In the military field we now had network-centric warfare. Coming up was the exploitation of space, quantum computing, fully autonomous systems, full electromagnetic spectrum dominance and global strike. In the digital battlefield everyone talks together. Target information is fed to central control where target tracks are determined from sensors, analysed and prioritised, then advised to the operators.
    Moving on Mick stated that stealth was now paramount. Ways of achieving stealth were then covered. Give-away radar emissions could be minimised by utilising memorised one-pulse bursts which might well go unnoticed or be misinterpreted by the enemy. This is known as Low Probability of Intercept Radar technology. Vehicle radar returns had to be minimised so appropriate shaping and absorbing treatments (known as RAM-Radar Absorbent Material) was fundamental and accurate manufacture and high quality finish with no discontinuities was essential, hence the structure is fitted inside the finished skin. Various radar-absorbent treatments could then be applied externally or built into the aircraft skins or structure. Stealth was very expensive to achieve and maintain so usually survivability, performance, weight and cost were traded to achieve an affordable requirement. However, the B-2 is said to have had no cap on stealth cost with the outcome that each bomber had a radar cross section (RCS) reported to be slightly less than a golf ball…but cost $800 million.
    Radar detection range is proportional to the fourth root of the RCS; reduce the RCS to reduce the detection range. For every 10 db reduction in aircraft RCS, detection range is halved so a 100 mile detection range becomes 12.5 miles for a 30 db reduction resulting in improved survivability rates.
To be avoided are: slots and cavities which enhance the radar return through internal reflection, points which scatter the radar signal resulting in some returns, circular protuberances round which the radar waves creep back to the sender, joint gaps, discontinuities and joints between different materials which all cause scatter.
    Aircraft configuration contributors to the RCS are: radome, radar antenna, cockpit and air intake cavities which all reflect, visible engine fans, external stores, wing leading edge direct reflection and trailing edge scatter, fins and tailplanes which need to be angled to avoid reflections, and engine nozzles. The objective is to ensure that the azimuth spikes in the radar reflection polar diagram are limited in number. Four is the minimum achievable on a bomber (B2) compared to a non stealth aircraft's plethora of spikes allowing detection from any angle. The stealthy fighter design will have a larger number of spikes due to retention of tailplanes and fins dictated by manoeuvre requirements. Each reflecting section is then carefully designed to minimize and control the direction of the spike.
    This spike direction control is achieved by careful shaping such as the forward fuselage section with flat planes and chines and by using radar absorbent material (RAM). On wings and tails all sweeps are aligned to give one spike, and fins are deleted or angled. (The B-2 has no fins using split ailerons for yaw control, but in the target area these are locked and differential thrust is used.) All panel edges and hinge lines are similarly aligned. Radomes are designed as filters allowing transmission of only the user's frequencies and the bulkheads are treated with RAM. Engines are buried and fed by long, smoothly curved, RAM-lined, 'S' shaped ducts which hide the fan and attenuate radar waves entering and reflecting within the intake. Boundary layer ducts and ramps are replaced by aerodynamic shaping of the fuselage sides ahead of the intake. Canopies are coated with gold or tungsten carbide to deflect the radar and prevent it entering and being reflected back by the cockpit cavity. Wing leading edges are made from Kevlar and act like radomes so the radar enters the edge cavities to be absorbed by RAM. Joints are filled with "butter"- plastic putty containing ferrous materials (eg iron filings). Pitot sensors are flush and all antennas are buried in the skins (surface mounted).
    Radar signature measurement cannot be scaled so all ground rig testing must be done using full size aircraft or components on a special range such as that at Warton. In hostile areas manoeuvring, especially in roll, is to be avoided because this would negate the carefully contrived azimuth spikes and display spikes from the upper of lower aircraft surfaces; approach to and exit from the target is straight and level, a test of pilot nerve. Interestingly there have so far been three generations of stealthy aircraft approximately a decade apart: F-117A of 1983, B-2 of 1993 and the F-22 of 2003.
    Thermal control is also necessary to prevent infra-red (IR) sensing. Outlets on the front fuselage are avoided, all hot exhausts being collected and dumped in the engine efflux which is itself mixed with cool air and possibly released, hidden from ground observers, over the top of the wing. Airframes can be treated to minimise IR emissivity, in fact, G-HAWK was used for such trials. The effects of kinetic heating and exhaust plumes cannot be accurately predicted so it's a case of build and test. However, the use of reheat in the target area is to be avoided.     
     This had been a concentrated, clear and completely absorbing lecture, especially enjoyed by the retired engineers amongst us who felt that they had been brought up to date in one easy lesson. The vote of thanks was given by Mick's old boss at Kingston, Ralph Hooper.