KANSAS CITY, Mo. (TNS) — Imagine you order a new toaster from Amazon. Instead of one of those dark blue electric vans rolling up your driveway, a four-propeller drone zips to your front door just hours later, drops your package and disappears back into the sky.

That’s the idea, anyway, with Amazon planning its Prime Air drone delivery service in the near future.

I’ve never understood why people don’t call out Big Tech for its constant overhyping and overpromising. For every iPhone smash success, there are vastly more Google Glass and Segway gigaflops. So I’ll believe it when I see it.

Why am I skeptical? The predictions of skies full of drones sound just like the promise of flying cars. Which — have you noticed? — we don’t have yet, despite 100 years of assurances that they’re just around the corner?

That’s because making anything fly is difficult, expensive and above all highly dangerous.

The ‘MODEL T OF THE AIR’

Automotive innovator Henry Ford set his designers to create “the Model T of the air” — the Ford Flivver — way back in the 1920s. It was just one of several proposed personal aircraft of the day, which Popular Science Monthly touted breathlessly as the next inevitable step in travel: “With inventors producing foolproof, nonsmashable aircraft, experts say we’ll all fly our own machines soon.”

I don’t know who those prophets were a century ago, but here in the actual future, our experts are pretty sure that until some unforeseen technological revolution changes everything we know about getting off the ground, flying cars aren’t remotely feasible.

Do we already have the technology? In theory, yes. Mankind has invented a few basic ways to fly:

• Airplanes, with wings and an engine to achieve thrust and lift.
• Rotorcraft, as in helicopters and drones, using propellers to push against the atmosphere.
• Lighter-than-air craft with large bladders of hot air or a gas such as hydrogen.
• Rockets that achieve liftoff with jet propulsion.

We can rule those last two out instantly for mass transit or delivery. Balloons and dirigibles are huge, hard to control precisely and slow. They’re not suitable for delivering us to work and school, or packages to our stoops.

And despite Elon Musk’s laughable suggestion to zoom passengers from New York to Delhi on suborbital rockets, the vast amounts of energy those require for terrestrial air travel or shipping — along with the catastrophically high failure rates of rockets in general — make the Cybertruck look like a good idea.

PHYSICS, MAINTENANCE CHALLENGES

So that leaves us with airplanes and helicopters for our flying cars, which are called “personal air vehicles” in the industry. There are already several companies marketing them. They all have the same problems: You can’t overrule the laws of physics. What makes a good road vehicle — speed, capacity, long range — isn’t what makes a good aircraft, which is lightness above all. Maintenance is also a huge, crucial issue. If you lose part of a bumper when someone sideswipes your SUV, you can usually still drive home safely. If you get into a fender-bender in your flying car, that dent could have fatal aerodynamic effects in the air. And let’s be honest about some of the hoopties we regularly see on the highways: Can you imagine trusting your fellow pilots to keep their vehicles flight-safe?

Existing airplane-style models require tons of runway space to take off and land. When in street mode, something has to be done with the wings, and keeping the vehicles at an air-worthy weight means they can’t perform anything like a standard car on the road.

The helicopter types maneuver with a great deal more precision. That makes them more suited to personal travel and deliveries. But when winged airplanes malfunction, they can often glide to a safe landing (assuming there’s enough real estate around). Helicopters have many more moving parts to keep in working order, and fewer options when they lose power. One commercial airline pilot I know refuses to step into a helicopter under any circumstances. I trust his judgment.

Helicopters and drones also share a challenge that’s so far insurmountable: Propellers are incredibly loud. If you’ve ever been around a drone, you know even the small ones sound like a leaf blower. As they grow larger and more powerful, so does the noise. Yes, there are proposed technological improvements such as ring-shaped “toroidal” propellers, which are supposedly quieter — but they are much more expensive and complex to manufacture than traditional propellers, and their efficiency and quiet are questionable in the real world. There’s a reason they haven’t caught on.

Even if you think the idea is cool, I don’t think most of us would enjoy a string of drones buzzsawing over our houses all day. The NIMBYism will be high if they materialize, and calls for restricting them will be loud at city halls across the country. Until engineers invent “Star Wars”-like antigravity and force field technology to keep small aircraft silent and safe from collision, I don’t believe we’re ready for widespread individual flight.

TRAFFIC IN THE AIRWAVES

There’s an even bigger obstacle facing both flying cars and delivery drones: air traffic. Kansas is still mourning the 67 people who died when an airplane from Wichita collided with a military helicopter earlier this year. That was at Reagan National Airport, with professional pilots operating under guidance from a control tower.

Americans own almost 300 million personal and commercial vehicles. Amazon delivered about 6 billion packages in the U.S. last year, according to estimates. Imagine just 1% of that traffic moving from the streets to the skies. That’s some 3 million personal air vehicles and 60 million drones in the air, carrying packages up to 5 pounds apiece.

Do you like those numbers? I don’t.

I’m not saying drone delivery is impossible. It’s not — and it’s already saving lives in Africa, where it’s carrying medical supplies to locations cut off from urban centers by rough terrain and roads. And we see how unmanned aircract have transformed the way we wage war all too efficiently.

Since Big Business never misses an opportunity to cut labor costs, executives around the world would love to fire as many truck drivers as possible. There’s no question more autonomous transport and delivery are in our future.

But are we ready for strings of noisy, intrusive drones swooping smartphones and cat toys to homes already well-served by a network of streets we pay a lot of tax money to maintain? That’s an idea still not ready for takeoff.