unmanned aerial vehicle propulsion sean brown a project
TRANSCRIPT
Unmanned Aerial Vehicle Propulsion
by
Sean Brown
A PROJECT
submitted to
Oregon State University
University Honors College
in partial fulfillment of
the requirements for the
degree of
Honors Baccalaureate of Science in Mechanical Engineering
(Honors Associate)
Presented February 27th, 2015
Commencement June 2015
2
4
5
Β©Copyright by Sean Brown
February 27th, 2015
All Rights Reserved
6
Unmanned Aerial Vehicle Propulsion
by
Sean Brown
A PROJECT
submitted to
Oregon State University
University Honors College
in partial fulfillment of
the requirements for the
degree of
Honors Baccalaureate of Science in Mechanical Engineering
(Honors Associate)
Presented February 27th, 2015
Commencement June 2015
8
TABLE OF CONTENTS
Table of Contents ............................................................................................................................. 8
1 Introduction ............................................................................................................................ 12
2 Propulsion Systems ................................................................................................................ 12
2.1 Piston-Propeller.............................................................................................................. 12
2.2 Gas turbine ..................................................................................................................... 12
2.2.1 Turbojets ................................................................................................................ 12
2.2.2 Turboprops ............................................................................................................. 13
2.2.3 Turbofans ............................................................................................................... 13
2.2.4 Afterburner ............................................................................................................. 13
2.3 Hypersonic ..................................................................................................................... 13
2.3.1 Ramjets and Scramjets ........................................................................................... 13
2.3.2 Pulse Detonation .................................................................................................... 14
2.4 Rocket ............................................................................................................................ 14
2.4.1 Solid Propellant ...................................................................................................... 14
2.4.2 Liquid Propellant ................................................................................................... 14
2.4.3 Hybrid Propellant ................................................................................................... 15
2.5 Electric ........................................................................................................................... 15
2.5.1 Battery Powered ..................................................................................................... 16
2.5.2 Fuel Cell ................................................................................................................. 17
2.5.3 Solar Electric .......................................................................................................... 18
3 Parameters comparison .......................................................................................................... 18
3.1 Velocity .......................................................................................................................... 18
3.2 Weight/Payload .............................................................................................................. 21
3.2.1 Cargo Aircraft ........................................................................................................ 21
3.2.2 Heavy Transportation Aircraft ............................................................................... 21
3.2.3 Midsize Transportation Aircraft ............................................................................. 22
3.2.4 Light Transportation Aircraft ................................................................................. 22
3.2.5 Military Fighter Aircraft ........................................................................................ 23
3.2.6 Light Aircraft ......................................................................................................... 23
3.2.7 Light-Sport Aircraft ............................................................................................... 24
3.2.8 Ultralight Aircraft .................................................................................................. 24
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3.2.9 Conclusion ............................................................................................................. 25
3.3 Mission ........................................................................................................................... 26
3.3.1 Stealth .................................................................................................................... 26
3.3.2 Reconnaissance ...................................................................................................... 26
3.3.3 Air Superiority ....................................................................................................... 26
3.3.4 Attack Aircraft ....................................................................................................... 26
3.3.5 Bombers ................................................................................................................. 27
3.3.6 Trainers (Military and Private) .............................................................................. 27
3.3.7 Aerobatic Aircraft .................................................................................................. 27
3.3.8 Transportation ........................................................................................................ 27
3.3.9 Amphibious Aircraft .............................................................................................. 27
3.3.10 Conclusion ............................................................................................................. 27
4 Parameters Comparison of UAVs .......................................................................................... 28
4.1 Types of UAVs .............................................................................................................. 28
4.1.1 Micro Air Vehicles ................................................................................................ 28
4.1.2 Vertical Takeoff and Landing (VTOL) .................................................................. 29
4.1.3 Low Altitude, Short Endurance (LASE) & Low Altitude, Long Endurance
(LALE) 29
4.1.4 Medium Altitude, Long Endurance (MALE)......................................................... 30
4.1.5 High Altitude, Long Endurance (HALE) ............................................................... 30
4.1.6 Conclusion ............................................................................................................. 31
4.2 UAV Missions ............................................................................................................... 32
4.2.1 Military .................................................................................................................. 32
4.2.2 Research ................................................................................................................. 34
4.2.3 Commercial ............................................................................................................ 36
4.3 Electric Motor vs. Internal Combustion Engine: Case Study ........................................ 38
4.4 How UAV Engine Types Compare to Manned Engine Types ...................................... 39
5 Engine Research..................................................................................................................... 39
5.1 Introduction .................................................................................................................... 39
5.2 Experimental Setup ........................................................................................................ 40
5.2.1 Engine Assembly ................................................................................................... 40
5.2.2 Test Stand Construction ......................................................................................... 42
5.2.3 Data acquisition systems ........................................................................................ 43
5.2.4 Systems verification ............................................................................................... 45
5.2.5 Safety features ........................................................................................................ 46
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5.3 Data Collection .............................................................................................................. 46
5.3.1 Reason for data collection ...................................................................................... 46
5.3.2 Procedures .............................................................................................................. 46
5.4 Data Analysis ................................................................................................................. 47
5.4.1 Initial Data Analysis .............................................................................................. 47
5.4.2 Secondary Data Analysis ....................................................................................... 50
5.5 Results ............................................................................................................................ 51
5.5.1 Power, torque and efficiency ................................................................................. 51
5.5.2 Brake Specific Fuel Consumption of Different Fuels ............................................ 52
5.5.3 Brake Mean Effective Pressure .............................................................................. 53
5.5.4 Published Data Comparison ................................................................................... 56
5.5.5 Uncertainty Analysis .............................................................................................. 57
5.6 Discussion ...................................................................................................................... 58
5.7 Conclusions .................................................................................................................... 59
6 References .............................................................................................................................. 59
7 Appendix A: Experimental Data ............................................................................................ 62
Figure 1: Pratt & Whitney R-2800, a 2,000 hp radial piston-prop engine ("Vought F4U
Corsair,") ........................................................................................................................................ 12
Figure 2: Pratt & Whitney F-100, engine for F-15 Eagle ("McDonnell Douglas F-15 Eagle,") ... 13
Figure 3: Diagram of a scramjet ("Scramjet," 2010 ) .................................................................... 14
Figure 4: One of the space shuttle main engines during testing ("Space Shuttle Main Engine Test
Firing," 1981) ................................................................................................................................. 15
Figure 5: The all-electric Yuneec E430, taking off at just 40mph ("Yuneec International E430,"
2009) .............................................................................................................................................. 16
Figure 6: Energy density of common combustibles in [MJ/kg] (Ronneau, 2004 ) ........................ 17
Figure 7: Propulsion system speed limits (Raymer, 2012) ............................................................ 19
Figure 8: Specific fuel consumption trends at typical cruise altitudes. (Raymer, 2012) ............... 20
Figure 9: Power available for (a) a piston-prop and (b) a jet engine. (Anderson, 2012) ............... 20
Figure 10: Lockheed Martin C5 Galaxy taxing on the runway (Lewis, 2009) .............................. 21
Figure 11: Airbus A380 in flight (Lewis, 2009) ............................................................................ 22
Figure 12: Boeing 787 in flight (Lewis, 2009) .............................................................................. 22
Figure 13: Bombardier Q400 in flight (Lewis, 2009) .................................................................... 23
Figure 14: Beechcraft T-6 Air Force trainer ("Beechcraft T-6 Texan II," 2003) ........................... 23
Figure 15: Epic Victory, a very light jet, in low altitude flight ("Epic Victory," 2007) ................ 24
Figure 16: Ikarus C42, a certified LSA (Lewis, 2009) .................................................................. 24
Figure 17: An ultralight aircraft in flight (Lewis, 2009) ................................................................ 25
Figure 18: Aerovironment's Nano Hummingbird (Watts et al., 2012). ......................................... 29
Figure 19: Dragonflyer X6 VTOL UAV (Watts et al., 2012). ....................................................... 29
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Figure 20: LASE and LALE on display at the 2005 Naval Unmanned Aerial Vehicle Air Demo.
Pictured are the RQ-11A Raven (1), Dragon Eye (2), Skylark (3), Evolution (4), Arcturus T-15
(5), NASA FLiC (6), Tern (7), RQ-2B Pioneer (8), and Neptune (9) (Watts et al., 2012). ........... 30
Figure 21: A maintenance crew preparing a Global Hawk for flight (WikipediaCommons,
2006). ............................................................................................................................................. 31
Figure 22: Boeing YQM-94A, the 1968 turbojet reconnaissance UAV ("Boeing YQM-94A
Compass Cope B," 2013) ............................................................................................................... 33
Figure 23: Two Ryan Firebees ready for deployment from a DC-130 ("DC-130 Mounted
Firebees,") ...................................................................................................................................... 33
Figure 24: The MQ-9 Reaper taking off in Afghanistan, 2007 ("MQ-9 Afghanistan Takeoff,") .. 34
Figure 25: Shown are the six UAS Test Site locations across the United States (FAA, 2013) ..... 35
Figure 26: VTOL UAV in use at the 2014 Sochi Winter Olympics .............................................. 36
Figure 27: The Elbit Hermes 900 in flight, capable of a 770lb payload ........................................ 37
Figure 28: 3W-28i engine (3WModellmotorenGmbH) ................................................................. 41
Figure 29: The carburetor used with the 3W engine (3WModellmotorenGmbH) ......................... 41
Figure 30: Spark plug ignition system ("Agape Racing and Hobby, LLC.,") ............................... 42
Figure 31: APC 17x12 propeller, one of the three used on the 3W engine ("APC Propellers,") ... 42
Figure 32: Assembled engine attached to test stand ...................................................................... 43
Figure 33: Sean Brown recording engine speed data off the Tektronix DPO3012 oscilloscope ... 44
Figure 34: PDI DM-930 Multimeter being used to measure ambient temperature ....................... 44
Figure 35: Test cell energy flow diagram ...................................................................................... 45
Figure 36: Power verses RPM for 12x6 and 13x8 propellers. ....................................................... 48
Figure 37: Coefficient of power verses RPM for 17x12 propeller ("UIUC Propeller Databases,"
2015) .............................................................................................................................................. 49
Figure 38: Power vs. RPM for all three propellers ........................................................................ 51
Figure 39: Engine efficiency vs. RPM for three different propellers ............................................ 52
Figure 40: Brake specific fuel consumption vs. RPM for 13x8 prop ............................................ 52
Figure 41: Brake specific fuel consumption vs. RPM for 12x6 prop ............................................ 53
Figure 42: Brake specific fuel consumption vs. RPM for 17x12 prop .......................................... 53
Figure 43: Brake mean effective pressure vs. RPM for 13x8 prop ................................................ 54
Figure 44: Brake mean effective pressure vs. RPM for 12x6 prop ................................................ 55
Figure 45: Brake mean effective pressure vs. RPM for 17x12 prop .............................................. 55
Figure 46: 3W-28i published data (Rowton, 2014) ....................................................................... 57
Table 1: Summary of Engine Type by Max Takeoff Weight ........................................................ 25
Table 2: Summary of Engine Type by Mission ............................................................................. 27
Table 3: Summary of UAV types with ceiling, endurance and engine type .................................. 31
Table 4: Case study variables ........................................................................................................ 39
Table 5: 3W-28i Engine specifications (3WModellmotorenGmbH) ............................................. 40
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1 INTRODUCTION
This thesis is made up of an extensive literature review and an experimental project. The purpose
of the literature review is to familiarize the reader with the types of aircraft propulsion used in
both manned and unmanned systems. Following the literature review, the experiments conducted
are described in detail. These experiments involve the assembly of a UAV engine, construction of
a test stand, and collection of data for comparing to already published data. Both the literature
review and experimental portion of this project were conducted under mentor Dr. Chris Hagen,
Energy Systems Engineering Professor at OSU Cascades.
2 PROPULSION SYSTEMS
2.1 PISTON-PROPELLER Piston-propeller combination engines are operated by
compressing outside air, mixing with fuel, burning the
mixture and extracting energy from the resulting high
pressure gasses (Raymer, 2012). This energy, usually
converted into shaft work, is then used to drive a
propeller. These systems were the first to be used in
powered flight, starting with the Wright Brothersβ
gasoline engine. Both reciprocating and rotary piston-
prop systems are used in aviation (Griffis, Wilson,
Schneider, & Pierpont, 2008). On the right is a very
powerful version of a piston-prop engine: the 2000 hp
Pratt & Whitney R-2800-8 radial engine. Eventually, a
need for more powerful engines lead to the invention of
gas turbine systems for aircraft.
