The Pilot's Lounge #34:
Of Ag-Planes, Fire Bombers, and Inventions

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One of the most stressful and dangerous kinds of aviation operations is aerial application also known as crop-dusting or ag-aviation. When a younger man, AVweb's Rick Durden worked (hard) in this industry, eventually moving on to saner endeavors. Still, he kept up with his contacts in the industry and recently went back to his roots to check in with an old friend who now specializes in improving ag-planes and even turning them into fire bombers. Read all about it.

The Pilots LoungeThe combination of the arrival of spring and daylight savings time seems to have a way of luring pilots back to their airports from months of hibernation. Here at the virtual airport, the pilot's lounge is getting more crowded. From where I sit, I hear plans being made by a group to fly out for breakfast; other pilots are scheduling some recurrent training to clean off the rust from winter and one is scanning Trade-A-Plane because he is determined to finally buy the airplane of his dreams or at least one he thinks he can afford. In general, pilots seem to be doing something so they can do more flying. I found myself experiencing the itchy-feet syndrome as well and thinking I should wander off somewhere. I thought about it a bit and decided to accept a long-standing invitation from good friend Bill Hatfield to stop by his airport. It had been over a year since I'd been there, so it was high time to go marvel at the latest products of his creative genius.

Looking Backward

Bill Hatfield

On the way over to Nunica, Mich., home of Hatfield Airport, I reflected on Bill Hatfield's career. Bill started his professional aviation life as an aerial applicator or, as I tend to say, a crop duster in the early '70s. He made his living down low, inches above the small, tree-rimmed fields of Michigan, flying the barrel-chested airplanes Ag-Cats, Ag-Trucks, Pawnees and others built to work hard for a living and keep their pilot alive should the flight terminate with a sudden, unpleasant stop. He, as with all other ag-pilots, had the times where he tried to bend the throttle forward over the quadrant in the hope there might just be one or two more horsepower to be had because those trees were right here, right now, and omigawd, come on Baby, just a little higher and stall speed is only two knots slower, come on, climb, dammit, and whew, we made it we're alive and okay get the nose down and keep flying this thing and get turned around and back into the field because they don't pay us to fly around up here and sightsee, we have to work for a living.

Wasted Youth?...

As I flew along, I couldn't help but think about the world of aerial application and how it has changed. I'd worked as a ground crew member every summer during high school, either waving Day-Glo orange flags to give the pilots a reference point for the next pass, or loading and servicing the airplanes and cautiously mixing chemicals or fertilizers used to treat the fields. When I turned 18 and got my commercial certificate, I began flying the same airplanes I had served. That only lasted until my father found out and exercised his parental prerogative for the first and only time in my flying career and forbade me from continuing that particular form of employment. Nevertheless, I did it long enough to still have the occasional nightmare dominated by power lines. The airplanes we used those 30 summers ago were modestly engined, 235 to 300 horsepower, Call Air A-9s, Cessna Ag-Wagons and Ag-Trucks and Piper Pawnees. We rarely carried as much as 200 gallons of liquid. A few of the larger operators were running Ag-Cats or modified Stearmans with 450 hp Pratt & Whitney radial engines. We envied them. We heard of, but never saw, the Aero Commander Thrush with a 600 hp radial up front and speculated about Grumman's plan to put the same engine on the Ag-Cat. We figured that it would be to glimpse heaven to have that kind of power too often we were badly frightened as we tried to climb out of ground effect on hot days to clear a power line or row of trees only, to discover that the airplane was exceedingly reluctant to answer our control inputs.

PZL Dromader M18

Even then, there were involved regulations on aerial application of herbicides, insecticides and fertilizers. We were extremely careful to use only measured amounts and place them where they were desired because we had read the labels on the bags and drums of chemicals. After all, we too occupy a position on the food chain forcing us to eat many of the things that we sprayed. Perhaps our sense of caution was a result of enlightened self-interest. Perhaps that level of care was partially responsible for my continuing interest in conservation, leading me to fly regularly for LightHawk and my ongoing fascination with agricultural aviation.


