[HN Gopher] Cracking Open and Controlling a 747 Fuel Gauge
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Cracking Open and Controlling a 747 Fuel Gauge
Author : zdw
Score : 52 points
Date : 2023-06-08 17:21 UTC (5 hours ago)
(HTM) web link (bikerglen.com)
(TXT) w3m dump (bikerglen.com)
| RcouF1uZ4gsC wrote:
| From the drawing in the article, the fuel capacity is 47,210
| gallons. Also from the article the weight of fuel is 6.7 - 6.8
| pounds per gallon.
|
| Thus, a fully loaded 747 has 316,000 pounds of fuel.
|
| To put this in context, the maximum takeoff weight of a 737-700
| is 154,000 pounds.
|
| A fully fueled 747 has 2x the maximum weight of a 737 just in
| fuel!
| sokoloff wrote:
| The 747 _horizontal stabilizer_ has an area of 136.6 m2, while
| a 737 _main wing_ has an area of only 102m2 to 127m2.
| selectodude wrote:
| The engine nacelles on a 777-300 are the same diameter as the
| entire fuselage of a 737. The big planes are very, very big.
| Melkman wrote:
| I really like this picture that demonstrates this size
| difference:
| https://www.flickr.com/photos/ramonkok/27081197680
| adhesive_wombat wrote:
| Man, I need to think of any reason I can spec a 0.06% linearity
| potentiometer without having the BOM guy put a hit out on me.
| kloch wrote:
| If you want to see a bunch of these classic steam gauges in
| action this is a great video (starts right before spool up):
|
| https://youtu.be/JSKYoqVPtWw?t=86
|
| Here's a video of a 747-100 from 2001 that has run through of the
| flight engineers console but low-def:
|
| https://www.youtube.com/watch?v=x00ta8xC4oc
|
| Then there is this amazing video that captures the sound of the
| 747 classic "buzzsaw" sound better than any other (due to
| microphone placement and the 747SP having engines closer to the
| cockpit):
|
| https://youtu.be/3lhHwKK-6ms?t=313
| esaym wrote:
| I guess I've never heard the "classic" 747 engines. But reminds
| me of the GE TF39 used on the c5 galaxy.
| formerly_proven wrote:
| Much more of this
| https://m.youtube.com/channel/UC4Kz0sEXSqNkfi7W1PBKyMg
| seabass-labrax wrote:
| The centre tanks are so much larger than the outboard wing tanks.
| I would be very interested to know if the rate at which the fuel
| can be pumped up from the centre tank to the wing tanks exceeds
| the rate at which the engines consume it. If so, is fuel
| transferred on multiple separate occasions during the flight, or
| is it instead pumped continuously throughout the flight at a rate
| approximately matching the rate of consumption by the engines?
| readyplayernull wrote:
| The rate at which fuel can be pumped from the center tank to
| the wing tanks does exceed the rate at which the engines
| consume fuel, so fuel transfer can occur continuously
| throughout the flight.
|
| The actual rate of fuel transfer and the frequency of transfers
| will vary depending on the specific flight conditions, such as
| the weight of the airplane, the distance of the flight, and the
| amount of fuel remaining in the tanks. The fuel management
| system on the 747 is designed to optimize fuel usage and ensure
| that the airplane remains balanced throughout the flight.
| sokoloff wrote:
| There are two possible interpretations of GP's question. I
| took the opposite one of the one you did. "Can the fuel be
| transferred more quickly than engines consume it, such that
| there is a risk of the wing tanks becoming overfilled from
| the center tank?" is the one I took. You took "Can the fuel
| be transferred fast enough such that there is no risk of
| engine fuel starvation?" which is also valid.
| kayodelycaon wrote:
| Fuel tanks have vents to prevent overfilling from damaging
| them. From one of the Boeing documents I found, the
| 767-400ER will vent tanks into the fuel dumping system,
| passively pushing the excess overboard.
| sokoloff wrote:
| That fuel was presumably loaded for a reason. Pushing it
| overboard still represents a risk to the flight.
| esaym wrote:
| The fuel pump rates are very extreme. A plane can take off
| heavier than it can land. So if it is fully fueled and shortly
| after take off it needs to land due to emergency, it will need
| to dump thousands of pounds of fuel in minutes. The typical
| design and workflow of a larger jet like this is the engines
| are feed by the fuel tank nearest them. The flight engineer is
| on constant duty to continuously pump fuel from the center tank
| and/or other fuselage tanks to the tanks feeding the engines.
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(page generated 2023-06-08 23:01 UTC)