Flying Cars: Challenges In Design And Implementation

Whenever people find out that I’m involved in aerospace research, I get asked the question “Hey what do you think about flying cars?”. Invariably, my drawn out utterance of the word “Wellllllllll” serves as a precursor to me depressing the entire group with copious servings of aerodynamic reality.

Most of the current flying car designs are from startup companies with no history or focus in full-scale aviation. This isn’t necessarily a problem as many times a novel solution is discovered by firms outside of a given industry. Several companies have went with the “Let’s scale up a quad/octo/dodecacopter and stick a person inside it” method. Some others have taken the Star Wars pod racer look and gave it a more utilitarian slant. I will admit, several of these designs look pretty awesome. But unfortunately, the laws of physics don’t respond to awesome. It appears that many of the designs were made without consideration of aerodynamics, human factors, the atmosphere or the realities of being in a small flying vehicle.

Established aerospace companies such as Boeing, Cessna and Bell should theoretically be all over the flying car craze. Bell, as a large helicopter manufacturer is well versed in the techniques associated with vertical takeoff and landing. Cessna not only makes some of the fastest business jets available, but they are responsible for the best selling light aircraft type in history, the Cessna 172 Skyhawk. And as if you didn’t know, Boeing dominates the US commercial aircraft industry.

So far Bell has teamed with Uber to help accelerate the technological leaps required to enable the development of point-to-point, electric VTOL vehicles. This doesn’t mean they’re working on a prototype, it just means they’re helping guide a company that has little to no experience with anything that flies. Boeing for their part has had a few limited projects in the past to design flying cars but were canceled before ever getting to a flying prototype. Finally Cessna is not involved at all with any type of flying car construction or collaboration (at least not publicly).

What could be some of the reasons for wide-eyed startups to be chomping at the bit to build these vehicles while grizzled industry veterans keep a wary distance? Could it be that they’ve seen some things that the new companies haven’t yet? Do Bell, Boeing and Cessna have the thousand-regulation stare? In this piece, I’ll highlight some of the issues facing flying car designers and why it will probably take a lot longer than the public thinks to make them a safe and widespread mode of travel (notice I didn’t say impossible…just a longer wait).

Automation

There is a misconception today amongst the non-aviation public that all modern airplanes are flown by computers and the pilots just sit there eating chocolate cake and watching Top Gun on their tablets. The reality is that pilots still fly the airplane, there’s just a computer that stands as a gatekeeper to ensure that the aircraft stays within limitations. Even still there are regions of flight where human skill is faster and more accurate than the computers. Autopilots/FMS still have to have flight plans loaded in advance and these plans invariably change multiple times per flight. Pilots still monitor and adjust systems during flight. They regularly deal with failed systems, changing weather conditions, rerouting by ATC and a multitude of other tasks. The automation is there to help the pilots focus on things that the automation can’t do.

Yet when reading articles on flying cars, the answer to everything seems to be automation. How will these flying cars operate in congested cities with skyscrapers all around them? Automation. How will the vehicle transition from vertical to horizontal flight? Automation. What will happen if an engine fails or a blade gets thrown? Automation. No detailed discussion of thrust vectoring or ducted fans or control surfaces. No mentioning if the omnipotent automation will activate systems via pushrods, cables, hydraulics or electric servos. Just automation. This shows a disconnect with actual flying vehicle design and a mere concept.

In order for automation to work, it needs something to work with. And once it has something to work with, it has to know the static and dynamic stability margins for the vehicle to ensure it remains flyable (better hope the occupants understand weight and balance). It also has to know where all other vehicles are. And all obstructions. And all restricted airspace. And considering that the passenger-not-pilot won’t have any control, the automation also has to identify and handle any conceivable emergency situations. Given the amount of effort being put into self-driving cars that only operate in 2 dimensions, a 3 dimensional activity like flying will require automation that is going to be unlike anything ever coded.

