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Theses and Dissertations 1. Thesis and Dissertation Collection, all items 


1996 


Power plant and drive train improvements of 
the NPS Hummingbird remotely piloted helicopter 


Conway, Robert E. 


Monterey, California. Naval Postgraduate School 
http://ndl.handle.net/10945/8837 


This publication is a work of the U.S. Government as defined in Title 17, United 
States Code, Section 101. Copyright protection is not available for this work in the 
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NAVAL POSTGRADUATE SCHOOL 
MONTEREY, CALIFORNIA 


POWER PLANT AND 
DRIVE TRAIN IMPROVEMENTS 
OF THE 
NPS HUMMINGBIRD 
REMOTELY PILOTED HELICOPTER 


by 


Robert E. Conway 


September, 1996 


Thesis Advisor: E. Roberts Wood 





Approved for public release; distribution is unlimited. 


DUDLEY KMOx LIBRARY 


NAVAL POSTGRADUATE SCHOO! 
MONTEREY CA 93943-5101 


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11. AGENCY USE ONLY (Leave blank) — DATE REPORT TYPE AND DATES COVERED 
: September 1996 Master’s Thesis 


TITLE AND SUBTITLE POWER PLANT AND DRIVE TRAIN 5. FUNDING NUMBERS | 
IMPROVEMENTS OF THE NPS HUMMINGBIRD REMOTELY | 
PILOTED HELICOPTER | 


16. AUTHOR(S) Conway, Robert E. 


7. PERFORMING ORGANIZATION NAME(S) AND ADDRESSES) 
Naval Postgraduate School 
Monterey CA 93943-5000 


| 
9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING/MONITORING ! 
AGENCY REPORT NUMBER : 


11. SUPPLEMENTARY NOTES The views expressed in this thesis are those of the author and do not reflect the 
official policy or position of the Department of Defense or the U.S. Government. 


12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE 
Approved for public release; distribution is unlimited. 
13. ABSTRACT (maximum 200 words) 
Originally designed as a target drone for the U.S. Army, the NPS Hummingbird has undergone several 
modifications to convert it into a reliable research platform. The 165 pound remotely piloted helicopter (RPH) 
| is powered by a Weslake Aeromarine Engines Limited (WAEL) 342 two stroke, twin cylinder, 25 hp, gasoline 
engine. An engine failure due to cylinder overheating halted research efforts until investigation as to the cause 
and subsequent corrections could be made. Costing approximately $3000 per engine, another failure is 
unacceptable. The tasks undertaken in this thesis were to investigate the cause of the overheat failure and 
improve the engine cooling system. Cooling system corrections required total redesigns of the engine cooling 
| and engine start systems. Additionally, research of the RPH’s history revealed a need for a torsional shock 
absorber to be incorporated in the drive train to increase component life. The changes made to Hummingbird | 
provide a decrease in empty weight, minimal center of gravity change and, most importantly, an increase in user | 
safety furnishing the Department of Aeronautics and Astronautics with a dependable vehicle for rotary wing 


15. | 
NUMBER OF PAGES 

® | 
16. 
PRICE CODE | 


| 























SUBJECT TERMS: Helicopter, Radio-Controlled, Power Plant, Drive Train, Unmanned 
Aerial Vehicle 




























19. ’ 
SECURITY CLASSIFICATION | LIMITATION OF 
TION OF REPORT OF THIS PAGE OF ABSTRACT ABSTRACT 

Unclassified Unclassified Unclassified 


NSN 7540-01 -280-5500 Standard Form 298 (Rev. 2-89) 
Prescribed by ANSI Std. 239-18 298-102 


18. 
SECURITY CLASSIFICATION 


‘17. 
SECURITY CLASSIFICA- 








Approved for public release; distribution is unlimited. 


POWER PLANT AND DRIVE TRAIN IMPROVEMENTS 
OF THE 
NPS HUMMINGBIRD REMOTELY PILOTED HELICOPTER 


Robert E. Conway 
Lieutenant Commander, United States Navy 
B.S., United States Naval Academy, 1985 


Submitted in partial fulfillment 
of the requirements for the degree of 


MASTER OF SCIENCE IN AERONAUTICAL ENGINEERING 
from the 


NAVAL POSTGRADUATE SCHOOL 
September 1996 





DUDLEY KN 
NAVAL prve OX LIBRARY 


iGRADUATE 
MONTEREY ¢ CA 93943. 7h 


ABSTRACT 


Onginally designed as a target drone for the U.S. Army, the NPS Hummingbird 
has undergone several modifications to convert it into a reliable research platform. The 
165 pound remotely piloted helicopter (RPH) is powered by a Westlake Aeromarine 
Engines Limited (WAEL) 342 two stroke, twin cylinder, 25 hp, gasoline engine. An 
engine failure due to cylinder overheating halted research efforts until investigation as 
to the cause and subsequent corrections could be made. Costing approximately $3000 
per engine, another failure is unacceptable. The tasks undertaken in this thesis were to 
investigate the cause of the overheat failure and improve the engine cooling system. 
Cooling system corrections required total redesigns of the engine cooling and engine 
start systems. Additionally, research of the RPH’s history revealed a need for a 
torsional shock absorber to be incorporated in the drive train to increase component 
life. The changes made to Hummingbird provide a decrease in empty weight, minimal 
center of gravity change and, most importantly, an increase in user safety furnishing the 
Department of Aeronautics and Astronautics with a dependable vehicle for rotary wing 


research. 





TABLE OF CONTENTS 


ho LIN SU DLLCGS ye nn oe 1 
Il. BACKGROUND INVESTIGATION  .......... ccc cece ccc c cscs cccccces 3 
Il. BASIS FOR MODIFICATIONS ..........-cccccccccccccccccccccccces 5 
A. STARTER ..... Baa ca ssa! alaleeioletetstaia!'c's states save steers co etenevonereroerene 5 

1. Original Configuration ..........ccc ccc cccccccccccccees 5 

72 TATLEIMEFCMCIOMEIES 500s cc cc cscs cccs sc ecsceeewens oe oe 

B. ENGINE COOLING SYSTEM .......... ccc ccc cece cece cence 7 

1. Original Configuration .............ccccccccccccccceces 7 

z Cooling System Deficiencies ..........cccccsssccccscces 8 

C MP eanRy Im PLURRO AMIN o244 "s-axsisie-s:s ovaxerexenessnavexeie « 6 sininpe » 0 sleleiarens 6 a eeiereie s 13 

i. Original Configuration ............ccccccccceccccccces 13 

2: Drive Tram Deficieii€tes. ..........cccccsscccccccesene 14 

IV. ENGINE BREAK-IN AND TESTING ....... 0... cece ccc cece csc ceneee 17 
A. MINGHINE, PES TING SET-UP 2.2... ccs ccwccscccscvccsecsvces 17 

1. imneennie WSs Gate 5c. sre aie o's 5 0 aisle «ch ete eerie si oe uae 17 

3 Hand-held Engine Starter ............ ccc cccccccccccces 19 

B. FINGINGE TEST PROCEDURES . . . . ... «5 sicisicssisuataleia eleieya eee oe cues 21 


Vi 


C. ENGINE TEST RESUEGSIH: 9. 826.500. cece c cece sccecess 22 

V. BESIGN VIG IIICATIONS |. . oo 050000005 50 6c aiuieleieieisieiieisiers|eistelelee rere 27 
A. OI eer nC 27 

1. Design Considerations ...........ccccccccsccccsccccces 27 

2; Starter Design Implementation ........ iets a ennpainoueuseenseneee 28 

3. Starter Operation ...........ceeee. ee ee 33 

B. ENGINE COOLING SYSTEM .......... ccc ccc ccc ccc ccccces — «33 

1. Design Considerations. .........cccccccccccccccccccces 33 

he. Cooling System Design Implementation .............. 2. 34 

a. CCV UO TRING io saisincpeisisiaiaieasers.wcigiaielss 4 <igs.« 0 014 34 

(1) Upper Engine Mount. ............0.scccceee 36 

(2) Adapter Installation. ................ ee 36 

b. Component Removal ...........ccccececccccece 33 

C; Coolim® Systt im iscciiein caps epee es seins « 0 o's.00 0 0 0 39 

C. PRGA IML ERENCRIN ofc < (cle to ele aja /aanleselele'='« cists se ais leisieieisic's's oe «s/s sie's ¢ 41 

1. Design Comsideratioms. « ... 6 /n:sjojn:e:«:0)0isisiiaisia)aieieiaiaisieieieie <0,010Ks 41 

2. Shock Absorber Design .........cccccccccccccccccccces 41 

IE ec ER MO NIC MIDEUSSMULINGS ~ 5.0 5 6 cai 5 6 0:0 's sicpauessintanein. « esse Misialeiegicicsaieces © + wicisia's « 45 
VH. CONCLUSIONS AND RECOMMENDATIONS .........c-ccccccccccs 47 


Vill 


RECOMMENDATIONS ... 2... ccc ccc ccc cccccccsccccccccecs 49 
1. Lelio Fis CN rod ae ee. re ant eae 49 
2. AVL aC CO I oso sioaicicicccccccccccccweties 49 


3. Complete Implementation of Torsional Shock Absorber ...50 


4. Bower Plantes. ...2cccccccccccccccs CT me 50 
5. Configure Hummingbird for Forward Flight ............ 50 
6. Main Rotor Head Design .............. oe eee $1 
7 NOTAR?® Research .......... WO Ss «See, OS eee Oat 51 
Ai EINIDIXCAS TISTIOR SUPPLIERS 2.1... ccccccccccccnccccscccscssecen 53 
APPENDIX R: POINTS OF CONTACT 3.2... cccccccccccccscccevccccsccs 55 


APPENDIX C: PRESTOLITE MBJ-4407 PERFORMANCE CHART AND 


ELECTRICAL SCHEMATICS ......... 2. cece ccc ccc cece 57 


APPENDIX E: OPERATORS HANDBOOK FOR WAE 342 LIMITED ENGINE 


SEES 21 OOD ie ce aia ee wos a ee 65 


LIST OF REFERENCES ...... 


INITIAL DISTRIBUTION LIST 


@®e@eeeeeseeeeeeepeeeeeeeeeeeeeeoeneeoeeoeeeesaeoaweneaeaeeeee 8 


@ee@eeeee¢ceceseseeeeeeeoweeneaweaeeeaeaseoeeeoeeesneoaneese*e7eeoeeee 6 @ 


LIST OF FIGURES 


Figure 1. Original Starting System Configuration .............cccccccccccces 6 
Figure 2. Layout of Engine Cooling Components ..............cccccccssccccs 8 
Figure 3. Existing Engine Cooling Cowling ............cccccccscccccccccces 10 
Figure 4. Exhaust Manifold Position ..........cccccccccsecccccccccccccees 11 
Figure 5. Right Side View of Hummingbird Without Ventilation Port .......... 12 
Figure 6. Main Transmission ...........ccceee. ee a Batetare sanetetetets 14 
Figure 7. Engine Test Apparatus ...........ccceeeees peer e ee ee cece sc eme 
Figure 8. WAEL 342 in the Test Configuration ........ Se 19 
Figure 9. Hand-held Starter ..............000. ooo. Ree 20 
Figure 10. CHT Comparison for Large and Small Cylinder Heads. ........... 25 
Figure 11. Top View of Starter. ..... eee ee ee 28 
Figure 12. Bottom View of Starter. ........ccccccccccccccecccccccccccccces 29 
Figure 13. Starter Mounted to Landing Gear. ...........ccccccccccccccccecs 31 
Figure 14. Starter Coupled to Engine. ............0cscccccccecccccccuccees 32 
Figure 15. Size Comparison of Cylinder Heads. .............0-0-cccccccces 35 
Figure 16. Upper Engine Mount. ........ 2. ccccccccccccccccccccccccccccess 37 
Brea ES ACER TOON) siace « « oicunse.+ © ocgeie's' 6 6 Sxagagepigeemumueugys’s << <6 cus © meemagels oleae 38 
Figure 18. Cooling Fan and Drive Configuration. ...............ccccccccceee 40 
Figure 19. Intermediate Shaft of the Main Transmission. ................... 42 
Figure 20. Layout of Shock Absorber Components. ...............ecceeceees 44 


ACKNOWLEDGMENTS 


I wish to acknowledge several key individuals without whose help this project would 
not have been possible. First and foremost I would like to thank God for the strength and 
perseverance to get through these last nine months. I would also like to especially thank the 
Aerospace Engineering Technician Mr. Don Meeks. His knowledge and expertise in UAV’s 
was invaluable to me not having any background at all in model aviation. His dedication 
shown by working after hours until my work was completed was uplifting. Also deserving 
my gratitude is Dr. Wood. After all the setbacks and aggravations he was always there to 
help me gather myself back together, sort out the problem and move on. I would also like 
to thank my family for providing me with encouragement and understanding during the 
trying times of my thesis research. Finally, a general thank you to all those who I pestered 


as I used them as sounding boards for my ideas and theories. 


