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Old 04-14-2010, 08:49 PM   #4156
Dfender110
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Retreating blade stall is the biggest killer of for top speed in a helicopter. At a given speed the retreating blade will stall and cause a roll to the retreating side. Aircraft with counter rotating blades are not as limited by the phenomenon.

By putting the load on the stub wings and the tail Prop (Fan) providing forward flight stability the rotor system can then unload and retreating blade stall is no longer the limit to top speed.

Thats the basic idea anyway.

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Originally Posted by EvilGenius
I dunno what it's called, but I thought the whole idea was to get it up to speed, then transfer the power from the main rotor entirely to the rear fan to provide the forward thrust and use the lift from the already spinning main rotor to keep it in the air.

I dunno that it'd make it really any faster, but I'm betting it'd be a hell of a lot more efficient while in cruise.

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Old 04-14-2010, 09:14 PM   #4157
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Quote:
Originally Posted by tpknueven
Retreating blade stall is the biggest killer of for top speed in a helicopter. At a given speed the retreating blade will stall and cause a roll to the retreating side. Aircraft with counter rotating blades are not as limited by the phenomenon.

By putting the load on the stub wings and the tail Prop (Fan) providing forward flight stability the rotor system can then unload and retreating blade stall is no longer the limit to top speed.

Thats the basic idea anyway.

Tim Knueven
FAA A&P IA CFII Rotorcraft (H)
I understand that.

Would it be safe to say that two helicopters with similar HP ratings, same blade diameter, same blade number, but spinning at two different speeds. Would the one with the higher rotor speed have a higher top speed before running into RBS?
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Old 04-14-2010, 09:21 PM   #4158
Dfender110
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In a simple sense yes. Its a non-linear formula but in a basic sense it would and the limiting factor for rotor speed.....Blade tip speed if it goes supersonic a whole nother set of factors play in


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Originally Posted by EvilGenius
I understand that.

Would it be safe to say that two helicopters with similar HP ratings, same blade diameter, same blade number, but spinning at two different speeds. Would the one with the higher rotor speed have a higher top speed before running into RBS?
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Old 04-15-2010, 05:13 AM   #4159
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Quote:
Originally Posted by tpknueven
In a simple sense yes. Its a non-linear formula but in a basic sense it would and the limiting factor for rotor speed.....Blade tip speed if it goes supersonic a whole nother set of factors play in
That's why some blades have the little swept back angle on the tip right, or is that something else?
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Old 04-15-2010, 07:02 AM   #4160
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Yep, Swept tips are the early easy fix, along with Ridgid rotor systems and unloading the rotor system.

One question the Speed Hwak design leaves me with is... What happens when you are flying along using the stubs and pusher and have an engine failure?

Would the rotorsystem reload soon enough to allow a smooth entry into autorotation? I guess in that sense its an Auto Gyro so its a non event. I will have to do some more reading. Piasecki didn't want to answer many
questions at the Heli-expo.
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Originally Posted by EvilGenius
That's why some blades have the little swept back angle on the tip right, or is that something else?
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Old 04-15-2010, 07:43 AM   #4161
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Quote:
Originally Posted by tpknueven
One question the Speed Hwak design leaves me with is... What happens when you are flying along using the stubs and pusher and have an engine failure?
Yeah, I've been really curious about the initial pitch reaction myself.
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Old 04-15-2010, 07:51 AM   #4162
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Watching the video at the expo it looked like the airframe attitude was pretty level 100-110kt attitude in fast forward flight with the wings loaded.

The rotor system looked really slow and coned up but that may have been just the shutter speed of the camera.


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Yeah, I've been really curious about the initial pitch reaction myself.
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Old 04-15-2010, 07:54 AM   #4163
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Quote:
Originally Posted by tpknueven
Watching the video at the expo it looked like the airframe attitude was pretty level 100-110kt attitude in fast forward flight with the wings loaded.

The rotor system looked really slow and coned up but that may have been just the shutter speed of the camera.
Typical gyro, really. Just a damn expensive one
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Old 04-15-2010, 07:58 AM   #4164
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Yep, I always thought the Carter-Copter was a cool one.

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Typical gyro, really. Just a damn expensive one
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Old 04-15-2010, 08:42 AM   #4165
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This guy was out along Military Highway here along the Tex/Mex border last weekend. He was hovering around in the marshes, and then later in the day I saw him buzzing along in the center of the Rio Grande at tree top height.

Supposedly the Border Patrol operates a similar model around here that's painted in blue and with a fenestron tail rotor, but what is unusual about this particular 'copter is that it appears to be from the Army Guard.

I didn't see any markings but they would be tiny under any circumstance. The Border Patrol claims that they don't operate any unmarked helicopters or "black helicopters."

As an aside, one of the nearby Sheriff's has been up in arms because a Mexican Marine Mi-8 has been overflying a neighborhood on the US side several times during the last month.

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Old 04-15-2010, 09:12 AM   #4166
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Quote:
Originally Posted by EvilGenius
That's why some blades have the little swept back angle on the tip right, or is that something else?
It was my understanding that the swept tips quieted the rotor system.
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Old 04-15-2010, 10:06 AM   #4167
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It quiets the rotors by breaking up the tip vorticies and also allows them to spin faster.


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It was my understanding that the swept tips quieted the rotor system.
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Old 04-15-2010, 10:12 AM   #4168
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Quote:
Originally Posted by PirateJohn
This guy was out along Military Highway here along the Tex/Mex border last weekend. He was hovering around in the marshes, and then later in the day I saw him buzzing along in the center of the Rio Grande at tree top height.

Supposedly the Border Patrol operates a similar model around here that's painted in blue and with a fenestron tail rotor, but what is unusual about this particular 'copter is that it appears to be from the Army Guard.

I didn't see any markings but they would be tiny under any circumstance. The Border Patrol claims that they don't operate any unmarked helicopters or "black helicopters."

As an aside, one of the nearby Sheriff's has been up in arms because a Mexican Marine Mi-8 has been overflying a neighborhood on the US side several times during the last month.

UH72A LAKOTA known in Civilian paint as the EC145. Its a Eurocopter product.
It won the Army Light Utility Helicopter contract. It is used by the National Guard for Law enforcement, Drug interdiction and Medical Evac. It is replacing the UH60 Blackhawks in the National Guard so they can be reassigned to the regular Army to replace the ones getting beat up in the GWT.

Its an off the shelf FAA approved airframe so that at the end of the contract the Army will be able to sell them on the civilian market without the hassle of the Restricted catagory and hopefully recoup more money.

The markings are there. Flat black on Dark OD green makes them almost impossible to see.
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Old 04-15-2010, 10:34 AM   #4169
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Quote:
Originally Posted by a65l
It was my understanding that the swept tips quieted the rotor system.
Things get loud when you go supersonic.

I've heard some RC plane props go supersonic and it's a nasty loud sound, plus it did a number on the blades.
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Old 04-15-2010, 10:35 AM   #4170
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Quote:
Originally Posted by tpknueven
It quiets the rotors by breaking up the tip vorticies and also allows them to spin faster.
That too.
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