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Piston engines and props

P

Pgleize

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5
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france
Hi everyone,

I am trying to figure out how to fine tune engine piston and props parameters.
If anyone has a methodology or a document that describes the internal model of piston engine and props I would be very interested. I heard that Ron produced long time ago such doc but it’s no longer available.

thanks all
 
Hello,

I'm just about doing the same, and I am very curious about props.

I've done some fiddling with .cfg files and I am fairly sure something is off with static thrust of propellers.

I've found tables for thrust when in motion, however, i'd like to know how and where to affect static performance when propeller advance ratio is nearing zero, as in that range i'm not getting good results.

Thx,
kind regards.
 
FS2020. I apologize if i posted into wrong topic, I figured just now this one does not have a tag for 2020. I'll open another one if need be.
 
No problem ! I also meant FS2020. It turns out only legacy mode enables props tables. You can figure it out easily by removing these entries in cfg. It still loads fine.
I think I got what represents prop cf and prop efficiency: prop cf represents the force generated by each blades (think of it as a lift and drag vector suummed) and prop efficiency the lift component that gives useful thrust.
 
Wait... so cf table and prop efficiency tables are not used in modern model?

So, how are we supposed to model propeller performance in new model?

Thing is, domain of propeller efficiency table is not static case, but when aircraft is already in motion.

I've been using modern model. Static thrust is to low. For example:
On a 3 bladed 6,4 ft propeller with beta 15.2 deg, driven by about 380 HP at 2800 RPM at MP 34 inches i've been getting forces (thrust to be specific) as low as 400ish lb static. I would expect something twice that. That means that rolling from the start is noticeably slow, and then by the time you reach 100 kts force is more than doubled. Ofcourse, start was not a rolling start, but brakes-fullpower 10 s -release.

So, how do we do it with modern model? Use of factors within config only? Must experiment more.
 
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Try yourself... for instance we can play only with the global scalars. It’s a bit the same with CL vs aoa... Modern flight model use a predefined profile of the CL vs aoa that auto scale with a subset of the CL vs aoa table entry in the flight_model.cfg. In fact it seems to use CL @ 0 aoa and CL max. Post stall aoa is not modifiable...
 
"In fact it seems to use CL @ 0 aoa and CL max. Post stall aoa is not modifiable.."
If you need a good example of the problems that brings, try flying the Pitts inverted
Roy.
 
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