The Fascinating Spin History of the T-37 Tweet.
If you haven't guessed by now, I am fascinated with spins. So much that I actually have had the honor of providing a few lectures on them (you can watch one here.) While I am pursuing my Masters Degree in Education, I have focused much of my attention on Civilian, Military and Airline training programs, and which ones seem to be the most effective at "getting the job done." While compiling my research, I have come across, and collected, several US Air Force "Dash Ones." Which are training manuals specific to certain aircraft, such as the Cessna T-37 "Tweet, The Northrop T-38 Talon and the North American T-39 Sabreliner. I was astonished with how much detail these manuals provided pilot trainees and how useful condensed material like what these manuals could provide general aviation pilots. While reading through several training binders for the T-37 Tweet, I came across the story of how this aircraft became a staple in spin training for the United States Air Force.
In October of 1954, the first prototype of the Cessna T-37 Tweet (the XT-37) made its first flight. The aircraft was part of a highly competitive program to establish primary jet training aircraft the to United States Air Force. One of the requirements of this competition was that each participants design had to have the capability of providing spin training, and with years of providing all-types of aircraft to the market, Cessna was the lead contender in this competition.
The problem with the XT-37 (pictured above) was that when it underwent spin testing, the results were less than desirable for student pilots. The aircraft spun at nearly 70 degrees nose low, at almost 2 seconds per full 360 degree rotation, and took almost 5 turns with full anti-spin control inputs to fully recover. Cessna went back to the drawing board and added some pretty interesting features to the XT-37 to make its spin characteristics more desirable.
From USAF Dash-1 Attachment II;
1) The empennage was extended 25 inches to put the tail further from the spin axis.
2) The vertical tail size was increased.
3) The upward travel of the elevator was increased to flatten out the T-37's spins.
4) A ventral fin was added to dampen the aircrafts rotations.
5) Spin strakes were added to the nose to manipulate the pressure around the nose. The USAF cites this as the most important addition to the T-37 to improve its spin characteristics.
The results showed a vastly improved Tweet. After testing concluded, the production T-37 Tweet spun only 45 degrees nose low, at a slower rotational velocity, and only required a little over one turn with anti-spin control inputs to recover. Look at the difference between the top picture of the XT-37 Tweet prototype and the production T-37 Tweet. It is noticeable that the top portion of the nose has added strakes, the tail is larger, and the empennage is longer.
The T-37 Tweet ended its USAF service in 2009, and while we someday hope that small turbine training aircraft will become a feasible reality, we can appreciate all the aerodynamic research and enhancements that went into the T-37 Tweet, and came out of the Tweet when it progressed into a research aircraft for NASA. Check out this video here of a T-37 spinning.
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