Can the pitch stabilizer in the picture really work for a plane or glider?

The image shows an automatic pitch stabilizer (the mechanism in the black rectangle) that is based on the vane 50 whose movements up and down would drive, with the help of a force amplifier system, the horizontal front elevator of a Wright glider or plane in such a way as to maintain the aeroplane in horizontal flight.

More precisely if, for a reason or another, the plane have the tendency to dive there will appear a vertical component of the relative wind that will push the vane 50 upward and, through the mechanism already mentioned, the vane will drive the front rudder in such a way as to make the apparatus climb again. If the plane tend to rise, the vane will go down and command the front rudder to make the plane descend.

The question is, can this mechanism really work, at least theoretically? (A stabilizer based on a pendulum is a fallacy, it will not work. In an accelerated system (the plane) the pendulum does not align to the vertical).

US patent No. 1075533

Source: US patent No. 1075533 (filed by WRIGHT Co in 1908)

(I am not interested in answers regarding the automatic stabilizer in roll, also described in the patent. It is based on a pendulum and it can not work. My question is only about the pitch stabilizer.)

UPDATE: My question has nothing to do with a pendulum stabilizer. The vane-based stabilizer (the subject of my question) works on a completely different principle. In consequence, the answers given to this question, that refer strictly to a pendulum stabilizer, do not help.

  • $\begingroup$ @RobertDiGiovanni Yet somehow this guy seems think pendulous vanes actually prove the earth is flat. He seems to know his stuff yet his delusion persists. $\endgroup$
    – TomMcW
    Commented Nov 24, 2019 at 17:03
  • $\begingroup$ Yes, unless he is seeing how many people will fall for his reasoning. The earths rotation may be too slow to overcome friction required to move the gyro, but laser attitude indicators are worth checking out. $\endgroup$ Commented Nov 25, 2019 at 17:02
  • $\begingroup$ This is basically FBW works on every jet fighter after F16: introduce a negative feedback on the pitch axis to add pitch stability, although a pure mechanical implementation. $\endgroup$ Commented Nov 25, 2019 at 19:07
  • $\begingroup$ @user3528438 As described, this system would introduce positive feedback. A steep angle of attack (descending or nose high) would result in up elevator, and a shallow angle of attack (climbing or nose low) would result in down elevator. Or maybe I'm misunderstanding something. $\endgroup$ Commented Nov 25, 2019 at 23:59
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    $\begingroup$ Possible duplicate of Can a pendulum stabilizer for airplanes really work? $\endgroup$
    – user14897
    Commented Dec 1, 2019 at 19:42

4 Answers 4


Yes, this vane-based stabilizer really did work. In fact the pendulum system for direction control also worked as it was used to sense yaw in a slip, just like the ball in a turn and bank indicator.

The entire system worked so well that Orville Wright received the 1913 Collier Trophy "For development of the automatic stabilizer" after demonstrating it for the judges.

The Wright Bros work in automatically controlled flight was overshadowed the following year when Elmer A. Sperry won the 1913 Collier Trophy "For gyroscopic control".


In the fall of 1913, Orville installed the stabilizer on a special Wright Model E airplane that utilized a single pusher propeller. He kept the details of the stabilizer secret even from the Wright Company. He purposely waited until the last day of the year to fly for the prize.

He invited the Aero Club’s judges to Huffman Prairie to see a demonstration of his new device on a cold snowy day, December 31st.

He turned up his coat collar, put on a pair of goggles and took off. He made a total of 17 flights.

His most spectacular flight consisted of 7 full circles of the field with both hands held in the air. The automatic stabilizer kept the same angle of bank and almost the same altitude. He wowed the judges and was awarded the prize on February 5, 1914.

The stabilizer was then offered as an option for use with the sale of Wright 1910-1911 Model B flyers.

However, it saw little use, because on June 18, 1914, a young Lawrence Sperry, as part of a great safety competition, unveiled a totally new type of stabilizer to the world. The safety competition was jointly sponsored by the Aero-Club de France and the French War Department.

