(EST PUB DATE) THE "QUIET" HELICOPTER

• Document Type: FOIA
• Keywords: ARMED FORCES
• Keywords: HELICOPTER
• Keywords: ENGINEERING BRANCH
• Collection: FOIA Collection
• Document Number (FOIA) /ESDN (CREST): 0001230446
• Release Decision: RIPPUB
• Original Classification: U
• Document Page Count: 7
• Document Creation Date: June 24, 2015
• Document Release Date: January 4, 2011
• Case Number: F-2005-00724
• Publication Date: January 1, 2000

APPROVED FOR
RELEASEL DATE:
(bi11
28-Dec-2010
(b131
A Technicgl Triumph
The "Quiet" Helicopter (S)
66
The program's goal was
to develop a vehicle that
could clandestinely
insert equipment or
personnel into
denied areas.
99
erved in CIA's
former Technical Services Division.
Editor's Note: In 1970, CIA's Techni-
cal Services Division (TSD) of the
then Directorate of Plans under-
took a program to construct a
"quiet" helicopter which would be
able to undertake dead-dark opera-
tions at low altitudes. The program's
goal was to develop a vehicle that
could clandestinely insert equip-
ment or personnel into denied
areas. (U//FOUO)
The details about the operation that
the helicopter would support and
the results of that operation cannot
yet be revealed. But the speed with
which the Agency met the project's
technical demands is an outstand-
ing example of managerial
excellence. The ability to enlist the
backing and participation of a
number of technical personnel in
the government, the military, and
private industry, and to mold them
into an effective team was at the
heart of this successful project, one
whose long-term benefits have been
substantial. And it was achieved at
a remarkably low cost. (U//FOLIO)
During the course of theprogram, a
minimum of documentation was
assembled. This article is aimed in
part at providing some background
on the program. (U//FOUO)
I returned to TSD in January 1970,
after attending the Armed Forces
Staff College, and was assigned to
head up the Engineering Branch.
After
examining many other options, it
became apparent that it would
take something like a helicopter to
accomplish this mission. It was
generally believed that any heli-
copter would have both an
acoustic and radar signature that
would be unacceptable and that
range considerations would also
be unacceptable. Despite these
negatives, we decided to at least
look at all the options for this
approach. (C)
After examining several potential
helicopters for this mission, the
range and capability of the Hughes
OH-6 suggested that it could be
successfully modified. In 1964, this
chopper had established a world
record for unrefueled range by fly-
ing directly from Culver City,
California, to Daytona Beach, Flor-
ida. The Advanced Research
Projects Agency (ARPA) had done a
low-effort study of three helicop-
ters to see if their "noise" signature
could be reduced. Again, the OH-6
had shown the most promise in this
area. ARPA was then headed by Dr.
4y boss, Dr. Sidney
Gottlieb, C/TSD, backed us on pure
guts, and he tracked our progress
closely. This survey took less than a
month. (C)
T 73
 Helicopter
Assembling the Team
Within TSD, this effort was almost
entirely put together by members of
the Engineering Branch, with dep-
chie
uty
an roviding t e most
direct participation from
the operations side o ecame
the principal test pilot and hands-on
operator. At that time, he was in a
reserve Navy helicopter unit, and he
had more than 1,000 hours in heli-
copter operations. He was key to a
lot of our accomplishments. (C)
On the industry side, A. L. "Al"
Browning of the Hughes Aircraft
Corporation in Fullerton, Califor-
nia, was the principal leader and
coordinator of this effort. At
Hughes, Carl Schalbe was, in fact,
the actual program manager, and
he spent countless hours coordinat-
ing every aspect of the project. The
Hughes "Aircraft" group does not
build planes of any kind, but it is a
world leader in electronics and air
defense systems. The Hughes Tool
Company in Culver City was the
actual builder of the OH-6. Rod
Taylor, a brilliant helicopter engi-
neer, led a team of about 30
engineers and craftsmen that began
constructing these helicopters. (C)
It was truly a "Skunk Works" type
of operation that was located in an
outbuilding at the Tool Company's
Culver City factory. This building
housed the original H-1 racer with
which Howard Hughes had set sev-
eral world records in the 1930s. In
addition, it housed all the engines
from the "Spruce Goose" were
stored there, and every two weeks
hot oil was run through the engines
to keep them operable. (C)
There were several other key play-
ers in the Agency who supported
this program, especially Charles
Briggs, who was then the Comp-
troller. He guided this program
through the bureaucracy with great
skill and kept the naysayers off our
backs. (C)
Our TSD contracting office
_vorked miracles with
ntractual;and payment
aspects with the various industrial
participants (not the least of which
was getting the Hughes people to
accept the fact that the Agency con-
tracting officer would)
There were egiti-
mate questions about this all the
way up to DCI Richard Helms on
how we were going to make it all
work, but the DCI approved it,
based on our research and the
urgency of the requirement. There
was a lot of faith involved with
these key decisions. (C)
Through Dr: Lukasik, we made pre-
sentations to the principal Army
staff about our program, including
the vice chief of staff, General
Palmer, and the chief of Army Avia-
tion, Lieutenant General Williams.
