First Impressions: If you ever wistfully looked at those big-engined crop dusters and thought how fun it must be to zorch low level over the fields, ducking under wires and pulling up into a wingover to begin the next pass, then join the club! Most of us probably will never join the ranks of crop duster pilots, but there are uses for these planes besides applying product over America’s farmlands. The CallAir A-9, while designed as a crop duster, is also ideally suited for use as a glider tow plane.
Background: Reuel Call, like many early aircraft designers, was self-taught. He designed, built, and personally flew his first aircraft, the Model A in 1940. All the initial CallAir designs were single engine cabin monoplanes specifically designed with high-lift wings to fly from high elevation airstrips. Like many aircraft manufacturers, production plans changed after Pearl Harbor. Although the newly founded Call Aircraft Company tried to acquire license to build planes for the war effort, their location in Afton, Wyoming was too “off the beaten track” to interest the War Department. So instead, the company added to the war effort by repairing airplanes that were “cracked up” from training incidents.
After the war, production of the CallAir began with the “A” series cabin planes until the company shifted gears to agricultural aircraft. The A-5 was a crop duster version of the three-seat A-4 with a hopper, wind-driven spray pump, and spray bars added. The strange configuration of the A-5 put the pilot side-by-side with the hopper. Interestingly, in the 1950s, CallAir also produced snow cars and aviator snowshoes! The snow cars were built like an airplane and utilized Continental C-65 or C-85 engines with pusher props and cabin heat from exhaust shrouds.
In 1959, Reuel Call sold his company. After floundering a couple years under new ownership, the company was bought out and reorganized as the Intermountain Manufacturing Company (IMCO). IMCO was responsible for designing the A-9, which was purpose-built as an ag airplane from the ground up, unlike the A-5. In 1966, Rockwell Standard not only bought out IMCO, but also purchased Aero Commander and numerous other companies. The following year (1967), the factory in Afton, Wyoming shut down for the final time, and manufacture of the A-9 was continued by Aero Commander under their agricultural division, Ag Commander. Under Ag Commander, the A-9 was named “Sparrow Commander” and the A-9B, “Quail Commander”. Additionally, the flight manual references the A-9B as the “Super A-9”. In 1971, Rockwell transferred the manufacture of the A-9 to Aeronáutica Agrícola Mexicana Sociedad Anónima (AAMSA), where the A-9B-M was manufactured until 1984.
Design Features: The A-9’s low-wing, long nose, and high, single-place cockpit gives it the unmistakable crop duster look, even without spray bars hanging beneath the wings. Of course, the long nose has a very important design purpose. A 210-gallon fiberglass hopper is located immediately forward of the windscreen and keeps the weight over the aircraft’s center of gravity. The hopper door is closed with two over-center, quick-access latches, making it easy for loaders to refill the hopper during quick ground turns. It’s no secret that aerial application is not the safest job on the planet, but the fabric-covered 4130 chrom-moly steel cage fuselage makes surviving a crash more likely. There are also aluminum side panels on the fuselage making for easy access during an inspection.
The low wings have Sitka spruce spars and are supported by V-Struts and smaller bracing that is attached to the upper fuselage. These struts act in tension while on the ground and compression when the wings are producing lift. With the flaps selected to half or full (24 degrees), the ailerons mechanically droop down to 10.5 degrees, giving responsive aileron control at slow speeds.
In order to convert the A-9 from agricultural to tow plane, the spray pumps and bars were removed, and a tow hook mechanism was installed immediately aft of the tailwheel. Glider towing also has its hazards, the most dangerous being if the glider pilot flies too high during the tow - especially while still low to the ground. As one can imagine, a glider flying higher than its tow plane will pull the tow plane’s tail high, which creates a negative angle-of-attack with potentially fatal results. This is why it is critical for the tow plane pilot to have easy access to the rope release lever. In the CallAir, this crucial lever is safely located just aft of the throttle quadrant. A short aft-actuation of the ball-handled lever will immediately release the tow rope from the airplane.
One of the most unique and distinguishing features of the CallAir is its landing gear. It goes without saying that ag planes are designed to handle rough dirt and gravel landing strips. The A-9’s rugged landing gear features a coil spring shock absorber that is maintenance free, other than for normal corrosion control. For those with a keen eye, it’s an easy way to distinguish a CallAir A-9 from a Piper Pawnee, for which it is commonly mistaken.
Powerplant: The baseline A-9 has a 235-horsepower Lycoming O-540, and the Super A-9B (as flown) has a 290-horsepower IO-540-G1C5. All A-9 models use fixed-pitch McCauley propellers that vary in size depending on the engine. Both the A-9 and A-9B will tow single and two-place gliders with no issues, even launching from relatively short grass strips. The A-9B, however, will shorten the time required to get to the glider release altitude! The wings hold 20 gallons of fuel each, and fuel pressure is supplied by an engine-driven fuel pump with an electric pump as backup.
