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How Is Fuel Amounts Measured?  
User currently offlineStaffan From , joined Dec 1969, posts, RR:
Posted (12 years 6 months 2 weeks 5 days 23 hours ago) and read 1944 times:

Can someone tell me how the remaining amounts of fuel in the fueltanks are measured on commercial aircraft?

Thanks,

Staffan

13 replies: All unread, jump to last
 
User currently offlineStaffan From , joined Dec 1969, posts, RR:
Reply 1, posted (12 years 6 months 2 weeks 5 days 23 hours ago) and read 1882 times:

What I mean is the type of sensor that measures it and how it works!

Staffan


User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 2, posted (12 years 6 months 2 weeks 5 days 23 hours ago) and read 1879 times:

There are a couple of designs of course. The one I've seen the most uses a capacitative sensor. This is basically a metal tube with a metal rod in the middle, making up a crude capacitor. This is installed going from the top to the bottom of the tank.

I suspect you're familiar with capacitors but for those who aren't, the capacitance will vary depending on the properties of the substance isolating the inner rod from the outer tube. Fuel and air have different properties in this respect, so the capacitance will be an indicator of the level of fuel in the tank.

Cheers,
Fred



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineStaffan From , joined Dec 1969, posts, RR:
Reply 3, posted (12 years 6 months 2 weeks 5 days 23 hours ago) and read 1862 times:

Ok, thanks for the reply, but it brings up another question, isn't the fuel conductive? Or are the two metal parts isolated from direct contact with the fuel?

Staffan


User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 4, posted (12 years 6 months 2 weeks 5 days 22 hours ago) and read 1852 times:

Hydrocarbons are essentially insulators. Found this through a quick google search:



Conductivity of fuels is usually expressed in conductivity units (CU), 1 CU = 1 pico Siemens/meter (1 pS/m) = 1 × 10^–12 ohm^–1 meter^–1. Kerosenes may have conductivity ranging from less than 1 CU to perhaps 20 CU. For comparison, deionized water has a conductivity of about 10 million CU.



Not a very good conductor.  Smile

Cheers,
Fred



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineStaffan From , joined Dec 1969, posts, RR:
Reply 5, posted (12 years 6 months 2 weeks 5 days 22 hours ago) and read 1843 times:

Tack så mycket! (Thank you very much!)

Staffan  Smile/happy/getting dizzy



User currently offlineTsufang@ci From Taiwan, joined Feb 2002, 39 posts, RR: 0
Reply 6, posted (12 years 6 months 2 weeks 4 days 12 hours ago) and read 1798 times:

on boeing 777
measure by supersonic
wave through different material will chang the speed


User currently offlineStaffan From , joined Dec 1969, posts, RR:
Reply 7, posted (12 years 6 months 2 weeks 4 days 10 hours ago) and read 1788 times:

Tsufang, sounds interesting, can you tell more about it, or do you know where I can find more info?

Thanks,

Staffan


User currently offlineRatzz From Sweden, joined Sep 1999, 198 posts, RR: 0
Reply 8, posted (12 years 6 months 2 weeks 4 days 9 hours ago) and read 1782 times:

Remaining fuel can also be measured by utillizing s.c "dripsticks",located in various positions in each tank,easily accessible from the bottom of each tank.
On older a/c´s such as the L-188 Electra and the Sud-Aviation Caravelle,these "dripsticks"were considered more reliable than the actual gauge readouts.


User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 9, posted (12 years 6 months 2 weeks 4 days 7 hours ago) and read 1770 times:

Varies with the Aircraft.
Can have the Float gauge in old Small Aircrafts,where a float indicates the fuel qty.
The Electrical type where in a transmitter conveys the level of fuel to an indicator in the cockpit.
Or the common used Capacitance type,where fuel or fuel/air is used as the dielectric depending on the qty of the fuel.
These capacitance probes are evenly distributed in the fuel tank taking into account the contour & profile of the wing to give an accurate reading irrespective of aircraft attitude.There is also a comparator unit located in the tank located at the bottom most part of the tank as it requires to be submerged in fuel, it corrects the fuel qty for fuels with various dielectric.
The signals from the comparator + capicatince probes is transmitted to the Indicator to register the Fuel qty in Lbs or Kgs or any appropriate unit.
regds
HAWK.



Think of the brighter side!
User currently offlineJet-a gasguy From United States of America, joined Dec 2000, 266 posts, RR: 1
Reply 10, posted (12 years 6 months 2 weeks 4 days 3 hours ago) and read 1753 times:

On newer Boeing commercial aircraft, in addition to the capacitance probes and weight compensators, there are also densitomiters. Fuel Density plays a large part in the total wieght of the fuel. The FQP(Fuel Quantity Processor) takes information from all three sources and in turn provides an accurate fuel weight to the Fuel Quantity Indicators. The information from the FQIS(Fuel Quantity Indicating System) is sent via seperate channels to both the Flight Deck Gauges and to the Underwing panel indicators. Since both Flight Deck and Underwing Indicators receive input directly from the FQP, they can both be considered "Master" gauges. Although Flight Deck Indicators will always be considered the final authority if there are any discrepencies between the two. On the Boeing 777, ultrasonic waves are also used to measure Fuel quantity. This and other fuel system components can be accessed on the computer in the Flight Deck through the Fuel Quantity Maintenance Pages. Accessing this will provide:
1) Fuel Quantites
2) Fuel temperature
3) Fuel densities
4) Height of Fuel in each tank(through ultrasonic sound)
5) VTO(Volumetric Top-Off) Values
6) Water detection status.

Hope that helps.

Jet-A gasguy



Find a job you love, and you'll never work a day in your life.
User currently offlineStaffan From , joined Dec 1969, posts, RR:
Reply 11, posted (12 years 6 months 2 weeks 3 days 22 hours ago) and read 1731 times:

Thank you, helped a lot!!  Smile





User currently offlineTsufang@ci From Taiwan, joined Feb 2002, 39 posts, RR: 0
Reply 12, posted (12 years 6 months 2 weeks 2 days 15 hours ago) and read 1712 times:

boeing 777
meausre by supersonic wave
and a device generate this wave
this wave will reflect when it touch the surface between the fuel and air in the tank
a special sensor install in the tank caculate the time difference between the wave transmit and reflect to receive by the sensor
then the computer accord the data to show the quantity to gnd staff ,pilot or for the a/c system
that's all i know !
best regards!!


User currently offlineL-188 From United States of America, joined Jul 1999, 29800 posts, RR: 58
Reply 13, posted (12 years 6 months 2 weeks 2 days 14 hours ago) and read 1709 times:

Ratz is exactly right on those dipsticks on the Electra.

Without going into details I know of aircraft that the inboard tanks read out in quanity, 1/4, 1/2, 3/4 ect. and the outboard tanks read out in lbs.



OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
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