The dramatic disclosure last month that the United States
has manned airplanes that are secretly cruising at speeds above Mach 3 was good
news to the aviation community.
President Johnson, in revealing the Lockheed A-11 program,
showed understandable pride in this important US "first." He said
that "several" A-us were being flown "at more than 2,000 mph and
at altitudes in excess of 70,000 feet," and are "capable of
long-range performance of thousands of miles." The President added that
the A-11 "has been made possible by major advances in aircraft technology
of great significance for both military and commercial application."
He mentioned only one specific application. He said that the
A-11 was being tested extensively to determine its suitability as a
"long-range interceptor." Former White House Press Secretary Pierre
Salinger and Defense Secretary Robert S. McNamara stressed the interceptor role
in their brief expansions of the President's remarks. However, Mr. McNamara, in
response to insistent questioning by reporters, has indicated that the A-11 was
not designed originally as an interceptor but that he has considerable confidence
that it can be adapted to that role.
Beyond these minimum remarks, the secrecy lid has been
clamped on. The Administration opened the door on the most tantalizing aviation
news since the X-1 proved there wasn't a sonic barrier. But the door was slammed
From the technical viewpoint, the A-11 clearly is the most
important aircraft since the X-l. It is by far the most efficient airplane yet
to fly at supersonic speeds. It is the first to have adequately high
aerodynamic efficiency (low drag) and high powerplant efficiency to allow it to
carry enough fuel to sustain flight above Mach 1 for more than thirty minutes
or so. In the President's words, the A-11 also is extremely important because
it led to "the mastery of the metallurgy and fabrication of titanium metal
which is required for the high temperatures experienced by aircraft traveling
at more than three times the speed of sound."
As reported by Claude Witze on page 16 of this issue, a
tight information clamp has forestalled meaningful public discussion of the A-11,
its genesis, or its proper role in civil and military aviation.
The following questions are typical of those which should be
asked, for the answers concern the use of a very large sum of the taxpayers'
money. Congress and the public have a legitimate right to frank answers.
• How much did the A-11 and its engines cost? Judging from
previous pioneering programs that fought their technical battles out beyond the
"state of the art," the A-11, with its Mach-3-plus performance, titanium
construction, and high-temperature engines cost at least $500 million and
possibly $1 billion. That is $100 to $200 million per year for the five years
the program has been active. (President Johnson said the A-11 design work
started in 1959. The J58 program was initiated several years earlier by the
Navy.) This kind of money is in the cost range of the much-criticized and
now-defunct nuclear airplane, and programs of this magnitude should get a
thorough working over by the Congress.
• The "obvious" conclusion to be drawn from the
information available is that the A-11 was originally developed for the CIA as
a high-altitude reconnaissance airplane to replace the U-2. Most reporters
reached this conclusion, supported largely by the close secrecy on the
airplane, Mr. McNamara's refusal to divulge the original design objective, and
the fact that the project was not handled in normal management channels. If
this conclusion is correct, several questions arise immediately concerning the
past and future expenditure of large sums of money:
(1) Does the fact that a given airplane can cruise at Mach 3
also mean that it automatically has a multipurpose capability —
reconnaissance, interceptor, bomber — without a major design change for each
type of mission?
(2) If the answer is no, was there coordination between the
CIA and the DOD at an early stage to make certain that the A-11 was not
hopelessly boxed into one role?
(3) Can the A-11 development expedite the supersonic-transport
(4) Have reconnaissance satellites eliminated the need for
reconnaissance aircraft such as the A-11, and will it therefore end up only as
a high-cost experimental aircraft with limited capability?
Precise answers will require the most candid discussion of
the current version of the A-11 and its design and development history.
Certainly no one can judge the exact performance or mission capability of a
supersonic-cruise airplane using only the two side-view photographs and brief
statements currently available on the A-11.
Estimates of this type are riskier for supersonic-cruise
airplanes than they are for subsonic aircraft or for those that are capable of
only short dashes at supersonic speed.
