The flying car

Ullas Ponnadi

One of the most fascinating things we see and experience as children is watching sparrows and eagles flying up in the sky, often in formation, and sometimes all by themselves. Which child, or adult, does not fantasize about flying on their own, soaring and gliding up and down the sky and experiencing the beauty and the panoramic view of the world below while doing so?

From time immemorial, this fascination has led to several experiments and contraptions, be it sticking feathers and jumping from the top of a cliff, to invention of gliders that mimic a bird’s motion, to the first aircraft, to the more modern day Jetpack, a controlled rocket that can, using the principles of Newton’s third law of motion, propel one into the sky, and is intended to provide a very personalized, quick and controlled mode of safe transport!

Continuous improvements in aviation has led to all kinds of aerial vehicles, be it the Jumbo Jet that can now carry 500 or more passengers across continents, supersonic fighter jets that fly at great speeds and can escape radar detection, vertical takeoff helicopters and hovercrafts that can fly over all terrains.

At the same time, road transport research has also kept pace, from 12 cylinder engine cars that can reach 350 km per hour, to various forms of two and three wheelers and 1000 cc bikes, to Maglev trains that can literally fly above the tracks at great speeds and reach speeds of more than 450km per hour!

But the fantasy of a personal flying vehicle that one can fly with ease had still eluded human dreams for a very long time, until researchers came up with the bright idea of what is now called a flying car.

Flying car
In simple terms, this is a transport vehicle that looks like a regular car when it is on the road. It uses the same fuel as a premium car, unleaded gasoline (petrol). No special devices or contraptions are needed to fill up the fuel; it has a similar fuel tank. And it has a set of wheels and a steering wheel, just like a normal car. But this is a car that is designed to fly!

The physics of a flying car
So how can a normal car that can be driven on the road like a midsized sedan magically transform itself within seconds, and then in a short moment be airborne? Is it as simple as a helicopter lifting itself via the lift provided by its powerful rotors on top? Or is it like a regular aircraft where it has to taxi for a few hundred metres and reach good speed, so that it magically lifts into the sky? Or is it like a rocket that is propelled via its powerful solid fuel combustion, which results in a straight lift off into mighty heights?

Well, the last one is difficult and is not quite possible yet. This is also the principle behind Jetpack. The first one would be an amazing solution, since if we are stuck in a traffic jam, we can simply push a button that will turn the powerful rotor on top of the car and then we can zoom past the traffic block! But that is still not a reality.

The second scenario looks possible, but you cannot drive such a car to a regular airport. This requires commercial aviation license, and the airports are already crowded. Plus the car as we see on the road today is not designed to fly! So how do we design a solution?

The answer lies in designing the car’s framework and aerodynamics, where it can have foldable structures that can magically open and retreat, depending on whether you are in the air or on the road. Quite similar to a sparrow that can completely retract its wings while it is on the ground and is hopping around. Or a duck that is wading in the water and is too lazy to fly!

Since there are several such cars at various stages of development, for simplicity, we will take the example of one such Flying Car, called the Terrafugia. This car is being designed and manufactured by Terrafugia Inc and is going to be available with all the approvals in place by year 2016. Let us understand how this car can fly.

The Terrafugia looks almost like a regular car, when its wings are folded. It is five times lighter and four times stronger than a regular road car. One can drive this car to a small runway and here is where the transformation happens. The wings of the car-plane that are folded to the side of the car now open up. There is a propeller that is driven by the same engine that drives the car on the road. And in a short takeoff, the plane is up in the air and soaring like a bird!

So how does a plane really fly? As the plane moves forward, air flow around the wings create an upward force called lift. The lift increases as the plane gathers speed. The plane takes off once there’s enough lift to overtake gravity. When the plane’s in the air, thrust from the propeller pushes the plane forward.