Xi 


I. INTRODUCTION 


Recent achievements of the Naval Postgraduate School’s Aeronautics and 
Astronautics Department in helicopter research have emphasized the importance of the work 
done here. The outstanding performance of NPS design teams in the American Helicopter 
Society’s annual helicopter design competition , valuable student and staff research and 
exposure in local media and professional publications have positioned the Aeronautics and 
Astronautics Department as a leader in helicopter research. Among the many resources of 
the department is the NPS Hummingbird, part of the remotely piloted helicopter (RPH) 
research program. The Hummingbird is a unique rotary wing aircraft that possesses 
characteristics well suited for scale model research in Higher Harmonic Control (HHC), 
NOTAR?® , and other rotary wing fields. To date there have been at least three inquiries 
from outside sources for future experimentation on the NPS Hummingbird. In order to 
comply with these and other requests, several design deficiencies have been corrected to 
bring the aircraft from its original configuration as a target drone to its current status as a 
reliable rotary wing test platform. 

Thus far, necessary design modifications to the airframe, main rotor and transmission 
have been completed and implemented in order to have a reliable RPH suitable for quality 
research. Due to an overheat failure of one of the Hummingbird’s two inventory Weslake 
Aeromarine Engines Limited (WAEL) 342 engines, ground and flight testing was halted 
until an investigation as to the cause of the overheat and subsequent corrections could be 


made. The WAEL 342 engine is a 342 cc, two-stroke, simultaneously firing, twin cylinder 


gasoline engine produced by Target Technology Ltd. in the United Kingdom. It possesses 
a maximum power rating of 25 hp at a rated speed of 7000 rpm and a maximum torque of 
24 ft-lb at 4000 rpm. It is an ultra-lightweight power plant designed, developed and 
manufactured specifically for remotely piloted vehicles (RPV) and unmanned aerial vehicle 
(UAV) installations. The scope of the following research is to investigate current power 
plant deficiencies and to provide adequate solutions for effective engine cooling and drive 
train reliability in order to avoid future costly delays in RPH research. 

Modification of the engine cooling system included increasing engine cylinder heat 
dissipation and improving interior fuselage ventilation. To facilitate the cooling system 
improvement a redesign of the engine starting system was implemented which allowed for 
a significant increase in payload capability and a decrease in gross weight while, most 
importantly, increasing user safety. A drive train modification consisting of the design of 
a torsional shock absorber was also required to prolong the life of the drive train and main 
rotor components by protecting it from observed engine torque impulses. The ultimate goal 
of this study was to modify the current power plant and drive train to provide sufficient 
power and man airframe dependability and safety while keeping gross weight changes, 


center of gravity shifts and modification costs to a minimum. 


il. BACKGROUND INVESTIGATION 


In order to effectively trouble shoot the engine cooling problems, it was first 
necessary to obtain information about the WAEL 342 engine. There was no supporting 
documentation except an engine operators manual which was included with the RPH and 
spare parts from Mr. John Gorham, the original designer. The engine operator’s manual had 
a company name, Weslake Aeromarine Engines Ltd. in the United Kingdom, but no address 
or other points of contact. Investigation began by tracking down the engine listing in the 
1980-1981, 1981-1982 and 1982-1983 editions of Janes’ All the World’s Aircraft. Weslake 
Aeromarine was the company that buult the engine as of that year and a telephone call was 
put through to find out more, current information. It was learned that Weslake was bought 
out and included as subdivision of the company Normalair-Garrett Ltd. who had sold the 
manufacturing rights of the WAEL 342 to a company named Target Technology Ltd., also 
in Great Britain. Information concerning the engine’s performance, cost and support was 
requested from this company. and received via facsimile. 

The engine documentation stated that the WAEL 342 engine was designed for 
external use only m air streams of approximately 150 kph or 93 mph. This definitely meant 
that some sort of cooling system designed specifically for the Hummingbird’s internal use 
was required. The fax also contained information on engine performance and a larger 
cylinder head that was used for improved cylinder cooling purposes. Included price 


information made it absolutely clear that purchasing a replacement engine was to be a last 


resort. A thirty day price quote on 25 April 1996 put the WAEL 342 at £1855.85 or 
$2969.36 per unit for a quantity of one to nine engines. 

An American affiliate of Target Technology Ltd. was also listed in the fax. 
Southwest Aerospace in Tustin Ca. was contacted to find out more information about the 
WAEL 342. A Mr. Ian Matyear was able to provide data on purchasing the WAEL 342 
engine and its components. He also provided another source of information, Mr. Ken 
Beckman, who had vast experience with similar size RPH’s. Mr. Beckman proved to be an 
invaluable source of information as he was quite familiar with the Hinmingbird’s original 
design. During the RPH’s initial development as a target drone for the U. S. Army, Mr. 
Beckman reported on the status of this project to Boeing Aircraft Company, the primary 
contractor, as to the progress of the subcontractor, Gorham Model Products. He mentioned 
that the cooling system installed was an after thought as engines before had failed due to 
overheating and also described many of the other deficiencies as they had existed prior to 
NPS student’s modifications. He also mentioned that there existed “wild” torque 
fluctuations in the engine and that there was a possibility of main rotor and drive train 
damage and, most importantly, a potential safety hazard. Reports of engine runaway and 
main rotor separation due to excessive shock and vibrations were among his so told cautions. 
He suggested that some sort of torsional shock device be installed to remedy this situation. 

In all, the above investigation proved to be very necessary and of great benefit in 
providing adequate solutions to the current problems. Mr. Beckman’s information and 
advice from his first hand experience with this RPH was an inestimable value to this project. 


The above sources will be of great help throughout the life of the Hummingbird program. 


li. BASIS FOR MODIFICATIONS 


As previously stated, in order to successfully modify the Hummingbird’s engine 
cooling system it was necessary to include improvements and redesigns of the starting, 
engine cooling and drive-train systems. Investigation of the Hummingbird’s history, both 
prior to and after the Naval Postgraduate School’s acquisition, and close inspection of the 
drive-train layout yielded observation of several design weaknesses. The following is a 


discussion of the deficiencies in the original power plant and drive train configurations. 


A. STARTER 

1. Original Configuration 

The original starter was a permanent attachment to the Hummingbird. The starter 
motor was a 12 volt electrical motor which was hard-mounted to the airframe close to the 
forward engine cylinder. The starter motor shaft was fitted with a 1 inch diameter sprocket 
which drove another 7 inch sprocket through a chain drive providing a 7:1 mechanical 
advantage for the starter motor. A one-way bearing on the 7 inch sprocket provided for 
starting force in the counterclockwise direction and freewheeling in the clockwise direction 
as viewed from the top of the RPH. Two DC power cables ran from positive and negative 
cable receptacles in the left side of the forward fuselage to the starter motor. Figure 1 shows 


this configuration. 





~y 


Figure 1. Original Starting System Configuration 

To start the Hummingbird, external power cables were hooked up to a 12 volt automobile 
battery which provided power to the starter motor. Once achieving a starting rpm of 
approximately 1000 rpm the WAEL 342 cc gasoline engine ran independently. The external 
power cables then had to be physically pulled out of the receptacles from approximately ten 
feet away. 

2. Starter Deficiencies 

The starter motor was found to be under powered. Prior starting attempts required 
two fully charged 12 volt marine batteries connected in series (24 volts total) for the electric 
—_ to provide enough starting torque to the engine. This configuration ran the risk of 


burning out the starter motor and causing an electrical fire on the airframe. 


Removal of the power cables risked entanglement of the cables in the main rotor 
system as the cables were free to whip as they were pulled from the fuselage. The main 
rotor arc extends 5 feet from the rotor hub and sits approximately 3 feet off the ground. 
Entanglement of the cables is an unnecessary risk to the program and a safety hazard. 

The starter motor and its associated hardware weighs approximately 8 pounds or 
approximately five percent of the Hummingbird’s advertised gross weight. Elimination of 
this weight would provide an attractive thirteen percent increase in payload capability or 
compensate for the weight of the modifications. 

Finally, the starter which was mounted very close to the forward engine cylinder and 
the 7 inch sprocket mounted on the lower engine drive shaft restricted cooling air from 
flowing smoothly over the cylinder’s heat fins. A fiberglass cowling that directed airflow 
over the engine had to be modified by cutting away an approximately 3x5 inch section in 
order to accommodate the starter motor installation which reduced the engine-cooling 
system efficiency. 

B. ENGINE COOLING SYSTEM 

1. Original Configuration 

The configuration of the engine-cooling system was as follows. A 6 inch diameter 
vane-axial impeller was mounted to the engine drive shaft which rotated at speeds between 
3000 and 7000 rpm. A crudely manufactured cowling was installed over the engine and 
impeller with the top of the impeller exposed just above the cowling. The cowling was 
constructed of fiberglass and fit closely around the engine. A make-shift diffuser, similar 


to those found in smaller scale model helicopter cooling systems, was molded into the top 


of the cowling to provide an increase in pressure to reduce losses in the system. The air was 
directed out the bottom of the fuselage and into the atmosphere. Figure 2 shows the layout 


of the cooling system components. 





Figure 2. Layout of Engine Cooling Components 


2. Cooling System Deficiencies 

The original design of the Hummingbird’s engine-cooling system was proven 
inadequate by failure of the engine due to overheating. The engine manual states that the 
maximum cylinder head temperature measured at the spark plug gasket is not to exceed 482 


F and maximum exhaust gas temperature 1s not to exceed 1022° F. Upon inspection of the 


failed engine, deep scoring was found in both cylinders. The pistons were locked into the 
cylinders and unable to be removed. Deposits of metal were also found fused to the cylinder 
walls pointing to a massive overtemp of the engine. 
A partial reassembly of the power plant and drive train provided clues to the 
overheating problem. The engine manual specifically states: 
CAUTION: 

THE ENGINE IS AIR COOLED AND MUST NOT 

BE RUN IN STATIC CONDITIONS UNLESS AN 

ADEQUATE COOLING AIRFLOW IS SUPPLIED. 

MAXIMUM CYLINDER HEAD TEMPERATURES 

MUST NOT BE EXCEEDED. 
The “cooling air-flow” was insufficient for the following reasons. First the cooling system 
was designed to draw air in to the center of the engine and then to direct it out along the 
cylinder. The cooling fins were perpendicular to the direction of flow causing the airflow 
to be disrupted as it moved further away from the center of the engme. Sufficient airflow 
to the cylinder head was therefore not available. A significant amount of the fiberglass 
cowling that directed the airflow over the engine had also been trimmed away to 
accommodate the starter and exhaust components. In order to mount the starter an 
approximately 3x5 inch square had to be removed. Other cut-outs for the engine exhaust, 
decompressors (small ports mounted on both cylinder barrels to aid in engine ignition) and 


mounting hardware, shown in Figure 3, had widdled away at the intended design rendering 


this component ineffective. 


