Gyroscope Basics And The Pendulous Vane Fallacy


This post is intended to be a detailed response to the wannabe gyro debunkers that think research means hanging out in debunk forums, cutting and pasting the first excuse that triggers their confirmation bias in defense of the ball busting characteristics posed by gyroscopes.

The fallacy in question is that artificial horizon indicators run by gyroscopes use pendulous vanes to somehow automatically correct for the non-existent curvature of earth.

A Brief History Of Gyros
It’s important to know the time-line of gyroscope development in order to understand that gyros were in constant commercial/private use long before the introduction of any stabilizing mechanisms like pendulous vanes, which were largely developed due to the exaggerated aerial manoeuvres needed during times of war.

The earliest patent I could find for a gyroscopic artificial horizon was filled by Joshua Nickerson Rowe in 1892.

Gyroscopes were used in torpedoes and as ship stabilisers and navigation devices before they were used in aircraft. In 1909, Elmer A. Sperry built the first automatic pilot for aircraft using gyroscopes. Later in 1916 the first gyroscopic artificial horizon was used in a plane.

The first patent for a pendulous vanes system was filed in 1941 by the inventor Frederick D. Braddon, with the assignor being the Sperry Gyroscope Company, Inc.

So it seems absurd to claim the invention of pendulous vaned gyros in the 40’s were the first to provided curvature correction, when non-stop transatlantic flight by Alcock and Brown was achieved in 1919. They flew from Newfoundland to Ireland which would have needed a curvature correction of more than 400 miles of drop. To realise why this curvature correction is absurd we need to quickly cover the basic principles of a gyro.

Two basic Principles of Gyroscopic Instruments
Gyroscopic instruments are essential instruments used on all aircraft. They provide the pilot with critical attitude and directional information and are particularly important while flying under IFR (Instrument Flight Rules). The sources of power for these instruments can vary. The main requirement is to spin the gyroscopes at a high rate of speed. Originally, gyroscopic instruments were strictly vacuum driven. A vacuum source pulled air across the gyro inside the instruments to make the gyros spin. Later, electricity was added as a source of power. The turning armature of an electric motor doubles as the gyro rotor. Various systems and powering configurations have been developed to provide reliable operation of the gyroscopic instruments.

Three of the most common flight instruments, the attitude indicator, heading indicator, and turn needle of the turn-and-bank indicator, are controlled by gyroscopes. A mechanical gyroscope is comprised of a wheel or rotor with its mass concentrated around its perimeter. The rotor has bearings to enable it to spin at high speeds. [Figure 10-93A]

Different mounting configurations are available for the rotor and axle, which allow the rotor assembly to rotate about one or two axes perpendicular to its axis of spin. To suspend the rotor for rotation, the axle is first mounted in a supporting ring. [Figure 10-93B] The ring and rotor can both move freely 360°. When in this configuration, the gyro is said to be a captive gyro. It can rotate about only one axis that is perpendicular to the axis of spin. [Figure 10-93C]

Attachment of a bracket to the outer ring allows the rotor to rotate in two planes while spinning. Both of these are perpendicular to the spin axis of the rotor. The plane that the rotor spins in due to its rotation about its axle is not counted as a plane of rotation.

A gyroscope with this configuration, two rings plus the mounting bracket, is said to be a free gyro because it is free to rotate about two axes. [Figure 10-93D] As a result, the supporting ring with spinning gyro mounted inside is free to turn 360° inside the outer ring.

Unless the rotor of a gyro is spinning, it has no unusual properties; it is simply a wheel universally mounted. When the rotor is rotated at a high speed, the gyro exhibits a couple of unique characteristics. The first is called gyroscopic rigidity, or rigidity in space, meaning the rotor of a free gyro always points in the same direction no matter which way the base of the gyro is positioned. [Figure 10-94]

Gyroscopic rigidity depends upon several design factors, including rotor weight, angular velocity, rotor radius and bearing friction

The characteristic of gyros to remain rigid in space is exploited in the attitude-indicating instruments and the directional indicators that use gyros.

Gyroscope Basics And The Pendulous Vane Fallacy


Well-known member
How am I just now seeing this? Thanks for that educational tutorial. Do I understand you to be saying that aircraft (with or without gyroscopes) do not compensate for curvature of the Earth during their flights?


Well-known member
There is absolutely nothing unusual about a spinning gyro, from a force diagram, Newtonian physics perspective. It may look counterintuitive, but the math is clean and straightforward.

I think I already posted my favorite gyro lecture on this site somewhere.

I'm sure you'll find, when doing your due diligence as an open minded researcher, that they had manual curvature correction devices on the old gyros. Crossing the Atlantic was about as accurate as you could be, and you still needed to know your landmarks when you got near your destination.

More importantly than any of that, gyros were used for heading and not altitude, refer your bolded section. That means that even with a gyro with no way to correct for curvature, you could calculate the heading margin of error. Curvature essentially alters the scale of the heading reading as it changes making results increasingly inaccurate as the distance increases. Hence the importance of landmarks. This is why a trans Atlantic flight was such an achievement. If gyros and altimeters were that accurate, as I would think they should be on a flat earth, anyone could have done it.

I'm open minded about earth shape. For all I know it could be multiple shapes simultaneously, but I don't see the gyro as any kind of smoking gun.

Most people have a smart phone with gyros, and there must be an app that reads the gyros directly. I can't believe no one has done an experiment with those gyros on a plane. Some actual data would help this discussion a great deal. As it stands, I could come up with theories to explain the readings given various shapes. Would have to test them, and see how they fared.