Airspace

A few questions about how this system will integrate with the National Airspace System are probably in order: Will this system work with the upcoming ADS-B mandate in 2020 that most aircraft in the United States will have to conform to? Will there be an international standard to allow sales in other countries? Will the system communicate to local air traffic control? What about operations near airports? Will flying cars be banned within X miles of a runway, or will they be allowed to funnel into the airport parking lot via strictly monitored ingress routes? Will air traffic control need to monitor and separate commercial, private and military traffic from flying cars? What about military training routes? What about prohibited areas? How will flying cars integrate with news and medivac helicopters? What about sightseeing…at some point people are going to want to see the Grand Canyon, Niagara Falls and Yosemite from their own flying car. Will people on the ground have to hear the constant drone of, well, drones? What about Washington D.C.? The entire nation’s capital has a permanent TFR which, short of some landmark change in legislation would rule out any flying cars within its vast boundaries. The same issue arises at football and baseball games since they too are ensconced in TFRs during games. In all honesty, even if every technical issue is surmounted, just figuring out integration and getting FAA approval for the plan is going to take the wind out of the sails of all but the hardiest of companies.

Weather

So far most of the animations show the flying cars operating in clear skies or silhouetted against a fiery sunset. While it looks really nice, it is not the full story of where these vehicles are going to be operated. They have to consider that people are going to expect that they can jump in their flying car and head home even if it starts raining, snowing or blowing 30mph out of the northwest. Are these vehicles going to be certified for known ice? The fact that even the largest commercial airliners have to be serviced with de-icing fluid before takeoff demonstrates the seriousness of the threat. After takeoff, hot bleed air from their jet engines can be routed along the leading edge of the wing to melt ice off. Just as critical is the engine anti-ice (different than de-ice) system that keeps ice from collecting on the nacelle lip. Needless to say, a chunk of ice down the inlet of a jet engine spinning at several thousand RPM is not an ideal situation so they take steps to prevent it from happening in the first place.

Now imagine a small flying car with uninformed passengers riding in it on a cold night. They have no knowledge of the environment in which they’re in, no ability to affect the flight and no way to save themselves other than perhaps a land-now button or a ballistic recovery parachute. A flying car encountering ice will rapidly collect it on the windshield, flying surfaces and engine nacelles, robbing the rotors of thrust, disrupting smooth airflow over the wings and weighing the aircraft down. Since these aircraft are intended to be electric, its only means of protection is to draw a lot of current to heat the critical surfaces, or carry the extra weight of a fluid known as TKS that is pumped out of tiny holes to retard ice accumulation.

There are other weather threats besides ice. Most of the designs presented are not touting the use of aviation aluminum as the primary construction material. Thus we can assume that a composite such as carbon fiber will be used instead. While very strong for its weight, carbon fiber does not react well with electricity. In the event of lightning striking a flying car…and it will happen…the manufacturers must prove that no strike will damage the structure beyond airworthiness limits and just as importantly, that it will not disable any of the automatic flight systems. Exhaustive testing and shielding will be required before any design is certified. Some existing aircraft use lighting diverter bars on composite parts to give the current a path to follow. It is then able to follow these routes and discharge through static wicks rather than blow holes in structure. All parts of the airplane must have a conductive path to these wicks in order for them to function properly. Again these are the realities of the atmosphere in which we fly and why airplanes cost so much to design.

Passenger Comfort

I make it a point to ask people who have mentioned wanting to have a flying car if they have ever flown in a small plane before. The answer is invariably “No.” This is very telling as the fantasy of flight is sometimes more attractive than the reality. However, most of those same people have flown in commercial aircraft before and remember experiencing turbulence of some kind.

Turbulence can range from gentle rocking to quite literally bouncing people off the ceiling. Mind you, these are heavy aircraft with high wing loadings. They have a lot of inertia and they can still be thrown around like ragdolls in the right conditions. Small aircraft by obvious virtue of being lighter are affected to a greater degree than large aircraft. Imagine the effect of 5 foot waves on a cruise ship and then picture an inflatable raft in the same size waves and you get an idea of the large plane vs small plane dilemma.