- - 7 : Gs * * 
i Rud 





pa 
Ad i* Hg Bis - dpi a z J 4 
oi ie. his! Lilet ot eae 


Figure 3. Existing Engine Cooling Cowling 

One of the main contributors to the cooling problem was the engine exhaust system. 
The exhaust system consisted of an exhaust manifold and a 12 inch long, 1 2 inch diameter 
flexible steel tube. The manifold collected exhaust from both cylinders and provided limited 
noise muffling. The manifold is constructed of stainless steel with an attachment for the 
flexible tube m the rear. The tube ran from the mnntniifoldl around the rear of the engine and 
exited from the bottom of the fuselage. The maximum allowable cylinder head temperature 
is 482 °F and the maximum allowable exhaust gas temperature is 1022 °F. As will be 
discussed later, average observed exhaust gas temperature with proper fuel-air mixture 1s 
600 °F to 700 °F. The manifold and exhaust pipe were radiating 600 °F to 700 °F over 182.7 


square inches inside a mostly enclosed fuselage with virtually little outside air entering the 


10 


fuselage interior during ground runs aside from an insignificant amount of main rotor wash. 


The exhaust manifold was also positioned just 2 inches from the intake of the cooling fan 


as seen in figure 4. 


ie eer 





Figure 4. Exhaust Manifold Position 


The result was an intake of cooling air with an equal or higher temperature than the 
maximum cylinder head temperature. | 

Prior ground tests of the Hummingbird at NPS were conducted with the fiberglass 
front body shell off to allow the maximum heat dissipation and ventilation possible. 
ritiedieieb of RPH’s similar to the Hianmingbird show ventilation holes cut in both sides 
of the front body shell. The Hummingbird, however, only had one hole cut in the left side. 


Figure 5 shows a right side view of the RPH with no ventilation hole cut in the fiberglass 


1] 


a 


a - 
aoe tee ee 
j : iY 2: i 
“ ta4 t ‘ 
yk ee S 
| jaan 
| jaek = 
foe ! 


mm 8 
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‘ ’ 





Figure 5. Right Side View of Hummingbird Without Ventilation Port 
body shell and the exhaust manifold’s position just inside the fuselage. The solid fiberglass 


shell on right side allowed a build up of the exhaust manifold temperature which could have 
further increased the cooling air temperature at the intake of the cooling fan. The object 
seen in the hole in the fuselage in Figure 6 is the exhaust manifold. 

One final cause of overheating was an improper engine operation and improper 
adjustment of the eaaiiee fuel mixture in the carburetor. The engines received from 
Gorham Model Products had no information as to total engine time and previous carburetor 
adjustment settings. The damaged engine was most likely a new engine requiring a two hour 


break-in period which was not accomplished. The carburetor’s high and low speed needle 


12 


jets, initially set at the factory and possibly moved during shipment, were not checked for 
proper adjustment. Cylinder head and exhaust gas temperatures were seen to vary a great 
deal (+100° for cylinder head and +150° for exhaust gas temperature) during the engine 
break-in period carburetor adjustments. Thus, maladjustment of the carburetor settings can 


very easily cause an overheat problem. 


c. DRIVE TRAIN 

1. Original Configuration 

The drive train begins at the engine drive shaft. The vane-axial cooling fan and 
centrifugal coupler were mounted on a shaft extension and a drive pulley is attached to the 
top of the centrifugal coupler. A drive belt connects this pulley to an intermediate shaft to 
which a sprague clutch is mounted for autorotational capability. Another belt drive is 
connected to a pulley which is keyed to the main rotor shaft. The tail rotor take-off is driven 
by bevel gear mounted to this pulley. Total gear reduction is 10:1 from the engine to the 
main rotor shaft and 3.2:1 to the intermediate shaft. The tail rotor drive shaft turns at 40% 


of the engine shaft speed. Figure 6 shows the main transmission layout. 


13 





Figure 6. Main Transmission 


2. Drive Train Deficiencies 

As mentioned in the background investigation chapter, massive torque fluctuations 
due to unsteady idle speeds exist. These torque fluctuations were reported to, however 
unverified, snap the main rotor shaft of a similar RPH. In any case, fluctuations in engine 
torque are magnified ten times at the main rotor shaft due to the 10:1 mechanical advantage 
given by the transmission. With the exception of the hard rubber belts and limited slipping 


in the centrifugal coupling, there is nothing to absorb any sort of shock caused by torque 


14 


fluctuation in the unmodified drive train. The incorporation of a shock absorber was 
determined necessary in order to prolong drive train component life and reduce airframe 


vibrations. 





16 





IV. ENGINE BREAK-IN AND TESTING 


The engine tested was a brand new WAEL 342 with no operating time accumulated. 
The engine manual requires a two hour break-in period before it is put to any application. 
A break-in schedule consisting of several low power runs at short time durations (5-10 
minutes in length) and varying power runs at longer time intervals was conducted. In 
conjunction with these muns, engine cylinder head and exhaust gas temperatures (CHT, EGT) 
were monitored to determine the relationship between power and the measured 
temperatures, allow the correct setting of the high and low speed needle jets on the 
carburetor and provide clues as to how to contain the temperatures while mounted inside the 
helicopter’s fuselage. 
A. ENGINE TESTING SET-UP 

ne Engine Test Stand 

The engine was mounted on a test stand designed to measure thrust and rolling 
moment of the AROD UAV. The rolling moment was the only measurement taken and 
allowed the determination of engine power. Thrust measurements were not needed for the 
performance calculations. The moment was computed by reading a force gage which was 
mounted at the end of a 9 inch moment arm, as seen in Figure 7, and then converted to 
horsepower after obtaining engine rpm by a strobe tachometer. To provide a working load 
during the testing and break-in procedures a 30 inch diameter birch propeller (commonly 
used in ultra light aircraft applications) was installed. Figure 8 shows the engine rigged for 


testing. The direction of rotation of the engine was opposite to the direction of rotation of 


17 


1@50 Ib and 





THRUST 
a4 1@100 Ib 
AROD ~ a VY THRUST FORCE 
GAGES 


8.02 00.6 






50 Ib ROLLING 
MOMENT 
FORCE GAGE 







WHEEL RAISING 
RATCHET 







ES 
sores eretaleseree seenscersnestoteeatetmtenstecntetetgestse neta! 
Mona’ n". *nteP any’ a nt ater’ ove’ e naa tate a's Simin a's ss a 





BASE—ROLLS ON WHEELS AND IS 
LOWERED TO GROUND FOR ENGINE RUNS 


A te nen? # @ Max 
a ory 


Saree ae 
sreP oe oekel 





SLOT AND BOLTS ALLOW 
ADJUSTMENT 







SIDE VIEW FRONT VIEW 














1@5Q Ib and 1@100 Ib 
Toe] THRUST FORCE GAGES 


* 
on ata terete tat ete etetn tn as 210 's's 








WRB? 


| | SQA 






tars 


eron ere. 
wreterere 


FORCE GAGE 


Figure 7. Engine Test Apparatus 


18 





Figure 8. WAEL 342 in the Test Configuration 


the propeller. For this reason the propeller had to be mounted backwards. A one gallon fuel 
tank provided a 25:1 fuel-oil mixture to the engine. As a precaution a 24 inch diameter 
room fan was placed to direct airflow over the engine. This later proved to be ineffective. 
2. Hand-held Engine Starter 
The engine was started by a hand-held starter which contained a new starter motor 
shown in figure 9. With the need to start the engine in a counter-clockwise viewing the 


engine from the rear on the test stand, a starter with this rotation was sought. Also at this 


19 





Figure 9. Hand-held Starter 
stage of the research the direction of rotation of the external starter design had not yet been 


decided. Therefore a starter with the capability of providing adequate torque in both 
directions was prudent. The Prestolite MBJ-4407 winch motor was chosen for its 
availability, power and dual directional capability. The performance specifications for this 
motor can be found in appendix C. 

The coupling of the starter to the engine shaft was accomplished through the use of 
a hex-ball wrench on the starter and a hex-socket bolt mounted to the propeller. The hex- 
ball gives the advantage of providing constant torque while allowing small misalignments 


of the starter shaft. The hex-ball also does not jam into the socket which becomes a large 


20 


safety feature when hand starting a 25 hp engine. A 3/8 hex-ball was pressed into a 
cylindrical block of aluminum. The bottom half of this 2 inch block was bored to fit the 
‘ies motor’s 3/4 inch drive shaft. The wrench coupling was then pinned to the starter 
motor shaft. A mounting plate for the starter motor, a momentary contact switch, solenoid 
and two handles were fabricated and the above components assembled. A set of automobile 
jumper cables was modified by adding eye terminals to one set of ends of the jumper cables. 
The electrical connections were then wired to the assembly in accordance with the supplied 
wiring diagram. The hand-held starter is shown in Figure 10. 

Thermocouples were placed at the exhaust pipe and sparkplug to measure the EGT 
and CHT, respectively. The thermocouple leads were connected to a digital readout which 
displayed the two temperatures on two separate channels. Tests were conducted in static air 
conditions with the only air flow over the cylinders being a low velocity induced flow caused 

by the propeller. With the reversed mounting of the propeller, the induced air flow was 
drawn over the engine cylinders and thrust forward. Finally, a “kill” switch was installed 
to ground the electrical connection from the magneto to the spark plugs enabling controlled 


engine shutdown. 


B. ENGINE TEST PROCEDURE 

For each day of engine testing, the ambient air temperature was recorded. The 
safety procedures in the engine manual were then reviewed. The engine starting checklist 
also in the engine manual was then followed for engine start. The starter rig was connected 


to a 12 volt marine gel-cell battery via the jumper cables and the hex-ball wrench drive was 


21 


inserted into the hex socket on the propeller’s hub. The switch on the starter was thrown and 
the starter held in place until the engine fired. Once running the engine temperatures were 
recorded at various engine rpm. 

OA ENGINE TEST RESULTS 

Although ambient air temperatures were recorded for each day of engine operation, 
the difference in the temperatures from day to day was proportionally insignificant to the 
recorded engine temperatures. Therefore all engine temperature information assumes an 
average ambient temperature of 65 °F. 

The first engine run was conducted only to start the engine for break-in and to 
observe the engine and engine temperature behavior. Minor carburetor adjustment was 
made to obtain behavioral information also. This run revealed an idle rpm of about 3100 
rpm and idle cylinder head and exhaust temperatures of 235°F and 594°F, respectively. A 
maximum throttle setting was briefly set. This power setting showed a maximum rpm of 
4400, a maximum exhaust gas temperature of 618°F and a cylinder head temperature that 
would have greatly exceeded the 482°F maximum if left to continue operating. This power 
regime displayed evidence of the overtemp experienced by the failed engine and a 
requirement for cylinder cooling. 

Seeking a balance between temperature limits and reducing engine operating 
roughness, the high speed needle jet on the carburetor was set to minimize maximum power 
cylinder head temperature through a slightly rich air-fuel mixture and minimize roughness 
at idle throttle settings through a slightly lean mixture. The needle jets were adjusted by 


rotating them by 1/8 th of a turn and noting the results until a favorable condition existed. 


22 


The WAEL 342 is rated at 25 hp maximum power at 7000 rpm. After calculating the brake 
horsepower from the torque reading it was determined that the engine was delivering 
maximum power due to the propeller load at 4400 rpm. Until the final carburetor settings 
were achieved, the CHT and EGT were seen to vary as much as 100 °F and 150 °F, 
respectively. Subsequent runs on the engine began to show consistent temperature behavior 
with proper carburetor adjustment. The chart below shows the typical results for the 
properly adjusted engine. 


Typical CHT and EGT at Various Engine RPM 


See | araiace, [Had ven 
00 Ga 











: 


The maximum cylinder head temperature was unable to be contained but was reduced to a 





slow creep through 482°F. The room fan use was discontinued after noticing that there was 
no difference in cylinder head temperature with or without the fan running. The engine 
exhausted the one gallon fuel supply in 35 minutes putting the fuel consumption rate at 11.7 
lb/hr which is consistent with the engine performance data provided by Target Technology 
Ltd.. 

To see the effects of forced air over the cylinder a backpack-type leaf blower was 
borrowed from the greens keeper shack at the NPS golf course. The blower provided an 


advertised 150 mph air flow through a 4 square inch opening at full throttle. At a full 


23 


throttle setting on the WAEL and a mid to full throttle setting on the blower, the CHT was 
contained well below 482°F at approximately 420 - 450. The results of this experiment 
revealed that it was possible to contain the temperature through a forced air device. 

