However, basin experiments did provide some qualitative indication of depressor 

 behavior and did verify towing forces. The equipment, procedures, and results are 

 discussed below. 



EQUIPMENT 



Mechanical equipment consisted of a 4. 5 m length of the standard towcable, a 

 swivel located at the upper end of the towcable, and a variable depth towing strut. 



Instrumentation consisted of the following: 



1. A 17.8-kN (4000-lb) capacity strain-gage load cell with an estimated over- 

 all accuracy of + 90 N located at the towing strut for measurement of towing 

 tension; 



2. A magnetic pickup on the towing carriage to provide measurements of speed 

 to an accuracy of + 0.01 knot; 



3. The standard control electronics which provided measurements of body depth 

 and control flap angle; and 



4. A six-channel strip-chart recorder to provide readout of tension, speed, 

 depth, and flap angle. 



PROCEDURES 



Initially the depressor was towed without active control to examine passive tow- 

 ing behavior and to establish a satisfactory trim condition. The incidence angle of 

 the horizontal stabilizer (with respect to the fuselage centerline) was varied be- 

 tween 6 and 8 deg (leading edge down) , the control flap angle was varied between 

 + 20 deg, and towing speed was varied between 5 and 10 knots. Towing tension, speed, 

 and visual towing behavior were the only functions monitored during this series of 

 experiments. 



Following selection of a suitable stabilzer incidence angle, the depressor was 

 towed with active control. Both square and sine wave control inputs were examined. 

 The square wave inputs were primarily intended to investigate depressor control 

 stability. A square wave with a period of 28 sec and a nominal flap amplitude of 

 + 13 deg was used. This allowed observation of active control towing behavior at 

 both high and low tension conditions. During this experiment, the control flap gain 

 (the flap angle response per unit change in depth) was changed from a nominal value 

 of 19.7 deg/m to 6.6 deg/m. The sine wave control input was intended to examine the 



18 