The vice chief supported the entire
concept, but he pointed out that if
the Army became directly involved,
the whole program would be
slowed down by the military
bureaucracy. General Williams
agreed to "loan" US Army pilots
and OH-6s to support the pro-
gram. In return, they would get
considerable data on learning to fly
helicopters off of 2D (TV) displays.
That was one of the major
unknowns when we went into this
effort. (C)
Solving Technical Problems
From the first day, there were sev-
eral seemingly unsolvable problems
involving the "bird." For example,
to reduce main rotor noise, the
RPMs would have to be reduced.
To regain the loss of lift that this
would produce, we decided to cre-
ate a five-blade rotor to replace the
normal four-blade unit. (Both modi-
fications turned up later in the
civilian version of the helicopter
known as the 500D model.) (C)
The second major "noise" attack
had to do with the main gear box,
which was a product of Western
Gear, Inc. They modified some gear
boxes for us that included "sili-
cone" inserts in the main ring gear
as a way of reducing the gear con-
tact noise and improving the ability
of the box to handle higher horse-
power. The tail rotor and the tail
rotor gear box were similarly modi-
fied. (C)
The engine (the Allison C-18) had
its own story. It had a horsepower
rating of 317, but it was derated in
the case of the OH-6 to 250hp. It
was a product of the Allison Divi-
sion of General Motors in
Indianapolis. We visited them for
the specific purpose of finding
ways to "push" this engine and to
locate the ones with the lowest
specific fuel consumption per hour.
Talk about bureaucracy! The GM
people were afraid that we would
change even one "hair" on this
without years of testing, and they
 Helicopter
cited "liability" after "liability" rea-
sons. Finally, they made Paul
Baynes available to us. He was one
of their roaming troubleshooters,
and he took on our problems with
a vengeance. (C)
In less than a week, Paul had indi-
cated that horsepower possibilities
in the order of 400hp from "stock"
engines were possible and would
give us the lowest specific fuel con-
sumption per hour. He suggested
that we deal with a facility in Bur-
bank that was rebuilding these
engines for both civil and military
use, and that we select individual
engines that had demonstrated the
highest horsepower index when
they were tested. This led to a
quick program in which, as these
rebuilt engines were tested, those
that showed the highest output
were first put aside and then
replaced as even more powerful
ones came along. In the end, we
wound up with about six engines
that had been selected from sev-
eral hundred, and they were truly
blue-ribbon specials. Even the
Hughes people were astounded at
the quality of these particular
engines. (C)
Once the main quieting had been
accomplished with the changes in
the rotor systems and gearboxes,
other interesting "signatures"
started to emerge-things that
would never be noted on a stan-
dard chopper. There was a noisy
relief valve on the engine fuel sys-
tem that Bendix cured for us,
although they are probably still
wondering why a slight noise like
that would pose any problem,
There were also a couple of rotat-
ing inverters that emerged as noisy,
and these were replaced with
solid-state devices that were lighter,
better-and quiet. (C)
The final attack on the noise signa-
ture was the development of an
exhaust muffler. We initially con-
tracted with a famous acoustic
engineering company in Boston
which, after about three weeks,
came up with nothing usable. We
then found an engineer at Lock-
heed who was working on quieting
problems of the Rolls Royce RB-211
engines. We tried to obtain his ser-
vices, but Lockheed said he could
not be spared from their programs.
