One afternoon in early 1958, Jack Hansen and I were standing outside the shop
area of the north part of Building 82, discussing the day’s events, when I
heard what sounded like large trash cans or dumpsters rattling behind me. I saw
a startled look on Jack’s face, and then he said, “I think I just saw a car
drive into the building!”
We went to the guard at the door and said, “We think a car
just drove into the building,” but the guard did not believe it.
Jack and I went into the building, and sure enough, there was a car
with an unconscious male driver still in it, inside the building!
His car had crashed through a chain-link fence that
terminated a little short street parallel to Hollywood Way, into the building
wall, which, since it was corrugated metal, had given way but then returned to
its original position, so there was no obvious hole in it.
Inside, the car had passed by a row of work benches at which
people had been sitting only a few minutes before because it was, at most,
fifteen minutes after a shift change began.
The shift change stampede had left no one in that area, so no
one was hurt. The car went under a U-2 wing, missing the aircraft, and stopped just shy of a
“ping-pong” table. Hitting that table would have been a real disaster!
We went back to the guard and said definitely there was a car
in the building. He grumbled but he locked up his station and came inside. Once
he saw the car, pandemonium ensued!
Apparently the man had had an epileptic seizure. He was
removed while he was still unconscious.
“Chance
favours the prepared mind”
—Louis Pasteur
In the late summer of 1959, I attended a meeting with
several CIA, U.S. Air Force, and Lockheed people. The attendees included Dr.
Richard Bissell, Kelly Johnson,
L. D. MacDonald, and Melvin George.
The purpose of the meeting was to review our A-12 aircraft design proposal, and discuss the Customers’ concerns.
There was considerable apprehension about the echoes from the
nacelle exhaust outlets. The exhaust pipes were sixty inches in diameter, so
they returned large amounts of energy at all frequencies of interest and over
large angles to the rear.
A critical problem arose when the question of preventing
echoes from the engine exhaust outlets was addressed. We knew that the only way
to prevent such echoes was, in effect, to close the apertures. It was
impractical to incorporate absorbing structures within the tail pipes.
We had done some scaled model tests using metallic screens of
several different shapes that showed promise, but we were not enthusiastic
about using screens of any shape or material.
After reviewing our scaled model backscatter reduction data
during the meeting, there was a discussion about how to reduce the radar echo
from the huge exhaust outlets.
Dr. Bissell seemed discouraged about the chances for success. He was so
concerned about the problem that he considered abandoning the project.
Suddenly I thought of a solution. I suggested that we could
put something in the fuel that would be ionized by the high exhaust gas temperatures
and thereby absorb or scatter the radar energy.
My first proposal was to use cesium because, in vapor form,
it has the lowest first ionization potential of all the chemical elements and
therefore, would be the best source of free electrons that would do the
absorption and scattering required.
That suggestion was endorsed heartily by several of the Customer’s
consultants; one of the physicists actually stood up and exclaimed, “That’s
it!” There was a lot of excitement, and an enthusiastic discussion ensued.
Mel told me later that Kelly Johnson exclaimed that my suggestion may have
saved the program.
Within about a week, in August of 1959, the CIA awarded a contract to design the A-12. Production of real prototype aircraft was contingent upon demonstrating a sufficiently low RCS signature by January 1960.
The F-117—Doing It with Mirrors
“If you would from radars hide
Try tilted mirrors side by side.”
--- Edward Lovick, Jr.
Serendipity—“The gift of finding valuable or agreeable
things not sought.” The concept upon which the development of the F-117 stealthy aircraft was founded was a
classic example of serendipity.
I heard that J. Russell “Russ” Daniels discovered an Air Force “Fighter Mafia” interest in obtaining
a large number of small, stealthy, undetectable by radar, piloted aircraft for
air-to-ground attack. He asked Ed Martin,[1]
the Director of Science and Engineering, to talk to DARPA and Air Force people
to let them know (after obtaining CIA permission) that, for several years,
Lockheed had been producing stealthy aircraft for the CIA and the Air Force.
