For take-off and landing, gas from the turboprops was diverted to jets at the tip of the lifting rotor, providing the thrust to spin it. For level flight, the turboprops drove conventional propellers with the autorotating rotor providing about half the lift. Disadvantages compared with the V-22? Separate systems for vertical and level flight. Advantages compared with the V-22? The lift rotor and propellers were designed to be optimal for their tasks, instead of being a compromise. The autorotating ability of the big lift rotor provided a safety margin. And the whole thing was technically simple and trouble-free. It WORKED - decades ago! Its only really problem was noise from the tip-jets, but that would be far less of an issue for a military plane and they were working on that anyway. Noise is rather a large issue for the military, if you're trying to sneak up on people to prevent them from shooting at you. The V-22 is much quieter than a helo when in fixed-wing mode, which means the other side doesn't hear you coming several minutes in advance (on the rare occasions that a Huey flies around in the area, despite my lousy hearing I can usually be dressed and outside my house before it comes over). It was only cancelled due to political/industrial reasons. The company whose website contains the info listed above is proposing developing new gyrodynes by converting ewxisting fixed-wing planes - notably, the C-130 Hercules! This seems like a much lower-risk approach than tilt-rotors. It will be interesting to see if they can get development money, especially for something like the modified C-130 prototype, what the loss in payload is and what maneuver restrictions are imposed by the large rotor (below 1g I could definitely foresee problems). What's clear is that the military wants their next tactical transport to be either superstol or V/STOL, combined with roughly C-130 capabilities, so that they don't have to capture an airfield as was the case with FOB Rhino in Afghanistan. Conventional helos just aren't going to cut it. Piasecki is working on compounds again (UH-60 or AH-64 prototype, I forget which) under a DARPA project, and then Boeing, Bell, Lockheed and everyone else are looking at the next step beyond the C-130/CH-53E as well as a potential XC-14/15 type a/c, even if the acronym seems to change monthly. Guy |
#4
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In article ,
"Jim Atkins" writes: Aren't there severe weight problems involved with separate vertical and horizontal systems? Seems I recall things like Dornier's transport (Do 31?) with dedicated lift jets that could just barely transport the weight of the crew. There are, especially in teh case of lift-jet aircraft, like the Dornier, which had to haul around a bimnch of engines that were only used for a short time each flight, but it's not that much of a problem with something like the Rotodyne, or even the almost-contemporary Lockheed AH-56. In the case of those aircraft, the rotors still provide lift, but they're unpowered, acting as an Autogiro fotor, and a fair chunk of the lift is taken up by the fixed wings. I guess you'd lose a bit of hover performance becase of the extra wing area under the rotor, but that would also accur with a tiltrotor. I suspect that Vmax would not theoretically be as high, you'd still have to deal with stuff like rotor tip speeds and retreating blade stall, but it'd be a fair shot. For the Rotodyne, noise was a severe problem. (Engine selection wasn't - Fairey wanted to move to teh Tyne for any later developments) If the newsreel soundtracks of teh thing I've heard are accurate, it could only be described as that of a Huey carrying a large, running Steam Locomotive. Consider this - Rotodyne noise was considered objectionable during a time when acceptable noise included unsuppressed straight-jet 707s and the just-proposed Concorde. You gotta go some to beat them. -- Pete Stickney A strong conviction that something must be done is the parent of many bad measures. -- Daniel Webster |
#5
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"Jim Atkins" wrote in message et... Aren't there severe weight problems involved with separate vertical and horizontal systems? Seems I recall things like Dornier's transport (Do 31?) with dedicated lift jets that could just barely transport the weight of the crew. -- Jim Atkins Twentynine Palms CA USA Yeah but the rotodyne didnt really have separate systems except for the tipjets It was a large autogyro but the engines that drove it horizontally could be tapped for bypass air which when fed to tipjets and burned allowed it to function as a helicopter. Its flight tests were succesful and it lifted a respectable load, its real limitation, as with any helicopter is top speed. Due to the problems of imbalanced lift between advancing and lagging rotors it will never match a fixed wing aircraft for speed. Keith |
#6
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"Jim Atkins" wrote in message . net...
Aren't there severe weight problems involved with separate vertical and horizontal systems? Seems I recall things like Dornier's transport (Do 31?) with dedicated lift jets that could just barely transport the weight of the crew. There is a weight penalty, but that would have to be set against the greater efficiency of a rotor and turboprops which were specialised for their purpose (the V-22's prop-rotors are too small to be efficient rotors, too large to be efficient propellers). In any case, the weight penalty for the Rotodyne is probably at a minimum, as we're not talking about needing separate engines, just ducting the gas to the tip-jets. And compared with a fixed-wing plane, the extra rotor weight is offset to some extent by the need for a smaller wing, and probably also by the need for less rugged undercarriage. Tony Williams Military gun and ammunition website: http://www.quarry.nildram.co.uk Military gun and ammunition discussion forum: http://forums.delphiforums.com/autogun/messages/ |
#7
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Guy Alcala wrote in message ...
Noise is rather a large issue for the military, if you're trying to sneak up on people to prevent them from shooting at you. The V-22 is much quieter than a helo when in fixed-wing mode, which means the other side doesn't hear you coming several minutes in advance (on the rare occasions that a Huey flies around in the area, despite my lousy hearing I can usually be dressed and outside my house before it comes over). I'm not sure how much of a problem it would be in this case, as the noise came from the tip-jets which were only lit up when the Rotodyne was preparing to land. In level flight the rotor was just autorotating. I don't know if this would produce any more noise than a fixed-wing, but I suspect it would be much less than a helo. Tony Williams Military gun and ammunition website: http://www.quarry.nildram.co.uk Military gun and ammunition discussion forum: http://forums.delphiforums.com/autogun/messages/ |
#8
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#9
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In article , Peter Stickney
writes For the Rotodyne, noise was a severe problem. (Engine selection wasn't - Fairey wanted to move to teh Tyne for any later developments) If the newsreel soundtracks of teh thing I've heard are accurate, it could only be described as that of a Huey carrying a large, running Steam Locomotive. Consider this - Rotodyne noise was considered objectionable during a time when acceptable noise included unsuppressed straight-jet 707s and the just-proposed Concorde. You gotta go some to beat them. Wasn't that just because of the 'city' environment it was expected to operate in. IIRC PanAm wanted something like 50 for city centre to airport operations? -- John |
#10
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In article , Keith Willshaw
writes Its flight tests were succesful and it lifted a respectable load, its real limitation, as with any helicopter is top speed. Due to the problems of imbalanced lift between advancing and lagging rotors it will never match a fixed wing aircraft for speed. Didn't it carry a load of passengers to the Paris airshow from London, can't remember but something like 20-30 people? During development they kept reducing the wing angle as they found the rotor continued to provide most of the lift. As they did this, speed increased, I'm not sure if they got as far as finding the optimum configuration. -- John |
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