Stealth Aircrafts

Thursday, May 27, 2010

" No aircraft detected .. Radar is clear ... airspace is secure .. !! ????"

STEALTH meaning to hide, work secretly, hidden ...

Lots of Hollywood movies with the help of special effects would show aircraft disappearing from visual ... and trying to show how stealth works buts that's not how actually it works.

EARLY DESIGNS :-

The earliest of Stealth Aircraft of the world is seen to be the Horten Ho 229 fighter-bomber, developed in Germany during the last years of WWII.

Designed by Reimar and Walter Horten and built by Gothaer Waggonfabrik. It was the first pure flying wing powered by a turbojet and was the first aircraft designed to incorporate what became known as stealth technology.

The Ho 229 was of mixed construction, with the center pod made from welded steel tubing and wing spars built from wood. The wings were made from two thin, carbon-impregnated plywood panels glued together with a charcoal and sawdust mixture. The wing had a single main spar, penetrated by the jet engine inlets, and a secondary spar used for attaching the elevons. It was designed with a 7g load factor and a 1.8x safety rating; therefore, the aircraft had a 12.6g ultimate load rating. The wing's chord/thickness ratio ranged from 15% at the root to 8% at the wingtips.

Control was achieved with elevons and spoilers. The control system included both long span (inboard) and short span (outboard) spoilers, with the smaller outboard spoilers activated first.

The aircraft utilized retractable tricycle landing gear, with the nosegear on the first two prototypes sourced from a He 177's tailwheel system. A brake parachute slowed the aircraft upon landing. The pilot sat on a primitive ejection seat.

DEVELOPMENT HISTORY :-


In the end days of the world war II , the US allied forces and the USSR red army, both were in the race to capture the German R&D facilities and developed prototypes of war. With the US launched Operation Paperclip - large portions of German prototypes were captured mainly V1, V2, V3 (Ho-229).. .and numbers of scientist involved in these projects were given US citizenship on request. USSR too had its share taking V1 and V2 and Heinkel He - 178 and He - 280 prototypes.

Meanwhile, during the war US based Aircraft development company - Northrop - also was working on a similar project as of Ho-229 flying wing body aircraft known as YB - 49 series which later got scrapped due to funds problem as well as constant failures in YB - 49's flight stability.

The secured prototypes from Germany were sent to Northrop and Lockheed for analysis which laid the foundation for the advance stealth fighters in the coming years.

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After the war Reimar Horten said he used a mixture of charcoal dust with wood glue to absorb electromagnetic waves of radars. Though no documents exist to confirm that Germany was working on any stealth technology development, this information made grounds for further research. Later the theories of Mr. Horten on stealth were proved correct by Northrop- Grumman and Lockheed-Martin.


With the end of WWII and start of the cold war, the two most powerful states of the world were in a race to make each other feel inferior and to balance the power in the world. This lead to rapid development in various kind of technologies specially in the field of military and intelligence. USA and USSR fought numbers of wars , none face to face, but all with the weapons and intelligence gatherings. Thus it became important to both that they secure their countries, USSR started to develop a range of long-range RADARS and made it difficult for US to infiltrate its aerospace.

This initiated the requirement of a high altitude, Low Observable, High speed reconnaissance aircraft by USA. Lockheed-Martin's SKUNK WORKS under Clarence Kelly Johnson presented what is known as U-2 Spy plane codenamed "Dragon Lady".

Although not completely stealth , but designed to operate at very high altitudes U- 2 was suppose to be hidden from the radar detection of USSR air defense network. But on May 1, 1960 , a U-2 spy plane , flown by Francis Gary Powers, was shot down while taking photographs of USSR nuclear plants and vital SAM sites. This made clear that as previously expected , USSR 's long-range radar coverage was better than it was told.

With the aging of U-2 , USAF required a new and better spy plane. Once again Lockheed-Martin secured a contract. The previous research laid the way for a very high speed , high altitude low observable aircraft now known as the SR - 71 BLACKBIRD. Designed to have low Radar cross sections and drag at high speeds .. Blackbird used RAM or Radar Absorbing Material (came from U-2) , Operating at an altitude of 70,000 to 80,000 feet and at a speed of Mach 3.2 to avoid radar contact, Blackbird served in many wars collecting vital data, pictures and information on enemy.

Image of SR-71 Balckbird Cutaway.

SR-71 remained a spy/reconnaissance plane forever. The success of the SR-71 project encouraged USAF to launch a project "HAVE BLUE" for the development of a stealth fighter/bomber to invade enemy airspace and have first kill capability.

