Hybrid Power and Propulsion for Unmanned Systems

 

Hybrid Power and Propulsion for Unmanned Aerial Systems

Stanley D. Pebsworth

Bachelors of Science in Aeronautics

Embry-Riddle Aeronautical University

July 2016

A Research Project Submitted to the Worldwide Campus in partial fulfillment of the requirements for course UNSY 615, Unmanned Systems Power, Propulsion, and Maneuvering

Abstract

With an increased demanded for unmanned aerial systems (UAS), advanced technological alternatives must be found to meet the expanding mission requirements.  Developers and designers are often challenged with balancing the customer’s mission requirements with the customer’s budget constraints.  A new type of power and propulsion system must be found that will meet requirements while maximizing cost savings, improving safety, decreasing failure rates, and reducing acoustic signature.  The demand is for UAS to have longer mission times, utilize weight saving measures, and incorporate cost saving fuel sources.  An innovative research strategy that combats these issues is the combination of multiple power, propulsion, and storage technologies.  Research and development in hybrid technology is ongoing in the automobile industry and therefore, must be considered.  This research paper proposes the use of hybrid technology to satisfy the requirements of UAS greater than 50 pounds.  Through quantitative research, this paper will analyze current power and propulsion options and provide alternative hybrid solution that will fulfill the needs of various UAS.  This paper will also recommend research strategies that will concentrate on the need for the future development of alternative power and propulsion sources for UAS.  

Keywords: unmanned systems, hybrid systems, propulsion, power storage, power generation

Hybrid Power and Propulsion for Unmanned Aerial Systems

            Since the early days of aviation, the need to balance the requirement to fly farther and longer with the requirement to reduce weight and increase payload has been ongoing.  An unmanned aerial system with the ability to fly for 24 hours and carry no payload is useless to the customer.  As fuel cost fluctuates, the need to improve fuel economy also exists.  In addition, we must also consider the primary role of unmanned system to be reconnaissance and therefore must address the need for a reduced acoustic signature.

            Currently, there is no replacement for hydrocarbon fuels that can match its energy density known at this time.  Hybrid technology, in some cases, will be less efficient than heavy fuel systems.  However, there are several scenarios in which hybrid systems could be optimized and meet the requirements of its mission such as during long cruise flight and descents (Rupe, 2010). 

            The research and development of hybrid technology has the ability to address all of these issues confronting UAS today.  Hybrid systems have the potential to maximize power to weight ratios which will increase range and reduce fuel usage.  With hybrid technology, the potential also exists to reduce acoustic signature due to the reduced operating RPM of the engine.  Improved safety can also be accomplished with hybrid technology by removing the single point failure system of a hydrocarbon engine and replacing it with a lighter engine that generates electrical current to charge onboard batteries as well as operate an electrical propulsion engine.

            The primary scope of this research paper is to compare and contrast current power and propulsion system with comparable hybrid power and propulsion systems.  Furthermore, this paper will address the tradeoffs between hydrocarbon fueled systems and that of hybrid systems.  This paper will focus primarily on hybrid systems for use in UAS larger than 50 pounds and with a real world reconnaissance role.

Literature Review

            In an effort to find viable power and propulsion solutions for UAS, this research analyzed past and current research on hybrid automobile technology, power sources options, as well as current hybrid aircraft systems both in use and in development.  Hybrid technology has matured over the last decade and therefore has become a feasible solution for power and propulsion issues facing the UAS used in today’s military and civilian world security missions.

            The use of hybrid propulsion systems combining a heavy fuel engine with a battery storage system has the ability to produce significantly higher endurance for small unmanned aerial systems.  Aerial platforms typically require a large power range to support all modes of flight such as take-offs, climbs, descents, and cruise profiles.  A hybrid system that has the capability to provide short term increased power profiles through the combination of both a fuel engine and battery storage could produce an operationally viable system (Verstraete, Lehmkuehler, Gong, Harvey, Brian, & Palmer, (2014).