A pronounced torque fluctuation as described by Mr. Beckman was also evident. 
These fluctuations were load driven as they were seen to be more pronounced at low loads 
at lower rpm than at high loads. The fluctuations could not be determined during engine 
operation due to the test configuration; however, once the engine was shut down telltale 
scoring on the scale face showed an approximate +10 ft-Ib fluctuation at idle power and +1 
to 2 ft-lb fluctuations at full power. This multiplied by the 10:1 mechanical advantage 
provided by the transmission can mean a +100 ft-lb fluctuation at the main rotor mast. This 
observation confirmed the torque fluctuation claims of Mr. Beckman. 

During the engine testing phase the oversized cylinder heads were received. Several 
modifications to the engine had to be made in order to accommodate the increased size of 
the heads. The spark plug wiring had to be lengthened to reach over the new head to the 
spark plug. A spark plug cap retainer had to be manufactured to keep the spark plug cap 
from sliding off the longer plugs due to the engine vibrations. Finally, longer cylinder head 
bolts were installed to compensate for the increased head thickness. Once the new cylinder 
heads were installed, the engine was run to observe the effects of the increased area on CHT 
and EGT. 

The engine was again tested in static air conditions. Runs initially at idle power 
settings showed an approximate 25°F decrease in CHT and, as expected, no change in EGT. 


Runs at maximum throttle showed a maximum CHT of 435°F. The effect of the increased 


24 


area of the cylinder head reduced the maximum CHT by over 47°F in static conditions. A 


comparison of the EGT and CHT observed with the two sizes of cylinder heads is shown in 


Figure 10. 


po MXC 
Standard Cylinder = ] 
Pe 
a ee 


3000 3500 4000 4500 
RPM 


650 











60 


950 


S. 


ition 


\ 
mi 


200 





Figure 10. CHT Comparison for Large and Small Cylinder Heads 


This determination moved the cooling system design away from a high mass flow system 
to an interior ventilation or low mass flow system in which the induced air flow velocities 


over the engine on the test stand would be matched or increased inside the fuselage. 


pm) 


The engine break-in was accomplished without incident and approximately 3 hours 
and 20 minutes of engine operating time were accumulated. The engine performance 
information provided by Target Technology Ltd. was also verified as being consistent with 
observed engine performance. Most importantly it was shown that the larger cylinder heads 
provided enough heat dissipation to contam the maximum CHT at full throttle settings in 


static air conditions. 


26 


V. DESIGN MODIFICATIONS 


The following modifications were made in order to overcome the previously 
discussed deficiencies. The general design constraints throughout were to minimize 
complexity, minimize weight and CG changes, minimize cost and increase user safety. 

A. STARTER 

i: Design Considerations 

Looking at its airflow obstruction effects and inability to perform reliably, it was 
decided to completely redesign the engine starting system. A major factor considered along 
with overcoming the existing deficiencies was the requirement to start the engine on the 
UAV test stand. Most UAV engines including the WAEL 342 in a fixed wing application 
need a counterclockwise torque for start. However, due to mounting constraints on this test 
stand, a starter must be able to provide starting torque in a clockwise direction as one faces 
the propeller. This demonstrated early on m the design that a starter capable of providing 
torque in both directions would be practical. 

As mentioned earlier, removal of the starting system’s eight pounds would provide 
an attractive 13% increase in payload weight or compensate for the weight of the 
modifications. This benefit coupled with an assured starter motor weight increase due to the 
increased power requirement and dual direction capability drove the starter system redesign 
to an external configuration. 

Along with the external design requirement was the need to accomplish an engine 


start remotely and not to have the starter interfere with flight operations. Some sort of drop 


27 


away device would be useful and would allow the starter assembly to be removed from the 
operating area safely without possibility of main rotor entanglement or other interference. 
The final design provides a starter capable of starting Hiznmingbird on the ground for flight 
operations or on a test stand such as the one acquired in LT Booth’s thesis [ref. 5]. 

2 Starter Design Implementation 

The starter assembly’s final design is as shown in Figures 11 and 12. It consists of 
a 0.25" x 9" x 20" base plate to which the driving components are mounted. The starter 
motor is the 12 volt Prestolite MBJ-4407 winch motor used in the hand held starter. A 1:1 


drive ratio was proven effective by the hand held starter during the engine tests. Originally 





Figure 11. Top View of Starter 


28 











Figure 12. Bottom View of Starter 


the motor was mounted as follows. The starter motor mounts to the plate with the drive 
shaft passing through the plate from top to bottom. A 7 inch sprocket taken from the spare 
Hummingbird parts is mounted to the end of the shaft. An insert for the sprocket had to be 
designed and manufactured to replace a onesway bearing of the original design to eliminate 
any slippage. A chain drives another 7 inch sprocket which is mounted to the engine starting 
drive shaft. This sprocket contains a one way bearing which allows for torque application 
— start and freewheeling when the engine rpm exceeds the starter rpm. The original 
insert for the one way bearing was designed for the tapered shaft that mounted to the bottom 


of the engine by means of friction only which caused some damage due to metal-to-metal 


29 


slippage. A new piece was designed and manufactured to accommodate a straight shaft and 
key. The sprocket is attached to the drive shaft which passes upward through the plate. A 
3/8 inch hex-ball drive wrench is pressed into an adapter which rides on a thrust bearing to 
prevent excessive wear of the starter drive shaft components. The ball drive wrench again 
gives the benefit of allowing small misalignments which occur during engine start and 
allows the starting assembly to drop free of the structure without jamming in the drive 
socket. The thin neck of the wrench is also the most convenient place for the starter to 
structurally fail should normal starting forces be exceeded. 

In an initial functional test of the starter in the above configuration it was shown that 
there was insufficient power to turn the engine drive shaft. At best the starter was turning 
the engine at 60 rpm well short of the 1000 rpm called for in the engine specifications. A 
mechanical advantage similar to the one seen in the previous starter design was then 
incorporated. A 1.4 inch diameter sprocket, seen in Figure 12, was obtained and installed 
providing and approximate 5:1 mechanical advantage. A functional test on the starter in this 
configuration showed adequate rotational speed for engine start. 

A 3/8 inch impact socket is mounted to the bottom of the engine. To mount this 
socket, the original tapered mounting adapter which provided for attachment of the 7 inch 
sprocket to the engine shaft was machined from the original tapered shaft to a “% inch drive 
socket wrench mount. 

The starter is held in place at four pomts shown in Figures 13 and 14 keeping entirely 
off the ground when attached for engine start. The first two are on each landing gear strut. 


Two pins and mechanical stops prevent fore and aft as well as lateral movement. These two 


30 


pins are connected by a spring so that both pins release after an over-the-center lock is 
cleared. The third point is the 3/8 inch hex ball socket which limits horizontal planar 
movement when coupled to the engine. The fourth point is a spring-loaded latch assembly 
connected to a cross bar under the engine which keeps the starter coupled to the engine 
during start. Two 30 foot lengths of small diameter cable are connected to the assembly 
which allows starter disengagement and towing the assembly clear of the operating area. 
Skids are installed to pull the assembly clear. The skids are formed with a semi-circular 


protrusion on the front. This feature unloads the 20 pound weight on the pins that hold the 





Figure 13. Starter Mounted to Landing Gear 


3] 


rs yi 
Fy. 
‘ a q - 


» 


a” rs, . 
MS) 


“ = 
ie 


> ae 
* 


: ols 


E a i! 





Figure 14. Starter Coupled to Engine 


starter assembly to the landing gear skids when the starter 1s disengaged from the engine to 
ease in the pin release. 

The electrical configuration consists of two 30 foot lengths of 4 gage DC wire 
attached to the starter motor. This distance puts the operator well outside of the 5 foot rotor 
radius and allows operation from outside the test area behind Building 230 at NPS. The 
leads are connected to the starter for the desired direction of rotation. At the operator’s end, 
the leads are connected to a 12 volt car battery directly or through a solenoid. A momentary 
contact switch can be connected or direct momentary connection of the leads to the battery 


will start the engine. 


32 


3. Starter Operation 

Engine start is accomplished in the following manner. The starter is set into position 
with all pins in place. The electrical connections are checked for proper hook-up and 
security. Once the area is clear and it is determined that it is safe to start the engine, the 
momentary contact switch is thrown and the starter engages the engine. Once the engine has 
fired the small diameter cable is pulled to disengage the starter from the engine via the 
spring loaded latch. Once the starter has dropped away another cable is pulled to release the 
pins on the main landing gear struts. Once the starter assembly is disconnected from the 


aircraft it is towed clear of the helicopter’s operations area. 


B. ENGINE COOLING SYSTEM 

The engine cooling system was totally redesigned and modifications were made 
several engine components to accommodate the new system. Each deficiency listed in the 
engine cooling system deficiencies chapter was addressed and corrected resulting in a 
properly designed cooling system for the WAEL 342 engine’s internal use. 

1. Design Considerations 

In order to effectively cool the engine cylinders it was necessary to remove as many 
obstructions to the cooling air flow as possible. The interior of the engine compartment is 
approximately 2.5 cubic feet. The engine and drive train occupies approximately forty 
percent of this space. The objective was to maintain an unobstructed flow of air through the 
engine compartment and supply cooling air from outside of the fuselage without inadvertent 


preheating as found in the previous design. The amount of cooling air to pass through the 


33 


engine compartment was based on the observations of the induced flow while the engine was 
on the test stand. 

The need to know the maximum engine cylinder temperatures that the Hiwnmingbird 
could encounter drove the size and therefore the configuration of the cooling fan that was 
to be installed. The cylinder head temperatures with the enlarged cylinder heads once 
installed was the ultimate driving force behind the cooling system design. Once again a 
simple design was desired in order to increase reliability, simplify maintainability and 


minimize cost and center of gravity shifts. 


Pa Cooling System Design Implementation 

a. Cylinder Heads 

As previously stated, the standard cylinder heads which was originally 
installed on the engine was replaced with the larger cylinder heads and are shown in 
comparison with each other in Figure 15. The effects of the improved heat dissipation 
through the significant increase in surface area have already been discussed. The larger 
heads required a standard size spark plug rather than the short plug used in the standard 
head. The engine manual called for a Bosch W6 BC spark plug with a 12.7 mm reach. An 
equivalent substitute plug, Splitfire SF 412C, was used due to the unavailability of the Bosch 
plug. The Splitfire plug has a smooth ceramic insulator where as other spark plugs have 
ridged ones. The smoothness caused the spark plug cap to slide off and disconnect during 
engine operation. To remedy this problem, retaining clips were installed to prevent the caps 


from working loose. 


34 







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3 bo ve gs Sara 4 Ba 
ae A Cat aie ah ye OY ol 
4 phe meh Nein ie ice eaten tn Fo ; 
Pade Bop wh: Ye 2 > i 4 : 

ee tS, ‘ 

54 oy. Ree tey 


+ 


Pe 
Oe ae 
eS viet 
rhe a get pe 
7 ed, 
oan FF 


‘s 
So fi 
ey, nf 


*. ’ 
cok * Veal <4 
age ee 


i ee 


~ ails . Sage i s 
Wit t2 t3 t4 th 10 Cy fe ton 
al etry fg et tints 
Gms new cee wt 7) 
EECA. 3 Te r 
: insta Bandove. or Me a il Tey 


<4 SS - pa = 9 
‘ are Ay a 


a ! " 4 : la 


oe 
ee 
aa’ 

_ 
a eel ie : 





Figure 15. Size Comparison of Cylinder Heads. 


35 


(1) Upper Engine Mount. As the engine required some minor 
modification on the test stand, the Hummingbird required some airframe modification to 
accommodate the new enlarged cylinder heads. The four engine mounting points on the 
bottom of the airframe remained unchanged; however, the upper engine mounting bracket 
that was installed as a part of LT Greg Fick’s [ref. 3] modifications shown in Figure 16 had 
to be moved aft by at least 1.04 inches due to the difference in the cylinder head thicknesses. 
The two side stiffening plates were moved aft to provide the necessary airframe support for 
the bracket’s new position. 