Image of a HAVE BLUE/ Hopeless Diamond prototype.

In 1964, Russian mathematician P.Y.Ufimtsev published a seminar on " Method of Edge Wave in Physical Theory of Diffraction"and showed that the returning RADAR waves after hitting aircraft body is more related to the edges present in the aircraft than its size and one can calculate the RCS or Radar Cross-Section Area across the wings and edges of the aircraft. Thus no matter how big a aircraft is in size, it RCS (representing a DOT on the RADAR screen) can be reduced by producing multiple edges at certain angles. However such a design will make the aircraft system aerodynamically unstable to fly.

After suffering heavy causalities on bombers against sophisticated SAMs of Soviet origins in Vietnam war,in 1980, USAF decided to get a bomber that can penetrate enemy air defense silently. Thus DARPA (Defense Advanced Research Projects Agency) announced the project "HARVEY". The contenders being Northrop and Lockheed.


The Lockheed advance projects team now called as SKUNK WORKS started to work on a top secret project codenamed "HOPELESS DIAMOND" as the initial prototypes for such a aircraft/bomber. The designs this time came from Ben Rich , a team member of Kelly Johnson 's, and a engineer in SR-71 team. Using the research of Ufimstev and computer aided control systems they presented two prototypes of hopeless diamond.

As first thought , just like its name , Hopeless Diamond was not quite satisfactory to the design team , still the RCS of the HOPELESS DIAMOND came out to be 1/10th of the RCS of Northrop-Grumman team.The radar operators used to check the presence of the prototypes as they became completely invisible on the screen during RCS tests by DARPA. Success of the HOPELESS DIAMOND initiated a dark project, completely top-secret and unknown to the world and even to the pilots and the R&D team known as project "HAVE BLUE".

The Have Blue prototypes being test vehicles missed many advancements and sophistication. After the contract was awarded to Lockheed the modifications started and the HAVE BLUE was was upgraded to "SENIOR TREND" which finally was renamed, after rigorous tests, as F-117A "Nighthawk" Stealth Bomber.



It was not until April 1990, that F-117 made their debut in a war. In 1990, US launched an offensive on Panama in Operation JUST CAUSE , and for the first time it checked the effectiveness and long waited war operational capability of the bomber.

But the actual test and experience came during Operation DESERT STORM, which witnessed large numbers of F-117As in combat. Only F-117A was allowed as the first wave of attack as well as to enter the fortified Baghdad. Although only 42 Nighthawks were used, they inflicted a 80% hit rate using GBU / Guided Bomb Unit (LGB and JDAM) munitions, hitting more than 30 % of the high profile targets in first 24 hours of the Operation Desert Storm, thus rupturing the backbone of enemy by destroying the targets as well as the air defense network achieving the objective it was designed for.

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F-117 design success came with certain problems regarding its limitations with range and payload (as a compromise for stealth). Thus , in 1979, "BLACK PROJECT" , which involved the R&D of top secret stealth programs, started to look for new bomber , much better, versatile , advanced and have a larger payload (also nuclear) and increased range capability, was termed as the Advanced Technological Bomber (ATB).

This time, as per the requirements, the Northrop-Grumman Designs were selected in competition with Lockheed/Rockwell designs.

Based on the old , and scrapped designs of Mr. Northrop, design team started working upon the YB -49's blueprints. With latest and advanced CAD (Computer Aided Design) and presence of the composite material made the "FLYING WING" design possible and the previously encountered flight instability was counter-measured using advance on-board computers. In 1989, Northrop introduced B-2 "Spirit" heavy bomber with advance LO (Low Observable) features or stealth.But no one expected that it would take a decade to get this advance technology war tested.





In 1999, following massive uprising and hostile environment in Yugoslavia, USA sent its B-2 stealth bombers to invade and fragile the air defense network. B-2 was responsible for the 33% hits of the Serbian targets in the first eight weeks of US involvement in Kosovo War.


RECENT DEVELOPMENTS :-

With F-117 and B-2 becoming successful and popular world over their technology also became obsolete for USA who always like to have a edge in technology in war. The developments of anti-stealth defense systems as well as the maintainance cost and various trade-offs (compromises) on conventional functions of aircraft like range, speed, aerodynamics, countermeasure systems, payload, limited role in war and cost of production ... led to initiate the development of more mordern and advance projects in USAF both being awarded to Lockheed/Rockwell .. YF -22 now know as F-22 "RAPTOR" advance, air-superiority, multi-role stealth aircraft and X-35 , known as the latest F- 35 "JOINT STRIKE FIGHTER".








