(video via BAE Systems)

Today's modern wars are fought with a severe technology disparity between the factions. One side is making improvised explosive devices while the other uses augmented reality to call in air strikes. Despite the differences, the modern countries continue to innovate against a possible war with its hi-tech peers. BAE Systems has just released its "Adaptiv" vehicle camouflage that mimics the heat signatures in its surroundings.

The Adaptiv technology consists of hexagonal "pixels." An onboard camera samples the background and displays the IR-image on the pixels accordingly. The process happens fast enough for a moving vehicle to not even make an impression under IR surveillance. The pixels can also be arranged to make the vehicle look like another. In the video example, a tank is make to look like a Jeep.  The pixels could also be used to display words or a message, if need be.

The project is funded by the Swedish Defense Materiel Administration, who wanted a focus on IR cloaking. However, the BAE engineers combined the Adaptiv pixels with other electro-magnetic spectrum cloaking devices to provide further stealth coverage.

BAE plans on adapting the technology for warships and buildings. For this application, larger panels will be used.

I would like to see similar technology for use on soldiers. Seeing soldiers get taken out by UAVs at night, via infrared cameras, is disturbing. Again, the battles are usually one sided anyway. I have never heard of a drone on drone battle in any war.

Eavesdropper

Airbus A320neo (left). AA branded Boeing 737 (right)  (images via each respective company)

The news has hit the airwaves, American Airlines (AA) wants 460 new jets for their fleet. United States based Boeing will build 200, while France based Airbus will get 260 orders.

Currently, AA has an entire fleet of Boeing built aircraft. With a previous order of 207 jets, Boeing still has 52 to produce on that request along with the 200 more. Not to over strip Boeing's capability, American Chairman and CEO Gerard Arpey said, "No single manufacturer could provide the number and variety of aircraft we need to fulfill our vision for the future." Now, some of the burden is placed on Airbus.

What AA will ultimately get are not all new aircraft, but slightly modified existing planes. From Boeing, they will get 100 regular 737s, with an option for 40 more. Also from Boeing, AA will get 100 "re-engined" 737s, with an option for 60 additional. Re-engined planes are existing platforms with new, modern engines.

From Airbus, AA will receive 130 A320 Family planes with 130 re-engined A320neos, with an option for 365 more.

The engine options are LEAP-X from CFM International and the Pratt & Whitney Pure Power PW1100G. These engines will give the jets they are used on better fuel efficiency and less of a carbon foot print.

AA plans to replace all of their mid-80s purchased 757 and 767-200 airplanes. Aprey wrote, "These new aircraft will enable us to reduce our operating and fuel costs and deliver state-of-the-art amenities to our customers, while maximizing our financial flexibility. ... These new deliveries are expected to pave the way for us to operate the youngest and most fuel-efficient fleet among our U.S. airline peers in approximately five years."

Having flown on an AA 767-200 recently, the upgrade could not come fast enough. Hopefully, AA will start introducing biofuels to their new fleet. At the average of 1.2 miles per gallon on previous generation jets, anything improvement is worth it.

Side note: Boeing 737 operators want a newly designed airplane, not re-engined aircraft. U.S. Washington Gov. Chris Gregoire said the 737 is a piece of history. He welcomes a re-engined 737. More on this, in the coming years.

Cabe

BiPod on its test flight and car via Scaled Composites

While Terrafugia takes pre-orders on their Airplane Car, and Trek Aerospace consider civilian transport, Burt Rutan tests his last airplane before his retirement. BiPod, the flying car from Scaled Composites. A two seater, dual 15 kW motor driven hybrid-electric airplane that just happens to be drivable on the road. 

In just four months from the inception of the BiPod, the craft took its first flight on March 30, 2011. Able to reach a 200mph speed, the BiPod can fly a distance of 530 miles. It also have an "overdrive mode," that lets the user fly 760 miles at a slower 100mph. In ground driving mode it can go 35 miles on battery charge alone, or up to 820 miles on a single tank of gas. Batteries in the nose of the craft privide enough power for takeoff, and a reserve of two possible landing attempts for safety.

Two 450CC internal-combustion engines, one in each fuselage, drive generators that in turn power electric motors on the driving wheels and propellers. The driving of a generator by a gasoline motor is also the concept behind the Chevy Volt, under certain conditions. Four propellers, one on each wing and two on the horizontal stabilizer linkage on the tails.

