Unmanned Aircraft System (UAS) Integration In the National Airspace System (NAS)

The integration of UAS into the NAS is a challenging process. It is complicated by the fact that UASs simply don’t have pilots in the cockpit and the same type of manned aircraft equipment like transponders, traffic collision avoidance system (TCAS), etc, aren’t installed in the aircraft itself, nor is that information displayed in ground control stations (GCS) to provide at least some type of traffic awareness. In addition, the varying groups of UASs that extend from micro vehicles up to large aircraft and different classes of automation, makes it difficult to apply “a one solution fits all” approach. UASs have the added benefit of electro-optical and infrared sensors which could help in maintaining separation from other traffic; however, more acceptable levels of safety will be needed. More sensors that can automatically respond or alert the remote pilot in the GCS has been one answer. The process of UAS separation will depend on a number of factors. Most notably, those encompass aircraft and GCS equipment, and the type of flight rule is being used to fly in the NAS. 

Currently, on-board pilots, Air traffic Controllers (ATC) and Air Route Traffic Control Centers (ARTCC) form the backbone for separation services. ATC/ARTCC’s use radar and satellite based services to monitor and maintain traffic separation, while on-board pilots use good old fashion human eyesight. The type of flight rule used, and sometimes the airspace being operated in, defines the level of responsibility for all of these parties.

In visual flight rules (VFR) the pilot is responsible for detecting and avoiding other aircraft traffic. As the name implies, a pilot can see outside the aircraft and they are primarily responsible for motioning and maintaining separation at all classes except in class A where IFR is required (FAA, 2008). In class B and C airspaces, ATC will take responsbiltiy for separation services regardless of which flight rule is used (FAA, 2008). In every other case, ATC can provide flight following, workload permitting, to assist VFR traffic with separation from other VFR traffic but the pilot is still primarily responisble (FAA, 2008). Class G, E and D airspaces are; therefore, the most vulnerable when it comes to UAS integration because the pilot, not ATC, is resposnible (FAA, 2008).

In Instrument flight rules (IFR), controllers assumes separation duties because these rules imply that the pilot cannot see outside the aircraft. This area is less vulnerable than VFR as procedures define terminal and en-route flight paths. However, issues still exist with safely integrating UAS. ARTCC workload deals heavily with re-routing and route convergence in the en-route environment due to issues such as: weather, traffic congestion, and other factors (FAA, 2008 & FAA, 2015). The dynamic and unpredictable nature of these areas demand attention with respect to UAS integration. In the terminal environment, ATC workload involves monitoring procedural departure and approach activity for separation (FAA, 2008). It also entails approving user requested changes to flight plans, cancelling IFR for VFR, providing radar approach guidance for landing, issuing directions to amend standard procedures, and etc (FAA, 2008 & FAA, 2015). In either case, standard procedures are filed and ATC expects pilots to follow them with zero deviations (FAA, 2012). Traffic sequencing is the biggest issue here in maintaining separation that should be a focus for autonomous UAS, as semi and remotely piloted can be adjusted quickly by pilot inputs. 

To fulfil the task of monitoring air traffic and assist in maintaining separation with flight rules and procedures, ATC/ARTCCs use primary (radar returns) and secondary surveillance radar (transponders) and it is referred to as positive control (FAA, 2016 & FAA, 2008). Next-Gen efforts are ushering in automated dependent surveillance-broadcast (ADS-B) as the method to replace both of these systems (FAA, 2016). The latter moves traffic monitoring to a satellite and datalink (if user has ADS-B In and is in a certain range) based approach (FAA, 2016). In addition, ATC carries out broadcasts through the Traffic Information Service – Broadcast for uncooperative traffic (radar detected, non-ADS-B equipped aircraft until full integration is completed) and re-broadcasts through ADS-R for traffic transmitting on the Universal Access Transceiver frequency (FAA, 2016).

