Electromechanical drag balance device measures the aerodynamic drag force acting on a vehicle as it moves through the atmosphere and telemeters the data to a remote receiving station. This device is also used for testing the hydrodynamic drag characteristics of underwater vehicles

Freeman, R.

Judd, J. H.

Leiss, A.

English

NASA Technical Reports Server

June 1965 Brief 65-10195 
NASA TECH BRIEF 
NASA Tech Briefs are issued by the Technology Utilization Division to summarize specific 
technical innovations derived from the space program. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical information, Springfield, Virginia, 22151. 
Device Measures Fluid Drag on Test Vehicles 
Gasket 
Thrust Mount
 
Housing 
Forward Bore 
Gasket 
Drag Transfer Unit
Deflecting Arm 
Shoulder	
THRU 
Bolt
Deflecting Arms 
Leads to DC Supply
	
Recorder Mount
 
Electrical Coil 
Leads to Telemeter 
DRAG BALANCE (EXPLODED VIEW)
	 DRAG BALANCE ASSEMBLY IN ROCKET 
After Bore 
Coil	 Iron Rod
	 Bolt	 Thrust Mount 
Drag Balance Unit
	 Rocket Motor 
The problem: To measure the aerodynamic drag 
forces acting on a vehicle, such as a rocket, moving 
through the atmosphere. 
The solution: An electromechanical drag balance, 
integrally mounted inside the test vehicle, that senses 
the drag forces experienced by the vehicle and teleme- 
ters the data to a remote receiving station. 
How it's done: The drag balance device consists of 
a cylindrical housing with coaxial bores of two differ- 
ent diameters. The forward bore has a diameter suf- 
ficient to carry the loads imposed by the forward end 
of the vehicle, and the after bore has a smaller diame- 
ter so that a shoulder is formed about halfway through
the housing. The after bore holds a thrust mount, with 
space between the inner wall of the bore and the outer 
wall of the mount for damping fluid. A neoprene gas- 
ket at each end of the thrust mount closes the gap be- 
tween the thrust mount and the after bore. The gaskets 
are sufficiently flexible to allow relative longitudinal 
movement between the thrust mount and the after 
bore. The thrust mount is firmly attached to the for- 
ward end of the rocket motor in the test vehicle. A 
circular drag transfer element, with four equally- 
spaced radial arms and a diameter slightly less than 
the forward bore, fits against the shoulder at the hous- 
ing midsection and is rigidly fi xed to the thrust mount 
by a bolt. A magnetizable rod, such as iron, projects 
(continued overleaf) 
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	 this document, or that the use of any information, apparatus, method, 
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https://ntrs.nasa.gov/search.jsp?R=19650000193 2020-03-11T17:24:10+00:00Z
from the head of the bolt. A position recorder mount 
similar in construction to the drag transfer element is 
joined to the drag transfer element by means of bolts. 
The after end of the bore of the recorder mount is 
fitted with an insulated electrical coil that is connected 
to a dc power supply. The coil has a hollow core with 
a diameter large enough that the iron rod can pass into 
it without touching the walls. A telemetry unit is 
mounted in front of the recorder mount so as to move 
as a unit with the propulsion system. 
In operation, the drag forces imposed on the test 
vehicle and its integrally mounted drag balance cause 
the radial arms of the drag transfer unit to deflect, the 
outer ends bending rearward with respect to the inner 
ends, so that there is longitudinal relative motion in 
the forward direction of the thrust mount. As this 
occurs, the iron rod moves into the electromagnetic 
field of the coil in the recorder mount, varying the 
coil inductance and thereby the current flowing 
through the coil. The variation in coil current is di-
rectly proportional to the deflection between the ends 
of the arms of the drag transfer unit. This variation in 
coil current may be continuously telemetered to a re-
mote station where it may be recorded using conven-
tional equipment calibrated to measure drag in 
pounds as a function of time.
Notes: 
1. This device may also be used for testing the hydro-
dynamic drag characteristics of underwater ve-
hicles. Its main advantage is that drag data can be 
obtained rapidly under actual test conditions. 
2. Inquiries concerning this invention may be di-
rected to: 
Technology Utilization Officer 
Langley Research Center 
Langley Station 
Hampton, Virginia, 23365 
Reference: B65-10195 
Patent status: NASA encourages the commercial 
use of this invention. It has been patented by NASA 
(U.S. Patent. No. 3,001,395), and royalty-free license 
rights will be granted for its commercial development. 
Inquiries about obtaining a license should be ad-
dressed to NASA, Code AGP, Washington, D.C., 
20546.
Source: Abraham Leiss, Joseph H. Judd, 
and Robert Freeman
(Langley-34) 
Brief 65-10195	 Categories No. 01 and 05


Device measures fluid drag on test vehicles

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