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I'm putting together a little self-actuating industrial society in a post-nuclear desert. I want the chief mode of transportation for their military to be helicopters, similar to those used in the Vietnam-era. However, I though it would be interesting if those copters communicated not via radio but using signal lights instead (think Aldis lamp).

The question is, given the technical knowledge and production capabilities needed to make a Vietnam era Huey helicopter (sans radio) for instance, how ludicrous an idea would it be to have a society running around in these helicopters without knowledge of the vacuum tube?

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If your society is working without [easy access to] electricity, it might be easier to signal with a heliograph. – Wingman4l7 Jan 8 at 3:28
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Could somebody who knows more about helicopters tell me whether you can build helicopters with steel, or do you need aluminium? Aluminium requires large amounts of electricity, and I strong suspect that any electricity using civilization would discover radio by accident. – Stig Hemmer Jan 8 at 9:26
    
@StigHemmer The idea to build any but the most primitive helicopters without a routine everyday command of electricity, and probably electronics, seems remote to me. Aluminum is totally secondary to that. Or am I too young? Did the helicopters in the 60s fly completely mechanically/hydraulically? – Peter A. Schneider Jan 8 at 10:25
    
Well, the wikipedia article about the UH-1/Huey speaks of flight controls only in mechanical/hydraulical terms. They did have auxillary generators though. – Peter A. Schneider Jan 8 at 10:40
    
Do you really need for them to not have radio, or do you simply want for them to not use radio to communicate while in the air? Maintaining radio silence during certain operations is standard military procedure, and it might be easier to make the conditions such that you really want to maintain radio silence rather than to not have radio available at all. Now that this question has several answers, if you want to go down this route, it might be best to ask a new question about how to best explain the desire to maintain total radio silence while flying a helicopter... – Michael Kjörling Jan 8 at 19:56
up vote 4 down vote accepted

Helicopters with Vietnam-era performance like the Huey require turbine engines to get enough power-to-weight for air cav operations.

By comparison, Korean-War-era helicopters like the Sioux with piston engines could carry just an observer or a couple of casualties. The same applies to WWII-era helicopters like the R-4, only more so.

Turbines are difficult. Bearings, turbine blades, lots of highly stressed parts. A simple radio transmitter is much easier if they are recreating technology with the help of a decent encyclopedia. That means your post-apocalyptic scenario needs a widespread destruction of basic scientific knowledge. Then you can bring random factors into it -- a good location for a hydropower plant kindles interest in turbines, or something like that.

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Helicopters and radio are two technologies that effectively have no relation to each other, other than the fact that any civilization that is sufficiently good at mathematics and scientifically-minded thinking to discover one of them will probably discover the other one within a reasonable time frame, say 50-100 years.

In reality, radios preceded helicopters by about 30 years (the first functioning radio transmitters date from the late 1890's and the first functioning helicopters from the late 1920's, although there were some semi-successful attempts as early as 1907, not long after the Wright Brothers' demonstration of a working airplane), but the order could just as easily have been reversed. Indeed, the internal combustion engine (including the electric spark plugs that drive it), probably the main technological component of a helicopter, predates not just Hertz's and Marconi's work on radio but even Maxwell's equations (discovered in 1865), which were the theoretical development from which the idea of radio waves and their possible use for communication later arose.

To summarize, it seems very easy to imagine a fictional human civilization in which the laws of electricity and magnetism, and their uses for radio communication, are discovered at least several decades after functional and reasonably well-performing airplanes and helicopters have been built. (Incidentally, if you're planning to use only helicopters for your story, you may want to explain what it is about your post-nuclear society that makes airplanes unfeasible, since generally speaking they are both easier to invent and safer and more practical than helicopters as a means of transportation).

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"Post-nuclear" offers an extremely convenient way of avoiding a whole manner of inconsistencies such as the "'copters but no planes" dilemma. Assuming the society are indeed "survivors" of a previous nuclear-level civilisation (and that all absent technology is simply lost technology), one simply needs a helicopter wreck for inspiration and have no plane wreckage in the area. A practicality-driven survivor society wouldn't necessarily have the creative time to dream up an alternative to a perfectly functional method of transport. – I Stanley Jan 8 at 14:41
    
Didn't DaVinci invent the/a helicopter? – Wayne Werner Jan 8 at 14:59
    
Lighter-than-air craft such as dirigibles are even simpler than airplanes. – Steve V. Jan 8 at 20:41
    
@WayneWerner Da Vinci came up with designs for an ornithopter (a machine that flies like a bird, by flapping its wings) but he never created a working model because the state of the art in materials science in his day was not advanced enough to create something with sufficient lift-to-weight ratio to get off the ground carrying a human being. (It can be done today, but it's still pretty impractical compared to airplanes and helicopters. Flapping wings work well for little things like birds and bugs, but the physics involved don't scale up well.) – Mason Wheeler Jan 8 at 21:01

Not terribly so.

