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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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Hydrogen?
By Jedi2155 on 6/5/2012 2:08:31 PM , Rating: 2
Why would they choose hydrogen as fuel source over standard gas/diesel/avgas? Especially if its just using conventional internal combustion?




RE: Hydrogen?
By BladeVenom on 6/5/2012 2:24:40 PM , Rating: 1
Green research dollars.


RE: Hydrogen?
By lightfoot on 6/5/2012 2:36:11 PM , Rating: 5
Weight considerations may make compressed hydrogen a more viable solution than hydrocarbon fuels. The Carbon makes it easier to store the hydrogen, but adds nothing in terms of energy density.

Energy per unit weight is a critical consideration for both aircraft and spacecraft.


RE: Hydrogen?
By rs2 on 6/6/2012 1:25:43 AM , Rating: 3
Weight considerations aside, what is the intended use of this UAV? It does not appear to be particularly agile or stealthy or small (a 150 foot wingspan is certainly not tiny). Maybe it has sufficient power to muscle its way up to very high altitudes, though it doesn't really seem like it at first glance (particularly with that 4000 feet test flight altitude). A 4+ day loiter time is meaningless if detecting and shooting down the aircraft is a trivial prospect.

It seems like this UAV would be useful mostly for flying surveillance over regions that aren't expected to be able to mount any sort of coordinated anti-aircraft response whatsoever. Which implies that its intended use is primarily domestic spying/surveillance.


RE: Hydrogen?
By Samus on 6/6/2012 1:47:09 AM , Rating: 3
I find the choice of engine configuration more unusual than the choice of fuel. A prop configuration demands high RPM, not torque, which is why inline and V-configuration engines were terrible in world war-era planes. Since we looked to the auto industry at the time it was what we had to fight with, but was no competition for the Japanese which could fly nearly twice as far on the same amount of fuel.

Radial and rotary engines are probably better suited for this application as they produce a higher RPM in less displacement at the expense of torque, likely increasing fuel efficiency. But I'm not an engineer at Boeing, and I'm sure they know what they're doing...I just find it interesting why they're doing it this way.


RE: Hydrogen?
By AssBall on 6/6/2012 6:44:54 AM , Rating: 2
I was thinking radial too, but then again they can get 20k RPM out of a Honda motorcycle, so i don't know either.


RE: Hydrogen?
By 91TTZ on 6/8/2012 10:27:36 AM , Rating: 2
You're thinking about this backwards. Airplane engines favor low-rpm operation, not high RPM operation.


RE: Hydrogen?
By Amiga500 on 6/6/2012 8:06:50 AM , Rating: 2
The need for rpm depends on your propeller pitch (and span).

Ideally (from an aerodynamic point of view), you'll turn a larger blade slower.


RE: Hydrogen?
By 91TTZ on 6/8/2012 10:26:41 AM , Rating: 2
quote:
I find the choice of engine configuration more unusual than the choice of fuel. A prop configuration demands high RPM, not torque, which is why inline and V-configuration engines were terrible in world war-era planes.


I think you have that backwards. Prop aircraft don't require high RPM. Piston aviation engines usually turn at a much lower RPM than automotive engines. People that use automotive engine conversions on their homebuilt aircraft often have to use a speed-reducing gearbox so the prop doesn't turn at full crankshaft speed. This increases the weight of the aircraft.

A popular 4 cylinder aircraft engine like the O-320 produces 160 HP at 2700 RPM.

And rotary engines like the Wankel are very inefficient, so fuel efficiency would be horrible. For instance, a Mazda RX-8 gets slightly worse highway fuel economy than a larger, heavier Corvette Z06 with the 7 liter V8.


RE: Hydrogen?
By Strunf on 6/6/2012 7:19:36 AM , Rating: 2
"Energy per unit weight is a critical consideration for both aircraft and spacecraft."
So is volume and hydrocarbon fuels can store 7 times more energy per volume unit than compressed Hydrogen, while at the same time they are only 3x less efficient in terms of energy per weight.

Also compressed gas implies a complexer delivery system and add quite a bit in extra weight.


RE: Hydrogen?
By docawolff on 6/5/2012 2:46:09 PM , Rating: 3
It may also be that the operational altitude of the aircraft is high enough (note that first test flights never explore the highest, fastest, or most interesting portions of an aircraft's flight envelope) and the duration long enough that it is easier to use hydrogen than to keep a hydrocarbon fuel heated.

Hmmmm... I wonder if heating a hydrocarbon fuel to keep it liquid would make it more vulnerable to IR detection?

Just my two pennies.


RE: Hydrogen?
By geddarkstorm on 6/5/2012 3:03:12 PM , Rating: 2
I don't know of any hydrocarbon planes that can fly around for 4 days straight. There are a lot of numbers we don't know, unfortunately, to really tell us how potent this hydrogen system is compared to gas. My guess is it has a much slower top speed then if it used gas, kinda like an ion engine versus a chemical rocket; but no way to tell from a little test flight.


