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ADA091 074 BELL HELICOPTER TEXTRON FORT WORTH TX F/B 1/3EXPERIMENTAL INSTALLATION OF MAST MOUNTED SIGHT ON AN O-58C HE--ETC(U)OCT 80 J A RULE. H W HANSON, H K HARR OAAKIO-G78-C0115
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~PRMENTAL INSTALLATION OF MAST MOUNTED SIGHTANm~ OH-58C HELICOPTER
Jame A. Rule, Horace W. Hanson, Harry K. Harr, John P. Norvell,Dav" A. Popelka
P. 0. Box 482
Fort Worth, Teas 76101
Final Repor for Period March 1978 - January 1960
Approved for public release;Idistribution unlimited.
prepared for
APPLIED TECHNOLOGY LABORATORYU. S. ARMY RESEARCH AND TECHNOLOGY LABORATORIES (AVRADCOM)Fort Eustis, Va. 23604
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APPLIED TECHNOLOGY LABORATORY POSITION STATEMENT
The Mast Mounted Sight (MMS) concept shows promise of permitting a scout helicopterto detect and designate targets for precision guided weapons while operating behindmasking features, thus reducing the detectability of the helicopter by visual, infrared, andradar guided antiaircraft threat systems.
The presence of the MMS affects helicopter dynamics, handling qualities, and loads,while the vibrational environment of the rotor mast affects the performance and life ofthe MMS.
A dynamic environment analysis indicated that severe penalties in MMS performanceand component life, and a greatly restricted helicopter flight envelope, would resultfrom a hard-mounted installation on the OH-58C. Use of a Bell Helicopter-designedfocal mount reduced translational accelerations of the MMS center of gravity fromabove 6 g's to about 2 g's, well within the design envelope of the Rockwell InternationalMMS.
A carefully selected combination of main rotor mast, trunion, and split-cone set, resultingto minimal eccentricity with respect to the mast axis of rotation, was required to obtainacceptable one-per-rev vibration levels at both the MMS and the crew stations simultane-ously.
Results demonstrated the feasibility of installing a MMS on the OH-58C, with minimaleffect on either the performance or handling qualities of the helicopter.
Mr. Kenneth D. Hampton of the Aeronautical Systems Division served as project engineerfor this effort.
DISCLAIMERS
The findings in this report ara not to be construed a an official Department of the Army polition unless sodeeisntd by other athorized cocument.
When Government drewings, specification$. or other date em used for any purpose other than in connectionwith a definitely related Government procurement operation, the United State Government thereby Incurs noresponsibility nor any oblItWion whatsoever; and the fact that the Government may have formulated, furnished.or in any way supplied the mid drawinps, specifications, or other data is not to be agard by implication orotherwise es in any manner licensing the holder or amy other person or corporation, or conveying any riots orpermission, to manufacture, use, or sell any patented invention that may In any way be related thereto.
Trade names cited in this report do not constitute an official endorsement or approvl of the use of suchcommercial hardware or softw.re.
DISPOSITION INSTRUCTIONS
Deroy this report twn no lonia ded. Do not return it to the originator.
UnclassifiedSECURITY CLASSIFICATION OF THIS PAGE MWen, Dae. Entored _________________
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PREFACE
This report contains the results of a feasibility demonstra-tion program to install and test a Rockwell mast mounted sightsystem on an OH-58C helicopter. The effort consisted ofanalytical studies; design, fabrication, and test of an in-strumented dummy sight; and installation and test of theactual sight. This program was conducted by Bell HelicopterTextron (BHT) for the U.S. Army Research and DevelopmentCommand (ARRADCOM) from March 1978 to February 1979 and forthe Applied Technology Laboratory (ATL), U.S. Army Researchand Technology Laboratories (AVRADCOM) from July 1979 toJanuary 1980. Contract DAAKIO-78-C-0115 funded the totaleffort.
The ARRADCOM technical direction was provided by Kennard W.Raisner and ATL technical direction was provided by Kenneth D.Hampton. This program was conducted under the technical di-rection of James A,. Rule, Project Engineer, Bell HelicopterTextron.
3
TABLE OF CONTENTS
Page
PREFACE ............................... 3
LIST OF ILLUSTRATIONS. .. ................... 7
LIST OF TABLES ....................... 10
INTRODUCTION .......................... 11
TEST EQUIPMENT ....................... 12
TEST AIRCRAFT.......................12DUMMY SIGHT INSTALLATION .. ............ 12ROCKWELL SIGHT INSTALLATION .............. 12
DUMMY MAST MOUNTED SIGHT CONFIGURATION .. ....... 19
GENERAL ........................ 19FEASIBILITY STUDIES. ................. 19
Dynamic Analysis. .............. 20Structural Analysis .. ............ 20
GROUND VIBRATION TEST. ................ 21GROUND RUN ......................... 21DEVELOPMENT FLIGHT TEST ................ 23FLIGHT LOAD AND VIBRATION SURVEY. .. ......... 30
Fatigue Evaluation ................ 30Blade Loads ...................... 31Vibration ..................... 31
TORSIONAL STABILITY SURVEY. .............. 37HANDLING QUALITIES ..................... 41PRELIMINARY AIRWORTHINESS EVALUATION. .. ..... 43
ROCKWELL MAST MOUNTED SIGHT CONFIGURATION. .. ..... 44
GENERAL .......................... 44MMS HARDWARE MISALIGNMENT ............... 44VIBRATION SURVEY .. .................. 45HANDLING QUALITIES .. ................... 45PRELIMINARY SIGHT EVALUATION. ............. 48ROCKWELL FLIGHT TEST .. ................ 48ENC TESTS ......................... 51WEIGHT AND BALANCE .. ................... 52
5
TABLE OF CONTENTS - CONCLUDED
Page
CONCLUSIONS........................591
REFERENCES........................60
APPENDIX A -VIBRATION DATA WITH
ROCKWELL SIGHT INSTALLED. ......... 62
6
LIST OF ILLUSTRATIONS
Figure Page
1 OH-58C with dummy sight installed ........ ... 13
2 OH-58C with Rockwell sight installed ........ 13
3 Rockwell MMS equipment installed in aftpassenger compartment ........ ....... . 15
4 Rockwell equipment installed in avionics
compartment ...... ................. ... 16
5 Observer's and pilot's TV monitors in
OH-58C ....... .................... ... 17
6 Passenger's TV monitor and video recorder 18
7 Comparison of MMS focal mount 2/rev pitchresponse deflection shapes ............. ... 26
8 Dummy MMS cg average vibration versus levelflight airspeed - development flight test . 28
9 Pilot's seat vibration versus level flightairspeed - dummy MMS development flighttest ........ ..................... ... 29
10 Comparison of main rotor oscillatory bendingmoments for baseline OH-58C and OH-58C/MMSat 80 kn ...... .................. ... 34
11 Comparison of main rotor oscillatory bendingmoments for baseline OH-58C and OH-58C/MMSat 100 kn ....... ................. ... 35
12 Comparison of measured chord bending momentat Station 60 for baseline OH-58C andOH-58C/MMS ...... .................. ... 36
13 Dummy MMS cg average vibration versuslevel flight airspeed - load level andvibration survey .... ............... .... 38
14 Pilot's seat vibration versus level flightairspeed - dummy MMS load level and vibra-tion survey ...... ................. ... 39
15 Nonrotating dummy sight on OH-58C ...... ... 42
7
LIST OF ILLUSTRATIONS - CONTINUED
Figure Page
16 OH-58C configured for handling qualitiestests ........ .................... ... 42
17 Rockwell MMS average vibration versuslevel flight airspeed - vibration survey. . . 46
18 Pilot's seat vibration versus level flightairspeed - Rockwell MMS vibration survey. . 47
19 Recognition and detection boards ......... ... 50
20 Target boards installed for Rockwell sightevaluation ........ .................. 50
21 OH-58C with MNS gross weight versus centerof gravity plot ..... ............... ... 58
A-1 Rockwell MMS trunnion (cg) vibration at M/R1/rev versus airspeed .... ............ ... 62
A-2 Rockwell MMS trunnion (cg) vibration at M/R2/rev versus airspeed .... ............ ... 63
A-3 Rockwell M'WS trunnion (cg) vibration at M/R4/rev versus airspeed .... ............ ... 64
A-4 Rockwell MS trunnion (cg) vibration at M/R6/rev versus airspeed .... ............ ... 65
A-5 Rockwell MMS line-of-sight (roll) vibrationat M/R 1/rev versus airspeed .... ......... 66
A-6 Rockwell MMS line-of-sight (roll) vibrationat M/R 2/rev versus airspeed .... ......... 67
A-7 Rockwell MMS line-of-sight (roll) vibrationat M/R 4/rev versus airspeed ............ ... 68
A-8 Rockwell MS line-of-sight (roll) vibrationat M/R 6/rev versus airspeed .......... .... 69
A-9 Rockwell MS trunnion (cg) vibration at M/RI/rev and 2/rev in IGE hover .... ......... 70
A-10 Rockwell MS trunnion (cg) vibration at M/R4/rev and 6/rev in IGE hover .... ......... 71
8
LIST OF ILLUSTRATIONS - CONCLUDED
Figure Page
A-i Rockwell MMS line-of-sight (roll) vibrationat M/R 1/rev, 2/rev, 4/rev, and 6/rev inIGE hover ...... .................. . 72
A-12 Crew seat vibration at M/R 1/rev versusairspeed ....... ................... . 73
A-13 Crew seat vibration at M/R 2/rev versusairspeed ....... ................... . 74
A-14 Crew seat vibration at M/R 4/rev versusairspeed ......... ................... 75
A-15 Crew seat vibration at M/R 6/rev versusairspeed ....... ................... . 76
A-16 Crew seat vibration at M/R 1/rev in IGEhover ....... .................... . 77
A-17 Crew seat vibration at M/R 2/rev in IGEhover ....... .................... 78
A-18 Crew seat vibration at M/R 4/rev in IGEhover ........ .................... 79
A-19 Crew seat vibration at M/R 6/rev in IGEhover ........ . .................. 80
9
LIST OF TABLES
Table Page
1 INSTRUMENTATION MONITORED DURING FLIGHTTESTS WITH ROCKWELL SIGHT ........... . 14
2 COMPARISON OF ANALYTICAL AND SHAKE TESTRESULTS ....... .................. 22
3 MMS FOCAL MOUNT OPTIMIZED PARAMETERS . . . 23
4 DEVELOPMENT FLIGHT TEST PROBLEMSENCOUNTERED ...... ................ 24
5 BASIC COMPONENT FATIGUE LIFE SUMMARY . . 32
6 MAXIMUM MEASURED LOADS AND STRESSES. . . 33
7 TORSIONAL STABILITY COMPARISON ...... 40
8 ROCKWELL SIGHT PERFORMANCE ......... . 49
9 DERIVATION OF MAST MOUNTED SIGHT WEIGHTAND BALANCE ...... ................ 53
10 DERIVATION OF BASIC WEIGHT ......... . 56
11 GROSS WEIGHT AND BALANCE CALCULATIONS. . . 57
10
INTRODUCTION
Military tactics for scout helicopter missions require thehelicopter crew to detect, identify, and laser-designate tar-gets while minimizing exposure of the helicopter to enemydetection and attack. A mast mounted sight (MMS) and laserdesignator/range finder, located as high as possible above thehelicopter rotor, allows the helicopter to take maximum advan-tage of terrain features with only the sight exposed to theenemy.
