Industry workhorse returns

by Bill Lavender
ALBANY, GA—After almost 14 years, the venerable 600 horsepower radial Thrush is back in the marketplace. Ayres Corporation stopped building the 600 Thrush in 1994. However, the current owners of Thrush aircraft products, Thrush Aircraft, Inc., have received a firm order from the Libyan government for 20 of the radial engine Thrush. Two of these are dual cockpits with dual controls for training purposes, while the other eighteen are single cockpit versions. When I learned of all this, I contacted Thrush Aircraft and inquired about the possibility of making an evaluation flight. During my career, I have owned two 600 Thrush and had flown two other different ones for operators after selling my business. Thus, I am intimately familiar with four different 600 Thrush. Each flew a little differently, but all were basically the same.

No one can deny that the cost of a new ag-aircraft has reached record, sky-high levels. It is part of the times with the cost of labor and manufacturing materials ever increasing. However, the driving factor for the elevated cost is the turbine engine, which makes up almost half of the cost. With the reintroduction of the 600 Thrush, many things were looked at to help reduce manufacturing costs without sacrificing the safety features and workability of the aircraft.

Because the Libyan government has placed such a large order for the 600 Thrush, the factory can now bring the aircraft back to the marketplace, but it is not the same airplane that so many of us flew in the 1980s.

The new 600 Thrush has an all-metal empennage that is 20 pounds lighter than the current model 510 Turbo Thrush empennage. It is the same tail section as was used on the “Diet Thrush” of many years ago. The aircraft has extended wings that measure 45 feet overall in length and one bay shorter than the 510 Turbo Thrush. The wing has a life of 28,800 hours, with a large butterfly spar plate and 4340 chrome-moly steel spar caps. It also has servos in the ailerons, making for a very easy aircraft to turn.

There is no ballast in the aircraft. It’s CG, empty, is two inches inside of the rear of the CG envelope (all references are for the single cockpit 600 Thrush. The dual cockpit 600 Thrush was built for training purposes and has a different weight and balance configuration). The tailwheel is the same as on the 510 Turbo Thrush, as well as the same heavy-duty tripod gear with dual caliper Cleveland wheels and brakes and 29” high-flotation tires. The factory made the right decision to keep the heavier gear. I believe it is a good trade off in weight and a little drag for reliability.

The aircraft comes painted a basic white, using PPG’s DeSoto paint. This paint has proven, in the white color, to better withstand sun and chemicals than yellow. An accent stripe is optional. It does not have a baggage compartment making this an interesting place to install GPS components.

After a walk around, I climbed into the familiar cockpit. With way too many hours to count in similar cockpits, I found almost everything was like it used to be in the 600 Thrush. The three-piece panel was different, and of course, it smelled new with only one hour showing on the tachometer.

I like my rudder pedals extended away from me. I positioned the 600 Thrush’s fully out and could have used another inch or two. Using an electric boost pump to prime, the Aero Engines engine fired off immediately. Waiting on the radial to warm up, I gazed over the gauges. Everything looked good and ready to go.

The first flight was an empty flight, except for the 136 gallons of fuel on board. That’s right, the tanks have been enlarged from 56 gallons each to 68 gallons, more than enough fuel for most uses.

During the ferry to the field at 500 feet AGL, the airspeed bounced around between 120-125 MPH using 30 inches of manifold pressure and 2,000 RPM. I’d say that’s about 5-10 MPH faster than the rag tail, stock wing Thrush of yonder year. Being empty, it flew beautifully. Why wouldn’t it? Its stability was evident with the ATIS at the Albany airport reporting 21°C (about 70°F), a density altitude of 750 feet and the wind at 13 knots, gusting to 19, a little bumpy. But, Thrush aircraft are known for their stability in the wind and the new 600 Thrush is no exception.

Now it was time to return to the factory for a load of water. It had been at least eight, maybe even ten years, since I’d flown a 600 Thrush. No sense in pushing the envelope, so I asked for 225 gallons. I still had at least 120 gallons of fuel on board.

The 225-gallon load was no problem at all for this aircraft and, rightly, should not have been one. The takeoff roll was to the beginning of the first white stripe marking (Aiming Points) on the runway, about 1,000 feet. The 13 knots / 21°C wind was right on the nose of the aircraft. With the same power settings as the first flight, the aircraft lost about five MPH in the ferry. It went across the field at an honest 120 MPH. This was flown in a rather large field with runs long enough to allow the aircraft to settle down from the entry. Time to head back for more water.

I filled the hopper to 300 gallons and still had over 100 gallons of fuel on board. Anyone that has worked a radial engine ag-plane knows the amount of fuel on board is important when loading, not to mention to be sure there’s enough to return for more. Most pilots I know fill the left tank only when fuel is needed. The fuel will eventually cross feed to the right tank. The exception is the first load in the early morning when both tanks are usually full.

