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COIN Machine: Flying The Iomax Archangel

Apr 5, 2017Joe F. Edwards | Aviation Week & Space Technology
 

Flying at 180 kt. and 12,000 ft., I am perched high within the Iomax Archangel’s pagoda-like canopy greenhouse in air-conditioned comfort, surveying the countryside of rural North Carolina. A few minutes earlier we had launched from Iomax’s home base in swirling, 20-kt. gusting winds from a 40-ft.-wide strip completely surrounded by pine trees taller than the runway was wide.

Based on my view from the forward seat, I could be in a legendary Douglas A-1 Skyraider, although one with a head-up display (HUD), color flat-panel displays and modern avionics in a night-vision-goggle-compatible cockpit. 

Visiting the manufacturer in early March to fly the Archangel for Aviation Week, I had the opportunity to evaluate this weaponized development of an agricultural aircraft, one that is already performing missions in the Middle East and could compete in the U.S. Air Force’s OA-X light-attack demonstration this summer.

Based on the Thrush T660 crop sprayer, the Archangel is designed as an armed intelligence, surveillance and reconnaissance platform, but is more accurately referred to as a counterinsurgency (COIN) aircraft. It has advanced communications and sensor capabilities, but of key importance is that it is a versatile air-to-ground platform, which positions it in the close-air-support mix between attack helicopters operating at low altitudes and fast jets at higher altitudes. The Archangel’s weapons load consists of precision-guided munitions; it has effective targeting and weapons-delivery systems and an intuitive human-machine interface within the dual-control, tandem two-place cockpits. 

 

ARCHANGELPR_JohnCroft-AWST.jpg
Aviation Week evaluation pilot Joe Edwards sits high in the Archangel’s forward cockpit. Credit: IOMAX USA

Debate over a “high-low” force structure for close air support has been raging for decades. Does the word “low” mean less cost and maintenance or inferior capability? Based on my evaluation, reduced cost and maintenance are attributes of the Archangel, but low capability is not. This weaponized version of the rugged Thrush should be as easily maintainable as a general aviation aircraft, allowing front-line forces to reap the benefits of its exceptional endurance and solid handling qualities. 

At first glance, the crop duster and its COIN derivative look similar, but while Iomax retained the tubular steel substructure of the Thrush, it required significant reengineering to produce the Archangel. The pilot’s cockpit was moved forward 48 in. to improve visibility. The rear weapon-system operator’s position occupies the same real estate as the original Thrush’s pilot station, a location that is adequate for an instructor conducting training. Vertical tail height was extended 28 in.—increasing its area by more than 80%—to improve directional stability.

With a sloping nose, the forward placement of the front cockpit and a tall tailwheel, the aircraft has a tricycle-gear airplane’s field of view, the fuselage sitting nearly parallel to the ground. The Pratt & Whitney Canada PT6 turboprop was retained, but with a low-noise, five-blade carbon-fiber MT propeller fitted. Iomax’s United Arab Emirates (UAE) customer has said it greatly prefers this prop to the T660’s standard Hartzell because of its inflight noise characteristics. Finally, the wing is structurally beefed up by Thrush before delivery to Iomax to incorporate six weapon pylons in addition to the single fuselage station. 

 

The avionics and weapon system was designed by Iomax. At its heart is a custom mission computer integrated with a fuselage-mounted L3 Wescam MX-15Di electro-optical/infrared (EO/IR) sensor with laser designator. Guidance, navigation and control are provided by an Esterline CMC Electronics Cockpit 4000 display suite with integrated flight management system, HUD and five multifunction displays (MFD)—three in the front cockpit, two in the rear. The rear station also has a large, 17-in. Avelex display for the sensors and moving map. An autopilot provides typical cross-country functions as well as hands-off flight to the weapon-delivery point for a manual ordnance release. 

Flight control is via a conventional irreversible (nonboosted) system with the elevator and ailerons actuated by push-pull tubes and the rudder by cables. The longitudinal control system has a downforce spring, generally incorporated to produce a mechanical load on the elevator, inducing the surface to move trailing-edge down during the low dynamic-pressure conditions in and around the stall. 

I made two flights of 1.9 hr. total in the Archangel over two days. The first was with Carey Mills, lead test pilot for the original development program. I evaluated flying qualities and performance on the first day and landing/rollout handling qualities and weapon-system employment on the second. We operated from Iomax’s flight-test facility, a 3,147-ft.-long asphalt strip near Charlotte, North Carolina. 

