Unmanned air vehicles play an important role in todays military operations. They are invaluable in locating time critical targets, reporting enemy positions and movements to battlefield commanders, and destroying tactical targets. One important aspect of these operations is the ability to provide persistence in monitoring an area of interest.
Most of the current UAVs are designed to remain in flight for time periods of 20-40 hours, primarily limited by fuel capacity. For example America’s most expensive surveillance drone, the Northrop Grumman RQ-4 Global Hawk, can stay aloft for 32 hours. However, this creates a deployment and logistics challenge for battlefield commanders to maintain eyes on target for extended periods of time, which is usually achieved by deploying multiple waves of UAVs.
The inherent benefits of a long endurance, unmanned aerial vehicle are obvious when one considers the reduced costs involved in a platform not having to consistently return to base, land, refit and refuel before continuing its same mission. The unmanned nature of such systems also does not expose a pilot to unnecessary dangers when traversing over enemy territory. Add in the advanced capabilities of autonomy and a modern MALE UAV can complete multiple missions with reduced manpower committed to its operation and at lower operating costs due to the lessened need for repeat landings in a single sortie.
The Pentagon is now looking for a drone that can fly nonstop for a week or more at a time. In a solicitation published last November, the Department of Defense (DoD) is calling on contractors to submit designs for a low cost, ultra-long endurance UAV that can perform intelligence, surveillance, and reconnaissance (ISR) missions for seven days or more. Specifically, the DoD wants to eliminate the need for launching new waves of drones to replace the ones that have run out of fuel and have to return to base.
The longest flight record for internal combustion has been 5 days. In Oct 2017, after five days, one hour twenty-four minutes, and traversing over 7000 miles, Vanilla Aircraft’s VA001 touched down at NASA Wallops Flight Facility in Virginia, successfully completing the longest unmanned internal combustion powered flight in history.
One significant weakness in the US’s UAS space is for an ultra-endurance medium altitude UAS. The mid-altitude regime is the one most heavily utilized by all the services. It is best suited to exploitation of available sensors, most notably full motion video cameras, to support ISR and targeting missions, writes Daniel Gouré, Ph.D of Lexington institute. It is the operating regime of choice for supporting counter-terrorist missions. The demands for UAS flights in the medium altitude band continues to grow as the U.S. seeks to counter the rapid spread of ISIS and affiliated groups in Syria, Iraq, Afghanistan, Libya, Somalia, the Sinai and Nigeria.
The Aurora Orion program promotes a drone with 120-hour endurance and operational altitudes of 20,000 feet – outdoing many of inherent capabilities of other UAVs.
The VA001 breaks internal combustion UAS endurance record with 5-day flight!
The 36-foot wingspan, diesel-powered aircraft landed with three days of fuel remaining on board, successfully meeting its goal of a five day flight. Carrying multiple payloads, including a NASA-furnished multispectral imager and a DoD-furnished sensor and radio, this flight showed the practical use of an ultra-endurance heavy fuel aircraft with a logistics footprint a fraction of those required by other current unmanned air systems.
Imagined, designed, built and operated by a five-person start-up out of Falls Church, Virginia, the VA001’s success demonstrates the capability of a small, agile company to build a generic, i.e. “vanilla”, unmanned air system that can be customized to fit user needs. The aircraft carries up to 1.1 cubic feet of payload, with a 30 pound weight limit and provides 800 watts of power. Built to operate for up to ten days at altitudes up to 15,000 feet with a dash speed of 75 knots and loiter speeds of around 55 knots, the VA001 will enable users to devise many missions capitalizing on its open design.
This was the tenth flight of the aircraft, and showed the potential of its affordable, deceptively simple-looking design. The aircraft executed a pilot-controlled takeoff Wednesday morning, October 18, was switched to autopilot control, and quietly orbited above Wallops Island’s Virginia Space UAS Runway at 5,000 feet in a 2-mile orbit, maintaining the flight path to be flown with another soon to be installed camera system. On Monday, October 23, it made a successful autonomous landing back at NASA Wallops. The flight was completed under funding from the Office of Naval Research.
Chief Engineer Neil Boertlein said, “As exciting as this milestone is, the flight itself was quite boring. The plane did what it was designed to do and landed ready to go right back into the air again.”
Test Director Jeremy Novara added, “Previous flights had already validated our performance predictions, but this flight really demonstrated the reliability and ease of operation that a low-cost persistent unmanned aircraft can obtain.”
The ultra-long endurance capability of the VA001 will allow persistent operations for both commercial and military applications. It is expected that additional flights will demonstrate the capability to carry classified and unclassified payloads, including electro-optical and infrared imagers, synthetic aperture radar, SIGINT systems, communications nodes and more. Likely commercial applications include agricultural mapping, disaster zone imaging, cellular network and internet distribution, and infrastructure monitoring.
Tim Heely, CEO, stated, “We have begun to fully demonstrate the viability of this ultra-long endurance aircraft system and are anxious to test new payloads and realize capabilities heretofore unimagined. We are excited to bring a new affordable, easily sustainable capability to the quickly expanding Unmanned System environment.”
“The VA001 has transformational potential, providing a scalable aerial system solution without increasing personnel or operating costs. The ability of a low-cost platform to provide persistent surveillance, battlefield pattern of life, or aerial mesh network relay, in a responsive and robust manner, and without forward basing, does not currently exist,” said co-founder and chief engineer Neil Boertlein.
