If you read the How Stuff Works article, it says that's exactly what happened, with the variable resistor operating a heating coil wrapped around a bimetallic strip, attached to the needle on the gauge.
My own car doesn't work like that, because it registers changes in level instantly after filling up with diesel.
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[i]Different avaiation fuels (with/with out icing inhibiters) have slightly different SG values and a submerged SG capacitor will reflect these changes to the fuel reading if fuel quantity is displayed as weight and not quantity.[/i]
Bikemade3, your comments aren't entirely accurate. The specific gravity of the fuel is much more dependant on temperature & altitude and I don't know of any commercial aviation fuel (Jet A1 or Avgas) that comes with/without icing inhibitors, it is all supplied to a single specification. Jet A1 has a (global) standard freezing temperature of -47C where it starts to go waxy and will block filters/pumps. American jet fuel (Jet A) freezes at -40C.
If a plane flies from the US to the UK, any remaining Jet A fuel is then pumped into the tank that will use it first (the centre tank on a 747) before topping up with -47C fuel for a trip to Tokyo where the outside air temperature is often -70C for an extended period over Siberia and where low fuel temperature warnings are common. That way we burn the -40 fuel early into the flight and have more protection for the long cold sector.
All fuel, including car petrol and diesel, derives its calorific value (ie power) from it's mass, not it's volume, so strictly speaking a car should be quoted as doing x miles per kilo, not litre or gallon. As the specific gravity of the fuel varies, thus it's volume per kilo and so your mpg figure will vary in different temperatures whereas the miles per kilo figure won't change under the same circumstances.
The 747 uses capacitance fuel sensors in the tanks and indicate the quantity in kilos (or rather metric tonnes). At the same time fuel flow meters measure the consumption and the two figures are available to us as "calculated fuel", ie fuel we had at the start minus burn, and "totaliser" fuel (from the gauges). A discrepancy will throw up a warning.
As belt and braces, we have an anticipated "fuel remaining" at each waypoint on our flight plan which we compare to actual burn. The plan is usually very accurate.
The fuel burn on a 747 is pretty scary. During the take off and initial climb, we burn about 7-8 litres a second, so your average car tank would hold enough fuel for 6 or 7 seconds of flight.
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"During the take off and initial climb, we burn about 7-8 litres a second, so your average car tank would hold enough fuel for 6 or 7 seconds of flight."
Flight! at that rate your average car would not make V1
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A wooden stick, with notches every gallon, is the most accurate.
Wasn't there a car with a float connected to a mechanical dial mounted on the top of the tank in the middle of rear scuttle?
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A wooden stick, with notches every gallon, is the most accurate. Wasn't there a car with a float connected to a mechanical dial mounted on the top of the tank in the middle of rear scuttle?
Don't know about that, but early 2Cvs had a dipstick for the petrol tank as well as the sump. No Fuel gauge.
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And that V1 would be fairly high for a craft without any wings!
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Colin,
There is more thean 1 fuel i.e Jet A1.What about AVTUR( Aviation Turbine) with/without FSII(Fuel System Icing Inhibiter). Then again you could use AVCAT( Aviation Carrier Turbine)which has a higher flash point, caused it's used on ships with an aviation facility.
Jet A1 is universlly available worldwide, i should know i've used it from one end of the world to another. Even dropped onto a Oil Rig in the Fortes field and been fed Jet A1.The reason we fit a a sg capaciter at the bottom of one of the tank units is to correct for the different fuels we use i.e AVTUR/AVCAT/JET A1 or in the worse case Diesel but the maintenance penalty for using Diesel is pretty severe.
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Colin M and BikeMaid (as you two seem to be the aviation experts)
So what happened to the helicopter from HMS Nottingham, then?
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I suggest that they deliberately ditched the Aircraft as HMS Nottingham was not at the Lat/Long the flight expected it to be and the fuel they had remining was insufficient to make it back to mother. And not, as suggested in the papers that they took off with insufficient fuel.
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Whoops! Sorry "bikemade3" - No offense intended.
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How did they ditch, by the way? Put it into hover on autopilot, dive out and swim away?
