Page | 30

send those signals to a computer where the data can be seen in a more user-friendly manner

using software such as LabView.

The DAQ system used for this engine test stand will be the National Instruments

CompactDAQ system, shown in Figure 12.38 This DAQ is an easy to use plug and play

instrument that will provide fast, accurate measurements. It also has a modular design, so that in

the future if there is a need for new tests or new equipment it can be added without having to buy

a new DAQ system. For now the test stand will have 32 channels for the variety of inputs of the

different sensors, which will be more than adequate for our purposes. For more detailed

information on this DAQ system, see the specification sheet in Appendix A.10. LabView

software will need to be created in the future work done on this test stand to properly examine

the data and form conclusions on what is found.38

FIGURE 12 - NATIONAL INSTRUMENTS COMPACTDAQ SYSTEM38

7.0 CURRENT DESIGN

7.1 Background

The engine test stand has been used in engineering practices for as long as engines have

been developed. The engine test stand is still an integral part of design process for modern

Page | 31

engines. The test stand allows the engine to be operated in different conditions and allows

measurements to be taken.39 Although today much of the data that is found with test stands can

be found theoretically with computers, the theoretical data needs to be verified with actual

measurements. For this reason, an engine test stand needs to be developed for small to medium

size engines that are more conducive to Unmanned Aerial Vehicle engines.

UAV engines are smaller than passenger aircraft engines. However, there are many

different types of UAV’s and the size of the engines varies as much as the mission for which

each is intended. For this reason, the UAV engine test stand design will be versatile enough to

handle many different types of engines.

In the past, engine stands have been relatively simple devices. In most cases, the engine

test stand was simply a device to hold an engine in place while it ran and various tests were

conducted. The engine test stand itself was made strong enough to withstand the forces the

engine produced. Engine test stands were usually developed to test a specific engine. For the

UAV engine test stand project, the goal is to develop a test stand that can be used for various

types of tests on various UAV engines.

7.1.1 Test Stand Designs

Previous engine test stands have been designed in the past. However, the test stand was

commonly developed for a specific engine. As a result, the test stand size was usually directly

related to the engine. Figure 13 shows an engine test stand that is mobile and can be used to test

automotive engines.40 Test stands have also been developed for smaller engines. Figure 14

shows an engine test stand for a small gas powered engine that is used with RC aircraft. Both

test stands demonstrate methods of securing the engine, sensors, and a display system.

Page | 32

FIGURE 13 - MOBILE ENGINE TEST STAND 40

FIGURE 14 - RC AIRCRAFT ENGINE TEST STAND 41

The Air Systems Design Laboratory at the University of Texas at Austin currently has a

small engine test stand which is used for smaller electrical motors for the Design, Build, Fly

teams or the UAV group. The test stand is designed to determine the static thrust of the engine

Displays data

Displays data

Page | 33

and the power drain. Although the UAV engine test stand will serve a much different mission

than the propulsion test, many lessons were learned and concepts derived from the study of this

design.

7.2 Previous Design

The previous UAV ETS design shown in Figure 15 was simple in nature. The engine test

stand incorporated the technology to take many different types of measurements including basic

engine performance parameters, such as temperature and RPM, and propeller efficiency. The

test stand was designed to be constructed out of steel because of its low cost, ease of

maintainability, ease of manufacture, high strength, and durability. However, the two beam

structure was weak and likely prone to excessive vibration during operation. As a result, a more

robust design was needed.

FIGURE 15 – PREVIOUS UAV ENGINE TEST MOUNT

Page | 34

7.3 Design Modifications and Current Design

The current design for the UAV Engine Test Stand contains many modifications that

were made over the semester. The current design is a much stronger and stiffer structure and

incorporates more sensors which increase the data acquisition capability; the current design of

the structure is shown in Figure 16. The structure is composed of steel, except for the engine

mounting bracket which is Aluminum 7075-T6. Steel is a readily available material which is

sufficiently strong for the ETS. Steel is also is relatively cheap, easy to manufacture, easy to

maintain, durable.

