08 January 2016

Project Thunderstorm: Storm Chasing with P-61 Black Widows

P-61 crew with their hail damaged aircraft
(NOAA History)
In the immediate postwar period the Civil Aeronautics Authority (CAA, the predecessor organization in the United States to the current FAA) began to gear up several research efforts in order to establish guidelines for the regulation of the anticipated boom in civilian flying. One of the areas that the CAA placed emphasis on was understanding the dynamics of severe thunderstorms which were all too common across many of the trunk routes of the United States. In 1945, the U.S. Congress authorized $250,000 to the U.S. Weather Bureau (which would become the National Weather Service in 1970) to study severe thunderstorms with specially-instrumented Northrop P-61 Black Widow fighters. Cooperating with the U.S. Weather Bureau were a number of organizations- the U.S. Army Air Forces, the Naval Research Laboratory of the U.S. Navy, the National Advisory Committee for Aeronautics (NACA, the predecessor organization of NASA), the Meteorology Department of the University of Chicago, the Physics Department of the University of New Mexico, the Electronics Department of the Massachusetts Institute of Technology, and the Soaring Society of America. With the U.S. Weather Bureau as the coordinating agency, University of Chicago meteorologist Dr. Horace Byers was appointed director of the Project Thunderstorm. 

The P-61's SCR-720 radar
With the Second World War having ended just weeks prior to the Dr. Byers' appointment, there was a ready surplus of aircraft, pilots, and personnel to undertake the project. In addition, the CAA anticipated a rapid increase in postwar civilian flying. A spate of weather related accidents in the summer of 1945 also provided additional impetus to the endeavor. While other aircraft would be used in the study, the main storm penetration flights would use the P-61 Black Widows that once belonged to an Alaska-based USAAF weather reconnaissance unit. The aircraft were large with good range for multiple storm penetrations and were known to be tough. Pilots and crews were all volunteer and briefed in advance of the hazardous nature of the flights. The Black Widow in addition carried an onboard radar, the SCR-720. The radar was a joint development between Bell Laboratories and MIT as an improvement over previous airborne intercept radars which had a limited range of only five miles. Compared to previous AI units, the SCR-720 had a longer range (twenty miles in good conditions) and would be the primary AI night fighter radar of the Allies during the Second World War. One of the early problems of AI units in those days was attenuation and blocking of the radar beams by heavy precipitation- for Project Thunderstorm, though, this limitation was useful as it allowed the P-61's radar operator to get radar images of the thunderstorms at multiple levels. 

The pilots were selected from the Air Materiel Command's All-Weather Flying Division and were scrutinized closely for their skills and aptitude for the missions. The radar operators were all highly-trained and experienced individuals from the Navy and USAAF and the third member of the P-61 crew was a weather observer would would be responsible for collecting a variety of measurements during the storm penetration flights. 

The Soaring Society of America provided three Pratt-Read TG-32 two-seat gliders and pilots. The gliders were used to gather data on cumulus clouds before they had developed into thunderstorms as well as to make study flights on the storm periphery. Approximately 141 glider flights were made for the US Weather Bureau- one pilot, Paul Tuntland, got caught inside a thunderstorm updraft and was carried from 4,000 feet to 22,000 feet, setting a new national altitude record for gliders!

P-61s and a single F-15 Reporter getting ready to sortie
(NOAA History)
The first phase of Operation Thunderstorm took place over a sixty-square mile instrumented range near Orlando, Florida. Aircraft were based at Pinecastle Army Air Field, Florida (today's Orlando International Airport) using Black Widows fitted out with data recorders and weather instruments. Two seat glider aircraft were also used to gather data on the periphery of the storms as they entered the test range area. Microwave radar stations were set up around the Orlando area for early warning- as a storm was detected, the P-61s sortied and would penetrate the storm cell five aircraft at a time at 5,000-foot intervals from 5,000 feet to 25,000 feet. The same radar stations would also vector the P-61s into and around the the storms on their missions. Fifty ground based stations also were used to collect atmospheric data at ground level. Three radiosonde stations were also used to release multiple weather balloons into the storms in the test range. The test flights took place between 29 June and 18 September of 1946. The second phase took place at Clinton Army Air Field near Wilmington, Ohio (today's DHL Airborne Airpark), only this time there were 13 of the specially-instrumented Black Widows used plus four Northrop F-15s (the reconnaissance version of the Black Widow) owned by Northrop and single P-61 that was being used by Trans World Airlines for its own weather research. Starting on 1 May 1947, the aircraft would make storm cell penetrations every time a severe weather front passed through the area. 

SCR-720 radar image of a thunderstorm
Pilots made their penetration flights with the trim set for straight and level flight. Once in the storm, they were to do their best to minimize control inputs as sensors would record not just the pilot's instrument panel, but also the power settings, control surface movements as well as the aircraft's motion as it was buffeted by the storm. Aircraft routinely landed after their missions with damage from hail and lightning strikes. Despite the punishment of the storms and the hazardous nature of the penetration flights, over the course of 1,362 missions, not a single aircraft or crew member was lost. In recognition of their skill and bravery, all the crews were awarded the Distinguished Flying Cross. 

By 1949, the study ended and the meteorology department of the University of Chicago was given responsibility for analyzing the data from both phases. One of the most prominent severe weather researchers came from the University of Chicago's department having had his start with the Operation Thunderstorm data- Theodore Fujita, who would later become one of the world's foremost experts on mesoscale systems and tornadoes- and who developed the Fujita Scale for tornadoes used today as the Enhanced Fujita (EF) Scale. 

Operation Thunderstorm contributed a large body of data that not only increased the safety of civil aviation, but also set the stage for improvements in severe weather forecasting. The use of the Black Widow's SCR-720 radar also led to the development of airborne weather avoidance radar by commercial aircraft. 

Further reading: 

Sources: Wings of Fame, Volume 15. AIRtime Publishing, 1999, "Northrop P-16 Black Widow" by Warren E. Thompson, p91. "Thunderstorm Research Project" from In the Breeze Vol. 2, No. 12, January 10, 1946, pp1-2, accessed via NOAA History. "Project Thunderstorm" by Steve Zuger, Aviation History, July 2015, pp30-33.

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