2.2 GAS TURBINE Gas turbine engines have been used on aircraft heavily since the end of World War II. These
engines allowed for much faster and heavier aircraft than conventional piston-prop engines. The
many type of turbine engines are outlined below.
2.2.1 Turbojets
A turbojet system uses a series of fans to pressurize air into a combustion chamber, which is
continuously fed with fuel. The fuel and air are continuously burned, which pressurizes the air
even more, leading to high velocity exhaust exiting the system. This high velocity exhaust is what
produces thrust (Griffis et al., 2008). There are two different kinds of compressors used in
turbojet systems: a centrifugal compressor uses centrifugal force to push the air into an
increasingly narrow channel, while axial compressors use blade aerodynamics to force the air into
the same type of channel (Raymer, 2012). Unfortunately, turbojet systems are not very effective
at low speeds, and are overall not efficient, leading to the development of turboprops and
turbofans.
Figure 1: Pratt & Whitney R-2800, a 2,000 hp radial piston-prop engine ("Vought F4U Corsair,")
13
2.2.2 Turboprops
For an increase in efficiency of a pure turbojet engine, an extra turbine is added to extract power
from the exhaust gasses for the purpose of accelerating additional outside air. A turboprop uses
nearly all the turbojet output to drive a propeller. The propeller is able to accelerate a larger area
of outside air, giving it a higher efficiency (Raymer, 2012). A turbo-shaft uses the same principle
but converts the work to a shaft, not a propeller. Turbo-shafts are used extensively for rotorcraft
(Griffis et al., 2008).
2.2.3 Turbofans
A turbofan uses the extracted mechanical power on a ducted fan of one or more stages. This fan is
able to accelerate more air which, as stated above, increases efficiency. Often, turbofans are split,
with some of the air bypassing the engine to exit unburned, while the remainder is ducted into the
engine for further compression and burning (Raymer, 2012).
2.2.4 Afterburner
Inside a turbine system, the ideal air to fuel mixture ratio is about 15 to 1 for gasoline fuel.
Unfortunately, burning fuel at this ratio would create heats much too high for turbine materials to
handle, resulting in a destruction of the propulsion system. To combat this, excess air is used to
cool the system, creating an air to fuel ratio of about 60 to 1. The result is that about 75% of the
exhaust is unused hot air. At this point, downstream of the turbine, fuel is injected, mixed, and
burned. This process, known as afterburning, can double thrust. Because the burn happens in a
relatively low pressure volume and some of the oxygen is already depleted, this is an inefficient
use of fuel, doubling the fuel consumption per pound of thrust. Physically, the afterburners are
very large, doubling the length of the turbofan or turbojet engine, but only add 20-40% to engine
weight since they are mostly
hollow (Raymer, 2012). Shown
to the left in Figure 2 is a
cutaway of a Pratt & Whitney F-
100. The entire right side of the
engine, glowing orange, is the
afterburner.
2.3 HYPERSONIC Hypersonic engines are used mostly on experimental aircraft and high velocity missiles. These
engines, as the name suggest, allow for the aircraft to far exceed the speed of sound and speeds
reached by any turbine engines. A number of hypersonic engines are outlined in the following
sections.
2.3.1 Ramjets and Scramjets
At very high speeds, the inlet duct itself is able to compress air enough for fuel addition and
combustion to occur. Ramjets can operate at speeds of Mach 0.5 and below, but do not become
more efficient than turbojets until about Mach 3. A scramjet is a ramjet that operates with
supersonic internal flow (supersonic combusting ramjet), reducing the massive drag associated
with slowing down airflow to subsonic speeds. Injecting, mixing, and burning a fuel air ratio at
Figure 2: Pratt & Whitney F-100, engine for F-15 Eagle ("McDonnell Douglas F-15 Eagle,")
14
supersonic speeds is not easy and only effective when the scramjet is traveling faster than Mach 5
or 6. The biggest downside is that ramjets and scramjets need another propulsion source to
accelerate to the supersonic operation speeds; typically a turbojet or solid rocket booster is used
(Raymer, 2012). A diagram of the principle behind scramjets is shown below.
Figure 3: Diagram of a scramjet ("Scramjet," 2010 )
2.3.2 Pulse Detonation
Pulse detonation engines (PDEs) are under development for the purpose of increasing fuel
efficiency. Unlike a ramjet, where fuel is continuously fed, on a PDE it is βpulsedβ. The fuel is
ignited and burned so rapidly that it is considered to be a detonation rather than a deflagration.
These detonations move so quickly through the engine that there is not enough time for the fuel-
air mixture to expand, giving it higher efficiency based on it being a constant-volume combustion
(Tangirala, 2009).
2.4 ROCKET Rocket engines are used for craft that travel at extremely high altitudes because they are able to
bring along their own oxidizer to mix directly with the fuel. Unlike their air-breathing
counterparts, rocket engines are not reliant on the atmosphere for operation. They are also used
when a high thrust to weight ratio is required, as rocket engines are relatively simple and light
weight. The three main types of rocket engines are outlined below.
2.4.1 Solid Propellant
The components of a solid propellant motor are the propellant grain, igniter, motor case, exhaust
nozzle, and mounting provisions. Solid propellant motors historically have zero or very few
moving parts. Compared to liquid rockets, solid rockets are relatively simple and require little
servicing. They cannot usually be inspected prior to use and thrust cannot be randomly varied
(Sutton, 2000).
2.4.2 Liquid Propellant
A liquid propellant engine system generally consists of one or more thrust chambers, one or more
tanks to store propellants, a feed mechanism to force the liquids into the thrust chamber, a power
source to furnish the energy required by the feed mechanism, suitable plumbing or piping to
transfer the liquids, a structure to transmit the thrust forces, and control devices to initiate and
regulate the propellant flow rates. The principle advantages of liquid propellant rocket engines
15
are high performance, randomly variable duration for each start, repeated restarts, reusable for
several flight missions, and randomly variable thrust and thus flight path control (Sutton, 2000).
Shown below in Figure 4 is one of the space shuttle main engines, a liquid fuel engine that ran on
liquid hydrogen and liquid oxygen.
Figure 4: One of the space shuttle main engines during testing ("Space Shuttle Main Engine Test Firing," 1981)
2.4.3 Hybrid Propellant
Hybrid rockets make use of various combinations of solid and liquid propellants. The main
advantages of a hybrid rocket are low cost for applications where economy is essential and low
thrust compared to solid or liquid motors is acceptable. Hybrids also provide the benefits of a
simple solid grain fuel, a liquid for nozzle cooling and thrust modulation, start-stop-restart
capabilities, good storability traits, and safety during storage and operation (Sutton, 2000).
2.5 ELECTRIC There has been a high amount of traction gained recently with manned electric aircraft. The
winner of the 2011 NASA Green flight Challenge was able to achieve an electric equivalent of
404mpg per passenger and speeds of over 100mph. Yuneec International is claiming their E430
to be the worldβs first commercially produced electric manned airplane, with flight duration of up
to 3 hours and cruising speed of 52mph. Even Cessna has an electric airplane currently in
development (Raymer, 2012).
16
Figure 5: The all-electric Yuneec E430, taking off at just 40mph ("Yuneec International E430," 2009)
The U.S. military begun using electric power aircraft as reconnaissance UAVs in 1986 and has
continued using them since (Raymer, 2012).
Electric propulsion systems have no emissions, and can be over 90% efficient, compared to about
20% efficiency of gasoline engines. The systems are easy to start, are impartial to orientation, and
have much longer life cycles than fuel based engines. Unfortunately these systems combined with
their power supply weigh much more and take longer to βrefuelβ than fuel-based systems. This
added weight combined with an overall decrease in energy storage per weight leads to a much
lower range when compared to hydrocarbon fuel powered aircraft. Electric propulsion systems
are mostly powered by batteries, but can also be powered by fuel cells and solar cells (Raymer,
2012).
2.5.1 Battery Powered
Electric motors are very light, but have a heavy power supply. Gasoline powered systems can
store a considerably higher amount of energy per weight of fuel compared to battery powered
systems. For example, gasoline has an energy density of 44.4 MJ/kg, while lithium ion
rechargeable batteries have an energy density of 0.60MJ/kg. Gasolineβs 74 times energy density
of batteries makes flight on batteries quite the challenge. In Figure 6, shown below, is a chart
comparing the energy density of batteries to the energy density of common combustibles. It can
be seen below that lithium ion batteries have a very low energy density compared to common
hydrocarbon fuels. Also, though hydrogen has a very high energy per weight, it has a very low
energy per volume because it is in a gaseous form. The same can be said for methane, propane,
which is why many fuels are stored in their liquid form such as LNG and liquid hydrogen.
17
Figure 6: Energy density of common combustibles in [MJ/kg] (Ronneau, 2004 )
Nickel cadmium batteries have been passed up by the more energy dense nickel-metal hydride,
and those passed by lithium-ion batteries. Lithium-ion batteries tend to hold their charge for a
long time and are the battery type most common in consumer electronics today (Raymer, 2012).
Though lithium-ion batteries currently offer the highest performance per price, they are not the
only batteries available. Silver-zinc batteries do not survive many recharge cycles, but have a
very high energy density. They are also very expensive and only used in applications such as
launch vehicles or torpedoes (Raymer, 2012).
For the future of batteries, lithium-sulfur shows a lot of promise. Li-S batteries are relatively high
weight and have a higher energy density than batteries used today. One of their first large-scale
applications was in Boeingβs βSolar Eagleβ which is a UAV designed to fly at high altitudes for 5
years non-stop (Raymer, 2012).
2.5.2 Fuel Cell
Unlike most conventional propulsion systems, fuel cells do not derive power through direct
combustion, but from supplied chemical reactants in the form of an electric current. The current
most promising fuel cell type for unmanned aircraft systems is proton exchange membrane fuel
cells (PEMFC). In a PEMFC, hydrogen is exposed to a platinum catalyst, which causes the
molecular hydrogen to catalyze into its proton and electron constituents. The membrane,
separating the fuel cell anode and cathode, allows only the electron-stripped hydrogen proton to
pass through. In the cathode, oxygen combines with the protons in an electrochemical oxidation
process, requiring electrons. This draws the electrons left over in the anode across a load, thereby
supplying a current as a source of power. The electrochemical process is 2-3 times more efficient
than direct combustion (Griffis et al., 2008).
The word βhydrogenβ is often associated with the phrase βfuel cellβ and this is because the
normal fuel to use with fuel cells is hydrogen. Oxygen, which was used in the above example, is
18
the common oxidizer for fuel cells. The combination of these two elements creates a byproduct of
water, which is why fuel cells are claimed as emission free (Raymer, 2012).
Hydrogen fuel cells are more energy dense than batteries and about two times as efficient as
internal combustion engines. One of the problems with hydrogen fuel cells is that the operator
must purchase and pump hydrogen into the fuel cells. Besides being an explosive hazard,
hydrogen is not up for sale at many airports, making it even more difficult for the adoption of the
technology to occur. Fortunately, the automobile industry is investing billions of dollars into the
production of fuel cell cars. This research and development could also make its way over to the
aircraft industry in the near future (Raymer, 2012).
2.5.3 Solar Electric
There are many problems associated with solar cells as a power supply for aircraft. First, the
needed efficiency is rather lacking for todayβs cells. Current solar cells can generate roughly
0.02kW/ft2, meaning it takes about 40ft2 to generate 1hp. These efficiencies are improving every
year, but there is still a loss in overall efficiency of 1% per year of use (Raymer, 2012).
One of the more obvious downsides to solar cell propulsion is that power is only generated in
daylight. If flying through the night is part of the mission, batteries must be brought on board to
store energy gathered during the day (Raymer, 2012). The biggest advantage to solar cell
propulsion is the essentially βfreeβ energy. It is also unlimited, assuming the vehicle can make it
through the powerless night, giving solar panel airplanes a possibility to fly for days at a time to
years at a time (Raymer, 2012).
NASA is currently developing technology for solar electric propulsion (SEP) missions. NASA
names these systems as critical elements for future exploration activities to near Earth asteroids
and similar long-range destinations because they can reduce the number of required heavy lift
launches and thus substantially reduce mission costs (Piszczor, 2012).
3 PARAMETERS COMPARISON
3.1 VELOCITY Aircraft maximum speed is the main criteria used in choosing a propulsion system. The choice is
obvious from the figure below, and there is usually no reason to choose a propulsion system other
than the highest on the chart for the design Mach number (Raymer, 2012).
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Figure 7: Propulsion system speed limits (Raymer, 2012)
On Figure 7, the lower the engine system the higher the fuel consumption per pound of thrust.
