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Guest ThrottleUp

What is the deal with FS and turboprops?

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Guest GrouchoMarxist

I've often seen it said that there's some inherent difficulties with regards to FS and turboprops, making it difficult for them to be modelled with high fidelity.In layman's terms, what exactly are those difficulties? And what ramifications do they have on the resulting product?Thanks in advance.

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Guest bobsk8

I don't know what the difficulties are, but Flight1 ATR and Aeroworx KingAir solved them.

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Bob is right on the money. Don't forget the Majestic Dash8. I have all three AC and you won't be disappointed in any of them. Best regards, Jeff

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Guest allcott

AFAIK the fundamental problem is that FS only recognises `jets` and `pistons` as engine types. The turboprop flight model is a fudge of the jet engine and cannot represent the typical geared turboprop engine at all and is very poor at representing the fuel flow/temp/altitude gradient that is often the limiting factor to turboprop operations. The various solutions from the manufacturers above work because they often go OUTSIDE the flight model to fix the errors.The best minds in FS flight modelling cannot fix this as it is a core component of FS that needs fixing, but they have found various workarounds.Allcott

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Guest ThrottleUp

-----------------------------------------------AFAIK the fundamental problem is that FS only recognises `jets` and `pistons` as engine types. The turboprop flight model is a fudge of the jet engine and cannot represent the typical geared turboprop engine at all and is very poor at representing the fuel flow/temp/altitude gradient that is often the limiting factor to turboprop operations.-----------------------------------------------Thats interesting, I never knew that. Hopefully a Microsoft scout has read that and is reporting back to HQ!

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Guest Shalomar

Donny AKA ShalomarFly 2 ROCKS!!!It seems turboprops have problems taxiing on one engine too. I was on Elite Flyers with the Veneviveonnes 690B, killed my starboard engine 30 miles out and landed Runway 34L KSEA to show off a bit. Tried to turn off, wound up next to the taxiway. Had to restart the Starboard, after I stopped I couldn't get anywhere. Was just about to announce my intentions, check and cross 34R when I saw a DC-3 with gear up skidding toward me from 16L, but that's another story. Suffice to say after that I didn't have to taxi to wind up on the ramp.Best Regards, Donny:-wave

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Guest Ozark Dogfighter

I doubt it not, seeing in their blogs how often they peruse these forums..:-lolSHOUT-OUT to Taildragger!!!:-lol-Jeremy BurchThe Ozark DogfighterHappy Flying!Pilot-The friction locks are causing the throttle levers to stick.Mechanic- Umm, that's what they're there for...

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Don't really know anything about flight dynamics, but I do know that engine type 5 is turboprop in record 310. Whether the physics properly models a turboprop engine is a different story.I think air file designers have been complaining about the undocumented air file and physics modeling since day 1.scott s..