The main requirements to manufacture a helicopter would be metallurgy, machining, and aeronautics. If you were willing to go without running lights, and even without a starter motor (after all, airplane propellers were originally hand-started), it might not even need an electrical system -- especially if you're willing to fly by the seat of your pants, without avionics. Igniting the fuel could be done mechanically.

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You don't even need fly by the seat of your pants. An altimeter is simply a barometer, and speed can be found using a pitot tube. – Aron Jan 8 at 4:31
    
@Aron: Yeah, not sure why I said that -- even an attitude indicator is just a weighted ball in some fluid (I think). – Wingman4l7 Jan 8 at 4:35
    
I think you mean the artificial horizon. – Aron Jan 8 at 4:36
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Oh...attitude... Thought you said altitude. Stupid word choices in aviation... – Aron Jan 8 at 4:43
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You don't need much to pilot a helicopter, as long as you can build the dang thing. – Wayne Werner Jan 8 at 17:45

The Dragonfly DF1 could operate with no electrical system at all if it weren't for FAA regulations. You would need a hand-powered fuel pump to start it but it's not needed in flight. I find it hard to picture making the metals or the fuel in a civilization that didn't know about radio, though--monopropellants (it uses 70% H2O2) are awfully nasty beasts if you're not very careful about purity.

On the other hand, if your objective is to avoid detection by electromagnetic emission this becomes a good solution.

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For the curious, see gizmag.com/dragonfly-df1-helicopter/14539 – Mawg Jan 8 at 9:22

Do you mean like this?

enter image description here

The Da Vinci Aerial Screw.

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@BrianMcCann I think you are missing the point. The Da Vinci Screw already has most of the characteristics of the modern helicopter. Yes there are some major technological details to be worked out, such as a swash plate, tail rotor and a light weight engine. But all of that was just mechanics. Radio involved a string of scientific discoveries (people wouldn't even think in terms of electrical current without discovering electricity). – Aron Jan 8 at 3:02
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@AmaniKilumanga please refer to my previous comment about missing the point. – Aron Jan 8 at 7:10
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@AmaniKilumanga okay. To put it into words you understand. "It's more a helicopter than it is a radio". – Aron Jan 8 at 7:20
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@AmaniKilumanga If you're not trolling, I think he means that you could start with the Da Vinci Screw, and arrive at a helicopter in a reasonable number of steps, especially if you had stuff like internal combustion. While it's not a helicopter, it is pretty close, and if Da Vinci had a few more theories he could have evolved it into a helicopter very easily. – AndyD273 Jan 8 at 14:16

how ludicrous an idea would it be to have a society running around in these helicopters without knowledge of the vacuum tube?

Very easy, very early discovery of semiconductors (empirical, because you need advanced quantum theory otherwise) and there is no need to develop vacuum tubes. This is actually rather easy in post apocalypse world, if (say) 19th century level society has access to some pre-war technical literature. But that is not what you wanted to ask.

To miss the (re)development of radio, you need something else - working, reliable helicopter requires rather advanced and precise metallurgy, which presupposes big industrial and scientific base, and it's difficult to see how they would miss electromagnetic waves. Why a crude autogyro or even basic helicopter could have been build with 19th century technology, it would be ridiculously dangerous.

Instead, you might posit some external factor that makes radio communication impractical - perhaps a continuous electromagnetic storm that overwhelms any reasonably powerful radio communication. Perhaps caused by disappearing Earth magnetic field (geomagnetic reversal might be actually overdue by now) coupled with continuous solar flares. If your first experiments with radio waves show there is a lot of background static, the technology would not go along this path, since there is little practical use. Shielded coax cables will be still used for ground based communication, but light pulses will be the norm for distant messaging. Though, given reasonable advances in technology, the light pulses will be modulated for voice transmission.

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