Chopper crash

The OTHER Kevin in San Diego wrote:
On Tue, 16 May 2006 21:46:32 GMT, boB
wrote:


Not true. If you have enough power to retard the sink rate you can fly
forward out of the recycled air.

Isn't this what I just said? Recovery is not to pull in more power,
that just increases your rate of sink. You apply cyclic (preferrably
forward, but any direction will work) and altitude permitting, lower
the collective and fly out of it.. Once you're out of the vortex,
pull pitch and climb out.

That sounds the same to me.

--

boB
Wing 70

U.S. Army Aviation (retired)
Central Texas - 5NM West of Gray Army Airfield (KGRK)

"The OTHER Kevin in San Diego" skiddz "AT" adelphia "DOT" net wrote in
message ...
On Mon, 15 May 2006 21:14:51 GMT, "Steve R"
wrote:



Water will dissipate the downwash- kinda like "sorta ground effect".
Same with tall grass.. The water ops I've seen always had the heli
make a vertical pickup to a hover, then a normal takeoff.. I have to
wonder if dumping the collective when the water started coming over
the cockpit might have saved the heli.

I was wondering that myself. I tend to believe, though, that once he had
the nose of the aircraft under water, it wouldn't have made much difference.
If he was holding a lot of aft cyclic (I tend to think I would have been if
I were in that situation, especially after the nose of the aircraft started
going under!), wouldn't dropping collective risk a boom strike? Once he bow
was submerged, I'd think his options were extremely limited.

Lot's of questions to speculate on and not much in the way of answers.

The pilot definitely made screwed the pooch on that one. The real tragedy
is that someone had to die because of it.

I think the pilot was the one who died...

Well, if that's true, I'd call it natural selection. I can't help but
wonder what his flight loading was? What were the circumstances that got
him in trouble in the first place? The video shows the aircraft descending
vertically with a "lot" of visible coning in the rotor blades, suggesting a
low rpm issue. It would be interesting to know more about the specifics.

can't contribute a new technical issue, only that it seems to me like he
tried a power off landing, though a "hard" one.

I think the pilot was the one who died...

the speaker in the video says "all persons were rescued. However one of
them - an engineer from Zystech (?) - died in the hospital because of
his injuries.

Stefan Lörchner wrote:
can't contribute a new technical issue, only that it seems to me like he
tried a power off landing, though a "hard" one.

I think the pilot was the one who died...

the speaker in the video says "all persons were rescued. However one of
them - an engineer from Zystech (?) - died in the hospital because of
his injuries.

I wonder what the deceased person's role in the aircraft was. Is
"engineer" a loose translation into English and the fellow was part of
the flight crew (call it flight engineer, crew chief, navigator,
aircrewman, etc)? Or was he a company representative aboard the flight
for some other reason?

Regardless, what a shame.

The OTHER Kevin in San Diego wrote:


Once in the downwash, you can't apply more power to get out of it.
Doing so only accelerates the downwash and increases the sink rate.
You can't "retard the sink rate" by hauling up on the collective.

Again, the only way out is to apply cyclic to fly out of the
downwash...

Of course you can apply collective and slow the decent rate if you have
enough power. The rotor wash does not increase equal to the amount of
power applied. You don't "increases the sink rate" unless there is no
power left.

--

boB
Wing 70

U.S. Army Aviation (retired)
Central Texas - 5NM West of Gray Army Airfield (KGRK)

Bob
There is not a helicopter made with that much excess power unless it
is a UNLOADED sky crane. You have to fly out of the vortex into clean
air either forward, backwards or sideways. The more collective you
pull the faster you drop. Been there and done that and had the crap
scared out of me when it happened on a steep down wind landing.

A good demo of this is LTE loss of tail rotor effectness when doing
360 degree hover turns about a point with a strong wind. If you get
the turning speed just right it is going to do an uncommanded spin for
part of the turn and there is not a darn thing you can do about it
once it starts except ride it out and let it turn till the wind blows
the vortex away and your tail rotor is not in the tail rotor "side
wash" vortex any more.
John

On Thu, 18 May 2006 01:18:37 GMT, boB
wrote:

The OTHER Kevin in San Diego wrote:


Once in the downwash, you can't apply more power to get out of it.
Doing so only accelerates the downwash and increases the sink rate.
You can't "retard the sink rate" by hauling up on the collective.

Again, the only way out is to apply cyclic to fly out of the
downwash...

Of course you can apply collective and slow the decent rate if you have
enough power. The rotor wash does not increase equal to the amount of
power applied. You don't "increases the sink rate" unless there is no
power left.

"The OTHER Kevin in San Diego" skiddz "AT" adelphia "DOT" net wrote in
message ...
On Thu, 18 May 2006 01:18:37 GMT, boB
wrote:


Of course you can apply collective and slow the decent rate if you have
enough power. The rotor wash does not increase equal to the amount of
power applied. You don't "increases the sink rate" unless there is no
power left.

Every text I've read and every high time (10,000+ hour) heli pilot
I've spoken to disagrees with that statement

My experience on the stick (limited as it is) clearly shows the sink
rate increases as you pull pitch when you're in the downwash.


