...stealth is a specific word used for aircraft that truly possess this capability for e.g, f22, 35, 117, J-20.
What 'stealth' really mean is that the low radar observability methods are applied in
CONJUNCTION with aerodynamics exploitation at the
INITIAL design stage. All aircrafts are aerodynamically exploitative, meaning they know how manipulate the principles that Bernoulli formalized to make flight possible. But EM radiation analyses from these complex bodies have been a recent practice starting with Ufimtsev during the Cold War, and one that the Soviets (tragically) ignored and dismissed as mere scientific curiosity.
So the most we can do for the current 'non-stealth' designs are opportunistic RCS reduction methods in areas of the aircraft that would not produce adverse aerodynamic forces. Those opportunistic RCS reduction methods are absorbers at leading edges, a conductive or 'non-EM permissible' canopy, external store enclosures, and/or reduction of communication, navigation, and identification (CNI) antennas that so much festoons these famous aircrafts.
I will say this without trespassing the 'classified' info line: Based upon what we found in isolated EM anechoic chamber testings, and the US have plenty of airframes to test, those four opportunistic RCS reduction methods works for most '4th gen' fighters out there at reducing effective detection distance by about 1/4 of whatever each '4th gen' fighter was before these modeling/predicting testing.
The engineering degree of difficulty in rising level is:
- Absorber
- Canopy
- CNI antenna reduction
- External store enclosures
A lot of people think that CNI antenna reduction is easy but it actually is not. The location of CNI antennas are not arbitrary based upon their utility because the aircraft's body itself can block these antenna's radiation pattern, making communication and navigation difficult. GPS receiver antennas should be topside, correct? Conformal antennas have different radiation pattern than blade antennas, which is usually omnidirectional, so in order to have effective CNI capability in moving to conformal arrays, there must be an increase in antenna quantity to capture as much of the aspect angles as possible.
Here is an example...
The F-22 have been described as an 'antenna farm' but one would not know it just by visual alone. The CNI antennas' cumulative EM radiation effects not when they are in use but when the aircraft is under radar bombardment is just another contributorship towards the final RCS value. Removing a couple blades and installing four or more conformals would require you to strip the aircraft down to the frame, study the most optimum locations that would not interfere with fuel storage, hydraulics components, structural supports, and so on, and you can only hope to find a location for your new conformal antenna. Then comes wiring.
Now convince the Ministry of Defence to: 'Show me the money....!!!'