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Attach a *large* fan to a tank chassis or the bed of a truck. Park it in front of a high-value target. Point the fan upwards and turn it on when incoming is expected.
The bomb still lands and explodes, but, say, 100m beyond where it was meant to.
This thing ...
https://specular.co...gi-fan-wind-machine
... claims it can make a 60km/h wind, and it's only half a meter across. If we go to, say, a 2-meter diameter, we get sixteen times the surface area. I don't suppose the output wind speed increases linearly with that surface area, but that should get us enough puff to change the direction of something with wings but no engine. [pertinax, Nov 08 2023]
See the table entitled "Distance from Rotor Hub v Max Velocity"
https://jjryan.com....what-are-the-risks/
[pertinax, Nov 08 2023]
Jet Engine Thrust Hazards in the Airport Environment
https://www.boeing....20exhaust%20nozzle.
Helicopters pale in comparison [a1, Nov 08 2023]
re. "Postcard sized" wings, I was thinking more of this sort of thing ...
https://www.google....RAAgQMyhDegUIARC7AQ
[pertinax, Nov 09 2023]
Gliding bomb article with picture
https://en.defence-...rial_bomb-8481.html
[a1, Nov 09 2023]
Testing jet engines
https://m.youtube.com/watch?v=7DkxlNQDc1o
[a1, Nov 09 2023]
Testing NERVA
https://m.youtube.com/watch?v=j6gKFvPjGpQ
Better than a jet engine [a1, Nov 09 2023]
Early (earliest?) gliding bomb. Wings bigger than postcards.
https://en.wikipedi...iki/V-1_flying_bomb
If could hear the engine you were okay. When it cut off, that was the time to worry. [a1, Nov 09 2023]
Flip this over
https://arstechnica...cessful-test-of-its
Point thae exhaust at anything you want to blow away. [a1, Nov 10 2023]
[link]
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I wonder whether you could create a similar effect by running a grounded helicopter in reverse gear. Of course, a helicopter might not normally *have* a reverse gear, but I don't suppose that would discourage a half-baker. |
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Even if it didn't work in real life, it might make a good stunt for an action movie. |
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[+] for overall concept but I think you need something stronger |
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Put a jet aircraft engine in sturdy, aim-able mount. More powerful than a helicopter or souped up Vornado room fan. Thrust and exhaust speed could be varied during the run, making it harder for incoming bombs/guidance systems to compiensate. |
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I think a fan will allow the thing to get too close unless the fan is the size of a baseball field. Too non-directional. Not enough power. [+] for trying. |
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Top choice: A semi-automatic shotgun with a muzzle choke and/or a birdshot or FliteControl shell. Shorty shells for more ammo. Just nicking a rotary drone is usually catastrophic, while airfoil drones take a bit more. |
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I don’t know why UAF doesn’t provide at least one shotgun per unit for this purpose. |
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[a1] What do you do with the exhaust? More power up front means more in back, too. |
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Point the exhaust up, aimed at winged targets. Keep the inlet area clear - ingested FOD and ground personnel can ruin an engine. And ground personnel. |
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I don't think you're getting a very good handle on the concept of "glide" in guided munitions. Let's take the venerable GBU-15 glide bomb as an example. How "glide-y" is it? Terminal velocity is classified, but it's been around long enough that we know it's "high subsonic". So let's say 450mph. That's not soaring like an eagle at 40mph, it's "wings" are postcard sized. It's falling in a controllable manner considerably faster than a brick would. Directing a fan, even helicopter-size/power is going to represent nothing more than a light breeze at 300ft, and nothing major at 100ft. Certainly, you can't move enough air fast enough to overcome the significant momentum of the weapon. Plus, it's guided all the way, laser/TV/inertial etc. It's correcting all the way, plus it's likely vertical in the last phase of "flight". |
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Other challenges include: how often are you running this helicopter/jet? A big helicopter will burn 1200kg/hr of fuel, spinning the blades up is notoriously slow, so how are you deciding when to run/not run? Modern MBTs are routinely exceeding 60 tons, so adding another 30 or so tons of downward thrust is certainly on trend. It does make the tank somewhat hard on the ground however, also, helicopter blades and jet engines not ideal for sneaking about. |
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Still, I've often wondered what would happen if you fired an artillery shell into the back of a running afterburning jet engine. Does it destroy the engine? Does it sort of stop mid air and fall to the ground? Does it melt into a metal mist? |
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With more considered consideration, i think it would slow enough to fall out of the jet exhaust while still travelling very quickly and then obliterate the stand that you put the engine on. |
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// I've often wondered what would happen if you fired an artillery shell into the back of a running afterburning jet engine // |
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//how are you deciding when to run/not run?// |
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Suppose that the gliding bombs are used specifically in order to keep the bombing aircraft out of range of ground-based air defense. To maximize the range of the bomb, you must maximize the altitude of the bombing aircraft. Therefore, the bombing aircraft shows up on radar. |
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If the bomb has to travel a horizontal distance of, say, 50km at, 800km/h, that gives you almost four minutes' warning ... |
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//a jet aircraft engine in sturdy, aim-able mount// |
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So you have time for at least ten rousing choruses of "Hooray and up she rises!", as a precarious pylon is raised skyward. Inevitably, the assemblage at the top will fall to the ground repeatedly during its service life, which is why it is enclosed in a large, purpose-built zorb. |
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//it's likely vertical in the last phase of "flight"// |
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Therefore, like a big, goofy, gimbal-mounted Eye of Sauron, the jet engine (its fuel hose trailing back down to the ground) can direct its exhaust normally to the wing surface of even a vertically-falling bomb - for a very specific sense of "normally". |
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It always comes down to Zorbs around here, doesn't it? |
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I was thinking of just beefing up the kind of stands already used for testing jet engines (link). I also recall an an early nuclear rocket engine (the NERVA, I think) being tested in the ground - something like that would be even better than a jet engine. |
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Edit to add - found the NERVA film clip (linked). |
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Obviously possible to mount jet and rocket engines to hold in place for static firing. You don't have to gimbal or Zorb the whole assembly - just direct the wind with vanes. |
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The rocket engines and fans are awfully Jules Verne. Is that what you were going for, rather than something that would work? |
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I enjoyed visualizing the jet turbine from an F-16 on a huge angled, adjustable cannon mount that had a huge scoop-shaped exhaust diverter at the tail end. A platoon of lizard people are hauling on the arms of the thing to bring it into position to intercept a Rod From God, falling from orbit at 12,500 mph. Good luck. |
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//just direct the wind with vanes.// |
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I'm amused by the description of 20,000lb of superheated, supersonic jet exhaust as "wind". While "vanes" have been used to direct this "wind" - it's called vectored thrust, it's widely considered quite tricky. |
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// ... vectored thrust ... tricky // |
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yes it is, when you want to precisely control an aircraft or rocket. Precision isn't as important if you're just trying to blow something else off course. |
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Space-X had to upgrade Starship's launch pad flame diverter, maybe [pertinax] could dig onto their research. |
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//I think you need something stronger// |
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{Pours out a double measure of single malt, re-reads idea} |
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Ah yes, that's much better. |
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