Installation of an MMS on a helicopter affects helicopterdynamics, structural loads, aerodynamic drag and handlingqualities. The severe vibration environment found on top of ahelicopter mast which the MMS must tolerate affects the accur-acy of the sight and the life of the sight components.
To provide an insight into the effects of installing an MMS ona helicopter, two Army-sponsored studies were conducted byBHT. The first study (Reference 1) investigated the effectsof sight weight and height above the rotor on a Model OH-58Chelicopter. The second study (Reference 2) examined the fea-sibility of installing a TOW missile sight on the mast of anAH-IS helicopter using a nonrotating platform and standpipewhich were developed for the SATCOM antenna.
Since the OH-58C study indicated that a reasonably sized MMScould be installed, Contract DAAKI0-78-C-0115 was awarded toBHT for the experimental installation of a Rockwell sight onan OH-58C to demonstrate the feasibility of this system.
'Rule, J. A., et al, "OH-58C Mast-Mounted Visionics Analysis,"Bell Helicopter Textron Report Number 699-099-060, FortWorth, Texas, July 1977.
2Rule, J. A., et al, "AH-lS Mast-Mounted TOW Sight Analysis,"Bell Helicopter Textron Report Number 699-099-088, FortWorth, Texas, July 1978.
11
TEST EQUIPMENT
TEST AIRCRAFT
The helicopter, shown in Figure 1, was a bailed U.S. ArmyOH-58C, Army Serial No. 69-16214. The dummy sight is showninstalled on a focal mount on top of the mast. A BHT commer-cial Model 206 SCAS kit and hydraulically boosted tail rotorcontrols were installed in the helicopter to improve handlingqualities and provide a stable platform for sight operation.The airframe was strengthened and a stiffer main rotor pylonisolation mount was installed.
Other modifications made to the helicopter to install the MMSincluded the following items:
A standpipe with a splined fitting on each end was in-stalled inside the main rotor mast supported by a matingsplined fitting bolted to the bottom of the transmissionand two bearings near the upper end of the mast.
A splined nonrotating plate was installed in the upperend of the mast on the standpipe spline to support theMMS focal mount.
The focal mount was installed between the nonrotatingplate and the MMS.
The cable assembly from the MMS was routed through thestandpipe, out the bottom of the transmission, andthrough a hole in the cabin roof to the electronicsequipment in the cabin.
DUMMY SIGHT INSTALLATION
The test equipment consisted of a bailed OH-58C helicopter, aninstrumented dummy mast mounted sight which simulated theweight and shape of the Rockwell sight, a focal mount, instru-mented main and tail rotor blades, instrumented controls, aslip ring assembly, numerous transducers, a telemetry multi-plex package, a 13-channel telemetry transmitter and a heli-copter-installed magnetic tape recorder with 104-channelcapacity. The instrumentation package was installed on a rackin the aft passenger seat. A detailed list of the instrumen-tation used in flight tests with the dummy sight is includedin the flight test reports.
ROCKWELL SIGHT INSTALLATION
Figure 2 shows the OH-58C with the Rockwell nast mounted sightinstalled on the focal mount. In addition to -he sight, theRockwell system included a number of electronic boxes andinstrumentation equipment.
12
-~ ~~~~~ ..~-- .. . .. .. .... .-- ..
Figure 1. OH-58C with dummy sight installed.
Figure 2. OH-58C with Rockwell sight installed.
13
The BHT instrumentation rack and nearly all BHT instrumenta-tion were removed to allow installation of the Rockwell sys-tem. Figures 3 and 4 show the Rockwell electronics and in-strumentation installed in the rear seat and electronicscompartment.
The observer's monitor was a pantograph-supported TV monitor,with sight and monitor controls located on modified hand gripson either side of the display. The copilot's cyclic and pedalcontrols were removed to make room for the display.
A small TV monitor was mounted on the right-hand side of theinstrument panel to enable the pilot to maintain the correctaltitude by positioning the MMS line of sight just above aprotective hill or tree line. Figure 5 shows the observer'sand pilot's monitors in the cabin. A third monitor and avideo recorder were installed in the back seat for these testsas shown in Figure 6.
Instrumentation installed with the Rockwell sight consisted ofthe video recorder in the back seat and magnetic tape recorderinstalled in the electronics compartment. Accelerometers wereinstalled in the sight by Rockwell. BHT installed accelerome-ters under the pilot's and observer's seats, and position po-tentiometers were installed on the focal mount. Table 1 liststhe instrumentation transducers which were monitored duringflight tests with the Rockwell sight.
TABLE 1. INSTRUMENTATION MONITORED DURINGFLIGHT TESTS WITH ROCKWELL SIGHT
Descriptions Units
MMS Azimuth Stabilization Rad
MMS Elevation Stabilization Rad
MMS Line-of-Sight Angular Acceleration Rad/Sec2
MMS C.G. Lateral Acceleration G's
MMS C.G. F/A Acceleration G's
MMS C.G. Vertical Acceleration G's
Pilot Seat Vertical Acceleration G's
Pilot Seat Lateral Acceleration G's
Pilot Seat F/A Acceleration G's
Copilot Seat Vertical Acceleration G's
Copilot Seat Lateral Acceleration G's
Copilot Seat F/A Acceleration G's
14 j
JTIME CODE AND CHARACTER GENERATORS-
Figure 3. Rockwell MMS equipment installed in aft
passenger compartment.
15
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Figure 6. Passenger's TV monitor and video recorder.
18
DUMMY MAST MOUNTED SIGHT CONFIGURATION
GENERAL
The ground vibration test and most of the flight testing atBHT Flight Research Center at Arlington, Texas, were conductedwith a dummy sight installed in lieu of the Rockwell sight.The primary reasons for using the dummy sight were as follows:
1. The Rockwell sight was not available during the testprogram time frame.
2. The dummy sight incorporated a slip ring whichtransferred electrical signals from the instrumentedmain rotor blade and rotating controls to the non-rotating airframe.
3. Instrumentation could be more easily added orchanged in the dummy sight than in the Rockwellsight.
The dummy sight was designed to duplicate the weight, inertia,and general size and shape of the Rockwell sight. Because ofthe slip ring requirement, the outer shell of the dummy sightrotated with the rotor, whereas the Rockwell sight does not.The flat lens of the Rockwell sight was not duplicated on thedummy sight because of this rotation.
