The history of vertical flight is fascinating, largely because finding ways to go straight up in the air was historically nearly impossible and remains complicated, difficult to achieve and riskier than fixed-wing flight. So, why do people want to do it? Two reasons. For one, it’s practical. There are missions that only an aircraft capable of vertical flight can accomplish. Just try plucking a stranded hiker with a broken ankle off of a mountain top with a Cessna 172. The second thing is, it’s amazing. The idea of having freedom of movement in every direction while being able to stop the action right where you are is intoxicating. You just can’t get that with a conventional airplane.
Back to the “nearly impossible” part. If you think about the jet pack, you have the basic idea of what people looking up in the air at birds for millennia wanted to do—well, minus the screeching din. But that was really hard to accomplish, so people turned to fixed wings not as a superior means to get what they wanted but as a way to get up in the air at all, while still having some control over the flight path, as you don’t with balloons.
And the ways that people devised for getting to vertical flight were ideas that seemed completely nuts. “I know, let’s strap small rockets to someone’s back and fly around.” Who, I wonder, would have said, “A rocket backpack? Great idea!” Surely it wasn’t the test pilot who would be strapping that contraption on. On second thought (and knowing more than a few test pilots), it was probably the test pilot who gave a big grinning double thumbs up to the idea.
What vertical flight is, exactly, isn’t intuitive. It’s clear that it means going up in the vertical plane without the need to also be going forward, as helicopters can. A small plane might seem capable of vertical flight, but it isn’t. Imagine one sitting still in a very strong wind. When it’s blowing hard enough, the plane will rise up. But it’s not really flying vertically. It is, rather, moving forward relative to the air mass it’s in. True vertical flight has to be the capability to go upward at zero true forward airspeed. Conventional planes simply can’t do that.
Because wings only create lift by going forward, aircraft designers had to figure out different ways to make vertical flight happen, sometimes by ditching the wings altogether and sometimes by working around their limitations. None of these were easy to figure out. And what made it even harder to solve them was that none of them, as previously mentioned, sounded the least bit sane at first (or second) blush. But over the decades, vertical flight visionaries have created a number of paths that have given us the ability to go straight up and perhaps even hover once we get there, something that remains a dream for all but a few lucky pilots flying some pretty exotic hardware (think F22 Raptor or V22 Osprey).
Here are the major approaches to vertical flight that people have taken over the years.
We don’t often think of balloons when we think of vertical lift, but they’re actually really good at that. The thing they don’t bring to the ballgame, being not winged craft at all but objects that are lighter than air, is controllability, at least any significant amount of it.
Blimps and airships are better, but again, they’re floating much more than flying, so for the purposes of this discussion, we’ll ignore them…no disrespect intended.
Now we’re talking. The helicopter largely defines what we think of as vertical lift, and its development was contemporaneous to that of fixed-wing planes. Even Leonardo da Vinci dreamt of flight, and he didn’t create doodles of jets but of helicopters. He also liked the idea of parachutes; he was both a dreamer and a pragmatist.
The first helicopters, two of them, were built in 1907, less than five years after the Wrights took flight, but neither one was very practical. It would be another 32 years before useful helicopters took to the skies. That was when Igor Sikorsky flew his V-300. Within a decade, helicopters were ubiquitous.
The reason for the long gestation period compared to fixed-wing planes is that helicopter flight is really complicated, and finding ways to make stable, controllable flight possible was a vexing process. Helicopters have come a long way since and today dominate the vertical flight segment.
The fastest-production ones can fly at close to 250 knots. Still, helicopters, with their mechanically complex rotor blade systems (among other complexities), limited max forward speed and difficult-to-master flight controls, might make the helicopter an endangered species, though probably no time soon. And it’s more likely that helicopter technology will be incorporated into all new machines down the line, as you’ll see below.
VECTORED-THRUST VERTICAL FLIGHT
There are a few military jets that vector their thrust to achieve vertical flight. The Hawker Siddeley/British Aerospace/McDonnell Douglas Harrier jet is the most famous. In fact, it almost needs its own category of vertical lift because for a few decades, that is, before the arrival of the Lockheed-Martin F-35B, it was the only successful vertical takeoff and landing (V-STOL) jet.
Vectored thrust jets redirect their thrust, which normally goes straight back, downward. Though the mechanism is complex, the theory is pretty straightforward.
The engine’s thrust goes from pushing the craft forward to one pushing things upward. It’s really a simplified version of what a helicopter does, except with jet exhaust instead of with rotor blades.
There are huge downsides to doing this, including noise. Instead of the jet flying away from you with engines roaring, the Harrier puts out 125 dB from a distance of 100 feet. The F-35B is plenty noisy, as well, and the military branches here and abroad that operate the jet have faced issues with airport neighbors being subjected to noise “as loud as a vacuum cleaner 3 feet away.” And unlike other supersonic jets, which are also very loud, V-STOL jets hang around in one place at high power for extended periods of time.