He wound up doing this in his
garage at night, and, within a week,
had produced a design that was
almost perfect. This was one more
case where a specific individual
with specific skills came through
and saved the day. (C)
The helicopter would require an
auxiliary fuel-tank system which led
us onto severll paths. We finally
had tanks constructed that were
"semipliable" and were filled with
foam. These were tanks that had
been developed for the racing
world, and they had great crash
resistance and a light weight when
empty. A fast-acting "dump" sys-
tem was installed which would
enable the pilot to offload this fuel
immediately in the event of an
emergency. When fully loaded, the
OH-6 was considerably beyond the
weight limit that would allow a safe
"auto rotation," but this dump sys-
tem enabled the pilot to restore the
aircraft to a safe flight profile imme-
diately. (C)
This aircraft had an empty weight
of around 1,100 pounds, and we
were operating with takeoff
weights in the order of 3,000
pounds or more. Hughes consid-
ered a safe maximum to be about
2,400 pounds, a weight that would
make feasible an emergency land-
ing under all circumstances. Our
testing of this system proved it
worked exceptionally well. (C)
The "noise" signature on this vehi-
cle was a direct product of speed.
The quietest mode was about 85
knots, although it still had a low
detectability up to about 120 knots.
In fact, the mission could be tai-
lored so that the minimum noise
level would only be required at cer-
tain locations on the flight profile.
The maximum-range speed (lowest
fuel per mile) was in the order of
110 knots. This "quiet" envelope
became broader as the mission pro-
gressed and the total weight came
down with fuel burnoff.
(U//FOUO)
Professional flight planning became
the watchword. Missions would
have to be carefully planned
around both the quieting aspect
and specific speeds and altitudes in
order to avoid hostile radar detec-
tion. Fortunately, these profiles
were compatible and not mutually
exclusive. (U//FOUO)
The extra horsepower of this unit
required major changes in the con-
struction of the helicopter itself.
The tail-boom system had to be
reinforced and altered, and the new
five-blade rotor produced tail-rotor
interface problems that were even-
tually solved. The true key here,
CGCRGF___~5
 Helicop er
cc
however, was the speed with which
these problems were addressed and
corrected. The first test bird was up
and flying in about 60 days, and it
was fully operational in about six
months. (U//FOUO)
The Navigation Systems
At the same time that the develop-
ment of the chopper was under
way, the entire problem of navigat-
ing this unit at low-levels (100 feet
or less above ground level) in a
dead-dark environment was being
vigorously pursued. We had con-
cluded at the outset that the only
thing that would make cross-coun-
try flight over varied terrain under
dead-dark conditions work was a
high-performance Forward-Look-
ing Infra-Red (FLIR) system. This
was probably one of the major
innovations that emerged from this
program, and it has had a long-
term effect on many of our subse-
quent military aviation systems.
(U//FOUO)
A FUR is a TV system that looks at
temperature differences rather than
visible light-the world as seen
through the eyes of a thermome-
ter. Unfortunately, we had also
concluded that the maximum
weight we could stand for this sys-
tem was about 85 pounds, and the
experimental units then flying were
about 300 pounds. To make mat-
ters worse, they were terrible
performers, with low thermal sensi-
tivity. Using these units was a lot
like looking through a venetian
blind with some of the slats
skewed. We investigated several
units that were under development
at Hughes, Aerojet General, and
The first test bird was up
and flying in about 60
days, and it was fully
operational in about six
months.
99
Raytheon, but they all came up too
heavy, too insensitive, and had
poor thermal resolution. (C)
We approached the systems peo-
ple at Hughes with this problem
and told them we were,willing to
look at anything that might be
around, even if it were still in the
idea stage. There were two young
engineers who had a spectacular
idea that was totally unproven but
which would result in a system
weighing in at less than 15 pounds.
Despite the misgivings of the
Hughes management about taking
such a risk on an unproven idea,
we opted to turn the two loose to
see what they could do. We had no
real choice. Unless we could get
the weight and performance that
this idea envisioned, the program
would fail. (C)
Until this time, all the thermal-imag-
ing equipment consisted of long
linear arrays that were mechani-
cally scanned and had wide
variations in sensitivity line to line.