Basically, supersonic-cruise airplanes involve extremely
difficult design problems. Their payload-range performance is extremely
sensitive to engine weight, structural weight, fuel consumption, and
aerodynamic efficiency (lift/drag ratio, written L/D). Small mistakes in
predicting these values can lead to large errors in payload and range.
Fortunately, the supply of technical literature concerned
with these problems is large. This literature points to some general
conclusions about the A-11 and places some broad limits on the possible performance
of this new aircraft.
The difficulties described in this literature also provide
the best tribute to Clarence L. (Kelly) Johnson and his "Skonk Works"
colleagues at Lockheed, who, with the J58 engineers at Pratt & Whitney, led
the team that first achieved supersonic cruise.
Here is what can be deduced about the A-11, based on this
• Size. The
airplane is about ninety feet long based on scaling of the A-11 pictures, using
published data on the J58 diameter and estimating the size of the pilot's
helmet visible in the front window. There is room in the slim fuselage and in
the wing stub areas for more than 70,000 pounds of fuel, with space left over
for substantial mission equipment. Since efficient supersonic-cruise airplanes
have to carry at least fifty percent of their weight in fuel, the A-11 takeoff
weight apparently is more than 150,000 pounds. This is roughly the same as that
of the B-58 bomber.
• Wing. Densely
loaded aircraft such as the A-11 need large wing areas; otherwise their wing
loadings will quickly rise above 100 pounds per square foot and severely reduce
both cruise altitude and flight efficiency.
The side-view photographs obscure most of the A-11 wing, and
published drawings of the A-11 have not indicated a large lifting surface.
However, the aircraft must have an effective wing area in the neighborhood of
2,000 square feet. This includes not only the area outboard of the engine
nacelles (see drawing on the front cover) but also the area between the
engines, and the area of the long, very narrow wings on the fuselage, which
have been referred to in some reports as fairings. The long and narrow wings
form the forward section of a large double-delta wing similar to that used by
Lockheed in its supersonic-transport proposal. At supersonic speeds these long,
narrow wings plus the fuselage area between them generate much more lift than
they do at subsonic speeds.
This generation of additional lift up forward is important
in maintaining control over the airplane above Mach 1. The controllability
problem arises because the rear portion of the double delta acts like a
conventional lifting surface at supersonic speeds, and its center of lift moves
abruptly aft, a long distance away from the center of gravity. This can make
the aircraft so stable that it can't be controlled by a normal-size horizontal
tail. In any event, it calls for a large deflection of the tail and an
unacceptably big trim drag, which eats into range. On the A-11, lift on the
long, narrow wings counteracts the shift of center of lift on the main surface
and keeps the center of lift near the center of gravity. On some designs a
small canard (horizontal) surface near the nose serves this purpose. The
Swedish Saab Draken, the Mach 2 fighter operational for several years, was the
first of the so-called "tailless" (no conventional horizontal tail
and no canard) airplanes to use the double-delta planform.
• Design Mach Number.
The centerbodies of the engine air inlets on the A-11s in the photographs released
by the White House appear to have a ramp angle suitable for a maximum
economical cruise speed slightly above Mach 3.
• Cruise Altitude.
Most press reports have placed the A-11's maximum cruise altitude between
90,000 and 125,000 feet. This appears to be a serious error. There is a
well-established procedure for checking maximum cruise altitude. It indicates
that the A-11 must cruise between 70,000 and 80,000 feet or its range will
severely suffer. Thus, the A-11 can be expected to get its maximum range while
cruising about 5,000 to 10,000 feet below the U-2. The U-2's superior wing and
lower wing loading give it better altitude capability in unaccelerated flight.
But in a zoom climb the A-11 would outperform it.
To figure maximum cruise altitude you have to know two
characteristics of any aircraft—the wing loading (written W/S and equal to the
gross weight divided by the wing area), and the lift coefficient (written CL, a
dimensionless number indicating the lifting power of the wing) generated when
the aircraft is flying at the proper angle of attack for maximum range (maximum
aerodynamic efficiency). When the W/S is divided by the CL, it equals the
dynamic pressure required to keep the aircraft in level flight. The dynamic
pressure is the term that fixes the altitude of flight for any given speed.