Flight and driving controls are separated between the two fuselage sections. Left side are the flight controls, and right side is for driving. When in driving mode, the wings must be removed and stored between the two halves.

Scaled Composites announced the ambitious project to gauge the response and viability of the BiPod. All the while Burt Rutan spends most of his time working away on his final legacy. Scaled Composite's President Doug Shane said, "[Rutan] was here all the time - he worked really damned hard - and that was a good lesson to all our young engineers that you don't get something for nothing."

Concept design for the BiPod via Scaled Composites

You might recognize some of the past eclectic airplane designs from Burt Rutan and the team at Scaled Composites in the below video. Now you know where they all came from.

Eavesdropper

Radar Technology - Primary RADAR - Height, "the RADAR equation" abnd Reflections

RADAR is can be used to track and aircrafts hieght above the gorund while in flight. One the flight decks secondary instruments if often a RAD-Alt, or RADAR Altimeter.

The height of a target over the earth's surface is called height or altitude. This is denominated by the letter H (like: Height). The altitude can be calculated with the values of distance R and elevation angle ε.

The altitude cannot be so simply calculated on a flying airplane, while refraction is caused when electromagnetic waves cross airlayers at different density and the earth's surface has a bend. The calculation of the targets altitude is not only a trigonometrically calculation. The current location grounding bend must also be taken into consideration.

In addtion the propagation of electromagnetic waves is also subject to a refraction and are also dependent on:

• the transmitted wavelength,
• the barometric pressure,
• the air temperature and
• the atmospheric humidity.

These variables are one of many reasons why modern aircraft use static pressure and Air Data Computers, rather than RADAR, to calulate their altitude.

The RADAR equation

The radar equation represents the physical dependences of the transmit power, that is the wave propagation up to the receiving of the echo-signals. Furthermore one can assess the performance of the radar with the radar equation.

Nondirectional power density diminishes as geometric spreading of the beam.

Argumentation/Derivation

First we assume, that electromagnetic waves propagate under ideal conditions, i.e. without dispersion.

Nondirectional power density diminishes as geometric spreading of the beam. In the above image Nondirectional power density diminishes as geometric spreading of the beam.

If high-frequency energy is emitted by an isotropic radiator, than the energy propagate uniformly in all directions. Areas with the same power density therefore form spheres (A= 4 π R²) around the radiator. The same amount of energy spreads out on an incremented spherical surface at an incremented spherical radius. That means: the power density on the surface of a sphere is inversely proportional to the to the square of the radius of the sphere.

Since a spherical segment emits equal radiation in all direction (at constant transmit power),  if the power radiated is redistributed to provide more radiation in one direction,  then this results an increase of the power density in direction of the radiation.  This effect is called antenna gain. This gain is obtained by directional radiation of the power.

Of course in reality radar antennas aren't “partially radiating” isotropic radiators. Radar antennas must have a small beam width and an antenna gain up to 30 or 40 dB. (e.g. parabolic dish antenna or phased array antenna).

The target detection isn't only dependent on the power density at the target position, but also on how much power is reflected in the direction of the radar. In order to determine the useful reflected power, it is necessary to know the radar cross section σ. This quantity depends on several factors. But it is true to say that a bigger area reflects more power than a smaller area. That means:

A Jumbo jet offers more radar cross section than a sporting aircraft at same flight situation. Beyond this the reflecting area depends on design, surface composition and materials used. With this in mind we can say: The reflected power Pr at the radar depends on the power density, the antenna gain.

Radar Reflections from Flat Ground

The trigonometric representation shows the influence of the Earth's surface. The Earth plane surrounding a radar antenna has a significant impact on the vertical polar diagram.

The combination of the direct and re-reflected ground echo changes the transmitting and receiving patterns of the antenna. This is substantial in the VHF range and decreases with increasing frequency. For the detection of targets at low heights, a reflection at the Earth's surface is necessary. This is possible only if the ripples of the area within the first Fresnel zone do not exceed the value 0.001 R (i.e.: Within a radius of 1000 m no obstacle may be larger than 1 m!).

