Never averse to oddness, Rutan tried
putting the Defiant’s rudder at the front. But
didn’t that make the airplane want to swap
ends?
A ready asked me the purpose of the odd-looking fin projecting downward from the nose of the Defiant on the cover of our August 2011 “Rutan Retrospective” issue.
It’s the rudder. Rutan called it a “rhino rudder,” because in versions he tried on the VariEze and Long-EZ it was on top. But what was the rudder doing on the front of the airplane?
In an obscurely related development, I had just had a rather fractious exchange of e-mails with a person who was incensed that a certain Wikipedia article made reference to a “canard stabilizer,” citing in a footnote a 1992 article of mine. He had attempted to edit the Wikipedia entry, only to have it changed back again, Whac-A-Mole fashion, by the original author.
That one of my articles should be cited as an authoritative source in Wikipedia is flattering, but it somewhat shakes my faith in Wikipedia. It reminds me of Groucho Marx’s comment that he would not want to belong to any club that would have someone like him for a member. On the other hand, Wikipedia can be pretty ferocious about sources, which are the fig leaves of scholarship. Once, when I corrected some biographical information in a Wikipedia article about my own great-grandfather, the editors pounced upon my emendations as being inadequately sourced.
Nevertheless, “canard stabilizer” is a misnomer, and I would hate to think that I used the phrase, especially 20 years ago, when I knew so much more than I do now. Accordingly, I asked my computer to search all of my articles from 1850 onward. I was relieved to find that the words “canard” and “stabilizer” could be found in various degrees of proximity, but never adjacent to one another. I think the writer responsible for the Wikipedia footnote must have something in common with the authors of those promotional blurbs for films, and California ballot propositions, in which quoted words are cherry-picked, or ingeniously linked with ellipses, in such a way as to exactly reverse their original meaning.
But about that rhino rudder ...
The vertical tail surfaces of most airplanes — there were a few exceptions back when Baron von Richthofen was still with us — consist of a fixed component, the fin or “vertical stabilizer,” and a movable one, the rudder. To some extent they cooperate, but the fin’s main function is to keep the airplane’s fuselage aligned with the direction of its flight, while the rudder’s is to allow the pilot to adjust that alignment. Now, the rudder’s job can be done in other ways; on the B-2 bomber, for instance, both fin and rudder are dispensed with because of their radar reflectivity, replaced by spoiler-like split ailerons that manage yaw by tugging at a wingtip. On the Defiant, the rudder was placed below the pilot’s feet, eliminating all the guides and pulleys and long runs of steel cable that would have been required had there been rudders where you would expect to find them, on the big fins at the wingtips.
A directionally stable airplane is like a weathercock, with the pivot point at the center of gravity. It naturally tends to align itself with the wind — although there are some airplanes that, while they have no tendency to swap ends, will fly along in a steady sideslip, feet on the floor, because of excessive control system friction or minimal fin area. Any area behind an airplane’s center of gravity is stabilizing, and any area ahead of it is destabilizing. The rhino rudder therefore was destabilizing, but the vertical fins at the wingtips were much larger than the rudder and handily overcame its destabilizing influence.
