Fuel Loss May Cut Short GlobalFlyer's Journey

chris mazuc writes "Apparently the Virgin Atlantic GlobalFlyer has lost 2,600 lbs of fuel and might be forced to abort the attempt." According to the article, "Jon Karkow from Scaled Composites was unable to say whether it was due to leakage or evaporation. "We really don't know what it is... It's more than likely a system issue, such as a fuel venting line. It's been very puzzling for us, and we saw it quite early on.".

Comments

counting on fingers

[tedtimmons]

That is about 380 gallons of gas, if you calculate avgas at 6.84 lbs/gallon.

-ted

Re:counting on fingers

[iammrjvo]

It's a jet. It uses Jet-A, which is essentially diesel. I thought that 100LL weighed in closed to 6.0 lbs / gal, anyway.

I already saw it on CNN

[NeuroManson]

It was due to a defective fuel guage showing a full tankload, despite it being 2600 lbs short.

I think they are pushing it...

[brienc]

The article mentioned they will have to decide before departing Japaneese airspace, but you can see from the current posit, they are several uhnder miles off the coast.

Re:No pre-flight test?

[plover]

I think the problem with this live test is that the plane may not be capable of withstanding a landing fully loaded with fuel. It might be designed such that it wouldn't survive a hard impact (wings full of fuel have a lot of inertia, hit the ground hard enough and they WILL bend or fall off.)

Think of this plane as a one-shot deal. Reusability wasn't the goal -- getting around the world was.

Sure, pilot safety is a consideration -- in some emergency situations, the pilot could probably dump the fuel to land safely. In a worst case scenario, he could probably land with full tanks, but as I mentioned before that might not be without substantial risk to the aircraft. It might even be expected that the plane's airframe would fail if it landed full.

Re:Bit of a difference...

[sacherjj]

Actually they are testing it at full capacity. Right now. If it works, they finish the flight. If it doesn't, they modify the system. If you remember, the voyager only loaded full fuel on it attempt flight. And they pretty much ground off both winglets. Yet, the craft was still ok to fly around the world and set the record. Sometimes you have to take some exucated risks to set records.

they should have used the low tech fuel gage

[PW2]

When learning to fly a Cessna 150, my instructor always made me not trust the fuel gage since what it reports can safely be confirmed another way -- I'd have to look in the tanks and dip a stick in the fuel to be sure there was enough. When flying, it's a different story as you must trust your instruments.

Re:No pre-flight test?

[plover]

One other thing I failed to mention in the previous post: the fully laden wings droop substantially, and I believe they almost drag on the ground when full. It would be extremely difficult (if not impossible) to land a craft in a condition like that without accidentally dragging a wingtip.

Re:Used the wrong units.

[Target Drone]

His plane was supposed to be loaded with 12400 hogsheads to make the 18,000 hectaire journey. Instead they used gallons.

There actually was a case back in 1983 when they loaded a Boeing 767 up with X pounds of fuel when it should have been X kilograms so they were short by a factor of 2.2. Luckily the captain happened to be an experienced glider pilot.

Video and story here

Re:No pre-flight test?

[omahajim]

the fully laden wings droop substantially, and I believe they almost drag on the ground when full.

From my observation of the live takeoff video feed from the airport, I didn't see any drooping at all. At the end of RWY 35 where it sat a good portion of the day, the wings looked perfectly level in all shots I saw on the feed - including the moments immediately prior to takeoff. Once the takeoff roll was underway and especially once airborne, the wings appeared to have a slight bend upwards at the tips.

Re:Record Question

[emseabrown]

I read this on the website a while back, and my memory may be rough.

• The flight must be longer than the Tropic of Cancer
• Flight must not enter into the frigid zones (over 66 degrees latitude i think.)
• Flight must begin and end on the same runway

There may be more, but that is what I recall

you are right

[willCode4Beer.com]

Actually, due to a design to keep the structural mass low and due to the mass of the fuel, it can't land safely with a full (or even half) load of fuel.
The plane just isn't strong enough. Making the plane stronger would make it heavier, and a heavier plane would require more fuel. Its a compromise that had to be made.
On a side note, they actually wanted to use a different turbine that was more fuel efficient but, were unable to locate one. So since the turbine they are using consumes more fuel, more compromises had to be made in the design.

With a flight like this, you have to get rid of every last once of weight possible.

Re:you are right

[einhverfr]

The structural issue had not occurred to me. I was looking at the wings which are evidently designed for fuel-efficiency rather than an ability to maintain lift while moving slowly with a heavy load. This means two things: 1) Higher take-off speed/long runway requirement and 2) higher landing speed/long runway requirement.

Worse, this problem becomes worse as load is applied. This is because stall speed is dependent on the point where the lift is minimally equal to the weight of the aircraft. So higher load means higher stall-speeds, hence higher-speed takeoff and landing. Landing is more sensitive to this because the aircraft is slowing down to its stall speed rather than accellerating past it as in takeoff.

Most commercial aircraft get around this problem by morphing the shape of their airfoils in order to provide more lift during takeoff and landing (allowing for shorter runways and slower speeds) but I don't see that on this airplane. I could be wrong on this point, but I doubt it. Otherwise I doubt that the choice of runway would have been made primarily on the basis of length.

So if this plane is landing with 9 tons of extra fuel, assuming it is built out of a magical indestructable material, you still have the issue that you have a much larger ammount of kenetic energy because the plane is not only more heavily loaded, but also moving significantly faster. So it is harder to slow the vehicle down.