EXPERIMENTAL TECHNIQUE 
FACILITY AND DYNAMOMETRY 
All experiments were conducted on DINSRDC Carriage I using basically 
the same dynamometry and hardware as previously described in Reference 2. 
The port propeller, on which blade loads were not measured was driv-— 
en from inside the model hull as would be the case in a self propulsion 
experiment. The propeller rotational speed, which could be controlled 
independently of the starboard propeller, was measured via a toothed- 
pickup and recorded on a digital voltmeter. The time-averaged thrust and 
torque were measured for selected runs by a transmission dynamometer. 
The starboard propeller, on which blade loads were measured, was 
located in its proper position relative to the model hull but was isolated 
from the hull and driven from downstream (see Figure 4). This downstream 
drive system was necessary in order to obtain the required characteristics 
of the system for measuring unsteady loading. The general criteria for 
the design of an unsteady force measuring system are: : 
1. The support structure of the force measuring system should be 
soft mounted and possess a large mass to eliminate transmission of extra- 
neous vibration to the system. 
2. The natural frequency of the system should be well above the 
highest frequency of the quantities to be measured (to avoid phase shift 
and amplification of the signal). 
3. The system response in the force magnitude range should be suf- 
ficiently large to be measurable (sensitivity). 
4. The system should be free of interaction, that is, each measur- 
ing element should respond only to that force or moment which it is in- 
tended to measure. 
These four major aims are not complementary. The high natural fre- 
quency requires a stiff, rigid system whereas high sensitivity requires 
an elastic, soft system. The necessary compromise results in some inter- 
action between the force-measuring elements. 
Criterion 1 dictated that a massive flywheel be used, and Criterion 
2 dictated that this flywheel be connected: to the sensing elements (locat-— 
ed inside the propeller hub) by a short thick shaft. Therefore, because 
