Control Line: Aerobatics
Wynn Paul
FAI TRYOUTS: The capable troops of the Atlanta Stunt Conspiracy will put on the team tryouts for the 1978 World Championships over the Labor Day weekend at Ft. Gillem, Ga., an active Army base just south of Atlanta. The site features room for approximately five control-line circles with additional space within a quarter mile. This site has been used for the successful PAMPA Region 5 championships for the past three years and the Atlanta crowd puts on a great show. They are very well organized and run a relaxed, yet efficient contest.
The FAI team tryouts are open to AMA members who pay the $50 entry fee. Pre-registration should be to Keith Trostle, 10900 Phillips Dr., Upper Marlboro, MD 20870. Information about the site and accommodations should be directed to Jon Ramsden, 9035 Gatewood Dr., Jonesboro, GA 30236. Tom Dixon usually acts as CD at the Atlanta contests but will probably fly in the tryouts, so direct requests to Jon.
West Coast Model News: If you remember this name as a good little newsletter from California in the '40s and '50s then maybe you can help me find a copy which has the Nationals results from 1952. Probably will be August or September. None of the magazines ran complete results and AMA does not have a record of the event. You can keep the newsletter; just send me some quick copies of the results.
Fuel Tanks: I've been griping in print about the lack of fuel tanks for the 46-size engines since way back in September, 1975 but, alas, stunters will still have to make their own unless they want to try the clunk tanks that Jim Lynch and Bob Baron like. Randy's Model Aeronautics has stopped producing tanks for an indefinite time. There are only two sources to my knowledge: Lee Eaton, 12943 Winthrop Ave., Granada Hills, CA 91344, and Randy Hancock, 541 Columbia, Lexington, KY 40508 (606-252-8137).
It would seem that one of the tank manufacturers (Fox, World) would take a quick look at the results of the Nationals, and of the sales of ST 46's, and realize that stunt fliers are using the 46-size engines that require 5-, 5.25- or 5.5-oz. tanks.
Talking about tanks, Al Rabe was visiting Lexington recently and mentioned that for the past couple of years he has been using a fuel tank that is actually almost a parallelogram in shape; at least the back end is slightly extended on the outboard side. Al's reasoning is that this forces the remaining fuel at the end of the run to collect in the outboard corner. He uses the old familiar style Veco-type tank with the full-length bevel and the lengthwise baffle. He punches about five holes in the front of the baffle just like Veco did. He feels that, since the airplane is traveling in a circular path, the fuel can better be forced to the outside rear end of the tank if the end is not parallel to the radius from the center of the circle. Well, it's worth a try. Anyone who has ever watched Al knows that his engine run is always consistent and chops off very nicely after his patented loop at the end of the flight. He uses straight suction without muffler pressure on the 46's and the 60's.
Let's run over a couple of other items about tanks. Remember, if your engine runs rich when the plane is inverted (with an inverted engine installation) then you have to either move the engine away from the bearers (down in the upright plane position) or raise the tank (in the upright position). It is usually easier to move the engine down than try to move the tank up. Les McDonald suggests installing the spray bar at 3/8 in. from the mounts which, with a one-inch-thick tank, should give you a leaner run inverted.
However, Al Rabe argued in AAM that moving the spray bar on a 46 did not change the run. Well, try both ways yourself and see what works for you. I think that Al may have a valid point in his hypothesis that it is not the height of the spray bar that counts but the height of the fuel pickup tube and the mass of the fuel-head location in relation to the engine. Al is presently concerned with the internal volume of the engine crankcase and the distribution of the crankcase volume, stating that these volumes may cause difficulties with our crude yet usually effective fuel delivery systems. I agree it is a wonder that we can get such sophisticated engine runs through a complicated series of maneuvers with the amazingly simple fuel tank systems that we commonly use. Al tried the Perry pump on his big b'honker ST 60's but feels that it is not necessary on the ST 46 or 35-size engines.