            The Department of Defense (DoD) produced its plans for unmanned systems through the year 2032.  The DoD discussed their four primary needs as being reconnaissance and surveillance, target identification and designation, counter improvised explosive device (IED) warfare, and Chemical, Biological, Radiological, Nuclear, Explosive (CBRNE) reconnaissance (Rupe, 2014).  In order to be mission effective in these needs, range and endurance must be addressed (Rupe, 2014).

            On today’s battlefield, commanders have an appetite for constant intelligence updates.  Commands today list reconnaissance as their number one priority (Hiserote, & Air Force Inst of Tech Wright Patterson AFB OH School of Engineering and Management, 2010).

“The intrinsic characteristics of UAS are unmatched by their manned counterparts. “The attributes of persistence, efficiency, flexibility of mission, information collection and attack capability have repeatedly proven to be force multipliers across the spectrum of global Joint military operations.”6 In the asymmetric warfare of GWOT, the abilities of UAS have proven to be mission essential. The Air Force is currently posturing itself to develop and harness unmanned system capabilities to maximize current and future contributions to the Joint Force” (Hiserote, et al, 2010). 

            Mission effectiveness could be accomplished through the use of a parallel hybrid/electric power and propulsion system.  Current battery powered UAS do not offer the much needed mission time and their counterpart, the internal combustion engine driven UAS, often produce an unwanted and compromising acoustic signature.  A parallel hybrid/electric system for UAS has the potential to combat both of these issues (Hiserote, et al, 2010).

            Serial and parallel hybrid solutions were the topic of research conducted by Fusaro, (2016).  In her paper she describes serial hybrid solutions as one that has an electric motor connected directly to the propeller as the main element in the system and can be powered by the generator of an internal combustion engine or through a battery storage system.  In addition, she describes parallel hybrid solutions as one that has an internal combustion engine and an electric motor connected to the propeller through a gearbox (Fusaro, 2016).

            The aviation industry is projected to grow by over 10% in the next 20 years (Friedrich, & Robertson, (2015).  Coupled with the rising fossil fuel prices, alternatives to meet the propulsion requirements.  Hybrid-electric systems provide synergy between fuel and electric systems which improve performance over internal combustion engines alone.  This improved performance includes: reduced fuel consumption, reduced CO² emissions, reduced noise signature, and an increase in power to weight ratio (Friedrich, et al, 2015).

Design Overview

            There are currently several designs in development that could provide research as well as solutions for a conceptual design.  In 2009, Flight Design presented an aircraft that used a combination of a 115 HP engine coupled with a 40 HP electric drive motor to replace the normal 160 HP internal combustion engine.  This design allows for a more efficient fuel engine and incorporates electric boost power for climbs and take-off (Rupe, 2014).

Another design idea was developed by students from Embry Riddle University in 2011 called the Eco-Eagle.  This design used the smaller Rotax 912 100 HP engine coupled with a 40 HP electric motor.  This hybrid propulsion system was tested in the Stemme S10 motor glider (Rupe, 2014).

Hybrid electric distributed propulsion (HEDP) could be a possible solution to the design and mission needs of UAS as prescribed by the DoD’s plans for unmanned aerial systems through 2032.  HEDP combines powers sources and can provide supplemental power for takeoff and climbs (Schiltgen, Green, Freeman, & Gibson, 2014).  Having multiple power sources also adds a safety factor in the event of a one of the propulsion sources.  The following diagram illustrates the options of both direct drive systems with power supplement and distributed propulsion with a power supplement.

Design Decisions

            In the development stages of a hybrid system that would compare to the power output of its internal combustion engine counterpart, the ratio of weight to power output must be considered.  In research it has been stated through statistical data that the average internal combustion engine has a power to weight ratio of approximately 1:1 and an electrical motor has a power to weight ration of approximately .65:1 (Fusaro, 2016).  In comparison, a 195kW electric motor is similar in power to that of a 260hp internal combustion engine (Fusaro, 2016).  Therefore, full analysis of the propulsion requirements must be fully understood in order to apply the proper hybrid solution for the design.

            The batteries to be used also play a key role in the design decisions.  The batteries capacity and current rating provide critical response requirements during power load changes.  The battery recharging rate must be addressed as well to determine the best balance between the time it takes to fully recharge the batteries and the available time that the batteries can provide either complete or supplement power.  A compromise must be met between the fuel consumption required for recharging the batteries and the required endurance time (Verstraete, Gong, Lu, & Palmer, (2014).

