STEALTH TECHNOLOGY:STEALTH TECHNOLOGY:A REVEALINGA REVEALING

An investigative study on stealth technology.An investigative study on stealth technology.

What is it?• RADAR to detect position of objects.

• Counter measures 1. ECM ( e.g. chaff cartridges) 2. Non ECM

• Avoiding detection and innovating deception .

• RCS reductions, acoustics, thermal and other EM emissions

Examples

• F 117

• B-2 Bomber

• F-22 Raptor( From YF 23 Platform)

• SR-71 Black bird

• HMS Helsingborg

How is it achieved.

• Absorbs radar waves or deflects to other directions.

• Minimizes heat and other emissions from engine and other spots.

• Makes difficult to detect except closely.

• Smooth edges maximum radio wave reflectors.

• The size of a target's image on radar is measured by RCS (σ )

• For a square flat plate of 1m2 area, σ=13982 m2 at 10 Ghz

Vehicle shape and structure

• Mainly plan form alignment.

• The leading edges of wing and tail surfaces set at same angles.

Vehicle structure (contd..)

• Use of re-entrant triangles behind skin.

• Distinctive serrations used in external airframes.

• Propulsion subsystem shaping.

• Now in research is fluidic nozzles for thrust vectoring.

Vehicle structure (contd..)

Radar Absorbing Materials (RAM)

• RAMs often as paints used to absorb RADAR signals.

• Iron ball paint, ferrite in polymer matrix used.

• The cockpit canopy coated with thin layer of indium tin oxide .

• Small cell foams painted or loaded with absorbing ink.

• MAGRAM

• R- Card

• Absorbing honeycomb

• Transparent RAM

RAMs (contd..)

Other fields

• Reducing RCS alone not enough.

• More difficulty is reducing the IR signature.

• Interest is near IR region. (shorter than 10 µm)

• Major IR emission sources.

1. Tailpipe region

2. Turbojets have EGT’s of 1000oC

3. Exhaust gas plume

4. Hot engine parts

5. Aircraft skin (frictional heating)

6. Reflected and reemitted sunlight.

IR Emission

IR Reduction

• Using surface paints

• Non circular tail pipe

• Emissions from hot parts screened by airframe.

• The plume mixed with cool air.

• IR best transmitted 2.5, 4 and 10 micron bands.

• IR outside window absorbed by CO2

• Passive IR target acquisition systems more used.

IR Reduction (contd…)

Electromagnetic emissions

• EM emissions other than IR .

• The greatest source is RADAR itself.

• Shutting down RADAR a solution having negative effects.

• Radio /radar altimeters and Doppler navigation systems.

• Use of inertial navigation , laser or millimetric wave system

• Other EM emissions 1. Radio communication

2. ECM exploited (passive listening)3. Composite materials radiating switching

transients

• Passive sensors (LPI radar in F-22 ), LOS communication, inertial navigation are used.

EM emissions (contd…)

Acoustics• Most important for submarine & ground

vehicles.• Rubber mountings, AIP system, slow

turning propellers etc.

Visibility

• Matte paint, gray paint in disruptive schemes , yehudi lights ( active camouflage).

How to counter.

• Background of stealth craft than craft shall be searched for.

• High flying aircraft with SLAR, FLIR etc are used.

• Same method advantageously used using satellite.

• Uninterrupted radio waves from stars mapped.

• Failure or fainter image suggests probability of stealthy craft.

• Advantages of using lethal SAM’s and remain undetected.

• Low frequency radar nullifies stealth from shape.

Stealth counter (contd….)

• Disadvantages of LFR

1. Wavelength unavailability

2. Inaccuracy

3. Size

• 1. Bistatic radars and

2. Using reflections from civilian radio transmitters.

gives better detection.

Stealth counter (contd….)

Conclusion.• Stealth technology developed a lot.

• Investment needed is very high.

• High chance of low cost gain.

• A lot learned about signature reduction and absorption.

• Useful for other projects.

• Success yet to be proved extensively.

For the time spared