7.3.1 Test Stand Frame

The ETS design incorporates a rigid truss structure composed of two truss sections

attached by cross beams for the engine mount. The dual truss structure provides extra stiffness

for vibration dampening. The truss structure is composed of 3x3 in. square tubes that are 1/8 in.

thick and the cross beams are made of 1x1 in. square tubing. The truss structure is welded

together and welded to the lower frame which is made of 2x2 in. steel angles. Additionally, the

truss structure provides a convenient place to attach the terminal boards and modules necessary

for the sensors. The ETS is an open air design that allows maximum ambient airflow across the

engine. However, the stand may need an additional system to move the ambient air across the

engine to maximize heat transfer.

Page | 35

.

FIGURE 16 - CURRENT UAV ETS DESIGN

The ETS includes a rigid structure to mount the dynamometer which will be attached to

the engine shaft via couplers. Like the engine mount trusses, the dynamometer mounting truss is

composed of 3x3 in. square tubing that is 1/8 in. thick. The dynamometer mount is not, however

welded to the frame. This facilitates a large adjustment range along the axis of the engine

thereby allowing the stand to accept different sized engines. Additionally, the dynamometer

truss has two 2x2 in. square tubes that attach are welded to the truss cross member at a 45° angle

and sit atop the middle rail of the ETS structure. The angled beams are secure to the middle rail

with two large bolts. The bolts can be loosened to allow for axial adjustment and tightened to

secure the dynamometer truss.

The dynamometer is attached to the truss structure with a dynamometer mounting plate.

The dynamometer mounting plate is shown in Figure 17 and allows the dynamometer to be

adjusted in the horizontal and vertical directions. The elongated holes in the mount plate allow

for horizontal adjustments. Vertical adjustment is facilitated by four 1/2 in. bolts which are

Dynamometer Engine Mount

Radiator

Water Pump

threaded

the moun

Because

mount ne

still be u

If these a

adjustabi

T

is the rad

that is w

square tu

to nuts whi

nt and can

the recently

eeds to alter

sed but arms

arms are att

ility of the dy

The dynamom

diator shown

elded to the

ubes. The st

ich slide in t

be turned to

y-chosen dy

red accomm

s need to be

tached to the

ynamometer

FIGURE

meter requir

n at the front

e bottom rail

teel beams fo

the vertical

o the right

ynamometer

modate the ch

e designed w

e mount sho

r.

E 17 - DYNAM

es a water so

t of the ETS

l structure.

or the radiat

channels. A

to rail the d

has a mou

hosen dynam

which will wr

own in Figu

MOMETER MO

ource and a

S structure.

The steel fra

tor frame do

A long bolt e

dynamomete

unting face

mometer. T

rap around a

ure 17, the a

OUNTING PLA

fuel pump t

The radiator

ame for the

not need to

extents throu

er or to the

on the inpu

The existing

and bolt to th

arms will no

ATE

to operate. T

r is enclosed

radiator is c

o be as large

Pag

ugh the cent

left to low

ut shaft side

mount plate

he dynamom

ot alter the 3

The water so

d in a steel f

composed o

as the rest o

e | 36

ter of

wer it.

e, the

e can

meter.

3-axis

ource

frame

f 1x1

of the

Page | 37

structure because the stresses applied to the radiator are extremely small compared to the stresses

in the truss structure.

The pump for the dynamometer is located on the bottom frame of the ETS structure. The

placement of the pump is not germane to the design of the ETS structure. However, having the

pump placed lower than its water source allows for a wider selection of pumps. Also, having the

pump placed on the outside of the ETS allows for easy access for maintenance.

The engine will mount to the ETS via the engine mounting bracket as shown in Figure

16. The engine mounting bracket is shown in Figure 18. The engine mounting bracket is

composed of the aluminum allow 7075-T6 to prevent dissimilar metal corrosion on the UAV

engines. The hole on the top and bottom of the mounting bracket is used to attach the bracket to

the ETS with a bolt. The teeth shown in Figure 18 prevent torsional motion of the engine while

tests are being performed. The engine mount plate is designed to ensure that the axis of the

mount is collinear with the engine’s axis of rotation. The aluminum alloy has a yield strength of

503 MPa which is sufficient for the stresses placed on the mounting bracket. The mounting

bracket is easily removed without damaging the ETS or engine. A separate mounting bracket

will need to be manufactured for engines with different mounting patterns. The aluminum used

is widely available, easy to maintain, easy to manufacture. Also, the cost is relatively low

because it is a small component of the ETS.

