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Very rich running at high power is actually typical for the carburetted engines of the era.
Hi Flyboyj,
However, that's just the label on the mixture quadrant. Just how rich the mixture is might vary according to the actual settings of the automatic or semi-automatic mixture regulator. 346 g/HP/h is the actual figure for the R-3350, so it certainly ran richer than the V-1650-7 which consumed just 277 g/HP/h.
Regards,
Henning (HoHun)
Actually that is somewhat correct - those fuel consumption charts are based on "normal" mixture settings and also using a richer mixture for engine cooling, something earlier mentioned. At altitude you can continue to lean for air density based on CHT and EGT. And remember, for the most part - maximum power setting (take off and WEP) are always assumed at "full rich."
Engines curves over altitude always assume proper leaning is utilized. This will cause an accident and can lead to running out of fuel if a pilot does not properly lean as all the data assumes proper mixture control.
I think that is what you are saying as well FlyboyJ.
The pilot does have considerable control over how much or little he leans.
All the best,
Crumpp
It does if you're traveleing 2000 miles over an open ocean.Hi Flyboyj,
>I've flown modern GA aircraft with FI and pressure carbs and would always lean at altitude - I would usually see anywhere between 5 and 10% fuel consumption savings.
Since the R-3350 runs about 50% richer than the DB605A at WEP settings to begin with, 5 to 10% do not make not much of a difference for the overall picture.
I agree....I at least don't see much evidence for direct fuel injection being less efficient than carburetion in WW2 - quite to the contrary.
Hi Flyboyj,
>It does if you're traveleing 2000 miles over an open ocean.
I don't picture me traveling 2000 miles over an open ocean at take-off/emergency power anyway.
Regards,
Henning (HoHun)
Not necessarily - WEP application in a decent will build up airspeed but not as quickly as you might think especially in a large aircraft. I'm talking about seconds here...You are losing me - I would not travel 2000 miles while rapidly climbing or descending either, and I'd certainly not keep take-off/emergency power applied during a rapid descent as that would take me way past Vne.
OK...>My point was based mainly on cruise. WEP settings are just for that - emergencies.
Oh well - my point was that as soon as you move away from the optimum working point of the carburetted engine, efficiency drops markedly. Even at maximum continuous, which could be used for longer spells, specific fuel consumption had risen by 60%.
Actually FEs did manually lean, especially if at a certain altitude/ MPP setting/ CHT the engine began to run hot or cold.It also seems that using automatic mixture control was standard operation procedure even in the B-29 though it had a flight engineer on board whose primary task was to operate the engines. The USAAF doesn't seem to have thought there was something to gain from manual leaning.
I seen that - you could doubt it if you like - if you lean to the point that you're not running at high CHT you're going to save fuel.In fact, I seriously doubt that one could reduce the minimum 195 g/HP/h by any meaningful amount, but should you want to prove your point, here you can download the B-29 Flight Engineer Manual you might find helpful:
You also have to remember that the automatic fuel controllers found in pressure carbs weren't the most accurate pieces of equipment. They did go out of adjustment quite frequently and it is a maintenance activity to adjust them at specified hourly intervals.It lists a minimum of 201 g/HP/h at 15000 ft. Apparently, the automatic control knew how to lean with altitude, too. This is actually a higher figure than the minimum from the cruise control chart and reinforces my opinion that the abovementioned 195 g/HP/h are already the optimum. Daimler-Benz list their minimum with a tolerance of +10 g/HP/h - only towards higher figures. That's how I tend to read the US figures, too: no way you're going to shave off another 10% from the 195 g/HP/h figure.
If the engine is running sub-optimally, you might get it back to optimum performance by manual leaning, but that doesn't mean you can beat the minimum figure.
Regards,
Henning (HoHun)