            In a research paper by Jiménez-Espadafor, Guerrero, Trujillo, García, & Wideberg, (2015), research was conducted to produce an energy management system for serial hybrid systems.  Although this research was conducted to manage the power consumption of a wheeled vehicle, critical information was addressed that can provide a starting point for aerial systems.  In their research, the management of thermal energy is critical to maximize fuel efficiency.

            Acoustic signature is another design choice that must be addressed.  The desire to conduct covert reconnaissance requires certain aspects of the design to be taken into consideration.  First of which is the noise produced by the exhaust system of the internal combustion engine.  Design choices must be made to determine the desired location in which the systems acoustic signature must be minimized.  It is assumed that this requirement would be during cruise flight while the system is conduct reconnaissance missions.

A possibility to reduce acoustic signature is maximizing the noise reducing capability of the exhaust system.  In a hybrid system, the internal combustion engine runs at a constant RPM.  This constant RPM will produce a known acoustic signature and therefore, the muffling characteristics of the exhaust system can be optimized to focus primarily on targeting that signature.      

            Additional research must be conducted on propeller design and how it effects audible signature in the design decisions as well.  The desire is to produce a propeller design that optimizes the reduction in radiated noise, but does not significantly reduce cruise performance.

Addressing this criterion consists in research that addresses several design variables so that the objectives can be met.

“Although broadband noise contributions for rotors and propellers are generally non-negligible, in the present study, the tonal noise contribution due to the high-speed

flow in the tip region and the blade–exhaust interaction in the inner part of the blade plays a dominant role. The shape optimization revealed that the overall acoustic energy of the pusher propeller can be reduced up to a value of 3.5 dB. This reduction is nearly equally due to an optimal design of the blade planform in the tip and inner

regions. Compared with the five-blade production propeller, the new optimized six-blade propeller results in a 5.5 dB overall noise reduction” (Pagano, Barbarino, Casalino, & Federico, 2010).

Conclusion

            Baring entry of hybrid systems into current UAS design is the cost of implementation.  Future systems are believed to use this technology giving its recent technological advances in both ground and aerial platforms.  There are a number of tradeoffs that must be considered between heavy fuel and hybrid systems such as endurance verses stealth.  Hybrid systems offer a complete new range of options in design options as well as limitations.  Mission requirements must be carefully analyzed and options presented to the customer in order to determine if hybrid power and propulsion are the best option.  

This research paper presented a review of current literature found on hybrid propulsion technology and formulated a design idea based on this research.  Through this design idea, limitations were addressed and made available that will give design engineers the tools necessary to formulate goals for specific UAS power and propulsion design.  Results found in this research show that hybrid propulsion is a viable option for UAS due to its fuel savings of 6.5% compared to internal combustion engines (Hung, & Gonzalez, 2012).  This fuel savings results in increased payload capability or increased endurance.

            Additional research is necessary to provide quantifiable data on the increased safety aspect hybrid system over that of internal combustion systems.  It is proposed that hybrid systems have an increased safety factor due to the addition of optional power sources in comparison.  It is also recommended that this increased safety margin be considered in additional research into the acceptance of UAS into the national airspace system.

  

References

Friedrich, C., & Robertson, P. A. (2015). Hybrid-electric propulsion for aircraft. Journal of Aircraft, 52(1), 176-189. doi:10.2514/1.C032660

Fusaro, R. (2016). The advantages of a hybrid piston prop aircraft. Aviation, 20(2), 85. doi:10.3846/16487788.2016.1198093

Hiserote, R. M., & Air Force Inst of Tech Wright Patterson AFB OH School of Engineering and Management. (2010). Analysis of hybrid-electric propulsion system designs for small unmanned aircraft systems

Hung, J. Y., & Gonzalez, L. F. (2012). On parallel hybrid-electric propulsion system for unmanned aerial vehicles. Progress in Aerospace Sciences, 51, 1. doi:10.1016/j.paerosci.2011.12.001

