Hello, I am trying to wrap my brain around how War Thunder calculates actual thrust in propeller planes, and to get there I would like to understand how propeller efficiency is modeled in the game. From what I understand, propeller thrust emerges from a complex interaction of engine power, rpm, prop diameter, the plane’s forward velocity, drag and lift polar curves on each propeller blade, blade area, and blade angle of attack (including changes in pitch for variable-pitch propellers), but the interaction between all of these factors remains a mystery to me and everyone else who has publicly looked into the topic.
From what I can tell, there are tons of IRL models with all sorts of calculus and trigonometry involved to get close to the truth, but I assume War Thunder opts for a simple calculation for the sake of their server hamsters. There are some hints towards a solution on the old wiki’s flight model creation page, using the Lagg-3-4 flight model as of September 2018 as an example, but I still can’t understand how one can go from various propeller proportions and aerodynamics inputs to a complete propeller efficiency vs advance ratio curve (as seen on the right side of this image). Is there anyone here with an aeronautics background or a good hunch?
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i have a degree in aeronautics and the answer to your question as you touched on requires some pretty complex mathematical calculations, which of coarse would have been done by the original aircraft or propeller manufacturer. How gaijin would or could use those calculations in game i have no idea unfortunately. Or even if they would have access to that information for that matter. My guess would be that they use a few standard propeller efficiency ratings as opposed to having a unique one for each aircraft/propeller combination. That would require almost as much data as the flight characteristics of each aircraft and probably wouldn’t be worth the effort as far as gameplay is concerned. A LOT of data for a small difference in performance envelopes may not be worth the effort to them.
Just my opinion.
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a couple more items to consider for calculating propeller efficiency are resistance to twist, resistance to stretch, and believe it or not ambient operating temperature. There are many more that i can’t remember right now. If i get a few weeks of extra time i can dig up my school notes, but don’t bet on that happening.
Indeed, they probably go of some standard chart based on the NACA system (for wings, but can be applied to rotating systems).
I can see for example this : https://apps.dtic.mil/sti/tr/pdf/ADB804045.pdf
From this document you can find relatively simple evaluations of propeller efficiency for different type of propeller.
In game I would believe they base their curve mainly based on :
- propeller diameter
- propeller shape (NACA or other)
- propeller twist
Then they probably apply a curve (using a simplified model, and or a data based of different chart and according to the closest one to the propeller) for each aircraft. If necessary, for a variable angle of attack propeller (idk the work in English), they might recalculate the curve with the angle of attack as input.
