What is probably the greatest aviation short story recounted live, “The LA Speed Story,” has a moment in it that I only noticed after a few times hearing it. It’s just a phrase when Shul is describing how perfect the flight is: “Not a needle was moving.” Screaming through the sky faster than a scream can travel, the machine he was in was in stasis. There was no wiggle on the airspeed, altitude, or engine instruments. Riding the pinnacle of engineering, directing the thrust of a typical Southwest jet but only moving two people, the pilot’s control of the machine had the four forces acting on the plane arranged in perfect balance. The lift pulling up against the weight and the thrust pressing forward against the drag.
I love those moments in our little plane. The two engines both set at 75%, the revolutions per minute both reporting 2,100, the fuel flow on both engines at 5.4 gallons per hour, and the temperatures all sitting calm, still, unmoving.
In some twin engine planes there is a knob to twist called “Propeller Sync.” When you have two machines spinning the propellers around a couple thousand times per minute getting them to do it at exactly the same speed is difficult. Most engines, including the engine in our previous, single engine plane, use all mechanical linkages for controls. So I spent over a decade pushing forward a black throttle lever as we took off, fiddling with a blue lever for the propeller speed, and nudging a red lever to change the mixture of air and fuel fed to the engine.
The new plane has modern, automotive engines. There are two FADEC boards in each engine compartment. I have a single black lever for each engine: requested power. Mostly it is either at idle (when start or shutting down), 100% (for takeoff) or at 75% when we are sitting in cruise. The Fully Automatic Digital Engine Control translates my request into throttle position and some setting for the propeller governor.
It annoys me that the RPMs reported in the cockpit are apparently calculated, there is no sensor data on my screen. And, saddest of all, the engines do not talk to one another. If there was a sensor for the RPMs and the FADEC boards had a little network connection they could synchronize the propellers.
When they are not synchronized there is a harmonic beat that happens the RRRRRwwwwwwRRRRRRwwww that you hear in old WW2 movies with twin engine planes. Sometimes I can eliminate it by tiny nudges of the power lever, but not always.
Deep down I harbor some mistrust in the engines, which is foolish because they have carried us nearly a thousand hours with only one hiccup and never putting us in any tight spots. Even though I know intellectually how the diesel engines operate, I think my emotional sense of them is of a bunch of brass rings of various sizes spinning around a thick steel rod. Since they are different sizes there are times that they all synchronize at the apex of their rotation and that’s the smooth moment I enjoy. The rest of the time it is just chaos.
Of course, the reason I am listening so closely to the engines is that I want to know if something is going wrong. (When pilots are over water they report that the engine always sounds different.) There is an A.I. company that is working on a product where they put six audio sensors in the engine compartment and then the computer learns what different engine problems sound like. Then you drive (or fly) along and an expert who has listened to tens of thousands of hours of healthy and unhealthy engines is listening for you and will let you know when something is off.
I’m all for it. I’d install that immediately. Leave the listening to someone else. (I should do a few longer flights with my mechanic so he can say, “No, that’s fine, don’t worry about it.”)