Jiménez-Espadafor, F. J., Guerrero, D. P., Trujillo, E. C., García, M. T., & Wideberg, J. (2015). Fully optimized energy management for propulsion, thermal cooling and auxiliaries of a serial hybrid electric vehicle. Applied Thermal Engineering, 91, 694-705. doi:10.1016/j.applthermaleng.2015.08.020

Pagano, A., Barbarino, M., Casalino, D., & Federico, L. (2010). Tonal and broadband noise calculations for aeroacoustic optimization of a pusher propeller. Journal of Aircraft, 47(3), 835-848. doi:10.2514/1.45315

Pornet, C., & Isikveren, A. T. (2015). Conceptual design of hybrid-electric transport aircraft. Progress in Aerospace Sciences, 79, 114. doi:10.1016/j.paerosci.2015.09.002

Rupe, R. M. (2014). Analysis of UAS hybrid propulsion systems

Schiltgen, B., Green, M., Freeman, J., & Gibson, A. (2014). Terminal area operations for hybrid electric distributed propulsion. Aircraft Engineering and Aerospace Technology, 86(6), 584-590. doi:10.1108/AEAT-04-2014-0047

Verstraete, D., Gong, A., Lu, D. D. -., & Palmer, J. L. (2014). Experimental investigation of the role of the battery in the AeroStack hybrid, fuel-cell-based propulsion system for small unmanned aircraft systems. International Journal of Hydrogen Energy, doi:10.1016/j.ijhydene.2014.11.043

Verstraete, D., Lehmkuehler, K., Gong, A., Harvey, J. R., Brian, G., & Palmer, J. L. (2014). Characterisation of a hybrid, fuel-cell-based propulsion system for small unmanned aircraft. Journal of Power Sources, 250, 204-211. doi:10.1016/j.jpowsour.2013.11.017

Sensor Data Fusion for Improved Sense and Avoid

 

Sensor Data Fusion for Improved Sense and Avoid

by

Stanley D. Pebsworth

Embry-Riddle Aeronautical University

May 2016

A Research Project Submitted to the Worldwide Campus in partial fulfillment of the requirements for course UNSY 605, Unmanned Systems Sensing, Perception, and Processing

Abstract

See and Avoid is a Federal Aviation Administration (FAA) requirement to operate airborne systems within our National Airspace.  With the increased awareness of the need and want to adapt unmanned systems into the National Airspace, the need for improved Sense and Avoid technology has surfaced.  Current issues are the rate in which unmanned systems can react and avoid a collision as compared to their human counterpart.  The FAA and the National Aeronautics and Space Administration (NASA) have been collaborating to determine a safe way to incorporate unmanned systems into the current air-traffic system alongside commercial and private manned systems.  This research will identify current hardware and software relevant to sensor fusion and its application towards the See and Avoid requirements.  With the use of scholarly and peer reviewed material, this paper will review historical flight testing of Unmanned Aerial Systems (UAS) used to test Sense and Avoid technology.  Alternatively, this research will identify the underlying issues associated with the human factors in sense and avoid and relate how technology addresses these factors.

Keywords: unmanned aircraft systems, sense and avoid, sensor fusion, situational awareness

Sensor Data Fusion for Improved Sense and Avoid

            Currently Part 91.113 of the Federal Aviation Regulations (FAR) outlines the requirements for see and avoid (GPO, 2016).  In summary, the regulation states that “vigilance shall be maintained by the pilot of an aircraft to see and avoid other aircraft” and was last amended in August of 2004 (FAA, 2004).  A committee formed by the FAA is looking to amend Part 91.113 to include the allowance of see and avoid through electronic means.  A UAS subcommittee met for the first time on July 30, 2013 and is responsible for outlining the requirements for electronic sense and avoid (Carey, 2013).

            NASA has been working with the FAA to aide in research and outline the technical challenges associated with the integration of UAS into the national airspace.  NASA has chaired a program specifically for this project and key stakeholders have been identified to foster unencumbered national airspace access for civil and commercial UAS (Hackenberg, 2014). Figure 1 shows the key stakeholders for the UAS integration subcommittee.