Feasibility studies, including dynamic and structural analysesusing computer models, were conducted prior to the start oftesting. Following the studies the helicopter was subjectedto a series of ground shake tests with and without the dummysight installed. Flight tests were then conducted using thedummy sight. Results of these analyses and tests are pre-sented in the following sections.
FEASIBILITY STUDIES
Prior to the beginning of the mast mounted sight test program,dynamic and structural analyses were made to study the feasi-bility of installing the Rockwell sight on the OH-58C mast.The original plan was to hard mount the sight on a nonrotatingplatform located approximately 20 inches above the main rotorblade flapping axis.
19
Dynamic Analysis
A dynamic analysis of this configuration was conducted by BHTto determine the sight dynamic environment and the dynamiceffects on helicopter components (Reference 3, Volume 1).
This analysis showed that a hard-mounted mast mounted sight onthe OH-58C would reduce the main rotor hub mobility due to theinertia added to the hub and thereby greatly increase mainrotor blade loads, especially during gusts and maneuvers.
As a result of this analysis, BHT funded the design and fabri-cation of a focal mount for the MMS, for which a patent hasbeen applied. This mount utilized the same principle as thefocal-mounted pylon system on the OH-58C. The 1924 focal mountsystem reduced the translational and rotational vibrationlevels at the sight. In addition, it accomplished its mainpurpose of isolating the MMS from the main rotor hub. volume2 of Reference 3 describes the MMS focal mount system.
Supplementing the design of the MMS focal mount, the dynamicanalysis was repeated with the MMS installed on the focalmount. This analysis is presented in Reference 4.
Structural Analysis
A structural analysis, Reference 5, was conducted to determineif the fuselage, transmission, mast and other helicopter com-ponents were suitable to support the weight of a mast mountedsight during normal operation and under crash load conditions.
As a result of this analysis, the fuselage roof, transmissionmounting bolts, and drag pin were strengthened for the in-creased loads. The forward crash load factor on the mast wasreduced from 16g's to ll.2g's with the dummy mast mountedsight installed on the focal mount (124.4 pounds at W.L. 137.2inches).
3Anderson, H., and Andrews, J., "Dynamic Environment Analysisof OH-58C Helicopter with Mast Mounted Sight Installed,"Volumes 1 and 2, Bell Helicopter Textron Report No. 206-099-353, September 1978.
"Anderson, H., and Andrews, J., "Dynamic Environment Analysisof OH-58C with Focal Mounted Sight Installed," Bell Helicop-ter Textron Report Number 206-099-812, November 1978.
5Freeman, F., Hunt, G., Messick, J., Midgley, R., Rost, F.,Roessler, D., "Structural Analysis of Mast Mounted Sight onthe OH-58C Helicopter," Bell Helicopter Textron Report Number206-099-354, Revision A, November 1978.
20
GROUND VIBRATION TEST
A ground vibration test of both the baseline OH-58C and theOH-58C with a dummy MMS installed was performed during Octoberthrough December, 1978. The weight of the dummy sight used inthe shake test was 69 pounds. The test plans and test resultsare reported in Reference 6. A hub mobility and naturalfrequency comparison of analysis and shake test results forboth helicopter configurations is shown in Table 2.
The primary purpose of the ground vibration test was to eval-uate the MMS focal mount system to determine the proper focalpoint location and spring rate combination required to provideoptimal MMS two-per-rev vibration isolation. During theinvestigation of various MMS focal point and mount spring ratecombinations, it was found that the flexibility of the MMSfocal mount plates was degrading the performance of the focalmount system, resulting in larger MMS two-per-rev pitchingmotions than were predicted (see Figure 7 in DevelopmentFlight Test Section). For shake test evaluation, the upperfocal plate was stiffened by installing struts from the fourcorners of the plate up to the dummy sight vertical support atapproximately 45-degree angles. The lower focal plate wasartificially stiffened by installing braces from the fourcorners of the plate down to the main rotor hub nut adapter(rotating system). With the stiffened focal plates, the MMSfocal mount system was found to perform as the analysis hadpredicted, and the optimum MMS focal mount system parameterswere determined, as are presented in Table 3. It was con-cluded that stiffer focal mount plates would significantlyreduce the MMS two-per-rev pitching and rolling motions.
The MMS nonrotating static standpipe, which is installed in-side the main rotor mast, was instrumented to detect contactbetween the standpipe O.D. and the mast I.D. No contact be-tween these two shafts occurred during any of the ground vib-ration testing.
GROUND RUN
The first ground run with the dummy MMS installed was accom-plished on 22 December 1978. The aircraft was secured to theground during all ground runs. Cyclic and pedal reversalswith varying main rotor rpm were accomplished with no adverseeffects. On 3 January 1979 the OH-58C was ground run to checktorsional stability. Cyclic, collective, and pedal inputs
6Andrews, J., and Hanson, H., "Ground Vibration Test of theOH-58C with Mast Mounted Sight," Part I - Test Plan, Part II- Test Results, Bell Helicopter Textron Report Number 206-099-808, Revision C, March 1980.
21
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were made at increments of 10 percent M/R torque up to takeoffpower. Rotor response and damping were normal. A subsequentground run was done for EMC tests on the SCAS. No abnormali-ties were noted.
TABLE 3. MMS FOCAL MOUNT OPTIMIZED PARAMETERS
MMS Pitch:
Focal Point W.L. 74
Mount Spring Rate 350 lb/in.
MMS Roll:
Focal Point 0
Mount Spring Rate 350 lb/in.
DEVELOPMENT FLIGHT TEST
Initial development flight tests were conducted during Januaryand February 1979. During this period several problems wereencountered relative to the MMS focal mount system installa-tion, the most important of which are summarized in Table 4and discussed in the following paragraphs.
The first flight with the dummy sight installed on the OH-58Cwas accomplished on 9 January 1979. The helicopter was con-figured at a mid-center of gravity (cg) and 3100 pounds grossweight (GW). The weight of the dummy sight used during thesetests was 72 pounds. The A/C was hovered and inputs were madewith the cyclic stick and pedals. A high lateral main rotorone-per-rev vibration was evident. The pilot commented thatthe aircraft responded and handled very much like a standardOH-58C although it appeared to be somewhat more sluggish in ahover with SCAS off, i.e., required more pilot effort tostabilize in a hover. SCAS, when engaged, was a positive aidto the pilot in the hover mode.
The next several days were spent attempting to balance themain rotor. On 16 January 1979 with the main rotor still outof balance, a level flight sweep to 90 KIAS was made. Leftand right turns, cyclic pedal and collective inputs were ac-complished at several airspeeds. Flight test data verifiedthe MMS focal plate flexibility which was detected during theground vibration test. As shown in Figure 7, this additionalflexibility.in the MMS focal mount system resulted in raisingthe optimal focal point, thereby increasing the sight two-per-rev rotational response.
23
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06
On 19 January 1979, the main rotor was balanced so that thepilot's seat one-per-rev vibration level was reduced to 0.15inch-per-second (IPS) during a hover. The aircraft was thenflown for a level flight sweep to record sight vibrations.Approaching 85 KIAS the dummy MMS made contact with the focalmount stops, resulting in a main rotor pylon rocking modemotion evident in the cockpit. The flight was aborted.
It was noted that balancing the main rotor for minimum pilot'sseat vibration resulted in a higher sight vibration level inhover and forward flight; conversely, with the main rotorbalanced for minimum sight vibration, the pilot's seat vibra-tions were increased. The focal mount stops were opened up by0.1 inch. On the next flight, while taxiing IGE, the focalmount stops were again contacted and the aircraft experiencedpylon rock. It was noted that the abnormally high one-per-revvibration used up a significant portion of the stop clearance.Again the focal mount stops were opened up another 0.1 inch(total of 0.2 inch), and the main rotor pylon mount stiffnesswas increased to reduce the pylon gust response sensitivity.
The one-per-rev vibration anomaly was further investigated byevaluating various MMS weight configurations at several heli-copter center-of-gravity and gross weight conditions. It wasfound that practical sight weight variations had no appreci-able effect on the one-per-rev problem, perhaps due in part tothe flexibility of the MMS focal plates, but that sight two-per-rev vibrations were less with decreased sight weight(effectively the same as increasing the spring rate of the MMSmounts). For a 50-pound MMS weight configuration it waspossible to obtain 110 KIAS in a dive prior to slight stopcontact. In maneuvering flight at 85 to 90 KIAS and 1.3 to1.4g's, slight stop contact was encountered.
For a 72-pound MMS configuration and a compromise main rotorbalance providing marginally acceptable pilot's seat one-per-rev vibration, representative level flight vibration data forthe MMS cg and the pilot's seat are shown in Figures 8 and 9,respectively. MMS translational response did not exceed1.85g's, including maneuver and moderate gust conditions;pitch rotational response did reach the Rockwell limit duringsevere gusts at 85 KCAS. With the MMS installed, maximumcontinuous torque at level flight resulted in 96 KCAS, andVcruise was estimated 86 KCAS. Pilot's seat one-per-rev vib-
ration levels were significantly higher than on the baselineOH-58C aircraft, especially during hover and at the higherairspeeds. No adverse loads or handling qualities problemswere encountered.
