[Vhfcn-l] Retreating Blade Stall TINS

[Darryl James]

Darryl James

Americal Divarty Air Loach Driver

Chu Lai, Vn 68' - 69'

ORWAC 68-12 Wolters, 68-12 Rucker

Midland, Texas

 

THERE ARE Many Ways To "SCREW THE POOCH" DRIVING CHOPPERS In Vietnam

Retreating blade stall is a hazardous flight condition in
<https://en.wikipedia.org/wiki/Helicopter> helicopters  where the rotor
blade with the smaller resultant relative wind exceeds the critical angle.
Balancing lift across the rotor disc is important to a helicopter's
stability. In forward flight the advancing blade has a higher airspeed than
the retreating blade, creating unequal lift across the rotor disc. Excessive
airspeed and/or turbulence can cause the aircraft to have retreating blade
stall and roll to the left.[1]

Americal Division Artillery Officers Club

1745 Hrs. 11 January 1969

It was Happy Hour at the O Club, which often spawned story telling*one of
the favorite pastimes of the pilots. The pilot's tales or TINS[2] as they
called them were an important part of the culture and entertainment at Div
Arty Air. They young men loved to tell stories, especially flying stories.
Flying alone in a Scout helicopter, the TINS were a way of learning from
each other's experiences. The tales sometimes didn't get out, but secrets
were hard to keep at Div Arty Air. Once someone started a story, others
often poured out making for a lively evening. It was like that tonight.  

Captain Warren Fuller, Div Arty's Section Leader, said, "We heard some good
TINS tonight, maybe one more, Huh guys"?

He slowly pulled out two big fat cigars from his shirt pocket.  He bit off
the end of his stogie and lit up. Almost as an afterthought, Fuller handed
the remaining stogie to Lieutenant James. 

Fuller asked "And how was your day, Honey?"

James kind of flushed, a bit embarrassed. "Ah, how did? Ah, ah, ah," he
mumbled. "Oh well. Guys, I kind of messed up today. Came a little close to
screwing the preverbal pooch. I guess I got real lucky.  

"You're always lucky," said Lieutenant "Pops" Baker. "Come on. Tell us the
damn story."

"Well guys, I had the payroll duty today and." 

 

Early that morning 

James had been assigned to take one of the lowly Lieutenants in Division
Artillery Headquarters, Jack Ford, to visit Americal's southern LZ's. Jack
was given the mundane task of pay officer for Division Artillery. He had to
go around to the Artillery Battalions to pay any of the men requesting
money. This happened every month. 

Being the Pay Officer was a boring job. It was always assigned to a junior
officer. The Division Artillery Command Staff was loaded with Field Grades
and Captains and not many Lieutenants. The few that were there got all the
crappy assignments. 'Shit details' they were called. Ford, an assistant to
the Assistant S4[3] of Division Artillery Staff, acquired many of the 'shit
details.' 

Ford had been in Vietnam nine and a half months and was getting 'short.'
Short-timers were cautious and didn't want to tempt fate. This was the
reason he requested that Div Arty Air Ops have Lieutenants James fly him
today. 

I want James, thought the pay officer.  I heard he's real safe to fly with.
After all he is the Unit's Safety Officer, and James had the reputation for
flying high, away from the small arms fire?  He's got to be the most careful
and maybe safest guy there.  

Ford knew, from experience, that James flew high. One day flying north along
Highway One with him, the pilot kept climbing and climbing. It was freezing
in the open cockpit. The pay officer didn't know that James had put on long
johns under his cotton, gray flight suit. 

James asked over the intercom to his shivering passenger, "Jack would you
mind taking my Mamya Sekor 1000 DTL that's hanging from the first aid kit? I
want you to take a picture of the altimeter." 

"Huh? Oh sure, no problem."  

Pilots always take stupid pictures thought Ford, but who would take a
picture of instruments?  

Ford didn't know James was participating in a goofy Div Arty Air contest of
who could fly the highest this week. James didn't win. He gave it a good
shot and came in third with Ford's picture of his altimeter showing 12,650
feet.  

James and Ford flew south to several fire bases that morning. They left LZ
Professional and turned south along Highway One at an altitude of 1,800
feet.  Jack's next stop was the 'Rock.'  

The Rock was a prominent feature sticking up from the rice patties of the
coastal plain. The narrow, spire of basaltic rock looked something like a
huge pillar. It stuck up prominently near the Quang Nai River along Highway
One. It was a sort of navigation aid to the pilots who labeled it the
'marble VOR.'[4] The lonely spire was the lava passageway of an ancient
volcano. The volcanic cone that once surrounded the neck had long since
weathered away from eons of rain and wind. 

An important Division OP[5] was established on top of the rock. There was no
room for a helicopter to land on top. A sandbag helicopter pad was built at
the base of the structure. A narrow windy road led up to the outpost. 

James, the passenger's hand-picked pilot, the so-called model of aviation
safety, was feeling bored that morning with this rather dull taxi driving
assignment. After departing LZ Professional, James decided to give his
passenger a little thrill and autorotate to the base of the Rock. The OH-23G
had low rotor momentum. When the engine stopped and entered autorotation
flight, the helicopter would drop abruptly. 