 

After a professional flight brief, we climbed into aircraft N824KH, the 24th and last Block 1 production Archangel. All 25 Block 1 aircraft were purchased by the UAE, and Block 2 production of at least 30 aircraft, with options for 15 more, has begun for that country and other nondisclosed customers.

Approaching the aircraft for the first time, I got the impression that the original designers focused on utility, not aesthetics. This is a gangly aircraft with a wingspan of more than 57 ft. and the top of the propeller arc more than 12 ft. above the ground. The Archangel sits high on its gear, providing plenty of space to mount weaponry. Construction and finish, in military flat green, is high-quality. 

Strapped into a standard five-point harness, the field of view from the front seat is noteworthy and on par with tactical fighters such as the F-15. The canopy has an opaque section above the crew, which must improve comfort in desert conditions but at the cost of a blind area immediately above. 

The excellent visibility made taxiing safe, simple and drama-free. No taildragger S-turning was required—a benefit when operating from the small, unimproved strips this aircraft can use. I found the rudder to be ineffective for ground handling and preferred differential braking for directional control. 

Takeoff was conducted at 4,800 ft.-lb. of torque. The tail was raised at 20 kt. indicated airspeed (KIAS), with liftoff at 80 KIAS. We quickly transitioned to a 10-deg. pitch attitude for a 120-KIAS climb. The 12,500-lb. aircraft required an 1,800-ft. takeoff roll. More than adequate rudder was available to manage torque effects, even with the narrow runway and variable crosswinds.

 

Iomax Archangel
Archangel is based on the Thrush T660 agricultural aircraft but is significantly reengineered. Credit: IOMAX USA

Assessing the mechanical flight controls during the climb, I found the aircraft to have good control harmony, with positive centering of stick and rudder and no objectionable breakout or friction forces. The controls were not overly light, and sustained turns during tactical maneuvering required about 20 lb./g of aft stick force, a reasonable value considering the aircraft’s 2.8g limit.

The Archangel has a 25,000-ft. service ceiling, but we were flying without oxygen masks, so we stayed below 12,500 ft. Cruise and landing configuration stalls were benign, with no tendency to drop a wing or depart controlled flight. Pilot operating handbook values were attained for stall (75 KIAS clean, 73 KIAS with half landing flaps), but I was able to easily fly at and below the published stall speed with judicious use of rudder and centered lateral stick. I could pull full aft stick during the maneuvers with no unpredictable response from the aircraft; as it was designed to, the elevator downforce spring provided a nice feel of positive longitudinal static stability. 

I was interested in seeing how the enlarged tail improved directional stability. Carey says that during initial tests of directional stability, the T660 departed controlled flight, necessitating the modification. Performing steady-heading sideslips (the classic test for directional stability) at 10,000 ft. and 150 KIAS, the Archangel exhibited positive dihedral effect and directional stability with no control-force lightening or reduction in stability. The tail modification is clearly effective. At 120 KIAS pattern speed with half flaps, the normal landing configuration, I could develop at least 25 deg. of sideslip with full rudder, producing generous side forces useful to slip and skid into short, remote fields.

Endurance is a key characteristic of this aircraft and, while it has an autopilot, the spiral mode (lateral axis) and flightpath (longitudinal) stability are important contributors to pilot workload when flying the multi-hour missions this vehicle can perform. The Archangel tended to maintain a commanded angle of bank or slowly converge to wings level at angles up to 45 deg., exhibiting good spiral stability. At 120-170 KIAS, when flown hands-off, the aircraft maintained trimmed airspeed within 3-6 kt. Both are acceptable characteristics for the light close air support mission. The aircraft was easy to trim in each axis. The electric trim is actuated via a conventional control-stick coolie hat for elevator and ailerons and a console switch for the rudder. 

 

Spot-checking fuel flow at 12,000 ft. and 8,000 ft., at 100 KIAS, I saw the engine burning 360 lb. and 375 lb. per hour, respectively, closely matching the handbook values. With 648 gal. of Jet A on board, this gives an impressive endurance capability of up to 9.1 hr. With the centerline sensor ball installed, I attained 195 kt. true airspeed in level flight. Carey said we would see about 215 kt. without the turret. 

My second flight was with Will Challancin as safety pilot. As director of aviation operations, he has more than 800 hr. in the aircraft and extensive experience training UAE pilots in-theater, including hundreds of live weapons drops on training ranges in the Middle East.