There is enough information on the A-11 to put the above
relationships to work. For instance, when the A-11 is flying at Mach 3 at
70,000 feet, the dynamic pressure is nearly 600 pounds per square foot. The
lift coefficient for maximum L/D is about .1 (this has been confirmed in many
NASA reports on aircraft similar to the A-11). So 600 may be multiplied by .1
to give a maximum possible wing loading of about 60 pounds per square foot.
This is about the wing loading the A-11 would have if it had a 2,000-square-foot
wing area, weighed 150,000 pounds at takeoff, and burned about one-third of its
75,000-pound fuel load during its climb to altitude.
This procedure can be run through again to show that the
A-11's wing loading would be a little better than thirty pounds per square foot
once it had burned all its fuel. It, therefore, would end its cruise at Mach S
at 80,000 feet.
Speed would not change this picture too much. If the A-11
were capable of Mach 4, it would begin its cruise at about 82,000 feet and in
the lightened condition at the end of cruise would be flying at nearly 95,000
The press reports of 125,000-foot altitude completely fall
apart under check. If the A-11 flew at that altitude at Mach 4 it would need a
wing loading of less than ten pounds per square foot. In other words its
structure could not be any heavier than that of a Piper Cub.
Or, if the A-11 tried to fly at 125,000 feet at a wing
loading of about thirty pounds per square foot, corresponding to an
end-of-cruise weight, its speed would have to be at least Mach 8 to maintain
level flight and to keep it from stalling out.
The same procedures can be used to show that the U-2's
altitude during maximum range cruise will vary from about 75,000 feet to a
little more than 90,000 feet.
Another check on the operational altitude of the A-11 can be
made by examining the engine air inlets which appear to be about six feet in
diameter at the most. Therefore, the maximum capture area for both inlets to
take in air is between fifty and sixty square feet. This is just about enough
to fly an airplane like the A-11 at 80,000 feet at Mach 3. At 100,000 feet at
Mach 3 the required capture area goes well over 100 square feet. At 125,000
feet the inlets would become truly gigantic.
In recent years, the ability of Century-series fighters to
zoom higher than 100,000 feet has tended to distort the picture as far as
maximum cruise altitude and maximum level flight altitude are concerned. Most
of the Century-series fighters cruise best between 35,000 and 45,000 feet, and
their maximum level flight altitude is around 60,000 feet. Therefore, the
A-11's ability to cruise in the 70,000- to 80,000-foot level is certainly not
to be disparaged. With the A-11 cruising at Mach 3 at those altitudes, on a
gentle dog-leg course, it would be essentially impossible for any operational
fighter in the world to intercept it. And it is doubtful that any existing
ground-based missile system could down the airplane.
Efficiency. The A-11 came along in time to benefit from several years of
inspired aerodynamic research during the middle and late 1950s. By 1960 the
unclassified literature had made it clear that the old idea that L/D (aerodynamic
efficiency) was certain to be less than five at Mach numbers above 3 had to be
discarded. There were strong indications that L/Ds of seven and eight and
possibly higher could be attained.
These were still well under the L/Ds of eighteen to
twenty-three at which subsonic transports and bombers operate. However, an L/D
of eight is enough to bring the total flight efficiency (and range) of a supersonic
airplane up close to that of the subsonic jet because propulsive efficiency
increases rapidly at supersonic speeds. The idea that an economical supersonic
transport (SST) was possible grew out of supersonic L/D research in the late
1950s, and the idea of the A-11 undoubtedly had the same beginning.
The basic rules for obtaining high L/D have been discussed
exhaustively in NASA reports and the publications of the technical societies.
The A-11 appears to use all of them. First, the wing leading edges are as sharp
as possible, even sharper than those of the F-104. Second, the fuselage has a
fineness ratio (length divided by diameter) of around eighteen, which gives it
a very high internal volume for carrying fuel and equipment. Such design was
found to be the optimum means for carrying any given weight at supersonic
speeds, and the A-11 has the highest fineness ratio yet used on any aircraft.
