I've seen some complaints with respect to some popular addon twins, and not having any real-world experience with the planes I'm wondering if someone could enlighten me: Where exactly does FS9's turboprop modelling fail?Thanks for any info!Best,sg

I believe little changed from FS2002 to FS9 as far as turbine is concerned. You may find interesting to read this technical thread on the subject of FS2002 and its turbine model paying special attention to what Steve Small is saying since he is probably the most knowledgeable in this area.http://www.simforums.com/forums/forum_post...2499&KW=turbineMichael J.http://www.reality-xp.com/community/nr/rsc/rxp-higher.jpg

Thanks for that link...Best,sg

So I read that thread last night, and Steve's comments only confirm that the turboprop model in FS is faulted. I'm wondering where the fault lies...what specifically is deficient in FS9s modelling?Thanks!sg

I am by no means a flight model expert, nor a real pilot. However, if I remember the discussion from a while ago, I believe the basic problem was due to the fact that planes like the Kingair fly much more like a jet, than a bigger, more powerful GA airplane. But you would have to read the comments of Mr. Small to get more info. Honestly, I haven't flown the default twins in a very long time.

I think the Flight1 441 and the PMDG B1900 both have excellent flight dynamics for a turboprop. I don't know what their secret is, but it works for me. The largest fault I find with the King Air and other turbo props is the surge of power between 2-4% power when you're taxiing. You have to do that dance between F1 and the throttle to keep from rolling off the taxiway. In reality, it's not that hard to taxi a turboprop. I think the PMDG demonstrates the best feel of a TP on the ground. I'm sure someone has a technical answer for this.

>I'm sure someone has a technical answer for this.Yeah - I'm surprised it's been so hard to find. I agree that the 441 and the PMDG are quite convincing. I also think that the meridian and the cheyenne have excellent engine modelling. Just wondering what I'm missing - my though is that it has something to do with horsepower and engine gas temperature combined with power controlled with prop and mixture, but I'm not sure. The meridian and 441 have snuck by that with their advanced controls, however the cheyenne and B1900 seem pretty close to real world numbers. I can't quite get real-world fuel consumption rates with the cheyenne at cruise, but I'm not complaining...Thanks for the info.Best,sg

It is not flight modelling, it's modelling of turbine engine and most importantly the beta/reverse prop range that is faulty.Michael J.

That's an old post linked above. I can see the more things change, the more they stay the same !A lot of people much smarter than I have invested more time on this problematical engine template. As the post linked above says, the fixes we devise are a mix of maths and masking tape. That these problems could be fixed and then un-fixed during the FS2002 beta process, with no flight model changes made at all, is fairly conclusive. Nobody in a position to assist showed any interest then, or now. I'm sure Ron F could inject some colourful comment about that.The problems basically are :1. idle thrust;2. lack of effective dynamic engine braking;3. inconsistent reverse/beta behaviour; and to a lesser extent4. unpredictable throttle responseThe last new turboprop I published was the Meridian, for FS2002. I did improve the engine behaviour usefully on the turboprop for the Meridian for FS2004 (and quite easily, as it turns out) and whilst I provided Jean-Luc with a replacement .cfg it didn't include these useful changes. Recently, I usefully improved the Cheyenne's engine behaviour and when the opportunity permits we'll make it available to registered users.I never felt that solving the taxi problem was worth constraining the throttle's effective range to about the last 10% of throttle arc as I recently saw done, and as it happens it isn't necessary. But I never flew that type so I really cannot comment. Turboprops are not on-and-off like a tap with no-guts until almost full throttle : they are relatively linear and even a free turbine responds low down in the throttle range. I've only flown two types personally for any useful time (one geared Garrett, and one PT6) neither of which I was type rated in. I've had some RHS time in maybe another dozen types but linear definitely is a fairly good description for the way they all typically behave (on both power up and down) - the 'lag' of the prototypical push-and-wait free turbine aside. They are simply thrust machines but the difference is they slow your progress markedly when power comes off. The response in a geared twin of 850SHP a side on accelleration is both immediate, and very apparent. Taxi / idle speed problems have always been annoying in FS, they don't exist IRL in medium weight GA types. This FS problem is a function of a/c weight and installed thrust plus a few other key bits thrown in. The Meridian never really suffered from it, nor does the Porter, with both a/c being of similar HP and weight. Neither cross the fluid threshold at which point the problem presents and they run away at idle. Turns out the fix for designs that do cross that line is implemented in about two keystrokes once you know where to look : the fix works on every FM I have tried to date and it's not in the .cfg file but in another table Johan Dees and I collaborated on about 2 years ago. I consider taxi speed control to be pretty much a resolved issue now with a calibrated controller. That only really leaves (2) and (4) above unless some goo squeezes out somewhere else I haven't yet found. As always seems to be the case, these fixes are immediately obvious when you find them but are very hard to see. Some don't even relate to logic, which helps no end.Rgds,

