The Ag-Cat’s formidable looking Johnson Ram Inlet by Lindley Johnson with a pair of XE Vision HID xeon ‘eyes’ for night landings. The air inlet is part of the lower cowling and contains a K&N filter that is very efficient and easy to service. Note the Lund center boom mounted forward of the landing gear.
The Walter-powered Super B-model Plus Ag-Cat easily breaks ground on takeoff.
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by Bill Lavender
Although retired from flying ag-aircraft to make a living by spraying with them, I still enjoy the occasional evaluation flight. It had been almost eight years since the last time I had flown an Ag-Cat. Now, I was on my way to fly again that same 1982 G164 Super B-Plus model Ag-Cat owned by Sky Tractor in Hillsboro, North Dakota. Only this time, Sky Tractor had made several changes to it.
I used to own a 1977 B-model Ag-Cat powered by a 450 hp P&W R-985 engine. I later exchanged the engine for a 600 hp P&W R-1340. That sure made a difference.
It doesn’t seem to matter how long I’ve been out of the seat, flying an ag-plane is like riding a bicycle, you just don’t forget. I’m exceptionally fortunate to have logged flights in a wide variety of ag-planes, from the formidable 1200 hp Emair Diablo and a much less ultra-light ag-aircraft that I can’t remember the name of, to just about every known turbine powered ag-plane. I’ve not yet had the pleasure of flying a Super 600 powered ag-plane, or a turbine PZL Kruk and a couple of the new ag-planes coming out of Brazil and China, but one day...
Ron Deck has always offered me an ‘open door’ to flying his aircraft. He and the folks at Sky Tractor have put much effort into refining a proven airframe that is easy to fly, reliable and can get the job done. Although I switched from the Ag-Cat to the turbine Thrush in 1980 and flew Thrush aircraft for the next twenty years, I still have a soft spot in my heart for the Ag-Cat. No longer a current production ag-plane, there are many modifications available for it that can tailor the aircraft to your specific needs and desires.
Sky Tractor’s Ag-Cats are tricked out as much as any ag-plane I’ve encountered. The aircraft I flew used to be a 1982 G164 B-Plus model with a 400-gallon hopper, powered by a 600 hp P&W R-1340 engine. Sky Tractor upgraded it to a Super B-Plus model Ag-Cat, by raising the top wing and adding the tall tail. During its life, it has been repainted, with the wings extended. A second fuel tank has been added to each upper wing that cross-feeds with the center tank and other wing tank for a total capacity of 114 gallons that can be bottom loaded. This extra fuel helps with powering the 750 hp Walter M601E turbo prop engine with its 106-inch, three-blade Avia prop that has replaced the radial engine.
Sky Tractor added an electric Zee Air air-conditioner that is mounted in the rear fuselage allowing removal of the tail wheel ballast. The instrument panel has been completely redesigned by Ron’s son-in-law, Jay Alfson. He not only dramatically improved the instrumentation layout, Jay also installed the Satloc M3 8.4 Touch Screen System with the 20 hz Crescent receiver and the Intelliflow flow control, along with an Electronic International Instruments’ MVP-50T engine analyzer, in a very easy to use configuration. The pictures of this installation speak for themselves.
While making a round robin tour in my Bonanza to visit four operations in South and North Dakota, I arrived at Sky Tractor just before dark. The next morning proved to be a great day to fly with typical May temperatures for early morning and no wind. Mike Deck, the Ag-Cat’s pilot, towed the aircraft from its hangar over to the loading dock to top off with fuel and add about 200 gallons of water to the spray tank. He explained that the aircraft handled better with a little bit of weight in it. That was fine with me.
After the loading and fueling, I climbed aboard and Mike instructed me on the start-up of the Walter engine. Walter Engines has made its engine starting procedure pretty straightforward, almost pilot-proof. You basically turn on the Master switch, turn on the fuel pump and initiate the start process. From that point, the system takes over, recording all the parameters of the start. It is a fail-safe system.
The first time I flew Sky Tractor’s Walter-powered Ag-Cat, it had the five-blade Avia propeller. I was somewhat disappointed with the way the aircraft handled, especially during take-off with the side panels taking such a beating I thought they would come off. In my layman logic, I blamed the prop.
Many years ago, I had flown Allen Lawrence’s (Oklahoma) Thrush with the Walter engine and Avia five-blade propeller. I was very familiar with how a 750 shp turbo Thrush should fly, as I had been working a PT6A-34 version for several years. I told Allen that I thought the prop was interfering with the performance of the aircraft. He contacted Avia and I received a pile of faxes from the Czech company explaining in engineer-speak why I was wrong. Whatever the technical reasons are, I am pretty sure that today the three-blade, 106-inch Avia prop is the propeller of choice for ag-work with the Walter engine.
The 106-inch, three-blade Avia prop had been installed on Sky Tractor’s Ag-Cat. Also, the engine mount’s 2° down and to 2º the right offset had been reduced to 0°/0º and the torque was being compensated by the vertical fin. After the first evaluation flight made in 2000, Ron and I had discussed how there were degrees of offset incorporated into the engine mount that were virtually offset by the vertical fin. That did not make sense to me. This later version of the Ag-Cat was without any degrees of offset for the engine mount and combined with the three-blade prop, the airflow seemed to be cleaned up. In my opinion, this change greatly improved the overall performance of the aircraft.
With a piece of a load, full fuel and an ideal day for flying, I departed the Sky Tractor airstrip to simulate spraying an adjacent field. Sky Tractor’s Super B Plus flew excellent, hands-off trim. It had the normal amount of right rudder on take-off with its tall tail, no slamming of the side panels like in the past, smooth as a baby’s butt.
An Ag-Cat’s turning performance has always impressed me, along with its predictable flying characteristics. This particular plane had no problem hitting the 140 mph mark. Turns were easy and quick, although I most certainly did not push the time envelope to get back into the field.
Today’s ag-plane cockpit is a busy one compared to those of 15 years ago. The pilot has to discipline himself to not become focused too much on the GPS, flow control, ITT, torque, rpm, hopper load and all the other little nuances in the cockpit. The outside scan has to take priority over the one in the cockpit, or trouble is bound to come. It was real easy for me to visualize when learning a new GPS, GPS software, or any other new toy in the cockpit, that the pilot must allow himself some breathing room, taking an inordinate amount of time turning, and completing the job at hand.
A couple of landings in the Ag-Cat proved the first one wasn’t luck. I enjoyed my flight. With the Ag-Cat’s 55-foot swath, quick turns and appreciable airspeeds, there is no doubt, it serves the needs of Sky Tractor. A lot has been done to the machine to improve on the original design, as well as changes to the spray system to create an excellent spray pattern. This proves that every operation has a different mission with its aircraft that requires the operator to affect the set up of the aircraft to best suit that mission. In the case of the Sky Tractor Ag-Cat, numerous airframe modifications, engine and prop set up and spray system configuration have been accomplished to make this Ag-Cat the best ag-plane for Sky Tractor.
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