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a VERY close call....who'd be deck crew?



 
 
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  #11  
Old February 24th 07, 09:32 AM posted to rec.aviation.rotorcraft
JohnO
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Posts: 120
Default a VERY close call/ armchair pilots

On Feb 24, 12:31 pm, "B4RT" wrote:
"Nick" wrote in message

...

Thought you guys might be interested


http://www.videosift.com/video/Helic...s-A-Close-Call


But why wouldn't he have kept some negative collective to keep it nailed
to the deck?.... how far would the tips 'dished' down?.....not enough to
cause the crew more worries than they already had??


It seemed very light on the skids on the previous couple of swells??


Negative collective? .....ROTFLMFAO! Boy I dont think I have that option on
mine.


Heh! The only heli's I've seen that can do negative are the R/C ones -
they can fly upside down!


My armchair analysis is that the helicopter appeared to have a forward CG
and the deck was pitching as much as 15 degrees and rolling about 7 or 8. I
don't think the pilot really ever "wanted" to take off. It looked to me like
the deck pitched forward a whole lot and he thought the helicopter would
nose over if he didn't take off. The deck angle was pitched very far
forward at the moment of the tail strike, and the camera gives the illusion
that the helicopter was at far less level pitch that it was.

I'm thinking that the pilot was taking the lesser of two evils and got bit
by one of them. Its clear to me that he was pretty skilled because doing a
totally successful hovering auto to that platform like that couldn't be done
by an unskilled pilot. The only bad piloting in this incident appears to
have happened way before the engine started when someone decided that it was
ok to take off in seas like that.

Bart



  #12  
Old February 24th 07, 09:35 AM posted to rec.aviation.rotorcraft
JohnO
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Posts: 120
Default a VERY close call/ armchair pilots

On Feb 24, 12:31 pm, "B4RT" wrote:
"Nick" wrote in message

...

Thought you guys might be interested


http://www.videosift.com/video/Helic...s-A-Close-Call


But why wouldn't he have kept some negative collective to keep it nailed
to the deck?.... how far would the tips 'dished' down?.....not enough to
cause the crew more worries than they already had??


It seemed very light on the skids on the previous couple of swells??


Negative collective? .....ROTFLMFAO! Boy I dont think I have that option on
mine.

My armchair analysis is that the helicopter appeared to have a forward CG


Why would that be?

and the deck was pitching as much as 15 degrees and rolling about 7 or 8. I
don't think the pilot really ever "wanted" to take off. It looked to me like
the deck pitched forward a whole lot and he thought the helicopter would
nose over if he didn't take off. The deck angle was pitched very far


I don't think the problem was the angle of the deck - more that it's
acceleration down cancelled some gravity - a little POSITIVE
collective could have been enough to lift off. Seems like he had a lot
of forward cyclic as well though.
forward at the moment of the tail strike, and the camera gives the illusion
that the helicopter was at far less level pitch that it was.

I'm thinking that the pilot was taking the lesser of two evils and got bit
by one of them. Its clear to me that he was pretty skilled because doing a
totally successful hovering auto to that platform like that couldn't be done
by an unskilled pilot. The only bad piloting in this incident appears to
have happened way before the engine started when someone decided that it was
ok to take off in seas like that.

Bart



  #13  
Old February 24th 07, 02:13 PM posted to rec.aviation.rotorcraft
B4RT
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Posts: 28
Default a VERY close call/ armchair pilots


"JohnO" wrote in message
s.com...

My armchair analysis is that the helicopter appeared to have a forward CG


Why would that be?

I dont know, maybe there were two fattys on board with the pilot. I've flown
an Enstrom and don't recall it being nose heavy, but each time the ship
pitched forward I thought I noticed it get light on the aft section of the
skids.

and the deck was pitching as much as 15 degrees and rolling about 7 or 8.
I
don't think the pilot really ever "wanted" to take off. It looked to me
like
the deck pitched forward a whole lot and he thought the helicopter would
nose over if he didn't take off. The deck angle was pitched very far


I don't think the problem was the angle of the deck - more that it's
acceleration down cancelled some gravity - a little POSITIVE
collective could have been enough to lift off. Seems like he had a lot
of forward cyclic as well though.


Nah... I don't think so. Boats dont go up and down in seas like that with
negative G's that significant. Enstrom pilots don't tend to spend a lot of
time getting light on the skids either because of the damn oleo struts and
ground resonance tendancy of that machine. That guy flying was no amateur,
he was locked and loaded when he chopped the throttle and did that auto.

There's several HUGE differences in the flight dynamics of RC heli's and
real ones. RC's tend to have very low CG's, this makes them more stable.
RC's have an assload more collective juice than the big things, you don't
come off the helipad in a real one without really intending to do it. The
static and dynamic relative rotor mass of a an RC is very small, you can
move the cyclic much more quickly in an RC and have it take effect without
lag. The big spinny gyrosope thingy on top doesnt wan't to change that
quickly on a big helicopter. These differences can make it hard to
extrapolate the operation of a big one from experiences with a small one.
Just imagine trying to drive a semi truck in the same manner you'd drive a
Porche.