F-22 incorporates various new features of stealth , without setting any trade off with speed and conventional aircraft features, although payload still being a factor of concern. It uses advance radar and avionics systems to locate the target, and attain the "FIRST LOOK - FIRST SHOT - FIRST KILL" capability. Both F-22 and F-35 have the capability to obtain the information from various ground systems as well as even from the enemy locations. Incorporating AESA radar and surface fused sensors technology.




Unlike F-117 and B-2, F-22 and F-35 have the afterburners for dogfights and high speed scenarios. F-22 also exhibits THRUST VECTORING whereas F-35 for the first time after BAE - SEA HARRIER aircraft incorporates a VTOL (Vertical Take-Off and Landing) System.





On the other hand , now Russia, with its always new designs have introduced SU-47 "BERKUT" or "GOLDEN EAGLE" with the ideal stealth designs with the help of carbon-composites - Forward Swept Wings - and state of art avionics.



More advance researches are still going on now with various nations to get the hold of stealth technology, which have now chaged the face of the war limiting it to few days time giving hard precise hits on enemy without getting a scratch.

NEW ONGOING RESEARCH:-

Russian/India - PAK FA - FGFA and lot many more. We still will be seeing lots of advancements, limited, but still to come in the chapter of stealth systems.






(Stealth Technology, Working and Terms will be included in the upcoming articles)


CONCLUDED

Air to Air Missiles : An Introduction

Tuesday, February 16, 2010

At the time of outbreak of World War II, electronics was gaining momentum. Its role in war ended as radio equipment for communication and detection of enemy in a particular topography.The use of electronics in combat technologies increased only after World War II. Today, the military has electronic surveillance equipments like UAV’s, radars, jamming devices, GPS navigation systems, and precision weapons like guided missiles and smart bombs that are far more accurate than any other weapon. This article elucidates the technology behind air-launched anti-aircraft guided missiles with advanced guidance technologies and their basic design concepts.

Introduction:-

The use of electronics has increased after World War II. Today, military has electronic surveillance devices, jamming devices, GPS (Global positioning System) and precision weapons like guided missiles and smart bombs or GBUs (Guided Bomb Unit) which are more accurate in attacking their target then any other weapon.

Guided missiles are self-propelled air borne projectiles carrying explosive charge and guided in flight towards the target.

Classification:-

Missiles are broadly classified on the basis of:-

· Launch Environment Used

· Guidance Used

Launched Environment Used:

1) Air-launched Missiles

a)Air-to-Air Missile

b)Air-to-Ground Missile

2) Surface-launched Missiles

a) Surface-to-Air Missiles

b) Surface-to-Surface Missiles

Guidance Used:

1 Radar Command Guidance

2 Radio Command Guidance

3 Wire Guidance

4 Inertial Guidance

5 Astro Guidance

6 Terrain Comparison Guidance (TERCOM)

Air-Launched Anti-aircraft Missile:

The air-launched anti-aircraft missile is launched from an airborne aircraft to wipe out its target.

Various parts of this missile are:-

·

Rocket Motor - Provides thrust to the missile by burning solid propellant material.

Target-Seeker - Searches for the target.

Electronic Guidance Control (EGC) - Guides the missile.

Control Actuation - Adjust the fins on the instruction received from EGC.

Warhead - Explosive device which destroy the target.

Battery - Provides power to the missile onboard electronics.

Umbilical Cable - Connects the missile onboard electronics with the computer of the aircraft called as ‘avionics’.

Working:-

Before the launch, the pilot designates a target. The data goes to the missile guidance control. As soon as the missile is launched the target seeker is activated and it searches for the target. The rocket motor burns the solid propellant material which provides thrust to the missile. The wing of the missile provides the necessary lift and the electronic guidance control guides the missile towards the target.

Three types of guidance system are used in general:

Semi-active Radar Homing Guidance

Target has to be illuminated by a radar transmitter from parent radar. The reflected waves are received by the receiver in the nose of the aircraft.

Active Radar Homing Guidance

The missile carries it own target seeking radar. The inbuilt radar hunts for the target. This system is costlier and bulkier and is used in long range missiles also called as ‘beyond visual-range missile’ or BVR missile.

