CONTROL LINE: SPEED
Glenn Lee, 819 Mandrake Drive, Batavia IL 60510
I recently traveled to Chicago for the Radio Control Hobby and Trade Association's annual Model and Hobby Show. I went to visit friends and to see if there were any new engines (or other equipment) we could use in Speed.
Don Jehlik, old-time Speed flier and World Champion Team Race competitor (with Herb Stockton), was there with his imported gliders and rubber-powered models. He had flying semiscale versions of the P-51 and Me 109, stick-type models, hand-launch gliders, and even a helicopter with counterrotating rotors!
He got into the business through friends he made in world modeling competition. He started and sold many of my Speed models over the years, so we had a great time hashing over old times.
New Engines
I saw a bunch of new engines at the hobby show, but I was only interested in the ones that had potential for use in Speed. There were several new 3.5cc-sized engines—the trouble is, all of them are designed for RC cars. This doesn't mean that they can't be used in our .21 Sport Speed airplanes, but you would have to make a new head, a new carburetor, and a new spinner backplate. You would also have to make (or buy) an aero-version crankshaft, or make a special prop nut to work on the car-type crank. There just aren't enough engines sold for Control Line Speed use to warrant their production.
There were at least six new Novarossi engines with different model numbers—apparently referring to some internal modification to the porting or crankshaft design. They all had throttles, huge finned heads (for improved cooling in the cars), and were very expensive! It's big bucks to purchase one of these engines, but you do get a quality product.
For instance, the Ultracompetition 350 No. 6/SCT quotes 2.30 hp at 33,000 rpm. Tuning tricks can get the engines to near 40,000 rpm or more—it's impossible for manufacturers to hand-tune every engine.
It's fun to read their technical data sheet—let me quote a few of their design features:
- The cylinder is realized with a special copper alloy and is chromed and rectified and lapped. It has 8 ports (4 corrector ports). Exhaust ports are increased to obtain better washing of the combustion chamber, constant efficiency and higher power.
- The underhead is new with a groove where the air is conveyed thanks to lower head ribs to swallow the heat more rapidly.
- The crankcase has the piping throat and the exhaust under the shaft.
- The crankshaft is turbo-type with increased aspiration milling. It is super-checked and tested by a roughness control of the pin.
- The conrod is made with a new alloy of very high quality, ultrasonically checked, and has a new design being completely realized working center. Also the bushing is made with a new special alloy to keep its characteristics at high running.
That's what it says—maybe they could use a good Italian-English interpreter. I wish someone could give me a complete list of all the versions of the Novarossi 3.5cc engines, and note the differences of each. I'm totally confused by the multitude of variations!
Another engine at the show was the BMT (Blitz Model Technica); it was so new that little data was available. It is another 3.5cc car engine; it features three transfer ports, four flow-control slots, and two bypasses. The crankcase is stiffened with an extra set of mounting lugs near the front bearing. The crankshaft has a full disk web with swirl vanes and internal balancing to raise the crankcase compression, balancing holes close to the front bearing, and a patented stiffening rib on the intake opening.
Most crankshaft fractures occur where the rotary-valve intake slot cuts away too much material, and this rib reinforces the opening. No performance ratings were published.
Sig Manufacturing Co. (Montezuma, IA) sells the "other" Rossi engines, and they do have a control line version of the 3.5cc engine. It's slightly smaller and lighter than the Novarossi, and of course the mounting holes have different dimensions! I'll be testing one of these soon, so I'll let you know how it performs.
All of these car engines have quite small exhaust openings to fit their tuned-exhaust mufflers, and it is difficult to open them up as much as we need for our .21 Sport Speed minipipes. For instance, I'm running the same size pipe on my .21 that I used on my D&B .40 Formula 40 engine—just a little shorter to match the higher rpm! When you stop to think about it, at the rpm at which we run these engines, it's amazing that they hang together.
I'll try to get drawings and photos of some of my piston-and-cylinder laps for the next column; several people have asked about the need for (and the techniques of) lapping to improve performance.
SuperTigre and Prop Balancing
The big SuperTigre engine saga continues. In my September 1995 column I told you John Bishop's explanation of the "unbalanced" prop driver on the SuperTigre 2500 engine. I received a letter from my old friend Ron Moulton (former editor of the British Aero Modeller magazine) concerning some experiences in England with the big engines.
I first met Ron when I competed in Budapest, Hungary, in 1964. He is now flying old-time models in the Society of Antique Modellers (SAM), and sent a copy of an article from their SAM 35 magazine.
Many of those old engines were real shakers, with their heavy cast-iron pistons and inadequate crankshaft counterbalancing. He was having trouble with his Brown Jr's, so he called Dennis Nixon of Punctilio prop makers. Dennis told him about the method they use to reduce vibration in their models:
- Do as we do when we fit a circular saw. Mark a blade, fit and run it, and check how smooth the run is.
- Afterwards, rotate the marked blade 180° on the shaft and run it again. Note whether there is more or less vibration than before.
- Restart with the marked blade at 90° to the last position. Note the result again, then shift the blade 180° for another check.
- At this point, the prop will have moved 360° around the shaft at 90° intervals; my experience says that one of these positions will be better than the others.
A day or two later another letter arrived from Ron. He had called Mick Whilsher of World Engines (UK) about the "balancing prop-driver" on the big SuperTigres, and Mick told him the real story.
Mick had worked with Jaures Garofalo on the original big SuperTigre projects, and the plan was to allow for ignition later on. Mick designed the prop-driver casting to take a magnet, which would energize the electronic-ignition module. Balancing had nothing to do with it.
Mick also said that he has to use the balancing technique Dennis Nixon uses every time he takes the prop off his full-scale Piper Tomahawk. A 30° rotation on the studs is the difference between boneshaker and silky smooth! Those of you who are running big engines with big props might consider trying Ron's balancing act.
I always balance Speed props as well as I can. We are operating at rpm three or four times what the big engines turn, and I sure don't want my airplanes shaking apart during flight. Tommy Brown had a fiberglass prop on his .65; it threw the blade at St. Louis recently and he put the model into the ground rather than have it shake apart and come off the wire.
Transcribed from original scans by AI. Minor OCR errors may remain.
