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Old 07-08-2016, 11:20 PM   #1
1BOHO
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Default Is a well designed coaxial heli at any disadvantage in speed or maneuverability to a

...non coaxial one?

I ask because to date of at least what is not classified isn't this the fastest and most maneuverable helicopter in the world?
The Sikorsky S-97
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Old 07-18-2016, 10:57 PM   #2
megawhacker
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I do not know the answer to your question, but the photo you post is of a helicopter with a pusher prop. I will suggest that any aircraft with a pusher prop is not relevant to your which is faster question.
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Old 07-26-2016, 01:25 PM   #3
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The Eurocopter X3 concept is faster.

One disadvantage of a coaxial, is the taller mast which is difficult to streamline.
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Old 07-27-2016, 02:35 PM   #4
HeliXXL
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Default Maybe

I am not an engineer so this is my opinion only. First, the X3 is only marginally faster the the S-97 ( a few kts tas) and both are compound helicopters. Of note in regard to the X-3 is that it has achieved slightly better speed and was able to do so without the active vibration control required in the sikorsky. Sikorsky has been working on speed helicopters since the X-59 but abandoned that project because of expense and high vibration at high speed. Now maneuverability is a different story. According to sikorsky the S-97 is far more maneuverable the any standard rotor helicopter currently in production. Personally I would attribute that partially to the coax and partially to its rigid rotor system. Back in the 60s lockheed worked on the AH-56 Cheyenne which was also a compound helicopter but was somewhat more traditional in its layout in that it still utilized a tail rotor but used a pusher prop and stub wings. It was extremely fast (212 kts) and was also very maneuverable because it too had a rigid rotor head in contrast to the cobra with it's semi rigid teetering rotor. Not sure if that answers your question but I hope it helps some.

P.S. I love alternative rotor designs i.e. coax flettner etc.
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Old 11-28-2016, 11:56 PM   #5
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This might explain things:
https://www.youtube.com/embed/f72WZwvMTj4

So as long as heli speed is low relative to blade speed, it doesn't matter. But yes, a coax can fly faster if given the chance.
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Old 12-08-2016, 08:12 PM   #6
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Quote:
Originally Posted by velo24 View Post
This might explain things:
https://www.youtube.com/embed/f72WZwvMTj4

So as long as heli speed is low relative to blade speed, it doesn't matter. But yes, a coax can fly faster if given the chance.
Exactly. And with a puller or pusher prop the two rotors would only have to be set at a pitch that would maintain lift required to counter the weight and the prop can generate the speed.
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