Infrared Homing Guidance

The infrared homing guidance system is mainly designed to destroy the target using infrared homing. It seeks infrared radiations available and are also called as ‘heat seeking’ missiles.

Infrared Tracking:-

The target image appears as bright and dark shining spots which indicate the hotter and colder regions of the target. This image is called as the ‘infrared signature’ of the target. The infrared sensor array is coupled with a mechanical scanning system which scans a larger section of the sky. It continuously moves reflectors and lens to feed light to the sensors.

The guidance control system figures out position of the target based on the fluctuations in the detected infrared light.

Guidance System:-

· The Target Seeker.

The infrared sensor that will respond to the wavelength of IR radiation from aircraft are placed in a circular matrix arrangement and grouped into four arrays. An array is one sector of circle.

· Positional Information

If the infrared image falls exactly on the centre of the nose of missile, all the arrays will get IR radiations with equal intensity. When signal from any one array is stronger than other it indicates target has changed the position.

· Speed Information

If target is moving from right to left, right array will receive the image which will generate a pulse. Then the left array will receive the image and will generate a pulse. Measuring the time interval between the two pulses and calculating it with pre-calibrated values speed of target can be known.

· Distance Information

The strength of the signal diminishes as the distance between the missile and target increases. So, measuring the signal strength and comparing it with pre-calibrated values distance of target is obtained.

After calculating speed, position, distance, EGC designates control to fin actuator. Fin actuators are used to actuate the fins to steer the missile.

Merits:

· Ready to fire missile

· Highly Precise

· Cost Effective

· Could be shoulder launched

Demerits:

· Low Range

· Get deflected by Flares

By - Vishal Bhatnagar

The Blackbird: An interesting story

Lockheed-Martin SR-71 Blackbird

(story by a USAF pilot of SR-71 Blackbird)

Interesting history lesson for those of you so inclined

In April 1986, following an attack on American soldiers in a Berlin disco, President Reagan ordered the bombing of Muammad Qaddafi's terrorist camps in Libya . My duty was to fly over Libya and take photos recording the damage our F-111's had inflicted.. Qaddafi had established a 'line of death,' a territorial marking across the Gulf of Sidra , swearing to shoot down any intruder that crossed the boundary. On the morning of April 15, I rocketed past the line at 2,125 mph.

I was piloting the SR-71 spy plane, the world's fastest jet, accompanied by a Marine Major (Walt), the aircraft's reconnaissance systems officer (RSO).We had crossed into Libya and were approaching our final turn over the bleak desert landscape when Walt informed me that he was receiving missile launch signals. I quickly increased our speed, calculating the time it would take for the weapons-most likely SA-2 and SA-4 surface-to-air missiles capable of Mach 5 - to reach our altitude. I estimated that we could beat the rocket-powered missiles to the turn and stayed our course, betting our lives on the plane's performance.

After several agonizingly long seconds, we made the turn and blasted toward the Mediterranean . 'You might want to pull it back,' Walt suggested. It was then that I noticed I still had the throttles full forward. The plane was flying a mile every 1.6 seconds, well above our Mach 3.2 limit. It was the fastest we would ever fly. I pulled the throttles to idle just south of Sicily , but we still overran the refueling tanker awaiting us over Gibraltar.

Scores of significant aircraft have been produced in the 100 years of flight, following the achievements of the Wright brothers, which we celebrate in December. Aircraft such as the Boeing 707, the F-86 Sabre Jet, and the P-51 Mustang are among the important machines that have flown our skies. But the SR-71, also known as the Blackbird, stands alone as a significant contributor to Cold War victory and as the fastest plane ever-and only 93 Air Force pilots ever steered the 'sled,' as we called our aircraft.

The SR-71 was the brainchild of Kelly Johnson, the famed Lockheed designer who created the P-38, the F-104 Starfighter, and the U-2. After the Soviets shot down Gary Powers' U-2 in 1960, Johnson began to develop an aircraft that would fly three miles higher and five times faster than the spy plane-and still be capable of photographing your license plate. However, flying at 2,000 mph would create intense heat on the aircraft's skin. Lockheed engineers used a titanium alloy to construct more than 90 percent of the SR-71, creating special tools and manufacturing procedures to hand-build each of the 40 planes. Special heat-resistant fuel, oil, and hydraulic fluids that would function at 85,000 feet and higher also had to be developed.