I have personally been bounced around rather brusquely in small aircraft before. Friends of mine have hit their heads on the ceilings while wearing their seatbelt due to the severity of turbulence they’ve encountered. Since flying cars are going to be lighter than many general aviation aircraft, this does not bode well for the dyspeptic among travelers. Hot air, strong winds, wind tunnel effects near skyscrapers, outflow from rain showers, and even the wake from other vehicles can all be nauseating for the uninitiated. While manufacturers will probably try to say that computerized flight controls will smooth out the bumps, that’s going to be limited by the vehicle’s lack of inertia. All I can say is these flying cars better have a really good air conditioning system and a place to store used barf bags.

Preflight and General Safety

Before any aircraft takes to the sky, the flightcrew will perform a preflight inspection commonly referred to as a walkaround. This activity is standard for every airplane from Piper Cub all the way up to Airbus A380s. During this inspection, they are looking over the condition of the aircraft, verifying fluid levels and quantities and ensuring that there are no blatantly obvious deformations. So far, flying car concepts have intimated that a user just hops in, pushes a few buttons and flies away. While it may seem like a yeah-so-what detail, this has very important ramifications for who will actually have their butts in these machines. Are the sensors that detect buildings and other aircraft obscured by dirt or dead insects? Are the thrust vectoring vanes able to move freely? Did some idiot ram a shopping cart into my rear stabilizer?

Since a person can’t just pull over if there’s a problem, and more critically, there may not be time to land or deploy a parachute if certain items fail, inspecting a flying car before flight will be just as important as it is for real aircraft. This will require teaching non-pilots the importance of ensuring the airworthiness of their vehicle before every flight. Somehow I have a feeling that there will be a lot of lip service paid but very little attention. The allure of jumping in and flying away is just too strong.

As for general safety, some designs have serious issues with the placement of certain components. For example, when I see a 2 seat quadcopter with unprotected blades, I see a lawsuit because someone walked into a running rotor and was disfigured or killed. Therefore, regardless of the number or orientation of the blades, they would have to be recessed into ducts in order to keep people from getting maimed when entering, exiting or walking around the aircraft. This would also protect the blades from damage in the event of a bird strike (assuming none got sucked down into the duct) and allow for thrust vectoring without tilting the entire motor/rotor combination.

There should be a battery firewall feature since the risk of thermal runaway while remote, is still a possibility. Someone once suggested to me that the offending battery be jettisonable. I then mentioned that the people below who get crushed/burned by a 500lb lithium ion battery falling out of the sky would be pretty upset if they survived and he agreed the idea wouldn’t be socially acceptable.

Likewise, a land-now feature and ballistic recovery parachutes should be standard. If a passenger is not going to be allowed to be a pilot, they should at least have a way to save their own life if an emergency develops. With that in mind, occupant enclosures should have sufficient bracing and structural integrity to protect people in the event of a rollover or hard landing.

Building a flying car to a reduced power level is another good idea to help in the event of an engine failure (assuming multiple engines). Setting MTOW to correlate to 80% of total engine thrust gives the vehicle a margin in case of engine failure. If a powerplant takes an early retirement, the remaining engines can be brought up to 100%. This should be enough to help balance the reduction in power and prevent airborne rollover from the sudden loss of thrust in a given quadrant.

So those are some of the off-the-top-of-my-head observations about flying car design (we didn’t even bother talking about the motors and the energy density of chemical fuels versus batteries as that’s enough for another article). Mind you, these are considerations that anyone who builds an aircraft must incorporate into their design before cutting metal. Some people will complain and say “Well if you know so much why don’t you build one!”. To which I’ll respond “How do you know I’m not?”

In any case, I write this because I love aviation. I grew up involved in aviation and what I see is a collision course of people who have great imaginations and some wonderful ideas, but not enough grounding (punintentional) to know why some of those ideas are not wonderful. If flying cars are going to be commonplace and accepted, they have to be built right. People are not going to tolerate these things taking them to the wrong destinations, to say nothing of what would happen if they start falling out of the sky due to underestimating the laws of aerodynamics.

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About Christopher Williams
Co-Founder of Whelan & Williams Industries Inc. Sole proprietor of Liftlazy. Photographer, musician, writer, pilot and all around good guy to know.

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