In the time since Bill Hatfield started working in ag-aviation, the business has changed greatly. The number of operators has diminished greatly due to a combination of continuously falling prices the farmers receive for their produce and the imposition of incredibly rigid regulations and tests for each person involved in the handling of agricultural chemicals. For example, one of my old jobs no longer exists: No more are flaggers needed, because differential GPS tells the pilot within millimeters left and right where to fly for each pass. On completing the process of treating a field, the unit then provides a report showing the time of treatment, the precise location of each pass across the field, the wind direction and temperature. The fly-left or -right indicator to help the pilot determine where to make each pass is thoughtfully mounted near the nose of the airplane so the pilot can see it without having to look and focus inside the cockpit when flying very low.

That 600-gallon hopper occupies the space between the cockpit and the engine. That flat, black box just aft of the engine is a GPS-based indicating system used to help plan passes.

With fewer operators and the need to charge less per acre for treatment as the years went by, the airplanes being used became bigger so that they could do more without stopping to reload. It was always an axiom of ag-aviation that one cannot make money with the hopper closed. Every minute in ag-aviation may matter, because it is so often the case that there is a window of only two or three days to treat several thousand acres of crop land before it is lost. Once a person has seen what corn borers, grasshoppers or locusts can do to a field in a matter of hours, the idea that time can be crucial becomes forever internalized. Ever-larger hoppers were desired so that the pilot could land less often. More power became the watchword. Pilots mouthing incantations to Our Lady Of Perpetually Increasing Horsepower during pull-ups over obstructions were finally heard: Manufacturers began installing larger engines on the airplanes. Soon, 600 hp radials were hung on the Ag-Cat and even sooner became too small.

...And Innovation From Abroad

Turbine power was cautiously explored. There was a fear of the effects of the dusty and dirty environment on such powerplants. Ways of handling the problems were found, and the shockingly expensive PT-6 engine from Pratt and Whitney was found to be economically viable on ag-planes because it put out so much power and proved to last and last and last. It is now almost impossible to find a Thrush without a turbine engine on it. For those who want piston power, there are large radials, often repeatedly overhauled Pratts or Wrights. Ag-operators claim that one of the more satisfying radial engine installations is the metric version of the venerable Wright 1820, from MZL in eastern Europe, of 967 horsepower, attached just forward of a 660-gallon hopper on the front of the massive Dromader M18. A company that has building airplanes for many years, Pezetel, makes this airborne piece of farm equipment in Poland even though its name is only marginally familiar to U.S. pilots.

Frankly, one of the things I most wanted to see when I got to Bill's place was the piston-powered Dromader. I wanted to use the handles and steps to climb up the side of the mountain of an airplane and hope I don't fall the eight feet or so from the cockpit to the ground as I try to maneuver in through the window to the incredibly comfortable pilot's seat. I wanted to look out that long nose at a 967 horsepower radial and see if this time Bill would relent and let a former ag-pilot take it around the patch. Then I wanted to see what Bill was doing to modify those behemoths. I wanted to see if he was still hanging PT6s on them and enlarging the hoppers to an almost incredible 8000-gallon capacity.


Cockpit of an M18

Bill Hatfield was on the front line of the changes that were occurring in the ag-aviation business over the last 30 years. He came early to concept of installing turbines on ag-planes, and began doing the Pratt and Whitney PT6 conversions himself. He currently hangs 1,145 and 1,300 horsepower PT6 engines on the Dromader M18. He also began experimenting with the less well-known turboprop engines and the idea of mating them to existing airframes. Of course, along the way Bill formed a company to do the creative things he conceived. It is Turbine Conversions Ltd., which may be reached at 616-837-9428. I knew about the PT6s on the Dromader and that he was also putting the Czech Republic-built Walter turboprop engine on the Thrush and Ag-Cat, but I didn't know what else had come from his fertile mind in the last few years. I wanted to see what he was doing to give ag-pilots an increased chance of survival, both literal and economic.

I also found that I was curious as to what else might be on the airport. Bill has a soft spot for interesting and unusual machines that are good at what they do. I knew he had a Russian AN-2 biplane project and I was curious to see what else had piqued his interest since the last time I visited.

