High altitude Helicopter work

"David Lesher" wrote in message
...
"Simon Robbins" writes:


Rather than lack of oxygen, I imagine it would be that the lower air
pressure simply means the rotor is unable to achieve lift without an
unacceptable increase in rotor speed, which would likely overstress the
engines and gearbox.

I've wondered what keeps you from building a high-altitude version.

I envison big fat blades and an engine design for thin air. Or is there
some other issue I'm not seeing?

Lack of demand most likely.
Not a lot of places to land on mountains that tall.

On Tue, 18 Nov 2003 00:10:26 +0000 (UTC), David Lesher
wrote:

"Simon Robbins" writes:


Rather than lack of oxygen, I imagine it would be that the lower air
pressure simply means the rotor is unable to achieve lift without an
unacceptable increase in rotor speed, which would likely overstress the
engines and gearbox.

I've wondered what keeps you from building a high-altitude version.

I envison big fat blades and an engine design for thin air. Or is there
some other issue I'm not seeing?

Density altitude is a crucial factor in high-altitude helicopter
operations.

In a helicopter, the higher you go the more power is needed. But due
to density altitude, the rotor system and engine(s) are less efficient
at higher elevations, and the engines develop less power. A
helicopter may be able to fly at high altitude but may not be able to
hover, and even in level flight might need to use full throttle, and
if it lands it may not be able to take off.

Also, most helicopters don't routinely carry oxygen systems.

The current altitude record for a small helicopter is:

FAI Class E1b - Altitude Without Payload - takeoff weight 500-1000 Kg
International: 40,820 ft; 12,442 m.
Jean Boulet (France)
Alouette SA 315-001 Lama
Artouste IIIB 735 KW engine
Istres, France June 21, 1972

John Hairell )

The current altitude record for a small helicopter is:

FAI Class E1b - Altitude Without Payload - takeoff weight 500-1000 Kg
International: 40,820 ft; 12,442 m.
Jean Boulet (France)
Alouette SA 315-001 Lama
Artouste IIIB 735 KW engine
Istres, France June 21, 1972

John Hairell )

Well then, poor "Pedro", a stock H-43 didn't do too badly in 1959 at
somewhere near 10,000 m., wooden blades a'flappin'!

Old Chief Lynn

John Hairell wrote in message . ..

snip

Coming into the thread a bit late.

The current altitude record for a small helicopter is:

FAI Class E1b - Altitude Without Payload - takeoff weight 500-1000 Kg
International: 40,820 ft; 12,442 m.
Jean Boulet (France)
Alouette SA 315-001 Lama
Artouste IIIB 735 KW engine
Istres, France June 21, 1972

It should be pointed out that Boulet achieved the helicopter (not just
the class) absolute altitude record above by climbing the Lama until
it ran out of fuel, and then making the world's longest autorotation
descent. Not exactly representative of practical operational
capability. But the Lama may still be the best high altitude light
utility chopper, even all these years later -- it's still in
commercial service in parts of the world that need its hot/high
capability, although its operating costs rule it out for more routine
work.

In addition to the above altitude record, it also holds the (far more
useful) record for highest landing and takeoff. In 1969, an SA-315B
making demonstration flights for the Indian military, carrying a crew
of two and 308 lb. (120 kg)of fuel, landed and took off again at
24,600 ft. (7,500m) in the Indian Himalaya, so lifting a pilot and
single patient from the lower end of the Western Cwm of Everest (ca.
21,000 ft) should be (relatively) easy (depending on the density
altitude and the winds) for a stripped-down Lama, especially as you
can cache fuel at Everest Base Camp (18,000 feet) a mile or two away
for the trip back down the valley to the hospital.

Unlike the Indian army (for whom it was originally developed; they
call it the Cheetah), the Nepalese military doesn't have any Lamas.
Getting a Squirrel (Ecureil) up that high is quite a feat, and Col.
Madan has rightly been recognized for the rescue. While lift is a
problem at such heights, engine limitations (temps, torque) and
control issues (loss of tail rotor effectiveness, etc.) are often of
equal or greater importance.

Even assuming that adequate control in high, gusty mountain winds and
sufficient power/lift was available to allow routine operations at
such heights, the market for helos that meet these specialized
requirements would be extremely small. Unless your army has got a
good chance of needing to fight in the Himalayas, Andes or the few
other ranges of similar height, such performance isn't routinely
necessary, and you generally sacrifice much else (speed,
maneuverability, operating costs) to get it.

In Afghanistan the U.S. military had such a requirement for the first
time, but fortunately the CH/MH-47s (and probably Marine CH-53Es) had
the ability to operate at such heights with useful (albeit
considerably reduced) payloads. From what I've read the SpecOps
MH-47s were transiting at up to 18,000 feet or so (pax would need
supplemental O2) to get over the Hindu Kush (one of the Himalayan
sub-chains; the highest point in Afghanistan is over 24,000 feet, but
they didn't need to go that high) from their base in one of the
surrounding 'stans, and then making insertions or extractions at
heights in the 10-13,000 foot MSL range. MH-60s were able to get high
enough along with a reasonable payload, but not while carrying
sufficient fuel to eliminate the need for AARs, given the transit
distances involved. Sikorsky S-70 (H-60) altitude versus weight
graphs for IGE and OGE hover and service ceiling are available at
Sikorsky's website.

The Mi-8/17 family (the Mi-24 uses the same powertrain and rotor
system) has also developed a reputation for good high altitude
performance; the Indian military was apparently carrying supplies and
doing troop movements with them at altitudes up to 15,000 feet MSL
(density altitudes probably a couple of thousand feet higher) during
the Kargil fighting in 1999.

BTW, AFAIK the highest piston-engined helo rescue was by a civil
Hiller UH-12E on Mt. McKinley back in the early '60s (IIRR). Two
climbers were brought down (singly) from 18,000 ft. +, and IIRC the
UH-12 in question had a normally aspirated engine rather than a
turbocharged one (the latter may not have even been in production yet,
but I forget).

Guy