Bart


  #14  
Old February 24th 07, 04:15 PM posted to rec.aviation.rotorcraft
Nick
external usenet poster
 
Posts: 9
Default a VERY close call/ armchair pilots

Negative collective? .....ROTFLMFAO! Boy I dont think I have that option
on mine.


What is the pitch range on this helicopter?......anyone?......I 'fly' RC,
but it'd be interesting to know that negative pitch as not possible.....does
that go for all full size helis?

So the fact that the machine appeared light on its skids could not have been
corrected?....or minimised?


"B4RT" wrote in message
...

"Nick" wrote in message
...
Thought you guys might be interested

http://www.videosift.com/video/Helic...s-A-Close-Call

But why wouldn't he have kept some negative collective to keep it nailed
to the deck?.... how far would the tips 'dished' down?.....not enough to
cause the crew more worries than they already had??

It seemed very light on the skids on the previous couple of swells??


Negative collective? .....ROTFLMFAO! Boy I dont think I have that option
on mine.

My armchair analysis is that the helicopter appeared to have a forward CG
and the deck was pitching as much as 15 degrees and rolling about 7 or 8.
I don't think the pilot really ever "wanted" to take off. It looked to me
like the deck pitched forward a whole lot and he thought the helicopter
would nose over if he didn't take off. The deck angle was pitched very
far forward at the moment of the tail strike, and the camera gives the
illusion that the helicopter was at far less level pitch that it was.

I'm thinking that the pilot was taking the lesser of two evils and got bit
by one of them. Its clear to me that he was pretty skilled because doing a
totally successful hovering auto to that platform like that couldn't be
done by an unskilled pilot. The only bad piloting in this incident appears
to have happened way before the engine started when someone decided that
it was ok to take off in seas like that.

Bart



  #15  
Old February 24th 07, 08:54 PM posted to rec.aviation.rotorcraft
JohnO
external usenet poster
 
Posts: 120
Default a VERY close call/ armchair pilots

On Feb 25, 2:13 am, "B4RT" wrote:
"JohnO" wrote in message

s.com...

My armchair analysis is that the helicopter appeared to have a forward CG


Why would that be?


I dont know, maybe there were two fattys on board with the pilot. I've flown
an Enstrom and don't recall it being nose heavy, but each time the ship
pitched forward I thought I noticed it get light on the aft section of the
skids.

and the deck was pitching as much as 15 degrees and rolling about 7 or 8.
I
don't think the pilot really ever "wanted" to take off. It looked to me
like
the deck pitched forward a whole lot and he thought the helicopter would
nose over if he didn't take off. The deck angle was pitched very far


I don't think the problem was the angle of the deck - more that it's
acceleration down cancelled some gravity - a little POSITIVE
collective could have been enough to lift off. Seems like he had a lot
of forward cyclic as well though.


Nah... I don't think so. Boats dont go up and down in seas like that with
negative G's that significant.


Definitely not true. Ever watch thet tv show 'Deadliest Catch' where
they embed a camera guys on crab boats in the Bering Sea? One of the
things they do to pass the time between getting cold and wet is to
jump up just as the boat plunges into a swell. They float like
astronauts for a moment. I've never done that but have certainly been
on the deck of a boat many times and felt very much unweighted as the
boat plunges into a trough. I assume it would be normal practice for a
vessel to steam into the wind when carrying out aircraft operations
and this gives the fastest drops into the swell.

Enstrom pilots don't tend to spend a lot of
time getting light on the skids either because of the damn oleo struts and
ground resonance tendancy of that machine. That guy flying was no amateur,
he was locked and loaded when he chopped the throttle and did that auto.


He sure did that beautifully. But even pros sometimes get sloppy for a
moment on rare occasions. It's not out of the question that he slipped
up, but then his training and experience snapped in to save the day.



There's several HUGE differences in the flight dynamics of RC heli's and
real ones. RC's tend to have very low CG's, this makes them more stable.
RC's have an assload more collective juice than the big things, you don't
come off the helipad in a real one without really intending to do it. The
static and dynamic relative rotor mass of a an RC is very small, you can
move the cyclic much more quickly in an RC and have it take effect without
lag. The big spinny gyrosope thingy on top doesnt wan't to change that
quickly on a big helicopter. These differences can make it hard to
extrapolate the operation of a big one from experiences with a small one.
Just imagine trying to drive a semi truck in the same manner you'd drive a
Porche.

Bart



  #16  
Old February 25th 07, 12:06 AM posted to rec.aviation.rotorcraft
Steve L.[_3_]
external usenet poster
 
Posts: 2
Default a VERY close call/ armchair pilots

Negative collective? .....ROTFLMFAO! Boy I dont think I have that option
on mine.


What is the pitch range on this helicopter?......anyone?......I 'fly' RC,
but it'd be interesting to know that negative pitch as not possible.....does
that go for all full size helis?


I know of only one big helicopter that ever had negative pitch (-3°). It
is a military American one; can't recall the type.
The reason for that is that it should be able to do a very quick
vertical descent while hovering just over tree tops.

For all other helicopters it were pretty useless but would cost a lot
because the control rigging would need far more travel.

