Author Topic: Helicopter Questions  (Read 81261 times)

Offline Frank N. O.

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Re: Helicopter Questions
« Reply #30 on: March 24, 2006, 05:08:31 PM »
That UND accident sounds horrible :(
But that Chinook did not look very well either! And now the question to get the asnwer I couldn't find: Was anyone hurt?`

Now we're discussing all those different types of twirlybirds, what about the Hughes/McD NOTAR helicopters? Is the NOTAR system good to reduce accidents and still having a simple plane (a twin-rotor regardless of the type requires more gearboxes right? Wether it's tandem or co-axial). I also read the modern NOTAR's has automatic directional control, IE. you don't have to adjust the NOTAR when applying more force to the rotor to keep the nose in the same direction.

Frank
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Offline Ted_Stryker

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Re: Helicopter Questions
« Reply #31 on: March 24, 2006, 05:11:33 PM »
Wow.  Is that something that's repairable, or does that just go for scrap?

Hehe, no way!
You're talking destroying the whole running gear AND the fuselage structure.
If you roll a helo over you can sometimes rebuild it by replacing the running gear and keeping the airframe, but in this case it's better to just call the insurance and take your radios out...

To Jim:
You have a point. But I still like being able to land in a parking lot! ;)
A Chinook by the way is a little like the V-22 we talked about, too many blades and gearboxes...

The flexibility of landing in a parking lot is nice, though I still tend to agree that a chopper is a collection of parts doing it's best to tear itself apart  ;D  Ok... maybe not that bad... and I DO enjoy flying on them.... but they are mechanically more complex than their fixed wing world counterparts.

We had a really great chopper pilot here in St. Louis.  His name was Alan Barklage.  He was a Vietnam chopper pilot, and decorated.  When he went civi he got into news helo flying.  He had a number of incidents over the years.  One where he was taking off of a landing pad at our riverfront, with one skid still hooked by a tie-down rope.  The chopper ended up on it's side in the river on that one.  Another where he was landing in a parking lot during Christmas time (I think with a Santa on board), and his tail rotor clipped a parking lot light pole.   And one time he was taking a passenger on a flight with him and she hijacked him, trying to get him to fly her boyfriend out of a jail here!   That one didn't end well for her, as he kept a .357 under his pilot's seat.  Ironically, he survived all that, and then died in a crash of his personal chopper, a Robinson, when he had delayed putting on an A.D. required retrofit part.  He got up to 300 ft AGL, then his engine siezed up and he dropped out of the sky.   His brother still flies helo's and does news reporting locally.  Just amazing how a guy can go through Vietnam, all those accidents and incidents, and then, something seemingly minor that "should have been" able to wait came up to bit him in the tail rotor compartment!

We're going to have to come in pretty low!  It's just one of those things you have to do... when you land!  -- Ted Striker - Airplane!

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Re: Helicopter Questions
« Reply #32 on: March 24, 2006, 05:40:55 PM »
"land in a parking lot"   :o

Mike, I can do that too----it's just that that the pieces need to be trucked off afterward.   :P

Offline Mike

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Re: Helicopter Questions
« Reply #33 on: March 24, 2006, 10:27:28 PM »
To Ted: Not to sound arrogant, but I am not sure how good of a pilot that guys was to be honest. (or were you being sarcastic?)
All the things you said happened to him were pilot-induced. Not looking around your aircraft before take-off (preflight!) and clipping a pole (low recon! slow approach!) and not taking care of an AD.... Being a good pilot also includes other things other than just motorskills....

I think if you do it right and work with the right people, a helicopter can be a very safe machine.

To Frank:
The NOTAR system hasn't really added safety in my mind. They are actually getting away from that again because it's sluggish and slow and doesn't have as much power as they thought it would have.
The only cool thing about it that you can't get your T/R hooked in anything (see Ted's post). I don't know what "automatic directional control" is supposed to mean in a helo anyways but it doesn't sound like a safety thing either...

 The latest craze in that area is the "Fenestron" from Eurocopter (an enclosed tailrotor).
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Offline Ted_Stryker

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Re: Helicopter Questions
« Reply #34 on: March 24, 2006, 11:05:57 PM »
To Ted: Not to sound arrogant, but I am not sure how good of a pilot that guys was to be honest. (or were you being sarcastic?)
All the things you said happened to him were pilot-induced. Not looking around your aircraft before take-off (preflight!) and clipping a pole (low recon! slow approach!) and not taking care of an AD.... Being a good pilot also includes other things other than just motorskills....

I think if you do it right and work with the right people, a helicopter can be a very safe machine.

To Frank:
The NOTAR system hasn't really added safety in my mind. They are actually getting away from that again because it's sluggish and slow and doesn't have as much power as they thought it would have.
The only cool thing about it that you can't get your T/R hooked in anything (see Ted's post). I don't know what "automatic directional control" is supposed to mean in a helo anyways but it doesn't sound like a safety thing either...