 

Archangel specifications table

Challancin gave me the opportunity to sample the Archangel’s weapon system. The MX-15Di targeting system can be operated via controls in either cockpit—the rear seat has a specific right-hand “mission grip” dedicated to its operation. Display and software operations were intuitive with familiar formats and clear color symbology with legible labeling and fonts. The HUD is used for both navigation and weapon delivery and has a nicely mechanized flightpath marker. The rear-seat 17-in. display is large, centered high on the instrument panel and had good readability during our test conditions (from direct sunlight to variable overcast). It serves well as the primary targeting tool for the rear-seat weapons officer. 

Several miles in the distance, I spotted some light industrial buildings clustered in a clearing. To attack a specific warehouse within this complex, I designated my target through the HUD via the control-stick target designator controller. The Archangel’s weapon system automatically selected the next air-to-ground munition for delivery, in this case a 500-lb. laser-guided bomb. I confirmed we had the correct target via the EO/IR image on an MFD.

A vertical line appeared on the HUD—my azimuth steering cue displaced slightly left of the circular target designator. Centering the steering command, I flipped Master Arm on, then depressed and held the stick’s bomb button. A few seconds later, release parameters were met and the bomb drop commanded. I broke off the attack with a hard right turn, switched Master Arm off and began scanning for another target. I had just completed my first ordnance delivery in the Archangel, albeit a simulated one using the onboard training system. I wondered if folks on the ground saw what they thought was a crop duster gone rogue.

The Archangel is flown around the landing pattern like a turbojet aircraft, with similar performance. I flew military racetrack landing patterns and approaches and found the aircraft intuitive and easy to establish on the runway centerline with the proper visual glideslope. Judicious elevator trim helped in maintaining the correct approach pitch attitude and establishing a proper flare. 

Landing rollout with 3-5 kt. of crosswind was about as low a workload as I have experienced in a tailwheel aircraft, the superb over-the-nose visibility being a great asset. In these conditions, with touchdown at 75 KIAS, I could stay within 3 ft. of centerline with rudder inputs of less than half-throw and no braking required for directional control. The aircraft can consistently stop within 2,000 ft. with judicious use of reverse thrust and moderate braking. Below 20-30 kt. on landing rollout, directional behavior was similar to a tricycle-gear aircraft. 

The Archangel is an aircraft designed to be used at forward operating bases without complex training. In Middle East operations, Iomax says, the weapon system is enabling young, 100-hr. pilots to transition out of flight school, begin practicing weapons delivery early in their training and perform combat engagements with as little as 45-50 hr. in the aircraft.

The aircraft has made over 3,000 combat weapon deliveries, the company says. The weapons loadout includes 250-lb. GBU-58 and 500-lb. GBU-12 laser-guided bombs, AGM-114 Hellfire missiles and Cirit 2.75-in laser-guided rockets. The GBU-58s are effective low-collateral-damage weapons, Iomax says, while the Turkish-made rockets have been particularly effective against moving targets. 

How does this aircraft fit into the 21st-century battlespace? The Archangel is a low-cost option for close air support—$9-14 million, depending on configuration—and may be preferred over tactical jets in many scenarios because of its ability to persist over a target area to deliver its precision munitions load. Its sweet spot is operating in the low 20,000-ft. altitudes, above small-arms fire and anti-aircraft artillery. An Archangel crew can even land and talk to the ground commander before or after a mission. And they can employ modern weaponry for a fraction of the cost of most fast jets.

Based upon photographs of the Archangel, I began this assignment half-expecting to have to wrestle the aircraft into the air on each sortie and back to the ground on each landing pass. Instead, after my final flight, I saw a robust, utilitarian aircraft in which I would have gladly spent the rest of the day practicing my air-to-ground weaponry skills. With its flexibility and endurance, the Archangel is to me a spiritual successor to the A-1 Skyraider—versatile and closely coupled to the ground warfighter but carrying modern precision air-to-ground weaponry. 

Joe F. Edwards is a former U.S. Navy test pil

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The air tractor version looks like a better product to me...for the roles required for the most part now i think 10 or 15 COIN aircraft would be way more useful than one high altitude fighter. As to speed, etc, its faster and cheaper than a helicopter, with far more range and loiter time

http://www.airforce-technology.com/projects/air-tractor-at-802u-surveillance-and-light-attack-aircraft/

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