There is no civilian helo with negative pitch, not even 0°. The minimum
pitch might be as high as +4°.

  #17  
Old February 25th 07, 10:40 AM posted to rec.aviation.rotorcraft
Nick
external usenet poster
 
Posts: 9
Default a VERY close call/ armchair pilots


"Steve L." wrote in message
news
Negative collective? .....ROTFLMFAO! Boy I dont think I have that
option
on mine.


What is the pitch range on this helicopter?......anyone?......I 'fly' RC,
but it'd be interesting to know that negative pitch as not
possible.....does
that go for all full size helis?


I know of only one big helicopter that ever had negative pitch (-3°). It
is a military American one; can't recall the type.
The reason for that is that it should be able to do a very quick
vertical descent while hovering just over tree tops.

For all other helicopters it were pretty useless but would cost a lot
because the control rigging would need far more travel.

There is no civilian helo with negative pitch, not even 0°. The minimum
pitch might be as high as +4°.

Thanks for the reply. But what happens during autorotation to keep the
headspeed up? ......headspeed will surely decay very quickly at +4degrees?


  #18  
Old February 25th 07, 03:09 PM posted to rec.aviation.rotorcraft
Steve R
external usenet poster
 
Posts: 34
Default a VERY close call/ armchair pilots

"Nick" wrote in message
...

"Steve L." wrote in message
news
Negative collective? .....ROTFLMFAO! Boy I dont think I have that
option
on mine.

What is the pitch range on this helicopter?......anyone?......I 'fly' RC,
but it'd be interesting to know that negative pitch as not
possible.....does
that go for all full size helis?


I know of only one big helicopter that ever had negative pitch (-3°). It
is a military American one; can't recall the type.
The reason for that is that it should be able to do a very quick
vertical descent while hovering just over tree tops.

For all other helicopters it were pretty useless but would cost a lot
because the control rigging would need far more travel.

There is no civilian helo with negative pitch, not even 0°. The minimum
pitch might be as high as +4°.

Thanks for the reply. But what happens during autorotation to keep the
headspeed up? ......headspeed will surely decay very quickly at +4degrees?


I fly RC helicopters too and have "very" limited experience in the full size
counterparts. What most RCer's don't understand is that you don't need
negative pitch to autorotate. What RCer's refer to as "negative" collective
is simply an measurement of blade incidence. It has nothing to do with the
rotor blades aerodynamic angle of attack (AOA). Nick, even if you're
running your model with a -5 at full down setup, the blades are still flying
a positive AOA in the auto at that setting. Granted, it'll be dropping like
a rock in that mode but the blades are still seeing a positive AOA. I've
played around with autos on my RC birds and, with a bit of a breeze, have
made sustained autorotative approaches and a safe landing with the
collective as high as +3 degrees. Granted, I wasn't carrying a lot of rotor
rpm on the descent so the collective "pull" at the bottom was a bit critical
but it's definitely doable.

The full size birds, as Steve L pointed out, rarely if ever go into the
negative incidence range. First, because the simply don't need to and more
importantly, because they are "much" more critical about maintaining a
specific rotor rpm. If they dropped into a negatie incidence range, they'd
overspeed the rotor with obvious results. The big guys simply can't stand
the rpm swings that our models do in their stride.

FWIW!
Fly Safe,
Steve R.


  #19  
Old February 28th 07, 07:15 PM posted to rec.aviation.rotorcraft
B4RT
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Posts: 28
Default a VERY close call/ armchair pilots

I didn't measure it, but from the look of it the blade pitch at the tip of
the main rotor of my jetranger when its at 90 degrees to the right (the
most negative pitch point) and the collective full down is roughly 0
degrees, it might even be a shade negative.

Bart


"The OTHER Kevin in San Diego" skiddz "AT" adelphia "DOT" net wrote in
message ...
On Sat, 24 Feb 2007 15:06:40 -0800, Steve L. wrote:


I know of only one big helicopter that ever had negative pitch (-3°). It
is a military American one; can't recall the type.
The reason for that is that it should be able to do a very quick
vertical descent while hovering just over tree tops.


A&P buddy of mine who was in the Marines told me the CH-53 can do
about -3 degrees collective. Not sure of the reasoning behind it..

For all other helicopters it were pretty useless but would cost a lot
because the control rigging would need far more travel.

There is no civilian helo with negative pitch, not even 0°. The minimum
pitch might be as high as +4°.


The negative twist in the blades might get parts of the blade into
negative pitch in an auto (or even a rapid power descent) but I don't
know if the AoA ever goes negative...



  #20  
Old February 28th 07, 07:59 PM posted to rec.aviation.rotorcraft
Don W
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Posts: 52
Default a VERY close call/ armchair pilots



B4RT wrote:
I didn't measure it, but from the look of it the blade pitch at the tip of
the main rotor of my jetranger when its at 90 degrees to the right (the
most negative pitch point) and the collective full down is roughly 0
degrees, it might even be a shade negative.


Was that with the cyclic neutral? If so, it would
be interesting to have someone in the ship apply
full down collective and full back cyclic while
you looked at it.

Don W.

 




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