Third, proper distribution of the pressure forces, the lift
and drag forces, is a key to getting high L/Ds with any airplane. Several
important techniques which bring pressure distributions closer to the ideal
were developed during the 1950s. They primarily involved "twisting"
and "cambering" the wing. The side-view photographs of the A-11, both
looking endwise at the wing, clearly show its "twists" and
Supersonic vehicles offer designers one unique opportunity
for reducing drag and improving L/D. This is to arrange the vehicle components
(fuselage, wing, tail, nacelles, etc.) so that they "interfere
favorably" with each other. At subsonic speeds interference effects are
negligible at a distance of more than a few inches away from any surface.
However, at supersonic speeds strong shock waves and
pressure fields spread away from all objects. Pressure fields spreading from
an aircraft's components can combine unfavorably to make the total vehicle drag
much higher than the drag of the components taken separately.
Happily, this situation can be reversed. The components can
be arranged so that their pressure fields and shock waves "cancel"
out each other and reduce total drag. For instance, an engine nacelle outboard
from a fuselage can throw a high-pressure field on the curved aft side of the
fuselage to create a "thrust" force and reduce fuselage drag. The
"ultimate" in favorable interference is a theoretical supersonic biplane
postulated by Adolph Busemann in the 1930s. This was an arrangement of two
wings, properly shaped and spaced apart, which canceled all of each other's
wave drag at one particular Mach number.
In the 1950s supersonic interference effects were the object
of intensive research, notably by Antonio Fern of the Polytechnic Institute of
Brooklyn and A. J. Eggers, Jr., of NASA. Their basic information was applied
on the B-70, which is arranged so that a powerful positive pressure field is
created on the lower wing surface by the engine air duct during Mach 3 cruise
to increase lift and improve L /D. Design techniques for favorable interference
have been under continuous refinement and are very important in the SST proposals
now being evaluated by the FAA.
On the A-11, the area on the back of the fuselage between
the engine nacelles is a highly critical flow area in which several strong
pressure fields meet. Undoubtedly, the fuselage slopes off continuously in this
area and forms a gentle ramp ending in the sharp point visible in the
photographs. It would be possible to reduce drag, improve L/D, and increase the
effectiveness of the vertical tails by creating favorable pressure fields
along this ramp. The slope and contour of the ramp, the spacing and shape of
the engine nacelles, the location of the vertical tails, and the flight speed
all would be important in creating a favorable flow field and a high L/D. This
leads to the conclusion that the A-11 is a single design point airplane. That
is, it has a high L/D at its cruise Mach number, but its aerodynamic efficiency
falls off at both lower and higher speeds. Consequently, the airplane probably
doesn't have much growth potential in speed and would be in serious trouble
about making its range if one engine were lost.
• Structure. The
extent and the manner in which titanium is used in the A-11 has not been
disclosed. However, the President's remarks hinted that titanium was the main
load-bearing metal. If this is true, the A-11's airframe must be relatively
light and efficient for a high-temperature structure. According to data from
the SST program, it would have been possible to design the airframe for Mach 4
temperatures with only a slight increase in weight and probably the
installation of new leading edges made of higher temperature material. The
refractory metal alloys developed in the Dyna-Soar program, for example, would
have a long life on a Math 4 airplane.
After the heating problems the most important structural
question about the A-11 is its design load factor. If the load factor were low,
say two Cs at cruise, the structure would be
extremely light, and amount to only about twenty percent of the airplane's
total weight, or even less. Consequently, maneuverability would be sharply
limited and the aircraft certainly would be marginal as an interceptor even if
its missiles were extremely maneuverable. However, the light structure would
result in a low-wing loading and a high cruise altitude, and it would allow a
greater percentage of the airplane's weight to be carried as fuel, which would
If the design load factor were high, to allow seven-G turns,
for instance, the structural weight would go up sharply. Such design would make
the aircraft very useful as an interceptor or a bomber, but it would substantially
reduce maximum cruise altitude and range.
The question of adapting the A-11 to an interceptor or a
bomber mission depends largely upon the design load factor, which, of course,
is a closely held secret. Structural strength is more important in this case
than the problem of incorporating the necessary electronics and missiles, for
the A-11 is big enough.
