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cnc

Numerical control (NC) refers to the automation of machine tools that are operated by abstractly programmed commands encoded on a storage medium, as opposed to manually controlled via handwheels or levers, or mechanically automated via cams alone. The first NC machines were built in the 1940s and '50s, based on existing tools that were modified with motors that moved the controls to follow points fed into the system on paper tape. These early servomechanisms were rapidly augmented with analog and digital computers, creating the modern computer numerical controlled (CNC) machine tools that have revolutionized the design process.

In modern CNC systems, end-to-end component design is highly automated using CAD/CAM programs. The programs produce a computer file that is interpreted to extract the commands needed to operate a particular machine, and then loaded into the CNC machines for production. Since any particular component might require the use of a number of different tools—drills, saws, etc.—modern machines often combine multiple tools into a single "cell". In other cases, a number of different machines are used with an external controller and human or robotic operators that move the component from machine to machine. In either case, the complex series of steps needed to produce any part is highly automated and produces a part that closely matches the original CAD design.

Financial planninf advice July/1

Should the Fed be in the business of pricking asset bubbles?

This week, we step back a moment to think about monetary policy. Still, the Fed faces severe downside risk to the economy – commercial real estate and state and local budgets alone cause havoc on the outlook. Furthermore, the Fed will likely be in easing mode for some time, especially with the pile of assets it must eventually unwind.
However, the future of Fed policy is being challenged. Last week, the Board of Governors Vice Chairman, Donald Kohn, defended the Fed’s need for autonomy from Congressional oversight, as “Any substantial erosion of the Federal Reserve’s monetary independence likely would lead to higher long-term interest rates as investors begin to fear future inflation”.1 As the economy recovers from the grandest housing bubble in modern history, the Fed will once again assess its mandate to promote maximum sustainable employment, stable prices, and moderate long-term interest rates. Should this mandate include a policy of targeting asset prices?
Bill Cheney
Chief Economist
617-572-9138
bcheney@mfcglobalus.com
Oscar Gonzalez
Economist
617-572-9572
ogonzalez@mfcglobalus.com
Rebecca Braeu
Economist
617-572-0868
rbraeu@mfcglobalus.com
Economic Research
The short answer is going to be YES and NO. Yes, the Fed and related agencies should further explore their roles as financial regulators, which is part of the Fed’s job of ensuring financial stability. No, even a pre-emptive strike against asset prices requires that the Fed reliably identify the bubble given the information at the time. Furthermore, the Fed’s dull monetary policy tool, the short-term rate, is likely to rip through key macroeconomic variables while slowing down asset-prices.
The evidence supporting a policy of targeting asset prices is mixed at best. Furthermore, in the last year it has become abundantly clear that the Fed’s toolbox is more fluid than previously thought - there is a much to do in the area of regulation before changing its policy toward pricking bubbles.
Why do bubbles matter?
The Fed already follows asset prices to the extent of their effects on the real economy. Asset prices affect consumer spending behavior via wealth effects (tangible, housing, and non-tangible, financial, wealth). Second, stock prices affect the ability of firms to raise funds for growth and new investment.
Research shows that the Fed already incorporates asset prices into its policy decisions. According to Rigabon and Sack (2003)2, the probability that the Fed eases (tightens) increases by roughly 50% in the face of a 5% shock to the S&P 500. Simply put - the Fed currently reacts to the expected macro-economic instability that is caused by asset pric

Enginnering

Engineering is the science, discipline, art and profession of acquiring and applying technical, scientific and mathematical knowledge to ...

Audio engineering Audio engineering is a part of audio science dealing with the recording and reproduction of sound through mechanical and electronic means ...

Civil engineering Civil engineering is a professional engineering discipline that deals with the design, construction and maintenance of the physical and ...

Electrical engineering Electrical engineering, sometimes referred to as electrical and electronic engineering, is a field of engineering that deals with the ...

Computer engineering Computer Engineering (also called Electronic and Computer Engineering , Computer Systems Engineering, or "'Hardware Engineering"') is a ...

Mechanical engineering Mechanical Engineering is an engineering discipline that involves the application of principles of physics and chemistry for analysis, ...

Engineer An engineer is an engineering professional. Engineers are concerned with developing economical and safe solutions to practical problems, ...

Aerospace engineering Aerospace engineering is the branch of engineering behind the design, construction and science of aircraft and spacecraft . ...

Industrial engineering Industrial engineering is also known as operations management , management science , systems engineering , or manufacturing engineering ; a ...

Software engineering Software engineering is the application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance ...

