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S-97 RAIDER first ground testing begins

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posted on Feb, 12 2015 @ 06:32 PM
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a reply to: Zaphod58

Wow...

Sounds like a hell of a machine! Little wonder that it looks like such a mean bugger!

I would imagine that in terms of its acceleration to maximum forward speed, it must leave other helicopters standing, what with the tail rotor being angled as it is.

I would love to see a diagram which depicts the various angles at which air is moving through the rotors, and away from them, during maximum forward thrust. Normally, with a chopper which has its nose pointed downward during forward movement, there must be a speed which it would be inadvisable to exceed, because there would be more air moving past the rotor, than being moved BY the rotor, robbing it of purchase on the air around it, and therefore robbing it of lift as well.

This might have something to do with the reason you never see a whacking great pair of jet thrusters on a helicopter?

This design would seem to have far fewer limitations in that regard though!




posted on Feb, 12 2015 @ 06:40 PM
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a reply to: TrueBrit

The UH-60 has a never exceed speed of 222 mph, and a top speed of 183 mph. At 222 mph, both the airflow around the rotors, and the airframe stresses would reach that point.

Other than the added complexity to the gear box, this is an amazing design.



posted on Feb, 13 2015 @ 05:25 AM
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a reply to: TrueBrit

I would love to see a diagram which depicts the various angles at which air is moving through the rotors, and away from them, during maximum forward thrust. Normally, with a chopper which has its nose pointed downward during forward movement, there must be a speed which it would be inadvisable to exceed, because there would be more air moving past the rotor, than being moved BY the rotor, robbing it of purchase on the air around it, and therefore robbing it of lift as well.

Well kudos to you TrueBrit, that was a very insightful deduction. May I suggest that you look up the following terms to get a better idea?
Settling under power and Ring vortex state. Google/Wiki should be able to give you a nice explanation, better than I could anyway.

LEE.



posted on Feb, 13 2015 @ 07:25 AM
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a reply to: thebozeian

That was a very interesting read!

Thank you for that thebozeian! The vortex ring state I have just read about, appears to refer to a circumstance caused by a chopper trying to move downward through its own rotor wash, which would obviously cause problems, or trying to operate above its flight ceiling, where one would assume, the air is thinner, and harder to gain traction with, similar to the loss of grip a motor car will have on a less solid surface, in terms of its being prone to throwing the vehicle out of control.

Zaphod has confirmed the concern I was expressing in the post you quoted, but I thank you for the opportunity to learn a little more about the thermodynamic elements of chopper flight!



posted on Feb, 13 2015 @ 12:47 PM
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This is a neat aircraft, and it's interesting to see the North American take on a produceable counter-rotating rotorcraft. Zaphod has correctly summed up the advantages of such a system and also noted the extra complexity of the gearbox. The good news is that planetary-style gearboxes are intensely strong compared to other gearing systems, and as long as no corners are cut I would expect long, reliable service from those gears. They also have the added benefit of being handled as one-piece units with a shaft in, and a shaft out. The equipment we use has planetary gearboxes aplenty, and if for some reason one becomes suspect (which is very rare) we have the capacity to change them in and out at an extremely fast rate. Obviously tight-quarters of aircraft geometry will hurt that a bit, but I would be very surprised if the gearbox even approached the type of failure point that a tail rotor system presents.



posted on Feb, 13 2015 @ 03:01 PM
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a reply to: Darkpr0

I'd just like to see all of the snickering that's surely going on at Kamov as Sikorsky finally recognizes how much better coaxial rotors are.



posted on Feb, 13 2015 @ 05:51 PM
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originally posted by: Zaphod58
a reply to: TrueBrit

The UH-60 has a never exceed speed of 222 mph, and a top speed of 183 mph. At 222 mph, both the airflow around the rotors, and the airframe stresses would reach that point.

Other than the added complexity to the gear box, this is an amazing design.


The limiting factor on helicopter is an effect called retreating blade stall (RBS) which happens at higher speed. This is usually the major factor in establishing a never exceed speed. A helicopter has an advancing blade and a retreating blade while in forward flight. Let's say the helicopter is flying at 100 MPH and the rotor is turning at 100 MPH. The advancing blade will be advancing at 200 MPH and 200 MPH worth of lift. The retreating blade while turning at 100 MPH minus 100 MPH forward speed equals 0 MPH worth of lift. The helicopter will roll hard left and pitches nose up which can ruin your day.

A coaxial rotor systems with rotors turning in opposite direction will always have an advancing blade on each side. This allows the helicopter to fly faster than a conventional rotor helicopter because RBS is no longer an issue.

Chinooks and SeaKnights are faster than Hueys due to NO RBS issues.

Helicopter cruise speed is usually .30 to.40% of rotor RPM in FPS.



posted on Feb, 13 2015 @ 05:52 PM
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a reply to: buddah6

Which is a more technical explanation for what he was asking about.



posted on Feb, 13 2015 @ 06:45 PM
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originally posted by: Zaphod58
a reply to: buddah6

Which is a more technical explanation for what he was asking about.
Sorry!



posted on Feb, 13 2015 @ 07:00 PM
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a reply to: Zaphod58

Hm...

