The Renovation of N613S

//The Renovation of N613S

The Renovation of N613S

This is a story about the renovation of a vintage WWII Stearman. It begins with the partners, then discovery of the airplane, restoration, test flights, flight training and sustained operations.

The Partners
There were three of us, all Pratt & Whitney engineers stationed in South Florida, who had daytime jobs developing and improving advanced fighter engines, scramjets and rockets. All three were (and still are) private pilots, and we flew as often as possible after work and on weekends. One of the partners was a native of South Florida and a retired Navy pilot. After retirement from the Navy he bought enough land for an airstrip and built a hangar with a shop next to his house. In addition, he came from a family of crop dusters and had experience working on Stearmans used in the family business. This combination of partners and their common interests in flying, along with near ideal South Florida weather, created a perfect setup for light planes. The other two partners were reasonably high-time light plane enthusiasts with extensive taildragger experience. Every occasion was appropriate for flying.

One day in the P&W cafeteria we were discussing the usual subjects, airplane’s, flight characteristics, engines, and anything related to aviation that came to mind. When the subject of renovating a Stearman came up, the conversation immediately focused on the Stearman and how to do a project of this type. The project was judged doable: we had the facilities, tools and equipment, expertise, and could share the costs. We agreed to make the end result look as closely as possible like it did when it was delivered from Boeing, which would require researching sources of information. The project was too good an idea to pass up, and was immediately elevated to high priority on the list of things to do. All we needed was a reasonably complete Stearman.

We live in a general aviation-rich area. Within a 25 mile radius of our airport there are about two dozen additional airports and many pilots. Through the local pilot network we found a Stearman for sale from a gentleman who had decided to leave Florida and return to his original home in the Midwest. The Stearman was at an airport community a short drive from our base of operations, and the very next Saturday we hit the road to check it out. Upon arriving at the airport we located the T hangar where the plane was tied down.

First impressions are remarkably accurate and in this case formed so vividly in memory that they will not be forgotten. There sat N613S in a T hangar with a dirt floor and no door. The good news was that it was complete, including two cockpits with all instruments and original seats. The plane had been re-engined at some point in its past with a 300hp Lycoming R680-13 and Hamilton Standard 2B20 constant speed propeller. And it ran! After a couple of weekends of work we were able to get the engine started and then taxi the plane before we removed it from the location of sale. Possibly it would require buying some missing or replacement parts, but these could be found at existing hardware sources. The bad news was that it had sat neglected for who knows how long, as manifested by a dirty exterior/interior, deteriorating fabric and countless dirt dauber nests (the engineer in each of us caused us to wonder how such a magnificent piece of machinery could be treated this way). However, all deficiencies appeared correctible with the extent of renovation we had planned. To make the proposition more attractive, the owner was anxious to leave Florida and he gave us a sale price too good to pass up. Soon after we heard the price, the deal was done.

This project was called a renovation rather than a restoration because we wanted to be thorough enough to be airworthy, yet get to flight status and enjoy flying it within as short a time as possible. The end result did not have be up eye-dazzling shiny. Everything was done under the watchful eye of a local A&P/IA mechanic, who provided an independent, arms-length, and nonnegotiable assessment of the work. The project took two calendar years, most of the time working six days a week.

Two sets of documents were invaluable for the renovation. A copy of “Erection and Maintenance Instructions for Army Model PT-13D and Navy Model N2S-5 Airplanes” was found at Air Repair in Cleveland, Mississippi. This book had a complete parts list, assembly diagrams at the component level, and assembly instructions for the airplane. A copy of Stearman Drawings on CD was obtained from Russ Aircraft. The three of us were experienced blueprint readers (and at work, blueprint originators), and we referred to the erection manual and original prints on a daily basis.

I won’t belabor the actual renovation; anyone who has done a Stearman project will understand that it involves hundreds of hours of labor while paying close attention to countless details. It is worth mentioning, however, a few of the details such as discovering and removing all local hardware store coarse thread bolts and nuts left behind by the previous owners and replacing them with bill of material AN hardware; removing and replacing engine and airframe control link bearings which were dirty and corroded; inspecting, cleaning, priming and inventorying each and every part; and building back up with methodical attention to the blueprints and component part callouts. Wing fabric was in excellent shape, as were underlying wing spars and ribs. We wet sanded the wings with 3M wet or dry paper until they were smooth in preparation for re-painting.