Start/Taxi/Takeoff: Climbing into the CallAir requires technique! First place a foot into the stirrup step below the cockpit; then step onto the wing root while holding a hand grip mounted to the fuselage. From there, I then grab the vertical machete blade wire-cutter that bisects the windshield with my left hand (it’s not too sharp) and reach inside the cockpit with my right hand to grab a segment of steel tube. Then step on a small fuselage foot peg and swing your right leg through the swing-down window and slide in. It is awkward at first, but once you get the technique down, you’ll feel as cool as one of the Duke boys sliding in the General Lee!
The cockpit is not complicated. A quick familiarization is all it takes to figure out where everything is. Try not to drop anything in the cockpit as there is not any sort of floorboard. It’ll go straight to the bottom of the fuselage and believe me when I say that your arms are not long enough to pick up anything you dropped!
Basic flight and engine instruments are on the panel, and the throttle quadrant is on the left side wall. A fixed pitch prop means no prop control lever is required. The Johnson bar flap lever is behind and below the throttle quadrant and a thumb push button action is required before moving the handle between the three positions (up/half/full). The trim lever is awkwardly positioned between the left fuselage side wall and the flap lever. It is not an issue until you pull the flap lever up to select full flaps and then would like to move the trim lever back for aft trim. You will find the flap lever is now in the way, which will require reaching behind it to find the trim lever. After doing this a few times, I finally made it easier on myself by setting aft trim before full flaps.
The A-9 with the O-540 requires a couple pumps of the throttle and it will crank up with no hesitation. To start the fuel-injected IO-540 A-9B, use of the electric fuel pump to prime the engine is required. When the engine is warm, use of the electric fuel pump to clear vapor from the lines. Making turns, especially tight turns during taxi, requires large rudder pedal movements, so it’s important to have the seat adjusted to get full throws on the rudder pedals.
After run-up is complete, ensure the electric boost pump is on and lineup on the runway. Without a glider to tow and with no material in the hopper, the A-9 will be off the ground before you have time to finish adding full power and can even think about raising the tail. The climb rate with the high-lift wings is impressive. With a glider attached 200 feet behind, you will have more time on the runway. But once clear of the ground, you must set a relatively high nose angle to keep the glider at its optimal tow speed.
Flight Characteristics: Smooth and predictable is the name of the game with a glider trying to stay in position behind you. This is especially true on hot and bumpy days, when glider pilots generally love to fly! Rearview mirrors help the tow pilot keep tabs on the glider’s position. Once the glider’s release altitude is attained, you will feel a “thunk” as the glider pilot releases on their end of the rope. The standard contract is for the glider pilot to immediately turn 90 degrees right and the tow pilot turn 90 degrees left, to avoid being in the same piece of sky. The rearview mirrors assist in confirming that the glider is going in the expected direction. Once the glider is released, you can explore the handling characteristics of the CallAir. Slow flight and stalls are non-events. Power addition and relaxing the back-stick pressure returns you to normal flight. The only thing noteworthy is that all control movements are large. The control stick is big and requires a lot of movement to get full throws of the flight controls. These full control movements make you feel like you’re on the elliptical machine at the gym. That might be a bit of an exaggeration, but after my first day of towing with the A-9, my right shoulder was a bit sore for a couple days.
Landing/Rope Drop: If you have a clear area to drop the rope, it’ll be an easier landing for you and will increase the longevity of the nylon rope. Furthermore, rope dropping is fun! Ensure your drop area is clear of people and equipment and make your high-speed approach always considering the 200-foot rope with the metal attachment ring at the end. Generally, make a shallow diving approach from around 400 feet AGL and level off around 50-100 feet above the ground. When you reach the desired release point, grab the release lever and pull back. The rope will detach from the hook and fall to the ground, where a recovery crew will take and reposition it for the next glider.
If you must land with the rope, make a relatively steep approach to avoid dragging it across the ground or hitting obstacles on short final. With full flaps, hold 65 knots on final and you’ll maintain plenty of control without floating too much. After landing, taxi back to the launch area and turn around, but be careful not to taxi over the rope you are dragging behind. Reset flaps and allow the ground crew to hook up the next glider!
Wrap-Up: Flying the A-9 is fun and towing gliders for your local soaring club is a great way to spend an afternoon! The CallAir A-9 flight manual states, "NEVER EXCEED THE LIMITATIONS OF THE AIRCRAFT AND THE PILOT. FLY SAFELY, ENJOY YOUR WORK, LIVE LONG, AND MAKE MONEY”. For a rugged airplane designed to work, it doesn’t get any simpler than that!