Edward Martin had been in charge of manufacturing some of the U-2 aircraft.
Ed was told that the money for the XST[2]
program already had been allocated to other companies. If Lockheed wished to
participate, they would have to fund their own proof of concept work.
Dick Scherrer was a design engineer in Leo Celniker’s ADP Preliminary Design
Group. He was assigned the task to develop a conceptual stealthy design.
The Fighter Mafia group wanted a stealthy attack aircraft
that could disable or destroy a very dangerous Soviet Union field artillery
vehicle codenamed “Gun Dish.” It consisted of an armored vehicle carrying a
rotary gun (like a Gatling gun) that could fire several thousands of “rounds”
per minute with devastating effect. Its fire control system used a radar
operating near 15 GHz whose wavelength was about eight tenths of an inch.
The gun could be aimed at a target very quickly, as I
observed while sitting inside a reconstructed vehicle at Fort Huachuka, Arizona,
while a technician operated it.
Sunlight coming through bullet holes in its sides emphasized
the fact that it had been used in the 1967 Israeli-Egyptian war!
A crucial bit of information that I gave to Dick Scherrer was that, if a flat reflecting surface
was large enough compared to the wavelength of impinging radiation, its
reflection would be specular, or mirror-like. By tilting it sufficiently, most
of the energy could be directed away from returning to its source.
In December of 1958, Mike Ash,
Jim Herron, and I had measured the backscattering from triangular
cylinders and had demonstrated to Kelly Johnson that very nearly specular reflection
would occur if the sides of the triangular cross section were more than about
25 wavelengths wide. At 15 GHz, that would correspond to about twenty inches. As the reflecting surface measured in wavelength[3]
decreases, the primary reflection lobe centered on the specular vector widens.
In the early 1970s, the
computers and or computer programs available to us at Lockheed could not calculate
adequate representations of complicated curved surfaces characteristic of
aircraft technology, so curved or warped surfaces were approximated by
collections of flat areas.
Basically the Lockheed computer program could not correctly
calculate the backscatter from curved or warped surfaces or edges. Also, it
could not predict the different responses to radar wave polarization. It was a
very simplistic program and in fact, it was basically an optical ray tracing
program.
Working with Denys Overholser, Dick Scherrer realized that, despite inadequacies in
Lockheed’s ECHO code, it might be possible to design an aircraft that would
take advantage of some of the results of the calculations.
Bill Schroeder, who was a mechanical
engineer and a good mathematician, wrote the original ECHO computer code. His
protégé was Denys Overholser. Denys was able to run the simple code and generate huge piles of
paper! Denys, please do not take umbrage
for that remark.
I do not know whether Denys Overholser had any significant practical experience in the art and
science of electronic measurements. I do not know what his educational
background was (because I never asked him) but I think it may have been
electrical engineering. It made little difference because he was more than up
to the challenge.
The results of the radar backscatter calculations were so
favorable as to be almost not believable. They promised a real breakthrough in
the technology.
Ed Martin directed a proposal to the Air Force to build an aircraft
based upon Scherrer’s design and the predictions of the “ECHO” computer code, which
was a good marketing tool.
Ed invited me to participate. We had been in the Navy radar
group in Chicago and we had worked at Lockheed both before and after World War
II Navy service.
Our original in-house name for the
proposed aircraft was Harvey, named for an invisible rabbit from a 1950s
movie, Harvey, starring Jimmy Stewart.
Harvey’s faceted design was a significant departure from
prior ADP aircraft, and management was unwilling to fund a proof of concept RCS
model and tests. After failing to get ADP management interested, Ed approached Dr. Andrew Baker in Lockheed Corporate. Dr. Baker played a major role in
helping Ed obtain company funding for the RCS demonstrator[4].
The “Hopeless Diamond” was a simple RCS test body that
was used successfully to validate its computed backscatter by measurements at
an outdoor test facility. It was named by preliminary design engineer Ed Baldwin. He was skeptical of the possibility of controlling a
flying faceted aircraft.