We painted for over a year on parts and components. We had available a sandblasting cabinet to remove corrosion and loose paint from metal parts, and a turbine-powered warm air source and spray gun that did a magnificent paint job. All metal components were painted with primer to protect the parts from future corrosion. Interior parts not normally visible were painted with primer only. Almost all metal parts that could be seen from the outside or from in the cockpit were finish-painted with appropriate color polyurethane enamel. Wood surfaces such as the seats and floorboards were painted with conventional enamel. The only problem with the wings was that they had been previously painted with a brush. The fuselage and one elevator had bad fabric and both required recovering before painting.

As the fuselage interior parts accumulated and were reinstalled, the plane began to take shape and we were faced with a final decision on exterior appearance. The partners agreed at the beginning of the project that the finished airplane would look as much as possible like the Stearman delivered in 1943, and that information should come from credible documented sources. Using the aircraft serial number, 75-7346, the Smithsonian Air and Space Museum, the Army Aviation Command and the Naval Aviation Office were able to find the Bureau of Aeronautics number, 07742, and inventory records of plane delivery and assignment stations during WWII. From these records we learned that N613S was originally delivered to the Navy as an N2S-3. To obtain information about the plane’s as-delivered appearance we contacted the Museum of Naval Aviation in Pensacola, Florida, where one of the volunteers combed thru their archives and found black and white pictures of companion airplanes from the same squadron (we will forever be in debt to the individual who did this work for us).

Thus the exterior painting strategy was set: make it look like a sister aircraft delivered to the Navy in the same shipment. All exterior fabric was painted using the Randolph process and ended up with about twenty coats of butyrate dope. One criteria we established was to apply enough paint to the fabric that the fabric weave disappeared, which resulted in an excellent fabric finish. To help all exterior surfaces appear the same color Stearman yellow, both exterior metal and fabric had two undercoats coats of white before applying yellow.

Two renovation items of special interest deserve special discussion, the AN fuel line fittings and the five pointed stars on the wings.

The February, 2008 issue of the Stearman Flying Wire contains an article by Jack Davis titled “AN vs AC Flared Fittings”. This issue arrived just before we began trial fittings for the fuel lines. Suffice it to say, the article was timely. One of our partners was an expert in “externals” on gas turbines and understood the article immediately. What the article amounts to is that there are two of the same size fittings, one called AN, and the other called AC, but they have different thread pitches. This is important because when the thread pitch in the fitting is not the same as the thread pitch in the B nut, the nut can only be turned ½ to 1 complete turn. Because this connection is not completely threaded it is possible for it to come loose. If the fitting or nut is in a fuel line, for example one of the lines from the fuel tank sump on the bottom of the center section and visible to both pilot and copilot, and it comes loose in flight then there is no remedy and one is headed for a very difficult situation. When we looked at our hardware, sure enough, the fitting and B nut threads were mismatched. This problem was corrected immediately, fortunately before everything was assembled.

The second item of discussion is the five pointed star insignia on upper and lower wings. I can’t tell you the number of compliments we received on the appearance of the five pointed stars. Most often people would ask “Where did you get that beautiful decal?” to which I would reply “That’s not a decal, it’s painted!” which generated somewhat doubtful reactions and quizzical looks. Most people just had a hard time believing the stars were painted. It doesn’t take a rocket scientist to figure out how to paint a five pointed star. Or does it? So far no one I have encountered has come up with a method that results in a five pointed star (this includes my two partners). I am sure there must be articles that explain how, and the Russ Aircraft drawings show star size and locations. As a related issue with the stars, the Naval Aviation Museum sent us a copy of the early WWII directive (1942 as I recall) that removed the “meatball” from the center of the star. Therefore the stars were painted without the red center.

Final Assembly
After all of the component assembly and installation, after all of the fabric covering and metal and fabric painting, and generous checkout along the way for correct function of everything, we were left with an engine, a fuselage, a center section, four wings and some tail feathers, and numerous connections to be made. At this point the Erection and Maintenance Manual was indispensable. It describes how to level the plane, the sequence for installing the center section, cabane struts and wires, the wings, wing struts and flying wires, how and where to drop plumb lines and make measurements for relative locations, how to tighten flying wires, all necessary for a Stearman that will fly straight and level. We worked our way through final assembly in a couple of weeks. We would not find out how well we had done until it flew.

