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MSFS Engine/Propeller take-off performance vs. climb performance

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145
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unitedkingdom
Any quick (haha, as if) clues for how to tweak prop/engine parameters for 'ground run to takeoff' performance VERSUS climb performance with a fixed-pitch prop?

I've been able to adjust engine power and prop beta to get my aircraft to lumber down the runway and get airborn, but then it climbs unrealistically easily. It's not a thrust vs. rpm thing as these are the same (i.e. max rpm) for the ground run and the climb.
 
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15
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portugal
I noticed in MSFS2020 there is a "bug" that makes the Prop Efficiency way too high since standing still. It's never below 0.30 if I remember right. Check that, maybe that's causing the issue with the Takeoff Run being way too fast if the climb performance is spot on. Just an idea.
 
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145
Country
unitedkingdom
Thanks Alex, that sounds like a very very helpful clue - I need to understand the "prop_efficiency_table" entry in engines.cfg - TBH (as a long-time glider developer) I have no clue how that table works and the MSFS SDK entry just says it's an "nD Table" without giving the actual parameters used. My self-launching glider so far has that value copied from the MSFS DA62. FWIW my aircraft has a fixed-pitch prop and the plane is very slow to accelerate on the ground but once flying speed is reached it climbs strongly.

This post from OzWookie explains engines.cfg prop_efficiency_table is derived from Table 511 in FSX

I.e. Propeller Efficiency (0..1) vs Advance Ratio, Blade Pitch(degrees)

Where Advance Ratio = Flight Speed (feet/sec) / ( Prop rotations per second * Prop diameter feet)

So it looks like Advance Ratio is how far the plane has moved forwards compared to the distance swept by the tips of the prop.

It seems for a fixed-pitch prop, and a constant RPM, the Advance Ratio is linear, starting at zero when you've just released the brakes for takeoff and climbing with airspeed (?).

So thanks! I'll copy another prop_efficiency_table into my glider from another plane with a fixed pitch prop (I bet the DA62 is variable pitch, I didn't know enough to check), see how that goes, and increase the efficiency at low Advance Ratio if I need to.
 
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