Thank you, Steve! That's the info I was looking for.I'd love to see the Cheyenne improvements, but she flies pretty well as is!Best,sg

Thanks Steve for that explanation,As always your knowledge in this area impresses hugely and your explanations are informative, insightful and entertaining.Best regards,Chris Porter:-outtaPerthWestern AustraliaMy "Around the World 4" flight pagehttp://members.iinet.net.au/~portercbp/fly...e%20World_5.htm

>I've seen some complaints with respect to some popular addon>twins, and not having any real-world experience with the>planes I'm wondering if someone could enlighten me: Where>exactly does FS9's turboprop modelling fail?>sg I think we* are well on the way to working out the remaining details.* A combination of engineers, knowledable programmers, and SS wizards. Some of who are pilots. Some things are related to the max and minimum blade angle settings. The Cp (Power Coefficient) sticks at the last value, and may result in too much or too little torque in the Beta range and when feathered. Then, there is still a question of the Friction Torque table. I have noted that many of the CN2 entries related to the turboprop tables (such as the throttle) are really related to the Gas Generator. Which can be considered Ng rather than N1. While N2 applies to the tubine, and is geared to the prop. These changes in ID's are now in Aired.ini at Herve' Sors' site. Check Info for each table. Some Props require the 'power_absorbed_cf' setting in aircraft.cfg be set above 0. I even had a recip engine model that required that to get the idle speed down. The normal turbine model is now completly understood. To the point an experimental AFSD can display the throttle setting for a given cruise condition. Conscise equations are in Aired.ini, but I didn't have room to explain what 'Deta' and 'Theta_total' are. Standard parameters used in real turbine analysis. A command line app reads a jet tranport Air file and some lines in aircraft.cfg and ouputs a large set of data, in the form of an FM table. One can see N1, CN1, NAM, and PPH for each combination of Weight, Mach, and FL. This app gave good tables for one of my jets, but messes up on another. When it works it calculates the signficant Delta's, Theta's, and combines them with the turbine tables to find their exact effect. Incidenly, even the variation of Horiz Stab Lift with Mach shows in the output tables. Some settings with variable intake, etc. still have some work to finish. They are not used for most turbines. Knowing exactly what the parameters and tables do still doesn't tell us how to set them. Be assured a lot of work is going on in this area. We just got more turboprop info that may help work out the turboprop model better. However, this will at most, suggest what might help in the Beta and feathered ranges. Ron

Thanks for those details, Ron.In your (collective) experiences, is the model pretty accurate at cruise settings and only fails at low throttle/condition settings?Thanks again!sg

>Thanks for those details, Ron.>>In your (collective) experiences, is the model pretty accurate>at cruise settings and only fails at low throttle/condition>settings?>sg The turboprop clearly depends on both the Prop and Turbine performance. Prop Efficiency can be adjusted independently of turbine efficiency, but one needs to have the jet thrust component vary reasonably with FL to get an accurate model for total thrust. AFSD also displays overall SFC, and I noted it changed a bit as turbine settings and flight conditions changed. I felt that was a good sign. Overall SFC is adjusted with the fuel_flow_scalar, however Prop Efficiency should be set by the Prop Efficiency table entries. Typically, FS props are too efficient in climb conditions, though they appear to have improved at cruise. Prop efficiency in cruise should be near 85%, but more like 70% in climb. Jet thrust is fairly small, but drops quite rapidly with FL, so it also affects ESHP and SFC. A new table appeared in the FS2K2 turboprop model. It adjusts relative shaft torqe vs Density. I haven't had to adjust that much, but it could be the key to getting power to vary appropriately with altitude. I recently did a new C208B model, it appears to be reasonable at all conditions. However, I'm not that familar with the range of turboprop powerplants available and haven't tried to model all that many. Fortunately, people more familiar with them inform me of problems and how they shouild really operate.Ron

>Overall SFC is adjusted with the fuel_flow_scalar,>however Prop Efficiency should be set by the Prop>Efficiency table entries. Typically, FS props are>too efficient in climb conditions, though they >appear to have improved at cruise. That's interesting and may explain why I have issues with obtaining real-world fuel burn rates at cruise setting with some of these aircraft. I've just downloaded the new aired.ini file - I'll have to fiddle some more!Thanks again!Best,sg