CONTROL LINE SPEED - 2001/01
Scott Newkirk 4840 N. Glendale, Bel Aire KS 67220
There has been a great deal of discussion about bringing new fliers into the fold. In this day and age of computers and Ready-to-Fly (RTF) models, we have much competition for drawing people into "easier" activities.
Bringing the builder-of-the-model rule back to Speed flying has been discussed. We will be shooting ourselves in the foot if we don't make models easier to obtain, and come up with kits that are easy to assemble or RTF models.
I strongly urge all Speed fliers to pass your old equipment on to modelers who have an interest in Speed flying, and help them learn to fly it.
I also urge you to build a trainer that you can make available to interested fliers, and show them that the pylon isn't such a terrible obstacle to flying.
At the end of the column, I have listed a few web sites for engines. When I was compiling the information, I noticed that the companies' main business is car engines. The availability of ready-to-run cars and kits that are easy to assemble has made them very attractive. I hope we can learn to apply their examples to our favorite hobby.
Engine Cooling
In 1995 I went to England to learn about engine-building from Sergei Kostin. Sergei looked at the cooling on my model and said, "Hmmm, I've never seen anybody who did it right before; where did you learn to do that?" I learned a great deal during five years in Boeing's wind-tunnel model shop. I've also done considerable computational fluid dynamics (CFD) testing on the computer. All my cowlings have exhaust-cooling vents that go to the front of the cowl. On the F2A models, the top of the engine is cowled, except for glow-plug access.
Current F2A airplanes are considered the epitome of Speed models, but a couple things in them make it difficult to get maximum horsepower from the engines. The side vents on the cowls of current F2A models suck air out of the cowl—not ram it in, as fliers want them to do. Many of the models have carefully configured air to the front of the engines, but they don't direct that air around the back of the engine. My F2A models have side-exhaust cooling channels that go to the front of the cowl, so they are in positive-pressure areas of the cowl. I cowl the backside of the engine just as carefully, so the cooling air is forced around the cooling fins on the hottest side of the engine. I'm convinced that Carl Dodge's homemade engines and Sergei Kostin's Zalp engines would go several miles per hour faster with reconfigured cooling.
Several years ago we experimented with Nelson .40s for Formula I Pylon models. We built a shroud around the engine to direct cooling air around the back of the engine. We learned that dropping the head clearance .004 to .008 inch increased horsepower and improved plug life. I cowl so tightly around the fins on my engines that grooves are worn in the cowl from the fins rubbing against it when the engine runs. I've been told that if the cowl contacts the engine in any way it gives up horsepower; that is not true. I also cowl the top of the engine, so there is only access to the glow plug.
Something else frequently done wrong is having the exit vents larger than the inlet vents. By having the outlet vents with 5–10% less area, you increase the pressure of the cooling air and tremendously increase its cooling ability by increasing its density. I learned about that from Formula I car racers. The current trend in F2A is to have a tightly cowled engine with additional air introduced at the back of the engine onto the exhaust stub, in addition to the air forced through the cooling fins. I use this method on all my models. The only real exception to this is the Zalp setup, which I think is in error.
The Zalp setup has a bifurcated inlet (splitting the air into two paths). It splits the cooling air so it hits the engine at 2 o'clock and 10 o'clock if you're looking at the engine with the exhaust at 6 o'clock. There are no baffles to force the air around the backside of the engine. In addition, there are two NACA ducts at the widest point of the cowl in the lowest-pressure area to add air near the exhaust stub, but there are no baffles to direct this air around the exhaust-stub fins. The CFD work I've done says it's pulling air out, not introducing it.
The Zalp engine is the most powerful one out there for F2A, but the cooling is holding it back and making the engine much more difficult to run.
The Russians purposely tilt the cylinder bore in the case because they know it's still hotter on the exhaust side of the engine. They work hard to thermally isolate the exhaust stub from the rest of the engine by cutting a groove in the case above the exhaust port before the first cylinder cooling fin, and they cut notches in the fins on the exhaust stub to prevent the heat from traveling up the fins to the rest of the crankcase.
Jim Clary's comments on the Coandă effect are interesting. The work I've done on this indicates that you need air dams that stick out quite a way to get past the boundary layer and into a usable airstream.
I've experimented with (but haven't gotten repeatable results with) trying to keep the heat in the exhaust—i.e., polished combustion chamber, polished chrome in the liner, and highly polished piston tops. The theory is to keep the heat in the gases, and not into the metal of the engine. Then you would get more expansion in the combustible gases while in the cylinder, which should convert to more horsepower. I haven't been able to measure more horsepower, but I have noticed that I can drop the head .001 to .002 inch without damaging plugs. Carbon and soot buildup on the piston and head make this difficult.
When you build cooling ducts, the leading edge should be round, which will allow them to operate in the outside of the cowl. Make one curved exhaust-side vent 1/4 inch wide, and slowly taper it (roughly 2 inches) to its exit point in the cowl.
If you can vent the cowl at the top of the fuselage where it's at its largest cross-section, this will help draw out the hot air. You can also split the inlet air so you're not putting cold air directly on the front of the engine; this is the coolest part of the cylinder.
I spoke with my old friend Alberto Dona in Southern California, who owns Hobby Club (a hobby distributor). Alberto carries a large number of great engines, and his business has been largely unknown to the Control Line community.
Engines Alberto is importing to the U.S. include:
- Cipolla (a couple of the .21s look interesting for sport .21, and there are two interesting-looking .15s)
- CS (including the GZ .049)
- HPI
- MVVS
- OPS
- Picco
- Profi (he has the good F2A, F2C, and F2D engines)
- PUMA
- Rossi
Alberto is sending me samples of several of these "unknown" engines for my inspection, and I will report on them in the next issue.
Sources
Hobby Club Box 6004 San Clemente, CA 92674 Phone: (949) 240-4626 Fax: (949) 240-5931 www.hobbyclub.com
Cesare Rossi's NovaRossi engines
Transcribed from original scans by AI. Minor OCR errors may remain.