The bracket modification led to another problem. The upper engine mount 
braced the engine through two of the six 6 mm cylinder head bolts. There existing cylinder 
head bolt was not long enough to provide support for the cylinder head and also pass through 
the upper engine mount. Attempts to find longer bolts and 6mm threaded rod failed as no 
local supplier carried the longer bolts or metric size threaded rod. As a result, two adapters 
which acted as a cylinder head bolt, spacer and upper engine mount attachment point were 
designed to custom fit this application. Figure 17 shows this piece. The cylinder head bolt 
segment 1s 6 mm in diameter and includes the correct cylinder head bolt thread length. The 
spacer was designed to provide a gap between the cylinder head and upper mount brace so 
there will be no damage inflicted on the cylinder head heat fins while the both the engine 
and airframe vibrate. The remainder consists of the mounting bracket threads which are also 
6 mm in diameter. 

(2) Adapter Installation. To install the adapter the cylinder head bolt 


portion is first screwed in to place. To accomplish this two nuts must be locked 


36 


UPPER REAR ENGINE SUPPORT BRACKET 


0.1875" Holes 





TOP VIEW 


Jp 25" —___________________ 






(One Oa 


0.5" [e- 


Os Tae rf I 0.1875" Holes 


AFT VIEW 


Figure 16. Upper Engine Mount 


37 





Figure 17. Spacer Bolt 


against each other on the mounting bracket end and then the whole piece torqued to the 
cylinder head bolt torque specification. The two nuts are then removed and the mounting 
bracket is then slid over the free end. The mounting bracket is then secured by a two lock 
washers and nuts. 

b. Component Removal 

Several original components were removed in order to improve cooling air 
flow and/or to make room for design improvements. As previously mentioned the starter 


was removed as a weight saving measure. Removing this equipment also freed room for the 


38 


cooling air to flow more efficiently. The fiberglass cowling that previously directed the 
airflow over the cylinders and the vane-axial impeller was removed to accommodate a new 
air moving system and to further reduce the obstructions to the cooling air flow. Finally the 
original exhaust manifold and exhaust pipe were removed and replaced with two aluminum 
tube exhaust pipes that exhaust below the fuselage eliminating the undesirable heat source 
inside the fuselage. 

C. Cooling System 

After considering many options of cooling fans, configurations and 
suggestions from industry, a simple and reliable design was implemented. The cooling air 
velocity through the engine compartment was observed during the engine tests and a system 
to move air through at this speed was introduced. Two air-conditioning condenser fans rated 
at 500 cfm at 3000 rpm were purchased for less than $6.00 and mounted to ventilate the new 
1.3 cubic foot engine compartment. One fan was modified to fit on the tail rotor drive take- 
off shaft off the main transmission which rotates at 40 percent of the engine rpm or 1200 to 
2800 rpm. The other fan was mounted to the rear wall of the engine compartment. As 
shown in Figure 20, the lower fan is driven by a belt drive configuration and rotates at the 
same rpm as the tail rotor drive shaft. The tail rotor shaft mounted fan provides cooling air 
primarily to the forward cylinder while the belt driven fan provides ventilation to the aft 
cylinder. 

Information on this fan was unavailable. Measurement of the cooling fan air 
flow at 1500 rpm (approximate fan rpm at engine idle) showed approximately 345 cfm. 


Assuming, a linear increase in air flow with increasing rpm as seen in several other fan 


39 





Figure 18. Cooling Fan and Drive Configuration 


performance charts, the air flow at 2800 rpm is estimated at 480 cfm. Thus the two fans 
together produce 960 cfm at 7000 engine rpm through the engine compartment which 
exceeds the air flow pattern seen on the engine test stand. 

The engine compartment was partitioned to keep the cooling air close to 
outside ambient temperature and direct the airflow to the critical engine areas. Thin sheet 
metal was installed to form fore to aft bulkheads on the left and right sides of the engine. 
Another partition was placed between the two longitudinal bulkheads to direct most of air 
from the belt driven fan over the aft cylinder. This partitioning reduces the space to be 


ventilated and directs the flow of air from the exterior of the fuselage, through the engine 


40 


compartment and out the bottom of the aircraft. Cooling air enters primarily through the two 
ports on the left and right sides of the compartment in forward flight to the fan inlets without 
interfering with the cooling air flow inside the partition. 

LT Greg Fick [ref. 3] recommended in his thesis that the WAEL 342 engine be down 
rated from 25 hp to 18 hp which leaves ample power available for the fan drive system. The 
power required to operate the installed fans is estimated to be a small fraction of the 7 hp 
rated excess power. 

C. DRIVE TRAIN 

1. Design Considerations 

The foretold and observed torque fluctuations of the engine were measured at a 
maximum of 10 ft-lb. Ideally the location in which to dampen the shock would be at the 
point of the maximum moment which in this case is the main rotor shaft. However, there 
is no room for any addition to this space due to the main rotor control rods and other 
connections. Balancing available space and shock reduction requirements placed the shock 
absorber design location at the intermediate shaft where the transmission picks up the engine 
drive. At this point the mechanical advantage is 3.2:1 putting the torque impulses at +32 ft- 
lbs. A shock absorber must be able to withstand and dampen this shock moment in addition 
toa maximum constant driving torque of 77 ft-lbs (24 ft-Ibs from engine) at the intermediate 
shaft. 

2. Shock Absorber Design 

The intermediate shaft on the transmission shown in Figure 19 was selected as the 


location for the shock absorber assembly. The shock absorber itself is a Metalastik® 


41 





Figure 19. Intermediate Shaft of the Main Transmission 


Rotoflex® coupling. It consists of a hexagon of rubber with six metal inserts bonded into 
position. It also contains metal interleaves bonded into the rubber for increased torque 
capacity when required. The coupling must be able to withstand a 76.8 ft-lb sustained load 
plus a 32 ft-lb impulse load totaling a maximum load of 108.8 ft-lbs. The 76.8 ft-Ib moment 
was obtained by using the maximum torque rating of 24 ft-lbs and multiplied by 3.2 for the 
load at the intermediate shaft... A coupling closest to this specification was ordered. This 


size coupling gives a safety margin of 1.33 computed for rated maximum torque to estimated 


42 


torque applied and is the largest size that will fit in the design location. 

In the unmodified configuration the drive gear seen in Figure 19 is keyed to the 
intermediate shaft. In the modified configuration the gear is free to rotate about the shaft 
on a needle bearing. Mounted to the bottom of the gear’s web by four bolts is the top plate 
of the shock absorber. This 0.375 inch thick and 4.5 inch diameter plate connects to the 
coupling with three of the six bolts and is also free to rotate about the shaft. The other three 
bolts connect the bottom plate of the shock absorber assembly. This plate is also 0.375 inch 
and 4.5 mch diameter and is keyed to the shaft and allows a shock dampened driving 
moment to pass through the rest of the drive tram. A 0.125 inch thick spacer rmg is mounted 
between the top plate and gear web to provide space for the bolt heads and washers 
mounting the two plates to the coupling. The design dimensions of the plates were obtained 
by strength of materials methods using the expected loads and applying a 1.5 safety factor. 

The current intermediate shaft had to be lengthened to accommodate the extra 
components. The original shaft was 3.5 inches and was redesigned as a 6 inch shaft. A 
snap ring on the bottom of the shaft keeps the components in place. Two key slots in the 
shaft provide a mounting point for the bottom plate. 

Due to unforseen delays the shock absorber was unable to be installed. The 
installation calls for the upper plate and spacer ring to be mounted directly to the gear’s web 
by four small bolts. A needle bearing is to be pressed into the inside of the drive gear 
allowing it to move freely about the shaft. The Rotoflex® coupling is then bolted to the 
upper plate and the lower plate bolted to the coupling. After the shaft keys and snap ring is 


in place, the assembly is then placed into the transmission. The Figure 20 shows the 


43 


unfinished components of the shock absorber system in the position they are to be mounted. 
The drawings in appendix D show the final form of the upper and lower plates, spacer ring 


and modified drive shaft. 








Figure 20. Layout of Shock Absorber Components 


VI. GROUND TESTING 


Initial ground tests of the Hummingbird were conducted to confirm the effectiveness 
of the design modifications. The tests were run in the fenced helicopter test area just behind 
building 230 at the NPS golf course. The Hummingbird was assembled without the forward 
fiberglass and tied to the ground with straps hooked to pad-eyes. The starter was put into 
position on the aircraft and the starter cables and electrical wires were connected and placed 
outside the fenced in area. A momentary hard connection to the battery was used to operate 
the starter. 

Several attempts were made at starting the engine. The starter was determined as 
having enough rotational speed but the engine did not fire. Engine start was attempted seven 
times in two separate tests. Trouble shooting the systems led to the following possible 
problem areas. 

First, the engine had not been started for four weeks prior to this test. Slow starting 
characteristics were noticed when long periods between engine tests existed in the engine 
test phase. In an effort to obtain ignition the throttle was opened fully and closed several 
times possibly flooding the engine. Flooding was confirmed by a strong gasoline smell 
from the exhaust pipes upon initial mspection of the RPH. 

A possible inadvertent grounding of the magneto was another hypothesis and 
subsequently investigated. Prior to the test the UAV technician had difficulty with the 
aircrafts radio operated engine “kill” switch. However, the investigation showed proper 


electrical connection and continuity. 


45 


Finally, the strongest theory resulted from the above investigation. When removing 
the rear cylinder spark plug cap it was noticed that it was easier to remove than the forward 
one. This could indicate that the rear spark plug was not electrically connected causing the 
problem. The spark plug caps had not been inspected for security since the engine’s 
installation approximately two weeks prior to the ground tests. 

Along with the above problem the starter had suffered minor damage. The head of 
the hex-ball drive snapped off twice during the engine start attempts. The design feature of 
structural failure location convenience was proven by this. During the repair of the hex-ball, 
minor damage to the insert of the 7 inch sprocket was discovered. The insert was peeked 
where the clutch mechanism engaged. The shallow depth deformations were found around 
its entire circumference. The design dimensions and material of the insert was copied 
exactly from the Azenmingbird’s original starter with the only difference being a straight bore 
to fit the 0.75 inch starter motor shaft where the original design incorporated a tapered bore. 
The aircraft mounted starter insert showed no evidence of this damage. 

The most probable cause for the starter damage and engine starting trouble is thought 
to be the eileen Prior to the first wrench head failure a popping noise indicative of 
engine ignition was heard; however, ignition was not sustained. Disconnection of one spark 
plug could cause this. The sudden unloading and loading of the starter caused by the firing 
of one cylinder would cause the peeing and wrench head failure. Necessary corrections are 
currently underway to remedy the starter damage and spark plug cap problem. Further 


ground testing will be an area of future study. 


46 


Vi. CONCLUSIONS AND RECOMMENDATIONS 


A. CONCLUSIONS 

The critical shortcomings of the Hummingbirds power plant and drive train have 
been overcome through careful redesigning of the affected systems. While the power plant 
still possesses certain undesirable characteristics such as excess noise and vibration levels, 
the major design weaknesses of the discussed systems have been rectified in through design 
and experimentation. Hummingbird is now a more reliable platform ready for further 
ground testing and RPH research. 

An extended reference list of personnel and information was developed in the 
background investigation of the WAEL 342 engine. Companies, points of contact and other 
information that will aid throughout the life of the Hianmingbird have been documented. 

The WAEL 342 engine was successfully tested and broken in with approximately 3.4 
hours of accumulated operating time. Proper high and low speed needle jet setting were 
made to give the engine the smoothest operation and lowest possible cylinder head 
temperatures. The previous heavy and bulky exhaust manifold and pipe were replaced by 
lighter and more directly routed exhaust pipes preventing excess temperature build-up in the 
engine compartment that caused inefficient cooling in the original RPH design. 