I agree! I know some full size pilots around here won't take this seriously
because it didn't happen with a 100% scale machine but, I've had this happen
with an RC model. We had mounted a camera system to an RC model (a Bergen
Observer, www.bergenrc.com if you're curious) and was using it to do aerial
inspections. We had a video downlink on the machine so the camera operator
(there were two RC control systems, one to fly the helicopter and one to
operate the camera pan, tilt, zoom, and shutter functions) could see what he
was taking pictures of.

The machine flew Ok but it was carrying about as much weight as could be
expected. It was mid summer so temps and humidity were in the upper 90's
(can we say, "high" density altitudes!) and it was a "dead calm" day.
Absolutely no wind to speak of so no help from ETL in an OGE hover. At one
point, the camera operator needed me to do a vertical descent. I lowered
the collective and it started down. For the record, I was trying to be
gentle with this. When he said, that's good, I raised the collective back
up to stop the descent. Needless to say, it didn't work. Next thing I
know, the model was dropping "very" fast. I understood what was happening.
The rotor blades, which are normally relatively quiet, were really mixing it
up. I finally applied full cyclic to move off the column of air I was
descending in and found, to my total horror, that it didn't seem to be
working. At full control input, that model should have come close to doing
a flip, right there. It seems that when the rotor is in full on vortex ring
state, cyclic authority goes way down too. It did eventually react and fell
off to one side. When the rotor blades finally caught clean air, there was a
loud aerodynamic pop and the model shot off in that direction. It was very
close. The model started at about 300 ft and recovered around 75 ft. The
rate of descent was truly amazing and the entire ordeal couldn't have lasted
more than a couple of seconds. We were "very" lucky!

The advantage you full size pilots have is that you're "in" the machine.
I'd imagine that you can feel this coming on, or have other clues to warn
you about it's inception. Flying a model helicopter is a totally visual
exercise. I had no warning that this was going to happen until after it
started and then it took a split second to recognize what was going on. If
it hadn't been for all the reading I'd done on helicopter aerodynamics back
when I was learning to fly the models, I wouldn't have had a clue as to what
was happening and what to do about it. I would have buried the model and
about $10k worth of electronics right along with it.

I know this much. I never want to repeat that experience and I "certainly"
NEVER want to experience it in a full size machine with "my" butt on the
line!

FWIW,
Fly Safe,
Steve R.

Kevin: There is a section in Prouty where he reports on a series of tests
conducted at Cal Poly that claimed to demonstrate no change in hover power
required over water. I've put that in the magazine once and received a
bunch of howls from helo pilots claiming other wise. The Cal Poly guys did
have some instrumentation with numbers to support their argument.??

--
Stuart Fields
Experimental Helo magazine
P. O. Box 1585
Inyokern, CA 93527
(760) 377-4478 ph
(760) 408-9747 publication cell
"The OTHER Kevin in San Diego" skiddz "AT" adelphia "DOT" net wrote in
message ...
On Mon, 15 May 2006 21:14:51 GMT, "Steve R"
wrote:


I know nothing about operating an aircraft off of water like that but I
thought it strange how far he put the nose down in his attempt to lift
off.
I'd imagine that he was trying to achieve ETL but really?? He buried the
nose, all the way over the windshield, "under" the surf. Once that
happened, it's no surprise that he didn't have enough power to pull out,
or
cyclic authority to level the ship.

Water will dissipate the downwash- kinda like "sorta ground effect".
Same with tall grass.. The water ops I've seen always had the heli
make a vertical pickup to a hover, then a normal takeoff.. I have to
wonder if dumping the collective when the water started coming over
the cockpit might have saved the heli.

The pilot definitely made screwed the pooch on that one. The real tragedy
is that someone had to die because of it.

I think the pilot was the one who died...

Kevin: There is a section in Prouty where he reports on a series of tests
conducted at Cal Poly that claimed to demonstrate no change in hover power
required over water. I've put that in the magazine once and received a
bunch of howls from helo pilots claiming other wise. The Cal Poly guys did
have some instrumentation with numbers to support their argument.??

Nice that somebody mentions!

"Mike Baker and Jonathan Scarcello made ground effect measurements over
astroturf and over water. The astroturf results tend to refute the
pilots' observations. The ground effect at half a rotor diameter was
roughly 30% stronger than over the smooth solid surface. Over water,
however, there was _little_ measurable difference"

Prouty in "More helicopter aerodynamics" Chapter 2.

I got kicked in the ass on mentioning that towards some of my CFIs.
And I noticed that I need little more power in hover over tall
grass/bushes. However, that's not astroturf.
I never hovered over water.

I've actually wondered about the over water stuff myself. It's been
drilled into my head that hover IGO over water takes more power, but
other than some surface wave action dissipating the downwash, the
water is, in effect, a solid surface. (Ever jumped off a 40' cliff
into water? It spanks you pretty hard!)

That's just the speed. I remember a nice program on television where
some guy had two pieces of pork fat and a plate. The first piece of fat
was smeared over the plate, the second one loaded into a gun and shot
the plate to pieces.

Actually, when you hover above the water, you deform the water, forming
a shallow pit. If the helicopter would suddenly disappear in a puff of
magic, the water would flow back into it. I think it is this deformation
that dissipates the energy.

Best regards