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May 09, 2021, 05:10 PM
DJS Johnny
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K&B 15RS Crankcase


This is the long-form of my journey of the K&B 15RS (aka Wart, aka Racing Schnürle). First, I must acknowledge my friends without whom this project would have been impossible. Luke Roy (of Rattler fame) provided invaluable data. He has an original barstock case and sleeve from the prototype phase plus one of the investment case cases that came after the 15RS. This provided the details of the sleeve porting and case transfer shapes. Luke also reverse-engineered the stroke based on the cylinder bore. Bill Hughes contributed detail photos (aka Mug Shots) of Glenn Lee’s engine used at the 1964 F2A WCs. Additionally, he provided certain critical dimensions and important information like the engine used a K&B 15R rod. Darron Black (aka “Boy Wonder” because he reminds Dub and me too much of ourselves at his age) is a friend of Dub and mine that provided invaluable support for me learning Autodesk Fusion 360 and identifying Shapeways as a source of 3D printing directly in aluminum. Bill Wisniewski, of course, is the designer of the of the K&B 15RS and provided critical information about its design and development in personal conversations. And last, but not least, is Dub Jett, my life-long flying partner and friend who supported my efforts with his excellent advice. As the Beatles’ song says “I get by with a little help from my friends”!

The precursor of the K&B 15RS is the developmental prototype engine by Bill Wisniewski used to incorporate schnürle porting into a model engine for the very first time. It has a barstock crankcase with the transfer ports cut in from the outside and a thin aluminum sheet bonded over the outside to close off the openings. Very ingenious for development work. Exactly the type of out-of-the-box thinking one expects for Bill! The engine is K&B 15R based. It is on-center and long rod like the 15R, but with a larger bore (0.625 inches). After proving the design concept of this porting configuration, Bill moved quickly to design and implementation of the K&B 15RS engines used at the 1964 World Championships. Bill actually used one of the barstock prototype engines to become World Champion for the first time. The rest is history.

In my opinion the K&B 15 RS is one of the finest and most innovative engine designs ever. Bill Wisniewski designed this engine for use at the 1964 F2A World Championships and built engines for the US team to use at the championships. An unusual feature is the K&B “branding”. After the pattern was completed John Brodbeck, Sr. wanted the engine branded as a K&B Torpedo. Bill chiseled a rectangle in each side of the wooden pattern and used raised letter marking strips to add the TORPEDO and 15RS (racing schnürle). This was done hastily after the patterns were at the foundry and were in cue to be cast and certainly not up to Bill’s usual standard of quality. It is the first true schnürle design with porting through the piston skirt. The schnürle porting originally was very close to the patent disclosure of Adolf Schnürle (1897-1951) from 1926. Bill said this porting only ran slightly better than the very best Super Tigre G20/15 Jubilee engines. He said he was looking at the cylinder and thought “That is a lot of wasted port area opposite the exhaust”. So, he invented the “boost port” by placing a port in this unused space. As he said “This really made the engine come to life”. In many ways this engine changed forever the trajectory of model engine design the way the Super Tigre Jubilee porting had done in 1959. Sometime way down the road I asked Bill what WART stood for. He just gave me that wry smile of his and replied “Just look at that thing!” Enough said. I think it is a very handsome engine in an unusual kind of way. It is very disappointing that K&B did not move quickly in the schnürle engine market to become the world leader.

Ok, back on subject. You may ask why I so interested in the K&B 15 RS. When I was in University (1963-1967) 4 years getting my BS I could not do much modelling. I did not have the time or money. All I did for these 4 years was go to class, study and work 40 hours a week as a janitor and all summer to pay my way through school. No time for modelling. However, I did keep up by reading about what was going on. This is when Bill W. was doing revolutionary work on engine design. I am a student of history and knew something very important was happening. I had been trying to find a K&B 15 RS to buy for MANY years. There were only 6 cases cast. To this day I have never seen one for sale. So, I decided to make my own. Using information from the afore mentioned sources I developed a 3D solid model using Autodesk Fusion 360. I then exported a .stl file and sent it to Shapeways for direct 3D printing in aluminum. 13 days later I received my part. It looks great! Better than I would ever have expected. But, I don’t know what my expectations were. Surface finish is unique. It looks somewhere between a good sand casting and an investment casting, but not either, really. The accuracy is quite good. I sampled and averaged 8 as printed external dimensions. The tolerance on this part is +0.003 / -0.002 inches. I judge this as very good. The lettering is quite exceptional. The integrity looks great. No visible signs of any inclusion. All-in-all I would deem this a complete success! The physicals seem to be good. Yield is 30 compared to 40 for 6061-T6 and 30 for A356-T6. Hardness is 114 compared to 95 for 6061-T6 and 90 for A356-T6.

Next, I will be machining the “as cast, oops as printed part”. I hope you enjoyed hearing about my journey so far. I think this may be an exciting development for engine builders who only make one or two engine parts.

Johnny
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