A Look at the Ayres Thrush S2R Series

The S2R Series is a fixed undercarriage low-wing single-engine tailwheel configuration agricultural aircraft of all-metal construction with the welded steel-tube fuselage. The hopper is located forward of the cockpit, and the aircraft is available in single or dual (tandem) cockpit configurations. The S-2R model was developed by Rockwell from the S-2D by widening the fuselage from 38” to 46” to accept a larger 400 US gallon hopper, to be able to carry a greater volume of low-density materials used by Rice growers, and adding flaps.

Type Acceptance Certificate FAA Type Certificates A3SW and A4SW

In 1977, the Ayres Corporation, of Albany, Georgia, purchased the Thrush Commander line and continued to build the S2R, with the same constructors serial sequence, finally ending at 2582R. Previously the type certificate had been held by Snow Aeronautical Company (up to February 18, 1970), North American Rockwell Corporation (up to April 3, 1973), and Rockwell International (up to November 28, 1977) .

A new sequence was started by Ayres with the 750 hp P & W PT6A-34AG with constructors numbers beginning with 6001, and incorporating one major change, the fitting of a 500 US gallon hopper. The 5000 sequence was used for the 100 or so 800 hp Wrights built by Rockwell.

The Turbo Thrush S2R-T34 was then developed for Ayres by installation of a PT6A engine under STC, the first such turbine application for an agricultural aircraft. This was type certificated under A3SW in the Normal Category, but the manufacturer advises virtually none have been delivered in that category. All subsequent S2R derivatives (basically different turbine engine options) were only certificated in the Restricted Category under A4SW, including several using the TPE331 family (these were popular because overhauled engines were much less expensive than a new PT6A). Some engine and propeller options for the S2R-T34, and the Dual Cockpit trainer option originally approved by STC, are only approved in the Restricted Category.

Once Ayres had taken over, one of the new versions was named the Bull Thrush, powered with a 1200 hp Wright R-1820-97 and fitted with a 500 US gallon hopper. One of the new features was a Dual Cockpit variant, being denoted by a DC at the end of the constructor’s number. From this time Ayres were to start a whole new series of constructors num­bers, prefixed by S2R, followed by engine model fitted and then a number, in most cases, starting at -001. As example, S2R-1340-… (600 hp), S2R-1820-… (1200 hp), S2R-RS3-… (PZL R83, 595 hp) and S2R-T34-… (750 hp).

The new turbine models incorporated a wing extension from a span of 44 feet, 5 inches to 47 feet, 6 inches with a wing area of 350 square feet. The wing extensions can also be fitted to the smaller round engined versions, as well as adding an all metal tailplane. The Ayres tail version being the same outline as the tube and fabric original, and another is being offered by Weatherley.

PNC-264 Ayres S2R-T65 Thrush

Colombian National Police November 2000. Via RedRipper on Flickr.com

A further development by Ayres was the Model S2R-T65, which was fitted with a larger 500 US gallon hopper and 1300 shp PT6A-65 engine. This had an increased span wing but was initially approved at the original 6000 lb. gross weight. Later an improved wing with steel spar webs was tested and the S2RHG-T65 (High Gross) version was certificated with a MCTOW of 10,500 lb. Thrush also certificated a similar high gross S2RHG-T34 version with a 550 US gallon hopper and a MCTOW of 9500 lb. However Report ER-568 stated that performance was marginal and only a few were produced. Report ER-538 states that all aircraft manufactured by Thrush since 2003 have been produced to a common fuselage and wing configuration.

Since 1991, some of the T34 aircraft have had a PT6A-41AG of 850 hp fitted and, likewise, the T15 line has had one PT6A-27 of 680hp installed. Another version available is the T45, with its own c/n sequence fitted with a PT6A-45 of 1173hp

In the eighties, the US Government required a long range sprayer for anti-narcotics work. Ayres developed the T34 model and fitted it with the PT6A-65A of 1376 hp, self-sealing fuel tanks, and armour plate around the pilots seat.  Up until December 1990, eight had been built with the unusual T65-1X sequence. From October 1987, Dual Cockpit versions entered the production line, beginning with T65-001DC and all going to the US Government. The first to a civil operator was 011DC, going to Gwydir Air as VH-NFH in 1990. This was re-powered by a PT6A-65AG of 1230 hp turning a five blade prop. Not only is it quieter, the length has been increased to 34 feet and the hopper has been increased to hold 625 US gallons. In 1994, the T65s were back in production, with several being delivered to South Africa.