Being There

Business end of a Walters-powered Ayres Thrush

I wasn't the least bit dissatisfied. The first thing that came into sight was a Walters-powered Ayres Thrush, standing large, yellow and shiny in front of the hangar. Around the corner were two Yak-52s, the wonderfully agile Soviet-era aerobatic trainers. They will soon be sold to some lucky folks who will probably spend a great deal of quality time happily flying aerobatics and causing minor sensations when they land at small airports.

When I located Bill he took me into his hangar where he showed me the first of his prizes, a modification for the Dromader and Thrush that would allow single-point refueling from a location near where the chemical load is pumped into the airplane. Currently the airplane must be fueled at the ordinary fillers on each wing tank. It wastes a lot of time to run around and fuel the airplane through two wing fillers when there is only one loader. With only one loader, fueling usually cannot be done simultaneously with filling the hopper. The single-point system allows the pilot to program how much fuel is desired in each tank. The loader only has to plug in and start pumping fuel while the chemical mixture is being loaded. In a business where time is money, single-point refueling should pay for itself in short order.

A Pressure Cowling For a Radial...

When we walked back outside, Bill pointed me at a Dromader and asked me if I noticed anything different. It didn't take long. It looked stock, but wrapped around the whacking great radial was what, at first glance, looked to be one of the ugly, old "speed ring" cowlings that NACA (forerunner of NASA) had developed for radial engines in the '20s that actually made radial-engined airplanes faster. (They had an airfoil shape and the resultant lift vector was forward, so the cowling itself generated thrust.) Looking closer, it became apparent that this was a pressure cowling. It was much longer front to back than the old speed ring, and it had baffling for the cylinders. It turned out that on hot days and at high altitudes, the big radial needs some channeling of the cooling airflow around the cylinders to keep them from running up near redline. The pressure cowling channels air around the cylinders effectively solving the cooling problem. The pressure cowling pays a number of dividends. By providing a bit of thrust, the pressure-cowled airplanes need less power to fly at any given airspeed, so fuel burn is reduced. Better cooling means longer engine life, saving operators some hard-earned money. I learned that there was a side effect that didn't play so much in the wallets of operators, but rather in the hands of the pilots. The new cowling improves airflow over the fuselage and tail of the airplane, improving handling in pitch and yaw. All that seems to be in keeping with what we've learned about working airplanes in the last 20 years or so: often, ugly is good. The cowling may cover up the lines of the radial engine but it provides thrust and improves cooling and handling; not a bad bit of modifying in my book.

...Putting Out the Fire

967-horsepower MZL radial with pressure cowling installed.

When I looked underneath the Dromader, I noticed that the "gate" area under the hopper, where the guts of the spray mechanism all come together and where the emergency dump door lives, had been replaced with a thing that looked a bit like a miniature bomb bay. It had a door on each side and a mechanism to open them. Bill explained that this is the "firegate." Because of the ability of the Dromader to carry several hundred gallons of water, Bill figured that the airplanes would make great fire-fighting tankers. He also figured that given the seasonal nature of ag-aviation work, and the slack times even during the growing season, he could turn ag-planes into quick change artists, able to treat crops at one moment, then dart into a nearby hangar and emerge as Aerial Tanker, scourge of the evil wildfire, providing a better economic return for the owners of the airplanes.

I expressed my doubts, based on my knowledge of airborne fire fighters as World War II and Korean War-vintage bombers that pound into the smoke and unload vast quantities of water on raging fires. I figured the adrenalin-charged world of firebombing was a place no mere ag-plane could possibly enter.