Then came the day for the first startup. There was trouble-shooting to be done with the wiring of the starter, and after that problem was solved we began trying start procedures. It started on the fourth or fifth try, as I recall, and I also recall marveling at the Lycoming R680 radial engine start and idle show as it came to life. And it was a show! A radial engine is a mechanical masterpiece, and watching the R680 start for the first time was, by itself, worth every day of the two years of hard work invested. After a few days of troubleshooting and tinkering, we had the A&P mechanic do the final inspection, endorse the log books, and complete the Form 337 and the new Airworthiness Certificate. Once these were done, our Navy veteran partner, who had lots of previous experience in Stearmans, took her up for the initial flight check. The airplane performed perfectly. It trimmed for “hands-off” straight and level flight and did not have any adverse flight characteristics. Then the real adventure began. The partner with Stearman experience, who also was a CFI, began to teach the other two partners how to fly her. It flew like nothing I had flown before, with characteristics of both a tail dragger and a very large airplane. This required developing a feel for what the plane was going to do in advance of when it did it, especially on takeoff and landing, so that control actions could be anticipated before things went astray. This feel only came with experience. The intermediate milestone of solo was accomplished, and was followed by many takeoffs and landings. With extended practice, operating the plane became easier and easier, to the point that I was eventually able to take off and land in about 10 knot crosswinds.

Aviation in our part of South Florida is a joy and a delight no matter what the aircraft. We have excellent weather year round, especially in the winter, with mostly sunny days, beautiful blue skies and uncrowded, uncontrolled airspace. The joy of flying is magnified by being in an open cockpit Stearman with nearly unrestricted visibility and the sounds of the engine and airstream. We operated N613S for more than five years and accumulated a few hundred hours of flying time.

It seems like a Stearman is welcome everywhere it goes, with people along the way waving to the pilot and hoping for a wave in return. Near our airport there are numerous public, private and community airports with aviation friends to see. And if you don’t land, just fly down the runway and wave at friends who have been alerted by the sound of a big radial engine. We took the plane to Sun ‘n Fun in Lakeland where it was parked in a line of vintage aircraft and drew many compliments. Another trip we made was a short flight to Sebring, which is a hub of activity for all sorts of light aircraft. On a clear day from 1000 ft altitude one can see the entire perimeter of Lake Okeechobee, and one of my favorite trips was to fly the perimeter of the lake and on the west side see parts of Florida that that most people do not visit. Another favorite trip was to fly over to the Atlantic coast, then fly north along one of Florida’s great beaches. This scenery with intensely blue water and sky, white sandy beaches, lush green vegetation and abundant sunshine is so beautiful from the air it must be seen to be believed. And we gave many rides to light plane novices who without fail thanked us for the ride of a lifetime.

The Sale The partnership was great while it lasted, but inevitably circumstances changed. Once the partners began discussing sale of the aircraft, faster than you could say lickety-split we had buyers, the bill of sale was signed and there she went, headed for the horizon making the distinctive putt-putt-putt that only a radial engine makes, and without any of the partners in the cockpit. But we know where she is located and occasionally will be able to get rides. Plus we know that the new owners will give her the attention required to keep her operating and in tip top shape.

Acknowledgements In addition to all who contributed to the project, two entities deserve special mention. The first is the large collection of designers and fabricators who developed the Stearman model 75 and its engine. Over the life of the renovation we had a detailed, hands-on look at the airplane and its components and parts, design methods and fabrication strategies. As engineers we could not help but compare current airframes and powerplants with the Stearman. The 1930s-1940s was a time period in which aviation technology was changing rapidly, and we were amazed, almost on a daily basis at how creative, innovative and clever the designers and fabricators were. I worked in a development culture at Pratt & Whitney and know how difficult it is to make an aviation product perform to specifications with reliability and efficiency. The Stearman is a solid, robust and dependable airplane that served the country well by preparing many war time pilots to fly higher performance and larger aircraft. The number of Stearmans still in operation is testimony to its lasting value. I continue to admire the results of the previous-generation designers and fabricators. Their efforts produced the most magnificent flying machine in the sky.

Final restoration of the N613S.

Final restoration of the N613S.

A special remembrance goes to my uncle, William Kern McClendon, who as a young man was a line mechanic in the Army Air Forces during WWII. After the war he returned to his home in McGehee, Arkansas, and established McClendon Dusting and Spraying Service to work in the agricultural corridor along the Mississippi River. At its peak the company had five or six Stearmans and pilots. We often visited my uncle, aunt and grandparents on short road trips from our home in northeast Louisiana. As we passed on the highway my uncle would be dusting crops in some adjacent field and would recognize our car and always do some special maneuver and wave at us. Over the years he took me on many local trips in his Cessna 180, and after I had my driver’s license I would make day trips to his airfield to go flying and talk about airplanes. One of my fondest memories is from a time when I started taking flight lessons. I asked him how many flight hours he had, and he responded “I quit writin’ ‘em down when I got to 18,000 hours”. He was the individual most responsible for my unending interest in all things aviation.

By |2016-11-13T09:33:06+00:00May 19th, 2015|Flying-Wire|Comments Off on The Renovation of N613S

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