For UAS, the easiest answer is make ATC controllers responsible for traffic separation while operating under VFR, in addition to IFR, by using primary and secondary radar, and ADB-S later on down the road. However, this increases ATC workload substantially and doesn’t necessarily solve the problem for the see and avoid requirement in VFR operations (Fern, Kenny, Shively, & Johnson, 2012). For UAS groups 1 and 2, current sizes of transponders are too big and radar may not be able to see UASs that operate at low altitudes. Thus, internal radar and transponders, or smaller ADS-B out/in components, are needed to interface with the autopilot system for autonomous avoidance of other group 1 and 2 UASs. Due to the small nature of these UAS types and lack of exhaust plumes, it can be hard to detect them visually through electro-optical or infrared sensors. For UAS groups 3-5, a combination of any and all these types of sensors should be used. It is highly recommend that combinations are used as sensor fusion provides a level of redundancy and accuracy of information.

Levels of delegation offers a different approach, because it depends on the level of sophistication of the UAS’s sense and avoidance systems. This allows the proper risks to be managed at the right level and defines the responsibility between the controller and the UAS pilot. These levels of delegation are defined as: limited (ATC identifies and issues direction, pilot performs), extended (ATC identifies and pilot decides and performs a maneuver) and full (UAS pilot does all three) (Fern, 2012).This technique could allow UAS integration to happen now for aircraft like the MQ-9, which possess an electro-optical/infrared sensor to detect air traffic if given a bearing and range. In addition, it has the required transponder which allows ATC to obtain altitude, airspeed and heading information necessary for limited delegation operations. With a sensor and a transponder, the MQ-9 could perform limited and extended delegated separation. This would be no different than any other UAS in group 3 to 5 that has the same capabilities. Full delegation is the biggest issue because it requires the UAS to perform sensing in a timely fashion. Traditional rotating sensors have soda straw like views (30 degrees to be exact) and situational awareness is lost as soon as that view is no longer present, thus a continuous sight picture is not the same as a human on-board the aircraft would have (equates to 120 degrees or more). Full delegation will require a combination of sensors dedicated to detecting, sensing, and avoiding other aircraft.

                                                       References

FAA. (2008). Pilots Handbook of Aeronautical Knowledge. FAA.gov. Retrieved from http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/pilot_handbook/

FAA. (2012). Instrument Flying Handbook. FAA.gov. Retrieved from http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/FAA-H-8083-15B.pdf

FAA. (2015). Instrument Procedures Handbook. FAA.gov. Retrieved from http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/instrument_procedures_handbook/

FAA. (2016). Equip ADS-B: Ins and Outs. FAA.gov. Retrieved from http://www.faa.gov/nextgen/equipadsb/ins_and_outs/

Fern, L. (2012). UAS Integration into the NAS: Unmanned Aircraft Systems (UAS) Delegation of Separation. Proceedings of the 2012 Human Factors and Ergonomics Society Meeting. Retrieved from http://human-factors.arc.nasa.gov/publications/UASIntegrationInto TheNASDelegation.pdf

Fern, L., Kenny, C.A., Shively, R.J., Johnson, W. (2012). UAS Integration into the NAS: An Examination of Baseline Compliance in the Current Airspace System. Proceedings of the 2012 Human Factors and Ergonomics Society Meeting. Retrieved from http://human-factors.arc.nasa.gov/publications/UASIntegrationIntoTheNAS.pdf

Systems Engineer’s Approach to Manage Weight in UAS Design and Development

Introduction

Our company is responsible for designing a precision crop-dusting Unmanned Aircraft System (UAS) for the domestic U.S. market. We were chosen for the project due to our experience in UAS. However, unlike our other successful projects, the task of a integrating in an ad-hoc payload design has had its challenges (Loewen, 2013). Time still exists to correct this problem as the project hasn’t completed the final system-level critical design review (CDR), that is required for fabrication, integration, and developmental test and evaluation of our final product (Loewen, 2013).

Background

The current guidance, navigation and control (GNC) for our baseline UAS is a commercial off-the-shelf (COTS) design that allows us to save money on research, development, and manufacturing costs. We decided to stick with this option as continued investment with the current system allowed lower manufacturing costs, and easier support/sustainment from an existing contract. The payload is comprised of several components that allow storage and distribution of insecticide or fertilizer for crop-dusting operations. In an effort to reduplicate success that we had with our GNC system, we decided to take the same approach and purchase a COTS system for the payload. However, the use of ad-hoc systems has increased the weight of the baseline UAS, which might require a newer engine or force us to reduce weight by decreasing storage capacity. The systems engineering department has been tasked with figuring out a solution that keeps the program on schedule with minimal delays. 