Could some of these issues have been addressed in the so-called "stealth" helicopters used in the Bin Laden raid? Some kind of modified tail rotor and dampened turbine assembly?



posted on Feb, 13 2015 @ 07:11 PM
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a reply to: buddah6

No reason to be sorry. I don't know rotary nearly as well as I know fixed wing. So that increased my knowledge base, which I'm always looking to do.



posted on Feb, 13 2015 @ 07:12 PM
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a reply to: MystikMushroom

The stealth helicopters used features like rotor hubs, and extra blades to help alleviate the sound. There are other tricks that can be used, like they used on the Little Birds to make them ultra quiet. There were other methods in use on those as well that didn't include physical features.



posted on Feb, 13 2015 @ 07:15 PM
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a reply to: MystikMushroom

I think the bin ladin stealth chopper had some features to make it more quite. The orientation of the tail rotor blades looked like the designers were trying to mitigate the traditional "thump, thump" of evenly spaced rotor assemblies. It's probably a safe assumption that they would have done something to the main rotor blades too. It probably had a more whooshing sound.



posted on Feb, 13 2015 @ 07:18 PM
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a reply to: Sammamishman

Rotor hub covers would be one feature that would alleviate sound, as well as curved rotor blades. If you listen to the Blackhawk compared to the Huey, you'll get an idea what curving the rotor tips will do for the sound.



posted on Feb, 14 2015 @ 11:33 AM
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Stealth in helicopters is a pipe dream! You can go a long way to improve the RCS but it will never be the same level as fixed wing aircraft. The best representative of rotary wing stealth is the RAH-66 Comanche. The stealth blackhawk used in the bin Laden raid was to only improve the RCS of the MH-60 not to make a truly stealth helicopter.



posted on Feb, 14 2015 @ 12:42 PM
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a reply to: buddah6

Stealth is the wrong word, but is closest to what we're trying for. You're right that there will never be a stealthy helicopter. The best that can be done is to reduce detection ranges, both audible and electronic.



posted on Feb, 14 2015 @ 02:48 PM
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There is a few ways to reduce the noise/ audible signature. The use of a fenestron or notar instead of a tail rotor and angle the engine exhaust upward. The RCS can be reduced by angular panels like the F117 with attention to the rotor hub and it's vertical components. Retractable landing gear helps too.

The major detractor to the stealth components is the additional weight which shortens range and reduces payload of the helicopter. Everything on a helicopter is a compromise in one form or another.
edit on 14-2-2015 by buddah6 because: (no reason given)



posted on Feb, 14 2015 @ 05:47 PM
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I would assume the co-axial design also helps with retreating blade stall issue? No benefit in having a pusher prop if the helo is gonna roll over on its side..



posted on Feb, 14 2015 @ 07:00 PM
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originally posted by: tomra
I would assume the co-axial design also helps with retreating blade stall issue? No benefit in having a pusher prop if the helo is gonna roll over on its side..

That's right. The Kamov helicopters have used the coax system for a long time in Russia. They found that it was much faster and capable of lifting heavier payloads than single rotor helicopter. Presently, they have built two attack types with this configuration called the Black Sharks that are coaxial.

I think that the Kamovs are controlled in a more conventional way than the fly-by-wire used on the Raider. I don't know if computer control does anything for the high speed flight envelop in helicopters. Sikorsky has a single rotor compound helicopter with a pusher prop that flies in the 250 MPH area that is also fly-by-wire.



posted on Feb, 14 2015 @ 08:48 PM
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originally posted by: buddah6

originally posted by: Zaphod58
a reply to: TrueBrit

The UH-60 has a never exceed speed of 222 mph, and a top speed of 183 mph. At 222 mph, both the airflow around the rotors, and the airframe stresses would reach that point.

Other than the added complexity to the gear box, this is an amazing design.


The limiting factor on helicopter is an effect called retreating blade stall (RBS) which happens at higher speed. This is usually the major factor in establishing a never exceed speed. A helicopter has an advancing blade and a retreating blade while in forward flight. Let's say the helicopter is flying at 100 MPH and the rotor is turning at 100 MPH. The advancing blade will be advancing at 200 MPH and 200 MPH worth of lift. The retreating blade while turning at 100 MPH minus 100 MPH forward speed equals 0 MPH worth of lift. The helicopter will roll hard left and pitches nose up which can ruin your day.

A coaxial rotor systems with rotors turning in opposite direction will always have an advancing blade on each side. This allows the helicopter to fly faster than a conventional rotor helicopter because RBS is no longer an issue.

Chinooks and SeaKnights are faster than Hueys due to NO RBS issues.

Helicopter cruise speed is usually .30 to.40% of rotor RPM in FPS.


Well maybe you can explain this to me a little bit more. Im kind of confused now. I thought that the whole point of the coaxial blades were to get two RBS regions instead of a retreating blade stall and advancing blade with the tips breaking the sound barrier. Wasnt this config the reason for the roughness of helos in certain configurations? Or am I missing something?



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