Choosing an engine design with the lowest possible specific fuel consumption leads to the most
economical fuel usage, as long as the design Mach number is achievable by that system. For
example, a large passenger aircraft wishing to cruise at Mach 0.8 would not choose a piston prop,
as that engine type is generally not compatible with such high speeds. It also would not choose to
be powered by rockets, as the specific fuel consumption is too high. The aircraft would likely
choose a turbofan, which is used on most aircraft of this type.
A general range of specific fuel consumption for each propulsion systems is shown in Figure 8
below. Specific fuel consumption is a term used to describe efficiency with respect to thrust
output. As can be seen below, engines with higher thrust tend to have higher fuel consumption.
0 1 2 3 4 5 6 7 8 9 10
Rocket
Scramjet
Ramjet
Afterburning turbojet
Low-bypass turbofan
High-bypass turbofan
Propfan
Turboprop
Piston-prop
Design Mach number
Propulsion system speed limits
20
Figure 8: Specific fuel consumption trends at typical cruise altitudes. (Raymer, 2012)
At low speeds, piston-prop engines work very well as they are cheap and the most fuel efficient.
Their velocities are limited however, as an increase in velocity for piston-prop engines causes
thrust to decrease (Raymer, 2012).
At high speeds, piston-prop engines run into issues with propeller tips reaching Mach 1, when air
compressibility and heating become significant factors (Anderson, 2012). Unlike piston-props,
jet engines have an increased power available as velocity increases. This can be shown in Figure
9 below (Anderson, 2012).
(a) (b)
Figure 9: Power available for (a) a piston-prop and (b) a jet engine. (Anderson, 2012)
Because of the differences shown in Figure 9, piston-prop engines are generally not efficient and
therefore not used for speeds above the sonic range.
0
0.5
1
1.5
2
2.5
3
0 1 2 3 4 5
Eq
uiv
alen
t je
t S
FC
[lb
/hr/
lb]
Mach Number
SFC at typical cruise altitude
Afterburning Turbojet
Ramjet
Turbojet
Low-bypass turbofan
High-bypass turbofan
Turbo prop
Piston-prop
Po
wer
Speed
Piston-prop
Po
wer
Speed
Jet engine
21
3.2 WEIGHT/PAYLOAD This comparison shows the types of propulsion systems used by aircraft when categorized by
weight class. Also taken into account is the payload of the aircraft. For example, a cargo 747 and
passenger 747 may weigh the same, but the payload is very different. The comparison will run
generally heaviest to lightest.
3.2.1 Cargo Aircraft
Nearly all of the larger cargo planes, commercial and military, utilize turbofan engines. Examples
of these heavy cargo planes are the Airbus A380-Cargo (1.3 million pounds), Lockheed Martin
C5 Galaxy (840,000 pounds, shown below) and the Boeing Dreamlifter (803,000 pounds). There
are some very large cargo planes, such as the Airbus A400M (310,000 pounds) and the Lockheed
Martin C-130J Super Hercules (155,000 pounds), which use turboprop engines (Lewis, 2009).
The Airbus A400M utilizes the Europrop TP400-D6, which is the most powerful single rotation
turboprop, rated at 11,000 shaft horsepower (Rolls-Royce, 2014). The only turboprops which
output more power use contra-rotating propellers. Based on this, we can start to see an upper limit
for the feasibility of using turboprop engines based on aircraft weight.
Figure 10: Lockheed Martin C5 Galaxy taxing on the runway (Lewis, 2009)
3.2.2 Heavy Transportation Aircraft
Heavy transportation aircraft, both passenger and business class, are predominately propelled by
turbofan engines. Examples of heavy transportation aircraft are the Airbus A380 (1.3 million
pounds, shown below), Boeing 747 (950,000 pounds), and Boeing 777 (766,000 pounds). The
business versions of these planes, although they have far fewer seats, have a very similar gross
weight (Lewis, 2009).
22
Figure 11: Airbus A380 in flight (Lewis, 2009)
3.2.3 Midsize Transportation Aircraft
These aircraft are also very large, but carry fewer people and are lighter than the heavy βjumboβ
category above. Examples of these are the Airbus A350 (650,000 pounds), Boeing 787 (484,000
pounds, shown below), Bombardier CS300 (139,000 pounds), and the Embraer 190 (110,000
pounds). Like heavy transportation, these aircraft also generally use turbofan engines for
propulsion (Lewis, 2009).
Figure 12: Boeing 787 in flight (Lewis, 2009)
3.2.4 Light Transportation Aircraft
Once we get down to light passenger and business transportation aircraft, propulsion is no longer
limited to just turbofans. Some planes, such as the Bombardier CRJ 1000 (92,000 pounds), and
the Embraer ERJ 140 (46,000 pounds) do use turbofan engines. Other planes, such as the
Bombardier Q400 (64,500 pounds, shown below) and the ATR 42-500 (41,000 pounds), use
turboprop engines instead (Lewis, 2009).
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Figure 13: Bombardier Q400 in flight (Lewis, 2009)
3.2.5 Military Fighter Aircraft
Most of the heavier fighter aircraft, such as the Lockheed Martin F-22 Raptor (83,500 pounds),
Lockheed Martin F-35 (60,000 pounds), and Mikoyan MiG 29M (49,400 pounds), use turbofan
engines with afterburners. Lighter weight fighter aircraft, such as the Mikoyan MiG-AT (18,000
pounds), can also use turbofan engines. Additionally, there is a group of light weight military
planes that use turboprop engines. These are mostly trainers, such as the Beechcraft T-6 (shown
below), Pilatus PC-7 Mk II and the Marchetti SF-260, each weighing in at well under 10,000
pounds (Lewis, 2009).
Figure 14: Beechcraft T-6 Air Force trainer ("Beechcraft T-6 Texan II," 2003)
3.2.6 Light Aircraft
For light airplanes, cost is a major consideration and piston-props are almost exclusively used for
this reason (Raymer, 2012). Light airplanes are defined as those with a maximum gross takeoff
weight of 12,500 lbs. or less (Crane, 1997). The large list of light aircraft uses includes, but is not
limited to, aerial surveying, primary flight instruction, agricultural, banner towing, skywriting,
personal, and homebuilt aircraft. For those where cost is not a consideration, there are a fair
number of very light weight jets. These jets, such as the Cessna Citation Mustang (8,600 pounds)
and the Epic Victory (5,500 pounds, shown below), utilize a very small family of turbofan
engines (Lewis, 2009).
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Figure 15: Epic Victory, a very light jet, in low altitude flight ("Epic Victory," 2007)
3.2.7 Light-Sport Aircraft
These aircraft are defined in the United States as having a takeoff weight of no more than 1,320
pounds and a cruising speed at or under 120 knots. They also are defined as having both a
reciprocating engine and a fixed-pitch propeller (FAA, 2014). As long as they fit within the
guidelines, types of light-sport aircraft can be gyroplanes, powered parachutes, trikes (also known
as weight-shift control airplanes), and lighter-than-air craft such as balloons and airships. An LSA
example, the Ikarus 42, is shown below in Figure 16. This aircraft has two seats and a maximum
takeoff weight of 1,041 pounds, or about 0.08% of the weight of an Airbus 380.
Figure 16: Ikarus C42, a certified LSA (Lewis, 2009)
3.2.8 Ultralight Aircraft
Ultralight aircraft, a sub category of light aircraft, also use primarily piston-prop engines. An
Ultralight Aircraft, as defined by United States FAR 103, is a single seat vehicle with less than 5
gallons of fuel capacity, an empty weight less than 254 pounds, a top speed of no more than 55
knots, a maximum stall speed of no more than 24 knots, and is used only for recreational or sport
flying (FAR, 2014). Ultralight aircraft are similar in type to light-sport aircraft, only with a large
reduction in weight and power. Nearly all ultralight aircraft utilize piston-prop engines. Shown
below in Figure 17 is an ultralight aircraft in flight. These aircraft are not much more than an
engine, wing, pilot and some landing gear.
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Figure 17: An ultralight aircraft in flight (Lewis, 2009)
In 2007, Electric Aircraft Corporation began offering kits to convert ultralight trikes to electric
power systems. These include a low RPM, high torque motor with 20 horsepower, boasting 90%
efficiency at cruise. The system also claims a 1-2 hour flight time, depending on the weight of the
vehicle and prop size purchased (Fishman, 2014).
3.2.9 Conclusion
The examples from the Weight section are summarized in Table 1 below. From the table we can
see that turbofans are used almost exclusively for heavy and midsize transport aircraft, as well as
for larger cargo aircraft. The heaviest turboprop aircraft is the Airbus A400M, weighing in at
310,000 lbs. Below that weight, either turbofans or turboprops are possible, until a lower limit
for turbofans is reached at around 5,000 lbs. Anything lighter than this and turboprops are used
almost exclusively.
Table 1: Summary of Engine Type by Max Takeoff Weight
Aircraft Name Type Weight [klbs] Engine Type
Airbus A380 Cargo Cargo 1300 Turbofan
Airbus A380 Heavy Transport 1300 Turbofan
Boeing 747 Heavy Transport 950 Turbofan
Lockheed C5 Galaxy Cargo 840 Turbofan
Boeing Dreamlifter Cargo 803 Turbofan
Boeing 777 Heavy Transport 766 Turbofan
Airbus A350 Midsize Transport 650 Turbofan
Boeing 787 Midsize Transport 484 Turbofan
Airbus A400M Cargo 310 Turboprop
Lockheed C-130J Cargo 155 Turboprop
Bombardier CS300 Midsize Transport 139 Turbofan
Embraer 190 Midsize Transport 110 Turbofan
Bombardier CRJ 1000 Light Transport 92 Turbofan
Lockheed F-22 Military Fighter 83 Turbofan + Afterburner
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Bombardier Q400 Light Transport 64 Turboprop
Lockheed F-35 Military Fighter 60 Turbofan + Afterburner
Mikoyan MiG 29M Military Fighter 49 Turbofan + Afterburner
Embraer ERJ 140 Light Transport 46 Turbofan
ATR 42-500 Light Transport 41 Turboprop
Mikoyan MiG AT Military Trainer 18 Turbofan
Cessna Mustang Light 8.6 Turbofan
Beechcraft T-6 Military Trainer 6.5 Turboprop
Pilatus PC-7 Military Trainer 6 Turboprop
Epic Victory Light 5.5 Turbofan
Marchetti SF260 Military Trainer 2.9 Turboprop
Light Sport <1.32 Piston Prop
Ultralight <0.99 Piston Prop
3.3 MISSION Mission has a large influence on how the aircraft operates in terms of altitude, range, speed,
engine noise and flight duration. Categorizing aircraft into their mission categories may provide
insight on which engines are chosen for each mission. Examples of aircraft for each engine are
outlined in the following sections.
3.3.1 Stealth
The Northrop Grumman B-2 Stealth Spirit Bomber is the most advanced of its kind. Like most
other military aircraft, the B-2 uses turbofan engines. Another aircraft that can be categorized as
stealth is the F-22 Raptor. Similarly, as noted in section 3.2.5, the Raptor also uses turbofan
engines and also has the addition of afterburners (Lewis, 2009).
3.3.2 Reconnaissance
The Northrop Grumman Global Hawk is an unmanned reconnaissance vehicle capable of 28
hours of flight up to 60,000 feet. For propulsion, it uses one Rolls-Royce turbofan engine
("Northrop Grumman Global Hawk," 2014). A much smaller unmanned reconnaissance vehicle is
the ScanEagle, built by Insitu. The ScanEagle, weighing only 40 pounds with a 10 foot wingspan,
uses a 1.5 horsepower piston engine (USAF, 2007). The Lockheed U-2, which was introduced in
1957 and is still in service, is a high-altitude reconnaissance aircraft which uses a single turbofan
engine ("U-2 Dragon Lady Overview," 2014).
3.3.3 Air Superiority
Air superiority fighters serve the purpose of entering and taking complete control of enemy
airspace. The highest performing engines are extremely important for these aircraft. Examples of
air superiority fighters are the F-15 Strike Eagle and Eurofighter Typhoon. Each of these aircraft
use an afterburning turbojet power plant (Lewis, 2009).
3.3.4 Attack Aircraft
The primary role of an attack aircraft is attacking targets on the ground or sea with a much higher
accuracy than bombers. Attack aircraft are also prepared to encounter strong low-level anti-
aircraft defenses. Strong examples of attack aircraft are the F-35 and the A-10 Warthog. Both of
these aircraft use turbofan engines, the F-35 also having an afterburner (Lewis, 2009).