 The latest craze in that area is the "Fenestron" from Eurocopter (an enclosed tailrotor).

Mike,
I agree with you!  The guy was a well liked news chopper guy, and he was a terrific military pilot from his Vietnam days, but I suspect he was rather ... hmm... arrogant... in terms of safety anyway.  I would never dream of flying any aircraft without a very thorough preflight (just ask my FBO where I shedule a plane 30 minutes in advance of my planned takeoff time :) ), and it sounds like this guy either had lapses of judgement or care in his preflight at times, or let his "It's not going to happen to me" arrogance get him in trouble.  Possibly a combination of both.  I say he was a good pilot in terms of his ability to handle emergencies, and still live to tell about it... well.. until that last time.  Actually, had he not been in a hover, he could have auto-rotated and probably landed the thing had he had some forward momentum and some more altitutde.  Things never happen when it's convienient though.  So, not to worry... I feel his skills were excellent... but his judgement on preflighting... not the best.  I have no idea why the guy felt the A.D. didn't need immediate compliance.  Maybe it was a money issue with him, who knows.  In any case, he paid the ultimate price for his poor safety attitude.
We're going to have to come in pretty low!  It's just one of those things you have to do... when you land!  -- Ted Striker - Airplane!

Offline Frank N. O.

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Re: Helicopter Questions
« Reply #35 on: March 24, 2006, 11:21:38 PM »
Poor description on my part sorry, I'm a bit tired. I heard it described as a system that meant you only used the torque-pedals (that's the correct name for them right?) when wanting to rotate the helicopter where in a conventional helicopter you had to adjust manually every time you changed the thrust of the main rotors since that would turn the helicopter, which I guess is like an airplane needing trim for different airspeeds.

Btw, where did the term Sling-Wing come from?

Sad to hear about the other pilot :(

Frank
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Offline Gulfstream Driver

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Re: Helicopter Questions
« Reply #36 on: March 24, 2006, 11:41:34 PM »
Mike,
I agree with you!  The guy was a well liked news chopper guy, and he was a terrific military pilot from his Vietnam days, but I suspect he was rather ... hmm... arrogant... in terms of safety anyway.  I would never dream of flying any aircraft without a very thorough preflight (just ask my FBO where I shedule a plane 30 minutes in advance of my planned takeoff time :) ), and it sounds like this guy either had lapses of judgement or care in his preflight at times, or let his "It's not going to happen to me" arrogance get him in trouble.  Possibly a combination of both.  I say he was a good pilot in terms of his ability to handle emergencies, and still live to tell about it... well.. until that last time.  Actually, had he not been in a hover, he could have auto-rotated and probably landed the thing had he had some forward momentum and some more altitutde.  Things never happen when it's convienient though.  So, not to worry... I feel his skills were excellent... but his judgement on preflighting... not the best.  I have no idea why the guy felt the A.D. didn't need immediate compliance.  Maybe it was a money issue with him, who knows.  In any case, he paid the ultimate price for his poor safety attitude.

And everyone in unison:

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Offline Mike

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Re: Helicopter Questions
« Reply #37 on: March 25, 2006, 12:51:23 AM »
Hmmm...
I hope some of our student pilots in this forum read this thread. Very nice reply Ted.

To Frank:
Btw, where did the term Sling-Wing come from?

"Sling Wing" is a U.S. slang term for rotorcraft. The "stuck wing" guys give us Chopper Jockeys a hard time about our wings getting slung around our airframe (and in the old days slung OFF the airframe)
I guess it came from somebody watching some of the videos you guys have been posting here  ;) ;D
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Offline Roland

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Re: Helicopter Questions
« Reply #38 on: March 27, 2006, 11:44:52 AM »
The reason for tying down a helo to the ground like the Chinook which gets destroyed in that video are power checks. To check the performance of a twin-engined powerful helo like the Chinook without wanting to fly one ether packs the helo full of weight or ties it down to the ground. Or one checks engine performance in-flight.

Ground resonances occur in situations when vibrations created in/by the rotor are not properly dampened against the ground. Dampening can be done within the rotor head/system, the landing gear (shock struts) or the skid gear (shock struts, spring plates). A soft ground like grass will also help to dampen vibrations. If one or more of the dampers fail, the fuselage has to deal with vibrations and, as you can see, mostly it is not build for that. On that video one can see the vibrations on the rear tower right from the beginning on. To me I would not let the engine run at full speed with this kind of vibrations. (But o.k. there is no heroism in being smart afterwards. Sorry.)

Avoiding ground resonance before rotor turning: Check all dampening devices. Especially after overhaul work.
« Last Edit: March 27, 2006, 11:53:30 AM by Roland »
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Offline STL206

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Re: Helicopter Questions
« Reply #39 on: March 30, 2006, 09:45:34 PM »
Correction from up above:

Alan Barklage died in a Revolution Mini 500 kit helicopter, not a R22.

http://www.mini500.com/oldmini/channel4.html
« Last Edit: March 30, 2006, 09:49:04 PM by STL206 »

Offline Frank N. O.