At this time the decision was made to suspend further testinguntil stiffer MMS focal plates were fabricated and installedon the helicopter.
27
NOte: Rotational velocity data taken at 0-200 Hz frequency40 range. Average rotational acceleration in 0-30 Hz
range then calculated by straight addition of the)1/rev and 2/rev acceleration harmonica.
I Rockwell MMS rotational acceleration limit30 (28.3 rad/sec2 peak, 20 rad/sec2 rms for 5-30 Hz)
0
4j PitchRoll
" 20
o0
* 10Yaw
04-1
o- 0 I!I I l
0 20 40 60 80 100 120
Calibrated airspeed, kn
8.0-
0 tRockwell MMS translational acceleration limit0 6.0- (5.66 g's peak, 4.0 g's rms for 5-30 Hz)
(200 40
2.0-.d-o( o
Vertical __ ,,, Fore/AftU)I ___'__Lateral
f 0 iT -_iiiI
0 20 40 60 80 100 120
Calibrated airspeed, kn
Figure 8. Dummy MMS cg average vibration versus level flightairspeed - development flight test.
28
0 .05-
- 0.04
O Lateral
00.03
w 0.02Fore/Aft
> 0.01-0)14Vertical
00 20 40 60 80 160 120
Calibrated airspeed, kn
0.20- r
.)I>1
0.15. MIL-H-8501A Para 3.7.1(b) 4U) Vertical
0."I
4 0.10
0)
LateralU
> 0.05.
-- Fore/Aft
0 ,4 1, •i0 20 40 6 80 1oa
Calibrated airspeed, kn
Figure 9. Pilot's seat vibration versus level flightairspeed - dummy MMS development flight test.
29 ji
FLIGHT LOAD AND VIBRATION SURVEY
Complete results of the flight load and vibration survey withthe dummy MMS are presented in Reference 7. No excessiveloads were measured either in basic OH-58C components or inMMS components. One-per-rev vibration level was higher thanthat of the basic OH-58C during the dummy MMS test program.This was mainly due to the tilt and eccentricity of the dummysight with respect to the main rotor mast axis of rotation, asdiscussed later. Two-per-rev vibration was slightly higherthan that of a basic OH-58C, primarily because stiffer pylonand MMS focal mount springs were installed to alleviate theone-per-rev vibration problem. Time constraints preventedfurther testing, but it is felt that a standard OH-58C pylonspring and softer focal mount springs would have providedtwo-per-rev vibration levels equal to those of a basic OH-58Cafter the one-per-rev vibration problem had been eliminated.
Fatigue Evaluation
To provide data for a fatigue evaluation of the OH-58C heli-copter with the Rockwell mast mounted sight (MMS) installed,an abbreviated flight load survey was conducted. The resultsof this survey are presented in Reference 7. With the excep-tion of the components of the sight system, the fatiguestrength of each component was determined from data presentedin Reference 8. The fatigue strengths of the sight componentswere determined using conservative analytical methods. Sincethe flight loads survey of the OH-58 with the MMS installedwas flown at only 3200 pounds gross weight, forward and aftcg, only these conditions were used to calculate fatiguelives. A 50/50 breakdown was used on flight time betweenforward and aft cg conditions. Some flight conditions wereomitted from the complete OH-58C spectrum during the loadlevel survey with the MMS installed. These conditions areconsidered to be low load conditions and their deletion shouldhave minimal effect on the resulting fatigue life calcula-tions.
7Andrews, J., Hanson, H., Harr, H., Norvell, H., Popelka, D.,Spence, W., "Flight Load and Vibration Survey of OH-58C withMast Mounted Visionics," Part I - Test Plan, Part II - TestResults, Bell Helicopter Textron Report Number 206-099-809,Revision B, March 1980.
8Cassidy, B., and Norwell, J., "Fatigue Life Substantiationfor the Dynamic Components of the Model 206B-1 Helicopter andthe Model OH-58C Helicopter," Bell Helicopter Textron ReportNumber 206-099-148, February 1973.
30
The effects of flight loads measured during operation with theMMS installed were evaluated for the following components:M/R blade, M/R yoke, M/R mast, M/R pitch link, upper R/Hcyclic tube, lower collective tube, pylon support link, pylonsupport fitting, and T/R blade. These components are consid-ered representative of the most critical elements in each ofthe fatigue-sensitive areas of the basic aircraft. Table 5lists these components with name, part number, endurancelimit, baseline fatigue life, and fatigue life in the MMSconfiguration. Components having no flight loads greater thanthe respective endurance limit are listed with their maximumload/stress values in Table 6.
Blade Loads
The measured main rotor beam and chord loads for the OH-58Cwith the dummy sight installed were compared to those for thebaseline OH-58C. Figures 10 and 11 present the spanwisevariation of the oscillatory loads for two airspeeds at for-ward and aft center of gravity. The beam loads are essen-tially unaffected by the addition of the dummy sight; however,the chord loads are reduced for the dummy sight configuration.
The reduction in oscillatory chord loads is attributed to theincrease in hub mobility due to the focal mount of the dummysight. The first chordwise bending frequency of the rotor ishighly dependent on the hub mobility. An increase in the hubmobility will increase the chordwise bending frequency, whichmoves it farther from resonance with the one-per-rev airloadexcitation. The dummy. sight configuration for the flight loadsurvey utilized a stiffer main rotor pylon mount and a stifferMMS focal mount than the ground vibration test configuration.These stiffer mounts result in a two-per-rev hub mobilitywhich is higher for the dummy sight configuration than for thebaseline OH-58C configuration. Thus, it would be expectedthat the chordwise loads would be lower for the dummy sightconfiguration.
The chordwise bending loads at the critical blade station 60are presented in Figure 12 for both the baseline and dummysight configurations. The loads for the dummy sight config-uration are below the endurance limits, and are generallylower than for the baseline configuration. A number of low-speed maneuvers are included which show acceptable blade loadsfor nap-of-the-earth operation.
Vibration
Evaluation of the vibration characteristics with the stifferMMS focal mount plates installed and the subsequent flightload and vibration survey were conducted from September 4through 14, 1979. The dummy sight weight was adjusted to 64pounds by removing three of the tungsten weights to be repre-sentative of the Rockwell MMS weight projected at this time.
31
4)C- In 4)4-)~'- 4J)
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4 4.) 0 0 0 0 0 0 0 0 0 (d
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32
o w r, 0 C0 k0 '.0 VU~) 0 M ' CY G) O 00
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33
GW = 3200 LB(BASELINE & MMS)0 BASELINE OH58C AFT CG
0 -O- 0 BASELINE OH58C FWD CG-• OH58C/MMS AFT CG
x *OH58C/MMS FWD CG
4J
5.
0 20 40 60 80 100
Blade radius - %
30
x20-
I.00- ---r. 11h JAENDURANCE LIMIT.
S10 '
o .
0 20 40 60 80 100
Blade radius -%
Figure 10. Comparison of main rotor oscillatory bendingmoments for baseline OH-58C and OH-58C/MMSat 80 kn.
34
GW = 3200 LB(BASELINE & MMS)U'BASELINE OH-58C AFT CG
-- 0 BASELINE OH-58C FWD CG-A 0 OH58C/MMS AFT CG.0- O OH58C/MMS FWD CG
i0-4
4J to) II
0 20 40 60 80 100
Blade radius - %
30
x20
"ENDURANCE LIMIT
.4
S10 -- - - - - -
0
U
0 20 40 60 80 100
Blade radius - %
Figure 11. Comparison of main rotor oscillatory bendingmoments for baseline OH-58C and OH-58C/MMSat 100 kn.
35
=2 E-4
U D4E4 H HN
E4~
C4iz 4 F~ F:C H
04 :E w P
04 z
00
E 0
co U H
0 Cl
ol 0 >
z u 0) 00000Z 1
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'-~ 0 0)
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C) C) :z36
As predicted, it was found that the stiffer MMS focal platesdid reduce sight two-per-rev rotational vibration. A stifferMMS mount was then installed, which reduced sight one-per-revrotational response sensitivity, especially in hover, butnegated the reduction in sight two-per-rev rotational responsewhich was gained by the stiffened focal plates. As a result,the one-per-rev response anomaly was somewhat desensitized butstill very much in evidence.
Attention was then directed toward possible misalignment ofthe MMS mounting hardware on the main rotor mast axis of rota-tion, or perhaps a bent main rotor mast, as the source of theone-per-rev problem. Several attempts to measure these param-eters with the MMS installed on the helicopter proved incon-clusive. However, a compromise main rotor balance configura-tion was achieved so that the remainder of the feasibilitytesting could be accomplished without further delay. Aftercompletion of all testing with the dummy MMS, it was decidedto remove the main rotor mast and MMS mounting hardware fromthe helicopter for bench test measurements to check runout andmisalignment. It was found that the centerline through the cgof the dummy sight was not coincident with the center ofrotation of the mast. A detailed description of this problemis presented on page 44.
