Spreading Super in Mangamahu Valley

by Mike Feeney

(Circa 1960s) Landing just after dawn, I had Pete, my loader, to top up the fuel tanks of ZKBUX, a Cessna C-180 with a 230 BHP engine outfitted for spreading super phosphate fertilizer, known as super. We had a cup of tea while I told him that I wanted to keep flying without refueling to see how long we could work until we had only about half an hour of fuel remaining.

The area to be covered was a rectangular field rising up to a western ridgeline. There was a number of small dams and lakes, a very pretty area of about 500 acres in the Mangamahu Valley, New Zealand. The rate of application was to be around 250 pounds per acre.

A half ton load should sort of fit one run, perhaps stretched just a little and finished with two runs at 90° to tidy up the job.

As usual I divided the block into halves, then quarters. It was a dream job with first runs being a tad lower than the airstrip and last runs being only a few hundred feet higher. The paddock was close with just a sixty degree left turn to get lined up, another left turn back to the strip and curving right bank to the touchdown point on the right wheel.

The time on the ground was about 50 seconds. Pete was very good on the tractor, as he had grown up on the family farm. We completed about 15 loads per hour on the close work, decreasing as I needed to climb and the distance increased to the paddock.

After about 55 loads and three and a half hours, I got Pete to dip the tanks. He looked over to me holding up three fingers; three more loads only. I called a halt after three hours and forty-five minutes. It felt great, but I did need a pee for sure. I had to go behind the fertilizer bin, as a bit of a group had gathered, including a nice lady with tea and hot scones.

The next job was about ten miles further north up the valley, on the east side quite high. It was a perfect morning with traces of fog still remaining down in the valley. The job was for 45 tons of super.

I can clearly recall the airstrip after nearly 60 years ago. It was about 1200 feet high. To the north was Mount Ruapehu and far out to the northwest was Mount Egmont.

I was airborne from our base headed for the airstrip right at early dawn and landed well before the sunglare hit us. Pete warmed the loader truck’s Nuffield’s engine and hydraulics, then loaded 800 pounds of super into the hopper. This was a light load to see how the Cessna C-180 with its 230 BHP engine would perform in the cold morning air.

The aircraft easily cleared the fence line. I retracted flaps and climbed at 80 knots. The large farm sloped up and the boundary was only a mile away from the airstrip to the east and straight into the rising sun. Because of that, I wanted plenty of height, so I noted the altimeter reading I had to attain to be well clear of the bush and trees.

I usually hung my pocket watch beside the airspeed indicator to time sorties. The time for landing roll, hopper loading and takeoff on level ground was about 55 seconds, call it one minute. Then the climb out and sowing sector at an average of 90 knots took about 2.5 minutes. The downhill run was only 1.5 minutes, at about 140 knots. The C-180 is a fast machine. You have to carefully plan the landing. For a straight in approach, cowl flaps closed, power back to 20 inches, then flaps to 20° followed by another notch of flaps to 30°. If landing with a tailwind, which was very common, you set the flaps to 40°.

The mental landing and takeoff check list went something like this: during landing roll with flaps set to 20, cowl flaps opened, check for enough fuel for next sortie, elevator trim well forward, temps and pressures in the green, hopper loaded, loader driver and equipment clear, check airstrip clear of sheep, cattle, humans and kids before adding power for another takeoff.

Over the next two days, Pete and I spread 50 tons which was 110 sorties at about twelve loads per hour, five minutes per load with a climb of about 600 feet going to the paddock.

A C-180 with full fuel, pilot and three passengers can climb at about 1000 FPM. With an ag load of 500 KG and max power, it will climb at 450 FPM. If you decide to reduce power to 80%, the Rate Of Climb (ROC) will reduce to approx 250 FPM. That’s not too good if trying to climb at low level over rising farmland. If flaps are not retracted fully after takeoff, the ROC will be reduced even further. If the pilot tries to climb slowly using Vx (best angle of climb) his speed’s safety margin will be hopeless and sooner or later he will crash into rising ground, trees or wires.

Fifty tons does not seem like very much if you are flying a 750 SHP PT6 Cresco or Air Tractor, less than 30 sorties. But in a 230 BHP C-180, it is a very different matter. A Cresco can hold two tonnes of fertilizer and a C-180 only 500 kilograms.

My ZK-BUX was 1700 pounds empty. I was about 170 pounds. With oil, fuel and a HF wireless, ZK-BUX weighed about 1900 pounds. Add me and the ag C-180 weighed 2100 pounds empty. Add a full hopper of super, 1100 pounds, and the aircraft had a takeoff weight of 3200 pounds. That is a large overload for a C-180 with a very aft centre of gravity, indeed.

The Cessna C-180 was a lovely machine to fly at normal legal weights, but a highly dangerous one when grossly overloaded. There were rare times that the ag-version of the Cessna C-180 took off at less than an overloaded configuration. However at the time, it was one of the best, if not the best, flying machine for hilly New Zealand spraying operations.