Why did the Wright brothers take steps to increase the amount of vertical surface area in front of the CG on some of their aircraft?

Could this have actually improved the flight characteristics in any way that could not have been equally well accomplished by slightly reducing the size of the aft-mounted vertical fin or all-moving rudder?

(End of actual question)

Supplemental content that may help inform an answer--

If the goal was a decrease in "weathervane" stability1, wouldn't reducing the size of the vertical fin or rudder aft of the CG have given the same result, with less drag?

If the goal was to prevent sideslip, wouldn't increasing the vertical surface area forward of the CG actually be counterproductive? Wouldn't increasing the vertical surface aft of the CG have given the desired result?

Did the Wrights have a notion of that sideslips were caused in part by gravity trying to "pull" a banked aircraft sideways through the air toward the low wingtip, while the aircraft had insufficient side area to resist this "pull"? If so, wouldn't this have been a faulty notion of the fundamental cause of sideslips, and of the balance of forces in a non-slipping (coordinated) turn?

Or did the Wright brothers have some conception that it was desirable to maximize the sideforce generated during a sideslip for some other reason? If so, does this conception really make any sense from a modern perspective?

Did the Wright brothers have a misconception of the basic nature of spiral instability, leading them to mistakenly suspect that an increase in the sideforce generated by sideslipping, rather than a decrease in "weathervane" stability along with an increase in dihedral, would be the most productive approach toward making an aircraft less prone to "winding up" into a steeper turn?

The Wrights left many letters and other written notes, so it should be possible to answer these questions with some degree of authority.

Related quotes from outside sources:

"1905 Flyer III: Semi-circular [vertical] "blinkers" between the surfaces of the canard prevent the nose from dropping in a turn. With this aircraft, the Wrights were able to fly until their fuel ran dry. In 1908, they adapted the Flyer to carry the first airplane passenger." -- From http://www.wright-brothers.org/Information_Desk/Just_the_Facts/Airplanes/Wright_Airplanes.htm

"The crash convinced the Wrights to make radical changes to the aircraft design. They almost doubled the size of elevator (in front) and rudder (in back) and moved them about twice the distance from the wings. They added two fixed vertical vanes (called "blinkers") between the elevators to serve as stabilizers and help prevent the Flyer's tendency to slip or slide sideways in a turn." -- from http://www.wright-brothers.org/Information_Desk/Just_the_Facts/Airplanes/Flyer_III.htm

Photographic examples:

1)http://wrightbros.org/History_Wing/Wright_Story/Airplane_Business/Airplane_Business_Intro_images/1911_Exp_Glider.jpg , from http://wrightbros.org/History_Wing/Wright_Story/Airplane_Business/Airplane_Business_Intro.htm

2)http://www.wright-brothers.org/Information_Desk/Just_the_Facts/Airplanes/Wright_Airplane_images/1905_Flyer_III/1908_Flyer_III_at_Kitty_Hawk.jpg , from http://www.wright-brothers.org/Information_Desk/Just_the_Facts/Airplanes/Flyer_III.htm

3)http://www.wright-brothers.org/Information_Desk/Just_the_Facts/Airplanes/Wright_Airplane_images/1905_Flyer_III/1905_Flyer_before_rebuild.jpg , from http://www.wright-brothers.org/Information_Desk/Just_the_Facts/Airplanes/Flyer_III.htm

4)http://www.wright-brothers.org/Information_Desk/Just_the_Facts/Airplanes/Wright_Airplane_images/1907_Model_A/1909%20Launch%20in%20Italy.jpg , from http://www.wright-brothers.org/Information_Desk/Just_the_Facts/Airplanes/Model_A.htm

5)http://wrightbros.org/History_Wing/Wright_Story/Airplane_Business/Airplane_Business_Intro_images/Vin_Fiz_Takes_Off.jpg , from http://wrightbros.org/History_Wing/Wright_Story/Airplane_Business/Airplane_Business_Intro.htm

6)http://www.wright-brothers.org/Information_Desk/Just_the_Facts/Airplanes/Wright_Airplane_images/Model%20CH/1913_CH_at%20anchor.jpg , from http://www.wright-brothers.org/Information_Desk/Just_the_Facts/Airplanes/Wright_Airplanes.htm

Footnotes --

1-- In this question, "weathervane stability" is used to mean "yaw stability", i.e. "directional stability". No implication is intended that an aircraft in flight "feels" the external, meteorological wind, apart from the effect of sudden gusts.

Addendum-- it seems possible that in some cases, part of the motivation for installing these vertical surfaces may have had to do with the Wright brothers' experiments with an automatic stabilization system, which included a pendulum, which would only give useful indications if the aircraft tended to generate a significant amount of sideforce whenever it was banked and turning. So the present question is confined to aircraft that were not being used for experiments with the automatic stabilization system and were not given specific design features for the purpose of helping the automatic stabilization system work better.