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3.3.5 Bombers
These aircraft, like the B-2 bomber mentioned in section 3.3.1, stay far out of the way of combat
by cruising at high altitudes. The Dassault Mirage 2000N is specifically designed for nuclear
strike and sports an afterburning turbofan (Lewis, 2009). Another bomber is the B-1 Lancer,
which is also powered by an afterburning turbofan (GE, 2012).
3.3.6 Trainers (Military and Private)
As outlined in section 3.2.5, many military fighter trainers are turboprops. More advanced
trainers, such as jet trainers like the supersonic T-38, have turbofans with full afterburners ("T-38
Talon," 2014). Most civilian trainer aircraft are piston prop aircraft. Examples are Cessna 152 and
Piper Warrior.
3.3.7 Aerobatic Aircraft
Aerobatic aircraft are mostly for airshows and competitions. Today, nearly all of them use piston
prop engines. Examples are the Aviat S-1 and Cirrus SRS. Aerobatic craft require high agility,
but not necessarily high speed, so piston prop engines work very well for this application (Lewis,
2009).
3.3.8 Transportation
Transportation aircraft were outlined in detail in section 3.2. As described in that section, all
ranges of size use turbofan engines (all without afterburners), while smaller transportation craft
have the ability to install turboprop engines instead.
3.3.9 Amphibious Aircraft
These aircraft can be very versatile, from small two seat privately owned Cessnaβs to Bombardier
415 water bombers. This aerial firefighting Bombardier needs extra thrust to carry its 6,400
pound water payload so it utilizes two turboprop engines (Lewis, 2009). The Aviat A-1C Husky,
a two seat plane that can easily be fitted with floats, uses a Lycoming piston-prop engine (Aviat,
2013).
3.3.10 Conclusion
Outlined in Table 2 below, we can see the different types of engines used for specific missions.
Fighter aircraft almost all use afterburning turbofans or turbojets, whereas transports, bombers,
stealth, reconnaissance, trainers, aerobatic and amphibious aircraft do not have speed as their top
priority and are therefore able to use other types of engines. Many civilian aircraft use piston-prop
engines, most likely for their low fuel consumption and therefore low cost.
Table 2: Summary of Engine Type by Mission
Aircraft Name Mission Engine Type
Northrop Grumman B-2 Stealth Turbofan
Lockheed Martin F-22 Stealth Turbofan + Afterburner
Northrop Grumman Global Hawk Reconnaissance Turbofan
Insitu ScanEagle Reconnaissance Piston-Prop
McDonnell Douglas F-15 Air Superiority Turbofan + Afterburner
Eurofighter Typhoon Air Superiority Turbofan + Afterburner
Lockheed Martin F-35 Attack Turbofan + Afterburner
Fairchild Republic A-10 Attack Turbofan + Afterburner
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Northrop Grumman B-2 Bomber Turbofan
Dassault Mirage 2000N Bomber Turbofan + Afterburner
Rockwell B-1 Bomber Turbofan + Afterburner
Beechcraft T-6 Military Trainer Turboprop
Northrop T-38 Military Trainer Turbofan + Afterburner
Cessna 152 Civilian Trainer Piston-Prop
Piper Warrior Civilian Trainer Piston-Prop
Aviat S-1 Aerobatic Piston-Prop
Cirrus SRS Aerobatic Piston-Prop
Boeing 777 Transport (Heavy) Turbofan
ATR 42-500 Transport (Light) Turboprop
Bombardier 415 Amphibious Water Bomber Turboprop
Aviat A-1C Amphibious Piston-Prop
4 PARAMETERS COMPARISON OF UAVS
4.1 TYPES OF UAVS Unmanned Aerial Vehicles (UAVs), also known as drones, unmanned aircraft systems (UAS),
and remotely piloted aircraft (RPA), are aircraft without a pilot onboard. They are either piloted
remotely or completely autonomous. There are slight differences between UAVs and remote
control aircraft. RC planes are controlled by in-sight radio communication and nearly always
under manual control, whereas UAVs are out of sight aircraft with the ability to be piloted both
autonomously and from thousands of miles away (Raymer, 2012). Six general categories of
UAVβs and their respective engines are detailed in the following sections.
4.1.1 Micro Air Vehicles
MAVs, which also encapsulate the category of Nano Air Vehicles (NAVs), are named for their
size. The miniscule nature of MAVs allow them to be transported by single soldiers in the
battlefield, but have a limited flight ceiling of around 1,000 feet and limited flight time in the 5-
30 minute range due to constrictions on battery size. MAVs are designed as short mission profile
surveillance platforms, allowing reconnaissance of nearby hostile environments and in confined
spaces. An example of an MAV is the AeroVironment Nano Hummingbird. This vehicle weighs
19 grams, has a 16 cm wingspan, and a flight endurance of only 8 minutes. It can, however, fly in
all directions and is equipped with a camera. The Nano Hummingbird is pictured below in Figure
18 (Watts, Ambrosia, & Hinkley, 2012).
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Figure 18: Aerovironment's Nano Hummingbird (Watts et al., 2012).
4.1.2 Vertical Takeoff and Landing (VTOL)
VTOL UAVs are perhaps the most popular non-military UAVs. They can often be seen in parks,
at large outdoor events, or wherever aerial video footage or photographs are desired. Many of
these vehicles come in the form of a multicopter, and today are available at most hobby stores.
For example, the entire Dragonflyer X6 system, pictured in Figure 19 below, can be purchased
for under $10,000. These vehicles require no runway for landing or takeoff and are therefore used
in situations where terrain limitations require this ability. However, because copters do not have
wings, they require far more energy to remain airborne and therefore have a shorter mission
duration than a UAV with wings. Most VTOL UAVs operate on battery powered electric motors,
which generally limits flight time to around 1 hour. Larger VTOL, such as the Yamaha RMAX
VTOL which can be used for precision agriculture, may be equipped with small internal
combustion engines. Even larger systems, which could be used for military transportation, are
currently in development (Watts et al., 2012).
Figure 19: Dragonflyer X6 VTOL UAV (Watts et al., 2012).
4.1.3 Low Altitude, Short Endurance (LASE) & Low Altitude, Long Endurance (LALE)
LASE and LALE come in a variety of sizes and shapes, from smaller hand launched platforms to
the larger size catapult launched platforms. The most common LASE/LALE used today are small
and hand-launched, which allows them to be used in all kinds of environments and does not
depend on a solid runway surface. Because of their size, they are limited in both flight duration
30
and payload capacity. Simple controls, much like regular remote control airplanes, allow for the
vehicles to be operated by small one to two person ground crews (Watts et al., 2012). Examples
of LASE and LALE platforms, some of which can be seen in Figure 20 below, are the
AeroVironment Dragon Eye, NASA J-FLiC, and the Arcturus T-20. Most LASE and LALE use
piston prop engines, but some systems, such as the NASA J-FLiC, use jet engines.
Figure 20: LASE and LALE on display at the 2005 Naval Unmanned Aerial Vehicle Air Demo. Pictured are the RQ-
11A Raven (1), Dragon Eye (2), Skylark (3), Evolution (4), Arcturus T-15 (5), NASA FLiC (6), Tern (7), RQ-2B Pioneer
(8), and Neptune (9) (Watts et al., 2012).
4.1.4 Medium Altitude, Long Endurance (MALE)
These are no longer βRCβ type aircraft. MALE UAVs fly in the 10,000-50,000 foot altitude range
and are generally much larger than UAVs discussed in the preceding sections. An example of a
MALE UAV is the Predator B, which has a 50,000 foot ceiling, 27 hours of endurance, and is
equipped with a single turboprop engine (NASA, 2014).
4.1.5 High Altitude, Long Endurance (HALE)
HALE platforms are among the most recent UAVs introduced to the already large variety of
unmanned aircraft. A prime example of a HALE system is the Northrup-Grumman Global Hawk.
This UAV is used for both reconnaissance and for research purposes. The Global Hawk has an
operating altitude of 65,000 feet, endurance of over 30 hours, and can house up to 10 different
instruments for measurement capabilities. Currently one of the largest UAVs in use, the Global
Hawk sports a Rolls Royce Turbofan engine to carry its 32,000lb weight at cruising speeds of
357mph (USAF, 2008). An Air Force version of the Global Hawk can be seen in the figure
below. Note its immense size for being a UAV!
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Figure 21: A maintenance crew preparing a Global Hawk for flight (WikipediaCommons, 2006).
Even with its long endurance, it is hard to keep increasing the endurance time of high altitude
UAVs without switching to an βunlimitedβ power source. The Qinetiq Zephyr, which currently
holds the UAV endurance record of over 336 hours, is powered by an electric motor that takes
energy from the solar cells which make up the top of its wings. It is thought that in the coming
years it will be possible for HALE UAVs to stay aloft for flights lasting one month up to five
years. These sub orbital flights would provide large cost savings over satellite programs, with the
ability to return to Earthβs surface at any time for maintenance and upgrades. These returns are
not feasible with todayβs satellites. Such long endurance flights would provide near continuous
coverage of phenomena on Earthβs surface (Watts et al., 2012).
4.1.6 Conclusion
The five different types of UAVs are summarized in the table below. They are organized
according to both maximal altitude and flight endurance.
Table 3: Summary of UAV types with ceiling, endurance and engine type
Aircraft Name Class
Max
Altitude (ft.) Endurance Engine Type AeroVironment Nano
Hummingbird MAV 11m Electric Motor
Dragonflyer X6 VTOL 8,000 25m Electric Motor
AeroVironment RQ-14
Dragon Eye LASE 1,000 1h Electric Motor
AeroVironment RQ-11A
Raven LASE 15,000 1.5h Electric Motor
Skylark LASE 15,000 3h Electric Motor
Neptune LALE 8,000 4h Piston Prop
Tern LALE 10,000 4h Piston Prop
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AAI RQ-2B Pioneer LALE 15,000 5h Piston Prop or Rotary Engine
General Atomics GNAT
750 MALE 25,000 48h Piston Prop
General Atomics MQ-9
Reaper MALE/HALE
25,000-
50,000 >14h Turboprop
Arcturus T-15 MALE/HALE
23,000-
65,000 12-24h Electric Motor or Piston Prop
Northrup-Grumman
Global Hawk HALE 60,000 32h Turbofan
Qinetiq Zephyr HALE >70,000 336h Electric Motor (Solar)
According to the data above, it can be seen that short endurance UAVs use electric motors almost
exclusively. Long endurance UAVs use mostly internal combustion engines, with high altitude
aircraft taking advantage of more powerful engines such as turboprops and turbofans. Given the
current battery energy densities, these results were expected. As energy densities continue to
improve, it will become reasonable for longer duration aircraft to use electric motors. Until then,
hydrocarbons are far more energy dense so internal combustion engines are used when a lot of
fuel is required.
4.2 UAV MISSIONS Unmanned aerial vehicles are quickly taking the place of manned vehicles in missions where
pilots may be in danger or long flight duration is preferred. Removing the pilot from the vehicle
not only creates a safer environment, but significantly reduces aircraft weight. Necessities such as
the cockpit, ejection seat, armor, flight controls and environmental controls for maintaining
pressure and oxygen levels are no longer needed, making for a light weight aircraft that can carry
out missions more efficiently than ever before.
4.2.1 Military
Military use of unmanned aerial vehicles has been one of the main drivers for UAV technology.
Aerospace giants such as Boeing and Lockheed Martin have been developing military UAVs for
many years, helping to advance UAVs to where they are today.
4.2.1.1 Reconnaissance
The technology for reconnaissance UAVs has been around for decades. One of the older
examples is the Boeing YQM-94A which made its first flight in 1973. The vehicle is one of the
few examples of a UAV that uses a turbojet, in this case using a General Electric J97 which was
developed for UAV applications and creates about 5,300lbs of thrust on takeoff ("Boeing YQM-
94A Compass Cope B," 2013).
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Figure 22: Boeing YQM-94A, the 1968 turbojet reconnaissance UAV ("Boeing YQM-94A Compass Cope B," 2013)
Another reconnaissance UAV that uses the GE J97 was the Ryan AQM-91 Firefly, which made
its initial flight in 1968 and was the long range version of the 1963 Ryan Modal 147 Lightning
Bug (Parsch, 2002).
The origins of modern day reconnaissance UAVs are now over 50 years old and newer versions
are constantly being developed. These UAV systems come in all shapes and sizes, from the hand
held RQ-11 Raven to the 32,000 lb Global Hawk.
4.2.1.2 Unmanned Combat Air Vehicles
UCAVs, more commonly known as drones, refer to unmanned aerial vehicles that are armed.
