Maybe it wasn’t quite worth the time to dig so deep into something that only accounted for 5% of a flight profile. But this felt important.
Climb rate depends on your available excess power. In my flight envelope code, I was using the engine’s output to the propeller to calculate excess power. Looking at my equations, I realized this never took into account whatever efficiency percentage the propeller had at a given operating condition.
And because the climb rate depends on the power available to move the airplane—which comes from the propeller—that oversight definitely mattered. Basically, all of my excess power estimates were about 25% higher than they should have been.
I added that propeller efficiency factor in and surprise, everything lined up the way I expected.
I adjusted my flight envelope code too, and the impact was interesting: the biggest change was decreased max rates of climb in the middle of the airspeed range. But the maximum altitudes barely changed. The problem had been hiding there the whole time.
So what did I take away from this? What should you take away?
My advice of weighting impact vs effort largely applies to optimization and improvement. How fine a grit of sandpaper will you go down to before you decide you’re done polishing?
But if something genuinely itches at you, if it doesn’t feel right, take the time to look into it.
Maybe it’s nothing, and you just validated your choices and assumptions and can better defend them.
Or maybe it’s something—a physics gaffe, an incorrect multiplier, a coefficient you didn’t use—that genuinely impacts your output.
My “itch” helped me uncover an actual problem in my calculations that would overpredict our performance, and gave me the opportunity to fix it. Fixing this issue also gave me a more realistic calculation for climb and descent, by assuming the prop absorbs either ALL available power (for climb) or zero power (for descent), and calculating the resulting prop thrust.
My code is much more flexible now and able to handle whatever unique cases I want to throw at it.
It also enhanced my own understanding of the physics underpinning my models, and to me that’s priceless. Now I’m always careful to distinguish between the electrical/mechanical power that an engine generates, and the physical power from a spinning propeller. They’re technically the same, but some calculations only make sense for one or the other.
This is probably Engineering 101 stuff, sure—but it’s helpful to me. Sometimes you go so deep into the more advanced concepts that you need a refresher on the basics.
So if something itches at you, if it just doesn’t feel right, maybe take an hour and dive into it. I’d argue any time you spend cementing your knowledge and becoming a wiser, better engineer is time well spent.