The idea was to take a single array
of about 15 detectors and electroni-
cally "stack" them into a single
point by the use of delay lines
between each element. It could
then be treated as a "single-point"
detector with the power and sensi-
tivity of 15 units and could scan
mechanically in both the horizon-
tal and vertical planes. Near-
standard TV rates could be
achieved. To increase sensitivity
even more, we elected to use a
detector operating at liquid helium
temperatures rather than liquid
nitrogen; In fact, the best sensor
then available was actually being
made by Raytheon (but not used in
this time-delay mode), and they
made this available to us for this
program. (C)
In less than 60 days, the two engi-
neers had a fully operational FLIR
system on the bench and operat-
ing. It performed so well that it was
truly a ten-year jump in the tech-
nology and instantly rendered just
about every other idea or system of
this type obsolete. From both a dis-
play and sensitivity standpoint, it
was even possible to recognize
facial features just by the tempera-
ture differences in the blood-vessel
patterns inherent in any person.
(Pilots inside the helicopters in
which these FLIRs were eventually
installed could recognize individ-
ual ground-crew members as they
walked in front of the aircraft.)
(U//FOUO)
Although the FLIR was to become
the primary navigation aid, we also
installed an inertial Navigation Sys-
tem (INS) made by Singer-Kearfoot.
At that time, the best unit available
had an error rate of about 1 nauti-
cal mph, but Singer put some
packages together for us that used
"selected" gyros that yielded us an
error rate of less than one-fourth
nautical mph. This was to be an
"option" package, but, after testing,
the pilots all wanted it retained
because it enabled them to take up
an exact heading when they left
each checkpoint. Normally, with
other navigation systems, the pilot
has to fly a course for some time
 Helicopter
cc
and then "split the needle" to com-
pensate for crosswinds. With the
INS system, they could immedi-
ately take up a heading that was on
the money. (C)
The Testing Program
One of the great unknowns was
whether or not pilots could safely
adapt to flying this unit from a TV-
type, that is, two-dimensional dis-
play. Even before the first chopper
was flying, we took one borrowed
OH-6 and installed a standard TV
unit with the cockpit on one side
completely closed off. With this as
a training vehicle, Cal Lacey, the
Hughes test pilot, and the two
Army pilots on loan started an
intensive investigation of this in
normal flying situations. The bot-
tom line was that it turned out to
be possible, but the "adjustment"
time was just about equivalent to
learning to fly for the first time. It
took about 8 hours before a pilot
gained any confidence, and about
another 30 hours to become profi-
cient. By 50 hours total time, they
were doing amazing things flying
with this 2D display. (C)
As a practical matter, while flying
initially on the TV and later on the
FLIR, the pilots experienced no sig-
nificant problems in learning to
hold heading or to follow a pre-
scribed track over the ground
(given the assistance of a radar
altimeter). Similarly, no great prob-
lems were experienced in learning
to hold heading and altitude in a
hover (once a hover had been
established), to go down from a
low hover to a landing, or to take
off and climb out. But learning to
DCI Helms was still
concerned about what we
meant by quiet, and he
did not trust the
evaluations of the
engineers.
99
transition from forward flight to a
stationary hover over a preselected
point was a problem of unex-
pected magnitude. This problem
was experienced by all pilots, and
the reaction of each new pilot on
his first attempt was easily pre-
. dicted and invariably observed.
(U//FOUO)
When a helo transitions from for-
ward flight to a hover, it has to
decrease and eventually cease its
forward movement over the
ground. This is accomplished by
putting the helo into a nose-up atti-
tude. Then, as the hover altitude
and position are reached, and as
ground speed decreases to zero,
the helo is put back into a level
attitude. This. means that just as the
helo reaches a hover, the pilot
pushes the nose down, and this
meant, in our case, that the nose-
mounted FLIR was pushed closer to
the ground. Hence, although the
helo itself was merely changing its
attitude (not its altitude) to the
pilot, who was watching things
through the FLIR, everything in the
FUR picture of his ground refer-
ence suddenly began to get closer
and bigger. It appeared that the
helo had suddenly started forward
and down at an alarming rate of
descent. The immediate pilot reac-
tion was to climb and back up. This
exaggerated backward climb gener-
ated a lot of humor at the expense
of each pilot on his first attempted
landing on the FLIR. (U//FOUO)
Following several weeks of flight
testing, which proved the opera-
tional feasibility of the overall
system and refined pilot and mis-
sion procedures
There was an interesting side devel-
opment in this period. DCI Helms
was still concerned about what we
meant by quiet, and he did not
trust the evaluations of the engi-
neers. As a result, CIA General
Counsel Larry Houston asked us to
arrange a night demonstration flight
for him a We had a
standard OH-6 make a low-level
flyby, and then, about three min-
utes later, we had the quiet bird fly
 Helicopter
over with no lights. Houston, who
was chatting with project officers,
did not even notice it. We then had
it fly over a second time and had
the pilot turn on its running lights
when he was directly overhead.