Like reconnaissance UAVs, UCAVs have been in use for many years, with the Ryan Firebee
making its first, unmanned flight in 1955.
Figure 23: Two Ryan Firebees ready for deployment from a DC-130 ("DC-130 Mounted Firebees,")
More recent examples of UCAVs are the General Atomics MQ-1 Predator and MQ-9 Reaper.
The Predator was initially used for observation roles but has been modified to fit two Hellfire
missiles, putting it in the UCAV category. However, this MALE UAV has a top speed of only
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135mph, powered by a turbocharged four-cylinder 115 HP engine. The Reaper is a much more
advanced combat vehicle, able to carry 15 times more payload than the Predator and travel nearly
three times as fast at 300 mph, powered by a 900 HP turboprop engine. The HALE Reaper and its
MALE brother were developed for and are used mostly by the United States Air Force ("MQ-9
Reaper Factsheet," 2010), ("MQ-1B Predator," 2010).
Figure 24: The MQ-9 Reaper taking off in Afghanistan, 2007 ("MQ-9 Afghanistan Takeoff,")
4.2.2 Research
A very popular market for UAVs is for research. These research applications, ranging from
atmospheric sensing to crop harvesting optimization, are growing easier and less expensive due to
the availability of UAVs for research purposes. Several of these research opportunities are
outlined in the following sections.
4.2.2.1 FAA UAS Test Range Program
Six sites have been selected by the Federal Aviation Administration allowing the agency to
develop research findings and operational experiences to help insure the safe integration of UAVs
into the nationβs airspace. Through the research at these sites, data and information collected will
help the FAA to answer key research questions such as solutions for βsense and avoid,β human
factors, airworthiness, command and control, lost link procedures and interface with the air traffic
control system. Regulations and procedures will then be developed for the commercial and civil
use of UAVs in national airspace (Dorr, 2013).
With the help of NASA and the Department of Defense, the FAA chose its research needs, taking
into account varying climates, geography, and location of ground infrastructure. In early 2013,
the agency called for proposals from public entities, including state and local governments and
eligible universities. Complete proposals were received from 25 entities in 24 different states,
with six ultimately selected to operate the UAS Test Sites (Dorr, 2013).
The six test sites operators are University of Alaska, State of Nevada, New Yorkβs Griffiss
International Airport, North Dakota Department of Commerce, Texas A&M β Corpus Christi,
and Virginia Tech. The exact locations can be seen in Figure 25. Together, these tests sites
represent cross-country climatic and geographic diversity. The University of Alaska dramatically
increased its climatic and geographic diversity by naming four test site range locations in Oregon
and three in Hawaii in addition to Alaskaβs seven sites. Named the Pan-Pacific test site, this group
of three states is the home of climates and geographies of all kinds, from oceans and frozen
monstrous mountains to dry high deserts and lush tropical forests (Dorr, 2013).
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Figure 25: Shown are the six UAS Test Site locations across the United States (FAA, 2013)
The research plan for the Pan-Pacific test complex includes developing standards for UAS
categories, state monitoring and navigation, and safety standards for UAS operations. While the
FAA will not contribute financially to research at the UAS test sites, they will help to set up a
safe testing environment. The test sites and all their test ranges will be in operation until at least
February, 2017 (Warwick, 2013).
4.2.2.2 Hurricanes
In 2006, NOAA began utilizing the Aerosonde UAV, a system that weighs only 35 pounds but
can fly into a hurricane and transmit real time data. Additionally, the Aerosonde system has a
range of over 1,800 miles and can fly very close to the waterβs surface in a hurricane, something
too dangerous for a pilot (Aerosonde, 2010). For extended collection of data, NASA then began
using a Northrup Grumman RQ-4 Global Hawk for hurricane data collection. The use of UAVs
for hurricane data collection takes out the human risks and removes the restrictions on how close
an aircraft can get to the storm.
4.2.2.3 Remote Sensing
The ability for a VTOL UAV to hover for extended periods of time for low cost, and the ease in
which they can fly from waypoint to waypoint to collect data makes them excellent tools for
remote sensing. Common remote sensing vehicles today are manned aircraft and satellites, which
have the drawbacks of lower spatial resolution and limited availability based on weather and high
cost. UAVs offer a low cost alternative and are able to record data while flying at extremely low
altitudes. For example, the University of Illinois is designing the use a UAV for agricultural
remote sensing. The helicopter UAV, weighing only 30 pounds, autonomously flies to
preprogrammed waypoints and collects data while hovering. The UAV, equipped with a multi-
spectral camera and able to fly at low altitudes, has been demonstrated and is shown to have a
very high spatial resolution. The high resolution allows for the observation of individual plants,
patches, gaps and patterns of the landscape that has not previously been possible (Xiang & Tian,
2011).
36
Despite their popularity, VTOL UAVβs are not the only types used for remote sensing. In 2002,
NASAβs solar-powered Pathfinder-Plus was used as a proof of concept above Kauai Coffee
Companyβs plantation in Hawaii. The UAV had a payload of both high resolution color and
multispectral cameras and was able to capture data to help the plantation determine the location
of evasive weeds and look for irrigation and fertilization anomalies. This mission demonstrated
the use of a low-speed UAV for remote sensing above an agricultural area for an extended period
of time (Herwitz, Johnson, Dunagan, & Higgins, 2004).
Although referenced in the previous two examples, agriculture is not the only use for remote
sensing. More information can be found in the Oil, Gas and Mineral Exploration and Production
section.
4.2.3 Commercial
UAVs for commercial use has recently been an exploding market. Endless applications from
atmospheric sensing to farmland optimization are continually made easier and cheaper as UAVs
advance into the commercial market. Uses for UAVs in commercial applications are outlined in
the following sections.
4.2.3.1 Aerial Surveillance
Now that advanced UAVs are readily available for purchase outside of military applications, they
have become a large player in commercial applications. Compared to the conventional use of
helicopters and airplanes, UAVs present a far more economical and environmentally unobtrusive
option. Some of the aerial surveillance uses include road patrol, livestock monitoring, home
security, pipeline security and wildfire mapping (Gaszczak, Breckon, & Han, 2011).
4.2.3.2 Sports
UAVs have become popular in filming sports,
especially those that are fast moving and cover a lot
of ground. Examples of these are ski racing,
mountain biking, cycling and surfing. For sports
applications, VTOLs are used nearly exclusively.
This allows for a high variability of speed starting
from a stop, close proximity video, and an easy
takeoff and landing from places where there is surely
no runway available. The video captured by these
UAVs can be transmitted instantly for live television,
which was employed heavily at the 2014 Sochi
Winter Olympics. Just like any other film, it can later be used for commercials, training, or even
movies. (Feltman, 2014)
4.2.3.3 Filmmaking
Vertical takeoff and landing UAVs are used for professional filmmaking for mostly the same
reasons they are used for sports. They provide an inexpensive way to get aerial footage compared
helicopters, are extremely maneuverable, and they donβt need a runway to start filming. On top of
that, VTOL UAVs are generally easy to use, requiring only a two man crew: one person to fly the
aircraft and another to control the camera(s). There are some issues stemming from the fact that
these aircraft can only be flown up to 500 feet AGL, above which they are regulated by the FAA
(FastCompany, 2012).
Figure 26: VTOL UAV in use at the 2014 Sochi Winter Olympics
37
4.2.3.4 Oil, Gas and Mineral Exploration and Production
UAVs give the enormous Exploration & Production market big advantages. Some of these UAVs
have the ability to stay airborne for more than 30 hours, vastly increasing the efficiency of aerial
E&P. Because there is no pilot on board, these vehicles are also able to fly in hostile regions
where there would be real danger to a pilot. Simply being flown by a computer has its distinct
advantages. The vehicle is able to fly steadily and perform very precise raster scans of the area
and is also able to fly at very low altitudes, increasing data resolution.
The very low cost of UAV operation allows for repeated surveys of the same area, creating a time
differential representation to detect changes such as the depletion of an oil reserve or leakage of a
pipeline.
Many different types of imaging and detecting can be used with a wide variety of UAV sizes.
Differential thermal imaging using a microbolometer camera could be used to detect leakage in
underground pipelines. This system would be equivalent to a payload of no more than 20 pounds.
On the other end, an Airborne Electromagnetic Probing system weighs on the order of hundreds
of pounds and would require the use of a very large UAV, such as the Hermes 900 which has a
payload capacity of 770 pounds.
Regardless of the imaging type used in Exploration & Production activities, large savings can be
realized by E&P companies using UAVs as opposed to manned aerial vehicles (Barnard, 2007).
Figure 27: The Elbit Hermes 900 in flight, capable of a 770lb payload
4.2.3.5 Disaster Relief, Search and Rescue
Like other aircraft, UAVs are capable of reaching inaccessible regions for transporting medicine
and relief supplies. Using their imaging systems they can gather data to build a picture of the
situation which helps disaster relief efforts become safer and more efficient (Marks, 2013).
Following the 2008 hurricanes that heavily affected Louisiana and Texas, UAVs were used in
both search and rescue as well as damage assessment. A Predator B, owned by U.S. Customs and
Border Protection, was used extensively at this time, operating 18,000-29,000 feet ASL. The craft
carried an optical sensor and a Synthetic Aperture Radar, which were able to penetrate all kinds
of weather including thick clouds, rain and fog and had the ability to operate during the daytime
and nighttime. These sensors allowed for exceptional search and rescue ability, while before and
after shots highlighted damaged areas (JAW, 2011).
38
A huge operation such as the Predator B mentioned above is not required for search and rescue.
The Aeryon Scout, a 3lb VTOL quadcopter, has been used by police for the search of a single
missing person (Pearson, 2012).
4.2.3.6 Forest Fire Detection
Compared to the current methods of watchtowers and helicopter patrol, using UAVs for forest
fire detection could make a big difference. UAVs could be surveying the ground nearly
constantly day and night, reporting fires immediately along with critical information such as wind
speed, temperature, and exact location allowing for firefighters to reach the fire scene prepared
and in a timely manner. Perhaps an autonomous version of the Bombardier 415 Amphibious
Water Bomber would then be automatically deployed to the fire.
4.3 ELECTRIC MOTOR VS. INTERNAL COMBUSTION ENGINE: CASE STUDY The following case study is based off the case study in Shyam Menonβs PhD thesis βThe Scaling
of Performance and Losses in Miniature Internal Combustion Enginesβ (Menon, 2010). Because
there is so much variety of small electric motors and small combustion engines, either one may be
used on UAVs. While electric motors have a much higher efficiency, the amount of energy that
combustion engines can carry in the form of fuel is much higher than the amount electric motors
can carry via batteries. Consider two nearly identical AeroVironment RQ-11 Ravens, one
powered by an electric motor and one powered by a combustion engine. The electric motor used
is the Ravenβs stock Aveox 27/26/7-AV, with a power output of approximately 250W and an
efficiency of 95% ("AeroVironment RQ-11 Raven,"). The internal combustion engine, a 40NX
RC Glow Engine has an efficiency of 8% and a power output of around 300W (HorizonHobby,
2015).
The total vehicle weight is 2kg, half of which we can assume is battery weight. Because the
motor and engine weigh about the same, we can swap out all the batteries for a fuel tank of the
same mass on the combustion Raven. To compare these two planes, we will use the Breguet
range equation, shown below (Raymer, 2012). Both engines have the same propeller, which we
give a propeller efficiency, Ξ·p, of 0.8. We can assume a lift over drag of 7 and we know that
gravity is equal to 9.81 [m/s2]. The energy densities, Qr, are the last difference between the two
UAVs
π = ππππ‘βππ
π
πΏ
π·ln(1 + π₯)
The following table sums up the variables for this equation and the range calculated for each
vehicle.
39
Table 4: Case study variables
As we can see in Table 4, the combustion engine UAV has a 12% higher range than the electric
UAV even though its engine is less than one tenth as efficient. The reason for this is the energy
density of gasoline verses batteries. Much more energy can be carried aboard via gasoline than
can be carried by batteries.
This case study illustrates that there is a place for combustion engines on small UAVs, even
where electric motors are the go-to solution.
4.4 HOW UAV ENGINE TYPES COMPARE TO MANNED ENGINE TYPES UAV engines compare closely to manned aircraft engines when considering altitude, speed and
flight duration. Only the lightest of aircraft currently use electric motors, which is true for both
UAVs and manned aircraft. Aircraft that require longer duration or distance will used some type
of internal combustion engine. However, very few UAVs use internal combustion engines that
are not piston-props. This is most likely due to the weight of UAVs, which in general is much less
than that of manned aircraft. An exception to this is the turbofan-wielding Global Hawk, which is
one of the largest UAVs in use. Another reason mostly piston-props are used is that the majority
of UAVs fly at altitudes under 25,000 feet, where it is still reasonable to use propellers.
