Ask the Captain: Are solar and biofuel jets coming soon?

Question: Hello, Captain Cox. With the completion of the fully solar powered round-the-world flight, does this mean that commercial jets will start incorporating solar energy at some point, at least partially?

— Submitted by reader J from Ottawa

Answer: The impressive flight of Solar Impulse 2 is a great step forward in alternative energy. It is unlikely commercial jets will begin to use solar power in the near future for several reasons. Solar Impulse 2 uses electric motors with power collected via solar panels. Currently there are no electrically powered jet engines, making the burning of jet fuel necessary for the needed thrust. All of the electric airplanes made so far use propellers and are dramatically slower than airline jets.

There is an industry commitment to utilize renewable fuels where possible, but the limitations of solar power make it more likely that the focus will be on biofuels. In the future we may see solar power being used in limited applications, but in the near future it is unlikely that commercial jets will find it economically justifiable.

Q: What is the future of biological fuels for aircraft?

— Andrea Granahan, Bodega, Calif.

A: Clearly, the use of biofuels is growing. As the price of these fuels decreases, they increasingly become a reasonable alternative, and their use will continue to expand.

Some form of biofuel could become the standard, and today’s Jet-A fuel would be used only where biofuel was unavailable.

Q: Washington state ferries had problems with biodiesel gelling in cold weather and plugging filters. It makes me wonder if biodiesel jet fuel is safe.

— Submitted via email

A: All jet fuel is tested for gelling. It is permitted to fly only after it is proven that it is safe in the flying environment (temperature and pressure).  Because this is a change from Jet-A fuel, it will be watched closely, but the testing has been extensive. I do not expect it to be a problem.

Q: Why isn't magnetic propulsion used instead of jet fuel to power the engines? 

— submitted via email

A: Magnetic propulsion has not been proved usable in such an application.

John Cox is a retired airline captain with US Airways and runs his own aviation safety consulting company, Safety Operating Systems.