Oswald factor

[jgf]

Have an older (ca 2005) free aircraft whose flight parameters were supposedly designed by someone knowledgeable (not calling any names, but you would recognize it).  But noticed its oswald factor was 1.4(!?);  everything I read, for FS and real world, says 1.0 is the max, as that indicates a perfect wing (which of course does not exist).  Real world values, not always applicable in FS, for this aircraft are 0.56-0.65 depending on production run;  the Carenado version, representing a late production model, uses 0.85.  So I arbitrarily tried 0.72 ... the plane took nearly the length of Seatac's main runway to get airborn, and climb was pathetic until around 2k ft, when performance became similar to the original setting.  Landing was just as bad, can't slow enough to use two notches of flaps, and only one notch means approaching too fast.  So tried setting oswald to 0.85.  That's better, can take off on average runways with one notch of flaps and massive nose up trim, but climb is 600fpm at around 85kt (normal is 800fpm at 100+kt);  again, once above around 2k ft performance seems normal.  Landing is dicey, 105-110 kt with one notch of flaps, tire screech and once bounce is a good landing.

 

So, is there a setting I can tweak to compensate for the more correct oswald factor that would improve the low altitude low speed performance without upsetting the rest of the flight?  Or should i just return to the obviously incorrect oswald setting and live with it?

[Airbasil_1]

The Dreamfleet Piper Archer III is even worse than all of the Carenado models  

[chris_eve]

1 hour ago, jgf said:

So, is there a setting I can tweak to compensate for the more correct oswald factor that would improve the low altitude low speed performance without upsetting the rest of the flight?  Or should i just return to the obviously incorrect oswald setting and live with it?

Having "played" with these factors many years ago I do remember that the air-file editors are mostly not perfect and also there's usually more than one other setting that can be "tweaked" to compensate for what was, to all intents and purposes, bad design in the first place.

Usually my solution, as brutally crude as it may be, was to get it working and leave well alone, irrespective of the "real world" parameters that might suggest it was "wrong"

[jgf]

Well, my philosophy is to plug in all the hard data available then tweak the "unknowns" for proper performance.

 

Funny thing is, even after twenty years the editors still show so many parameters as unknown, and MS has been strangely quiet about all this (probably because they're afraid we'd find out how much they fudged everything just to make it work ...hence all the scalar adjustments).

[ScottishMike]

There is probably no one left at Microsoft who knows or cares. The FS team will have all moved on to other jobs and other companies. As chris_eve said if you get it working to your satisfaction what else matters? Because certain variables have names that are similar or the same as real world ones it does not mean they are the same, or act in the same way in FS flight equations as they do in the real world.

[PhrogPhlyer]

1 hour ago, ScottishMike said:

Because certain variables have names that are similar or the same as real world ones it does not mean they are the same, or act in the same way in FS flight equations as they do in the real world.

A point I'd never considered in the past.

Without a clear list of variables and how the original programmers used each one, we are all shooting in the dark.

I do like jgf's approach, as close to real as possible for settings and adjust, but SM's statement may make all that effort moot.

 

This is the last I wa able to find from MS on these settings in FSX.

https://learn.microsoft.com/en-us/previous-versions/microsoft-esp/cc526949(v=msdn.10)?redirectedfrom=MSDN

 

[ViperPilot2]

I have noticed that when discussing FDE's there are two schools of thought; one is that the .air File draws many of its Parameters from the Aircraft.cfg and that is the more important Data, the other is that the .air File is just as critical because it lays out the Parameters of the Flight Model.

 

However, finding a clear, concise and coherent Answer in all of the Documentation is just as elusive as deciphering the .air Files themselves.

 

Everybody talks about "Ranges" in the .air File, but the question still remains; do the Ranges need to cover so wide a scope, or do they need to be narrowed down a bit? No one seems to either know the Answer, or else they're keeping that 411 TS/SCI and very, very close to their Vests.

 

So, we're left with what chris_eve and SM said; if it's close enough and it works, go with it. If it's just too unmanageable, find another one.

 

Perfect example is the airplane I was initially going to use in our Route 66 Air Rally; the Tachometer will not function as it's supposed to, and at V1 she pitches up close to 40° so abruptly that I'm using way too much Elevator Trim to compensate, then I go the other way with the Trim once the Flaps are up to get the airplane stable.

 

By the by... what does everyone use for an .air File Editor? I have older copies of both AirEd and Airwrench. I also refer to Bob Chicolo's Tweaking Manual from time to time. The Microsoft page detailing Aircraft Configuration tells you about the Parameters but nothing about where they should be Optimized.