Genetic engineering (section Engineering) Genetic engineering, recombinant DNA technology, genetic modification/manipulation (GM) and gene splicing are terms that apply to the ...

Biomedical engineering Biomedical engineering (BME) is the application of engineering principles and techniques to the medical field. skills of engineering with ...

Structural engineering Structural engineering is a field of engineering dealing with the analysis and design of structure s that support or resist load s ...

Bachelor of Engineering Bachelor of Engineering (commonly abbreviated as BE or BEng) is an undergraduate academic degree awarded to a student after three to five ...

Environmental engineering Environmental engineering is the application of science and engineering principles to improve the environment (air, water, and/or land ...

National Academy of Engineering The United States National Academy of Engineering (NAE), a private, non-profit institution that was founded in 1964 under the same ...

Architectural engineering Architectural engineering, also known as Building Engineering, is the application of engineering principles and technology to building ...

Materials science (redirect from Materials engineering) Materials science or materials engineering is an interdisciplinary field involving the properties of matter and its applications to various ...
25 KB (3051 words) - 15:02, 19 July 2009
Civil engineer A civil engineer (in English usage) is a person who practices civil engineering , one of the many professions of engineering. ...
9 KB (1222 words) - 04:57, 23 June 2009
Combat engineering Combat engineering is a combat arms role of using the knowledge, tools and techniques of engineering by troops in peace and war, but ...
18 KB (2380 words) - 08:48, 14 July 2009

Science

Science (from the Latin scientia, meaning "knowledge") refers to any systematic knowledge-base or prescriptive practice that is capable of resulting in a prediction or predictable type of outcome. In this sense, science may refer to a highly skilled technique or practice.[1]

In its more restricted contemporary sense, science refers to a system of acquiring knowledge based on scientific method, and to the organized body of knowledge gained through such research.[2][3] This article focuses on the more restricted use of the word. Science as discussed in this article is sometimes called experimental science to differentiate it from applied science—the application of scientific research to specific human needs—although the two are often interconnected.

Science is a continuing effort to discover and increase human knowledge and understanding through disciplined research. Using controlled methods, scientists collect observable evidence of natural or social phenomena, record measurable data relating to the observations, and analyze this information to construct theoretical explanations of how things work. The methods of scientific research include the generation of hypotheses about how phenomena work, and experimentation that tests these hypotheses under controlled conditions. Scientists are also expected to publish their information so other scientists can do similar experiments to double-check their conclusions. The results of this process enable better understanding of past events, and better ability to predict future events of the same kind as those that have been tested.

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Design and operational details

The flight instrumentation of SR-71 BlackbirdA particularly difficult issue with flight at over Mach 3 is the high temperatures generated. As an aircraft moves through the air, the air in front of the aircraft compresses and this heats the air, and the heat conducts into the aircraft's airframe. To help with this, high temperature materials were needed and the airframe was substantially made of titanium, obtained from the USSR, at the height of the Cold War. Lockheed used many guises to prevent the Soviet government knowing what the titanium was to be used for. In order to control costs, Lockheed used a more easily-worked alloy of titanium which softened at a lower temperature. Finished aircraft were painted a dark blue (almost black) to increase the emission of internal heat (since fuel was used as a heat sink for avionics cooling) and to act as camouflage against the sky.[citation needed] The aircraft was designed to minimize its radar cross-section, an early attempt at stealth design.[11]


[edit] Air inlets

Operation of the air inlets and air flow patterns through the J58.The air inlets were a critical design feature to allow cruising speeds of over Mach 3.2, yet provide subsonic Mach 0.5 airflow into the turbojet engines. At the front of each inlet was a sharp, pointed movable cone called a "spike" that was locked in the full forward position on the ground or when in subsonic flight. During acceleration to high-speed cruise, the spike would unlock at Mach 1.6 and then begin a mechanical (internal jackscrew powered) travel to the rear.[12] It moved up to a maximum of 26 inches (66 cm).