A composite of flight vibration data taken during the loadlevel and vibration survey, Reference 7, is shown for the MMScg and the pilot's seat in Figures 13 and 14. MMS transla-tional response was well below limits, and rotational responsein hover was much improved. Qualitatively, both one-per-revand two-per-rev vibration levels at the pilot's seat weresomewhat higher than those on the baseline OH-58C helicopterbut were acceptable for feasibility testing. Twice during thesurvey there was evidence of MMS stop contact, with both in-stances occurring during high-speed l.5g maneuvers. Under nocircumstances did the MMS static standpipe ever come into con-tact with the main rotor mast.
TORSIONAL STABILITY SURVEY
Ground and flight tests were conducted during September 15through 18, 1979, to demonstrate that the OH-58C engine-gover-nor-drive train system was torsionally stable under all speedand power conditions appropriate to operation of the helicop-ter with the MMS installed. The system was disturbed by pilotcollective lever and rudder pedal input oscillations at theapproximate system 1st torsional natural frequency duringrepresentative engine power and rotor speed conditions toevaluate torsional stability margins. The test plan and test
37
Note: Rotational velocity data taken at 0-200 Hz frequencyN 40" range. Average rotational acceleraton in 0-30 Hz
range then calculated by straight addition of tlea1/rev and 2/rev acceleration harmonics.
Rockwell MMS rotational acceleration limit30-(28.3 rad/sec2 peak, 20 rad/sec2 rms for 5-30 Hz)
0
4jJ
4 20
All level flight data'roll, pitch, yaw
0"H
0j0 20 40 60 80 100 120
Calibrated airspeed, kn
En 8.0"
Rockwell MMS translational acceleration limit."1 0 6.0- (5.66 g's peak, 4.0 g's rms for 5-30 Hz)
oi 4.0-r0 W
r-I 4
'U All level flight data
o4 =f/a, lat, vert4o o 2.0"i N
$4 010 20 46 160 120
Calibrated airspeed, kn
Figure 13. Dummy MMS cg average vibration versus level flightairspeed - load level and vibration survey.
38
0 .05-
0 .04-
0
*-P 0.03-Vertical
H4 Fore/AftU 0 .02- Lateral
>
0 0.01-
00 20 40 60 80 100 120
Calibrated airspeed, kn
0.20-
i
~ .5 MIL-H-8501A Para 3.7.1(b) U Vetia
.i0.10--
0.H
0.0
O Lateral
S0.05-
00 20 40 60 80 100 110
Calibrated airspeed, kn
Figure 14. Pilot's seat vibration versus level flightairspeed - dummy MMS load level and vibration survey.
39
results are reported in Reference 9. All test conditionslisted in the test plan were evaluated. In each test the mainrotor mast torque oscillations were found to be positivelydamped and exhibited no tendency to diverge. System torsionaldamping characteristics for selected conditions are shown inTable 7 as compared to the same conditions for the basicOH-58C helicopter. Basic OH-58C values are given in Reference10. It was concluded that the engine-governor-drive system ofthe OH-58C with MMS installed is torsionally stable and freeof excessive sustained torsional oscillations throughout theflight envelope for which the helicopter is to be operated.
TABLE 7. TORSIONAL STABILITY COMPARISON
Flight Damping (% Critical)Condition Excitation OH-58C OH-58C/MMS
Hover Collective Input 3.1 3.1Hover Pedal Input 3.5 3.7
48 KCAS Collective Input 2.2 2.248 KCAS Pedal Input 3.1 3.3
90 KCAS Collective Input 3.8 2.890 KCAS Pedal Input 2.4 3.1
MCT* Collective Input 3.1 3.7MCT* Pedal Input 4.5 3.7
*Maximum Continuous Torque:Basic OH-58C level flight (VH) = 102 KCAS (Ref. 10)
OH-58C/MMS level flight = 96 KCAS (Ref. 7)
9Andrews, J., and Hanson, H., "Torsional Stability Survey ofthe OH-58C with Mast Mounted Sight," Part I - Test Plan,Part II - Test Results, Bell Helicopter Textron Report Num-ber 206-099-807, Revision B, March 1980.
10McEntire, K., "Engine/Airframe Compatibility Demonstrationfor OH-58C Helicopter," Bell Helicopter Textron Report Num-ber 206-099-748, Revision A, November 1978.
40
HANDLING QUALITIES
The OH-58C with a dummy mast mounted sight installed on afocal mount was extensively tested to determine what handlingqualities, if any, were changed by the addition of the mastmounted sight. A detailed description of the tests and testresults is presented in Reference 11.
In addition to the mast mounted sight, the test helicopter wasequipped with a BHT Model 206 three-axis SCAS, which improvedhandling qualities and provided a more stable platform for themast mounted sight.
Handling qualities tests were conducted with a modified dummysight installed on the focal mount as shown in Figure 15.This version of the dummy sight did not rotate (as did theoriginal dummy) and the shape was more nearly the same as theRockwell sight. The main rotor slip ring was not installed,as all rotating loads data on the main rotor had been taken.Main rotor flapping data could not be obtained without theslip ring. A tail rotor slip ring was installed. A nose boomwas installed to provide pitot and static sources for airspeedand altitude measurements, as shown in Figure 16. The pitothead was the swiveling type which provided accurate airspeedinformation during helicopter sideslips. instrumentationvanes for measuring angle of sideslip and angle of attack werealso installed on the nose boom.
Tests were conducted in relatively stable air with data re-corded for the following parameters:
- Static longitudinal trim stability
- Collective-fixed static longitudinal stability
- Static lateral-directional stability
- Dynamic stability
- Controllability
- Maneuver stability
- Autorotation entries
1'Gastinger, D., Hardesty, D., Harr, H., Hester, M., "HandlingQualities for the Model OH-58C Helicopter with Mast MountedVisionics," Part I - Test Plan, Part II - Test Results, BellHelicopter Textron Report Number 206-099-423, Revision C,
February 1980.
41
4-)
.4W4-
) ..-I
4 -
0
.i
o
4J
42
A thorough pilot qualitative evaluation was conducted duringhover, sideward and rearward flight, transition and maneuver-ing flight. Results of the tests showed that the installationof the dummy mast mounted sight did not significantly changethe handling qualities from those of the basic OH-58C.
The flight envelope of the OH-58C with the mast mounted sightinstalled is the same as the basic OH-58C with the followingexceptions:
1. Maneuver loads at design gross weight (3200 pounds)are limited to 0.6 negative to 1.4g's positive dueto increased vibration and the focal mount hittingits stops, compared to 0.5 and 2.34 for the basicOH-58C.
2. Vne is limited to 100 knots indicated airspeed
(KIAS) between sea level and 3000 feet density al-titude. Vne is reduced three knots per 1000 feet
above 3000 feet density altitude. Basic OH-58C V neis 145 knots.
The gross weight (GW), center of gravity (cg) and sideslipflight envelopes are the same as those of the basic OH-58C.
PRELIMINARY AIRWORTHINESS EVALUATION
A preliminary airworthiness evaluation (PAE) was conducted onthe OH-58C with the dummy mast mounted sight installed. ThePAE was performed by U.S. Army personnel from the UnitedStates Army Aviation Engineering Flight Activity (USAAEFA)with support from BHT personnel at the BHT Flight ResearchCenter. Purposes of the PAE were to verify results of BHTtests, evaluate the OH-58C with SCAS installed, and determineif the OH-58C with MMS was safe for further testing by theU.S. Army. It was concluded that the OH-58C with MMS pre-sented no problems that would prevent continuation of thefeasibility testing. Complete results of the PAE are pre-sented in Reference 12.
12Bishop, J., et al, "Preliminary Airworthiness EvaluationOH-58C Helicopter Configured with a Mast Mounted Sight,"USAAEFA Project Number 7809, to be published 1980.
43
ROCKWELL MAST MOUNTED SIGHT CONFIGURATION
GENERAL
The dummy sight and most BHT instrumentation were removed andthe Rockwell mast mounted sight and associated electronics andinstrumentation were installed in the OH-58C following the PAEtests. Flight tests were conducted to balance the rotor,check vibration levels, and qualitatively evaluate handlingqualities. Since most of the instrumentation was removed, thehelicopter tests with the Rockwell MMS were mainly qualitativecomparisons of the Rockwell MMS versus the dummy MMS.
MMS HARDWARE MISALIGNMENT
During the entire flight test program with the dummy sight, itwas not possible to balance the rotor and/or the dummy sightto get a good ride in the helicopter while getting a low vib-ration level at the sight. Improving the ride one-per-revvibration levels resulted in increased one-per-rev levels atthe sight and vice versa. A marginally acceptable compromisewas achieved which was suitable for the flight test program.One theory on this anomaly was that the MMS nonrotating plat-form either was not installed on the mast straight or was notconcentric with the M/R mast axis of rotation. Attempts tomeasure these parameters on the helicopter with the rotorinstalled proved inconclusive. When the helicopter was torndown to install the Rockwell sight, it was possible to measurethe run-out of the nonrotating platform with respect to themast.
