Help solve a weather mystery

The second in the series of Dr. Masters' vacation blogs.

Help solve a weather mystery

I'm often asked why it is that the Hurricane Hunters are unafraid to fly in extreme Category 5 hurricanes with 200 mph winds, but refuse to fly in garden variety thunderstorms with winds of perhaps 30 mph. Well, airplanes don't care about wind, as long as it's all moving the same direction at the same speed (i.e., there is no wind shear). Granted, some hurricanes have outrageous wind shear that creates severe turbulence capable of damaging the airplane. However, threats of this nature pale in comparison to the chief hazard of flying into thunderstorms--hail. Even small hail poses a significant threat to airplanes. Hurricanes rarely have hail, except at high altitudes in some of the stronger storms. On a mission I flew into Category 3 Hurricane Emily of 1987, one of our airplanes encountered pea-sized hail in the eyewall at 18,000 feet, and the ice scoured off the airplane's paint job in some places. More seriously, hail damaged two of the engines, causing oil leaks that forced the airplane to abort the mission after a record 34 penetrations of the hurricane's eyewall.

Large hail can seriously damage an airplane, as seen in the incredible photos below. These origin of these photos is unknown, but they have been circulating on the Internet for a few months. Presumably, they were taken on August 10, 2006, but no one knows where. If you can shed some light on this mystery, drop flightglobal.com and myself an email.





Armored T-28 hail research aircraft retires
Speaking of hail and airplanes, the world's only aircraft equipped to safely to fly into mature thunderstorms, the South Dakota School of Mines & Technology's armored T-28, is being retired this year after over 900 penetrations of thunderstorms and 37 years of service. The famed aircraft, which has survived updrafts as strong as 115 mph, 2-inch hail, and numerous lightning strikes, will go on display at the Strategic Air and Space Museum at Ashland, Nebraska. The National Science Foundation has requested to the Pentagon that a two-engine A-10 Thunderbolt aircraft be made available as a replacement. A two engine hail penetration aircraft is a good idea! I spoke with one of the pilots of the T-28 back in 1987, during a thunderstorm research program I was involved with. The pilot told me that he had done several "dead stick" landings on highways after lightning strikes had knocked out power to the single engine of the T-28.

Here's the specs on the special modifications the T-28 aircraft had, taken from the web site above:

The leading edges of the wings and tail surfaces are covered with 2.29 mm (0.090 inch) 2024T4 heat-treated aluminum sheets formed to fit and bonded to the existing wing and tail surfaces. The tops of the wings are covered with 0.81 mm (0.032 inch) sheets of the same material. The leading edges of the cowling are covered with an additional sheet of fitted 3.18 mm (0.125 inch) aluminum. This armor plating adds about 318 kg (700 lb) to the aircraft weight.

The carburetor is protected from ingestion of large hailstones by the addition of a metal grate to the air intake to break up the hailstones prior to entry. A similar device was installed over the oil cooler intake to prevent damage to the relatively fragile oil radiator.

The canopy also required substantial modification since the standard Plexiglas bubble canopy was much too weak to withstand encounters with large hail. The windshield was replaced with flat sheets of 1.91 cm (0.75 inch) stretched acrylic and the side panels were made of flat sections of 1.52 cm (0.60 inch) stretched acrylic. The windshield and the leading-edge armor were tested to withstand 7.6-cm diameter hail at penetration velocities by firing ice balls from a specially-built hail "cannon" at test sections of the aircraft.


Figure 1. The South Dakota School of Mines & Technology's armored T-28 weather research aircraft. Photo taken by Jeff Masters in June, 1987 in Huntsville, Alabama during T. Theodore Fujita's Microburst and Severe Thunderstorm (MIST) field program.

Jeff Masters