James glanced left and looked at the unsuspecting passenger. He smiled and
rolled off throttle, then abruptly lowered the collective and shoved in
right pedal. The chopper dropped like a rock and had the desired effect on
the short-timer passenger.  

Ford screamed. His stomach felt like it fell off a cliff. Instinctively, he
looked for something to grab on to. He put his knuckles around the doorframe
and squeezed them so tightly, they turned white. It took him several seconds
before he regained enough composure to work the intercom switch.

"What happened?" he asked. "Did we lose an engine?"  

James laughed. After Ford realized he was not going to die, he started
laughing and said, "You sorry sack of shit you know how short I am? Don't do
something like that."  

James continued laughing as he turned 180 degrees to point the aircraft into
the wind. Just before touchdown, he rolled on the throttle and checked the
tachometer to insure that he closed the rotor and transmission RPM needles
and didn't over-rev the transmission or engine. With the needles closed, he
pulled in collective to bring the chopper to a hover over the pad. The pilot
landed smoothly and shut down, feeling cocky.  

Ford with a case full of money jumped in a waiting jeep, which took him up
the hill. James got out of the helicopter to stretch his legs. Young boys
came around waving cokes to sell. The pilot declined but let two boys sit in
the helicopter and took the youngsters' picture.  

There is a good size crowd of kids now, thought the pilot.  Where in the
heck do they all come from so fast selling cokes and cigarettes? 

Ford soon returned and climbed in. The feisty pilot decided to give the
young Vietnamese boys gathered around a demonstration of his flying prowess.
As his passenger strapped in, James said, "Jack, I am going to low-level
around the Rock one time to give these young rascals a thrill, so hang on
and try not to brown your panties this time."  

"OK James; no sweat," he said a bit nervously.  

James lifted the Raven to a hover and accelerated smoothly through
transitional lift keeping the nose low and power applied. The aircraft
accelerated rapidly to 80-knots. He low-leveled counter clockwise around the
base of the Rock. The chopper came around the hill and roared over the heads
of the kids. The kids yelled and waved. They loved it. James continued
circling the Rock.  His airspeed indicator indicated he was at VNE[6], the
maximum safe speed for the helicopter, but he never looked at it. As he
continued his turn, a sudden gust of wind blasted the aircraft created
severe turbulence. The nose pitched up abruptly and the helicopter rolled
left almost out of control. The tip path plane of the main rotor came very
close to the ground. They were mere seconds from disaster. 

Flying was often described as 90 percent boredom and 10 percent terror. The
Raven's pilot and passenger were on the 10 percent side of the graph. The
young, cocky pilot had entered into retreating blade stall, a condition that
could be fatal. 

The helicopter's main rotor was cambered like a wing to create lift as it
turned in a counter clockwise direction. When the helicopter was moving
forward, wind came across the rotor blades from front to back. The lift
force on the forward moving rotor blade on the right side of the helicopter
was always greater than the retreating blade on his left side. This
differential lift occurred in forward speed. The helicopter compensated for
this lift unbalance by the rotor system's design. The rotor system
automatically increased the pitch slightly for the retreating blade to
balance left. A problem occurred, however, when the helicopter's airspeed
became too high. The retreating blade on the left side reached a pitch angle
where it could not compensate enough without stalling. When it stalled it
created a sudden differential loss of lift to the left side of the
helicopter. This caused the helicopter to roll left resulting in a sudden
loss of control. Turbulence aggravated the problem.

The pilot's savior to the pending disaster was his recent flight school
training. He reacted correctly and lowered the collective, inserted right
pedal and eased back on the cyclic. Immediately the helicopter leveled and
slowed.  As it slowed it came back under the control of the pilot whose
vascular system was now flushed with adrenaline. The Raven climbed away from
the rock. 

Well cowboy, thought James, you nearly screwed the pooch. Retreating blade
stall is one of those things you were never supposed to let happen. You were
lucky this time.  You may not be, if there is a next time.

A speechless, thoroughly shook up passenger was thinking to himself, And
James is their fly-by-the-book, safe as shit pilot? I am too short for this
shit. Just 44 days and a wake up and I am out of here.

"Great story" said Fuller, "A little birdie from the S4 Shop told me a
little something about this incident." 

He held up his drink and said, "To survive here, a pilot must be lucky
enough to learn from his mistakes; he'll make some."

"Here, here," echoed the pilots.  

"Girls," said Fuller, "I for one have had enough of these lies. Let's play
another round of liars dice to see who pays for dinner." 

Every night they played liars dice to see who paid for each round of drinks
and for the ten-cent service charge every officer gave to the Club for the
dinner meal. 

They rolled. Fuller had to pay. Great thought James. It's about time.

 

 

 


  _____  

[1] https://en.wikipedia.org/wiki/Retreating_blade_stall

[2] An acronym for war stories that are more or less supposed to be true.
"This is no shit."

[3] Supply Staff Officer

[4] VOR. High frequency radio signals used for navigation.

[5] Observation post; usually positioned at a high elevation to spot enemy
positions.

[6] Velocity never exceed.  The maximum safe speed of the helicopter.