JETPACKS AND ROCKET PACKS
Jetpacks also use vectored thrust to go vertical and then to control their flight path. The idea is simple. A person straps the jet pack on and then, using vectored thrust of the rockets on their back, goes up and forward, and even hovers. If it sounds awesome, we agree. If it sounds terribly risky, agreed again. (But have we mentioned the “awesome” part?)
Real working versions of these sci-fi inspired devices have been on the world stage for 60 years now, ever since (arguably) the first one, manufactured by Bell, started showing off its Rocket Belt in 1960. Before you knew it, James Bond himself (R.I.P., Sean Connery) was flying around in one. Well, a stunt double was, anyway.
And, as you probably know, jetpacks have been in the news lately, with the claimed sightings of jetpack flyers in the arrival corridor at LAX by several airline pilots, though informed thinking is that they weren’t jetpacks at all.
Despite the wow factor, jetpacks haven’t been very successful commercially. Yes, the hardware is proven. The problem is, they just aren’t practical for anything but aerial demonstrations, a.k.a., public relations stunts. They have very little endurance, there’s no safety backup should anything happen to the rockets (or jet engines…both have been used), and they’re loud.
There’s one jet pack that’s exceeded expectations. NASA astronauts use jetpacks on space walks. They have the advantage of zero gravity (well, very low gravity, anyway), nearly unlimited endurance and the blissful lack of noise in space, where, while no one can hear you scream, at least your jetpack is quiet while you’re trying.
A completely different kind of vertical flight for fixed-wing planes (or is it horizontal flight for rotorcraft?) is to take that wing and rotate it vertically. Sounds like a natural, so you’d think there’d be lots of tiltrotors out there. You’d be wrong. Only three types have ever flown: an experimental model that made a handful of flights in the mid-1950s, the Bell-Boeing V-22 Osprey and a couple of abandoned or in-process experimental programs.
While the Osprey might not be the first or only tiltrotor in the world, it’s by far the most successful one. Despite its overbudget woes and safety concerns, the Osprey is still an impressive machine.
While it’s in flight, it transitions from a huge, heavy-lift helicopter with two giant rotors to a boxy-looking but really fast turboprop (better than 300 knots). Bell was working on a smaller version, which started life as the XV-15. That model morphed into the Bell 609, which the company marketed as a business aircraft. After lots of spending but not great progress, Bell partnered with helicopter giant AgustaWestland and later sold the program outright to that European consortium. It has been in development for nearly 20 years now, so hopes are modest, but the idea still lives.
The advantages of tiltrotor technology are evident: Vertical flight with forward speeds are faster than helicopters. For military operations, this is the holy grail, allowing forces to get troops on the ground—the V-22 can carry up to 32 troops into a combat zone, unload them, and turn around and fly away at 300 knots.
Why aren’t there more tiltrotors? The complications of the technology, including the large size of the propeller/rotors, the weight and complexity of the drive train and the need for mechanical interconnection, so both blades stay powered even if one engine were to fail, make the technology difficult to engineer, expensive to develop and costly to build. This hasn’t stopped Uber and Hyundai from launching an urban air vehicle concept that makes use of eight electrically powered tilt rotors that deploy or stow strategically depending on the phase of flight. It’s just a concept, but we already want one.
Perhaps the most promising vertical flight technology is the multicopter, which, as drones large and small, are manufactured by the millions. The human-carrying kind are still emerging. What does a multicopter look like? We can’t really say for sure, as the number of configurations that have been floated is mind-boggling.
The idea is to take the concept of a helicopter and instead of one rotor or two, make it eight or 10 or 15, who’s counting? The vertically oriented propellers act as rotor blades (though without many of the capabilities of a helicopter’s blades, which can be sped up or slowed down, tilted forward or back, and/or be adjusted in pitch variably throughout the blades’ rotation).
Multicopters are at once far simpler than conventional rotorcraft, in that they don’t typically have complicated drive and control systems, and in some ways they are far more complicated, in that variable power is used in most multicopters to control direction of flight. Computers typically handle those adjustments, as controlling four or eight propellers simultaneously would be quite the challenge.
While there have been no successful commercially produced models at this point, with none that we know of on the horizon, there are dozens in the works, a handful of which have flown successfully.
The main problems are these: Because most of these Jetson-style craft will be electrically powered, given the current state of the battery art, even with one person aboard, the endurance of these machines is not long enough to be very practical. The other thing is this. Unlike helicopters, multicopters can’t autorotate, that is, descend under their blades even when they aren’t producing power. So, a total power loss equals an unthinkably terrible fate. Some manufacturers are planning to include whole-aircraft parachutes to address this concern, while others are installing redundant power sources and supplies to mitigate the hazard.
So, will multicopters emerge as the transporta- tion mode of the future? If you’re to believe the many companies developing aircraft to robotically fly people from one urban hotspot to the next quickly and quietly. Will it happen? At this point, your guess is as good as ours. PP