Who has measured their actual flow rate?
Well said!
Only point I was making was to be careful whenver 'gallons' are quoted!
The flowmeter in the Bulldog was indeed a simple fuel pressure gauge; I think the one in the Rockwell was somewhat different?
Only point I was making was to be careful whenver 'gallons' are quoted!
The flowmeter in the Bulldog was indeed a simple fuel pressure gauge; I think the one in the Rockwell was somewhat different?
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Most fuel flow gauges are pressure sensing devices.
If you saw something like this then that would use a remotely mounted turbine transducer, typically a Floscan 201B, which sends pulses back (of the order of 30,000 per USG) which are totalised. Such systems can be accurate to 1% or better, if they are correctly installed and calibrated. All TB20s made after 2000 or so had their Shadin totaliser out of cal by anything up to 25%; there is a U.S. STC fix for it but it's not legal to implement it on a G-reg
Dublinpilot's "tacho unit" method is interesting. I guess this tacho simply counts engine revolutions which, in typical usage and with a fixed pitch prop, is going to approximate total fuel used. It should not be that close however because prop thrust is the cube of RPM, so fuel flow should also be the cube of RPM, whereas the tacho is just counting straight RPM.
If you saw something like this then that would use a remotely mounted turbine transducer, typically a Floscan 201B, which sends pulses back (of the order of 30,000 per USG) which are totalised. Such systems can be accurate to 1% or better, if they are correctly installed and calibrated. All TB20s made after 2000 or so had their Shadin totaliser out of cal by anything up to 25%; there is a U.S. STC fix for it but it's not legal to implement it on a G-reg
Dublinpilot's "tacho unit" method is interesting. I guess this tacho simply counts engine revolutions which, in typical usage and with a fixed pitch prop, is going to approximate total fuel used. It should not be that close however because prop thrust is the cube of RPM, so fuel flow should also be the cube of RPM, whereas the tacho is just counting straight RPM.
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You maybe correct IO540, but you're forgetting that most of us pilots are creatures of habit! We fly generally fly with the same RPM or RPM/MP combination!
I reckon that's why it works, and am very conceous that if I vary that or fly well beyond my usual altitude bands, then all bets are off.
That was also why I was determined to get my own fuel usage figures. They are relevant for how I fly the aircraft, and not some figure for how someone else flys it (or has remembered from someone else who told them, who heard from someone else who ought to know, etc etc).
dp
I reckon that's why it works, and am very conceous that if I vary that or fly well beyond my usual altitude bands, then all bets are off.
That was also why I was determined to get my own fuel usage figures. They are relevant for how I fly the aircraft, and not some figure for how someone else flys it (or has remembered from someone else who told them, who heard from someone else who ought to know, etc etc).
dp
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To answer the original question, no I haven't.
Do I consider this to be a problem? No, because I am always conservative when it comes to fuel planning. Does this prevent me from flying "longer" legs? Yes, but in the type of flying I do at the moment, I have no need to fly longer legs, so I am perfectly happy with my conservative fuel-planning.
On the other hand, if I had any reason to fly longer legs and push the endurance of the aircraft close to its limits, of course I would make sure I knew exactly how much fuel my aircraft used. But I would guess that very few piston-engined aircraft (whether flown by a PPL or commercially) are operated in this way.
FFF
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Do I consider this to be a problem? No, because I am always conservative when it comes to fuel planning. Does this prevent me from flying "longer" legs? Yes, but in the type of flying I do at the moment, I have no need to fly longer legs, so I am perfectly happy with my conservative fuel-planning.
On the other hand, if I had any reason to fly longer legs and push the endurance of the aircraft close to its limits, of course I would make sure I knew exactly how much fuel my aircraft used. But I would guess that very few piston-engined aircraft (whether flown by a PPL or commercially) are operated in this way.
FFF
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I wasn't suggesting that cruise settings vary.
Mine never vary either (10.5GPH, LOP) unless I am above about 10,000ft and then I am happy with what I get with the throttle on full-bore
What I was getting at is that one has to do something to separate the fuel usage during climb/descent, so one can get a decent grip on one's enroute/cruise fuel flow.
On most flights, one can estimate the climb usage fairly easily (straight out of the POH; all levers are fully fwd anyway), and the descent one similarly. It is the cruise one which needs to be determined extra carefully in order to do accurate flight planning.
Mine never vary either (10.5GPH, LOP) unless I am above about 10,000ft and then I am happy with what I get with the throttle on full-bore
What I was getting at is that one has to do something to separate the fuel usage during climb/descent, so one can get a decent grip on one's enroute/cruise fuel flow.
On most flights, one can estimate the climb usage fairly easily (straight out of the POH; all levers are fully fwd anyway), and the descent one similarly. It is the cruise one which needs to be determined extra carefully in order to do accurate flight planning.
...which was why you got the wrong answer 
The correct method is to convert SG@60F to density at 15C in vac, you can either use a formula similar to BEagles above (but using dens water at 60F and then using volume factors to convert to 15C) or simply accept it from me that in the gasoline range the difference is 2 Kg/m3. Thus for an SG@60F of .7523 the density@15C would be 0.7521 in vacuum. To get the density in air you should then subtract a further 0.0011 from that, giving a density @15C in air of 0.7510. Thus 1000 litres would weigh 751.0 Kg.
Of course, for aircraft sized tanks the above is irrelevant as the differences are insignificant
The correct method is to convert SG@60F to density at 15C in vac, you can either use a formula similar to BEagles above (but using dens water at 60F and then using volume factors to convert to 15C) or simply accept it from me that in the gasoline range the difference is 2 Kg/m3. Thus for an SG@60F of .7523 the density@15C would be 0.7521 in vacuum. To get the density in air you should then subtract a further 0.0011 from that, giving a density @15C in air of 0.7510. Thus 1000 litres would weigh 751.0 Kg.
Of course, for aircraft sized tanks the above is irrelevant as the differences are insignificant
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I have a FS450 in my aircraft linked to the GPS. When I get to the top of the climb and trim for the cruise I put cruise config and finish the lean (I lean in the climb to airways height), at this point I check the fuel flow against the laminated excel sheet I created from the POH. At 10,000ft indicated airspeed of 120kts I am doing doing 32lph. This is bang on with book figures. The FS450 is accurate to a fraction of a liter when I refuel.