With the parts assembled on a bench it was found that the non-rotating platform had 0.026-inch radial run-out and 0.020-inchface run-out with respect to the mast axis of rotation. Thisamount of run-out and tilt would cause significant one-per-revvibration when projected to the MMS cg. In addition, it wasprobably amplified by the MMS focal mount which was designedto isolate two-per-rev vibration.
In order to improve the alignment of the nonrotating platform,the following parts associated with the mounting were mixedand matched:
2 sets of MMS hardware3 M/R masts2 M/R trunnions2 pairs of split-cone sets
It was found that changing the trunnion made the most signifi-cant difference and reindexing the cone set resulted in asmall difference. Using the best combination of the aboveparts, the reassembled nonrotating platform had only 0.004-inch radial run-out and 0.002-inch face run-out with respect
44
to the mast axis of rotation. This configuration was in-stalled on the helicopter and was used with the Rockwell sightinstallation. Flight test vibration data, as discussed in thenext section of this report, showed that one-per-rev vibra-tions were reduced signifigantly.
VIBRATION SURVEY
The Rockwell MMS, which weighed 73 pounds, was flight testedduring December 1979. The main rotor was balanced usingconventional methods; as expected, one-per-rev vibrations weregreatly improved with the properly aligned MMS nonrotatingplatform hardware.
Quantitative vibration data of the Rockwell sight was measuredusing Rockwell instrumentation, and helicopter ride qualitywas measured using two tri-axis accelerometers installed underthe pilot's and copilot's seats. Harmonic analysis of thisdata is presented in Appendix A of this report.
A summary of the vibration data for the Rockwell sight and thepilot's seat is shown in Figures 17 and 18. Translationalresponse of the Rockwell sight was measured on the trunnionmount which is located inside the sight assembly at the ap-proximate cg of the sight. The Rockwell sight fore/aft aver-age oscillatory response is somewhat higher than was experi-enced with the dummy MMS. Rotational response of the sightwas obtained from the line-of-sight angular accelerometer, andsight vibration data was collected only with the sight in theforward-looking position, so that only roll response data wasobtained. Pilot's seat one-per-rev vibration levels are muchreduced, being qualitatively the same as those of the baselineOH-58C helicopter. Pilot's seat two-per-rev vibration levelsare comparable to those experienced with the dummy MMS, quali-tatively still somewhat higher than on the baseline OH-58Chelicopter. This is probably due to the stiffer main rotorpylon mount which was retained to reduce pylon gust responsesensitivity.
HANDLING QUALITIES
Handling qualities with the Rockwell sight installed werechecked qualitatively by the pilot and compared with dummysight test results. No instrumentation for quantitativeevaluation was installed with the Rockwell sight.
This evaluation showed no significant difference in handlingqualities between the dummy sight and the Rockwell sight in-stallations. The only noticeable difference was a slightsteady roll oscillation above 65 KIAS at a frequency of one totwo Hertz with one to two degrees amplitude. This was par-tially due to the change in drag caused by the flat lens ofthe sight turning back and forth. This effect was reducedafter the sight yawing oscillation was fixed by eliminating
45
Note: Rotational acceleration data taken at 0-625 HZ f£reuencyrange. Average rotational acceleration in 0-30 Hz rangethen calculated by straight addition of the 1/rev,2/rev, and 4/rev acceleration harmonic*.
"I
Rockwell MMS rotational acceleration limit30-(28.3 rad/sec 2 peak, 20 rad/sec 2 rms for 5-30 Hz)
0
.4
20"
10
U'U
0-44J
0
0 20 40 60 80 100 120Calibrated airspeed, kn
8.0-
Rockwell MMS translational acceleration limit-, ( 6.0- (5.66 g's peak, 4.0 g's rms for 5-30 Hz)
0 4.0-
- ,e-Fore/Aft
4,-O 2.0 _Lateral0 N Vertical
U) I:
0 20 40 6 80 100 120Calibrated airspeed, kn
Figure 17. Rockwell MMS average vibration versus levelflight airspeed.- vibration survey.
46
~h~i~bI
0.05,
!" 0.04,
o 0.03.
'U4 0.02
0.01 For/AfVertical
$4 Lateral
00 20 40 60 80 100 120
Calibrated airspeed, kn
0.20-
>1MIL-H-8051A Para 3.7.1(b)
.L 0Vertical
041-)
0.10
W Lateialu
4) 0.05.
Fore/Aft00 20 40 60 80 100 120
Calibrated airspeed, kn
Figure 18. Pilot's seat vibration versus level flight
airspeed - Rockwell MMS vibration survey.
47
the looseness in the standpipe splines (discussed in thefollowing section).
Subsequent testing of the SCAS on other OH-58C helicoptersindicates that this oscillation can be further reduced bychanges in the SCAS yaw channel. These changes will be incor-porated in the MMS helicopter.
PRELIMINARY SIGHT EVALUATION
The Rockwell sight was operated first with the helicopter onthe ground, using an external electrical power source and withthe helicopter rotor not turning. Following this check thesight was operated with the helicopter on the ground, usinghelicopter electrical power and the rotor turning at normaloperating rpm. A 4-foot by 4-foot high resolution targetlocated 500 meters away was used to check the vertical andhorizontal resolution of the system.
Results of these tests indicated satisfactory operation of theRockwell system; however, it was found that the sight oscil-lated or "hunted" back and forth approximately 7 degreespeak-to-peak at approximately 5 Hertz. This sight yawingoscillation did not produce a noticeable effect on the TVpicture, but it was considered unacceptable for the followingreasons:
1. It produced stabilization errors in the sight of 10to 30 microradians peak-to-peak which degrade re-cognition performance.
2. It cyclically torqued the standpipe with greaterthan 40 in.-lb impulse loads.
3. It produced excessive wear and heating in the sightservo system.
4. It looked bad.
The oscillation was caused by the sight azimuth servo systemreacting to the looseness of the standpipe splines. A tem-porary fix was incorporated which eliminated the oscillation.The splines at the lower end of the standpipe were bondedtogether and Teflon tape was added to the spline at the upperend. These steps eliminated the cause of the problem bygreatly reducing the free play in the splines. A system ofspring loading the splines appears to be the ideal way ofovercoming this problem in future designs.
ROCKWELL FLIGHT TEST
In order to evaluate MMS performance, recognition and detec-tion target boards (see Figure 19) were fabricated and in-stalled side by side on 8-foot-high supports as shown in
48
Figure 20. Targets were designated A, B, C, D from left toright. The stripes on the targets were painted white andgray, with a contrast ratio of 20 percent. The targets facedthe east to provide front-lighting in the morning and back-lighting in the afternoon. Range to the targets was markedoff in 500-meter increments by white X's and numbers paintedon the road running perpendicular to the targets, beginning3000 meters from the targets.
Tests were conducted with the helicopter at low altitude (100feet to 200 feet) coming to a hover over the "X"I marks every500 meters. Tests were also conducted with the helicopterflying toward the targets at approximately 80 knots. Sightperformance is shown in Table 8.
TABLE 8. ROCKWELL SIGHT PERFORMANCE
Range(Kilometers)
Performance NFOV WFOV
Detect 8-ft x 8-ft Target Boards 15 -
Detect Targets A & B 6 0.5(Resolve 2 Line Pairs)
Recognize Targets C & D 3 0.3(Resolve 6 Line Pairs)
Conditions
Weather: Clear, Unlimited Visibility
Target: Front Lighted
Helicopter: Hover
NOTE:
NFOV = Narrow Field of View
WFOV = Wide Field of View
Back-lighting the targets (afternoon flights) degraded theresolution approximately 500 meters. Flying toward the tar-gets at closing speeds up to 80 knots also degraded resolutionby approximately 500 meters.
In addition to the tests run with the target boards, the sightwas used to track moving trucks and automobiles on a nearbyfreeway. Only a qualitative evaluation was made of the track-ing system, with good results on vehicles moving somewhat
49
~s8 FT-.
8 F~ff
DETECTION BOARDS RECOGNITION BOARDS
Note: Recognition and detectionboards were painted togive 20% contrast betweendark and light panels
Figure 19. Recognition and detection boards.
Figure 20. Target boards installed for Rockwell sightevaluation.
50
toward or away from the line of sight of the camera. The MMSoperator had trouble locking onto close-in vehicles travelingat right angles to the line of sight; however, once the MMSlocked onto a vehicle, it was able to track it through 90degrees to the line of sight.
The only problem noted with the Rockwell sight was its inabil-ity to rotate forward from a 90-degree or aft position athelicopter speeds above 70 knots. This anomaly was apparentlydue to the aerodynamic forces acting on the flat plate area ofthe sight lens and laser cooler exceeding the slew torquecapability of the outer azimuth gimbal.
