One of the Authenticity items included in the Judging Criteria in the May issue of the Flying Wire has triggered some good response from members. At least that is a positive sign that the Flying Wire is being read.
The basis for the response, concerning “spoiler strips” has been valid and the subject is certainly worthy of more discussion and information.
There have been some good articles on the history of the “spoiler strips” also known as “spin strips”, “stall strips” and Deed Levy’s choice, “auto-rotation generators”.
The Deed Levy article on this subject was reprinted in the August 1994 issue of the SRA Newsletter, and you should take the time to read it.
Deed’s final paragraph in the article summarized his view on the matter:
“Whether or not they (spin strips) should be used on today’s Stearmans depends on what the owner wants to do in the way of aerobatics. If you are not disposed to auto-rotational maneuvers, they may be omitted. Without them, your Stearman is decidedly spin resistant and the danger of inadvertent spinning is greatly reduced. On the other hand, should you want to execute prolonged spins, multiple snap rolls, and vertical reversements, then by all means you should have them installed.”
The factory installed these strips on both wings during a certain time frame. Early on, it was determined that “spin strips” on the top wing only was not an acceptable configuration, and a restriction was placed on that configuration. There is no good information on what specific flight characteristic caused that decision.
The Type Certificate/Specification for the Stearman, A-743, as published by the FAA states that the strips, if used, can be on both wings or lower wing only.
However, there is another document that gives some later and important information on this subject that is less well known and has had little distribution.
On 24, July, 1942, the Navy Department, Bureau of Aeronautics issued a mandatory directive that all N2S-4 Stearmans and all spare wings have the “Spoiler Strips” removed from the upper wing. It referenced prior changes to the N2S-1, 2, and 3 which seems to indicate that there are other similar directives for those models. It is unlikely that they would take such action on one model and not the others.
On August 6, 1943 they issued the same mandatory directive for the N2S-5
The directives do not give any background as to why, except “to improve flight characteristics”.
However, this was certainly a major retrofit task for the Navy, and wouldn’t have been done casually.
So authenticity prior to 1942 is in conflict with the Navy’s action to remove upper wing strips to improve certain flight characteristics.
A copy of the July 42 directive is included on page 16 for your information. If anyone has similar documents for the N2S-1, 2, and 3, or anything similar issued by the Army Air Corps, we would like to have copies.
In the meantime, a plane would not be penalized in judging for having strips on both wings, but the owner should be aware of this other information.
Well I’m glad that we cleared all of that up!