Figure 1. Key stakeholder for UAS integration. Adapted from “UAS integration in the NAS project,” by D. Hackenberg, 2014, NASA.

Problem Statement

Currently unmanned aerial systems (UAS) are restricted from operations within the national airspace.  This restriction requires the operator of the UAS to seek special authorization to operate their system within the national airspace.  As mandated by the 2012 FAA re-authorization act, safe integration of UAS systems started in 2015 (Carey, 2013).  The safe integration of UAS into the national airspace is contingent on implementation of a safe and comprehensive aviation program (Hottman, Hansen, & Berry, 2009).  This program will require the complete understanding of sense and avoid technology in order to provide solutions that will enhance safety and provide UAS with access to the national airspace.  Therefore, it is incumbent upon key stakeholders in UAS integration to address not only safety on integration, but also address the technological requirements that will make up the electronic means of sense and avoid.

Significance of Problem Statement

            After years of development for military use, UAS have reached a culminating point and are starting to be applied more and more to civilian and commercial tasks.  The tasks proposed for UAS application are: environmental, emergency, communications, monitoring, as well as commercial applications in photography, agriculture, chemical application, and transportation.  UAS have the capability to offer major advantages when applied to these applications.  Currently, there are several companies producing hundreds of UAS designs.  Of course major defense contractors such as Boeing, Lockheed, and BAE are involved, but there are also new companies emerging to try and grab their share of the market.  The US currently holds approximately 64% of the UAS market share.  It is predicted that by 2020, the UAS market growth will reach an annual expenditure of 11.3 billion dollars for research, development and procurement (Angelov, 2012).  Figure 2 shows the forecasted growth for the world UAV market.

Figure 2. World UAV Forecast. Adapted from “Sense and avoid in UAS: Research and applications,” by P. P. Angelov, 2012 p.18. Hoboken: John Wiley & Sons.

The main funding for research and development for future UAS systems is the US Department of Defense (DoD).  In the Unmanned Systems Integrated Road-map published by the DoD, it was stated that the performance of UAS must evolve significantly in order for their safe integration into the national airspace (Angelov, 2012).  As civil and commercial UAS begin to be applied toward the possible missions discussed, they will need access to the national airspace. 

It was determined in 2007 by an FAA General Aviation Research board that nearly 54% of the current FAA Regulations would have to be revised in order to address UAS integration (Dalamagkidis, Valavanis, & Piegl, 2009).  The issue is that the current regulations have been developed over decades of experience and this new revision to integrate UAS will have very little experience to draw from.  Regardless, this new integration will be without problems and will require a complete understanding of the differences and challenges that may require a different way of thinking. The intent of this research is to focus primarily on the see and avoid requirement imposed by the FAA and the possible electronic means for which these requirements may be met.

Alternative Actions for See and Avoid

            Sense and Avoid is the technology designed to replace the human pilot’s requirement for See and Avoid (Angelov, 2012).  Sense and avoid technology will be required to avoid hazards such as aircraft, gliders, balloons and other UAS (Angelov, 2012).  There will also be the requirement to avoid hazardous obstacles such as buildings, towers, power lines and birds.  Sense and avoid must be able to provide detection, tracking, evaluation, prioritization, declaration, maneuver determination, and maneuver command execution. 

There are currently two primary cooperative technologies that aide in the tasks of detection and tracking.  These systems are “the Traffic Alert and Collision Avoidance System (TCAS) and the Automatic Dependent Surveillance Broadcast (ADS-B) system” (Angelov, 2012).  The issue with these two systems is that it requires that other aircraft be equipped with like systems.  Non-cooperative technologies that aide in sense and avoid are radar, laser, optical, and acoustic systems (Angelov, 2012).  No single approach provides the necessary safety level for See and Avoid, therefore the fusion of these cooperative and non-cooperative technologies is possibly the best alternative.

            There are also human factors to consider depending on the level of UAS autonomy.  The first issue is with the removal of the human from the cockpit the type of feedback perceived by the operator is in question and how will sensory perception be relayed to the operator.  The second issue is with the removal of the human, he/she is now reduced to simply a monitor of systems and the degradation of pilot skill may be degraded.  Finally, there is the issue of the transition of operator skill from direct control to indirect cognitive activity (Angelov, 2012).