Landing of the aircraft is a reversal of the above process. Instead of lift, a drag needs to be introduced by tilting the wings so that the wind resistance increases and slows down the flying body. Precise controls are then needed so that the flying body can touch the landing point in a smooth manner. Once that happens, the braking system of the vehicle has to come into efficient operations, so that the vehicle can stop in a smooth manner on the runway. We will not get into the details of these, since these mechanisms have evolved and are highly efficient for any flying vehicle these days.

The Terrafugia only needs 30 meters of runway space to take off, and less to land, and only about 30 seconds to extend or retract the wings. No commercial license is needed to use it. You will need a pilot’s license, and at least 20 hours in the air.

Once you have covered the destination, which can be a good 500 miles with one full fuel tank, the reverse happens. Fly to a small runway, land the aircraft, fold its wings, and there you go. Terrafugia is now back on the road as a car!

Role of physics simulation in the design of such a car
Any vehicle designed as above is a beautiful realization of the concepts of physics, mathematics, material modelling, and simulation. Terrafugia uses lighter weight motorcycle tyres instead of RV tyres, polycarbonate for the windshield and side windows, and basic airbags instead of advanced, dual stage airbags and do not include an electronic stability control system.

Let us understand how physics simulations help us design such a car
The car being designed has to be road worthy and also capable of flying. Which means that the material that is used should be light weight but strong. Aerodynamics has to be a critical aspect of such a design both on the road and in flight. Stress on the material is extremely important in flight. Thermal effect, electronic interference and electromagnetism are crucial in flight. Crash safety is crucial on the road. 4G manoeuvre is important in flight. All such parameters affect the choice of the composite material and the structural design of such a car.

Terrafugia uses a-composite material, which is essentially carbon composite; that has four times strength to weight ratio as compared to aluminium. This also means that it has five times less weight as compared to a standard road car! A quasi isotropic model is used for design so that strength is in all directions on the material and is not uni-directional. This is achieved by using a balanced mixture of fly direction while fabricating the structure. This is like the layered and strong plywood that we use for furniture these days in our homes. Finally, all of such designs are put through a very high quality simulation tool that tests the operations related to road and flight related parameters, safety parameters, crash worthiness of such a vehicle, its efficiency on the road and in flight, and any instability that can arise because of the dual mode transportation design on such a vehicle.

It is only after such extensive simulation that such a car enters the actual physical prototype building stage.

Research forward
Terrafugia is still a concept car and although it will be in the market next year, only limited quantities are available for purchase. In some sense, the inconvenience of finding a small airport with a runway to take off and land can be a deterrent for the purchase of such a vehicle. So is the cost of the vehicle, which is now about 2, 70,000 US Dollars, which is about 1.2 crores in Indian currency!

Terrafugia has a more traditional flying car concept coming up, called the TF-X. A hybrid-electric tilt-rotor aircraft with vertical takeoff abilities, with a plug-in hybrid power plant will allow such a car to take off vertically and also cover much larger distances while airborne.

There are also many other companies across the world working in the same space. These include cars like Aeromobil, Skycruiser, GF7, and SkyRunner. Most designs are at the concept or prototype stages and not yet ready for commercial production.

Technical specifications of Terrafugia
Here are the engineering specifications of the car, as taken from the Terrafugia site:

Performance Specifications:

Dimensions:

References
Following are links to articles and videos that were references to build the article above.
http://www.terrafugia.com/aircraft/transition#sthash.nOOVbxSn.dpuf
http://www.terrafugia.com/sites/default/files/TransitionSpecSheet-July2013.pdf
http://www.terrafugia.com/sites/default/files/TransitionSpecSheet-July2013.pdf
http://www.extremetech.com/extreme/184626-the-great-flying-car-dream-with-terrafugiatoyota-and-musk-on-board-have-their-time-finally-come
https://www.youtube.com/watch?v=bp2TWNpTA7s
http://en.wikipedia.org/wiki/Terrafugia_Transition
https://www.youtube.com/watch?v=bp2TWNpTA7s
http://www.gizmag.com/tag/flying-car/

The author is the Director and CTO of CREATNLRN, a venture focussing on creating an adaptive and interactive learning platform for high school students. He can be reached at uponnadi@gmail.com.