Official reports dating back several years describe the Pratt & Whitney J58
as a simple supersonic turbojet with an afterburner. An early version lost the
B-70 competition to the General Electric J93. If an early version is powering
the A-11, the specific fuel consumption (SFC) is high and the range is low.
Simple turbojets of the middle 1950s all ran on afterburner at Mach 3, and
their SFC was more than two pounds of fuel consumed per pound of thrust per
hour, compared to an SFC of about 0.8 for the best fan engines on subsonic jet
However, great strides have been made in engine design, and
it seems highly unlikely that a 1955 vintage supersonic engine would still be
in the A-11. The J58 undoubtedly has been improved in many ways through higher
operating temperatures, the use of advanced turbine-cooling techniques, better
compressor blading, and possibly the addition of a fan and new
If such engine improvements have been incorporated in the A-11,
the SFC during cruise is down near 1.5 pounds of fuel per pound of thrust per
hour. Figures almost this low are being quoted for the SST engines. And, in
1962, three Lockheed engineers—F. S. Malvestuto, Jr., P. J. Sullivan, and H. A.
Mortzschkyin a most interesting paper before the Institute of the Aeronautical
Sciences gave Lockheed's views of what could be done in the way of optimizing
supersonic and hypersonic-cruise configurations in the near future. On the key
question of achievable SFCs they said, "Propulsive efficiency [Mach number
divided by SFC] of 2.0. . . appears to be a reasonable value for any
chemically-fueled pure-turbojet or dual-cycle propulsive system now available
or projected in the near future." According to this estimate, the best
expected SFC is 1.5 in the near future for Mach 3 airplanes.
One point, continually emphasized in the literature, is that
the "match" between airframe and engine on supersonic-cruise
airplanes is much more critical than on any aircraft of the past. Engine weight
becomes a larger percentage of the total airplane weight, and fuel consumption
rises sharply compared to subsonic powerplants, so the engine becomes
relatively more important in achieving long range. Consequently, tailoring the
airplane to achieve the best possible engine air inlet and exhaust flow
conditions has a large payoff. This tailoring must be balanced by airframe
considerations, however. On the relatively narrow-span supersonic airplanes the
placement of engine nacelles, inlets, and exhaust flows can seriously affect
the total flow pattern over an aircraft, which is the determining factor in
achieving a high L/D.
On the A-11, the fuselage and the forward and aft portions
of the double-delta wing apparently ride at an angle of attack of about four to
five degrees during cruise. This angle gives maximum L/D for the A-11 type
configuration. The openings of the engine air inlets and the inlet spikes are
canted forward through the same angle to face directly into the airflow and
maximize inlet efficiency during cruise. The engine exhaust flow, however,
nearly parallels the fuselage and is directed downward at an angle of about
four degrees to the line of flight. Therefore, about seven percent of the
thrust force is realized as lift to improve LID and range.
In addition, the A-11 powerplants apparently have been
placed so their thrust line is slightly below the airplane's center of gravity
during most of the cruise flight. Therefore, the engines produce a nose-up
pitching moment and reduce the amount of elevator deflection needed to trim
the airplane. NACA reports have estimated that the proper placement of the engine
thrust line to reduce trim drag of the elevator can increase range five to ten
percent in aircraft of the A-11 type.
• Fuel. Several
years ago there were reports that the J58 was being tested with boron fuel. If
pentaborane were burned in the J5S afterburner—and research has shown this to
be possible—then a thousand miles or more could be added to the A-11's range.
US production of borane fuels has been stopped, but Defense
Secretary Robert S. McNamara last year told the Congress that enough was
stockpiled to satisfy projected needs for the foreseeable future. The boranes
are now being used in rocket-engine research, primarily by the Air Force, and
conceivably the A-11 could draw from this reservoir.
Borane fuels are expensive compared to the hydrocarbons,
and this is a major reason why the use of pentaborane was dropped from the B-70
plans. However, on a relatively small aircraft such as the A-11, with
relatively limited numbers involved, the extra cost could be justified by the
large performance improvement.