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How did they ditch, by the way? Put it into hover on autopilot, dive out and swim away?
>>Pretty much like that, get it in a 10-20 foot hover , throw the life raft out, then out jump the passengers, pilot takes the A/C away about 500M then gently as he can put's it in the water. Hopefully there is no/ negligeable swell set the flot gear off and get out. Invariable the thing capsizes and plummets like a stone.
Having been thru' the Underwater Escape Trainer more times than i care to remember, any crew that manage to get out of a ditched chopper have done well.
I magine what happens if there's a catastrophic failure and it ploughs in at speed say 125 knots.
1. Massive deacceleration forces cause major body trauma if it's fast enough possible detatching of the brain stem.
2. Having survived the initial crash attemps to evacuate are hindered by cockipt doors and windows being jammed from frame distortion.
3. Shock leads to disorientation, the route you identified when you manned up as your primary escape route if forgotten.
4. In the mean time the things sinking your still strapped in the seat having forgotten to release the harness.You release having waitedfor the Main Rotor Head and blades to stop rotating.
5. Water has flooded into the cockpit and cabin, it's pitch black, north Atlantic winter weather.Cold shock causes you to panic, you can't hold your breath as you are trying to get out.
6. The emergency air bottle you are breathing from in a controlled maner( not)is keeping you alive as to try to escape. The debris from the accident is hindering your escape, as you make your way aft you get snagged on dangling looms, broken control rods,broken frames, but you can't see that it pitched black.Then suddenly your emergency air bottle runs out!
Does anyone remember the Bristows Sikorsky that ditched about 28 years ago on the way to the Isles of Scilly from Cornwall.IIRC there were about 28 people on board the only people who got out were1. The Aircrew and 2. Two people who were sat immediately by the main cabin door.
That's why anybody who fly's over the ocean in a helicopter undergoes escape traing, it's a requirement for oil rig workers.
Come then end of the day you are in god's hands but the training you get will hopefully be remebered when you assume the crash position, find yourself inverted, in the back of the chopper, underwater hand have identified your primary escape route.
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Many modern Fords hold their the tank level too Andrew.
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Its not what you drive, its how you drive it! :-)
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Never look at my fuel gauge nowadays not since buying my new MKV Golf with multi-functional computer. Just look at the 'miles remaining' (based on the petrol left in the tank and average mpg) which, I suppose, is still related to information obtained from the crude float mechanism?
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I thought when ditching a helicopter you lean it to the starboard side so the rotor blades shatter away from the aircraft, and don't hit the pilot as he tries to escape?
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Instructed technique, although only practised in anger is to cut both engines and not use the rotor brake to slow the MRH down. Application of the rotorbrake causes a torque reaction which when you consider that the COG is high invariably tips it over.
Would i lean it to detatch the rotors probably not, the airframe reaction from 4/5 Blades each weighing roughly 80-120 Kg travelling with a tipcap speed of just under the speed of sound impacting the water is going to be pretty massive.IMHO it'll just compound the situation.
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bikemade3, I'll bow to your greater experience with aviation fuels. I've only ever seen 100LL and Jet A1 in my 17 years flying with Lycomings, Darts, GE90's and RB211's and assumed icing additives were added as part of the basic spec of the fuel rather than being an "option".
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Colin M
I thank you. My experience with Aviation fuels spans 18+ years as a Avionics/Electrical specialist on Rotary Wing aircraft and i have burned many a midnight candle tracking down fuel tank unit/wiring problems. I now find myself responsible for the Fuel Quantity indication ( And many other systems) on a aircraft type i have never actually worked on. How does that work i don't know!
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"I now find myself responsible for the Fuel Quantity indication ( And many other systems) on a aircraft type i have never actually worked on. How does that work i don't know!"
Its very easy. If you can read the index in the manual you are trained, and if you can take the inspection panels or covers off - you are an expert.
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Not hands on so to speak, more like at the end of a phone/fax/computer attempting to answer questions about systems that the hands on experts can't fix.
Bit like your average manufactures headquarters technical support, except the vehicles jost a dammed sight more i.e £5 Mill a piece.
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Toyotas generally for years past have held the fuel gauge reading when switched off; but how?
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