  
Problem Statement

The addition of a COTS payload onto the baseline configuration of our UAS has created a significant challenge for the design process. Because the payload was not custom designed and engineered with weight limitations in mind (we have no control of how much a COTS system weighs), the amount of advertised spraying capability that was presented to the customer is degraded by 20%. This is a significant reduction in capability that could mean the difference between two flights, rather than one, being necessary to get the job done.

Where Systems Engineer Fits Into Solving the Problem

As the systems engineer, I approached the situation with an unbiased view and coordinated with the respective Propulsion, Guidance, Navigation and Control, Payload, Safety and Aerodynamics areas to determine a solution to the weight problem. Even though the main problem is focused with the weight of COTS GNC and payload systems, bringing in other areas could help determine an out-of-box approach to our dilemma. The first task I accomplished was setting priorities to guide the respective engineering teams in developing a solution. There are three high-level priorities that would be given and they are as follows: (1) Try to find other payload COTS systems or sub-components that meet or exceed operational requirements but are less weight than the current system, (2) what other components, or systems can we change/delete on the baseline UAS that may be excessive for this requirement or a substitute available at a lower weight, and (3) what options do we have for increasing propulsion efficiency to maintain the same thrust-to-weight ratio (using less fuel capacity, etc) but with no changes in endurance and minimal changes to propeller design.

After setting these three priorities, I gave each team a week to research alternatives or courses of action to solve the problem, then reconvened them for a second meeting to address

specific solutions and look at how those solutions impact cost and effect the program’s schedule. This effort fell under the system critical design review (CDR) as this would be a collective effort from all of the program’s engineers (ACQuipedia, 2016). The Safety Engineer was primarily responsible for ensuring a good margin of safety with any and all design changes (Loewen, 2013). Once an acceptable solution was agreed upon, the CDR would be finalized and the program would progress into the next phase.

Results of the CDR

The results of the CDR revealed that the propulsion system, specifically the propellers, could be updated with a newer design that uses less fuel from take-off to landing. The dual counter rotating propellers, thinner propeller blades and more blades per propeller offered a significant advantage of the single propeller design of the baseline UAS (Jha, 2008). These advantages included greater thrust, lower fuel consumption with lower engine/propeller RPMs (Jha, 2008). This design is highly desirable as the aircraft will not need higher power thrust for sustained cruise flight to execute crop-dusting operations. Sufficient thrust would be retained for maximum weight take-offs. Due to the 30% reduction in fuel consumption over the course of a typical 45-minute flight time cross dusting operation, fuel capacity was reduced enough to allow only a modest 2% increase in overall weight of the vehicle, as compared to the 10% increase observed with the COTS GNC and payload systems together and no other weight modifications (Jha, 2008). Thus, the GNC and payload systems remain 100% COTS, allowing us to simplify our production process with overhead lower costs and decreased risk from an in-house design and development program. The small 2% increase in weight over the baseline UAS configuration was well within the safety margin, as determined by our safety engineer, for maintaining proper weight and balance for optimal flight control performance and dynamic stability during flight operations. In addition, and as a result of the new propeller design, the propulsion engineers suggested that future iterations of our UAS could employ twin engines and larger a payload for crop dusting operations with greater endurance. This would equate to larger fields or even multiple fields being serviced vice a single field the current UAS is design to support.

References:

ACQuipedia. (2016). Critical Design Review. Defense Acquisition University. Retrieved from https://dap.dau.mil/acquipedia/Pages/ArticleDetails.aspx?aid=dcc068fd-9994-44ed-9500-3a7ec7f81876

Jha, Alok. (2008). Rolls-Royce brings propeller engines back in vogue. The Guardian. Retrieved from http://www.theguardian.com/environment/2008/oct/20/travelandtransport-rollsroyce

Loewen, H. (2013). Requirements‐based UAV design process explained: A UAV manufacturer’s guide. Micropilot.com. Retrieved from http://www.micropilot.com/ pdf/requiremenv.3ts-based-uav.pdf