• Range. Maximum
range on the A-11, if it is hydrocarbon fueled and powered by a J58 model only
slightly better than the original version, probably is around 3,500 miles. This
assumes an LID of six, an SFC of 2.0, and fifty percent of the aircraft weight
in fuel, with about one-third of it being consumed in the climb to altitude.
Boron fuel would add around 1,000 miles to the range.
If it has been possible to achieve the maximum LJDs and SFCs
suggested in the Lockheed paper mentioned above, the range would go over 5,000
miles on hydrocarbon fuel. This assumes an L/D of eight and an SFC of 1.5. But
this level of performance probably will not be achieved for some time.
Schedule. It has been reported that the A-11 was delivered and flown for
the first time in 1961; that is slightly more than two years after design work
started. The same report also claims that the A-11 has been operational for two
years, meaning 1963 and most of 1962. That would leave about one year, early
1961 to early 1962, for flight testing.
If this report is true, it would have been necessary during
this one year to move in relatively small speed increments toward Mach 3 to
make sure that all systems were responding properly to all speed, temperature,
and vibration conditions. The inevitable "fixes" would have been made
and the modified systems rechecked. Finally, it would have been necessary to
move slowly toward maximum-range flights, by cruising at Mach 3 for longer and
longer periods to ensure that all systems were withstanding the high-temperature
Under any conceivable set of circumstances, designing,
fabricating, flight testing, and bringing a pioneering, first-generation, Mach
3 cruise airplane to operational status in three years would be an almost
miraculous achievement. True, the CIA-type management system is conducive to
rapid developments. In effect, the CIA simply says to the contractor,
"Bring us one of 'these.' We are making you responsible for performing
all tests and making all technical decisions."
The U-2 was designed this way and delivered for first flight
in little more than one year. But the U-2 was a completely straightforward
project with a well-known type of wing, aluminum construction, and a slightly
modified version of a well-developed turbojet. The A-11 designers were breaking
new ground in every department, although they did have access to development
data from the B-70 and J93 projects.
It seems reasonable that design, fabrication, and ground
testing of the A-11 and its systems took nearly four years and that the first
flight took place in 1963. Less than a year of flight testing probably would
have allowed President Johnson to say that the aircraft "has been tested
in sustained flight at more than 2,000 mph," and is "capable of . . .
long-range performance of thousands of miles. ....He didn't say the range had
But if the shorter development time reported is true, the
SST program certainly bears review. If any Mach 3 cruise airplane can be
brought to operational status from scratch in three years, then maybe the FAA
is correct in taking the position that SST costs, technical uncertainties, and
development time will be much lower than industry estimates.
Development of an economic supersonic transport is a much
more difficult problem than the A-11, but if the CIA's hands-off management
concept can indeed get us a Mach 3 airplane in three years, this concept
certainly should be considered for the SST. And the Pentagon could benefit from
this example as well.
Transport. The A-11 probably can spell the difference between success and
failure in any US Mach-2.5-plus supersonic-transport program. The A-11 provides
an immediately available means of getting vital flight-test time on all SST
systems. It will yield data on the performance of titanium structure at Mach 3
that could not be obtained by any other means. And, when the SST engines are
ready, the A-11 will allow them to be exhaustively tested in flight in a known
vehicle and not an unproven SST airframe. By allowing such testing, the A-11
will fill a gap in the government's SST plan that has worried many in industry.
The A-11 experience should make it possible to go ahead in an orderly manner
and build the SST, which must be a true second-generation, supersonic-cruise
airplane that has high aerodynamic and propulsive efficiency at all subsonic
and supersonic speeds, and an extremely rugged titanium structure which can
last through ten years of airline flying.
By any standard the A-11 is a magnificent technical
achievement. Quite obviously it can outfly any known aircraft in the world by a
substantial margin. It is a natural for reconnaissance. However, if the A-11 is
from the U-2 mold and built with an extremely light airframe, it will not have
significant combat potential as a bomber or an interceptor without major
redesign. Even if such redesign is not forthcoming, the A-11 will play a key
research role in building the technology of Mach-3-plus cruise airplanes of
all types—transports, fighters, and bombers. In this role its ultimate
importance to aviation and the nation may be as great as any aircraft ever
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