            Research in the area of UAS Sense and Avoid technology has found a multitude of alternative possibilities for see and avoid.  Fasano, Accardo, Tirri, Moccia, & Lellis, (2015), conducted research and proposed alternative algorithms for an obstacle detection and tracking system based on the integration of radar and electro optical/infrared cameras.  Their data fusion architecture was based on a hierarchy of sensors, cross-sensor cueing, and central-level fusion.  Radar is the primary sensor in their proposal while using electro optical and infrared sensors as auxiliary sources that improve accuracy (Fasano, et al, 2015).  These sensors were adapted to a fixed wing aircraft (Flying Laboratory for Aeronautical Research (FLARE)) along with autonomous navigation equipment as depicted in Figure 3.

Figure 3. Sense and avoid system hardware architecture, and FLARE aircraft. Adapted from “Morphological filtering and target tracking for vision-based UAS sense and avoid,” by G. Fasano, D. Accardo, A. E. Tirri, A. Moccia, & E. D. Lellis, 2015.

In research conducted by Tirri, Fasano, Accardo, & Moccia, (2014), it was proposed that particle filter algorithms had less limitations than the common Kalman filter algorithms.

Particle filters are Bayesian estimators that resolve the state estimation problems by determining the probability density function (PDF) of an unknown random vector using a weighted sum of delta functions. These filters have less limitations than the Kalman filter. Indeed, they can exploit nonlinear process and measurement models and they can be used with any form of system noise statistical distribution (Tirri, et al p.4, 2014).

            Sensors are being developed with commercial off the shelf parts such as Frequency Modulated Continuous Wave (FMCW) radar sensors.  As depicted in Figure 4, these sensors can provide distance and azimuth of possible targets in a unit as small as 3 x 2 x 1 ½ inch weighing less than 2 ounces (Mackie, Spencer, & Warnick, 2014).

Figure 4. Radar board with transceiver MMIC and RF signal chains. Adapted from “Compact FMCW radar for a UAS sense and avoid system,” by J. Mackie, J. Spencer, & K. F. Warnick, 2014.

           

            Due to their size and weight, some small UAS would be unable to carry the additional electronics onboard to meet the requirements for see and avoid.  There has been research conducted on ground based systems that could possibly fill this void.  Research by Barott, Coyle, Dabrowski, Hockley, & Stansbury, (2014), proposed that a passive radar could be used to monitor an area around the UAS for hazards while a second EO/IR sensor is used to further classify hazards detected by the radar sensor.

            Passive sensor target tracking has its problems and has been widely reviewed in literature.  Some specific issues are detection range and the maneuver capability of the airframe to avoid a collision.  Estimated ranges and closure rates are often unstable due to calculations having to be made as both the own-ship and target aircraft are maneuvering.  Kalman filtering can be used for target state estimation and increased accuracy and detection and classification ranges.  Once an obstacle is confirmed and a template generated, the target can be tracked using morphological filtering that produces modified spherical coordinates that stabilizes the target state estimation (Fasano, Accardo, Tirri, Moccia, & De Lellis, 2014).

Recommendations for See and Avoid

Sense and Avoid technology will soon be available and either replace or complement the human pilot’s requirement for See and Avoid.  This new sense and avoid technology will be required to avoid hazards as well as obstacles.  Sense and avoid must be able to provide the human operator adequate fidelity to allow for accurate hazard and obstacle detection, tracking and avoidance.   

It is proposed that both cooperative and non-cooperative technologies to aide in the tasks of detection tracking and avoidance must be used to fill the requirements of see and avoid though electronic means.  Currently, the best recommendation is the sensor fusion of TCAS, ADS-B and EO/IR sensors together with particle filter algorithms as proposed by Tirri, Fasano, Accardo, & Moccia, (2014).  Research has proven that these fused systems can be made small enough for SWAP UAS. 

