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One simple reason - separate from the less fun possibilities involving defense procurement politics - is that the F117 was a transition technology. It proved t
by dcposch 3y ago
One simple reason - separate from the less fun possibilities involving defense procurement politics - is that the F117 was a transition technology.
It proved that super low radar signatures were possible.
The design used those big low poly triangles not because it’s optimal (aerodynamically, very much not!) but because of the limits of computer simulation at the time.
There’s a whole fascinating story about how the theory behind low observable was developed by a Soviet scientist, published, ignored there, then implemented here.
But computer technology quickly advanced to where low-poly aircraft made airworthy by brute force were no longer necessary. See the B2 Spirit, also a very special simulation derived shape but streamlined.
- teruakohatu 3y agoI had never considered that the Northrop YB-49 [1] might have ultimately worked if computer simulation had been available at the time. [1] https://en.wikipedia.org/wiki/Northrop_YB-49 https://en.wikipedia.org/wiki/Northrop_YB-49
- amethyst 3y agoAnother key requirement would have been computer-aided flight control systems. The only reason the B-2 can remain stable during maneuvers is thanks to its fly-by-wire system that translates the pilot's directions into control surface adjustments that achieve the desired results, and continually adjust those controls faster than the human pilot can react.
- blamazon 3y agoThe curious may find this wikipedia article a good jumping point down this rabbit hole: https://en.wikipedia.org/wiki/Relaxed_stability https://en.wikipedia.org/wiki/Relaxed_stability
- deleted 3y ago[deleted]
- mc32 3y agoMy favorite is the Grumman X-29: https://en.wikipedia.org/wiki/Grumman_X-29 https://en.wikipedia.org/wiki/Grumman_X-29 (It worked and they built two, I think) but ultimately a dead-end.
- micah94 3y agoSaw these fly over my high school back when I lived in Ohio (close to Wright Pat AFB)
- deleted 3y ago[deleted]
- nomel 3y ago> but because of the limits of computer simulation at the time Is this true? I thought the low poly was that a curve always has an area whose norma vector points back to radar, where flat pieces (and their intersections) only do if they're perpendicular to the radar. So, unless you're unlucky enough to have one plate shining pointing back at the radar, the reflection is completely broken up, with the small corners being too small to effectively reflect radar wavelengths back. Or, maybe I'm just having trouble visualizing a smooth surface geometry that also has few normals back? I naively assumed the "smooth" planes were enabled by better absorption materials, rather than geometry. Maybe a mix?
- justsomehnguy 3y agoYou have the advantage of seeing the successor tech. Nothing later of 117 uses the 'big poly' design, with B-2 as an immidiate successor and F-22/35 as a years later one. There would be always a question why did they chose a flying iron design, but efficency clearly states it's not needed.
- nomel 3y agoFor all we know, there could be low poly panels under an RF transparent skin. The "efficiency" could be purely aerodynamic.
- micah94 3y agoI memory about this is rusty, but there was A LOT going on with this stealth tech. I vaguely remember color being important, too. The earlier (and stealthier!) designs had a camouflage look rather than black. But this looked "ugly". So they changed it. I think advancements in materials made this moot.
- wrp 3y agoThe story on the color is actually simpler. They had put a lot of effort into designing a camouflage pattern for it and there was still some debate over the final design. The project manager from the Pentagon heard about it and said, "This thing is only going to fly at night, right? So just paint it black and be done with it."
- lumost 3y agoIt’s always confused me, under the radar absorbent material is stuff like engines, cockpits, and other reflective material. I’ve always wondered if under the smooth aerodynamic shape was a polygon frame covered in carbon fiber. That way the polygons could reflect radar away from the more reflective parts.
- analognoise 3y agoI've heard this but can't remember the name of the book! Does anyone know?
- johncalvinyoung 3y agoSkunk Works, by Ben Rich. It's a classic, and the origin of my own fascination with the A-12/SR-71, and the F-117.
- scns 3y ago> The design used those big low poly triangles not because it’s optimal (aerodynamically, very much not!) It was so bad, they called it The Hopeless Diamond. To keep it in the air instead of dropping like a stone, flight computers had to be developed. Another stepping stone for the B2 which faced similar challenges.