|Piper's Ag Indian|
|Written by Jim Cavanagh|
The sight of a crop duster screaming along at corn-top level, towing a plume or cloud and pulling up to a 180 degree turn is a sight that everyone keeps in their “cool stuff” memory banks. Alfred Hitchcock locked the image in our minds with his movie North by Northwest. Aerial spraying or crop dusting has been a mainstay of agriculture for more than sixty years, particularly in the South and in areas of flat acreage along river flatlands and other plains.
One of the first agricultural airplanes was the retrofitted J-3 Cub that could carry up to 1,000 pounds of material. This airplane helped lead the way for the industry to create aircraft that were specially designed for aerial applications and pilot safety.
Modified Stearman aircraft and Cubs were adapted to the chore until Texas A&M University developed a prototype for the very first pure ag plane, the Ag-1. A variation of the Ag-1 was then developed by the legendary Fred Weick who, with John Thorp, designed the Piper Cherokee series. Weick’s design, the Ag-3, was so far ahead of its time that the basics were used to develop the Snow Ag Truck and the Piper Pawnee.
The Piper PA-25-150 Pawnee was one of the first, if not the first, specifically-designed ag planes. Introduced in 1957, it mirrored the construction of Piper’s popular Tri-Pacer series, with steel-tubing frame, fabric covering and Piper’s thick aluminum wing. Powered by a 150-hp Lycoming O-320, the Pawnee gave flying farmers a 20 cubic foot, 70 gallon hopper and a 183 square foot wing. It was also equipped with a tail wheel, bungee landing gear and a number of pilot safety features, including a fuselage designed to absorb forward and downward impact in the event of a crash, low stall speed (57mph without flaps and 51 mph with flaps), a high cabin for visibility and a safe and comfortable seat. For simplicity and the benefit of the former military men who would be flying them, the Pawnee retained a nice, heavy stick.
The Piper Pawnee was a top of the line airplane when it was first introduced. It was pilot-friendly, performed much better than the modified airplanes and was inexpensive to purchase and operate.
Dave Johnston of Johnston Aircraft, a Pawnee and Brave parts and Service stop in California, said the Pawnee literally knocked the Stearman right out of the marketplace.
The first Pawnee flight was at the old Lock Haven, Pennsylvania plant in August 1959. Although a jump seat could be installed in the hopper, the thought of riding in a cleaned out fertilizer bin really had no aesthetic appeal. The hopper itself was a 20 cubic foot fiberglass bin that held up to 145 gallons of liquid or between 550-1,200 pounds of solids, depending on the density of the material. The 150-hp models are placarded to an 800 pound limit.
The top of the hopper is the actual top of the airplane, so no matter what modifications are made to that area, the hopper remains in the airplane. In the Pawnees that are used as tow planes today, the bottom is simply cut out and the disbursal parts removed to clean up the airframe.
While I have never flown a Pawnee (due to single-seat insurance considerations), I have taxied a couple around the airfield. Getting in is simple and easy for a young guy, but a bit challenging for older pilots.
The seat is relatively comfortable and the view is tremendous! Weick hit the nail on the head with this feature, which is probably why nearly every ag plane developed since that time has adopted a high seat and canopy. It is like having a Barcalounger strapped to the top of a Cherokee Warrior.
The stick fits naturally in your hand and, with proper conventional gear technique, the airplane handles excellently. I’m sure that a full hopper would demand more throttle for takeoff and more brake or rudder for turns, however.
Friends who have flown the Pawnee say it flies like a heavy Tri-Pacer…“Apply a control and wait!” This isn’t a bad thing for something that does steep, lazy eight, nearly-hammerhead turns with hundreds of pounds of chemical onboard. The fact that the airplane has relatively few ADs and an excellent structural record underscores the fact that it was designed and built right.
The A model is the lightest of all the models and offers the best performance. As subsequent models gained horsepower, they also gained weight.
The 250 is the favorite model, because of its efficiency and performance. Dave Johnston reports that in answer to the acceleration and climb conundrum the Pawnee uses a large, three-bladed constant-speed (C/S) prop. Piper has a reputation for keeping things simple and inexpensive, but in the case of the Pawnee that may have hurt them.
