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After the Phantom Eye landed, it was slightly damaged when the landing gear hit the lakebed and broke

Boeing sent its Phantom Eye unmanned airborne system (UAS) on its first autonomous flight last week.

Boeing's Phantom Eye is a hydrogen-powered unmanned aerial vehicle (UAV) that is propeller-driven. The aircraft uses two 2.3 liter, four-cylinder engines capable of pushing 300 horsepower total and can loiter above a target for up to 10 days. Its main purpose is to gather information or conduct attack missions.

The Phantom Eye took off at 6:22 a.m. PST for a 28-minute flight. It reached an altitude of 4,080 feet and a speed of 62 knots. The flight took place June 1 at NASA's Dryden Flight Research Center at Edwards Air Force Base in California.

"This day ushers in a new era of persistent Intelligence, Surveillance and Reconnaisance (ISR) where an unmanned aircraft will remain on station for days at a time providing critical information and services," said Darryl Davis, president of Boeing Phantom Works. "This flight puts Boeing on a path to accomplish another aerospace first -- the capability of four days of unrefueled, autonomous flight."

After the Phantom Eye landed, it was slightly damaged when the landing gear hit the lakebed and broke. But overall, the flight was a success.

Previous to the June 1 flight, the Phantom Eye took part in a series of tests throughout April, such as navigation and control, pilot interface, and mission planning.

The Phantom Eye used for demonstration purposes has a 150-foot wingspan and can carry a 450-pound payload. It can fly up to 96 hours without needing to land, but Boeing is looking to make a new model in 2014 that can fly up to 240 hours without landing.




Source: Boeing



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RE: Hydrogen?
By geddarkstorm on 6/5/2012 3:08:24 PM , Rating: 2
I did find some numbers to compare the speed to some extent (we still don't know optimal cruise speed for sure). This test flight was 62 knots. A 180 horsepower Cessna 172GR has a cruise speed of 140 knots, and a 160 horsepower version goes 122 knots.

It seems this Phantom likely sacrifices speed for longevity by using hydrogen. Which is also more useful for continuous surveillance.


RE: Hydrogen?
By Gondor on 6/5/2012 5:11:11 PM , Rating: 2
Um, the article clearly states the engine provides 300 HP. That is 300 HP regardless of whether the engine runs of HC fuel, hydrogen or pink dinosaur poop - so if this airplane achieved its feat by maintaining cruise speed of 62 knots, it wasn't due to hydrogen but due to plane's construction.

Fuel might be able to get you closer to your target power requirement and may perform optimally at certain pwoer output but ultimately it's the plane (and its propellers) that determine how long it can stay up in the air. It's not the hydrogen/oxygen propulsion that makes the plane slow in comparison to your Cessna, it's the aircraft design ... and at the same time thatr's what keeps that thing in the air for so long, just like Rutan's thingy from decades ago.


RE: Hydrogen?
By HotFoot on 6/5/2012 5:24:30 PM , Rating: 2
Hydrogen stores much more energy per unit mass than gas/kerosene. However, it has much less for unit volume for any practical aircraft purpose - ie. no cryogenic storage and reasonable limits on pressurisation.

So, it's reasonable that hydrogen is more appropriate to vehicles with larger volumes - which means thick wings, fat fuselage, etc. These - esp. thick wings, are more appropriate for low-speed flight. I imagine this demonstrator is along the vein of "persistent surveillance" vehicles, so cruise/dash speed aren't so important.

It's interesting, though, that they went with IC engines instead of a fuel cell.


RE: Hydrogen?
By Jaybus on 6/6/2012 1:29:42 PM , Rating: 2
It is probably an efficiency issue. Since a higher mass of gas/kerosene would be required in order to provide the same amount of mechanical work, the aircraft would require greater lift, which equates to either higher airspeed or longer wings. Since a lower airspeed is desirable to reduce drag and so reduce the energy required to stay on target a given amount of time, and since long wings (more volume for fuel) are required in any case, hydrogen makes sense.

As for the fuel cell approach, I think that is likely a reliability issue. ICEs are simply more proven than fuel cells and probably considered less likely to fail.


RE: Hydrogen?
By geddarkstorm on 6/6/2012 11:41:07 AM , Rating: 2
The engine only gives 150 horsepower, but there are two. And horsepower doesn't tell you how fast a plane will fly, even if all other factors are the same. That's because torque and speed make up horsepower but have very different effects on a plane. High engine speed (high RPMs) is what gives a plane, well, speed.

Diesel engines are higher torque than gasoline engines. So, for the same horsepower a gasoline engine will have higher RPMs, and would make a plane faster than if it used diesel. Hence why diesel engines are rarer for aircraft (though used more on airships, which are lumbering and slow, with a lot of mass that needs to be moved). On the other hand, the slow speed but high torque of a diesel engine gives it higher specific fuel efficiency than gasoline. See how this works?

So, I was pondering on what performance these hydrogen engines would have. Since the UAV has such insane longevity in the air, we at least know the fuel efficiency of the engines should be enormous, but what is the actual speed? I compared the HP of these engines with known planes (which have far, far less fuel efficiency) and their speeds, just to try to get a sense of what the numbers actually mean. Though the test flight was 62 knots, it seems the top speed is meant to be something like 150 knots from what someone else said above. Even at 150 knots, that still makes the Phantom Eye far slower than other dual engine aircraft that use gasoline.

So what does that tell you about the hydrogen system? Very fuel efficient, but slow? Perfect for UAV surveillance; but would you necessarily want it in a consumer aircraft?

Also, if you look just above in this thread you see our talk about Rutan; the only known plan to go over four days. But it was also very specially constructed and one of a kind (and very weak, it could not even weather storms). This UAV is far more standard in design despite its "bomb" shape, and to be mass produced. Can't really compare it to Rutan.

Design has a critically important role as you point out, but the engines and fuel are -all part of the design-. Otherwise, why don't we design all our craft like Rutan to have 9 day longevity? Think about it a little more.


RE: Hydrogen?
By 91TTZ on 6/8/2012 10:45:01 AM , Rating: 2
quote:
Diesel engines are higher torque than gasoline engines. So, for the same horsepower a gasoline engine will have higher RPMs, and would make a plane faster than if it used diesel. Hence why diesel engines are rarer for aircraft (though used more on airships, which are lumbering and slow, with a lot of mass that needs to be moved).


If a diesel and a gas engine had no mass and had the same HP, they'd both be able to propel the plane the same speed. It doesn't matter which one has higher RPM, since maintaining a certain speed would require a certain amount of work, and HP is a unit of work.

In reality planes don't often us diesel engines because they're heavier than gasoline engines.

quote:
Also, if you look just above in this thread you see our talk about Rutan; the only known plan to go over four days. But it was also very specially constructed and one of a kind (and very weak, it could not even weather storms). This UAV is far more standard in design despite its "bomb" shape, and to be mass produced. Can't really compare it to Rutan. Design has a critically important role as you point out, but the engines and fuel are -all part of the design-. Otherwise, why don't we design all our craft like Rutan to have 9 day longevity? Think about it a little more.


This aircraft's endurance is largely achieved by its size. It's a very large and voluminous aircraft. It has a 150 foot wingspan and it about the size of an airliner. It's an evolution of a previous test aircraft, the Boeing Condor, which ran on gasoline and had about the same endurance.

This isn't the model that will fly for 10 days. That will be an even larger aircraft.


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