Page | 38

FIGURE 18 - ENGINE MOUNTING BRACKET

7.3.2 Sensor Configuration

FIGURE 19 - ENGINE SENSORS PLACEMENT

Page | 39

The integration of the sensors into the engine test stand is necessary to take accurate and

precise measurements. Figure 19 shows the placement of the sensors on the test engine. The red

lines represent the wires from the thermocouples. Thermocouples will be mounted to the engine

block, cylinder heads, and exhaust. The wires from the thermocouples will run to the truss

section of the engine test stand and be connected to a BSJ-K barrier jacket. The barrier jacket

will be attached to a standard terminal strip on the engine test stand as shown in Figure 20.

FIGURE 20 - BSJ-K BARRIER STRIP ATTACHED TO A TERMINAL BOARD

The wires from the thermocouples are nickel-chromium and nickel-aluminum. The wires

will be sufficiently large to ensure that no heat is shunted away from the measurement area.

Spades made of the same material, SLK-20 spades, will be used to attach the wires to the barrier

strip as shown in Figure 21. The wires will run from the other side of the terminal strip with

twisted pair extension wires to the DAQ system completing the circuit for measurements. The

use of terminal boards is necessary when utilizing long wires in thermocouple circuits. The

wires will be attached to the engine test stand and terminal boards ensuring proper strain relief

from mechanical stresses and vibrations.

Barrier Strip

Page | 40

FIGURE 21 - NI-AL AND NI-CR LUGS

The brown line on Figure 19 represents the wire from the O2 sensor to the DAQ board.

The O2 sensor is placed in the exhaust of the engine and the wires will run to the ES430 Lambda

module, which will be attached to the engine test stand. The connections for the O2 sensor and

the ES430 Lambda module are cannon-plug type connections and are easily manufactured. The

ES430 module will output the data to the DAQ system for data collection.

The green line represents the wires from the pressure sensor. The pressure sensor will be

placed on the intake manifold to determine the operating pressure of the engine. Wires will be

soldered to pins 1, 2, and 3 on the pressure sensor; the pressure sensor contains six pins however,

pins 4, 5, and 6 are internal connections. Pin 1 is the output voltage, pin 2 is the ground, and pin

3 is the voltage source. The wires from pins 1, 2, and 3 will be connected to a terminal board on

the engine test stand with high temp 12 gauge wires to ensure no damage will occur to the wires.

The other side of the terminal board will utilize standard 12 gauge wire to complete the circuit to

the DAQ system. The wires will be connected to the engine test stand to provide proper strain

relief. The use of the terminal board allows easy sensor replacement and the use of standard

wires for the longer runs to the DAQ.

Page | 41

The blue line in Figure 19 represents the wires for the dynamometer. The dynamometer

is connected directly to the shaft of the engine with the use of couplers. The dynamometer

output is a 5 pin cannon plug type connection. The wires from the connection will be attached to

the dynamometer frame portion of the engine test stand ensuring proper routing and strain relief.

The wires will run to a terminal board attached to the engine test stand to allow for slack in the

wire which is necessary to adjust the dynamometer’s position. The standard 12 gauge wires will

be attached to the opposite side of the terminal board and will be run to the DAQ.

Several other sensors are not shown in Figure 19 due to their placement. A hot wire

anemometer will be used in the intake pipe to calculate air flow. Additionally, a digital

manometer will be used to determine pressure and used as a redundant system for the hot wire

anemometer. These sensors both utilize a standard RS-232 connection to output the data. The

RS-232 for the hot wire anemometer can be purchased with the sensor. However, the cable will

most likely need to be extended to connect to the DAQ system. The manometer RS-232 will

also need to be extended to reach the DAQ system for data output.

The fuel flow sensor will be placed in the fuel delivery system. The fuel flow sensor

contains three wires. The red wire is the 12-15 (+) VDC while the black is the 12-15 (-) VDC.

The white wire is the transistor output. These wires will run to a terminal board and then to the

DAQ system.