An improved starter for aircraft engine start and a hand-held starter for engine tests 
were designed, manufactured and shown effective in starting the WAEL 342. The use of the 
Prestolite MBJ-4407 provides unique flexibility in starting the engine in the Hummingbird s 


various configurations. The same starter motor used with the two starter designs starts the 


47 


WAEL 342 on the engine test stand, in the Hienmingbird mounted to an aircraft test stand 
and in the Hummingbird configured for flight operations. 

An improved cooling system has been designed. The cooling air preheating problem 
of the previous design has been eliminated through the partitioning of the engine 
compartment and opening of the right side of the fiberglass body. Cooler engine 
temperatures attained during the engine tests by increasing the cylinder head size and 
properly setting the fuel mixtures reduced the cooling air volume required thus reduced the 
power requirements for the cooling system. Further ground testing is needed to confirm the 
efficiency of this system. 

The torsional shock absorber will effectively reduce the torque fluctuations reported 
by Mr. Ken Beckman and observed during engine tests. Once installed the drive train 
components will experience reduced shock which will lengthen the life and increase the 
reliability. 

The general goals in each of the system improvements have been successfully met. 
The reliability has been improved by the shock absorber and cooling system redesigns. The 
CG remained virtually unchanged as all the components removed and installed were at or 
very near the CG. Cost was kept to a minimum by incorporating a materiel acquisition 
hierarchy of recycling, old Hummingbird parts, purchasing off-the-shelf items and finally 
using commercially produced items such as the larger cylinder heads and flexible coupling. 
The empty weight of Hummingbird was decreased by 5 pounds after all modifications. The 
removed items totaled 11 Ibs and the installed items totaled 6 Ibs. The empty weight of the 


RPH is now 119 lbs weighed on a TOLEDO industrial scale. 


48 


Finally and most importantly, user safety was significantly increased by the remote 
starting system. The system’s components are kept on the ground at all times resulting in 
no interference with the rotor system and starts can be accomplished outside of the RPH test 
area for ground tests and at a safe 30 foot distance during flight operations. The Aeronautics 
and Astronautics Department is now in a position to continue with valuable RPH research. 
B. RECOMMENDATIONS 

The many design shortcomings of Hummingbird have been overcome to take the 
RPH from a target drone to a reliable research platform. However, there are still some 
ground and flight issues left to be resolved. Further improvements can also be made for 
specific fields of study such as Higher Harmonic Control (HHC) and NOTAR® research. 

1. RPH Storage 

The first six weeks of this research was spent identifying and assembling the parts 
of the Hummingbird. The RPH was haphazardly packed away and a box of small parts and 
other hardware was rolled over eliminating whatever order existed in the box. Valuable 
time was wasted. It is therefore recommended that the Hummingbird be completely 
assembled, with the exception of the main rotor blades and tail boom, prior to long term 
storage and that the RPH be stored in the helicopter research storage room in Halligan Hall. 
This will save valuable thesis time and better acquaint the student with the RPH. 

Zs UAV Lab Space 

Whenever the Hummingbird is an active thesis project, a work bench should be 
provided at the UAV lab and not Building 230. While Building 230 provides a lot of room 


to work, necessary tools and the expertise of the UAV lab technician, Don Meeks, is 


49 


unavailable. Duplicating the required tools for an RPH lab in Building 230 would be very 
expensive and Mr. Meeks’ presence 1s indispensable. 

3 Complete Implementation of Torsional Shock Absorber 

Unforseen delays prevented the installation of this item. While the Hummingbird 
can be run and tested without it, the shock absorber should be installed as soon as possible 
to prolong the life of the drive train components. 

4. Power Plant 

The current air-cooled power plant (WAEL 342) has been improved for use in the 
RPH. However, other similar size RPH’s use a liquid-cooled engine. An investigation 
should be made mto suitable power plants, both liquid and air-cooled, to study the 
advantages and disadvantages of both. Ultimately, a selection of the best power plant should 
be considered and possibly implemented in the Hianmingbird. As previously metioned the 
power plant still vibrates excessively. A study into isolating the engine from the airframe 
is warranted. Reducing these vibrations would increase the life of the Hummingbird 
airframe and provide better flight vibration analysis in HHC research. 

5. Configure Hummingbird for Forward Flight 

Horizontal stabilizers are required for Hienmingbird to achieve forward flight. 
Historical photos show similar RPH’s with the stabilizers in place and attachment points are 
evident on the Hummingbird. A sample tailboom stabilizer is included in the Hummingbird 
parts inventory. Design and implementation of horizontal stabilizers are required to explore 


the entire flight regime. 


50 


6. Main Rotor Head Design 

Currently the Hummingbird has a two-bladed main rotor head. In order to explore 
HHC, a three or four bladed rotor head is required. Instrumentation of this rotor head can 
also be implemented to research rotor blade and rotor head forces and moments when 
subjected to various flight maneuvers regimes. 

fe NOTAR?® Research 

The design modifications made in this thesis were geared not to interfere with the 
NOTAR*® tailboom designed and built by LT Robert King [ref. 4]. Investigation of 
configurations for counter-torque thrust should be commenced to further the NOTAR® 
portion of the RPH program. The NOTAR* tail is currently stored unprotected in Building 
230. The tail boom and associated equipment should be moved and stored in the helicopter 


research storage room in Halligan Hall. 


51 











APPENDIX A: LIST OF SUPPLIERS 


Company Items City Phone Number 
Allen’s Starter Shop Prestolite MBJ-4407 Seaside, Ca. (408) 899-7689 
Gerardi Bearing Co. Chain, Sprocket, Salinas, Ca. (408) 422-5371 
Bearings 
Grainger Inc. Cooling Fans Salinas, Ca. (408) 757-0991 
Grand Auto Splitfire Spark Plugs Seaside, Ca. (408) 394-1472 
Kragen Auto Various Engine Seaside, Ca. (408) 396-7515 
Support Equip. 
Lacey Automotive 3/8 in. Impact Socket Seaside, Ca. (408) 394-1418 
Metalastik Inc. Rotoflex Coupling Schaumburg, IL (847) 519-1300 
Orchard Supply Hardware/Hex-ball Sand City, Ca. (408) 899-5144 
Southwest Aerospace WAEL 342 and Tustin, Ca. (714) 832-1333 
its accessories 


5 








Mat 
"TE AWE LV D) 


re a 








Point of Contact 


Ms. Debbie Smith 


Mr. Ian Matyear 
Mr. Ken Beckman 


Mr. Dave Davis 


Mr. John Gorham 
Mr. Patrick O’Shea* 


Mr. Randy Messer 


APPENDIX B: POINTS OF CONTACT 


part 


Target Technology Ltd. 


Southwest Aerospace 


N/A 


Chief Designer for 
Gorham’s RPH’s 


Gorham Associates 
Russel Associates 


Prestolite Electric 


Phone 


011-44-1233- 
639762 


(714) 832-1333 
(204) 339-0791 


Unknown 


(818) 889-2151 
(206) 455-3694 


(800) 346-8093 


Fax 


011-44-1233- 
624883 


(714) 832-6090 
(204) 338-3702 


Unknown 


(818) 991-2740 
Unknown 


(800) 997-6202 


* Mr. O’Shea represents several companies in the Bay area that may be helpful in future 


RPH research. 


5) 





APPENDIX C: PRESTOLITE MBJ-4407 PERFORMANCE CHART AND 
ELECTRICAL SCHEMATICS 








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57 


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(4 LARGE TERM. - 2 SMALL TERM.) 


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TO IN-OUT TOGGLE SWITCH 


58 


APPENDIX D: SPECIFICATIONS FOR DESIGNED PARTS 


ENGING SHAFT STARTER Mov NT 





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64 


2.0 


APPENDIX E: OPERATORS HANDBOOK FOR WAE 342 LIMITED ENGINE 


SERIES 2100D 


SAFETY 


Throughout this Manual are WARNING and CAUTION notes to 
warn of safety hazards to be avoided while installing, 
operating, maintaining or servicing the W.A.E. Limited 342 
engine. 


Operators should be familiar with the contents of this handbook 
with emphasis on these notes. 


Make sure ignition switch is in OFF position and spark plugs 
leads are disconnected before working on any part of the 
engine or ancillary equipment. 


Make no attempt to clean or adjust an engine while it is 


running. Special care should be taken when covers/guards 
are removed and covers/guards must always be refitted when 
work is completed. 


Fire is a hazard; do not add fuel to tank while engine is 
running. Stop engine and allow a cooling period to prevent 
spilled fuel from igniting on contact with hot engine parts. 


Do not operate the engine is a closed building. 

It is extremely important to make sure that hands, feet and 
clothing are clear of all rotating and moving parts before 
starting the engine. 


All rotating parts should be guarded where possible. 


After servicing any part of the engine make sure all safety 
guards are refitted and secured. 


Warning/safety signs are supplied with the W.A.E. Limited 342 
engine and should be attached in a prominent position on the 
airframe and fuel tank as appropriate. 


It is the responsibility of the operator to ensure that the 


equipment is not operated unless it is maintained in a safe 
condition. 


65 


Sy 
ai} 
fur pa * 
aN 

N Sy iad 


. 
2 


Ne hae 
OBS 
pees ied 


. eset 
Gas 

By 
is ice 


ve 
{ 
Ce 
J 
& 


DON'T operate in a 
closed building 


engine is running 


66 


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Tha k: 
h ‘ogy 4~. 
EAE 
Po BS ter eee 


: a cy Feng. Ce 0 gl OO: 
‘ why 41 Kena: wgssts 
Pus Poe 2 
PEALE S, ty BAe 








su tee 1 
3 Ord. 

Ay oe 
WES : 





. SANTA 

PEER EE NR are 

Sela 
sages 


ee : 
DON'T add fuel while 


RS NAN EN GME tte pa 
Fa SO TE RS URE 
BSS Me fat 


prensa a 


ae 


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SBA Rew pte ob, 
PCs eC RNAN 
NI ERASE PBI 
HONG STS EN Cy 

fs ful. ie aA, < 
4) Mee <,f A 


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mG ty ? x Ne od £3 
RARE ifs ae : 





a0 









wk 





a 
Sore te ae 2) 


> ¢ (1% 
nT B 


DON'T smoke while 
mixing fuel 






- 
= - —— 


DO make sure all 
guards, if fitted, 
are replaced 





DO make:sure that all 
rotating parts are free 
from obstructions before 
Starting engine. 





<> 
etl! P . Oy) 
——_——— — “ee ” id _ 
i i Way 3 S Sa 


ee & 
— 







——— 


DO disconnect spark 
plugs before working 
on engine 





cA 
DO make sure engine is 
properly secured to 
mounting bracket and 
airframe 


4.0 


4.1 


SPECIFICATION AND GENERAL DATA 


The W.A.E. Limited 342 is an air-cooled, simultaneously-firing, 
horizontally - opposed, twin-cylinder engine of two-cycle 
operation. 


CAUTION: 
THE ENGINE IS AIRCOOLED AND MUST NOT 
BE RUN IN STATIC CONDITIONS UNLESS AN 
ADEQUATE COOLING AIRFLOW IS SUPPLIED. 
MAXIMUM CYLINDER HEAD TEMPERATURES 
MUST NOT BE EXCEEDED. 

Specification 


A three-piece forged-steel crankshaft, running on deep-groove 
ball bearings, is housed in a_ two-piece cast aluminium 
crankcase. 


Mounted on the crankshaft are two forged-steel connecting 
rods, running on caged needle-roller bearings, pistons and 
flywheel assembly. 


The cylinders are cast aluminium with vertically arranged 
cooling fins, to provide effective cooling from air Bee 
around the engine. The bores are specially treated. 


Ignition is provided by an engine-mounted, capacitor-discharge 
system, comprising an electronic module, ignition coils and 
spark plugs, and incorporating automatic-ignition advance. 


The carburettor is mounted on the crankcase on a reed valve 
housing and manifold. 