Later Dick Cantrell, who was responsible for stability and control factors, declared that he would teach it to fly—and he did, with considerable help from Robert C. “Bob” Loschke.
There were aerodynamicists who were aghast at the whole thing
until wind tunnel tests were performed. Possibly some people didn’t know about
or remember the Coanda Effect (discovered in 1932 by
Henri Coanda) in which a fluid, air in this case, tends to
follow a surface until it is forced to leave for some reason such as an abrupt
discontinuity.
My contribution at that time was to propose a special
treatment for the engine inlets. It consisted of an “egg crate”[5]
designed to operate as a collection of cut-off waveguides intended to prevent
entry of radar waves into the front parts of the engines while allowing adequate
air flow.
The smallest grid openings I was allowed by the propulsion
engineers were too large to cause cut-off at the Gun Dish frequency. Their
cut-off frequency was less than half the Gun Dish frequency.
At higher frequencies the grid would
act like waveguides and let the energy go through, so we made the tubular parts
of the inlet grids out of lossy materials. There was no metal in those grids.
They were fiberglass with resistive coatings, and the resistive coatings were
step tapered, not very conductive on the outside, and more conductive as waves
progressed in, and finally fairly conductive. In this case the desire was to
make the inlets blend into the surrounding absorber coated metal surfaces.
Ed Martin, whose experience included
Navy radar training, immediately recognized the merits of this modality.
The engine performance was degraded somewhat, but the egg
crates solved the radar backscattering problem. They also straightened the airflow
to the engines somewhat and that was beneficial.
We successfully tested the prototype grids in the large
anechoic chamber in Building 197.
Ed was looking for a way to aid the marketing of the XST
proposal, which led to Have Blue and the F-117.
Shortly before he and several others went to present our proposal, I suggested
to him that calculation implied that the aircraft seen nose-on would seem like
a 7/16th inch diameter metal sphere to a 15 GHz radar. He liked the idea, so I obtained ball bearings from our shop for
him. Ed took a bag of the bearings to his meeting with the Customer.
He told me later that after that information was disclosed a lot
of bearings were rolled on the conference table![6]
I never recovered my tool check.
A contract to build a full-scale Have Blue mockup to validate the radar reflection capabilities of our design was received and implemented. Simultaneously another company, Northrop, was building their entry for the competition.
[1] The
following material is paraphrased from “Pioneers of Stealth 2004 Nominees.”
“Ed Martin—Lockheed Martin. As Director of Science and
Engineering for Lockheed (Advanced Development Projects) he discovered DARPA’s
interest in low observable aircraft and enhanced survivability methods. (He)
Made the initiative to convince DARPA of Lockheed’s experience with Low
Observable aircraft and expertise for a new generation of aircraft. (He)
Recruited the original design team for Lockheed’s XST (later Have Blue). (He) Convinced Lockheed
Corporate to devote company funds to test the “Hopeless Diamond” that proved the faceted
design concept worked. (Validated the computed radar backscatter data). (He)
Directed the prototype design and development of the Lockheed XST project
during its initial feasibility engineering phases. (He was) Responsible for the
initial aircraft configuration concepts and the winning program entry in the
first competitive low observables program.”
[2] XST stood for Experimental Survivable Testbed.
[3] l is the conventional mathematical symbol denoting wavelength.
[4] Ben Rich had published a very different account of the initial contact with the Defense Advanced Research Projects Agency (DARPA).
[5] The egg crate inlet was derived from the metallic A-12 vent openings I had designed in the early 1960s. The original reason for this kind of grid was to make certain surfaces on the bottom of the A-12 aircraft appear to radar waves to be metallic like the surrounding airframe surfaces. The holes in the grids were waveguides beyond cut-off, so that they did have a reflection coefficient very nearly like a metal sheet.
[6] Ben Rich or his ghost writer had a different version of this incident. Ben was not directly involved in its origin.