[PhrogPhlyer]

3 hours ago, ViperPilot2 said:

By the by... what does everyone use for an .air File Editor?

I have not worked with the .air files at all.

Is there a decent tutorial you would recommend?

[ViperPilot2]

1 hour ago, PhrogPhlyer said:

I have not worked with the .air files at all.

Is there a decent tutorial you would recommend?

I don't know about a Tutorial, but Chicolo's booklet offers some 'guidelines' about working with AirEd and the .air File Values. What I gleaned from it was that it's a matter of Trial and Error. Adjust the Value slightly, and see how it translates in the Sim.

 

FDE manipulation seems to me a lot like Repainting; there are a few that are in the know, but are very recalcitrant at spilling any Secrets about making the Process easier.

[jgf]

Aired is the old basic editor and still quite useful, though many items are still listed "unknown".  AAM is newer, more items identified, and numerous notes on ranges of values and interaction.  The original aircraft container sdk gives basic descriptions of many of the parameters but little info on tweaking them.  I have found no comprehensive tutorial, just tons of information buried in threads (so individual searches for each parameter as you encounter them).

 

Most of the data is now contained in the cfg file, and anything there will override the same data in the air file;  but the air file contains many tables of aerodynamic  performance data that are referenced by the cfg file, and much data on items like oil pressure range, CHT, etc.  The simpler tables can be edited in aired, but the more complex ones have so many points that they are difficult to work with in the small space provided;  AAM will export these tables as columns of data, but throws an error when you try to import them (something in German about floating points).  With aired you can copy any table from one air file to another (just remember to "replace" not "paste" or you'll have two dissimilar tables in the same file;  this is often the quickest way to make a change.

[jgf]

7 minutes ago, ViperPilot2 said:

very recalcitrant at spilling any Secrets about making the Process easier.

 

Mainly because so much of what is there is still unknown, and in some cases you can make substantial changes to a parameter with little to no discernible difference in the aircraft performance.  For example, you would think several aircraft of similar dimensions, weight, performance, even identical engines, would have very similar specs for a particular item, yet you will find one with a value of -16482, another with +32951, a third with +10738 ...with no explanation of what these values represent, nor even what units are referenced (beyond perhaps some proprietary scale).  AAM goes a bit farther with these, listing the values for default aircraft for comparison ...even though there is no idea what is being compared.

 

I think that's why the scalars are in the cfg file.  You can use all the real world equations to get all the "proper" values for your aircraft, plug those into the cfg/air files ...then use the scalars to get that aircraft performing as desired.

 

Much like the engineering concept of "Finagle's Finagling Constant" - that number which, when added to, subtracted from, multiplied by, or divided by the number you got gives you the number you need.

[PhrogPhlyer]

1 hour ago, ViperPilot2 said:

Chicolo's booklet offers some 'guidelines'

Thanks

1 hour ago, ViperPilot2 said:

FDE manipulation seems to me a lot like Repainting; there are a few that are in the know, but are very recalcitrant at spilling any Secrets about making the Process easier.

So so true.

[PhrogPhlyer]

1 hour ago, jgf said:

Most of the data is now contained in the cfg file, and anything there will override the same data in the air file;  but the air file contains many tables of aerodynamic  performance data that are referenced by the cfg file, and much data on items like oil pressure range, CHT, etc. 

Good to know.

[PhrogPhlyer]

1 hour ago, jgf said:

Much like the engineering concept of "Finagle's Finagling Constant" - that number which, when added to, subtracted from, multiplied by, or divided by the number you got gives you the number you need.

And in real aircraft certification, when the weight of the paperwork equals the planned max gross weight, its ready for submittal to the FAA

[hjwalter]

A very interesting thread/subject indeed. However, I've always been lead to believe that the extremely complex real aircraft aerodynamics just cannot simply be scaled down to e.g. that of a much smaller exact scale model, let alone to that of an FS aircraft, which doesn't even have real air of different densities to fly in.

 

FS aircraft are designed to perform ..... LIKE ..... real aircraft but only visibly on different screen types, which in my mind automatically means that FS aerodynamics may never be directly compared to those of real aircraft, even although very much effort has quite obviously gone into making them visibly perform in a very realistic manner, mostly based on combined AIR file and aircraft.cfg "aerodynamic" parameters.

 

Long live FS9, independent of real world Oswald and other factors !!

 

Hans