7.3.3 Fuel System

The purpose of the fuel system is to mix, filter, and deliver to the engine a variety of

fuels. The system is designed to be self-sufficient which means that it will provide fuel to the

engine driven fuel system without relying upon the engine for power. Being independent of the

Page | 42

engine will make the test stand’s fuel system more versatile because no adjustments will need to

be made when the type of engine is changed. Additionally, to improve the efficiency of testing

different fuel mixture ratios, the fuel system was designed so that precise metering of each of the

components of the mixture. Finally, because the components will not be premixed, the system is

designed to ensure a homogeneous mixture will be delivered to the engine fuel system. The

schematic of the UAV ETS fuel system is given in Figure 22 and the system components are

listed in Table 2 - Fuel System Components Table 2.

FIGURE 22 - SCHEMATIC OF THE UAV ETS FUEL SYSTEM

Page | 43

Part  Part Number Supplier/Manufacturer 

Solenoid Valve   4738K138   McMaster‐Carr Needle Valve  7824K12  McMaster‐Carr Check Valve  7768K26  McMaster‐Carr Ball Valve  4629K11  McMaster‐Carr Sample Valve  5049K4  McMaster‐Carr Fuel Pump  12‐815‐1 Holley Pressure Regulator  17‐704 Holley Fuel Filter  555‐15005  Jegs Fuel Filter Element  555‐15007  Jegs 3/8" Steel Tubing (25')  555‐63036 Jegs 

TABLE 2 - FUEL SYSTEM COMPONENTS

7.3.3.1 Pump and Supply

Prior to the fuel pump, the different fuels are separate and join through a four-way

valve just before entering the pump.

7.3.3.2 Fuel tanks

As can be seen in the schematic, the UAV ETS fuel system has three fuel tanks so that it

can hold and mix as many different fuel types. The type of fuel container that is used will

depend on the hazardous materials regulations at the location at which the stand is constructed.

However each fuel tank should hold at least five gallons to ensure an adequate supply to operate

the engines for long periods of time if the need arises.

Each fuel tank has an inline filter, a needle valve, and a check valve. The inline filter is a

10 micron filter designed for gasoline and alcohol applications. The needle valve will provide

precise metering of the fuel, though it will need to be manually adjusted. Additionally, the

needle valve will act as a shutoff for its respective tank when that tank is not needed or the

engine is not operating. Finally, each fuel tank will have a check valve to prevent inadvertent

mixing of different fuels within the tanks.

Page | 44

The fuel pump is an electric inline pump manufactured by Holley Performance Products,

Inc. The pump provides a maximum of 120 gallons per hour (pph) at 9 psi and is compatible

with alcohol fuels. Mounting and operation instructions for the fuel pump are provided in

Appendix D.

7.3.3.3 Mixing Unit

The mixing unit is installed down the line from the fuel pump to ensure complete

mixing of the fuels. The mixing unit is a basic canister-type mixer. The pressurized fuels, which

are already flowing together in a single tube, enter the mixer in the center of the top of the

canister. The fuel leaves the tube approximately ¼ in. above the bottom of the canister and fills

the canister. This creates turbulent flow in the canister which will mix the fuel. The mixed fuel

will then be forced out of the top of the canister and, because water and heavy particulates are

denser than fuel, they should remain in the canister. Additionally, three 90 ° bends on the inlet

and outlet sides of the mixing canister should further mix the fuel. Finally, if the fuel is

premixed, the mixing unit can be bypassed. The mixing unit is shown in Figure 23.

FIGURE 23 - ISOMETRIC AND CUTAWAY VIEW OF THE MIXING UNIT

Page | 45

7.3.3.4 From the Mixing Unit to the Engine

Between the mixing unit and the connection to the engine fuel system are the pressure

regulator, flowmeter, fuel sample port, and the emergency shutoff valve.

7.3.3.5 Pressure Regulator

The pressure regulator prevents pressure fluctuations and over pressurization of the

engine fuel system and provides the operators the ability of adjust the fuel supply pressure. The

manually-adjusted, two-port pressure regulator was chosen to accompany the fuel pump used in

this design as suggested by the manufacturer. The regulator is made by Holley Performance

Products, is compatible with alcohol fuels, and can be adjusted from 4.5 to 9 psi.

7.3.3.6 Flowmeter

The flowmeter is necessary to measure the mass flow rate of the fuel and is discussed in

Section 6.8.

7.3.3.7 Sample Port

The fuel sample port will allow the operators to sample the fuel for analysis and should

be placed far enough from the engine so this can be safely accomplished while the engine in

running. The port is a simple stop cock valve which is available from McMaster-Carr.