  • 3
    $\begingroup$ There are a lot of questions here. $\endgroup$ – dalearn May 11 '20 at 21:33
  • $\begingroup$ @dalearn -- thanks, edited to try to help address that $\endgroup$ – quiet flyer May 12 '20 at 13:20

There was much controversy at the time over whether a flying machine should be statically stable in flight. It was known that a high degree of stability meant that the machine would sit in one attitude and be hard to manoeuver. The Wrights were firmly in the camp who believed that for a plane to be manoeuvrable, which is to say controllable, it would need to be unstable. This was why they put the elevator in front. According to their theory, a large control rudder at the rear would need a destabilizing fin at the front to counter its stabilizing tendency.

When Orville was over in England in 1910, as an honorary member of the Aeronautical Society of Great Britain he and his UK lawyer Griffith Brewer acted as official witnesses to the certification flight of the world's first stable airplane, the Dunne D.5. During the flight Dunne took his hands off the controls and wrote on a piece of paper provided by Brewer, before flying a full circuit and landing back near his takeoff point. Flight published an account and a facsimilie of Dunne's note. Orville was stunned both by Dunne's use of elevons (for it was a tailless swept biplane!) and by the ability of such small control surfaces to have such a great ability to control the machine in flight. It was one of the events which led to the Wrights abandoning forward auxiliary surfaces altogether at around that time.

  • $\begingroup$ Weren't already Liliethal gliders stable and the Etrich-Wels glider of 1906 the first stable tailless aircraft? $\endgroup$ – Peter Kämpf May 12 '20 at 20:51
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    $\begingroup$ The usual context when discussing the Wrights and their work is that of powered, controlled flight. In this context, weight-shifting is excluded as a permissible control mechanism. From your wider perspective, the first stable aircraft was a Montgolfier balloon. The first stable (but uncontrolled) manned heavier-than-air glider was built by George Cayley and "manned" by a boy. He later pressured his coachman into a controlled glide. Lilienthal, Biot, Pilcher and Weiss were relative latecomers. The manned kites of Hargrave, Baden-Powell and Cody were also aircraft and were stable. $\endgroup$ – Guy Inchbald May 12 '20 at 21:12
  • $\begingroup$ At your level of diligence, the first stable aircraft was Indian. Wouldn't it be better to stick with verified facts? $\endgroup$ – Peter Kämpf May 13 '20 at 5:06
  • $\begingroup$ @PeterKämpf. From your link: "The Sanskrit text that describes the ancient flying machines which Bodas cites, the Vaimanika Shastra, has itself been studied thoroughly by scientists who have concluded that very few of the craft it describes would likely be able to fly at all." I have to say, you normally do better than this. $\endgroup$ – Guy Inchbald May 13 '20 at 7:47

Biographies containing accounts of the Wright brothers' conversations at Kitty Hawk while developing the control system of their early gliders seem to suggest that they had some confusion about the difference between a sideslip and a spiral dive. They first encountered the problem of "adverse yaw" with their 1902 glider, and added a fixed vertical fin at the rear of the aircraft to counteract this, but reported that this seemed to make the aircraft even less controllable. A modern description of the problem might be that the fin converted the aircraft from one prone to experiencing extreme adverse yaw and sideslip, to one prone to experiencing spiral instability due to excess directional stability and resulting lack of sideslip. It's not clear that the Wrights ever thought about the problem in these terms. The situation was complicated by their choice to use an anhedral geometry on their early gliders and powered aircraft, to avoid a tendency for the aircraft to roll downwind when struck by a crosswind gust. By the time the Wrights were adding vertical surface area to some of their aircaft in front of the C.G., they had abandoned the anhedral geometry.

It seems unlikely that adding vertical surface area in front of the C.G. really changed the stability or control characteristics of the Wright aircraft in any beneficial way that could not have been accomplished with less drag simply by reducing the size of the rear-mounted vertical fin or all-moving rudder. In fact, it seems rather unlikely that adding vertical surface area in front of the C.G. really had any beneficial effect on the aircrafts' stability or control characteristics at all.

As a general rule, a modern designer would never take steps to intentionally increase the amount of vertical surface area in front of an aircraft's C.G., notwithstanding a few exotic exceptions where a moving rudder control surface was placed in front of the C.G..

  • $\begingroup$ Still would reconsider the, shall we say, forward half delta. With head on wind it is smaller in area than the vertical stabilizer/rudder assembly, itself a squareish flat plate. This would be directionally stable. In a crosswind, the "assembly" weathervaning force would stall, whereas the little half delta in front would keep "lifting", helping reduce the weathervane. If course the other way is opposing rudder input, but at the very slow speeds the Wrights flew, one can see why they chose the "jib". $\endgroup$ – Robert DiGiovanni May 12 '20 at 18:57
  • $\begingroup$ I can see a beneficial aspect: What that forward area adds is yaw damping. Maybe this created the desired effect, making the Flyer more sluggish in its yaw movements. By distributing areas on both sides of the center of gravity, the Wrights could independently tailor directional stability and damping, something we today do by choosing the right fuselage length. $\endgroup$ – Peter Kämpf May 13 '20 at 5:24
  • $\begingroup$ @Peter Kampf Copy that, see the swept wings and forward fuselage of the 727. Fuselage side area and shape make for some interesting possibilities. May be why Bleriot did not cover the aft fuselage, though these days we know covering can make the structure much stronger. $\endgroup$ – Robert DiGiovanni May 13 '20 at 13:52

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