The original air inlet computer was an analog design which, based on pitot-static, pitch, roll, yaw, and angle-of-attack inputs, would determine how much movement was required. By moving, the spike tip would withdraw the shock wave, riding on it closer to the inlet cowling until it just touched slightly inside the cowling lip. In this position shock-wave spillage, causing turbulence over the outer nacelle and wing, was minimized while the spike shock-wave then repeatedly reflected between the spike centerbody and the inlet inner cowl sides. In doing so, shock pressures were maintained while slowing the air until a Mach 1 shock wave formed in front of the engine compressor.[13]

The backside of this "normal" shock wave was subsonic air for ingestion into the engine compressor. This capture of the Mach 1 shock wave within the inlet was called "Starting the Inlet". Tremendous pressures would be built up inside the inlet and in front of the compressor face. Bleed tubes and bypass doors were designed into the inlet and engine nacelles to handle some of this pressure and to position the final shock to allow the inlet to remain "started." It is commonly cited that a large amount of the thrust at higher mach numbers comes from the inlet. However, this is not entirely accurate. Air that is compressed by the inlet/shockwave interaction is diverted around the turbo machinery of the engine and directly into the afterburner where it is mixed and burned. This configuration is essentially a ramjet and provides up to 70% of the aircraft's thrust at higher mach numbers.

Ben Rich, the Lockheed Skunkworks designer of the inlets, often referred to the engine compressors as "pumps to keep the inlets alive" and sized the inlets for Mach 3.2 cruise (where the aircraft was at its most efficient design point).[14] The additional "thrust" refers to the reduction of engine energy required to compress the airflow. One unique characteristic of the SR-71 is that the faster it went, the more fuel-efficient it was in terms of pounds burned per nautical mile traveled. An incident related by Brian Shul, author of Sled Driver: Flying the World's Fastest Jet, was that on one reconnaissance run he was fired upon several times. In accordance with procedure they accelerated and maintained the higher than normal velocity for some time; afterwards they discovered that this had reduced their fuel consumption.[15]

In the early years of the Blackbird programs the analog air inlet computers would not always keep up with rapidly-changing flight environmental inputs. If internal pressures became too great and the spike was incorrectly positioned the shock wave would suddenly blow out the front of the inlet, called an "Inlet Unstart." The flow of air through the engine compressor would immediately stop, thrust would drop, and exhaust gas temperatures would begin to rise. Due to the tremendous thrust of the remaining engine pushing the aircraft asymmetrically an unstart would cause the aircraft to yaw violently to one side. SAS, autopilot, and manual control inputs would fight the yawing, but often the extreme off-angle would reduce airflow in the opposite engine and cause it to begin "sympathetic stalls." The result would be rapid counter-yawing, often loud "banging" noises and a rough ride. The crews' pressure-suit helmets would sometimes bang on the cockpit canopies until the initial unstart motions subsided.[16]

One of the standard counters to an inlet unstart was for the pilot to reach out and unstart both inlets; this drove both spikes out, stopped the yawing conditions and allowed the pilot to restart each inlet. Once restarted, with normal engine combustion, the plane could accelerate and climb to the planned cruise altitude.[citation needed]

The analog air inlet computer was later replaced by a digital one. Lockheed engineers developed control software for the engine inlets that would recapture the lost shock wave and re-light the engine before the pilot was even aware an unstart had occurred. The SR-71 machinists were responsible for the hundreds of precision adjustments of the forward air by-pass doors within the inlets. This helped control the shock wave, prevent unstarts, and increase performance.[citation needed]


[edit] Fuselage
To allow for thermal expansion at the high operational temperatures the fuselage panels were manufactured to fit only loosely on the ground. Proper alignment was only achieved when the airframe warmed up due to air resistance at high speeds, causing the airframe to expand several inches. Because of this, and the lack of a fuel sealing system that could handle the thermal expansion of the airframe at extreme temperatures, the aircraft would leak JP-7 jet fuel onto the runway before it took off. The aircraft would quickly make a short sprint, meant to warm up the airframe, and was then refueled in the air before departing on its mission. Cooling was carried out by cycling fuel behind the titanium surfaces at the front of the wings (chines). On landing after a mission the canopy temperature was over 300 °C (572 °F), too hot to approach. Non-fibrous asbestos with high heat tolerance was used in high-temperature areas.[14]


[edit] Stealth
There were a number of features in the SR-71 that were designed to reduce its radar signature. The first studies in radar stealth technology seemed to indicate that a shape with flattened, tapering sides would avoid reflecting most radar energy toward the radar beams' place of origin. To this end, the radar engineers suggested adding chines (see below) to the design and canting the vertical control surfaces inward. The plane also used special radar-absorbing materials which were incorporated into sawtooth shaped sections of the skin of the aircraft, as well as cesium-based fuel additives to reduce the exhaust plumes' visibility on radar.

The overall effectiveness of these designs is still debated; Ben Rich's team could show that the radar return was, in fact, reduced, but Kelly Johnson later conceded that Russian radar technology was advancing faster than the "anti-radar" technology Lockheed was using to counter it.[17] The SR-71 made its debut years before Pyotr Ya. Ufimtsev's ground-breaking research made possible today's stealth technologies, and, despite Lockheed's best efforts, the SR-71 was still easy to track by radar and had a huge infrared signature when cruising at Mach 3.2 or more. It was visible on air traffic control radar for hundreds of miles, even when not using its transponder.[18] SR-71s were evidently detected by radar, as missiles were often fired at them.