In his demonstration flight, Sperry took off from the Seine in a Curtiss C-2, climbed to altitude and flew back down the river. At the appropriate moment, his mechanic, Emile Cachin, crawled 7 feet out on the wing as Sperry lifted his hands from the controls and stood up in the cockpit. The plane sped by the judges as the crowd went wild.

What Sperry had done was adapt a balancing mechanism invented by his father, Elmer, for counteracting the rolling of ships, to an airplane. The device employed two gyroscopes that performed the function of the pendulum and vanes in the Wrights’ device.

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    $\begingroup$ Mike +1. In fact, the pendulum would prevent an AOA only system from being "fooled" by relative wind only inputs. Pendulums are not "fallacies", as you pointed out, they are turn (and gravity) acceleration force indicators. Combining that with a relative wind indicator would allow one to SET and HOLD an attitude. But, ah yes, the Sperry gyroscopes eclipsed the Wright patent. Really a +10! $\endgroup$ Commented Nov 24, 2019 at 14:22
  • $\begingroup$ The Wrights could've achieved the same end by incorporating an anti-servo tab on the canard surface, as is used on stabilator tails (invented by John Thorp in the 50s) for which the tab is the primary source of static pitch stability. $\endgroup$
    – John K
    Commented Nov 24, 2019 at 16:31
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    $\begingroup$ See this demonstration: Drone Pendulum Fallacy (youtube.com/watch?v=OYHCP3-mpxk). Therefore, a pendulum can not stabilize a flying machine. $\endgroup$
    – Simplex11
    Commented Nov 24, 2019 at 20:54
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    $\begingroup$ The article: Wrigh Stabilizer Greatly Refined ( chroniclingamerica.loc.gov/lccn/sn84026749/1914-01-05/ed-1/… ), Washington Times, January 5, 1914, talks about Orville Wright as taking a prize after flying in a circuit a few times with his hands removed from the controls but the 1913 Wright planes were naturally stable and there is no guarantee that Orville did not drive the plane by moving his seat (with his body), as the Wrights did in 1902 with their glider. $\endgroup$
    – Simplex11
    Commented Nov 24, 2019 at 22:41
  • $\begingroup$ A pendulum will move from its vertical position if velocity is changed. This movement can activate a control surface to create force in the other direction. A pendulum can be used to MAINTAIN a given attitude, as Wright did in flying a circle at constant speed. The pendulum would swing outside the turn, and remain there until the aerodynamic turning forces were removed. Importantly, it would then return to its original position. In steady state flight, the pendulum, like the pilot, experiences 1 G towards earth (straight down). $\endgroup$ Commented Nov 25, 2019 at 16:53

Based on all comments the question received, I will try to formulate a clear answer illustrated with a picture.

The vane V will always tend to stay in the same plane as the axis XX' no matter what the glider does: climbs, descends or flies horizontally. If the vane goes toward the upper or lower wing then automatically it will drive the mechanism that changes the angle of the front rudder till the air current pushes the vane in the opposite direction and so on. In consequence, there is no way to predict which direction the plane will align to if a perturbation changed its initial direction of flight.

As a remark, the weight E together with the weight of ED just counterbalance the weights of DC, CB, BA and that of the vane V that is bolted to BC. The sum of momentums of all these weights with respect to pivot D is always zero. The weight E will not tend to skew the parallelogram ABCD in any way.

Wright automatic pitch stabilizer Top: Glider descending. Bottom Glider in horizontal flight. In both cases the position of the vane V is the same.

  • $\begingroup$ "Vane will tend to stay in the same place", yes that's how it works. The Wright system could only be set for one condition. It would respond to a "perturbation" to return it to its original condition, but, unlike a gyro attitude indicator, could not provide information as to where the original attitude was, there for the pilot was "out of the loop" if additional changes were desired. $\endgroup$ Commented Dec 3, 2019 at 7:21

This appears to be a mechanical version of the modern computer driven Angle of Attack vane / Stabilator pitch control system. The catch is it is based on relative wind. A plane can do an entire loop without changing its AOA with a very good pilot using throttle and gravity.