68 


4.2 


GENERAL DATA - SERIES 2100D ENGINE 
Wi, ow cee sees Ranges from 8.0 kp (17.5 Iba) fo 


‘10. 4 nee (23 lbs) Depending on configuration 
See appropriate Inst. Drawing 


Dimensions...... ceccccccccccceseees (See Installation Drawing) 
MERE RIS ASSIA GS coco seeeeeeeeececcevsescececsese +. O6Gtime(CeapeEn ) 
SURO C es cc cece ecce eee suemeiice ec cetcee ee es 00 Mmm]. Oeeinn 
GW GRGADACILY «ss. ccceesecescescccscesess 342 CO (2069 Chemin) 
COMPresSsion ratio. ccccccccccccccccccsececcees tel (effective) 


Compression pressure (cold)..cccecsceseseeeseese 930-965 kPa 
(135-140 psig) 


Pewemeiterated. SPCEC nic cccccscascos esac 25 bhp (18,64 kw) 
to SAEJ 607(a) 


Maximum speed rated...ccccccccccccccccces eseee 7000 rev/min 
Idle SD CCCisicl cess ecccss cess eececeec0cen ecevcecen 1500-3000 rev/min 


(Depending on propeller) 


Maximum f@rqteveeiti ss «2a. ae eee S2eo0eNme(24 lb tit) 
at 4000 rev/min 


aE DUrettor . ss caperetmeeters 6 + 6 6 «sis 6 cieie ei ieusiate Mikuni BN-34-30 
Diaphragm Type 


CAUTION: 


CHANGES IN EXHAUST SYSTEMS 
AND/OR AIR CLEANERS WILL 
REQUIRE RE-ADJUSTMENT OF 
GARBUREDIOR NEEDEER Jiis- 


69 


Fuels@onsumption..c6. sess. cee ee Approx. 5.6 litres/hour @ 


5250 rev/min 
Against propeller load 


Type of Fuel....... SugRebeWe lens 'o:iSnapionslver 5 xe Mus gasoline/oil 4% (25:1) 
Gasoline..... ISTE TRC areT eres: o 0-6 0:0%s ecacshatoletens occ RON 92 octane minimum 
CAUTION; 


LEAD-FREE GASOLINE 
MUST NOT BE USED 


Dilly ee... ee eee ee Finamix 2-stroke 
or Silkolene Comp 2 


Pre-mix 
CAUTION; 
MULTIGRADE OIL ‘ 
MUST NOT BE USED 
Fuel Poe eis so os sls sis 66 cols 6s se oss @#eee¢eee¢ 6,0 mm se (0.25 in) 


(not supplied) to SAE J30d 


Airgap between electronic 
module and flywheel.......cssccsccees So ee 0,46 to 0,51 mm 
(0.018 to 0.020 in) 





Spark Plug 

Standard Cylinder head....... Bosch WSR 6F (9.5 mm reach) 
Slt hie Sie FIZC 2 & come 

Large Cylinder head........... Bosch W6 BC (12.7 mm reach) 

Spark Plug Gap 

BGS einem ore Oeics + oie aa 5 etememenebetene «every 6 suai tens 0,50 to 0.56 mm 


(0,020 to 0,022 in) 


70 


sel! WiGeel> Grower. scuwwiieiels suis otans « tier en nam: 0,7 to 0,8 mm 
(0.028 to 9.031 in) 





Cylinder head temperature (maximum)......... > ‘wee 250 Gep .G 
(Measured at spark plug gasket) (482 deg F) 


Exhaust gas temperature (maximum).........+....- 550 deg C 
(Measured 25-30 mm from exhaust flange) (1022 deg F) 


Spark plug torque setting....cccccsccccsescccevccees. 29,80 Nm 
(22 bf. ft) 


CAUTION: 
SPARK PLUG GASKET MUST BE REMOVED 


IF A CYLINDER HEAD TEMPERATURE 
THERMOCOUPLE IS USED. 


Cylinder head screws.....-ceesssseeeeees 12.2 Nm (108 Ibf.in) 
torque setting. NOTE: RE-TORQUE CYLINDER HEAD © 
SCREWS AFTER INITIAL 2 HOURS RUNNING. 


Cylinder base SCrewS.......eeeceeeveseee 12.2 Nm (108 lbf.in) 
torque setting 
CAUTION: 


TORQUE WRENCH MUST BY USED TO 
ENSURE CORRECT TORQUE SETTING 


NOTE: ALL TORQUE CH@@RS MUST BE 
CARRIED OUT WITH THE ENGINE COLD. 





71 


0.0 


Teg 
0.2 


2.3 


9.4 


INSTALLATION 


WARNING: 


BEFORE OPERATING, ENGINE MUST BE 
SECURED TO MOUNTING BRACKET OR 
AIRFRAME. FAILURE TO SECURE 
ENGINE CORRECTLY MAY RESULT IN 
DAMAGE TO AIRFRAME AND/OR LOSS OF 
ENGINE AND INJURY TO OPERATOR. 


CAUTION: 
ALWAYS ENSURE IGNITION IS SWITCHED 
OFF (GROUNDED), WHEN ROTATING 
ENGINE CRANKSHAFT WITH SPARK PLUGS 
REMOVED FROM CYLINDERS, OTHERWISE 
DAMAGE TO IGNITION SYSTEM WILL 
OCCUR. 

Remove all protective coverings. -. 


Remove keeper-plate from ignition flywheel. 


Fit recommended air inlet horn and/or air filter suitable for the 


_installation. (See Installation Drawing). 


WARNING: 
THE MOUNTING BRACKET MUST BE OF A DESIGN 


THAT WILL NOT FAIL UNDER NORMAL RUNNING 
CONDITIONS. 


Fit engine to engine mounting bracket on airframe (refer to 
Installation Drawing). 


Base Mounting 4 x M8 screws with suitable fastener locking 
evice, minimum thread engagement 15 mm. Torque screws to 
14 Nm (124 1lbf ins) maximum. 

Rear Mounting 6 x M6 screws with suitable fastener locking 


device, minimum thread engagement 10 mm. Torque screws to 
8 Nm (72 Ibf ins) maximum. 
a 


NZ 


Fit 73 mm stub exhaust pipes or installation exhaust system, 
using gaskets supplied (refer to Installation Drawing) and 
torque tighten bolts to 6 Nm (53 lbf ins) maximum. 


2.6 Connect fuel line (customer supply) to carburettor fuel 
connector (FIGURE 5-1). Ensure a fuel filter 50 microns 
(0.002 in) is incorporated in fuel line. 


died Connect throttle cable (customer supply) to carburettor throttle 
lever (FIGURE 5-1). 


IDLE SPEED 
SCREW 














on | se |\ EE 
e 7 © 
\ ES | ) a | 
anal <a 























_ 
| — TRAVEL tO 2! 
TO OPEN | ae 
: turoTmLe T(J 
=a Ze Scio5\|( ao | 
— A J ta ~*~ 
= 1. =~ A ; 
Oj 
15mm(0.59 1in) 
FUEL INLET 
CONNECTOR 


FIGURE 5-1 : CARBURETTOR 


Ws 


9.8 Connect ignition cut-out wire to ignition switch (customer 


supply) (reference FIGURE 5-2). 


ae, Remove protection caps from spark plug holes and rotate engine 
crankshaft 4 - 5 times to clear excess oil from the engine. 
Check and gap, new spark plugs and install. 


Nm (22 lbf ft). 


NOTE: Spark plug gap, see general data. 


~ 










| SPARK PLUG 


YELLOW WIRE 


IGNITION COIL 


| SPARK PLUG - 


IGNITION COIL 


ie”, YELLOW WIRE 





ELECTRONIC MODULE 


BLACK WIRE. 





IGNITION CUT OUT 
7 oN 














IGNITION ON 


IGNITION OFF 


eS 





FIGURE 5-2 : IGNITION SYSTEM - CIRCUIT DIAGRAM 


74 


Torque to 29.80 


9.10 


WARNING: 


MAKE SURE ALL ROTATING PARTS ARE 
FREE OF OBSTRUCTIONS BEFORE 
STARTING THE ENGINE 


Start engine and set carburettor to give an engine idle speed of 
2400 rev/min or as_ required. (See adjustments and 
maintenance for setting of carburettor). 


~ 


CAUTION: 


ENGINE MUST BE UNDER NORMAL 
OPERATING LOAD (PROPELLER 
INSTALLED) BEFORE ENGINE 

IS STARTED. 


75 


6.0 


6.1 


6.2 


OPERATION 


WARNING: 


‘DO NOT FILL FUEL TANK TO MAXIMUM 
CAPACITY. COOL GASOLINE EXPANDS 
CONSIDERABLY, DUE TO HIGHER OUTSIDE 
TEMPERATURES, AND BUILDS UP PRESSURE 
IN FUEL TANK. THIS CAN CAUSE FUEL 
LEAKAGE AND A POTENTIAL FIRE HAZARD. 
ENSURE FUEL TANK IS PROPERLY VENTED. 


~ 


‘Recommended Gasoline 


Use only leaded automotive gasoline that has a minimum octane . 
rating of 92 RON. 


If recommended gasoline is not available, contact the engine 
manufacturer. ; 


CAUTION: | 
DO NOT USE UNLEADED GASOLINE. 
WARNING: 


GASOLINE IS EXTREMELY FLAMMABLE AND 
HIGHLY EXPLOSIVE UNDER CERTAIN | 
CONDITIONS. ALWAYS STOP ENGINE AND 
DO NOT SMOKE OR ALLOW NAKED FLAMES 
OR SPARK NEAR WHEN REFUELLING. 
ALWAYS MIX IN WELL-VENTILATED AREAS. 


Recommended Lubricant 


Use only (Petrofina) Finamix 2-stroke oil or Bel-Ray MC-1+. If 
recommended 2-stroke oil is not available, contact the engine 
manufacturer. 


CAUTION: 


DO NOT UNDER ANY CIRCUMSTANCES USE 
MULTIGRADE OILS. 


76 


6.3 


Fuel Mixture 


The correct fuel mixture is 1 part of oil to 25 parts of gasoline 
(43 oil mixture). 





Metric U.S. Measure Imperial 
Measure Measure 
160 cc oil to 9 fluid oz oil 6 fluid oz oil 
each 4 litres to each 1 U.S. to each 1 Imp 
of gasoline gallon of gallon of 
gasoline gasoline 


USE AT 25:1 RATIO, AS SHOWN ABOVE 


IMPORTANT: 


USING LESS THAN THE RECOMMENDED 
PROPORTION OF OIL MAY RESULT IN 
SERIOUS ENGINE DAMAGE FOR LACK OF 
SUFFICIENT LUBRICATION. USING MORE 
THAN THE RECOMMENDATIONS COULD 
CAUSE SPARK PLUG FOULING, ERRATIC 
CARBURATION,EXCESSIVE SMOKING AND 
FASTER-THAN-NORMAL CARBON 
ACCUMULATION. 


CAUTION: 


GASOLINE IS EXTREMELY FLAMMABLE AND 
HIGHLY EXPLOSIVE UNDER CERTAIN 
CONDITIONS. OBSERVE FIRE PREVENTION 
RULES, PARTICULARLY THE MATTER OF 
SMOKING. MIX FUEL OUTDOORS OR AT 
LEAST IN A WELL VENTILATED LOCATION. 


Use only clean oil and gasoline containers as even a very small 
particle of dirt can cause carburation problems. 


Mix fuel accurately in a remote tank. To ensure thorough 
mixing of oil and gasoline, fill container with gasoline to one 
quarter full, add oil and then add balance of gasoline. Mix 
thoroughly before using. 


NOTE: © Always use fresh gasoline. 





igi 


Startin 


6.4 


e 
e 


WARNING 


MAKE SURE ALL ROTATING PARTS ARE 


FREE OF OBSTRUCTIONS BEFORE STARTING 


ENGINE. 


CAUTION 


FLOW IS SUPPLIED. 


THE ENGINE IS AIRCOOLED AND MUST NOT 
BE RUN IN STATIC CONDITIONS UNLESS AN” 


ADEQUATE COOLING AIR- 


tuated on cylinder 


securely connected to spark 


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FIGURE 6-1 


78 


6.4.9 


6.4.6 


6.4.7 


6.4.8 


6.5 
6.5.1 
6.5.2 


6.6 


Origa cold engine (first start), move throttle control to 
approximately half-open position. 


