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One of the most amazing fact I'd learned was that invisibility to radars was not mostly due to the absorbing material but rather a specific geometry of the plan

One of the most amazing fact I'd learned was that invisibility to radars was not mostly due to the absorbing material but rather a specific geometry of the plane! The materials certainly enhanced it but it was still like 25% or so contribution. Even more amazing fact was that this possibility was first discussed in a Russian research paper but that was never followed through because it was too complex to compute such shape and no one believed it would actually work. The folks at Stunkworks got hold of the paper, hired a mathematician and used computers to do the computation to actually find the shape that would have invisibility property to radars. No one in army at the time believed that some special shape can just become invisible to radar. They did the demo to army to prove it and landed their contract. Considering all these was in 1960s, its just amazing.

vlehto 9y ago
>because it was too complex to compute such shape and no one believed it would actually work I don't want to put down your enthusiasm, but this is not very exact info. Stealth design never makes the plane invisible, it just increases the detection distance or the power requirement of the radar. You get relatively long way by simply avoiding corner reflectors. There are rumors that Avro Vulcan used to disappear from friendly radars accidentally just because of that. One of the features that increases stealth is the radar. Because radars tend to show on radar. SR-71 had "side looking radar" which might have been optimized not to show the array towards any hostile ground stations.
- engi_nerd 9y ago
  Those side looking radars were primarily used for gathering imagery through synthetic aperture radar mapping.
mikeash 9y ago
Unfortunately they didn't quite count on the radar reflectivity of the exhaust plume, which apparently made it a pretty big target in the end: https://www.globalsecurity.org/intell/systems/sr-71.htm https://www.globalsecurity.org/intell/systems/sr-71.htm

vlehto 9y ago

>because it was too complex to compute such shape and no one believed it would actually work I don't want to put down your enthusiasm, but this is not very exact info. Stealth design never makes the plane invisible, it just increases the detection distance or the power requirement of the radar. You get relatively long way by simply avoiding corner reflectors. There are rumors that Avro Vulcan used to disappear from friendly radars accidentally just because of that. One of the features that increases stealth is the radar. Because radars tend to show on radar. SR-71 had "side looking radar" which might have been optimized not to show the array towards any hostile ground stations.

engi_nerd 9y ago
Those side looking radars were primarily used for gathering imagery through synthetic aperture radar mapping.

mikeash 9y ago

Unfortunately they didn't quite count on the radar reflectivity of the exhaust plume, which apparently made it a pretty big target in the end: https://www.globalsecurity.org/intell/systems/sr-71.htm https://www.globalsecurity.org/intell/systems/sr-71.htm