Overall, there is little discrepancy between the engines used for manned applications and the
engines used for unmanned applications.
5 ENGINE RESEARCH
This section makes up the experimental portion of this thesis. The following experiments were
conducted under mentor Dr. Chris Hagen, OSU Professor in Energy Systems Engineering.
5.1 INTRODUCTION UAV Engine research took place in December 2014 at the OSU Cascades Energy Systems
Laboratory in Bend, Oregon. The first goal of this research was to create an engine test bed that
would act as an all-in-one data collection site. Using this test bed, collected data can then be
leveraged in characterizing UAV engine performance. The second goal of this research period
was to collect data by running the engine at different power outputs using various propellers and
engine speeds. Upon analysis, findings may be compared to published data for the same engine.
Should the experimental findings be similar to published data, the test stand and its sensors will
40
be proven as an effective test bed for UAV engine data collection. The knowledge gained during
these activities can then be applied towards a future, second generation test cell.
Throughout the construction and testing of this engine and test stand we will realize many
considerations that must be taken in order to improve upon the test cell. These considerations will
be reviewed in the Discussion section.
5.2 EXPERIMENTAL SETUP Simply starting the engine was a major task in itself. Both assembling the engine and building the
test stand turned out to be quite time consuming, as was developing proper procedures for data
collection. The steps taken to get to the data collection phase of this research project are outlined
in the following sections.
5.2.1 Engine Assembly
The engine chosen for this experimental research was a 3W-28i (3WModellmotorenGmbH). This
is a 2-stroke, spark ignited, air cooled, and gasoline powered engine with a power output of up to
3.35 hp. It has a speed range of 1500-8500 rpm and a total weight of 2.67 pounds. Engine
specifications are shown below in Table 5.
Table 5: 3W-28i Engine specifications (3WModellmotorenGmbH)
An assembled version of the 3W-28i engine can be seen below in Figure 28.
41
Figure 28: 3W-28i engine (3WModellmotorenGmbH)
The first step in engine assembly was to attach the carburetor, which was attached to the engine
with bolts and separated from the engine by a gasket. A photo of the carburetor used can be seen
below in Figure 29.
Figure 29: The carburetor used with the 3W engine (3WModellmotorenGmbH)
The installation of the carburetor was followed by the installation of the air intake cone. This
component was attached to the back of the carburetor using the same long bolts that attaches the
carburetor to the engine. Next, the ignition sensor was installed and main hub was calibrated for
drilling. Two high strength magnets, placed at specific angles from each other with one magnet
corresponding to top dead center, were recessed into the main hub and secured using J-B Weld.
As the drive shaft rotates, these magnets trip the ignition sensor, allowing the spark plug to fire at
the most efficient point during fuel compression. The reason there are two magnets as opposed to
just one is that the first triggers the capacitor to charge and the second, which is aligned with top
dead center, triggers the sending of energy to the spark plug. In the future, the placement of these
magnets with respect to top dead center could be a research topic to find the highest efficiency
42
spark location. Below is a photo of the photo of the ignition sensor components. The silver box is
the main ignition timer, with a braided cable leading to the spark plug. The red, black and colored
leads running into the timer are the power source and engine speed output. The two black plastic
fittings are the sensors, which pick up the rotating magnets.
Figure 30: Spark plug ignition system ("Agape Racing and Hobby, LLC.,")
Once the magnets were installed, the hub was attached to the main drive shaft. Following the hub
modifications, the first propeller was drilled to fit precisely between the hub and prop washer. Six
holes, one for each prop screw, were drilled using a milling machine. The prop was then installed
onto the drive shaft. An example of the props used is shown below in Figure 31.
Figure 31: APC 17x12 propeller, one of the three used on the 3W engine ("APC Propellers,")
The final integral engine component installed was the muffler. This part was bolted to the exhaust
outlet and sealed with high temperature sealant.
The entire engine assembly took several days, during which much trial, error and problem solving
occurred, as this was the first engine of its kind assembled at the OSU Energy Systems
Laboratory.
5.2.2 Test Stand Construction
The purpose of the test stand was to safely house the engine and all its vital components for
operation and data collection. The main body of the stand was a large, wheeled cart, making the
test bed mobile for painless location changes. A rectangular ΒΌ inch steel plate was cut to size and
43
mounted on the cartβs top, making the cart more durable and less susceptible to damage sustained
by intense engine vibration. Next, a steel I-beam was drilled for mounting onto the steel plate. A
pre-cut engine mount was welded to the I-beam and the two piece assembly was then bolted to
the steel plate. The engine could now be securely mounted to the cart.
Ignition systems were then installed on the test stand. The ignition module, provided by 3W, was
attached to the engine mount and powered by a large 6 volt battery. The hub-mounted ignition
sensor was wired to the ignition module, as was engineβs spark plug.
Fuel filters and fuel lines were properly installed on the fuel tank, which was then secured at an
elevation several feet above the fuel intake valve. This allows for a gravity assisted fuel feed
where carburetor suction may not be sufficient. The fuel line was then connected to the
carburetorβs fuel intake valve.
After numerous attempts at creating a remote throttle adjustment tool, there were mounting and
vibration issues so a screw was used instead to keep the throttle in one place. Because of the
throttleβs proximity to the propeller, mid test throttle adjustments would not be practical. No
problems were foreseen, as throttle adjustments were planned for only between tests.
Lastly, the large OSU Energy Systems Laboratory magnet was attached to the side of the test
stand. Below in Figure 32 is a photo of the assembled engine attached to the test stand.
Figure 32: Assembled engine attached to test stand
5.2.3 Data acquisition systems
Because of time constraints, manual data recording was chosen as the method for these engine
tests. Engine speed (rpm) was required to find engine power output. This speed was recorded
both by a handheld tachometer and by an oscilloscope wired to the ignition moduleβs data output,
allowing the oscilloscope to record the frequency of the square wave signal. The tachometer used
was the GloBee Intellitach and the oscilloscope used was a Tektronix DPO3012.
44
Figure 33: Sean Brown recording engine speed data off the Tektronix DPO3012 oscilloscope
Fuel consumption was captured using a scale, measuring the weight of the fuel before and after
the test run. The scale we used was a DYMO USB Postage Scale.
Temperature data was collected on a set point of the cylinder head and of the exhaust gasses. For
the cylinder head, an infrared laser sensor was used. For the exhaust gasses, a probe thermocouple
was installed and read using a multimeter. This thermocouple was also used to collect ambient
temperature data before testing. The infrared sensor was a Raytek Minitemp MT6. The
thermocouple was a probe type K and the multimeter was a PDI DM-930.
Figure 34: PDI DM-930 Multimeter being used to measure ambient temperature
The last data point collected was the airspeed coming off the propeller. The airspeed was captured
using a small anemometer. This instrument was also used to collect humidity measurements.
Because of large discrepancies between the estimated and measured humidity and temperature
levels on the anemometer multi-tool, online weather resource Weather Underground was used to
collect those data points from each testing day and time ("Weather Underground,").
45
At this time, the assembly of the engine, test stand and sensors was complete. An energy flow
schematic of the test cell was created in Microsoft Visio and can be seen below in Figure 35.
Energy flows into the system in the form of fuel. After combining with air, the fuel is burned and
converted to shaft work, heat, noise and some vibration. Shaft work leaves the system through the
drive shaft and propeller. Heat leaves the system both by conducting through the cylinder head
and by leaving the muffler in the form of hot gas. A small amount of energy escapes as noise, as
these engines are quite loud. Some of the energy is also dissipated from vibrations produced by
the propeller and by the piston. This energy flow is illustrated in the energy flow diagram. The
diagram also shows the sensors used and what each of them is used to measure.
Figure 35: Test cell energy flow diagram
5.2.4 Systems verification
Before the engine was run, numerous verifications were carried out to insure the engine and its
components were installed correctly.
The air intake reed valve was checked manually to insure that it operated correctly and was
installed in the appropriate direction. The carburetor needle valves were set to 3W suggested
settings. When the required information could not be found, an assumption was made as to which
needle valve was considered the βhigh passβ and βlow passβ. Eventually we learned that this
assumption was backwards and the valves were switched.
With the spark plug wired to the ignition module but disconnected from the engine, the propeller
was spun to signal the ignition module. In doing this, we confirmed that a spark was occurring on
46
each revolution of the drive shaft. This also confirmed that the ignition moduleβs 6 volt power
supply was functioning nominally. Finally, this test confirmed that ignition when the piston was
at top dead center.
With these systems verified, the list of possible problems dropped considerably, allowing us to
quickly solve engine problems as they occurred in the future.
5.2.5 Safety features
Safety is the number one priority at the Energy Systems Laboratory. As such, personal protection
and emergency shutoff precautions were taken.
A Plexiglas shield was installed radially around the propeller to contain all pieces should a
propeller failure occur during testing. Even with this safety precaution in place, personnel were
not permitted to walk in the radial path of the propeller during testing. The adjacent garage door
was kept open at all times during testing to ensure that proper flow of exhaust out of the
laboratory was taking place.
Safety glasses were worn at all times in the Energy Systems Laboratory with additional full face
and neck shields worn during engine testing.
Because of high power of the 3W engine, propellers were never hand started. A rubber starting
stick was used, limiting damage to the propeller and keeping all personnel a safe distance from
the rotating prop.
5.3 DATA COLLECTION Once the engine and test stand were fully operational, we could move on to the next phase. The
second phase of this research project is data collection. Using the instruments described
previously, procedures were used to capture information on the performance of the engine. This
data was recorded many times and later analyzed. The steps taken to complete the data collection
phase of this research project are detailed in the sections below.
5.3.1 Reason for data collection
Data was collected during this research project in order to conduct initial analysis both on the
performance of the UAV engine and on the performance of sensors and instruments used in the
testing. This preliminary data collection would allow the Energy System Laboratory to define its
needs for future test stand automation and advancement.
5.3.2 Procedures
Before the data collection can begin, a steady state of the engine must be reached. This is only
possible after the engine has been broken in. To break in the engine, we ran it for the factory
recommended 1.5 hours. After this break in time is complete, the engine may then be used and
steady state engine conditions will be reached.
The first step of the data collection process was to start the engine. Once the engine was running,
30 seconds were allowed for the engine to reach steady state. At this time, the propeller speed
was measured and recorded using a tachometer. The fuel tank was weighed using the scale and
this weight was recorded. As soon as the tank was weighed, a timer was started. Following the
start of the timer, the next measurements occurred in rapid succession. The exhaust temperature
was measured and recorded using a multimeter with a thermocouple and the cylinder head
47
temperature was measured and recorded using an infrared temperature gun. Finally, the propeller
airspeed was measured and recorded using an anemometer and the propeller frequency was
measured and recorded on an oscilloscope.
Once the timer reached 3 minutes, the engine was shut down by cutting power to the sparkplug.
The fuel tank was then weighed again and subtracted from the original fuel tank weight to get the
total fuel consumption weight. Lastly, the throttle was set to a different value and the testing
procedure would begin again.
This data collection procedure was used many times for several different propellers in order to
collect a wide variation of power outputs from the engine. By the end of the testing phase, the
engine had been run nearly 100 different times for a total run time of over 6 hours.
5.4 DATA ANALYSIS Data analysis occurred in multiple stages. Initially, the measured data was entered into excel to
calculate parameters such as power output, torque and efficiency. Secondary analysis involved
correcting power and efficiency for ambient pressure (the OSU ESL is at an altitude of ~1100 m
[3500 feet] and has an ambient pressure of ~0.88 bar [12.8 psia]) and temperature and calculating
further parameters such as brake specific fuel consumption and mean effective pressure.
5.4.1 Initial Data Analysis
Initial analysis was simple and assumed standard conditions and no losses. The following sections
outline the parameters calculated in the initial analysis.
5.4.1.1 Power
For both the 12x6 and 13x8 propeller, power calculations were simple. Power verses RPM data
has been previously published on these propellers. Figure 36 below shows the data and line of
best fit for each propeller.
48
Figure 36: Power verses RPM for 12x6 and 13x8 propellers.
Using a line of best fit, power can be interpolated for any given propeller speed. With this
procedure, all power outputs were calculated using their respective propeller speeds and the
following equations.