So, back in 1908, to maintain altitude, one might try a balloon mounted in a container, with a mechanical lever and spring attached to the carburetor. If the balloon expanded from greater altitude, the lever would lower fuel input, if the balloon contracted, the spring would pull the lever back to increase the fuel input. This could also come with disclaimers regarding changes in pressure due to weather.

Setting a plane up with weight slightly forward of the main wing Center of Pressure (Lift) and conventional tail downforce, or forward canard upforce (staticly stable), will do a pretty good job maintaining speed and AOA. Adding or subtracting throttle would make the plane climb or descend at the same speed to correct an altitude deviation.

It is interesting to note, though many hail the Wrights early canard designs, their first commercial success, the Model B, featured a rear mounted horizontal stabilizer and flew with an engine power output of 30-40 horsepower, enough to carry a passenger.

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    $\begingroup$ While the AoA vane is hinged at its quarter chord, the Wright vane is hinged at mid chord. This makes the AoA vane indifferent and the Wright vane highly unstable. $\endgroup$ Commented Nov 25, 2019 at 19:43
  • $\begingroup$ @Peter Kampf. Absolutely, and your writings explaining aerodynamic center are certainly good reading $\endgroup$ Commented Nov 25, 2019 at 22:05
  • $\begingroup$ @Robert DiGiovanni, I am not sure I understand your reasoning. I guess you are aware that "A Pendulum on a Merry-go-round" ( see: physicstasks.eu/1753/a-pendulum-on-a-merry-go-round ) will align to a direction making an angle alfa to the horizontal (after the oscillations die). So, if a Wright plane had flown in a circle in a perfectly stable way then the pendulum onboard would have made an angle alfa (dependent of the angular speed of the plane and the ray of the circle) to the vertical. There would have been no alignment to the vertical in the steady state regime. $\endgroup$
    – Simplex11
    Commented Nov 26, 2019 at 9:39
  • $\begingroup$ @simplex correct! 😊 "after the oscillations die" the pendulum would have made an angle alfa dependent of the angular speed... AND GRAVITY! Gravity still contributes to the direction of the pendulum AND the pendulum reaches a steady state! So, the Wrights "trick" is to enter the turn FIRST, then set the control device, then hands free. This is also why the "ball" is not perfectly centered in a steep turn, but works well to coordinate shallow turns. And even gyros need an "self erecting" pendulum to help remove accumulated errors from abrupt maneuvering. $\endgroup$ Commented Nov 26, 2019 at 10:00
  • $\begingroup$ @Robert DiGiovanni, The acceleration of the suspension point of a pendulum inside a plane is chaotic in general because the plane continuously tends to roll to the left or to the right, pitch down or up and turn around its vertical axis. In consequence, the pendulum tends to align to a direction that is dependent of g + acc_chaotic = acc1_chaotic (all of them vectors). In other words, the pendulum at each time tends to align to a chaotic direction and so it never aligns to anything. How can this chaotic oscillator be useful for stabilizing the flying machine?! $\endgroup$
    – Simplex11
    Commented Nov 26, 2019 at 13:21

No, I don't see how this would work as a controller for maintaining flight level. The angle of attack on any part of the airplane during a steady-state climb is identical to that of level flight, so there is no additional "relative wind" for the mechanism to work with.

However, a proportional feedback in angle of attack is a valid stability augmentation system. With the right gain, it has the same effect as adding positive static margin. The net effect is maintaining airspeed, which, given the same power input, would also contribute to flight level maintenance. This was a success for the Wrights' probably because its first flyer was statically unstable.

Positioned correctly, it may also serve as a pitch damper. But once statically stable aircraft prevailed, it's likely this was superseded by gyroscopically measured pitch dampers as mentioned in Mike Sowson's answer.

  • $\begingroup$ The pendulum, as well as your senses, work correctly in steady state flight (1 G straight down) and will "hold its place", albeit not "straight down" in a constant rate/constant speed turn. Gyros "know" where the horizon is, but even they can accumulate error. Sadly, our senses, like the pendulum, can get thoroughly lost after a few turns and attempted corrections. $\endgroup$ Commented Dec 3, 2019 at 7:39

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