Technique is described to reduce extraneous gyro output signals by using relatively inexpensive shrouds which do not increase power comsumption. Shrouds reduce noise by minimizing mass of gas spinning with rotor, reducing Reynolds number near rotor, and inducing laminar flow

Kraus, G. M.

Rupert, J. G.

English

NASA Technical Reports Server

December 1972	 B72-10743 
NASA TECH BRIEF 
•	 NASA Pasadena Office 	 A A 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Reduction of Noise in Gyro Outputs 
The problem: 
To reduce extraneous gyro output signals further 
than has been accomplished by using a light gas and 
by decreasing the pressure of gas around the rotor. 
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The solution: 
Minimize the mass of gas spinning with the rotor 
by use of shrouds which also reduce the Reynolds 
number of the gas near the rotor and induce laminar 
flow. 
How it's done: 
The ratio of the angular momentum of the sur-
rounding gas to the angular momentum of the rotor 
largely determines the accuracy with which a gyro 
can measure low input rates; by using a light gas 
(such as a mixture of hydrogen and helium) the an-
gular momentum of the gas at a given operating 
speed is reduced and noise torques produced by the 
spinning gas are decreased. For the identical reasons,
further reduction of noise can be obtained by de-
creasing the gas pressure in a gyro; however, this ap-
proach has offered only moderate noise reduction, 
and it interferes with the use of gas bearings because 
reduction of gas pressure is necessarily accompanied 
by an intolerable reduction in bearing stiffness. 
It has been found that gyro output noise originating 
from turbulent gas flow within the gyro gimbal can 
be significantly reduced when steady laminar flow 
within the gimbal of a gyro is established by sur-
rounding the gyro rotor with a shroud or by reducing 
the Reynolds number of the gas within the gimbal 
below the critical value, that is, the lowest Reynolds 
number at which unsteady flow can exist. The cross-
sectional schematic diagram of a simplified gyro shows 
that the shroud surrounding the rotor is separated a 
distance h from the rotor's cylindrical face and a dis-
tance k from its circular faces. 
Any arbitrary choice for distances h and k yields 
reduced gyro output noise because the gas outside 
the shroud is no longer affected by the spinning rotor 
and it is essentially stagnant; only the gas inside the 
shroud is in motion, and since the mass is small, the 
angular momentum of the gas is small. However, if 
distances h and k are carefully selected, additional 
noise reduction can be realized. Specifically, when 
the Reynolds number is less than 41, as established 
by gap h, gas flow in the area between the rotor face 
and shroud will be laminar and steady, and noise will 
be at a minimum; distance k must also be selected to 
be less than twice the boundary layer thickness of the 
gas at the circular rotor faces. 
The shrouds are relatively inexpensive and do not 
increase significantly either the gyro weight or the 
(continued overleaf) 
This document was prepared under the sponsorship of the National	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19720000742 2020-03-17T03:44:01+00:00Z
anisoelasticity coefficient. Moreover, power consump-
tion is not increased and in some instances the shrouds 
actually reduce power consumption. In any event, a 
steady laminar gas flow within a gyro gimbal reduces 
noise in the output by at least one order of magnitude. 
Patent status: 
Title to this invention has been waived under the 
provisions of the National Aeronautics and Space Act
[42 USC 2457 (f)] to Honeywell, Inc., Aerospace 
Division, 2600 Ridgeway Parkway, Minneapolis, Min-
nesota 55413.
	 0 
Source: Gerald M. Kraus and John G. Rupert of

Honeywell, Inc./Aerospace Division

under contract to

NASA Pasadena Office

(NPO-11603)
El 
B72-10743	 Category 06


Reduction of noise in gyro outputs

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