![Sometimes we have to wonder if stabilizer locations chosen for subtle aerodynamic reasons, as you would like to imagine, or merely aesthetic ones. [Credit: Adobe Stock]](https://flyingmag1.b-cdn.net/wp-content/uploads/sites/2/2025/11/FLY1125_1.2-Technicalities.jpeg?width=1168&height=775)
Practically all airplanes—flying wings and biplanes are exceptions—have two wings in tandem. Unless the wings are nearly the same size—a very uncommon arrangement—only one of them is honored with the name “wing.” The other is demoted to the rank of “stabilizer” or “canard.”
Canards raise uncomfortable philosophical and anatomical questions by conflating the “tail” and the “nose,” but at least they have had the salutary effect of dispelling many pilots’ mistaken belief that they understand longitudinal stability. The convenient analogy between a conventional empennage and the feathers of an arrow falters when the feathers are found on the pointy end of the arrow.
If you're not already a subscriber, what are you waiting for? Subscribe today to get the issue as soon as it is released in either Print or Digital formats.
Subscribe Now
Setting canards aside, as much of the world has done, we find designers in doubt about where to put stabilizers. Should they be on the midline of the fuselage, or on top of it, or at the top of the fin, or somewhere in between?
In the interest of shedding light upon those questions, I performed, pro bono, a laborious research project. Using published side views of two dozen different airplanes, I measured the angle, with respect to the horizontal, between the centers of pressure of the wing and stabilizer.
If no one has ever published this information before, I now know why. It explains nothing.
- READ MORE: Miracle on the Potomac: Samuel Langley Never Received Enough Credit as Aviation Pioneer
- READ MORE: The Performance: Sometimes Work Fashions Artist
As you know, the stabilizer is usually lower than the wing of a high-wing airplane and always higher than the wing of a low-wing one. How much higher or lower seems to depend on, more than anything else, the slope of the top of the aft fuselage, because, I guess for reasons of structural simplicity and easy disassembly, the stabilizer tends to be placed on top of the tailcone rather than piercing its middle.
Among high-wing airplanes, the most egregious is the chunky old Piper Tri-Pacer, whose stabilizer is 11 degrees below its wing. The Piper Cub and the 182 check in at minus-5 and minus-4 degrees respectively (the minus means the stabilizer is lower than the wing). Among low-wing planes, angles range, similarly, from 4 degrees (A36 Bonanza) to 11 degrees (Mooney M20 and Daher TBM).
However, not all stabilizers are attached to the top of a fuselage. Some migrate halfway up the fin (Commander 112, 16 degrees) and some all the way to the top (Pipistrel Panthera, 19 degrees; Pilatus PC-12, 20 degrees; Beechcraft King Air 200, 24 degrees).
You might have guessed that the one place not to put a stabilizer would be directly behind the wing, but you would have guessed wrong (Cessna Skymaster, Rutan Boomerang, and AeroCommander 560, all 0 degrees; Mitsubishi MU-2, minus-2 degrees).
Interference between the wing wake and the stabilizer is often mentioned as a consideration in design, as is the way that the interaction of the wing’s downwash with the stabilizer affects trim changes with flap deflection. You would therefore suppose the height of the stabilizer with respect to the wing would be a fundamental design parameter. But that seems not to be the case. Designers just seem to put the stabilizer wherever seems convenient. And when they don’t—for example, the cruciform tail of the Commander 112—you have to wonder: Was that location chosen for subtle aerodynamic reasons, as you would like to imagine, or merely aesthetic ones?
Aeronautical engineers, even famous ones, are not above making design decisions on the basis of looks. I interviewed Ted Smith about half a century ago and naively asked him whether he selected the mid-wing position on the Aerostar for its presumably low drag. No, Smith said. It was just to set his new airplane apart from all the others.
It’s too late to interview Karl Bergey, who designed the 112. Bergey died in 2019. I suspect his answer might have been the same as Smith’s, but then again Bergey might have said something like this:
“For reasons of passenger comfort, we made the 112’s cabin unusually wide. At the same time, we wanted to keep the airplane as compact as other single-engine four-seaters. So we ended up with the fuselage sides converging unusually steeply behind the cabin. Combining that with the low wing and flaps, there was a possibility that the inner portions of the horizontal tail would get into low-energy flow at low speeds, and elevator authority would be compromised during the flare.
“The solution was to put the horizontal above the top of the fuselage, where it would be in undisturbed flow, but still in the propwash for good elevator authority during takeoff. And, of course we didn’t have to deal with the additional flutter modes you can get with a T-tail.”
You can always count on an airplane designer for a fancy explanation.
During the 1970s a sort of pandemic of T-tails occurred. It wasn’t difficult to invent aerodynamic justifications, but the original application to airplanes like the BAC 111, Boeing 727, and DC-9 was pragmatic. The stabilizer had to be gotten away from the exhaust of jet engines mounted on the aft fuselage.
T-tails came into favor in general aviation propeller airplanes mainly because they seemed to signify modernity and speed. Piper went into production with T-tail versions of most of its models, with mixed results. Cessna looked at a T-tail for the 182 and thought better of it (although the so-called 187, which also had the 177’s cantilever wing, was a pretty nice-looking airplane). Beech tested a T-tail Bonanza and went no further with it but endowed both the King Air and the Skipper trainer with T-tails.
I don’t think you can make a general statement about whether a T-tail has significant benefits for either the performance or handling of an airplane. There were complaints about the T-tail Piper Lance from pilots who found that having the elevator out of the propwash reduced their ability to raise the nose early in a—presumably—soft-field takeoff.
On the other hand, I like to imagine that the effortless flaring and landing characteristics of my own one-off, which has a T-tail, are attributable to the wing coming into ground effect well before the stabilizer and causing the airplane to flare of its own accord.
One of the curious things my little investigation uncovered was that classic studies of how various tail arrangements affect spin recovery seemed to have made little impression. The majority of the airplanes I looked at placed the fin and stabilizer at roughly the same fuselage station—an arrangement that risks making the rudder ineffective in a spin.
Swept fins, which are practically universal, make the situation worse, because rudder deflection tends to raise the nose. Only the two French airplanes in my study—TBM and Trinidad—shift the stabilizer to a location aft of the rudder, as the ghostly voices of long-dead spin doctors advise.
This column first appeared in the November Issue 964 of the FLYING print edition.