Video tapes made during target board and tracking test-runsshowed good resolution and contrast. The overall performanceof the Rockwell MMS TV system on the OH-58C was very satisfac-tory. The laser was fired at BHT only during EMC tests. Thelens cover was kept in place during the laser firings.
EMC TESTS
Electromagnetic compatibility (EMC) tests were conducted onthe bailed OH-58C with the Rockwell MMS and BHT SCAS in-stalled. The results of these tests are presented in Refer-ence 13.
The OH-58C avionics and electrical system were first examinedas a source of electromagnetic interference (EMI) with the MMSTV and SCAS as victims of this interference. The tests wererepeated by operating the MMS TV and then the SCAS and check-ing the other two systems for interference.
The laser was fired with the protective cover over the lens asa noise source while checking the other systems as interfer-ence victims. Some slight interference from the laser coolerblower was picked up by the FM receivers when operated on ex-ternal power.
Results of all tests showed no significant electromagneticinterferences between the basic OH-58C systems, the MMS, andthe SCAS while using the helicopter electrical system as thepower source.
"3Wright, C., "Electromagnetic Compatibility Test Report ofRockwell Mast Mounted Sight and SAS on OH-58C Helicopter,"S/N 40435(69-16214), Bell Helicopter Textron Report Number206-099-851, Revision A, January 1980.
51
WEIGHT AND BALANCE
Weight and balance of the OH-58C with the mast mounted sightare presented in Reference 14 for both the dummy sight instal-lation and for the Rockwell sight installation. Tables 9, 10,and 11 and Figure 21 present the weight and balance for thehelicopter with the Rockwell system (as delivered to theArmy).
14 Pressley, J. D., "Estimated Weight and Balance Report forPrototype OH-58C Aircraft with Mast-Mounted Sight," BellHelicopter Textron Report Number 206-099-352, Revision B,November 1979.
52
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56
4.) %D 0 000 LO's 0 0 r-4 0 000 0 i .9: 0% 0 0 m)cN' %1 cq % LA) N1 0 0 cr 0) cr) C')
.4 4) M1 %Dt Dce 0 14 LA 0kD 0 r N %.0 OD4 a m CDOCOCO r-40 0 0 ' ON .0 '.0 CO OI r- t -
4) 0 t O -N 0 1O 1 1 + N->~ E 4 -4 -4 -4
z 4-) Nq 0000000 0 00 Nq 0: 000)C 0 LA LA)o Nr y 0 r, O O LAO k0 0 LA '.0 OON LA) 00 N1
a a) ON0' OODO N N N4C 1 1 0 Nq OD O 0 r-i %.E-4 O '0 53 % lC) 0 rICOD LA O r N ' LA CY0 er4 LA) C')
- 0 ULA r-4 N C') 'c' M' 0 a 4 r~-4N1q I r-4 CNcqI cv") C'Y I + '
C-)
u 0' -4I OL q lcoIt r n r )CLAI t0D0 000 CO -4 0t0 0 0 Nor-
s-I I r 0 0-4 04 N- LA i LA N
4-- 0AA'Cd 0L cr C -d t. 0 '0 00 '0 W) V
-4 0 -44-- - 4 -4 -- 1-4
0
000LA 0 0 000 0 LA L
0i 4- C) 0I+
I-'I
4) -4
4- - - 04-t k )0 0 4 l4 0 r-
r4~~~~.. ONm p NO m q-
U) r.r 0 -) 4
0t 4-) 0 . 0 )4 J4
0 .4) m, 4) 4.H .- ) - 4 0 )4 o o'U q i >r o 43t% -
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43~~")~ ~43~57
BASELINE OH-58C
3200-
3000
2800 2
-I
2600--4
U)m0 DEFINITION OF POINTS2400
1. Mission Gross Weight2. Most Forward C.G.3. Most Aft C.G.
2200
2000-
104.0 106.0 108.0 110.0 112.0 114.0
Center of gravity - fuselage station
(in.)
Figure 21. OH-58C with MMS gross weight versuscenter of gravity plot.
58
CONCLUS IONS
This program has demonstrated that a mast mounted sight weigh-ing 73 pounds can be successfully installed and operated 2feet above the rotor on an OH-58C helicopter. one of the morechallenging tasks in this program was to meet the Rockwellsight translational and rotational vibration limits whileminimizing increases in helicopter component dynamic loading.An isolation system (focal mount) was required between thesight and the rotor hub to keep the sight vibration levelswithin acceptable limits and to prevent large increases inblade loads. Helicopter speed in level flight using maximumpower was reduced from 99 to 96 KCAS due to the drag of theIMS. V ne was limited to 100 KCAS and maximum maneuver load
factor was limited to 1.4g to preclude excessive vibration andto prevent the MS focal mount from hitting its stops. Thetranslational vibrations in level flight did not exceed 50percent of the limit values, and roll rotational vibrationsapproached the limit in calm air at the higher airspeeds. Ingeneral, component loading with the focal mounted MS1 waslower than that of the baseline OH-58C.
The criterion limiting the weight and/or height of the focalmounted MS1 was the crash load factor of the existing mainrotor mast, transmission, pylon support and other criticalhelicopter structure. Redesign of these components to accom-modate a M'1S would permit a considerable increase in allowableweight/height of future mast mounted sights.
59
REFERENCES
1. Rule, J. A., et al, "OH-58C Mast-Mounted Visionics Analy-sis," Bell Helicopter Textron Report Number 699-099-060,Fort Worth, Texas, July 1977.
2. Rule, J. A., et al, "AH-IS Mast-Mounted TOW Sight Analy-sis," Bell Helicopter Textron Report Number 699-099-088,Fort Worth, Texas, July 1978.
3. Anderson, H., and Andrews, J., "Dynamic Environment Anal-ysis of OH-58C Helicopter with Mast Mounted Sight In-stalled," Volumes 1 and 2, Bell Helicopter Textron ReportNumber 206-099-353, September 1978.
4. Anderson, H., and Andrews, J., "Dynamic Environment Anal-ysis of OH-58C with Focal Mounted Sight Installed," BellHelicopter Textron Report Number 206-099-812, November1978.
5. Freeman, F., Hunt, G., Messick, J., Midgley, R., Rost,F., Roessler, D., "Structural Analysis of Mast MountedSight on the OH-58C Helicopter," Bell Helicopter TextronReport Number 206-099-354, Revision A, November 1978.
6. Andrews, J., and Hanson, H., "Ground Vibration Test ofthe OH-58C with Mast Mounted Sight," Part I - Test Plan,Part II - Test Results, Bell Helicopter Textron ReportNumber 206-099-808, Revision C, March 1980.
7. Andrews, J., Hanson, H., Harr, H., Norvell, H., Popelka,D., Spence, W., "Flight Load and Vibration Survey ofOH-58C with Mast Mounted Visionics," Part I - Test Plan,Part II - Test Results, Bell Helicopter Textron ReportNumber 206-099-809, Revision B, March 1980.
8. Cassady, B., and Norvell, J., "Fatigue Life Substantia-tion for the Dynamic Components of the Model 206B-1Helicopter and the Model OH-58C Helicopter," Bell Heli-copter Textron Report Number 206-099-148, February 1973.
9. Andrews, J., and Hanson, H., "Torsional Stability Surveyof the OH-58C with Mast Mounted Sight," Part I - TestPlan, Part II - Test Results, Bell Helicopter TextronReport Number 206-099-807, Revision B, March 1980.
60
Lar
10. McEntire, K., "Engine/Airframe Compatibility Demonstra-tion for OH-58C Helicopter," Bell Helicopter TextronReport Number 206-099-748, Revision A, November 1978.
11. Gastinger, D., Hardesty, D., Harr, H., Hester, M., "Han-dling Qualities for the Model OH-58C Helicopter with MastMounted Visionics," Part I - Test Plan, Part II - TestResults, Bell Helicopter Textron Report Number 206-099-423, Revision C, February 1980.
12. Bishop, J., et al, "Preliminary Airworthiness Evaluation,OH-58C Helicopter Configured with a Mast Mounted Sight,"USAAEFA Project Number 7809, to be published 1980.
13. Wright, C., "Electromagnetic Compatibility Test Report ofRockwell Mast Mounted Sight and SAS on OH-58C Helicopter,S/N 40435(69-16214)," Bell Helicopter Textron Report Num-ber 206-099-851, Revision A, January 1980.
14. Pressley, J., "Estimated Weight and Balance Report forPrototype OH-58C Aircraft with Mast Mounted Sight," BellHelicopter Textron Report Number 206-099-352, Revision B,November 1979.
61
APPENDIX A
VIBRATION DATA WITH ROCKWELL SIGHT INSTALLED
LATERAL..n I, WA_______H I r ~ j~ ~]DATC~1T7S.,. LAERAL I r -
'I I1 1 T tICATT. L...... w
35, Rem-
-7--r-
- - - 4 0 0 A1
-0.50T I
A 23d. 20 -
171
0.30 versus airspeed
. t62
BL LAN~TE IIhA PLAL-T 16
71WIND TSP,
4. .-. '.
