One of the other fantastic folks who subscribe to this email list replied back to me on Tuesday with a few comments that made me think (thank you, RSC!):
“As I read through this one, couldn’t help but think about how aero sometimes has the most impactful design levers – a small change in a parameter can snowball into large changes in the functional capability of the system. What makes it more challenging is that since aero performance is a system level metric, it’s not as simple as changing out a capacitor or adding braces/ribs to a stressed out mechanical component.
All to say, I respect my aero colleagues a lot because I know how difficult it is for them to wiggle from a baseline that works. Changes for me involve plugging and chugging at LTSpice whereas they are usually dragged into flight test and complicated CFD sims.”
I focused so much on how I strive to support other disciplines—that is, my engineering team. And in doing so, I completely glossed over how much those little tweaks and concessions cascade through the entire configuration.
Because it’s exactly right: you can’t just say “oh, I actually like this airfoil more, let me swap it out.” You have to check what it does to your full configuration.
Did that airfoil have a larger or smaller pitching moment than the original one? You may need to adjust your wing’s angle of incidence (angle relative to the fuselage) to ensure you have a large enough angle of attack range with positive pitching moment, to maintain your stability.
Angle of incidence also changes lift, though. Do you need to make your wings smaller or shape them differently? Longer wings have efficiency benefits; are you giving up some of that now? If you reduce chord instead, do you still have enough “meat” for all of the wings’ internal components?
What about your tails—are they still large enough? Do they need to be smaller now? Do you still have enough surface area for properly-sized control surfaces?
And at the end of it, what does all of this do to those final system-level metrics, our aero performance? Did that airfoil change help more than it hurt?
It’s a lot. I’m so sorry if you hear a tired sigh. I promise it’s not at you.
And I “just” work on UAVs, which are a lot simpler and lower-risk and let me have more leeway. I can only imagine how much pain engineers of crewed aircraft must go through, just to make everything fit together right to achieve the performance they need.
All of this proves how collaborative engineering has to be, especially for something as holistic as an aircraft. Everyone has to assume good faith on everyone else’s part. It’s about finding the solutions that best fit what every discipline or sub-team needs.
And if something absolutely cannot be changed, it’s about working together to find the best answer to that problem.