Posted on 07/31/2019 3:57:54 PM PDT by amorphous
While the vision of whisking passengers between rooftops in aircraft capable of vertical takeoff has largely solidified in the general shape of multiple rotors, some with airfoils and others without, the question of how to power this new kind of aircraft is less so. Some envision pure electric with lots of high-capacity batteries; others believe batteries alone will never be ready to produce the power required, and pitch hybrid designs—with a fossil-fueled engine producing electricity to assist the motors during some or all phases of flight.
However, one recent entrant in the field of some 150 such aircraft being developed stays out of that fray: The Skai eVTOL by Alakai Technologies promises to use a hydrogen fuel cell to generate electricity on the fly to power the six-rotor, five-place aircraft.
A tank of liquid hydrogen in the aircraft could propel it up to about 100 knots for up to 400 miles or four hours, carrying up to 1,000 pounds, according to Bruce Holmes, Ph.D., a director at Alakai. The electricity is produced via a hydrogen fuel cell—similar to the technology used to propel spacecraft like the Apollo ships that took the first men to the moon back in 1969.
A fuel cell is relatively simple: A fan propels gaseous hydrogen from the top of the liquid tank and mixes the elemental gas with ambient air through the fuel cell. The hydrogen passes through a platinum screen and in doing so loses an electron and produces electricity. The only emissions are water and heat. Holmes said because the hydrogen boils in typical ambient conditions, about 1 percent per day is lost—even with the best tankage technology available.
The resulting heat can be used for warming the vehicle. The cold liquid hydrogen can be used for cooling the cabin and is pumped beneath the six motors to help cool them.
Skai will use fuel cells from Hydrogenics, which is being acquired by a subsidiary of diesel-engine manufacturer Cummins.
The liquid hydrogen is stored on the aircraft at about 150 psi. Fueling infrastructure is not in place at airports, yet. However, Holmes envisions it being much like hydrogen fueling stations for cars cropping up in California and five other states as well as nine other countries, all of which are participating in a coordinated international effort to expand the use of hydrogen-powered electric propulsion. Refueling times will be as little as 10 minutes.
In addition to the six redundant rotor systems, Skai is slated to include an airframe parachute and will be designed to be piloted from the ground, piloted from the aircraft, and capable of autonomous operation. The company is proposing an aggressive certification plan that calls for a type certificate, perhaps as soon as the fourth quarter of 2020. Holmes expects military versions will be flying soon, and that experience, he believes, will help the FAA get comfortable with the vehicle’s simple design features—especially since, other than the rotors, about the only moving part is the fan in the fuel cell. Three conforming prototypes will be built for the certification process.
With hydrogen sourced through renewable resources such as hydropower, wind, and solar, and with the fuel cell 95 percent reusable and 99 percent recyclable, Holmes said the aircraft will be much more environmentally friendly than aircraft using batteries or fossil fuels. A fuel cell has a 20,000-hour life-cycle, he said.
Everyone survive the Hindenburg
Look it up and look at the video
It helps if you don’t coat the envelope or skin of the dirigible with a flammable cousin of thermite. Much of that fire on the skin is the skin itself going up.
Because somehow aircraft fuel that’s vaporized is not flammable?
There’s no smoking signs around every fuel point at my local airport. Same thing around hangars.
Challenger failed because the idiot NASA management launched when the engineers told them that the O-Rings were not rated for the temperature on launch day. Blaming it on the O-rings is like blaming your car’s manufacturer for your car breaking down when you put water in the tank instead of fuel.
Below is a short video from a AF contracted study from the 60's.
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Experimental Investigation of Liquid Hydrogen Hazards, 1960, Film Number 1
Indeed!
Would you let your kids drive around in it?
Quite right.
Texan friend insists your Aggie passage is a true story ;-)
Well known before launch. I know from Bechtal engineers involved in the testing of the solid fuel booster rockets.
As the age of robots approaches, cartoons seem especially predictive, with jokesters revealed as the unacknowledged legislators of mankind.
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