7.3.3.8 Emergency Shutoff Valve

To enhance safety and help protect the engine from damage due to a run-away throttle,

the fuel system incorporates an emergency shutoff valve. This valve is an electric solenoid valve

which is spring-loaded closed and energized to the open position. That means that if the test

stand facility looses power, the valve will automatically close and shutoff the engine.

Page | 46

Additionally, the operator’s emergency shutoff switch only needs to break the circuit to the

shutoff valve in order to stop the flow of fuel to the engine. Because of this feature, the shutoff

valve and switch should be on the same circuit as the fuel pump.

7.3.3.9 Tubes and Fittings

The fuel system was designed to be made of 3/8 in. steel tubing. This tubing is available

from many auto-parts suppliers but a system from JEGS which includes flare fittings is

recommended. Other fittings and adapters may be required to complete the system.

7.3.4 Recirculating Water System

The UAV ETS design incorporates a recirculating water system to support the

dynamometer. The system was designed to exceed the minimum specifications provided by

Kahn Industries, Inc., the dynamometer manufacturer, found in Appendix A.1. The system is

comprised of a radiator, an electric fan, a water pump, and a mesh screen. A schematic of the

water system is given in Figure 24 and the components of the system are listed in Table 3.

FIGURE 24 - WATER SYSTEM SCHEMATIC

Page | 47

Part  Part Number  Supplier/Manufacturer 

Radiator  555‐52009  Jegs Radiator Fan  555‐52116  Jegs Water Pump  4272K23  McMaster Strainer  43935K55  McMaster 

TABLE 3 - WATER SYSTEM COMPONENTS

7.3.4.1 Radiator and Fans

The water exiting the dynamometer will be at a maximum temperature of 140 °C. To

cool the water an aluminum, Chevrolet-style 2-core radiator and a dual electric fan system

manufactured by Jegs High Performance will be used.42 The radiator has 1 in. diameter core

tubes and is 31 in. wide and 19 in. tall. The dual electric fans will provide 2600 cfm of airflow

and are 24 in. wide by 15 in. high.43

7.3.4.2 Water Pump and Strainer

The water pump must provide a minimum of 6 gallons per hour per horsepower (gal/hr-

hp) at 50 psi and the system must have a 40 mesh screen. This will be accomplished using a 3

hp gear pump from McMaster-Carr. This pump will provide 24.8 gpm at 100 psi.44 The strainer

will be a 40 mesh screen from McMaster Carr.45

7.4 Engine Starter

Both electrical and mechanical starters are used in association with UAV engines.

Typically, midsized engines are started using an onboard electric starter motor or starter

generator to supply the engine with the initial torque. However, some engines require a

mechanical starter, similar to a modified hand-held drill, which is fitted to the engine and used to

create the required torque. Because each engine then has its own specifications, a starter will not

Page | 48

be included in the test stand itself, but should be acquired with each engine that is to be tested

using the ETS.

8.0 SAFETY

The safety of the personnel using the UAV ETS was an important factor to consider

when designing the ETS. As a result, several safety measures were designed for implementation

into the test stand and facility.

8.1 Safety shutoff

The first safety measure for the UAV ETS is an emergency shutoff valve in the fuel

system. The shut-off valve is an electric solenoid valve that is spring loaded to the closed

position. Under normal operation, the solenoid is energized to the open position thus allowing

fuel to flow freely. In the event of a power loss or an emergency stop the solenoid is de-

energized and the spring returns the solenoid to the closed position preventing fuel from flowing.

This will help prevent fuel spills and fires.

In addition to the emergency fuel shutoff valve, the remote throttle control unit contains a

built in safety measure. If the signal coming from the remote throttle control is interrupted for

any reason, the throttle returns automatically to the closed position which will cause the speed of

the engine to reduce to idle. Retarding the engine speed to idle will prevent damage to the

engine from overspeed if the signal from the throttle control is lost.

8.2 Building exhaust

The engine exhaust will be removed from the test facility to prevent carbon monoxide

poisoning and soot buildup in the lab. The exhaust system will be comprised of ventilation tubes

that connect to the exhaust of the engine and be routed outside the facility through a fan. The