The Firegate

Mr. Hatfield provided me with a little information regarding current aviation events (it's true, as my daughter says, I am out of it). The largest ag-planes are perfectly viable firefighters. It seems that there has been a demand for a quick-response airplane that can put out the "match" before it becomes a conflagration. It's akin to the lesson the fire departments learned in the '60s when they converted pickup trucks into vehicles that could scoot through traffic and extinguish small fires rather than commit the more expensive, full-scale pumpers. Historically, the problems with converting ag-planes to do fire fighting while still being able to do aerial application had been cost and technology. For years, when things have gone seriously sour, pilots have been pulling the emergency dump handle to open up the gate under the hopper and get rid of their loads in five or six seconds. Why not just use that emergency dump to unload water on the target? It sounded like a great idea. It just didn't work. The gate on the bottom of the hopper was a flat plate that was hinged on the forward end. On opening and being forced downward by the weight of the departing liquid, the aerodynamic effect was to sharply pitch the airplane up. That's all well and good when it's needed to get over an obstruction rapidly, but not when the desire is for a controlled, albeit rapid, drop of water in a particular area.

A firegate under construction in Bill Hatfield's shop.

The solution was to turn to a bomb-bay door design, used effectively since the 1920s. The doors open parallel to the airflow, with no pitch consequences.

The second problem was that the drop had to be controlled. While one might think that the idea is to splash as much water on a spot as possible, the reality is that it needs to come out at a fairly constant, determined rate. On top of that, there are times when either just a portion of the water needs to be dropped or there is a desire to lay down a trail of water so as to form a fire line to "herd" brush fires along a "V" so they may be snuffed out. That meant that the doors had to open in a controlled manner rather than simply flop out of the way of a couple of tons of water. How to open the doors a specific amount so as to meter the flow or, more interestingly, to close them again so that half the load could be kept on board to be dropped elsewhere proved a decided challenge.

Bill found that the solution was a hydraulically-controlled, electrically-regulated firegate. Hydraulics could keep the stainless steel doors open a specified distance and then close them quickly on demand. An electrical system, with an appropriate timer, could command the hydraulics to open and close the doors in a given amount of time.

Bill decided to see if his shop could build and get a Supplemental Type Certificate for a firegate. Not only could the shop do it, I learned his firegate has actually been in use in the U.S. and Australia for a few fire seasons. The response has been excellent. As the airborne leaders who direct drops on fires have learned just how agile ag-planes are and how fast they can turn around (they can be loaded with 800 gallons of water in under 2 minutes), they are being used more and more. While it is a hard truth of fighting forest or grass fires that the battle is won on the ground, having an additional airborne tool means that the men and women slugging it out on the deck are a little better off.

I heard some stories of firegate-equipped ag-planes diving into tight valleys and swales where the larger, lumbering tankers could not go, and snuffing out small blazes that could well have become major fires and were miles from deployed ground crews.

M18 with firegate and pressure cowling installed.

I was fascinated to learn that the dedicated fire tanker/bombers being built today the Canadair CL-215 (piston engines) and CL-415 (turbine engines) carry some 1,200 gallons of water. They are not cheap. A CL-215 runs about $7 million while the CL-415 goes for about $25 million per copy. Each requires a crew of two to operate. Turbine Conversions Ltd. can provide two turbine Dromaders for a total cost of $1,400,000 or two piston versions for $540,000. Together, the turbine Dromaders will carry 1,600 gallons of water; the piston team will carry a total of 1,200 gallons, the same as one Canadair. Each Dromader takes one pilot.

Already have a large ag-plane in the hangar? Turbine Conversions sells the firegate for installation on a Dromader or Thrush for $20,000. As a result, existing operators can make their airplanes capable of making additional revenue for a very reasonable price. When government contracts are being let to operators for fire fighting services (particularly the "come when called" contracts), it seems to this taxpayer that the choice of aircraft for at least some of them is pretty obvious. That's particularly true when the ag-planes can be making their living treating crops, and, when called, can change over to fire fighting in the time it takes to clean the hopper. It may prove very valuable in the Third World where there are a number of large ag-planes but no aerial tankers and forest fires must currently be left to burn themselves out. I've always liked the idea of doing more with less. The firegate seems to be a classic example.

I'm looking forward to Bill's next little invention: He is in the process of putting water pickup scoops on float-equipped Dromaders so that they can pick up the water by skimming a lake near the fire they are fighting, cutting the time it would otherwise take to ferry to the nearest airport. Like the other things Bill Hatfield has done, it should be a winner.

Bill, next time I visit, I'm either flying a Dromader or one of the Yaks.

See you next month.