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Guest IanK

Hello Groucho,This is a copy of material I was copying to make a FAQ:HartmannH Fri Jun-04-04 07:47 AM Member since Mar 09th 2002 25 posts #17803, "RE: Turboprops NP Value"In response to Reply # 5 Yes, for turboprop models in FS, N2 is always equal to NP.Hans -------------------------------------------------------Q2:Is there a way to correctly model a free turbine type turboprop, like the pt6 that equips B200's, in such a way that varying RPM at a constant altitude and power setting doesn't vary FF (it should remain constant)?Apparently MSFS ties FF to RPM somehow, and when, even in a turboprop engine, you vary the later, the former is affected.A friend of mine managed to introduce modifications in the AIR file for a well known B200 add-on in such a way that varying RPM will not affect FF, but other important parameters might be affected(?).Also, why do you sometimes make a difference between FF and PPH? Isn't it the same???? What about Corrected FF - how does MSFS calculate FF and CFF?A:well, indeed jmoss is basicly right, pulling back the prop rpm will have (pretty nearly) no affect on FF. first we have to differ from a classic two shaft turboprop and a two shaft free power turbine (like the PT6A).the difference is that in a free tubine the shaft resp the turbine disks connected on it are ONLY RESPONSIBLE FOR DRIVING THE PROP. so these shaft has NO MECHANICAL CONNECTION to ANY compressor. in a classic two shaft the one shaft drives the HP, the other drives the LP AND the prop. (its pretty close to how a turbofan works-one shaft for LP and the fan-one shaft for HP)in the PT6 the one shaft drives the LP AND the HP, the other shaft drives ONLY the prop, so it fully independent of the basic engine resp of feedind the compressors. so in a pt6 you can at the bottom spin the prop by hand and doing this you will not spin any of the compressors. of course the power drive shaft is mechanically connected with the main gearbox, these is every turbine so, but has nothing to do with the definition a a "free turbine". like described-the key is that in a free one the power drive shaft has mechanically nothing in common with the compressors. there are even three spool turbines (PW127 on a atr eg.) and one shaft direct drive turbines (TPE331 on a metroliner e.g), but these does not match our current discussion the advantages of a free construction is primary that you can variate the prop rpm very "free", you can even (by prop brake) stop the prop fully and the engine runs (see atr). you can do this, because the prop shaft has nothing in common with compressors-otherwise you would stop at least one compressor stage and so stop the engine...beating the theme to the top its in real world not absolute (but nearly) correct that on the pt6 pulling back the prop rpm will only increase TQ and all other things will stay the same. we have i a running pt6 a gasflow from the first compressors to the last turbine stages and the gases leaves via the exhaust.so when i pull back the prop rpm i will decrease the revolution of the last turbine discs (which are mechanically like described from all other independent). these will cause a little slow down in the gasflow of the engine and affect so a little the flow speed on the compressor shaft, which will a little (but really a little, barely readable on the gauges) slow down the compressors (PWC speeks regarding this about a "gasodynamic coupling"). these will from the physical point of viev indeed decrease the FF, but in such a minor way that you will hardly read it on the FF gauge, so for "tuning" FS9 its ok to say that pulling back the prop in a PT6 should have no affect on FF. but you will see (i have no idea if it its to manage at fs9)a little readable INCREASE in ITT (inter or interstage turbine temperature), because the slowed down gasflow in the turbine will let the "heat" of the gases a little longer in the engine and the a little slowed dowm compressors will provide minor less air for chamber cooling. regarding "my" edited airfile which will cause to increase TQ without decreasing FF pulling back the props:the secret is in line 509 at the airfile, I edited it with AAM. the thruth is that got the hint where to search from a passenger i have flown some time ago...i,m not in front of my FS9 pc, so i have now a problem to describe it further. i sent this edited airfile of a king air to jmoss. jose-please open this file with AAM, look at line 509 and then look to the difference between line 509 at the (hopefully backedup) original airfile. its a change of two minutes... maybe you can jump in here then and explain. it depends on which "angles" the responsible curve are standing to each other.the deal is that fs seem to couple FF to prop rpm (which is like described at leat in a pt6 basicly wrong) AND with tourque. so changing the airfile so that torque rises at lower rpms (which is correct) lets fs instantly increase fuel flow, the simultany decrease in prop rpm lets fs decrease fuel flow.after plying a little with the proportions these increase/decrease equals each other and the result is torque higher-FF the same!!! (and this pretty good matches the reality, the only issue is that ITT should also rise a little)ok, i truly hope that i was able to help a little, beyound this i have to knowledge in airfile eiting. i unfortunetly have to fly the whole weekend so i will be back on monday evening and then can look in the airfile.nice weekend to all!mariuswell, i,m riding on a tpe331 airplane, so regarding additional info i would have here better possibilities. but we have in our company also cessnas 425 eqipped with the pt6, so let me know what exactly you are looking for and i might try to get it. some copys of the AOM of the 425 with the performance charts should be no problem, if your are interseted in soome real pt6 deep details which may be helpful for editing i can ask the technicians who maintain the pt6 on our planes. my only shame is that i have no scanner...when you have some performance charts at home be careful interpretating them in accordance with our discussion. your often see there indeed a lover flow at lower prop rpm. this is because these tables are mostly regarded to "recommemeded cruise power" and to reach this you after top of climb mostly reduce the rpm AND the thrlottle a little to get the recommended TQ or the ITT. adjusting also the power will of course have an ffect on FF, here we discussed what happens when you LEAVE power and reduce rpm. ian: i would say its a workaround to basicly simulate the things, . IF fs9 in this case reduces significnant the power output of the engine my modification is wrong, no question. especially on a free engine where the gas generator is mostly unaffected by prop rpm the BHP on the shaft should stay nearly the same. you gave in your question with one formula the answer:prop rpm *TQ in lb ft/5252= SHP this is something from real aviation and you can by this formula calculate the horses running on your shaft on every turboprop when you know TQ and rpm.so the TQ rise at rpm drop should be as much that the final SHP result is nearly the same. some horses ok, but when it should make a difference of lets say 100-200SHP, my "tuning" is wrong. ( i did not tested it) jmoss, when you have some minutes try on my edited airfile the following: in cruise after the plane established a speed multiplicate the TQ you read with the prop rpm and divide this to 5252, then notice the result-its you shaft horse power output of the engine at this time. then reduce the the prop rpm by lets say 200revolutions without changing the power or the alitude and make the calculation again: the shp result should be the + - the same.nice evening to all!mariusI looked at the modifications operated by "acrobat" and basically he edited the 509 table in the following way:Default B350 acrobat's B200=============================================-10 -0.18130 -10 -0.210 0.17756 10 0.270 0.50061 70 0.8100 0.78 100 0.8-----#######################Jose Carlos (LPPT)Here are the results. Run at ISA weather (clear all weather through FSUIPC):============================================TQ RPM SHP KIAS ALT============================================2217,00 1838,00 775,87-----------12000,002189,00 1866,00 777,74-----------12000,002156,00 1898,00 779,15-----------12000,002153,00 1902,00 779,70-----------12000,002050,00 1998,00 779,87-----------12000,002189,00 1700,00 708,55 221,00 15000,002087,00 1800,00 715,27 220,00 15000,001986,00 1901,00 718,85 218,00 15000,001893,00 1999,00 720,51 212,00 15000,002186,00 1788,00 744,21 219,00 20000,002084,00 1888,00 749,16 217,00 20000,001979,00 1988,00 749,10 218,00 20000,00=============================================So... apparently your mod is very good. We see little SHP variations when RPM varies at constant Alt and throttle settings.-----#######################Jose Carlos (LPPT)------------------------------------------------------------------------------------------------------------------------------------Ian

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Guest ThrottleUp

-----------------------------------------------I doubt it not, seeing in their blogs how often they peruse these forums..-----------------------------------------------You mean the MS people? :)

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