-1;20
4 o JA.......0 .
*1 .7
;7 V --- .-- ---
...~ .. . Z7
.70 4. ..... .... .
Figure~~~~~~ A-2 Rokelmstuno c)vbaina /2/e vesu 2<r<41177I 63
-- ~------. --4. .IMODEL.- 6H-5SCt
A LATERAL,..-IV~V T;: Ae I-TT
.......... 354N~ RKT em~
1.46-
I-~~7 -10ti 1
7--
0.80
[~ --0.50-
1-1
0 I0 Iqo It
CA L I t 3 tK
Fiur A-3 Rokel62trnin(g ibaina4/e vessaised
r 064
_4 ~ - ... ... T
ALATERAL_ 1 pT- 177
I- ,11 i~ -I-- j-
_
It I
0.0----
I- 0.50-- - - -- 1- - .
A 0
6.0 -7-I
-0.B 0 0 4 o 0 IZO
.. 0 .. .. ..
FigueA4 Rokwl trnio (cg virto at6/re vesu Lisped
0130.. 65
400-~~~O I Ij j 54-
'46.01 - -4 -
L~ 40 0 ' I II
_T'
-PC- - - -I* .- - -~1 I 7-I I j
40-
I j j
0 . ... 2 i o . 10 , 2C_~ ~~ A I _P!TF7
Fiur A-5. Rokwl MM Ieo -i rl)vbainaM/ lOe vesu airspeed.
~ 66
T DATEK60 ~ N i ~ib K6TS V ,6
t 10W
440- --- ---------,I _
I -. 2 IR
- -- I -4 OT -3 ~ -------- j - .-
Fgr-6 Rokwl MM lieo-ih (olibraton aM/R0 2/e Fesu aised
L I __ __67
..~ . .1 7
___ M QDEL ; 0 1i- 5%f
-~ -- .......JIPi±JE±1-'I .7!1- ,W i ND-S '6
7~.. II ______
:1 T
J-
I I
LAI__
I ' r0-4.0 -i
Lii~ ~ .. ...I ...-..
Figue A7. Rckwll ms lne-o-siht (oll vibatin aM/R4/evvesusaisped
4 I68
- ~ 4 rSIN 40435
IF Ir ____-
.~~K!T 1P 56t___ _______V Rp
-T -T -
0. so -M 12i0 71".Lk~5 :p NT ,A . ...
Fiur A-8 Rokwl MM lieo-i rl)vbainaM/R 6rev ersu airpeed
r 69
AT EP, A, L ~WIND K- -3C0 VF rIhC FL a. 1
0.400 -
0.0
II0 DO te 0-0 3f
Figur A-9 RokelMStuno c)vbaina /
0
.~.. .~ SIN 40455
* .LE~qrND Ft-T II(-A
.. 0 LoNGmTI2.UfA&L - ... .I-yA LATERAL
0 EVPTICkL ...Nfk 354 lfy
-. -- -. 6,400 -- - - .
-~~ -.0 --- --------~ ~
/Rev .0i
W A
* -0 0
-6.000
* ~0,300 . . .
6/REV 20.200
. . 0
AA00
0 90 IO 270 360Vk*N'TVE JIN P7.ItAuTH rRG
Figure A-10. Rockwell MMS trunnion (cg) vibration at M/R4/rev and 6/rev in IGE hover.
71
N
41
-' .
o~~ a ,
1 14
cc Ad~ i
727
71 S/N 40435
LEGENDDATE Q17-79
T-9 PILOT SEAT - -,- -WIN 6 KTs- 36o'-
. O-PILOT SEAT o 'tN 354 rpm
- -T -++ol=. . .... +-:-.4- .. .-- '--- --- -' .. - -' - f -
.01f----t--
I .I
7 t
-- -- ------ --....... + :
-4-4
I
E1JL 4IRPE
Figure• I A C i a v
7*2- . I - -- r " "- , = - -I
A -. i.- l ' .t , 1 J
airspeed.
F 73
_____ 'I' . V.S/N :40435
S , .--- DAT- : IEGENDT2- --79I-* g iPLorsA . . I :.. : 6WIN KTS 0-60'"0 Po.-PI LOT SEAT ... ...... .... ...... 3. a-54 m
I 7
I : i ..j|:..I / | I 0'! 1:.
IM1
A 1 7 7KT i~
.- :I I i.- - t
r" ./ i • .jz ! I z ,z ' .
-... +;7h....1 :
I... I--- - -Q -
a-- -- - 4 .. ---- - -- --+ t :1!
A-: 1-L LL
Figure A-13. Crew seat vibration at M/R 2/rev versusairspeed.
74
I i.-I-i/ ...4----- -- + :- ..L ..... ' ..... l-- l.-i.i.--l.. i--.-:---. j--
'[L_ J1-6.I M. . .... .. . ] 1 -,: , 7
i-i OI .seI Zi NO_ .T,560"___
. O -PILOT SEAT t FO ,.. 354 rbm
----- -. - -----.. . . . . . . .,.
,- I .-I. I ... T-.
,.,I : . i ! I I I zt |4 . ,. [ : t .
Lot~
22.-
A . ... .... ,.. . --, - ...1- .. -- . ..t- --- ------ -----
I: 4 8 : i _ ....
, , I I I" it
.i-- -- ' t . - ;- ---,-- : I I _~ _ "• . I IIi -A
+ L 1-.: ........ ... L-' - - - ' '' , ± ' --. ... - ;. .- -_.4.ir. A C sa v
...- --4----0 3..0- :---- - .. . - I-- - .---, --- - .
ai r s.pee
Ii'- :! i lLi I E.I i I N.: Ij 5
Figure A-14. Crew seat vibration at M/R 4/rev versusairspeed.
75
T 1 7___ir O __ _ -,s
0 PlO .ET _ _ - - -WIND 9 KTS 5 3 60'L --t-- i-'i - .....x.. .... _ _ _+ _ _ _ ____.__ __I'... ;i I ____ _____-_____
LEGEN, : .. .AT 12 1-Io rWo-PILOT SEAT N. a354m *M
/ I j ! :
t le 4t .
...... ; • i ' " t •i • : - - '- - I.. ... ....1 - .. . .-
0. JJ_
... 2.,l .• : . .: i*i. .: +. . .: .+. I;.... .,:, ..I+I-- ++.! -::--++
-" i
I ..
t o . I
0- T . .I.050 ,- -, ' , . . - - -
_0 __0 1 o io 10
igure. A- C s v ia i a , I __ versus
l: e _ ' t-t I
H L .: 7- 7 7+ -r - . .. - t--P ... .. .. i - - r +
Figure ---. C-:rew sea ,t virtio at M/ 6/rev- versus+
airspeed.
76
! °l + +.... :.I_ I- !-+ I; + t r l-: -1: +-I +-I + ! + + + 'l ... -i ! A
rT
-- MODEL OH 50C-... ,--4.... -+-'--- .~1 _ _ _ __ . --
LEGEND . . DATE 12-17-79
- ,...*-PILOT .SEAZ _WIND.,;- 6 _ KT___ .36_
.1 CO-PILOT SEAT Ni t 354 rDm
" - -- .-o --
-.- .................
I' ,o~ -n- - ,1I-- -- ... -- -- -4-{....!., , - j
*11 4- . - "~
0-000-1 1
4 4-4
------ #0--
- IS 4 360
' .i 0 0; I F 1
- ! ..... -. .. .. T ' , . ' '4-
~MELATOVI
II_ ' j *90 ' 4 "0 30 ' ::i t
- 1 -- , . . : ! . ; I ' I - .
IK TVI WND AIIMWU DE2REE~J
LI , : r, i ,
Figure A-16. Crei seat vibration at M/R 1/rev in IGE hover.
77
:i,•: IZ7VVZIY. :7717.IO N : -, 5Bc "
------- .S/N 40435
.1LEGEND *ATE .12-17-79
I -WN D- 6 I 1. 3. , FO:'PILOT SEAT i 354 r
-A -
-4-. . . ; _ • I . ,
z ti r 1A...
- i- 0- , - .,. - - I 0 . r 7
9"lt IS 2711A7-.7 '- 7 4 .. __....,. I : i i ! i
1 iLE W IND i H QE1 RE!*I I :-'- '--- -.... t ,__-- -__, . , ! N
F ig. A..7 . _ • .a • 1/re i t
- -4 "030 : ' "t 78
,., - - '. - I . I . I
... i . . .L
_- 90 . .. . i .... 1- h-- • ~ f- -- * -n: .- " 1
I .i " i . , I , i I at> ! . i.-
Figure A-i7. Crew seat vibration at M/R 2/rev in IGE hover.
78
- i : : _ . .- - . , _ L __ MODEL.; OH -'581C _
I7V7I1 /'T 40435/
- .. ED . . . .. ... ... DATE a 12-17-79. LO EAZ -. ---- _._-1___WIND 6 KTS I 360',
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