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Old 04-16-2010, 12:16 PM   #4186
EvilGenius
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Is it possible to force a modern helicopter blade to go supersonic (intentional or not), or are there governers to prevent this?
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Old 04-16-2010, 12:37 PM   #4187
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Quote:
Originally Posted by EvilGenius
Is it possible to force a modern helicopter blade to go supersonic (intentional or not), or are there governers to prevent this?
Although it is possible, there are systems and controls in place to keep it from happening under power.

One issue, which you would not think about is in Autorotation. If the ship is heavy and you don't monitor the rotor rpm it can go high fast. Now if it would go supersonic I am not sure. i dont know how much margin the manufacturers plan in. I have seen a bell 206 go to 138% rotor rpm. No visual damage until you xrayed it....then UGLY. It made it to the ground and all walked away, that is what was important.
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Old 04-17-2010, 09:41 AM   #4188
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I flew a T6 Texan (fixed wing, WWII trainer) once. Its prop tips go supersonic very easily (about 2200 rpm iirc). Ordinary take-off power has the tips supersonic, but standard cruise does not. The Shell Aero team seems to keep them supersonic for about their entire routine (or so it seems from the sound they produce) You loose efficiency and make a bunch of noise, but I don't think it really hurts anything beyond that.
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Old 04-17-2010, 10:25 AM   #4189
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Quote:
Originally Posted by BikePilot
You loose efficiency and make a bunch of noise, but I don't think it really hurts anything beyond that.
In a propeller with a smaller diameter you can design and build in enough strength to handle it.

In a Helicopter rotor system there is no way to get enough strength in the big diameter to allow it to go SS. Even if you could I am not sure how much a helicopter would benefit with the loss of performance.
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Old 04-17-2010, 10:36 AM   #4190
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Well, the other factor is cost - sure, you can design a 20 ft composite blade to withstand the various forces involved in supersonic operation, but the average Robbie owner (let alone the average S76C operator) wouldn't be able to afford it.
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Old 04-17-2010, 11:43 AM   #4191
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Looks like it could be an OH-58 but at that angle the tail looks a little off. BTW there is an outfit in the Mid-Valley that has/had an surplus OH-58 set up for spray. It was a few years ago since I saw it last. I think BP is mainly using 500s.

Quote:
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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 04-17-2010, 11:47 AM   #4192
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Looks like it could be an OH-58 but at that angle the tail looks a little off. BTW there is an outfit in the Mid-Valley that has/had an surplus OH-58 set up for spray. It was a few years ago since I saw it last. I think BP is mainly using 500s.

Its a UH72A Lakota. Flown by the National guard for anti-drug, ems, and law enforcement support. Built by Eurocopter. BP is mostly out of the MD500 business. Mainly using EC120 and AS350 A-Stars also by Eurocopter
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Old 04-17-2010, 11:55 AM   #4193
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Thanks for the response. ITs been a few years since I was in the flying business with the Army. I did a google on it. Haven't actually seen one in real life yet.
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Old 04-17-2010, 12:13 PM   #4194
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Quote:
Originally Posted by AtkRWC
Thanks for the response. ITs been a few years since I was in the flying business with the Army. I did a google on it. Haven't actually seen one in real life yet.
They are great helicopters for the civilian roles. Not built to well for the military duty. Not very durable. It will be interesting to see how they hold up.....but they do have Airconditioning now that the Army wised up and stopped taking it off.
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Old 04-17-2010, 12:24 PM   #4195
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Quote:
Originally Posted by tpknueven
Although it is possible, there are systems and controls in place to keep it from happening under power.

One issue, which you would not think about is in Autorotation. If the ship is heavy and you don't monitor the rotor rpm it can go high fast. Now if it would go supersonic I am not sure. i dont know how much margin the manufacturers plan in. I have seen a bell 206 go to 138% rotor rpm. No visual damage until you xrayed it....then UGLY. It made it to the ground and all walked away, that is what was important.
Yeah, I can see that.
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Old 04-17-2010, 12:26 PM   #4196
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I currently fly a BK-117 which is what the EC-145/UH-72 Lakota are based off of. Very tough and dependable. Rigid rotor system with no life limit. Rotor head is carved from one piece of titanium also with no life limit.

The BK is and enlarged and expanded extension of the BO-105 which has been in use extensively by the military in several nations. Great machine for the Army.
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Old 04-17-2010, 12:32 PM   #4197
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Quote:
Originally Posted by Elvis70
I currently fly a BK-117 which is what the EC-145/UH-72 Lakota are based off of. Very tough and dependable. Rigid rotor system with no life limit. Rotor head is carved from one piece of titanium also with no life limit.

The BK is and enlarged and expanded extension of the BO-105 which has been in use extensively by the military in several nations. Great machine for the Army.
The mechanicals are great, the problems we are seeing is windows coming out (only glued in, no mechanical fasteners), Door hinges pulling out of compsite materials, cracks in the compsoite structure. All areas that are now composite that were metal in the BK and BO. I just don't think enough engineering went into the composite structure. When we approach them with a fix from the engineering side we are told it would have added too much weight to the airframe.
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Old 04-17-2010, 12:32 PM   #4198
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Quote:
Originally Posted by Hedge36
Well, the other factor is cost - sure, you can design a 20 ft composite blade to withstand the various forces involved in supersonic operation, but the average Robbie owner (let alone the average S76C operator) wouldn't be able to afford it.
Not just that but heli blades do all kinds of crazy flopping (especially in forward flight) that a regular prop plane never does.

Pretty much the only thing a prop plane can do is change pitch and that's really jus aerodynamics, not much rapid g force change there like you get in a single rotationg if the main rotor in a helicopter.
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Old 04-17-2010, 12:39 PM   #4199
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Regardless of the flapping mechanism (hinges, delta hinges, inherent blade flex), blade motion isn't really limited by rotational speed, even in the supersonic realm. The structural integrity of the materials - especially the blade tips and roots - is what you have to design around, and that's where cost and weight penalties really start to hold you back.

There have been some great studies showing that supersonic speeds in forward flight are actually more aerodynamically tolerated by the rotor disc than in the hover. Without the translation lift inflow, recirculation of the shockwave makes all kinds of interesting things happen.
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Old 04-17-2010, 03:02 PM   #4200
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Quote:
Originally Posted by tpknueven
The mechanicals are great, the problems we are seeing is windows coming out (only glued in, no mechanical fasteners), Door hinges pulling out of compsite materials, cracks in the compsoite structure. All areas that are now composite that were metal in the BK and BO. I just don't think enough engineering went into the composite structure. When we approach them with a fix from the engineering side we are told it would have added too much weight to the airframe.
Maybe they should of just bought used BK's.
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