Specialized Radars at lower (VHF) frequency band make use of the reflections at the Earth's surface and lobing to maximize cover at low levels. At higher frequencies these reflections are more disturbing. The following picture shows the lobe structure caused by ground reflections. Normally this is highly undesirable as it introduces intermittent cover as aircraft fly through the lobes. The technique has been used in ATC ground mounted radars to extend the range but is only successful at low frequencies where the broad lobe structure permits adequate cover at higher elevations.

Raising the height of the antenna has the effect of making the lobbing pattern finer.  A fine grained lobing structure is often filled in by irregularities in the ground plane.  Specifically, if the ground plane deviates from a flat surface then the reinforcement and  destruction pattern resulting from the ground reflections breaks down.  Avoidance of lobe effects is one of the prime considerations when selecting a radar location  and the height of the antenna.

Radar Technology - Primary RADAR - Detecting and Ranging

The electronic principle on which radar operates is very similar to the principle of sound-wave reflection.  If you shout in the direction of a sound-reflecting object (like a rocky canyon or cave),  you will hear an echo. If you know the speed of sound in air, you can then estimate the  distance and general direction of the object. The time required for an echo to return  can be roughly converted to distance if the speed of sound is known.

Radar uses electromagnetic energy pulses in much the same way, as shown in the below.

The radio-frequency (rf) energy is transmitted to and reflected from the reflecting object.  A small portion of the reflected energy returns to the radar set.  This returned energy is called an ECHO, just as it is in sound terminology.  Radar sets use the echo to determine the direction and distance of the reflecting object.

Radar is an acronym for RAdio (Aim)* Detecting And Ranging. Modern radar can extract widely more information from a target's echo signal than its range.  But the calculating of the range by measuring the delay time is one of its most important functions. The distance is determined from the running time of the high-frequency transmitted signal  and the propagation c₀.  The actual range of a target from the radar is known as slant range.  Slant range is the line of sight distance between the radar and the object illuminated.  While ground range is the horizontal distance between the emitter and its target and  its calculation requires knowledge of the target's elevation.  Since the waves travel to a target and back, the round trip time is dividing by two  in order to obtain the time the wave took to reach the target.

The angular determination of the target is determined by the directivity of the antenna.  Directivity, sometimes known as the directive gain, is the ability of the antenna to concentrate  the transmitted energy in a particular direction.  An antenna with high directivity is also called a directive antenna.  By measuring the direction in which the antenna is pointing when the echo is received,  both the azimuth and elevation angles from the radar to the object or target can be determined.  The accuracy of angular measurement is determined by the directivity,  which is a function of the size of the antenna.

Radar units usually work with very high frequencies. Reasons for this are:

• quasi optically propagation of these waves.
• High resolution (the smaller the wavelength, the smaller the objects the radar is able to detect).
• Higher the frequency, smaller the antenna size at the same gain.

The True Bearing (referenced to true north) of a radar target is  the angle between true north and a line pointed directly at the target.  This angle is measured in the horizontal plane and in a clockwise direction from true north.

The antennas of most radar systems are designed to radiate energy in a one-directional lobe  or beam that can be moved in bearing simply by moving the antenna. As you can see  the shape of the beam is such that the echo signal strength varies in amplitude as the antenna  beam moves across the target.

In actual practice, search radar antennas move continuously;  the point of maximum echo, determined by the detection circuitry or visually by the operator,  is when the beam points direct at the target. Weapons-control and guidance radar systems  are positioned to the point of maximum signal return and maintained at that position  either manually or by automatic tracking circuits.

In order to have an exact determination of the bearing angle, a survey of the north direction  is necessary. Therefore, older radar sets must expensively be surveyed either with a compass  or with help of known trigonometrically points. More modern radar sets take on this task and with help of the GPS Satellites determine the northdirection independently.

Transfer of Bearing Information

The rapid and accurate transmission of the bearing information between the turntable  with the mounted antenna and the scopes can be carried out for

• servo systems and
• counting of Azimth Change Pulses

Servo systems are used in older radar antennas and missile launchers and works with help of devices like  synchro torque transmitters and synchro torque receivers. In newer radar units we find a system of Azimth Change Pulses ACP).  In every rotation of the antenna a coder sends many pulses, these are then counted in the scopes.

Newer radar units work completely without or with a partial mechanical motion.  These radars employ electronic phase scanning in bearing and/or in elevation (phased array antennas).

Source "http://www.radartutorial.eu/" Copyright (C)  2009  R Colman. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License.