RE: Hydrogen?
By AppleMaggot on 6/5/2012 3:36:51 PM , Rating: 2
quote:
I don't know of any hydrocarbon planes that can fly around for 4 days straight.

Here's one you forgot about:
http://en.wikipedia.org/wiki/Rutan_Voyager


RE: Hydrogen?
By geddarkstorm on 6/5/2012 3:51:07 PM , Rating: 2
That is a very special exception, with some extreme engineering feats (and extremely fragile). Not your common or mass produced plane.


RE: Hydrogen?
By AppleMaggot on 6/5/2012 3:48:14 PM , Rating: 2
quote:
That is a very special exception, with some extreme engineering feats (and extremely fragile). Not your common or mass produced plane.


While certainly true (and I wouldn't argue the point), you forgot about this one as well. :)
http://en.wikipedia.org/wiki/Global_Flyer


RE: Hydrogen?
By geddarkstorm on 6/5/2012 4:01:44 PM , Rating: 2
That one only lasted 2.8 days; so is actually not an exception.


RE: Hydrogen?
By AppleMaggot on 6/5/2012 3:59:47 PM , Rating: 2
quote:
That one only lasted 2.8 days; so is actually not an exception.

Ahh, you're right, my bad.


RE: Hydrogen?
By geddarkstorm on 6/5/2012 4:14:18 PM , Rating: 2
No worries! The whole February is missing 2 days bit threw me off for a second too when I first looked at the page. Then the international date line counts for the next "missing" day.

Besides, it shows what Voyager did is truly special, and it's nice having one exception correcting my statement.


RE: Hydrogen?
By Calin on 6/6/2012 3:06:00 AM , Rating: 2
"Not your common or mass produced plane"
Unlike this flying eye plane, which is common and mass produced?
I think a Predator drone with a fuel tank instead of the missile would have a long enough loiter time. Also, surveillance planes were limited to the endurance of the weak link between the chair and the windshield, so there was no need for higher endurance.
And if we're talking about common and mass-produced (within limits), there's the Russian Tu-95 (?) patrol bomber, with 28 or so hours of endurance


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.


RE: Hydrogen?
By jRaskell on 6/5/2012 3:42:39 PM , Rating: 2
Likely for the flight ceiling, which is 65,000 feet. without super or turbo charging, hydrocarbon ICEs operate very poorly above around 20-30,000 feet.


RE: Hydrogen?
By 91TTZ on 6/8/2012 10:47:57 AM , Rating: 2
The same problem would apply to hydrogen fueled engines, since the problem is the amount of available air and not the fuel. That's why this thing also needs to be turbocharged.


RE: Hydrogen?
By Richard875yh5 on 6/5/2012 5:16:09 PM , Rating: 2
Because hydrogen is lighter than air.


RE: Hydrogen?
By spread on 6/5/2012 10:43:45 PM , Rating: 2
Exactly. Which is why people who drive hydrogen powered cars have to weigh them down with lead. Over 12 people have died after removing the ballast from their vehicles and floating away into space never to be seen again.


RE: Hydrogen?
By Alexvrb on 6/6/2012 9:29:30 PM , Rating: 2
Yes, but they all made good on their boasts of achieving out-of-this-world mileage!


RE: Hydrogen?
By spread on 6/5/2012 10:38:58 PM , Rating: 2
quote:
Why would they choose hydrogen as fuel source over standard gas/diesel/avgas?


Hydrogen can be very efficiently and quickly converted into electricity using a very small fuel cell. It powers not only the main motor but the rest of the power hungry electronics.

Much more efficient than an engine (with a big alternator) or a large generator which would run an electric motor anyways.

Hydrogen is simpler, and has a higher energy density and the whole system would be lighter.


RE: Hydrogen?
By Jedi2155 on 6/5/2012 11:13:40 PM , Rating: 2
They didn't mention using a fuel cell to convert the hydrogen to electricity but are simply burning up the hydrogen in a piston engine. I could see the benefits of the fuel cell but using it in a piston engine boggled my mind.


RE: Hydrogen?
By hartleyb on 6/6/2012 1:09:09 PM , Rating: 2
A little suprised by all the responses to this article. Have you ever tried to see something white with a 19 ft wing span at 65000 ft...hard even with help from optics. The engine choice, fuel, and design all have to do with high altitude operations. As a note the UAV is designed to reduce fuel consumption by using upper air currents. It would only last a couple days or less at low altitude. The idea is to replace the current P3 manned aircraft with an unmanned aircraft that can be both a relay for communications as well as a imagery reconnaissance. The DOD's move from the prop powered P3 to the jet engine power P8 leaves some huge gaps in operational capability i.e. on station time. The P8 has a 65% less capability to stay on station then the current P3. UAV's will fill the gap.


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