adrian%cs.heriot-watt.ac.uk@NSFnet-Relay.AC.UK (Adrian Hurt) (07/27/89)
From: Adrian Hurt <adrian%cs.heriot-watt.ac.uk@NSFnet-Relay.AC.UK> A long time ago, when no-one (except the privileged few who were working on it) knew what the stealth aircraft looked like, or even if they existed, the theory (to us outsiders) was that to make the aircraft less visible to radar, you had to reduce the number of sharp edges and straight lines. Edges, straight lines and flat planes reflected radar well; smooth, curved surfaces didn't. Model firms produced kits of nice, smooth, curvy stealth aircraft. Now we see the real things, and both the fighter and the bomber have nothing but straight edges and flat plane surfaces! What's going on? Is it all a secret subversive plot to drive model builders nuts? Or to get the Russians to build something which they think is stealthy, but isn't really? "Keyboard? How quaint!" - M. Scott Adrian Hurt | JANET: adrian@uk.ac.hw.cs UUCP: ..!ukc!cs.hw.ac.uk!adrian | ARPA: adrian@cs.hw.ac.uk
nak@cbsck.att.com (Neil A Kirby) (07/28/89)
From: nak@cbsck.att.com (Neil A Kirby) In article <8634@cbnews.ATT.COM> adrian%cs.heriot-watt.ac.uk@NSFnet-Relay.AC.UK (Adrian Hurt) writes: > >A long time ago, when no-one (except the privileged few who were working on it) >knew what the stealth aircraft looked like, or even if they existed, the theory >(to us outsiders) was that to make the aircraft less visible to radar, you had >to reduce the number of sharp edges and straight lines. Edges, straight lines >and flat planes reflected radar well; smooth, curved surfaces didn't. Model >firms produced kits of nice, smooth, curvy stealth aircraft. > >Now we see the real things, and both the fighter and the bomber have nothing >but straight edges and flat plane surfaces! What's going on? Is it all a secret >subversive plot to drive model builders nuts? Or to get the Russians to build >something which they think is stealthy, but isn't really? A number of things here... 1)Sharp Edges: Those sharp edges have to be sharp edges TO A RADAR BEAM. While the edges look sharp to the eye and to the airflow (makes aero designers life a bit easier) they need not be sharp to radar. If the e and u (epsilon and mu for those for us with Greek-impaired keyboards) of the surface is like that of air, the radar won't see the surface as being different from air. It's a tad more complex than that, but the point is that radar sees things differently than does the eye. A black cast iron skillet looks to radar like a silver mirror does to the eye - a perfect reflector. For all we know, the visual edges of the aircraft are not the edges that a radar would see. 2)Flat vs Curved: This has been touched before. Take the example of a flat mirror and a mirrored sphere. Shine a light on both in an otherwise dark room. No matter how you fiddle with the sphere, you can always see a reflection, and so can anyone around you. The flat mirror reflects all of the light in only one direction (Snell's law) and if you aren't where the reflection is going, you can't see it. In the case of the F16, its rounded surfaces slip through the wind, but they reflect in all directions. In the case of the stealth units, radar from low on the horizon comes up, hits them, and reflects to the ground low to the horizon BEHIND the aircraft. Radar sites like to see radar reflected back at them. This is where the 'over the horizon backscatter radar' gets mentioned, but I'n not familiar enough with it to comment on it. Passive radar watchers can still get you if you have a wide array of receivers using the reflections caused by other active radar sites - but this takes lots of cash to do. It's easier to track the curved surface craft. The reflection point moves smoothly across the curved surface. In the case of small flat surfaces, you get a now you see it, now you don't, type of effect. Neil Kirby ...cbsck!nak