In the end, the SR-71's greatest protection was its flight characteristics, which made it almost invulnerable to the attack technologies of the time; over the course of its service life, not one was shot down, despite over 4,000 attempts to do so.[19]

Development

[edit] Predecessors
The A-12 OXCART, designed for the CIA by Clarence Johnson at the Lockheed Skunk Works,[3] was the precursor of the SR-71. Lockheed used the name "Archangel" for this design, but many documents use Johnson's preferred name for the aircraft, "the Article". As the design evolved, the internal Lockheed designation progressed from A-1 to A-12 as configuration changes occurred, such as substantial design changes to reduce the radar cross-section.

The first flight, by an A-12 known as "Article 121", took place at Groom Lake, Nevada, on 25 April 1962 equipped with the less powerful Pratt & Whitney J75 engines due to protracted development of the intended Pratt & Whitney J58. The J58s were retrofitted as they became available, and became the standard power plant for all subsequent aircraft in the series (A-12, YF-12, M-21) as well as the follow-on SR-71 aircraft.

Eighteen A-12 family aircraft were built. One was a pilot trainer with a raised second cockpit for an Instructor-Pilot and 12 were reconnaissance A-12s to be flown operationally by CIA pilots. Three were YF-12A prototypes of the planned F-12B interceptor version, and two were the M-21 variant.


[edit] SR-71
The SR-71 designator is a continuation of the pre-1962 bomber series, which ended with the XB-70 Valkyrie. During the later period of its testing, the B-70 was proposed for a reconnaissance/strike role, with an RS-70 designation. When it was clear that the A-12 performance potential was much greater, the Air Force ordered a variant of the A-12 in December 1962.[4] Originally named R-12,[5] the Air Force version was longer and heavier than the A-12. Its fuselage was lengthened for additional fuel capacity to increase range. Its cockpit included a second seat and the chines were reshaped. Reconnaissance equipment included signals intelligence sensors, a side-looking radar and a photo camera.[4] The CIA's A-12 remained a better reconnaissance tool than the Air Force's R-12, however; the A-12 flew higher and faster,[6] and with only one pilot it had room to carry a superior camera[6] and more instruments.[7]

During the 1964 campaign, Republican presidential nominee Barry Goldwater continually criticized President Lyndon B. Johnson and his administration for falling behind the Soviet Union in the research and development of new weapons systems. Johnson decided to counter this criticism by announcing the YF-12A Air Force interceptor (which also served as cover for the still-secret A-12)[8] and, on 25 July 1964, the Air Force reconnaissance model. Air Force Chief of Staff General Curtis LeMay preferred the SR (Strategic Reconnaissance) designation and wanted the RS-71 to be named SR-71. Before the July speech, LeMay lobbied to modify Johnson's speech to read SR-71 instead of RS-71. The media transcript given to the press at the time still had the earlier RS-71 designation in places, creating the myth that the president had misread the aircraft's designation.[9][10]

This public disclosure of the program and its renaming came as a shock to everyone at the Skunk Works and to Air Force personnel involved in the program. All of the printed maintenance manuals, flight crew handbooks,[5] training slides and materials were labeled "R-12" and the 18 June 1965 Certificates of Completion issued by the Skunk Works to the first Air Force Flight Crews and their Wing Commander were labeled "R-12 Flight Crew Systems Indoctrination, Course VIII". Following Johnson's speech the name change was taken as an order from the Commander-in-Chief, and immediate reprinting began of new materials, including 29,000 blueprints, to be retitled "SR-71".

Lockheed SR-71

The Lockheed SR-71 was an advanced, long-range, Mach 3 strategic reconnaissance aircraft developed from the Lockheed A-12 and YF-12A aircraft by the Lockheed Skunk Works as a Black Project. The SR-71 was unofficially named the Blackbird, and called the Habu by its crews, referring to an Okinawan species of pit viper.[1] Clarence "Kelly" Johnson was responsible for many of the design's innovative concepts. A defensive feature of the aircraft was its high speed and operating altitude, whereby, if a surface-to-air missile launch were detected, standard evasive action was simply to accelerate. The SR-71 line was in service from 1964 to 1998, with 12 of the 32 aircraft being destroyed in accidents, though none were lost to enemy action.[2]

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