FSXA Superchargers and engine power

[NDORFN]

Ok in really basic (NDORFN speak) terms, if a turbocharger only begins to provide boost when sufficient exhaust pressure is reached, and a supercharger is driven by the engine shaft, does that mean a supercharger starts providing minimal boost at idle and increase throughout the RPM range?

 

[Dutcheeseblend]

Ok in really basic (NDORFN speak) terms, if a turbocharger only begins to provide boost when sufficient exhaust pressure is reached, and a supercharger is driven by the engine shaft, does that mean a supercharger starts providing minimal boost at idle and increase throughout the RPM range?

I would think so, yes. That's my observation as well. But, setting the min_design_mp, will already provide boost with a slow running engine. At least, that's the case when I enter a min_mp of 29.92 inches. It results in 11.something inHg at closed throttle, while with a 0.0 min_mp it gives 5.something at closed throttle.

The observed delay in a turbo does also occur at all throttle advancement speeds.

@WarpD: Ok, ok

 

[NDORFN]

I would think so, yes. That's my observation as well. But, setting the min_design_mp, will already provide boost with a slow running engine. At least, that's the case when I enter a min_mp of 29.92 inches. It results in 11.something inHg at closed throttle, while with a 0.0 min_mp it gives 5.something at closed throttle.

The observed delay in a turbo does also occur at all throttle advancement speeds.

@WarpD: Ok, ok

If you're using max_design_mp=40.08 and min_design_mp= 1.0, and you go full throttle and let the turbo kick in (until you're reading 40.08), are you getting a "boost gain" reading in AFSD of 1.188 by any chance?

 

[Dutcheeseblend]

If you're using max_design_mp=40.08 and min_design_mp= 1.0, and you go full throttle and let the turbo kick in (until you're reading 40.08), are you getting a "boost gain" reading in AFSD of 1.188 by any chance?

No. The boost gain that AFSD displays is the MP/Air pressure ratio and it doesn't change with changing the min_design_mp. However, I went up for a test: I compared the throttle to MP behaviour of various values of min_design_mp. This is what results:

Now, the interesting thing is, I tweaked TBL508 until I got some 600 rpm at closed throttle (as per the documentation AFAIK). The corresponding MP is 5.41. So having a min_design_mp lower than the minimum MP of the running engine, will result in a different throttle curve. With a min_design_mp of equal or greater than 5.41, the throttle profile appears to be linear.

 

[NDORFN]

Interesting. Did you know there's a TBL506 Throttle Profile? I'm not sure how it effects things or whether or not FSX even uses it. The two I've seen are linear but I wonder if you can edit it to your advantage. Another is TBL505 Engine CFS+ Piston Engine, which again I'm not sure whether or not FSX uses it... it may only be referenced by Combat Flight Sim. It's got all the same engine parameters as the aircraft.cfg with the added ability to set the Boost Gain so again could be useful.

Does AAM (whatever that stands for) allow you to edit the graphs in .air files easily? I can only edit as Hex data in AirEd, Looks like hieroglyphics to me.

 

[Dutcheeseblend]

I remember having seen a Throttle Profile table, but I don't have it in my file.

AAM stands for Aircraft Airfile Manager, very useful and far more intuitive IMHO.

 

[Paul Domingue]

I remember having seen a Throttle Profile table, but I don't have it in my file.

AAM stands for Aircraft Airfile Manager, very useful and far more intuitive IMHO.

I have AAM but just recently purchased AirWrench on recommendation. I haven't fully tested it but it looks promising. I just started reading the manual.

A lot of the tables in the AIR file that were functional in FS9 were dropped in FSX when they migrated to the CFG. That can get confusing if you start working with the older FS9 AIR file as your base. Don't forget that AAM was designed for FS9 and never upgraded.

 

[Roy Holmes]

The section names, or ideas about what each might be in Air Ed come from aired.ini. The latest version of that is dated 2006.
AAM is kept reasonably up to date so I prefer to use it.
Section 506 is indeed called "throttle profile in aired.ini.
It's real title is AIR_61S_VOLUMETRIC_EFFICIENCY. AIR_61S means it was related to FS98. It is not directly used in the latest versions of FSX or P3D.
Yves document lists all of the air file sections and some, for example 505, are listed as obsolete. This basically means that what they held is now in the aircraft.cfg.
In the P3D SDK there is a section called Flight Models which covers what is in .air files. This did not exist in the FSX SDK because MS kept in under wraps, but they did open their kimono when they promoted ESP and of course LM includes it in their SDK.
There actually is no great mystery any more about what is in the air file and the authority is absolutely not AirEd.ini.
Roy

 

[Paul Domingue]

I had forgotten about the FSX update for AAM. I wish they had updated ACM. There is also ASM but I have never used it.

 

[NDORFN]

I've downloaded AAM and it's like Christmas here for me now. I can actually edit .air files properly! Cheers guys.

 

[Ellover Dee]

Not gonna read this whole thread but some points to ponder:

Boost is absolute pressure, so depending on your engine, the numbers will have to be sorted based on American, British, or German methods. You may have to make some conversions and do some addition. With German planes, the ata is an absolute value starting at zero pressure. American planes, inches of Hg. British are the most confusing at first glance but a few calculations and conversions will get you the answer.

One thing that most folks may not know is that direct supercharged engines produce MORE BHP for any given set throttle position as they climb. So, say you have 46" of boost on your P-51 to climb out with; that 46" of boost will produce MORE shaft HP at the prop as the plane climbs.

This is because of reduced back pressure at the exhaust stacks and it is quite significant.

 

[Ellover Dee]

An earlier post lauded FSX, etc. for extremely high fidelity in modeling piston engines.

That post is exactly correct. One of the most rewarding things about FSX/P3D is to really get these engines right. Fuel flows, bhp at various altitudes, and so on.

It is baked-in and can be found with a lot of intellectual curiosity and diligence.

The MSFS team also got the flight dynamics right. Combine the two and you get thousands of hours of entertainment and edification.

 

[Ellover Dee]

The delay is all about design, and I have no idea what turbocharger they modeled.

The FS team used the turbocharged Allison V-1710 engine in the YP-37 as at least a partial basis for turbocharged engine models. All piston engines and their systems appear to be based on the state of the art of such engines circa 1950, which is perfect.

I found this out during a few thousand hours of testing over the last couple of decades or so.

One piece of evidence I uncovered is that a properly modeled V-1710 turbo as installed in the above airplane exactly matches fuel flows and bhp output at exactly the manufacturer's specifications, as tested in the simulation.

 

[bstolle]

Is there a reason why you are resurrecting countless 3 years and older threads (without even reading the whole thread)?
Furthermore I don't think that many FDE designers will agree that MS 'got the flight dynamics right'.