12π₯6πππ€ππ[βπ] = 8 β 10β13 β ππππππππππ ππππ[π ππ]3
13π₯8πππ€ππ[βπ] = 1 β 10β13 β ππππππππππ ππππ[π ππ]3.3182
The 17x12 propeller had a slightly more complicated procedure for calculating power output.
Using the paper by Brandt and Selig, power was calculated using the following equations (Brandt
& Selig, 2011).
π =πππ‘ππ ππππ
The above is used to calculate air density which is then used in the following equation. Patm
represents the ambient pressure and Tair is the ambient air temperature. R represents the gas
constant for air [0.287 kJ/kg-k] (Brandt & Selig, 2011).
πΆπ =π
ππ3π·5
49
The coefficient of power, Cp, is dependent on the specific propeller and its speed. D represents
the propeller diameter and n represents the propeller speed. For the 17x12 propeller, the
coefficient of power remained mostly constant at 0.052 and can be seen on the following graph.
Figure 37: Coefficient of power verses RPM for 17x12 propeller ("UIUC Propeller Databases," 2015)
5.4.1.2 Torque
Torque is a relatively simple calculation, as all components are already available. Using power
and RPM, the following equation was used to calculate engine torque (Serway & Jewett, 2003).
πππππ’π[ππ] =πππ€ππ[π]
π ππ [1π ]
5.4.1.3 Efficiency
Efficiency calculations were done by dividing the total work done during the three minute test by
the total energy contained in the consumed fuel. In order to achieve 100% efficiency, the work
done by the system must be equal to the energy put into the system through fuel. The efficiency
equation is shown below (Moran, 2010).
πΈπππππππππ¦ = ππππ[π½]
πΉπ’ππππππππ¦ππππ‘πππ‘[π½]
The fuel energy content was calculated by multiplying the total weight of fuel consumed by the
lower heating value of gasoline. The fuel energy content equation is seen below (Moran, 2010).
πΉπ’ππππππππ¦ππππ‘πππ‘[π½] = πΉπ’πππΆπππ π’πππ[π] β πΊππ πππππβπππ‘ππππ£πππ’π [π½
π]
Total work is the engine power multiplied by the engine run time. Total work was calculated
using the following equation (Moran, 2010).
ππππ[π½] = πππ€ππ[π] β ππππ[π ]
50
Time corresponds to the total time of the test, which in most cases was three minutes. Work was
calculated in joules.
5.4.2 Secondary Data Analysis
Secondary analysis takes into consideration the effect of ambient conditions on the engine power
output. Two other parameters, brake specific fuel consumption and mean effective pressure, are
also calculated for comparison with known values from other engines.
5.4.2.1 Power Corrections
To correct for power, the exiting power was multiplied by a calculated correction factor. This
correction factor was obtained using the SAE J 1349 Method from the paper Comparison of
Engine Power Correction Factors for Varying Atmospheric Conditions (Sodre & Soares, 2003).
The correction factor equation is shown below.
πΆπΉ =π
π0= (
π β ππ£π0 β ππ£0
) (π0π)0.5
The reference temperature T0 is equal to 302.4 K. The reference pressures p0 and p0v equal 0.990
and 0.013 bar respectively. These reference conditions were given as part of the SAE J 1349
method. In the above equation p is the ambient pressure, pv is the water vapor partial pressure,
and T is the ambient temperature. Water vapor partial pressure was calculated using the following
approximation from Thunder Scientific Corporation (Hardy, 1988).
ππ£[ππ π] = 0.0193 β exp(20.386 β5132
π[πΎ])
Using this correction factor, the engine power output was increased due to the low ambient
temperature and decreased due to the low ambient pressure. Overall, this correction factor
lowered the power output of each test by about 10%.
5.4.2.2 Brake specific fuel consumption
Brake specific fuel consumption, which can be used to calculate efficiency given a fuel heating
value, is used to compare the fuel efficiency of internal combustion engines that produce shaft
work. This parameter is the amount of fuel consumed divided by the energy produced. Brake
specific fuel consumption can be calculated using the following equation (Moran, 2010).
π΅ππΉπΆ [π
ππβ] =
π [πβπ]
π[ππ]
The variable r is fuel consumption in grams per hour. The variable P is power output in kilowatts.
By calculating BSFC for each test run, comparisons can be made to the BSFC for other aircraft
engines.
5.4.2.3 Brake mean effective pressure
Brake mean effective pressure (BMEP) is yet another parameter useful for comparing the
performance of one engine to other engines of similar type. The definition of BMEP is simply the
torque produced divided by the engine displacement. The division by engine displacement makes
BMEP useful for normalizing the performance of engines of different sizes. The equation for
BMEP can be seen below (Moran, 2010).
51
π΅ππΈπ[πππ] = πππππ’π[πππ]
π·ππ πππππππππ‘[π3]
By calculating BMEP, the performance of this 3W engine can then be compared to the
performance of other, similar engines.
5.5 RESULTS Following the data analysis phase, the results were then analyzed. These results are detailed in the
following sections.
5.5.1 Power, torque and efficiency
For the three propellers used in testing a large range of power outputs were achieved. This was
accomplished by setting the throttle at various positions in order to run the engine at its full range
of speeds for each propeller. Having a large range of power outputs allows us to better
characterize the engine while comparing fuel consumption and efficiency to power. The power
output verses RPM graph is shown below in Figure 38.
Figure 38: Power vs. RPM for all three propellers
A graph of efficiency verses engine speed can be seen as Figure 39 below. This graph was made
by compiling data from all three propellers, giving us the widest possible range of RPMs. The
minimum efficiency achieved was approximately 3%, found at a speed of 6000 RPM with the
12x6 propeller. The maximum efficiency recorded was approximately 19.7%, found when the
engine was running at 6500 RPM with a 17x12 propeller. During this run, the engine was
outputting approximately 1.5hp, or about half of its maximum power output.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
4000 5000 6000 7000 8000 9000 10000
Po
wer
[h
p]
RPM
Power vs. RPM: Combined
12x6
13x8
17x12
52
Figure 39: Engine efficiency vs. RPM for three different propellers
The difference in our efficiency values verses published data will be covered in the section 5.6.
5.5.2 Brake Specific Fuel Consumption of Different Fuels
The engine was run on both gasoline with ethanol and gasoline without ethanol. It was
hypothesized that the brake specific fuel consumption, a measure of total fuel weight consumed
per work output, would decrease for the fuel without ethanol. The reason for this hypothesis is
that the energy content of ethanol is lower than that of gasoline, meaning a higher weight of fuel
containing ethanol would be needed to have the equivalent energy of fuel containing no ethanol.
The data points and two separate trend lines can be seen below in Figure 40, Figure 41, and
Figure 42.
Figure 40: Brake specific fuel consumption vs. RPM for 13x8 prop
0.00%
5.00%
10.00%
15.00%
20.00%
25.00%
4000 5000 6000 7000 8000 9000 10000
Effi
cien
cy
RPM
Efficiency vs RPM: Combined
12x6
13x8
17x12
0
500
1000
1500
2000
2500
5000 5500 6000 6500 7000 7500 8000 8500 9000 9500
BSF
C [
g/kW
h]
RPM
BSFC vs RPM of E0 vs E10: 13x8
E10
E0
53
Figure 41: Brake specific fuel consumption vs. RPM for 12x6 prop
Figure 42: Brake specific fuel consumption vs. RPM for 17x12 prop
Brake specific fuel consumption, shown on the vertical axis, decreases as engine speed rises. This
can be explained by the increase in efficiency: as efficiency rises, the amount of fuel it takes for a
certain power output falls. The results of our experiment show the results that we expected.
Because E0 has a higher energy content, we expect it will have a lower brake specific fuel
consumption compared to E10. As can be seen in Figure 40, Figure 41, and Figure 42, there is a
small difference in the exponential trend as E0 has a lower fuel consumption than E10.
5.5.3 Brake Mean Effective Pressure
Brake mean effective pressure is a normalized measurement of torque for an engine. Since the
measurement is calculated per engine volume, it can be used to compare engines of all sizes.
Given two BMEP measurements, the higher measurement represents an engine that can pack
0
500
1000
1500
2000
2500
3000
5500 6000 6500 7000 7500 8000 8500 9000 9500 10000
BSF
C [
g/kW
h]
RPM
BSFC vs RPM of E0 vs E10: 12x6
E10
E0
150
250
350
450
550
650
750
850
950
1050
1150
4500 4750 5000 5250 5500 5750 6000 6250 6500 6750
BSF
C [
g/kW
h]
RPM
BSFC vs RPM of E0 vs E10: 17x12
E10
E0
54
more fuel and air into its given cylinder size. For this research project, we have calculated BMEP
in order to compare how much energy we can get out of different fuels in the same size engine.
As can be seen in Figure 43 below, the maximum BMEP of 213 kPa occurs at the highest engine
speed which is 9000 RPM.
Figure 43: Brake mean effective pressure vs. RPM for 13x8 prop
There is a slight difference in the trend lines of BMEP between E0 and E10. After plotting the
BMEP of two different fuels for a single propeller data set, 2nd order polynomial trend lines were
assigned to each fuel. Using the trend line equations, we calculate that at the speed ranges that the
data set falls in we have a consistent BMEP difference of around 6 kPa between the two fuels.
Gasoline with ethanol, E10, was consistently measured to have a higher BMEP than gasoline
without ethanol. The two fuel BMEP comparison of the 12x6 prop, which has a much smaller
difference than the 13x8 prop, is shown in Figure 44 below.
y = 4E-06x2 - 0.0124x + 22.869
y = 4E-06x2 - 0.0142x + 31.669
50
70
90
110
130
150
170
190
210
230
5000 5500 6000 6500 7000 7500 8000 8500 9000 9500
BM
EP [
kPa]
RPM
BMEP vs RPM of E0 vs E10: 13x8 Prop
E10
E0
55
Figure 44: Brake mean effective pressure vs. RPM for 12x6 prop
Just as calculated for the 13x8 propeller BMEP, a difference in the trend lines was found for the
12x6 prop. This difference showed that E10 was measured to consistently have a higher BMEP
by about 2kPa compared to E0. The final prop, 17x12, and its respective BMEP measurements
are shown in Figure 45 below.
Figure 45: Brake mean effective pressure vs. RPM for 17x12 prop
Here we do not see a clear difference in BMEP for part of the graph. At its highest difference,
E10 outperforms E0 by about 3kPa. We do, however, see our highest BMEP measurement with
y = 1E-06x2 + 0.0005x - 0.4704
y = 1E-06x2 + 0.0004x - 1.6959
40
50
60
70
80
90
100
110
5500 6000 6500 7000 7500 8000 8500 9000 9500 10000
BM
EP [
kPa]
RPM
BMEP of E0 vs E10: 12x6
E10
E0
y = 4.819E-06x2 + 2.709E-02x - 6.826E+01y = 7.387E-06x2 - 2.415E-15x + 9.607E-12
150
170
190
210
230
250
270
290
310
330
4500 4750 5000 5250 5500 5750 6000 6250 6500 6750
BM
EP [
kPa]
RPM
BMEP vs RPM of E0 vs E10: 17x12
E10
E0
56
this propeller. At 6500 RPM with a 17x12 prop, the 3W engine is calculated to have a BMEP of
312kPa, which is about one third of the naturally aspirated spark ignition engine maximum
BMEP (Heywood, 1988).
5.5.4 Published Data Comparison
In this section we will compare the data obtained at the OSU ESL to the data from a published
paper on the same 3W engine. Data from Rowton can be seen below in Figure 46 (Rowton,
2014). First we notice that the power output is very comparable to ours at the same RPM ranges
we were testing in. During our tests, we found a wide range of power outputs from about 0.15 kW
up to 1kW. Below we can see on the upper left graph that the power output ranged between 0.2
kW and 1.25 kW. Note that in our tests, we never had the throttle open 100%, which is the only
place that Rowtonβs data does not agree with ours for power output.
Our brake specific fuel consumption measurements are also in the same range as those from
Rowton. The published data shows BSFC range from around 650 to 1500 [g/kWh] where as we
measured BSFC in the range of 500 - 2000 [g/kWh].
Brake mean effective pressure in the Rowton paper ranges from 50 to 425 kPa where as our
BMEP data ranges from 45 to 312 kPa. These numbers, like power and BSFC, are very similar
and encouraging.
Lastly, we compare efficiency. Our collected data is still in the approximate range, but not as
close to Rowtonβs data as the last three parameters. Rowton measures an efficiency low of about
3%, which is what we measured as our low end efficiency. On the high end, Rowton measures
efficiencies up to about 12% where we measure efficiency up to 19%. That being said, the
majority of the two data sets are quite similar in power, brake specific fuel consumption, break
mean effective pressure and efficiency.