The company plans to begin production in the coming months, and is open to teaming with payload providers.
Aurora Flight Sciences Orion Medium-Altitude, Long-Endurance (MALE) Unmanned Aircraft System (UAS)
The Air Force has a platform that will fill the requirement for a long-range, high endurance UAS. The Orion, developed under contract to the Air Force by Aurora Flight Sciences, holds the endurance record for an operationally capable UAS at 80 hours with a 1,700 pound payload. The vehicle landed with sufficient residual fuel to have supported an additional 37 hours of flight. The operational Orion is expected to have a 120 hour mission profile with a 1,000 pound payload. Operating from bases in Italy or Djibouti, the Orion could cover virtually all of Africa with significant dwell time over the target area.
As it stands, the Orion has taken its first steps in fulfilling the proposed “120/1,000/20,000” project goals which fall in line with the American military as it looks to high endurance unmanned vehicles more and more. The possibility of military (as well as civilian) applications for such systems continues to grow.
In the meantime, the coast guard will experiment with the Orion for ultra-long-endurance surveillance missions over the country’s maritime borders,
Ultra-Endurance UAV SBIR
The objective of this topic is to develop a low cost UAV with very long endurance, of at least seven days, that would enable the ISR mission to be accomplished with reduced manpower and system resources (esp. number of vehicles) to maintain near continuous coverage. Operating footprint should minimize personnel and hardware as compared to other UAV systems. Notionally the UAV will transit from its launch point to the area of interest nominally several hundred miles away, and loiter in that region for the mission duration, although the ability to move quickly between nearby areas of interest is also desired.
The UAV should provide the capability to fly at 10,000-15,000 feet AGL, with a payload of 250lbs and 2000W power requirement. The system must be able to operate in 50 knot winds aloft, with minimal degradation in range and endurance or deviation from the area of interest. The system must also demonstrate minimal acoustic and visual signature to be virtually undetectable by ground personnel. The system must also be able to transit light to moderate icing conditions associated with climbing and descending through stratus cloud layers containing known icing conditions. The system does not need to loiter for prolonged periods in icing conditions. Typical take-off profiles are constant slope and minimum altitude changes are required once on profile.
A number of possible technologies can be considered to meet this requirement, but it is anticipated that the most likely candidates include hybrid power systems, solar power, and possibly power harvesting.
Other technologies such as conventional airships (may not meet winds aloft requirement), laser power transmission (difficult to provide laser transmission to remote areas of interest), and tethered aircraft (no flexibility to move to remote areas) may not be suitable unless innovative approaches can be developed to overcome their limitations for the envisioned missions.
Some key desired capabilities of the system are:
- Allow for >7 day vehicle endurance capabilities Support payloads of 250lbs while supplying 2000W Transit from launch location to area of interest up to several thousand miles and return safely Maintain ˜orbit over area of interest in most weather conditions, but primarily winds aloft of up to 50 knots and intermittent light to moderate icing conditions.
- Acoustic and visual signature should be virtually undetectable by unaided ground personnel Operate on logistically available fuels (diesel, Jet-A, Mo-Gas, etc.)
- Suitable for military operational environments, including typical site constraints and runway sizes in Forward Operating Bases (FOB) Minimal maintenance required in comparison to typical UAVs
- Minimum personnel and hardware footprint as compared to other UAS System cost to include the UAV, Broadband SATCOM, launch/recovery system (if any), fueling system (if unique), etc. < $1M
PHASE I: The contractor shall provide trade studies and engineering design necessary to define the operational system & associated technologies. The contractor shall show evidence that key enabling technologies are adequately mature (e.g., Technology Readiness Level >=6). Key enabling technologies shall include propulsion system, electrical power generation, flight control adequate to control necessary endurance parameters, energy storage, & anti-icing systems if required.
PHASE II: The contractor shall develop and test a UAV that provides the capability to loiter over an area of interest for >7 days. The test program shall culminate in a demonstration, on a government test range, of >7 days endurance at representative altitudes, carrying payload and mass simulators totaling 250 lbs.
PHASE III: The various technologies developed in Phase II are applicable to military and government applications. There are potential commercial applications in a wide range of diverse fields that include airborne communication nodes for cellular communications, crop monitoring, and site security.
Challenge of High Endurance Flight
Researchers Berk Ozturk and others from MIT have done analysis for Design of an Unmanned Aerial Vehicle for Long-Endurance Communication Support. With the worst-case operational scenario being high-wind conditions in the winter solstice, it was concluded that a solar aircraft cannot achieve the requirement for station-keeping with current technology.
In contrast, a gas-powered aircraft is not subject to time of year and latitude operational restrictions. Thus, the proposed aircraft design is powered by a piston engine. For loitering aircraft, endurance is maximized by minimizing power consumption, which requires flying at low airspeeds. However, the aircraft has to fly faster than the windspeed at a given altitude to station-keep.
Different altitudes require different propulsive capabilities because of changes in air density and mean wind speeds. The 90th percentile wind at 4.6km (shown by the bounding line hmin) is 25 m/s. It is estimated that normally-aspirated, piston-engine aircraft can operate at altitudes up to 7 km.
Theoretically, high endurance aircraft could also operate at higher altitudes (>20,000 m), where there exists a local minimum in wind speeds. However, higher altitude operations require a turbocharger or supercharger, which add cost, weight, and risk to the aircraft design.