Extension builds new hail machine from ground up

Slideshow: After using the same hail machine for 31 years, Nebraska Extension completes an improved version for research and demonstration.

Over the years, the people at the local Sun Mart in Wahoo have become familiar with the work of Justin McMechan and his Extension colleagues. "I was buying ten bags every time I would come in," says McMechan, Nebraska Extension crop protection and cropping systems specialist. "Last year, they were still calling in the winter asking if we needed any more ice."

Each year, McMechan and other Extension specialists use about eight pallets of ice (100 bags per pallet) to feed the hail machine that Extension has used for 31 years to demonstrate hail damage, evaluate the impact of timing of a hail event, the recovery of corn and soybean plants based on the time the event occurred, and associated yield loss.

Last year, McMechan found out the machine would be returned to National Crop Insurance Services, who built the original machine in collaboration with the UNL Engineering Department in 1986. However, NCIS did provide the schematics for the machine, and over the last eight months, McMechan teamed up with Mike Kocher, associate professor in the Biological Systems Engineering Department at the University of Nebraska-Lincoln, to build a new and improved version, which was unveiled at the recent Eastern Nebraska Research and Extension Center Open House in June.

And when engineers get involved with cropping systems specialists, a lot of new ideas get passed back and forth. "Mike said, 'If we're going to build this, let's make it a research-based machine,'" says McMechan.

Hail machine 2.0

Hail machines work by using an industrial fan to blow air through a series of pipes to simulate wind, and using that wind to launch "hail stones" at a crop.

On the old machine, the rate of ice delivery was directly tied to the fan speed, and McMechan wanted the two to be independent on the new machine. "One option was using another set of hydraulic lines on the tractor. But the tractors Justin is using didn't have that option," says Mike Kocher. "The other option was using an electric motor to turn the auger. So, in addition to the hydraulic motor to power the fan, the new machine uses an electric motor to power an ice auger that delivers the ice to the tube it's launched from."

McMechan also wanted to be able to track wind speed, and the best way to do that was by using a pitot static tube – another one of Kocher's ideas. A pitot system is essentially a tube within a tube. The inside tube measures the combined static and dynamic pressure, the outside tube measures static pressure, and a differential pressure transducer subtracts out the static pressure from the combined static and dynamic pressure to determine the dynamic pressure – which is directly related to the air velocity.

While the old machine's platform was suspended on four legs that made it difficult to move up and down, the new machine can be easily lifted up to eight feet in the air with a fork lift, allowing McMechan to test hail events from different angles.

And the updates are ongoing. One of McMechan's goals is to record specific simulated hail events so others can recreate them – and that includes everything from wind speed and speed of the ice flowing through the machine to time and real-time temperatures during the hail application.

In the coming months, the new machine will be upgraded with an Arduino system – a kind of on-board computer that takes various measurements it then uses to calculate and display this information. McMechan can then use the information to adjust the hail event using three valves that will be mounted on the side of the machine. These three valves can be used to regulate and fine-tune wind speed from 60 to 170 miles per hour. "The Arduino can record up to 100 times per second," Kocher says. "We can fill up an SD card and Justin's hard drive pretty quickly."

Real-world hail events

McMechan says the new machine should provide a way to control more variables related to hail events, including the recovery of corn plants based on timing of hail, different angles of application and wind speeds, all of which could be important factors for evaluating hail and plant pathogen interactions.

Of course, not all hail stones are created equal. Both size and density dictate the level of hail damage. So, McMechan plans to work with engineers in the future to vary the freeze rate of ice to simulate different densities of hail. This would mean making homemade ice with a machine – another project in the works.

"The current machine and the way it will be finished will allow us to have replicated results," says McMechan. "If someone builds another machine like this, they would be able to dial it to the same parameters of our hail event. That gives us greater continuity when we have specific environmental conditions during and following a hail event that we want to test."

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