NOTE: With the engine warm, it can be started 
at idle position. 


Turn the ignition switch to ON position. 
Crank engine until engine fires and continues to run. 


NOTE: A minimum starting speed of 1,000 rev/min is 
required. 


Move throttle control to ‘idle’ position. 


NOTE: Decompressors must be dePiseac’. « each time engine 
fires, but fails to start. 


Stopping ~ 

Move throttle control to 'idle' position. 
Turn ignition switch to OFF position. 
WARNING: | 


DISCONNECT SPARK PLUG LEADS BEFORE 
WORKING ON ANY PART OF ENGINE OR 
ACCESSORIES. 


Break-in (New engine) 
CAUTION: 
FOLLOW BREAK-IN PROCEDURE CAREFULLY. 


During the first 60 minutes, operate the engine for short 
periods of time at varying speeds up to three-quarters-open 
throttle. Avoid operating at low and continuous speeds to 
prevent build-up of heat. After this period use the engine as 
required without exceeding the specified maximum temperatures. 


NOTE: RE-TORQUE CYLINDER HEAD SCREWS AFTER 
INITIAL 2 HOURS RUNNING. 


NOTE: During break-in 10cc of "Molyslip E" per 5 litres 
of gasoline may be used to improve lubrication and 
protect the engine. Continued use of Molyslip E 
in the quantities specified will not adversely affect 
the engine and may prolong its useful life. 





79 


(CN 


(Gat 


7.3 


7.4 


INSPECTION AND SERVICE 
Check the following items before each period of operation. 


Fuel 





Before starting the engine, be sure that there is an adequate 
amount of fuel in the tank. The fuel ratio must be 25:1 
mixture of gasoline and oil. 


CAUTION: 


DO NOT FILL FUEL TANK COMPLETELY 
FULL. GASOLINE WILL EXPAND AS IT 
WARMS, CAUSING LEAKAGE AND A FIRE 
HAZARD IF THERE IS NOT ROOM FOR 
EXPANSION. 


Fuel Line Connections 


Check fuel line connections from fuel tank to engine for leaks. 
Make sure fuel line is firmly connected. 


Spark Plugs 


Keep spark plugs clean; a fouled plug can be the cause of 
serious engine problems. Make sure spark plug connections are 
tight. | 

Do not sand-blast, scrape or otherwise attempt to service spark 


plugs that are in a poor condition - best engine results are 
obtained with new spark plugs. 


Coolin g 


Make sure baffles and cooling shrouds (if fitted) are in place 
and secure. Check that air:intake openings are clean and 
unrestricted. Ensure cooling fins on the engine are clean and 
not damaged or broken. 


WARNING: 


DO NOT OPERATE ENGINE WITH DAMAGED 
OR BROKEN CCOULING FINS. 


80 


The engine is air cooled and must not be run in. sstatic 
conditions unless an adequate cooling airflow is supplied to keep 
the cylinder head temperature within the specified limit (see 
general data). 


WARNING: 


AFTER SERVICING, MAKE SURE ALL SAFETY 
GUARDS ARE REPLACED AND SECURED. 


81 


ee 


8. 


8, 


0 


1 


2 


ADJUSTMENTS AND MAINTENANCE 


WARNING: 


MAKE SURE IGNITION SWITCH IS IN OFF 
POSITION AND SPARK PLUGS LEADS ARE 
DISCONNECTED BEFORE WORKING ON ANY 
PART OF THE ENGINE OR ANCILLARY 
EQUIPMENT. 


Spark Plugs: 


Replace spark plugs every 25 running hours or as required. 


Remove spark plugs and check condition; replace if carbon 
fouled or if porcelain is cracked. The colour of the spark plug 
is a good indication of operating conditions. Take corrective 
action if other than normal operation is indicated. Refer to 
spark condition chart below: , 


BLACK TAN WHITE 
‘CARBON FOULING NORMAL OVERHEATING 


When installing spark plug, set plug gap (see general data) and 
clean the spark plug seat in the cylinder head. Install plug 
and gasket and torque tighten to 29,80 Nm (22 lbf ft.). 


Carburettor Adjustments 


WARNING: 


WHEN ADJUSTMENT IS MADE WITEH 
ENGINE RUNNING, BE EXTREMELY 
CAREFUL NOT TO TOUCH MOVING 
PARTS AND HOT AREAS. 


The tendency for the engine to "4 stroke” can be reduced by a 
Slightly lean mixture. A low idle speed will impair engine 
acceleration or throttle response when the throttle is opened 
rapidly. 


82 


If rich, the "4 stroking" will be pronounced and the engine will 
accelerate quickly up to a point - after which the rpm will not 
increase. A good rule is to have the idle mixture slightly rich, 
in order to avoid the possibility of having the engine stop, and 
to allow better throttle response. 


NOTE: All adjustments must be made with the air filter 
and/or inlet horn installed. If adjustments are 
made with the filter and/or inlet horn removed, 
the carburation will be incorrect when the filter 
and/or inlet horn is reinstalled. 





Adjustment of the high-speed needle jet must be done while 
monitoring the spark plug gasket temperatures and the engine 
speed. The high-speed adjustment is made with a hot engine, 
once the idle adjustments have been satisfactorily completed. 

a 
The engine should be fully warmed up before any adjustment is 
made to the carburettor. | 





LOW SPEED" HIGH SPEED 
NEEDLE JET NEEDLE JET 





IOLE SPEED SCREW 


83 


8.3 


Beek 





The initial carburettor "Hi" and "Lo" needle jets and the idle- 
stop screw are adjusted at the factory, if further adjustment is 
required due to installation and/or geographical location, then: 


= Screw idle-speed screw in or out to obtain required idle 
speed. 


- The low-speed needle jet should be adjusted to obtain a 
smooth idle. 


The carburettor will require repeated re-adjustments between 
the idle-speed screw and the low-speed needle jet, until a 
smooth idle is obtained at the-required idle speed... | 


NOTE: Clockwise adjustment of the adjusting screws 
decreases the amount of fuel/oil mixture 
delivered and vice-versa. 2 


Factors that can affect carburation 


In some instances, carburation which has been properly set up 
in particular conditions, can then be upset by certain factors, 
1.e.: 


change of fuel nee 
change in atmospheric pressure 
change in air temperature 
change in exhaust systems. 

If in any doubt, contact engine manufacturer. 


Check initially to see how easy the engine responds to the 
throttle when opened smoothly and fully. A certain amount of 
sluggishness is an indication of a lean mixture and it is 
necessary to quickly open the high-speed screw until the 
engine begins to "4 stroke". Again, open the throttle smoothly 
until it is fully open, while watching the rpms _ obtained. 
Continue this evaluation by slightly ‘leaning' the high-speed 
mixture each time the throttle response is checked and the rpms 
read. This is continued until the mixture needs to be richened 
in order to obtain the highest possible rpms with the propeller 
installed. 


The best initial choice is where the carburation is the richest 
possible but without an rpm drop. 


Following the running-in of the new engine a readjustment will 
be required. 


84 


8.3.2 


8.3.3 


NOTE: While optimising the carburation, it is necessary 
that the engine holds maximum rpm for a few 
seconds during each tachometer reading. For 
this reason a slightly rich mixture can prevent 
the risk of engine selzure, which can happen to 
new engines running lean. 





Change in atmospheric pressure and in air temperature 


Variations in pressure or temperature cause a change in the air 
density and consequently a change in the fuel/air ratio and 
further tuning may therefore become necessary. 


~ 


A decrease in atmospheric pressure, with consequent decrease 


in air density, causes a mixture enrichment and smaller needle 
jet openings will therefore be required. 


Altitude variations also produce changes in the carburation and 
they too cause changes in the air density. Prolonged use of 
an engine at an altitude higher than 1500 metres (5000 ft 
approx), for which. the carburation was originally set up for 
operation at around sea level, would require a change of needle 
jet settings in proportion to the pressure change. 


In this case too, a decrease in pressure should be compensated 
by a reduction of the needle jet openings. 


Furthermore, a lowering of air temperature produces an 
increase in air density and consequently a mixture weakening; 
therefore an increase in the needle jet openings is required. — 


Summarising, it can be said that any decrease in air pressure, 
increase in altitude or in air temperature should be compensated 
for by a decrease in the needle jet openings. 


Conversely, any increase in pressure or decrease in altitude or 
in temperature should be compensated by an increase in the 
needle jet openings. 


Changes in exhaust system 


The carburettor supplied is calibrated to suit a stub pipe 
exhaust system 73 mm long, if any other exhaust system is 
fitted, then the carburettor may require recalibration. 


85 


8.4 


Storage 


The storage of the engine is important to both its life and 
trouble-free operation. Before storage the following procedure 
should be carried out: 


Drain the carburettor by allowing the engine to run at idle 
speed with the fuel line disconnected, until the engine stops, 
indicating the carburettor has run dry. 


WARNING: 


MAKE SURE IGNITION SWITCH IS IN OFF 
POSITION AND DISCONNECT SPARK PLUG 
LEADS BEFORE WORKING ON ENGINE, 


Clean the exterior of the engine thoroughly and replace the 
keeper plate on the ignition flywheel. 


Remove spark plugs and pour approximately 5cc of the 
recommended 2-stroke oil (see general data) into each cylinder 
and crank the engine by hand a few times to spread the oil 
throughout the.cylinders. Replace the spark plugs leaving the 
spark plug leads disconnected. 


During storage crank the engine by hand each month, with the 
spark plugs removed. 


86 


ri 


Fa) 


10. 


11. 


i: 


LIST OF REFERENCES 


. Vandiver, J.L., RPH Preliminary Design, Trend Analysis and Initial Analysis of the NPS 


Hummingbird, Master’s Thesis, Naval Postgraduate School, Monterey, California, 
September 1992. 


. Bomo, L.M., Design and Construction of a 1/4 Scale NOTAR System for UAV and Full- 


Scale Research, Master’s Thesis, Naval Postgraduate School, Monterey, California, 
March 1993. 


. Fick, G.J., Aquisition, Design Modification, Assembly, and Ground Test of the NPS 


Hummingbird Remotely Piloted Helicopter, Master’s Thesis, Naval Postgraduate 
School, Monterey, California, September 1993. 


. King, R_L., Evaluation of Alternative Concepts for Rotorcraft Direct-Jet Thrusters for 


Circulation and Control Anti-torque Systems, Master’s Thesis, Naval Postgraduate 
School, Monterey, California, September 1993. 


. Booth, A.J., Final Modification of NPS Hummingbird Remotely Piloted Helicopter in 


Preparation for Flight, Master’s Thesis, Naval Postgraduate School, Monterey, 
California, December 1995. 


. Prouty, R.W., Helicopter Performance, Stability, and Control, PWS Publishers, 1986. 
. Taylor, John W.R., Munson, Kenneth, Jane’s All the World’s Aircraft, Jane’s 


Publishing Company, 730 Fifth Avenue New York, New York, 1980-1981. 


. Taylor, John W.R., Munson, Kenneth, Jane’s All the World’s Aircraft, Jane’s 


Publishing Company, 730 Fifth Avenue New York, New York, 1981-1982. 


. Taylor, John W.R., Munson, Kenneth, Jane’s All the World’s Aircraft, Jane’s 


Publishing Company, 730 Fifth Avenue New York, New York, 1982-1983. 


Incropera, Frank P., DeWitt, David P., Fundamentals of Heat Transfer, John Wiley & 
Sons, New York, 1985. 


Blair, Gordon P., The Basic Design of Two-Stroke Engines, Society of Automotive 
Engineers, Inc., 1990. 


Weslake Aeromarine Engines Ltd, OperatorsHandbook for WAE Limited 342 Engine 
Series 2100D, Normalair-Garrett, Ltd., 1985. 


87 


13. Aircraft Spruce and Secialty Company Catalog, Aircraft Spruce and Specialty, 
Fullerton, California, 1992-1993. 


14. Grainger’s Industrial and Commercial Equipment Supplies Catalog - Fall 1993 General 
Catalog No. 384, W.W.Grainger Inc., 1993. 


88 


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