In 1991 Ayres installed a Garrett TPE 331-6 (starting with c/ n G6-101) and up until 1994, twenty of these 750 hp versions have been delivered. Two more variants are offered, the G5 and G10, first appearing in 1993. Like the T15/34 range, they can be fitted with 400 or 500 gallon hoppers. The real advantage is the much cheaper Garrett engine.

Photo of the 660 Turbo Thrush from Agri-Spray Consulting


On 14 March 2000 Ayres received the type certificate for the all new Ayres 660 Turbo Thrush. The first three aircraft are fitted with the Pratt & Whitney PT6A-60AG turbine of 1050 hp, the fourth with the 1230 hp PT6A-65AG engine, which will be available as an option.


With a work force of 62 in 2004, Thrush Aircraft principals Payne Hughes and Larry Bays have already built six new Thrush aircraft – three model 660s and three model 550s, all sold to individual owners -since acquiring the company in mid 2003.


The new owners have made a substantial investment, not only in purchasing the Thrush line, but also in building renovations and new machine equipment.


The top of the range model is the Thrush 660. This aircraft was developed by the Ayres Corporation as the S2R-T660 at the end of last century and went into production in 2000. Only eight aircraft were built before Ayres closed it doors at its Albany, Georgia, plant. The aircraft was designed around a 660 US gallon hopper and this was the first time that the airframe had been completely reworked since the inception of the Rockwell S2R-600 in 1968. The standard main undercarriage was replaced with steel spring legs, the wings were modified and an unusual dorsal fin added to the tailplane with the idea of keeping the overall in-flight height the same as other Thrush ag-planes.


With the new aircraft, the name Thrush 660 remains the same, but with a new hopper design and a new gate box for spraying, 680 US Gallons is now standard capacity. In firebombing mode, this can be increased to 750 US gallons. The vacuum bag technology in the fibreglass construction allows for a more even wall thickness, saving about 100 Ibs of weight while creating a larger interior with the same external dimensions. The new hopper has also allowed changes in the hopper gates.


The new 660 will have a longer, straight cowling, similar to the TPE331-G series, with a new, more streamlined nose bowl. The squat tailplane has been replaced with a completely new fin, which is six inches higher and thus has more surface area.


Thrush Aircraft has addressed its wing spar problems head on. The 660 centre wing beam and spar configuration has been redesigned to make the outer wing panels lighter and incorporates stronger heat-treated 4340 steel spar caps, as well as a 4340 centre beam. The extra strength of the heat-treated 4340 steel spar caps allow for a reduction in the number of steel doublers and inboard steel webbing, which saves weight. The 660 wing has been static tested to 14,150 lbs.


The Thrush 660 will be fitted with the PT6A-65 or the PT6A-67. More performance enhancing features include the closing in of the rear portion of the fuselage, thus reducing air turbulence around the tail section.


The medium size version is the Thrush 550. Once marketed as the Ayres 510, the 550 has inherited the new vacuum bag technology fibreglass hopper as with the 660. The aircraft’s capacity has been increased by 49 US gallons and the top of the hopper is wider and has been redesigned to give a straight line between the propeller and the cockpit windscreen. Along with the redesign of the hopper, better fairings have been installed on the lower fuselage.


The Thrush 550 now incorporates a new 29,000-hour lower spar caps (made from 4340 heat-treated steel and giving the same weight advantages as the 660), which can be retrofitted to existing Thrush aircraft eliminating all requisite ADs on existing S2Rs.


For operators requiring extra fuel, new tanks can be provided outboard of the present fuel cells. The PT6A-34AG engine will be the main provider of power but the G-10 engine can also be fitted. However, the most notable change to the Thrush 550 is the fitting of steel spring undercarriage legs.

Thrush Aircraft has exclusively teamed with General Electric to produce the Thrush 510G powered by the GE H80 turbine engine. The H80 provides increased temperature margins to enhance hot-day takeoff performance and high-altitude cruise speeds. GE chose Thrush to launch this new engine.

The Thrush 550P has wide-stance spring landing gear capable of absorbing 8800 pounds on short, rough strips and optional spring steel landing gear can be added to increase weight for take off and landings. And it brings you a 29,000 hour Wing Spar Life and a 550 gallon clear-view hopper. 

The Thrush 550P has wide-stance spring landing gear capable of absorbing 8800 pounds on short, rough strips and optional spring steel landing gear can be added to increase weight for take off and landings. It has a 29,000 hour Wing Spar Life and a 550 gallon clear-view hopper.

Article first seen at http://all-aero.com/index.php/contactus/1293-ayres-thrush-s2r-t

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