Are there any serious concepts for aircraft in a post-oil world?

Biofuels and synthetic fuels (produced from coal or natural gas) are perfectly viable for use in aircraft. Many demonstration flights have been made. The US military has been pleased with the performance of 50/50 mixes of biofuel and conventional fuel, but it costs a huge amount more than conventional oil-based fuel.

There’s no technical reason why we can’t replace oil for all applications. You can synthesize every component of crude oil in a lab — it would just be idiotically expensive. Even at today’s prices, crude oil is ridiculously cheap when you consider what it lets us do. Oil is cheaper than bottled water, for heaven’s sake. A gallon of water and two pounds of rice will let a person walk 25 miles in a day, but a gallon of gasoline will move two tons of steel 25 miles in twenty minutes. The challenge with replacing oil is that oil is absolutely amazing at what it does.

As oil gets more scarce, it will get more expensive, and that will eventually drive the mass adoption of alternative energy carrier options. There are lots of alternatives; they just all kind of suck. Every major infrastructure system causes its own unique problems, but we can’t know what problems will arise from oil’s replacement yet. Biofuels require massive amounts of land to be dedicated to energy production. Battery-based electric vehicles require a radically different “refueling” network from what we have today, along with having energy density problems. Hydrogen requires special (expensive) metallurgy for fuel systems, as well as having that whole “Hindenburg problem.”

Or maybe we’ll invent something else. I’m not optimistic, since the physics of harnessing energy are so well-understood, but one thing you should never do is bet against human ingenuity when there’s money on the line.

There are several serious alternatives. the problem is none are really ready for prime time.

Ryan mentioned biofuels. These are probably the most likely to be used in the near future. They provide similar energy densities to traditional jet fuel. In addition, most jet engines require little if any conversion to use. There are several downsides to biofuels such as high cost, they still release hydrocarbons and the fact that in some cases (not all), you are “burning food.”

In a similar vein to biofuels are the various methods of creating liquid fuel from gaseous fuel. Gas-to-Liquid fuels are very promising. The U.S. is estimated to have 100-year supply of natural gas products that can be used to created aviation fuels. GTL fuels provide reduced emissions and noise compared to kerosene based jet fuels. For more information and history, google the Fischer-Tropsch (F-T) process.

Hydrogen burning aircraft was brought up by Joseph and LNG by Jackson. While good in theory, the are a lot of negatives to be considered before building a hydrogen powered aircraft. First, to get the same amount of energy from hydrogen as kerosene, you need 4 times the volume. This greatly increases the wetted area of an aircraft and therefore drag. This can (possibly) be offset by using a non-traditional fuselage (flying wing?) or the fact that hydrogen weighs 1/3 as much as kerosene to provide the same energy. Hydrogen also has crash concerns associated with it. Hydrogen is flammable and explosive. Proposed concepts have the tanks near the passenger compartment, which would be extremely dangerous in a crash. Finally, hydrogen suffers from “boil off” A plane would have to be filled up immediately before flight, which could increase turn around time. Water condensation could also get into the fuel system and freeze the lines. LNG has similar issues to liquid hydrogen, but is half as bulky for the same energy.

Electric propulsion is a promising field. Electric motors can have 90% efficiency compared to the 20% for gasoline engines. Obviously, storing power is the major concern. Increased battery densities, beamed power, or a hydrogen fuel cell could help. Also, electric power does not benefit from increasing range as fuel is burned and the airplane gets lighter. Currently, there are several experimental G.A. aircraft with electric engines. Solar cells in the wings could recharge the batteries (on the ground, the wouldnt provide enough energy for in-flight operations unless the wings were very large - good Solar Impulse).

All my information comes from Aircraft Design: A Conceptual Approach, 5th ed. by Daniel P. Raymer

Frankly the problem is not oil..WE ARE NOT RUNNING OUT OF OIL.. we are finding more and more oil resources day by day.. but its different debate why its getting more and more expensive…lobby politics etc etc

The problem is emission and to save from raising oil costs (operational costs).

So lets think of saving than finding another resource.

In my view the ideal choice would be non fossil based resources. Solar / electric. I am not a big fan of biofuels as Ryan mentioned, it needs some resources , infrastructure to generate and sustain. we need to think long term. Cant screw up environment further..

So to answer this there have been some major initiatives all over the world.

1. NASA is leading an effort through its advanced concepts like hybrid wing body, double bubble, high aspect ration wing designs. The goal is to reduce emission, noise and fuel burn by 70% with respect to 2008 baseline levels. By 2030.
2. The 2011 Google cafe Green General aircraft challenge provided some proof that. Electric and hybrid aircraft can become reality and highly efficient.
3. Hybrid Aircraft: for large scale operations . Battery technology is not so advance to provide so much energy for take off like conventional fuel. So Hybrid aircraft is one good solution. Both Boeing and Airbus is working on it.
4. Also we can save a lot by changing how we operate the aircraft in more efficient way. moving from inefficient radar based operations to satellite - trajectory operation. NextGen and Sesar programs.

Here is the link to one of EADS AIRBUS concept