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Hans_Petter

Engine mixture

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I know that this topic has been raised before, but still -- why don't the FU3 aircraft respond to altitude and leaning of the mixture?We've got beautiful red levers but all they do is to kill the engines if you go full lean. All of our aircraft will be quite happy flying at 10,000 ft on "full rich". For those of you who may not understand what this is all about -- if you fail to lean a piston engine at high altitudes it will stop. There's a correct fuel / air ratio that has to be observed and when the air gets "thinner" this must be compensated by lowering the fuel fraction to match the air (oxygen) fraction. To keep the fuel / air ratio right you'd want to lean the engine(s). This is accomplished by sliding the red levers down a bit, more as the altitude increases / ambient pressure drops. In real life you can go by the sound of the engine as it starts to struggle. When you get the mixture right it revvs up and provides maximum power again. To fine-tune mixture one may go by Exhaust Gas Temperature (EGT gauge) or by fuel flow gauge.This sim has all the controls and the parameters to get this right. Then, why hasn't mixture been implemented correctly? best regards,Hans Petter

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>why don't the FU3 aircraft respond to altitude and leaning of the mixture?I thought about and experimented with this a lot in FU (and others!). I could only make the following conclusions and philosophical statements:1. We are stuck with the integral part of FU that sets the atmospheric barometric pressure at 29.92.2. The programmers thought that we have this beautiful scenery, who wants to go that high as to control the engine mixture.3. FU3 was at its release time ahead with scenery complexity and elevation accuracy, it was rushed for released, which was part of its down-fall, and the fine settings were never attended to by the programmers.Just reading between the manuals of FU1-FU3, with optimistic claims of more scenery areas. The disappearance of the FU laminar flow mathematics to FU2 and the drab green link between FU3 SFO and Seattle scenery. The disappearance of the nice alive FBOs... and one can see the subtle deterioration of the enthusiasms of the programmers. All these resulted in this small group of internet surfer fans still sticking to a long gone and dead program.We have to live with it as is. One can only collect so many aircraft and so many VA's in one sim and others take over... FU3 was dead at release after LG's 3 excellent simulators. It is now surpassed by MSFS (and others) and into the future until it will look like MSFS1 compared to the newer programming, technical and computer advances.Pieter

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I still do lean the mixture - using the mouse of course becauseusing CTRL +- is too coarse. This is easiest to see on the Renegade as you have the peak temperature display so get feedback as to whenits correct, and you do get massive changes in engine performance when you go past the peak temperature which you can hear - that is definitely implemented in FU3. Forget to enrich on finals and have to go around - then you are in big trouble. But like you I have never noticed any altitude effect. The instrumentation on the Renegadeis one of the reasons why this is still among my favourite planesPossibly they only implemented this peak temp effect, not the gradual changes with throttle. I still like to think I'm saving Avgas by throttling to peak when clear.Keep up these technical points - they're very useful!I was always puzzled by the 29.92 being constant too. Surelythat's one of the easiest effects to implement?

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I'll spend some time on the Renegade, as Robert suggests. The FU3 atmosphere is certainly implemented even though the sea level pressure is constant and we can't calibrate the altimeter. We've got altitude and control limits as we fly higher. The engines lose power at extreme altitudes, which is correct. The piston aircraft won't go to unlimited heights and the Beechjet's air speed has max and minimum speed tabs that respond to altitude -- the higher you fly the lesser the usable speed "window". I think that true airspeed does increase with altitude. To check we might fly a (long) leg in a plane that will go high and try two different altitudes. For instance, one might fly the Beechjet at 5,000 ft doing 200 kias and then at 25,000 ft with the same indicated speed reading. The higher flight level should get you there faster. Ascent and descent time would mess up the comparison so the ideal experiment would be to fly straight and level from one fix to another. Thus, it seems evident that we have a modeling of the atmosphere. What we don't have is a functioning mixture lever -- my guess is that we're dealing with a missing ( mis-applied) engine parameter rather than a missing atmosphere. If so, something might be done about it. An aspirated (non-turbocharged) piston engine would not make it above 4,000 to 6,000 ft without some leaning. Then, with the correct leaning it would be able to proceed and climb to about 10,000 ft. A turbocharged piston engine would be able to go to twice this height or more. Turbocharging has nothing to do with speed -- it means that the carburetor is being fed air through a compressor to keep the "dosage" of air high even though the outside atmosphere has grown thin. We'd still have to lean the mix for high flight levels though. The compressor is able to generate a pressure difference / uphold a constant ratio but the engine does get less air as the ambient pressure drops -- the engine may for instance "see" a 10,000 ft pressure at 20,000 ft. Evidently, the pilot would experience that same low ambient pressure unless the cabin is "turbocharged" as well. If it is you have a pressurized cabin. If not, you'd better breathe oxygen above 14,000 ft.best regards,Hans Petter

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