Gyroscope Basics And The Pendulous Vane Fallacy

cockpit of a plane flat horizon Screenshot from 2017-06-06 20:49:16

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 defence 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 stabilising 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.

first gyroscopic artificial horizon attitude indicator 1893 patentScreenshot from 2017-05-31 19:36:21


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.

sperry pendulous vane gyroscope 1946 first patent Screenshot from 2017-05-31 19:25:30

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.

pendulous vanes blog gyros Screenshot from 2017-06-06 21:24:49

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]

10-94 pendulous vanes gyroscope around the world Screenshot from 2017-06-06 15:12:11.png

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.

Precession is a second important characteristic of gyroscopes, but I won’t go into detail here, suffice to say that by applying a force to the horizontal axis of the gyro, a unique phenomenon occurs.

pendulous vanes gyroscope precession drawing Screenshot from 2017-06-06 16:41:39

There are also Solid State Gyros and Related Systems like Microelectromechanical Based Attitude and Directional Systems (MEMS) & Ring Laser Gyros (RLG) but those are beyond the scope of this post.


So What Do Pendulous Vanes Actually Do

The attitude indicator, or artificial horizon, is one of the most essential flight instruments. It gives the pilot pitch and roll information that is especially important when flying without outside visual references. The attitude indicator operates with a gyroscope rotating in the horizontal plane. Thus, it mimics the actual horizon through its rigidity in space. As the aircraft pitches and rolls in relation to the actual horizon, the gyro gimbals allow the aircraft and instrument housing to pitch and roll around the gyro rotor that remains parallel to the ground.

pendulous vane blog 10-100 Screenshot from 2017-06-06 17:09:19.png

In a typical vacuum-driven attitude gyro system, air is sucked through a filter and then through the attitude indicator in a manner that spins the gyro rotor inside. An erecting mechanism is built into the instrument to assist in keeping the gyro rotor rotating in the intended plane. Precession caused by bearing friction due to air contaminants and other factors makes this necessary.

After air engages the scalloped drive on the rotor, it flows from the instrument to the vacuum pump through four ports. These ports all exhaust the same amount of air when the gyro is rotating in the horizontal plane. When the gyro rotates out of plane, air tends to port out of one side more than another. Vanes close to prevent this, causing more air to flow out of the opposite side. The force from this unequal venting of the air re-erects the gyro rotor. [Figure 10-101]

pendulous vanes figure 10-101 Screenshot from 2017-06-06 17:16:32.png

Early non-pendulous vane vacuum-driven attitude indicators were limited in how far the aircraft could pitch or roll before the gyro gimbals contacted the stoppers, causing abrupt precession and tumbling of the gyro.

Many of these gyros include a caging device. It is used to erect the rotor to its normal operating position prior to flight or after tumbling. More modern gyroscopic instruments are built so they do not tumble, regardless of the angular movement of the aircraft about its axes.

Failings Of The Vacuum Gyro System

In addition to the contamination potential introduced by the air-drive system, other shortcomings exist in the performance of vacuum-driven attitude indicators. Some are induced by the erection mechanism itself.

The pendulous vanes that move to direct airflow out of the gyro respond not only to forces caused by a deviation from the intended plane of rotation, but centrifugal force experienced during turns also causes the vanes to allow asymmetric porting leading to inaccurate display of the aircraft’s attitude, especially in skids and steep banked turns. Also, abrupt acceleration and deceleration imposes forces on the gyro rotor. Suspended in its gimbals, it acts similar to an accelerometer, resulting in a false nose-up or nose-down indication.

Electric attitude indicators Vs Pendulous Vanes

Electric attitude indicators address some of the inherent problems of vacuum-driven attitude indicators. Since there is no air flowing through an electric attitude indicator, air filters, regulators, plumbing lines and vacuum pump(s) are not needed.

Contamination from dirt in the air is not an issue, resulting in the potential for longer bearing life and more accuracy. Erection mechanism ports are not employed, so pendulous vanes are eliminated.

It is still possible that the gyro may experience precession and need to be erected. This is done with magnets [not gravity] rather than vent ports. Typically, electric attitude indicator gyros can be caged manually by a lever and cam mechanism to provide rapid erection. [Figure 10-102]

pendulous vanes blog figure 10-102 Screenshot from 2017-06-06 17:27:32

So as we can see, pendulous vanes have their uses and weaknesses, but one task they cannot perform is the mythical correction for the non-existent curvature of the earth. The simple principles of rigidity in space and precession provide all the knowledge capable of determining whether we are living on a spinning, hurtling, orbiting ball. The only conclusion that we can draw is that the earth is a stationary plane.

Here you can listen to a pilot of over 35 years discuss the gyroscope as the best flat earth proof, whilst explaining the myth of the pendulous vane.



twitter pilot pendulous vanes Screenshot from 2017-06-06 17:28:54.png


Click to access AC_65-15A.pdf

Click to access ama_ch10.pdf

Click to access PPL-1.1.3-Aircraft-Instruments.pdf

Click to access AircraftInstruments.pdf

Patent sperry pendulous vanes gyroscope attitude indicator 1946

Patent gyroscope horizon 1892