In 1962, the first Blackbird successfully flew, and in 1966, the same year I graduated from high school,the Air Force began flying operational SR-71 missions. I came to the program in 1983 with a sterling record and a recommendation from my commander, completing the weeklong interview and meeting Walt, my partner for the next four years He would ride four feet behind me, working all the cameras, radios, and electronic jamming equipment. I joked that if we were ever captured, he was the spy and I was just the driver. He told me to keep the pointyend forward..

We trained for a year, flying out of Beale AFB in California , Kadena Airbase in Okinawa , and RAF Mildenhall in England . On a typical training mission, we would take off near Sacramento , refuel over Nevada, accelerate into Montana , obtain high Mach over Colorado , turn right over New Mexico , speed across the Los Angeles Basin , run up the West Coast, turn right at Seattle , then return to Beale. Total flight time: two hours and 40 minutes.

One day, high above Arizona , we were monitoring the radio traffic of all the mortal airplanes below us. First, a Cessna pilot asked the air traffic controllers to check his ground speed. 'Ninety knots,' ATC replied. A Bonanza soon made the same request.'One-twenty on the ground,' was the reply. To our surprise, a navy F-18 came over the radio with a ground speed check. I knew exactly what he was doing. Of course, he had a ground speed indicator in his cockpit, but he wanted to let all the bug-smashers in the valley know what real speed was 'Dusty 52, we show you at 620 on the ground ' , ATC responded. The situation was too ripe. I heard the click of Walt's mike button in the rear seat. In his most innocent voice, Walt startled the controller by asking for a ground speed check from 81,000 feet, clearly above controlled airspace. In a cool, professional voice, the controller replied, ' Aspen 20, I show you at 1,982 knots on the ground.' We did not hear another transmission on that frequency all the way to the coast.

The Blackbird always showed us something new, each aircraft possessing its own unique personality. In time, we realized we were flying a national treasure. When we taxied out of our revetments for takeoff, people took notice. Traffic congregated near the airfield fences, because everyone wanted to see and hear the mighty SR-71 You could not be a part of this program and not come to love the airplane. Slowly, she revealed her secrets to us as we earned her trust. One moonless night, while flying a routine training mission over the Pacific, I wondered what the sky would look like from 84,000 feet if the cockpit lighting were dark. While heading home on a straight course, I slowly turned down all of the lighting, reducing the glare and revealing the night sky. Within seconds, I turned the lights back up, fearful that the jet would know and somehow punish me. But my desire to see the sky overruled my caution, I dimmed the lighting again. To my amazement, I saw a bright light outside my window. As my eyes adjusted to the view, I realized that the brilliance was the broad expanse of the Milky Way, now a gleaming stripe across the sky.

Where dark spaces in the sky had usually existed, there were now dense clusters of sparkling stars. Shooting stars flashed across the canvas every few seconds.. It was like a fireworks display with no sound.

I knew I had to get my eyes back on the instruments, and reluctantly I brought my attention back inside.. To my surprise, with the cockpit lighting still off, I could see every gauge, lit by starlight. In the plane's mirrors, I could see the eerie shine of my gold spacesuit incandescently illuminated in a celestial glow. I stole one last glance out the window. Despite our speed, we seemed still before the heavens, humbled in the radiance of a much greater power. For those few moments, I felt a part of something far more significant than anything we were doing in the plane. The sharp sound of Walt's voice on the radio brought me back to the tasks at hand as I prepared for our descent....

San Diego Aerospace Museum

The SR-71 was an expensive aircraft to operate. The most significant cost was tanker support, and in 1990, confronted with budget cutbacks, the Air Force retired the SR-71.

The SR-71 served six presidents, protecting America for a quarter of a century. Unbeknownst to most of the country, the plane flew over North Vietnam , Red China , North Korea , the Middle East , South Africa , Cuba , Nicaragua , Iran , Libya , and the Falkland Islands . On a weekly basis, the SR-71 kept watch over every Soviet nuclear submarine and mobile missile site, and all of their troop movements. It was a key factor in winning the Cold War.

I am proud to say I flew about 500 hours in this aircraft. I knew her well. She gave way to no plane, proudly dragging her sonic boom through enemy backyards with great impunity. She defeated every missile, outran every MiG, and always brought us home. In the first 100 years of manned flight, no aircraft was more remarkable.

The Blackbird had outrun nearly 4,000 missiles, not once taking a scratch from enemy fire.

On her final flight, the Blackbird , destined for the Smithsonian National Air and Space Museum, sped from Los Angeles to Washington in 64 minutes, averaging 2,145 mph and setting four speed records.


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