The takeoff was uneventful, running to the end of the first white marking on the runway before liftoff, perhaps an additional 200 feet than with the 225-gallon load and with the same wind and temperature conditions. However, in the climb out, I used a bit more power, setting the engine at 33 inches MP and 2,100 RPM. I also left in five degrees of flaps until I was clear of trees by about 200 feet. With this power setting, the 600 Thrush ferried to the field at the same 120 MPH as the 225-gallon load had with the lower power setting. It also worked the field at approximately the same IAS. There is no doubt the aircraft knew it had 300 gallons in it, or maybe I should say the pilot knew this. But, given the wind conditions, the load was reasonably comfortable with this power setting, albeit a little high.

With the same 300-gallon load, I reduced the power to 30 inches MP and 2,000 RPM. The pucker factor increased somewhat in the turns. I don’t recommend using this power setting in gusty wind conditions with 300 gallons on board. The same is probably true for high-density altitude conditions. However, after spraying out a few gallons of water and burning some fuel, the aircraft handles well, even with the wind.

The new 600 Thrush gets the AgAir Update stamp of approval. It performed as well, if not better, than the older and more familiar 600 Thrush. Weighing in at 4,671 pounds empty weight, my concerns about being heavier adversely affecting performance were alleviated. Even though it is 300 pounds lighter than a 510 Turbo Thrush, which is significant considering its radial engine’s weight, a turbine ag-plane it is not. A pilot should not expect it to perform like a Turbo Thrush. But, in a low volume application environment, it could be a challenger to any turbine-powered ag-plane for making a profit, especially for a smaller flying service. Primarily, the Libyans selected the 600 Thrush because when, and if, it is needed for locust control, multiple aircraft have to be at many different locations at the same time. For a more typical ag-operator, the 600 Thrush could fill the need for a “half-of-a-turbine”, or a good starter aircraft for a new pilot. At $398,500.00, the 600 Thrush offers many opportunities to improve the bottom line, with or without its accent stripes. Just maybe there’s “a little bit of history in your future”!

