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Sunday, August 1, 2010

Perspectives: Poor Man’s Radar

By U.S. Air Force Lt. Col Robert Haston

High-tech systems that allow you to hover blind won’t be coming to your helicopter anytime soon. Meanwhile, our critical need remains a few more seconds of good references and a few dozen more yards of visibility before touchdown. Like that old Lynyrd Skynyrd song about escaping a gun-wielding boyfriend, just “give me three steps toward the door.”

A common mistake is we see different techniques and technologies for reducing the risk of helicopter brownout as competing. In reality, they are highly complementary.

Part of the problem is we aren’t rigorous enough regarding site selection, surveying and marking. We don’t maximize the technology and techniques on hand. We need to use IR lights to spot obstacles such as fences or ditches before we commit. A long centerline of lights is better than a box or “Y” for judging drift and closure. They allow the pilot to put the line “under his seat” and finish with one light right outside his chin bubble. The British place chemlights in half-full water bottles. Taping sticks to the bottle necks props them up and stops them from rolling.

But why stop short? Tall bushes for reference are a godsend in brownout country. Why not make our own “burning bushes” out of black and Day-Glo fabric? They have to be frangible and not blow away, and air droppable versions would have to self-erect. But these aren’t major challenges. For example, the markers might drill themselves into the dirt upon landing.  

Brownout dust thickens exponentially closer to the ground. Big, bright markers will give more than twice the contrast, be elevated in dust that is half as thick, and be twice as close to the pilot’s window. Right now, pilots are removing their doors to shorten the eye to reference distance. A reference that is literally flapping against your leg would be hard to miss.

I was testing some quantum dot nanocrystal fluorescents under night vision goggles (NVG) and accidentally discovered that common orange-red fluorescents glowed rather brightly. NVGs aren’t supposed to see orange, but high spec safety vest material glowed at 250 yards when illuminated by a single 7-watt, deep purple LED (which is invisible to NVGs). This purple out, red back is sort of like poor man’s radar.

There was some trace IR, but a filter would eliminate 99 percent of this. Barely visible 390-nm LEDs cost around $50. Invisible UV costs a few hundred more. This offers some unique benefits over lighted markers. The same markers can be used day or night. They can be dimmed to match ambient light and strangled upon landing for maximum covertness. A square foot of fabric weighs less than an ounce and costs a quarter. Soldiers can tie them to hazards such as fences and to their packs for hasty landing zone markers.

On the other end of the spectrum, our outdated IR searchlights have so much glare and poor control that we often don’t use them on dark approaches. What I would like to be testing is a mini IR brownout landing light on the end of our refueling probe. This would give you another second of seeing the whole LZ under IR before the dust gets in front of your IR light source.

An included “probe-cam” could provide a view from a dozen feet forward and 4 feet closer to the ground. Once the dust shuts down the IR, you get another second or two (probably longer unless the dust is extremely thick) of good references with tall glowing/lit markers.

Hopefully, soon we will give ourselves those three steps. Hopefully we will be scanning the LZ with state-of-the-art IR lights and spearing it with glowing markers. Hopefully we might finally be worried more about the Taliban than our own dust devils.

U.S. Air Force Lt. Col Robert Haston is a 6,000-hour pilot and chief of safety with the 920th Rescue Wing, based at Patrick Air Force Base, Fla. Among other achievements, he designed the text interface now used in 25,000 survival radios. This column is a response to the article, “Beating Brownout,” published in the April 2010 issue of Avionics Magazine, page 20.

To contribute to the Perspectives opinion column, contact Bill Carey, editor in chief, at 301-354-1818 or bcarey@accessintel.com.

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