57
Figure 46: 3W-28i published data (Rowton, 2014)
5.5.5 Uncertainty Analysis
The largest source of error in our measurements was the resolution of the scale used for finding
fuel flow. Most fuel consumption measurements were under 30 grams and the scale resolution
was 2 grams, giving our measurement an uncertainty of Β±3.3%. This uncertainty propagates to the
calculations for both efficiency and brake specific fuel consumption.
Another source of uncertainty was the measurement for engine speed. Even though the
tachometer and especially oscilloscope have relatively high resolutions for their range, the actual
engine speed would fluctuate during the test. It was common to see a change of Β±25 RPM during
the recording period, making it difficult to get an accurate average reading of the engine speed.
This corresponds to a Β±0.42% uncertainty of the engine speed measurement. This uncertainty
propagates to equations for power, efficiency, brake specific fuel consumption and mean effective
pressure.
There is also an uncertainty in our power outputs that were calculated using previous performance
data. In the performance data, the entire prop was used, where as ours was partially covered by a
nose cone. Also, we had many blockages behind the prop, making for a non-ideal air flow
condition. These uncertainties are difficult to quantify but will become more apparent once
measurements are taken with a dynamometer.
58
Other sources of error are negligible compared to the previously mentioned uncertainties. Using a
root sum squared, the following uncertainties are calculated for each output parameter:
Power: Β±0.42% Brake Specific Fuel Consumption: Β±3.4%
Efficiency: Β±3.4% Brake Mean Effective Pressure: Β±0.42%
5.6 DISCUSSION The first goal of this research was to create an all-in-one test bed for UAV engine data collection.
Both the small piston-prop engine and test stand were successfully assembled and operated. The
engine was run for several hours, proving correct assembly and operation. The test stand was
successful in housing the engine and providing a platform for data collection.
The second goal was to collect data, compare it to published data on the same engine, and prove
the utility of the test bed. Upon analysis, collected data proved similar to published data. There is
a certain amount of error between these two data sources, which in this case is acceptable. For the
most part, our data and Rowtonβs data on the 28cc engine matched up very well, proving the
utility of the test stand and enforcing the appropriateness of our chosen sensors.
Minimizing data collection error in the future is one of the keys to successful engine analysis and
characterization. One major improvement to be made is the introduction of a dynamometer. This
component will allow for direct measuring of engine torque, instead of measuring propeller speed
and backing out power using propeller data. This would greatly reduce the error in our power
measurements and we would make far fewer assumptions and no longer need to use correction
factors based on ambient temperature and pressure. Additionally, the use of a dynamometer
would eliminate the need for manual hand starting of the engine.
A second major improvement is the use of a far more accurate instrument for collecting fuel flow
data. A scale may still provide desired accuracy if, for example, it had a resolution of 0.1 grams
instead of the 2 gram resolution used in the discussed experiments. Alternatively, a properly
calibrated fuel flowmeter would provide digital data output so that transient flow rates could be
corresponded to the respective transient operations of an engine.
The results of experiments were mostly as expected. Some unexpected problems were finding a
steady state engine condition and some issues gathering accurate sensor readings. Getting the
engine to a steady state mode of operation was a larger challenge than expected, with many small
problems ranging from the carburetor needle valves to the ignition system spark timing. Even
though these issues took longer than expected to solve, they were eventually overcome. A major
sensor issue was the tachometer, which for a time would not take readings. Similar to the
previous problem, this one was eventually overcome and accurate readings of engine speed were
taken. None of the issues we ran into during our engine, test stand and sensor integration
prohibited engine data collection.
Both numerical and analytical data collected during these experiments are important to the future
success of engine testing at the Energy Systems Laboratory. Most importantly, the data allows for
a more advanced test cell to be created in the future for high level engine analysis and
experimentation.
59
5.7 CONCLUSIONS This was the first UAV engine test stand to be built and operated in the OSU Energy Systems
Laboratory. Following the testing period, post processing showed that the collected data
correlated well with published data on the 3W-28i. Our peak measurements were a power of 1.29
hp, an efficiency of 19.7%, a BSFC low of 414 g/kWh, and a BMEP high of 312 kPa. This
correlation proves that the test stand functioned as desired and the sensors used were appropriate
for this application. Building the test stand and conducting experiments resulted in a significant
knowledge repository for the ESL with regard to UAV engine testing. These activities, performed
in December 2014, now serve as a launch pad for a next generation UAV test cell at the OSU
Energy Systems Laboratory.
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62
7
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2
5
6
18
95
5.2
6
16
.67
7
58146
8.9
5%
1.5
0
1.2
5
So
und
ing b
ett
er.
Abo
ut
50/5
0
smoo
th/k
nock
ing
31
13
x8
2
(50-
1)
3
7100
0.5
56
0.4
12
7
47
00
8
9
6
5
22
10
60
.67
1
7.8
3
92
6623
8.0
6%
1.5
0
1.2
5
32
13
x8
2
(50-
1)
3
7450
0.6
53
0.4
61
8
77
36
9
0
9
4
24
98
5.1
7
19
.96
1
010861
8.6
8%
1.5
0
1.2
5
So
unds
much
smoo
ther
. S
till
so
me
"knock
ing"/
"cra
ckin
g"
no
ise.
-14 C
am
bie
nt
33
13
x8
2
(50-
1)
3
8800
1.1
37
0.6
78
152
61
0
11
5
11
3.2
2
2
51
9.1
8
29
.39
9
26623
16.4
7%
1.5
0
1.2
5
Tem
p:
-16 C
am
bie
nt
34
13
x8
2
(50-
1)
3
9000
1.2
25
0.7
15
164
46
4
11
8
12
3
20
43
7.9
6
30
.97
8
42384
19.5
2%
1.5
0
1.2
5
66
35
17
x1
2
3
(50-
1)
3
6000
1.0
34
0.9
05
138
84
0
12
8
41
27
18
46
6.9
1
39
.22
7
58146
18.3
1%
5940
1.5
0
1.2
5
36
17
x1
2
3
(50-
1)
3
4800
0.5
29
0.5
79
7
10
86
1
22
3
2
27
19
96
2.6
0
25
.10
8
00265
8.8
8%
37
4740
1.5
0
1.2
5
37
17
x1
2
3
(50-
1)
3
5400
0.7
49
0.7
28
100
54
1
12
8
36
29
24
85
9.7
0
31
.56
1
010861
9.9
5%
41
5340
1.5
0
1.2
5
38
17
x1
2
3
(50-
1)
3
5900
0.9
73
0.8
66
130
69
8
15
2
40
30
22
60
6.2
2
37
.54
9
26623
14.1
0%
50
5940
1.5
0
1.2
5
39
17
x1
2
3
(50-
1)
3
6150
1.0
95
0.9
35
147
03
8
13
9
43
32
20
48
9.8
7
40
.52
8
42384
17.4
6%
49
6120
1.5
0
1.2
5
40
17
x1
2
3
(50-
1)
3
6400
1.2
34
1.0
13
165
70
9
16
5
58
32
22
47
8.1
4
43
.88
9
26623
17.8
8%
50
0
1.5
0
1.2
5
41
17
x1
2
3
(50-
1)
3
6300
1.1
77
0.9
81
158
06
2
15
7
45
32
20
45
5.7
0
42
.52
8
42384
18.7
6%
49
0
1.5
0
1.2
5
42
17
x1
2
4 (
no
E)
3
5500
0.7
83
0.7
48
105
17
0
10
5
3
2
22
75
3.3
7
32
.41
9
68000
10.8
6%
45
5640
1.5
0
1.2
5
43
17
x1
2
4 (
no
E)
3
4600
0.4
58
0.5
23
6
15
29
1
12
32
18
10
53
.59
2
2.6
7
79
2000
7.7
7%
33
4500
1.5
0
1.2
5
67
44
17
x1
2
4 (
no
E)
3
6200
1.1
22
0.9
50
150
65
4
13
3
3
2
18
43
0.3
0
41
.18
7
92000
19.0
2%
45
6180
1.5
0
1.2
5
45
17
x1
2
4 (
no
E)
3
6500
1.2
93
1.0
45
173
59
8
14
1
3
2
20
41
4.9
2
45
.27
8
80000
19.7
3%
51
0
1.5
0
1.2
5
46
13
x8
4
(n
o
E)
3
8850
1.1
13
0.6
61
149
47
8
11
0
26
35
18
43
3.6
8
28
.63
7
92000
18.8
7%
47
8880
1.5
0
1.2
5
47
13
x8
4
(n
o
E)
3
7300
0.5
88
0.4
23
7
89
05
1
05
2
8
35
18
82
1.5
7
18
.32
7
92000
9.9
6%
36
0
1.5
0
1.2
5
48
13
x8
4
(n
o
E)
3
7600
0.6
72
0.4
64
9
01
87
1
08
2
7
35
16
63
8.9
3
20
.11
7
04000
12.8
1%
40
0
1.5
0
1.2
5
49
13
x8
4
(n
o
E)
3
8000
0.7
96
0.5
23
106
92
1
11
0
30
35
22
.65
0
39
7920
1.5
0
1.2
5
Pro
p b
roke!
50
12
x6
4
(n
o
E)
3
9600
0.6
29
0.3
44
8
44
42
1
28
3
1
37
22
93
8.3
0
14
.91
9
68000
8.7
2%
48
9420
1.5
0
1.2
5
51
12
x6
4
(n
o
E)
3
9000
0.5
18
0.3
02
6
95
78
1
28
3
2
37
22
11
38
.75
1
3.1
0
96
8000
7.1
9%
42
9120
1.5
0
1.2
5
52
12
x6
4
(n
o
E)
3
7700
0.3
24
0.2
21
43
57
3
10
8
28
37
20
16
53
.06
9
.59
8
80000
4.9
5%
38
0
1.5
0
1.2
5
68
53
12
x6
4
(n
o
E)
3
7150
0.2
59
0.1
90
3
47
91
1
00
2
5
39
16
16
56
.24
8
.25
7
04000
4.9
4%
33
7080
1.5
0
1.2
5
54
12
x6
4
(n
o
E)
3
6500
0.1
95
0.1
57
2
61
39
9
0
23
39
18
24
80
.02
6
.82
7
92000
3.3
0%
33
0
1.5
0
1.2
5
Am
bie
nt:
4 C
, 43.5
%
hu
mid
ity (
Kes
trel
3000 -
als
o u
sed f
or
airs
pee
d)
55
17
x1
2
4 (
no
E)
3.1
67
5970
1.0
22
0.8
99
137
22
1
12
8
41
39
22
57
7.4
0
38
.96
9
68000
14.1
8%
5970
1.5
0
1.2
5
56
17
x1
2
4 (
no
E)
0
0.0
00
3
8
0
0
1.0
0
1.2
5
Did
no
t ru
n (
kin
d o
f
star
ted)
57
17
x1
2
4 (
no
E)
0
0.0
00
3
8
0
0
1.2
5
1.2
5
Did
no
t st
art
at a
ll
58
17
x1
2
4 (
no
E)
3
5820
0.9
50
0.8
57
127
56
6
12
6
43
38
24
67
7.5
7
37
.15
1
056000
12.0
8%
5820
1.7
5
1.2
5
59
17
x1
2
4 (
no
E)
3
5040
0.6
19
0.6
45
8
31
24
1
18
4
3
37
26
11
26
.48
2
7.9
5
11
44000
7.2
7%
5040
2.0
0
1.2
5
60
17
x1
2
4 (
no
E)
3
6240
1.1
75
0.9
89
157
75
7
12
6
52
37
30
68
4.8
7
42
.85
1
320000
11.9
5%
6240
2.0
0
1.2
5
61
17
x1
2
4 (
no
E)
2.7
5
5700
0.8
95
0.8
25
120
24
3
11
8
52
37
26
77
8.7
4
35
.75
1
144000
10.5
1%
5700
2.2
5
1.2
5
69
62
17
x1
2
3
3
6720
1.4
67
1.1
47
197
03
4
13
8
59
37
30
54
8.3
5
49
.69
1
263576
15.5
9%
6720
2.0
0
1.2
5
63
17
x1
2
3
3
6600
1.3
95
1.1
10
187
29
6
14
0
62
36
36
69
2.2
3
48
.10
1
516291
12.3
5%
6600
1.7
5
1.2
5
64
17
x1
2
3
3
6360
1.2
48
1.0
31
167
59
8
13
2
65
3
6
38
81
6.5
7
44
.66
1
600530
10.4
7%
6360
1.5
0
1.2
5
