Schnürle Tee Dee 049

Somewhere on this Forum I saw mention of incorporating schnürle porting into a Cox engine. I did this in 1973. The Tee Dee 049 engine design had proven to have great longevity from its introduction in ‘63. 1/2 A Speed was one of my flying partner Dub Jett’s favorite events. He had long ago reached the structural limits of the Tee Dee. However, our success with our DJS 29 design reinforced the belief that a tuned pipe applied to a 1/2 A could produce increased power at an RPM just below the structural limit of the Tee Dee 049 (about 30,000). Dub was sure he could design a tuned pipe with the correct tuning RPM and volumetric characteristics for a 1/2 A engine. He was right! His first design was perfect. I obtained some blank (unported) Tee Dee 049 pistons and sleeves from Dale Kirn. I ported the sleeves with a single exhaust and three bypass ports. These sleeves were fabricated in two different designs. Both had a relative small single exhaust port. The boost port was the same in both designs with an up angle of 50 degrees. This was accomplished by using an end mill with a 100 degree included angle conical tip. The difference in design was in the main transfer ports. One design had the mains angled up at 50 degrees just like the boost using the same special end mill. The other design had the main ports 90 degrees at the top accomplished with a standard flat end mill. To obtain the fit we were looking for we chrome plated these tiny jewels.

Fabrication was challenging. Or I should say it was challenging for me. The sleeves were first test fitted to the case to determine the rear location and the TDC dimension. A simple permanent marker line was good enough. This established the exhaust port location. The exhaust port was cut by visually aligning the mark straight up and using the TDC dimension for the position from the top. The bypass ports were a more difficult task. The sleeve was mounted on a stud that threaded into the glow plug hole. This was held vertically exposing the lower end of the sleeve in a rotary table. Angular position was established by dial indicating the already cut exhaust port. The end mills used were touched off on the bottom of the sleeve and then the mill bed was raised to get the port top at the correct dimension. Cutting the ports involved side cutting with the end mill to a length of about ??? inches with a ?? inch diameter mill. That is a 4:1 ratio. It is easy to break the end mill. The trick was to take very small cuts at very slow feeds. Essentially “worrying the port in place”. First the end mill was x-y moved to clear out material to the end position, then the rotary table was used to remove the material between the ends of the port. Going very slowly produced a really nice part, but took a very long time!

I built headers to adapt to the pipe. This can be seen in the grainy, but only, photo of the actual engine mounted in the pan. A couple of other interesting things can be seen, or not seen because of the quality of the photo. The header is all lathe turned with a bunch of facets at 10 degree increments. Just filing it to shape wound would have been faster! The other is the fuel piping. WHAT A MESS! You will notice an external fueler going to the centerpost where a glob job solder joint hooks together the fueler, pen bladder and exit line. Does this go to the NVA. OH NO! It goes out the right side of the model then back inside to the input to the NVA. The output of the NVA connects to a brass tube that goes to a hole drilled in the plastic front intake housing. What about a venturi you might ask. This is a glow plug drilled out to the max. Why might this be you should ask. Really simple the 1/4-32 thread matched the front end plastic housing. And why was all this Rube Goldberg used. The NV was preset at a position that would let the engine run rich, but on the pipe. This setting is, of course, way too rich for the engine running off the pipe. With the fuel line running outside the model the fuel could be regulated by simply squeezing on the fuel line after the engine was running to “put it on the pipe”. As the engine piped up it needs much more fuel and this is supplied by simply fully releasing the squeezed fuel line. Sounds very complicated, but with a little practice the procedure was mastered by even a couple of dunces.  

The real success of this project is not just Dub’s pipe design, but its fabrication. Dub has many things at which he is a wizard. His wizardry is never any greater than aluminum brazing of these thin wall tuned pipes! All I ever managed to obtain while attempting this task was a blob of melted aluminum on the work bench!

Using these engines I won the 1973 Nationals with a speed of 111 MPH.

This is an interesting story. Dub and I both flew identical models at the Nats. Or, more correctly, we both attempted to fly. The flying surface had very large humps at the expansion joints. Between the two of us we had six (6) attempts for a flight. The expansion joints had caused our light weight 1/2 As to release and clip the prop on the first 5 attempts. We were down to our last chance which just by luck was mine. Our procedure was, at best, less than desirable for flying this piped 1/2 A. Part is due to the fact that we did our test flying alone (so, a two person operation was required) and part due to stupidity. We were releasing these airplanes on the pipe close to peak RPM. The fragility of the Tee Dee crankshaft dictated hand cranking to start. I am not the best at this. So, Dub would hand start the engine. I would get it running rich, but on the pipe. Dub would run around and take over the airplane and take off dolly. I would run to the flying handle while Dub set the needle valve. He releases the airplane and off we go! A Keystone Cops’ routine at best! This last attempt I got the airplane safely off the ground and started my timed run. Now comes a critical decision. Bill Wisniewski (event director and good friend) had already disqualified other 1/2 A contestants for “whipping”. I was not taking any chance on our only (and winning) flight. So, after I got the airplane leveled off and in the pylon I simply lifted my hand off the monoline control button to eliminate any question! Many years later Mike Langlois viewed this action in a bit of a different light. He described my flight as running around the pylon waving to the crowd and “rubbing-it-in” at the spanking we were giving everyone. Now, for the stupid part? We should have hand launched the airplanes! These were airplanes with generous wing area and could have easily been hand launched and Dub and I finish 1st and 2nd!

Johnny

I guess I am the stupidest person in the world. I simply want to insert a picture below its description. The picture is on my computer. The picture does not have an http://. This is my first attempted post.

OK, I did not know there was a waiting period to upload images. Hopefully I have been successful.

1973 AMA 1/2 A Nationals Winner


Actual Engine with plumbing


Dub and John with their 1973 AMA Nationals Winners (in their 1973 costumes)


1/2 A Tuned Pipe

Great story!! Thanks for sharing, welcome to CEF!! You will be able to post photos shortly, there is a short wait for new members.