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Re: Helicopter Questions
« Reply #40 on: March 30, 2006, 10:10:54 PM »
Just to make sure I understood the problem correctly, the ground resonans is shock-waves from the rotors being bounced back towards the rotors right? Like the Thrust SSC had concerns with the sonic-book going back up from the ground and flipping the car.

That inclosed tail-rotor is not a new thing is it? The Gazelle has that, at least an inclosed rotor, I'm not if the name above also includes special designs for the rotors. The Apache and Commanche, that I believe was scrapped, also had this right?
And speaking of helicopters with native american names, and after reading a webcomic called 21st Century Fox, what about the Cheyenne? It seemed like an interesting concept for a fast helicopter, with a touch of auto-gyro and with NOTAR-systems and twin-rotors proved to be less than optimal for fast helicopters then how about that system?

Frank
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."
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Offline Mike

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Re: Helicopter Questions
« Reply #41 on: March 30, 2006, 10:36:24 PM »
Correction from up above:

Alan Barklage died in a Revolution Mini 500 kit helicopter, not a R22.

http://www.mini500.com/oldmini/channel4.html

Yeah, that thing is a death trap. I would never fly in these, they freak me out.
Looks like no matter how good of a pilot you are, they can still kill you...
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Offline Mike

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Re: Helicopter Questions
« Reply #42 on: March 30, 2006, 10:41:04 PM »
Just to make sure I understood the problem correctly, the ground resonans is shock-waves from the rotors being bounced back towards the rotors right? Like the Thrust SSC had concerns with the sonic-book going back up from the ground and flipping the car.

That inclosed tail-rotor is not a new thing is it?
Frank

It's not much like a sonic boom I would say. It usually starts out with a shock that is transferred from the ground into the rotor knocking two blades out of phase and then gets transferred back to the ground (ie. that one pesky little faulty damper) and right back to the rotor knocking the blades together even further...

The enclosed T/R is not a new concept, but the "Fenestron" is in my mind. It's stronger and quieter thanks to some aerodynamic wonders the Europeans came up with. I understand Bell tried to make one as well but it isn't nearly as powerful and quiet as the Fenestron.
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Offline Ted_Stryker

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Re: Helicopter Questions
« Reply #43 on: March 30, 2006, 11:10:59 PM »
Correction from up above:

Alan Barklage died in a Revolution Mini 500 kit helicopter, not a R22.

http://www.mini500.com/oldmini/channel4.html

Thanks for posting that!  I had heard differently via a third-party.  Glad to see the full detail on the incident and setting the record straight.
We're going to have to come in pretty low!  It's just one of those things you have to do... when you land!  -- Ted Striker - Airplane!

Offline Roland

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Re: Helicopter Questions
« Reply #44 on: March 31, 2006, 09:15:32 AM »
To the fenestron:
This is a shrouded tail rotor with the benefit, that it has nor advancing and retreating blade in forward flight (the main aerodynamic problem of a turning rotor in forward flight). So the layout of the tail rotor can be easier. Disadvantage is that it takes more power from the engine(s) and is heavier on the end of the tail-boom. One needs a shroud around the rotor at last.

I loved the fenestron on the Dauphin. Easy to maintain, no problems, hard to damage and a lot, lot, lot saver than the normal tail rotor layout.

Mike is right, first helicopter fitted was the Gazelle. So it is a patent of Aerospatiale, i.e. Eurocopter. Sikorsky had used this concept as a trial for the Comanche project on a modified S76. Why could they? Aerospatiale and Sikorsky work together from time to time and shear patents. Bell tried a sort of ducted tail rotor but it was more likely a ring around a conventional tail rotor. They stopped it.

To the ground resonance:
Frank, you are a technical man. So, let’s say the sinus wave of a vibration is even. It is constantly the same. The vibration will stay as it is. To dampen this sinus it has to be reduced. So the sinus wave declines. That is done by a good dampener. But if the sinus wave increases, the dampener is no good and vibration becomes more and more. Until the source of the vibration is destroyed.

Any rotation mass creates vibrations, relevant to the displacement of the centre of gravity to the centre of rotation and the revolutions. Think of your tyres on the car. To get rid of this vibrations you to put the centre of the mass exactly to the centre of rotation. If this is not enough or impossible, you try to dampen it. Here we are.  Ground resonances on helicopters occur slowly but increasingly. You have to be vigilant to catch it before it comes out of control. How? By controlling the revolutions, i.e. the main rotor speed. Can a pilot do this? Yes, of course. That is one of the reasons why a FADEC ( full authorised digital engine control) controlled engine always has to be observed during start up.
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