Houston was impressed and passed
this on to the Director. The ques-
tion of acoustic detectability was no
longer an issue. (C)
From the beginning, there was
great concern about the ability of
hostile air defense systems to detect
this vehicle, and we spent consider-
able time working on this problem.
Hughes Aircraft (Fullerton) was the
primary builder of most air defense
systems, and it had some remark-
able analytic abilities in this area. It
turned out that the main rotor on
this aircraft was made of compos-
ite materials and had a very low
radar "signature." In addition, it was
envisioned that it would be flying
mostly nap-of-the-earth missions,
which would provide considerable
direct protection from air defense
systems. (C)
Hughes had a computer program
called the Radar Coverage and Pen-
etration Analysis System (RACPAS),
which was primarily used for the
purpose of siting radars and air
defense systems worldwide. It was
designed to show optimum place-
ment of systems to ensure the
greatest possible coverage. We
turned this program around and
plotted the hostile radars. From
this, it was possible to work out
flight paths that had a low probabil-
ity of detection. (C)
There was one other characteristic
of the helicopter that further low-
ered its detection probability, and
that had to do with the technical
operation of Moving Target Indica-
tor (MTI) systems inherent in
virtually all radars. These are
designed to enhance detection of
low-flying targets that are theoreti-
cally "buried" in the ground clutter.
These systems are usually built with
"blind" speeds of between 50 to 75
knots and will not detect targets
with "radial" speeds below this. As
a result, even in those areas where
air defense systems would nor-
mally detect the helicopter, it was
possible to slow down below these
critical speeds and go undetected.
Our testing of this entire concept
produced some exceptionally good
results. (C)
Long-Term Benefits
This system had to be considered a
total technical success, and it was
employed operationally. Moreover,
there were several aspects of this
program that have had, and con-
tinue to have, long-range positive
effects:
? The development of this special
FLIR spawned a whole new gen-
eration of devices that
dramatically changed night mili-
tary operations. Much of what
happened in the Gulf War in this
area can be traced back to this
development.
? We proved that helicopter opera-
tions can be worked from 2D
displays and that, with proper
training, this can be done safely.
Later, these systems would be
backed up for precise landing
with night-vision goggles on one
pilot, with the FLIR providing pri-
mary guidance.
? Helicopters can be quieted to a
remarkable degree, and missions
can be configured to ensure a
low detectability by air defense
radar systems. (U//FOUO)
We proved anew that American
companies can be highly coopera-
tive when they are presented with
problems that have national signifi-
cance and when they are not
burdened with excessive red tape.
The number of companies that
freely supplied us with either
expert help or equipment would fill
a page. Both the official and unoffi-
cial help we received from the US
Army was outstanding. At one
point, they supplied us with their
transmission and component engi-
neers from St. Louis to evaluate the
maximum number of hours we
could "push" some of these compo-
nents with a high degree of
reliability. General Williams gave us
everything we asked for, and then
some. (U//FOUO)
Maintenance considerations, partic-
ularly pre-mission checking of
everything, took on a high priority.
Hughes made a two-man team
available for direct support and
these people were so professional
and competent that there were vir-
tually no system failures of any
kind while in flight. Based on the
fact that many components were
being "pushed" beyond normal lim-
its, we set a low useful life on
many components, particularly the
transmissions. Typically, these were
rerated at about 50 hours. Safety
 Helicopter
and mission reliability were para-
mount, and the Hughes team never
let us down. (C)
The last remaining bird was turned
over to the Army Night Vision Labs
at Fort Belvoir, where it continued
for many years to function as a test
platform. I was told later that they
finally contacted Hughes for a
replacement tail-rotor gearbox
when they had passed over 2,500
hours-far more than the 50 hours
we had contemplated. I was also
told several years later that they still
did not have anything in inventory
that could approach the perfor-
mance level that we had achieved.
If nothing else, we gave them a tar-
get to shoot at. (C)
A final word of tribute. One night
about 8 p.m., I stopped in the
Skunk Works at Culver City, where
I found 15 people hard at work. I
commented t that I
was going to get some horrendous
overtime bills from this, and he
informed me that each one of the
people who were there were work-
ing on this voluntarily. It turned out
that they considered 16-hour days
as normal. I wish we could have
given each one of those people a
medal. (C)