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sblzei
July 12th, 2010, 07:17
As it is known, FSX recognizes 2, 3, or 4 blades propellers only.
Since modern turboprops are fitted with 5 or 6 blades, I am looking for the best way to "cheat" the system and make it "accept" 6 blades props.

I'm not sure wether it would be better to set the number of blades to three and then double the power scalar, or make the blades four and apply a power scalar of 1.5.

I know that real physics are not exactly these, but I don't know how the FSX "engine" works in this respect. Flight test has not given significant results either.

Any suggestion is highly appreciated. :wavey:

Ezio

fliger747
July 12th, 2010, 08:46
I suspect that you will have to use a bend to fit, paint to match method. What you are simulating is taking shaft torque applied at a rate yielding power and converting it to thrust by creating a mass movement of air to which the aircraft will respond by moving in the opposite direction.

Twice as many blades usually does not result in twice as much thrust. The reason for increasing the number of blades usually has to do with a combination of issues concerned with aircraft design. The first one governing overall diameter is the rated output shaft RPM and the resulting tip speed. As tip speed prop approaches a high mach number efficency declines and noise increases significantly. Smaller diameter props with more blades can keep the overall diameter down, with a resultant decrease in noise. Sometimes the configuration of the aircraft will dictate a maximum prop diameter or it's use. As an example many Cessna 185's on floats use a three blade prop to improve spray clearance. Multiblade props are more expensive, heavier and create greater gyroscopic forces. Not untill very lightweight composite models have become available, and "quietude" has assumed a great importance has it been practical to utilize for example six blade props.

I realize none of this has been of a lot of help. Essentially you will have to use a prop that will simulate the thrust properties of the installed one without having to worry about noise or aircraft and operating conditions. You have an issue of working backwards to known performance. If you have good info on any of the variables, such as drag, and power, then one can derive the necessary prop efficencies.

I suggest the AFSD utility by Herve Sors as you can monitor all of the relevent parameters in your flight test. Also the "Aircraft Airfile Manager" shows graphic displays of the prop tables, and allows manipulation via base 10 entries rather than hex.

Good Luck! T

sblzei
July 12th, 2010, 12:44
Thanks Fliger 747,

I am aware of the fact that in real dynamics there is no simple direct relationship between the number of blades and the power produced. Besides noise (wich is more directly connected wit blade speed and shape), aerodynamic load and efficiency are the essential considerations behind multiple blade choice. A more "full" propeller disk, seems capable of moving more efficiently a bigger mass of air.
Since MSFS is not concerned with noise or loads, in my opinion the reason for putting this variable in the aircraft .cfg is either: 1) a way to introduce an efficiency factor, or 2) a way to take into account the gyroscopic forces created by the prop.
Who knows?

Brett_Henderson
July 12th, 2010, 16:39
The MSFS 'engine' doesn't acknowledge the number of blades. All it cares about is diameter, MOI, and blade-pitch.

fliger747
July 12th, 2010, 17:08
Even though you will be simulating a prop with a greater number of blades, the MOI should remain fairly low with the lighter weigh blades.

Cheers: T

sblzei
July 13th, 2010, 02:15
The MSFS 'engine' doesn't acknowledge the number of blades. All it cares about is diameter, MOI, and blade-pitch.

So, why there is an entry for number of blades in the aircraft.cfg ???

Brett_Henderson
July 13th, 2010, 02:54
So, why there is an entry for number of blades in the aircraft.cfg ???


Good question.. :wiggle:


I think it's one of the parameters that they thought they might use eventually (there are quite a few cfg entries that are ignored)..

sblzei
July 13th, 2010, 09:06
I think it's one of the parameters that they thought they might use eventually (there are quite a few cfg entries that are ignored)..

Another reason to regret that the development of a more realistic sumulation was canceled by MS...

fliger747
July 13th, 2010, 11:06
Ups and downs to everything. A better (completely new) sim engine would have made all of our previous efforts and projects obsolete. MS's attitude was that it was generally good enough, which it (generally) is. Most of the efforts went into graphics and world issues rather than (for example) autopilot capabilities etc. Their people who did have aviation experience were mostly bug smasher types so the sim engine has remained true to that genre.

Cheers: T

Milton Shupe
July 13th, 2010, 15:03
Good question.. :wiggle:


I think it's one of the parameters that they thought they might use eventually (there are quite a few cfg entries that are ignored)..

Back in FS2000 and FS2002, MS distributed the air file generator called FSEdit. Many of the parameters in the aircraft.cfg were put there for FSEdit to generate the many tables for the .air file.

Ron Freimuth did a thorough analysis of the aircraft.cfg parameters to determine which ones actually effected changes in the air file. The results are posted at Herve Hors site. If you cannot find it, I have a copy if you are interested.

Lastly, I have used FSEdit, and when it and the processes are properly understood and adhered to, it would generate a dang nice air file with very nice performance specs IMO. Most people just did not understand how to use it.