Industry workhorse returns		Volume 26, Number 3, March 2008
The all-new, redesigned 600 Thrush (as well as the dual cockpit version) was required to go through a complete FAA conformity and flight test, which it passed in November of 2007. For three years, 1973-1976, the 600 Thrush was built at the rate of almost one a day.	*by Bill Lavender* ALBANY, GA—After almost 14 years, the venerable 600 horsepower radial Thrush is back in the marketplace. Ayres Corporation stopped building the 600 Thrush in 1994. However, the current owners of Thrush aircraft products, Thrush Aircraft, Inc., have received a firm order from the Libyan government for 20 of the radial engine Thrush. Two of these are dual cockpits with dual controls for training purposes, while the other eighteen are single cockpit versions. When I learned of all this, I contacted Thrush Aircraft and inquired about the possibility of making an evaluation flight. During my career, I have owned two 600 Thrush and had flown two other different ones for operators after selling my business. Thus, I am intimately familiar with four different 600 Thrush. Each flew a little differently, but all were basically the same. No one can deny that the cost of a new ag-aircraft has reached record, sky-high levels. It is part of the times with the cost of labor and manufacturing materials ever increasing. However, the driving factor for the elevated cost is the turbine engine, which makes up almost half of the cost. With the reintroduction of the 600 Thrush, many things were looked at to help reduce manufacturing costs without sacrificing the safety features and workability of the aircraft. Because the Libyan government has placed such a large order for the 600 Thrush, the factory can now bring the aircraft back to the marketplace, but it is not the same airplane that so many of us flew in the 1980s. The new 600 Thrush has an all-metal empennage that is 20 pounds lighter than the current model 510 Turbo Thrush empennage. It is the same tail section as was used on the “Diet Thrush” of many years ago. The aircraft has extended wings that measure 45 feet overall in length and one bay shorter than the 510 Turbo Thrush. The wing has a life of 28,800 hours, with a large butterfly spar plate and 4340 chrome-moly steel spar caps. It also has servos in the ailerons, making for a very easy aircraft to turn. There is no ballast in the aircraft. It’s CG, empty, is two inches inside of the rear of the CG envelope (all references are for the single cockpit 600 Thrush. The dual cockpit 600 Thrush was built for training purposes and has a different weight and balance configuration). The tailwheel is the same as on the 510 Turbo Thrush, as well as the same heavy-duty tripod gear with dual caliper Cleveland wheels and brakes and 29” high-flotation tires. The factory made the right decision to keep the heavier gear. I believe it is a good trade off in weight and a little drag for reliability. The aircraft comes painted a basic white, using PPG’s DeSoto paint. This paint has proven, in the white color, to better withstand sun and chemicals than yellow. An accent stripe is optional. It does not have a baggage compartment making this an interesting place to install GPS components. After a walk around, I climbed into the familiar cockpit. With way too many hours to count in similar cockpits, I found almost everything was like it used to be in the 600 Thrush. The three-piece panel was different, and of course, it smelled new with only one hour showing on the tachometer. I like my rudder pedals extended away from me. I positioned the 600 Thrush’s fully out and could have used another inch or two. Using an electric boost pump to prime, the Aero Engines engine fired off immediately. Waiting on the radial to warm up, I gazed over the gauges. Everything looked good and ready to go. The first flight was an empty flight, except for the 136 gallons of fuel on board. That’s right, the tanks have been enlarged from 56 gallons each to 68 gallons, more than enough fuel for most uses. During the ferry to the field at 500 feet AGL, the airspeed bounced around between 120-125 MPH using 30 inches of manifold pressure and 2,000 RPM. I’d say that’s about 5-10 MPH faster than the rag tail, stock wing Thrush of yonder year. Being empty, it flew beautifully. Why wouldn’t it? Its stability was evident with the ATIS at the Albany airport reporting 21°C (about 70°F), a density altitude of 750 feet and the wind at 13 knots, gusting to 19, a little bumpy. But, Thrush aircraft are known for their stability in the wind and the new 600 Thrush is no exception. Now it was time to return to the factory for a load of water. It had been at least eight, maybe even ten years, since I’d flown a 600 Thrush. No sense in pushing the envelope, so I asked for 225 gallons. I still had at least 120 gallons of fuel on board. The 225-gallon load was no problem at all for this aircraft and, rightly, should not have been one. The takeoff roll was to the beginning of the first white stripe marking (Aiming Points) on the runway, about 1,000 feet. The 13 knots / 21°C wind was right on the nose of the aircraft. With the same power settings as the first flight, the aircraft lost about five MPH in the ferry. It went across the field at an honest 120 MPH. This was flown in a rather large field with runs long enough to allow the aircraft to settle down from the entry. Time to head back for more water. I filled the hopper to 300 gallons and still had over 100 gallons of fuel on board. Anyone that has worked a radial engine ag-plane knows the amount of fuel on board is important when loading, not to mention to be sure there’s enough to return for more. Most pilots I know fill the left tank only when fuel is needed. The fuel will eventually cross feed to the right tank. The exception is the first load in the early morning when both tanks are usually full. The takeoff was uneventful, running to the end of the first white marking on the runway before liftoff, perhaps an additional 200 feet than with the 225-gallon load and with the same wind and temperature conditions. However, in the climb out, I used a bit more power, setting the engine at 33 inches MP and 2,100 RPM. I also left in five degrees of flaps until I was clear of trees by about 200 feet. With this power setting, the 600 Thrush ferried to the field at the same 120 MPH as the 225-gallon load had with the lower power setting. It also worked the field at approximately the same IAS. There is no doubt the aircraft knew it had 300 gallons in it, or maybe I should say the pilot knew this. But, given the wind conditions, the load was reasonably comfortable with this power setting, albeit a little high. With the same 300-gallon load, I reduced the power to 30 inches MP and 2,000 RPM. The pucker factor increased somewhat in the turns. I don’t recommend using this power setting in gusty wind conditions with 300 gallons on board. The same is probably true for high-density altitude conditions. However, after spraying out a few gallons of water and burning some fuel, the aircraft handles well, even with the wind. The new 600 Thrush gets the AgAir Update stamp of approval. It performed as well, if not better, than the older and more familiar 600 Thrush. Weighing in at 4,671 pounds empty weight, my concerns about being heavier adversely affecting performance were alleviated. Even though it is 300 pounds lighter than a 510 Turbo Thrush, which is significant considering its radial engine’s weight, a turbine ag-plane it is not. A pilot should not expect it to perform like a Turbo Thrush. But, in a low volume application environment, it could be a challenger to any turbine-powered ag-plane for making a profit, especially for a smaller flying service. Primarily, the Libyans selected the 600 Thrush because when, and if, it is needed for locust control, multiple aircraft have to be at many different locations at the same time. For a more typical ag-operator, the 600 Thrush could fill the need for a “half-of-a-turbine”, or a good starter aircraft for a new pilot. At $398,500.00, the 600 Thrush offers many opportunities to improve the bottom line, with or without its accent stripes. Just maybe there’s “a little bit of history in your future”!
Thrush Aircraft is building two ag-aircraft a month. All of 2008 aircraft model slots are filled, the 600 Thrush with its 400-gallon hopper and the 510-gallon Turbo Thrush.
Thrush Aircraft, Inc. built two dual cockpits, dual controls 600 Thrush aircraft as part of a 20-aircraft order from the Libyan government. The DC 600 Thrush has a 100-pound steel bar forward of the hopper to balance the CG of the aircraft with two pilots on board. However, this is not the first DC 600 Thrush to have been built. Ayres Corporation built UV-3789A in May of 1980.
The 600 Thrush sports a three-section instrument panel that is easy to view and has plenty of room for adding accessory cockpit equipment.
Availability of the P&W R-1340 and prop with AG-100 blades is tight. Aero Engines and Tulsa Aircraft Engines overhauled the two engines pictured here. Sun Air Parts is the supplier of the 20-engine order for the Libyan government aircraft order. The props are Northwest Propeller overhauls. The aircraft is also certified for the Hamilton Standard prop with 6101 blades.