The issue with this recommended system is that it requires that other participating aircraft be equipped with like systems.  To combat this issue, it is recommended that there be requirements in FAA regulation that define the equipment required for both private and commercial UAS.  It is also proposed that any UAS operating above 400 feet above ground level (AGL) or within and airports defined airport traffic area (ATA) be required to follow the commercial electronic see and avoid requirements.  Figure 5 outlines the proposed UAS requirements.  See Appendix A for airspace classification.

Class G, E airspace
Surface to 400ft	TCAS or ADS-B	EO/IR Sensors	401ft & above	TCAS or ADS-B	EO/IR Sensors
Private	NR	NR	Private	REQ	REQ
Commercial	REQ	REQ	Commercial	REQ	REQ
Class A, B, C, D airspace
Surface to 400ft	TCAS or ADS-B	EO/IR Sensors	401ft & above	TCAS or ADS-B	EO/IR Sensors
Private	REQ	NR	Private	REQ	REQ
Commercial	REQ	REQ	Commercial	REQ	REQ

Figure 5. Proposed electronic sense and avoid requirements.

No single approach to the requirements for see and avoid through electronic means will provide the necessary safety level required however, the fusion of these cooperative and non-cooperative technologies is possibly the best alternative.  It is further recommended that this possibility of applying this technology to manned aircraft be considered to further enhance the safety within the national airspace system.

References

Angelov, P. P. (2012). Sense and avoid in UAS: Research and applications (2nd;1; ed.). Hoboken: John Wiley & Sons.

Barott, W. C., Coyle, E., Dabrowski, T., Hockley, C., & Stansbury, R. S. (2014). Passive multispectral sensor architecture for radar-EOIR sensor fusion for low SWAP UAS sense and avoid. Paper presented at the 1188-1196. doi:10.1109/PLANS.2014.6851491

Carey, B. (2013). FAA plans unmanned ‘sense and avoid’ rule in 2016. AINonline. Retrieved from http://www.ainonline.com/aviation-news/air-transport/2013-07-22/faa-plans-unmanned-sense-and-avoid-rule-2016

Dalamagkidis, K., Valavanis, K., & Piegl, L. A. (2009). On integrating unmanned aircraft systems into the national airspace system: Issues, challenges, operational restrictions, certification, and recommendations. New York: Springer.

Fasano, G., Accardo, D., Tirri, A. E., Moccia, A., & De Lellis, E. (2014). Morphological filtering and target tracking for vision-based UAS sense and avoid. Paper presented at the 430-440. doi:10.1109/ICUAS.2014.6842283

Fasano, G., Accardo, D., Tirri, A. E., Moccia, A., & Lellis, E. D. (2015). Sky region obstacle detection and tracking for vision-based UAS sense and avoid. Journal of Intelligent & Robotic Systems, doi:10.1007/s10846-015-0285-0

FAA. (2004). Code of Federal Regulations. Retrieved from http:// rgl.faa.gov/Regulatory_and _Guidance_Library/rgFAR.nsf/0/934f0a02e17e7de086256eeb005192fc!OpenDocument

GPO. (2016). Electronic code of federal regulations. Retrieved from http://www.ecfr.gov/cgi-bin/text-idx?&c=ecfr&tpl=/ecfrbrowse/Title14/14tab_02.tpl

Hackenberg, D. (2014). NASA UAS integration in the NAS project. Paper presented at the 1-11. doi:10.1109/ICNSurv.2014.6820068

Hottman, S.B., Hansen, K.R., Berry, M. (2009). Literature review on detect, sense, and avoid technology for unmanned aircraft systems. Retrieved from http://www.tc.faa.gov/its /worldpac/techrpt/ar0841.pdf

Mackie, J., Spencer, J., & Warnick, K. F. (2014). Compact FMCW radar for a UAS sense and avoid system. Paper presented at the 989-990. doi:10.1109/APS.2014.6904822

Tirri, A. E., Fasano, G., Accardo, D., & Moccia, A. (2014). Particle filtering for obstacle tracking in UAS sense and avoid applications. The Scientific World Journal, 2014, 280478. doi:10.1155/2014/280478

Appendix A

Figure 1. Airspace Classification. Adapted from “The National Airspace System” by http://www.americanflyers.net