The Pawnee soon evolved in response to a changing market. Larger engines were installed, beginning with the 235-hp Lycoming O-540. The C and D models offered a 260-hp engine and also featured a larger hopper. The D model also had oleo landing gear and moved the fuel from its fuselage tank in front of the pilot to the wings. Interestingly, Piper offered the PA-25-150 with a constant-speed McCauley prop and the PA-25-235 with either a fixed-pitch or a constant-speed prop.
The service ceiling for the Pawnee was 13,000 ft. Oddly, the last model Brave 300 had a service ceiling of only 6,400 ft., but could cruise at 140 mph over a distance of 460 miles.
Piper built exactly 4,400 Pawnees from 1957 to 1972, most of which have now found homes outside the U.S. A handful of Pawnees that are still in this country are towing sailplanes and banners or have been modified as two-seat trainers. The 150-hp models are excellent and economical for glider towing, while a number of the 260-hp models have been converted back to 250 hp with low-compression pistons that allow them to burn auto fuel.
Because this particular airframe matured as much as it could, in 1972 Piper introduced the Piper PA-36 Brave. The Brave was a slightly larger airplane and sported a Continental Tiara six-cylinder engine. The scuttlebutt on the flight line is that this engine was introduced well before it was ready, which may have contributed to a number of failures. Weaknesses on the first engines included the crankshaft flange and the cooling veins on the cylinders. They also experienced considerable trouble with hot starts, which is not good for reloading turnarounds. The problem areas were tweaked by Continental, but the damage to the engine’s reputation had already been done.
When Piper moved the fuel to the outboard ends of the wings—creating plumbing and balance problems—more fuel was added to the Pawnee’s already-tarnished reputation, despite the fact the improvement was better than having the gas in the pilot’s lap. Later, a company redesigned the airplane with the tanks inboard, resolving the balance and plumbing issues.
Throughout the years, a number of companies have modified or upgraded the Pawnee’s performance. Johnston Aircraft’s model PA-36-400 Super Brave uses a TCM Tiara eight-cylinder engine.
Gippsland Aeronautics, in Australia, based a design on the Pawnee Brave and called it the A9-Fatman. The company flew the prototype for ten years—accumulating more than 10,000 hours in the field—before it was finally certified as the GA-200C. This ag plane features two seats and a 270 gallon hopper, which makes it a very economical aero applicator.
The rest of the industry surpassed Piper, particularly with the advent of turbine engines. In 1982, Piper stopped producing and supporting the Brave. They sold the rights to do so to WTA Inc., a company based in Texas. WTA Inc. continued to sell the airplanes as the New Brave 375 and the New Brave 400.
Today, two companies in Argentina own the rights to the airplanes and are doing their best to provide parts to the world fleet.
The PA-25 and PA-36 are listed as restricted category civil aircraft. Legally, the planes are only to be used as working aircraft. Converting them to faux warbirds or using them as private aircraft has been done, but mainly under the experimental category. Most Pawnees today are used for other things besides ag work.
Soaring clubs love them. In fact, the Harris Hill Soaring Corporation worked with Schweizer Soaring School to develop a permanent fix for the expensive recurring AD 95-12-01 that affects the front carry through section and cluster. The planes have more than enough power and wing for towing sailplanes.
As I was driving through Salida to reach the Great Sand Dunes National Park during a recent road trip to Colorado, I put down my bucket and shovel long enough to watch Pawnee tow gliders aloft. They seem slow and loud, but there is only 150 hp pulling 3,000 pounds, and that’s a lot of work! Still, it is neat to watch them circle up, pop the tether and dive for the ground. If only the rest of us could work as hard at 60 years old!
Thanks to the original AG-3, the Piper Pawnee is often mistaken for other ag planes derived from the same prototype. But the Pawnee holds a special place in history and in the hearts of many old duster pilots. If Piper had decided to pick up the gauntlet and stay in the ag business, it is possible there would be some pretty nifty dusters flying today.