Be certain to keep the plumbing from the pickup tube to the spray bar in a good straight line with no large bends, kinks, up-and-down routing or over-and-under routing. Another point to remember: when adjusting the tank, engine, etc., be careful about the fuel tubing. Whenever I check the tank or remove the tubing from the spray bar or tank I always put on new clean tubing after carefully wiping off the spray bar nipple and the fuel pickup tube. Ten cents worth of tubing is better than losing a ten-month construction project.
Use a small fuel filter, such as the Hi-Johnson filter. A large filter can allow air to accumulate in the filter itself which can cause cutting out. Try different filter sizes if you think this may be a problem.
Make certain that the pickup tube goes all the way to the very back end of the fuel tank and is soldered to the outside wall in one or two places. Cut a 45-degree bevel on the end of the pickup tube where it is soldered to the tank. Make certain that the tank is clean on the inside and airtight. Don't let the tank vibrate.
If you are forced to build your own tank — since the manufacturers are not coming up with this essential item — there are a couple of very good articles lately on tank building, especially Dave Rees in FM, Jan., '77, p. 42. Harry Higley had some good pointers on construction in MAN, July, '75, and I had a whole column devoted to tanks in MA, Jan., '76. Use .008 K&S solderable tin (Werwagge, Higley, Rabe, Paul, etc.) or .006 (Rees). Don't use brass shim stock or the tank will come out weighing 2.5 oz. Use 60 tin-40 lead or 50-50 solid solder. Use flux such as Kester, Nokorode, or La-Co. Do not use silver solder as it will corrode terribly and you don't need that type of strength.
Be certain to use .125-in. OD soft brass or copper tubing. Don't use hard brass. Higley sells a very handy tubing bender for $1.25 that works. The Bisco bender is available from Harry at 433 Arquilla, Glenwood, IL 60425.
Just for review, the "Veco" configuration which has the outboard bevel the length of the tank. Outside cross-section dimensions are one by two inches. With this design the length of the tank equals the capacity in fluid ounces. Les McDonald (uniflow), Rabe and Gieseke all prefer this type of tank with the long bevel. The Randy Hancock tanks are rectangular in shape, 1 x 2 in., with a small bevel starting approximately 2 in. from the back end. A tank 4 1/8 in. long holds approximately 2.5 oz. of fuel.
For today's pattern the Fox 35 needs four oz. of fuel (5 percent nitro). Same for the Max. The Supertigre 46 with a .275 venturi and 10% nitro fuel needs approximately 5.5 oz. of tank capacity. Using 5% nitro usually works better with a .280 venturi, and you need about 5.25 oz. of fuel, or maybe just 5 oz. By the way, replacement venturi are available from Bob (No. 1) Hunt at C.S.C. Now I know that there will be 14 different opinions on some of the above specs but these are good starting points until you can see what works for you.
Bill Werwagge likes tanks that are only 1 3/4 or 1 5/8 in. wide in the fuselage, feeling that they have more fuel head pressure to feed the pickup tube. For a 46 this means that you need a tank that is about six inches long. If you try to make the tank thicker than one inch you may have spray bar-pickup tube problems, although Bill has used tanks 1 1/8 in. deep. Bill was flying his HP 40 in the Ares size last summer using a 5.5- or 5.75-oz. uniflow tank. With the Fox 35 and ST 46 he uses straight muffler pressure on the old-fashioned suction type tank. He alternates between using both vents hooked to a "Y" fitting and using just one vent to the muffler.
Dan Shafer, Dayton, Ohio, using the HP 40, reports that he uses uniflow with muffler pressure, a 5.75-oz. tank with the small wedge at the rear, a .280 venturi, 10% nitro fuel and makes his tanks 1 1/4 in. high by 1 3/4 in. wide.
For information on PAMPA or comments contact: Wynn Paul, 1640 Maywick Dr., Lexington, KY 40504.
Transcribed from original scans by AI. Minor OCR errors may remain.
