Winning R/C Racer - "Gold Rush III" Article & Plans
March 1962 American Modeler

March 1962 American Modeler Table of Contents Aeromodeling has seen significant changes over the decades both in technology and preferences. Magazines like American Aircraft Modeler, American Modeler, and Air Trails were the best venues for capturing snapshots of the status quo of the day. All copyrights are hereby acknowledged.

Winning R/C Racer - "Gold Rush III"

Keith Storey of Pasadena, Calif., with his National Champ radio control Pylon race plane; hez former AMA president.

Planning and designing Gold Rush III was a lot of fun, too. I included several things I have always wanted to try. I guess we have all dreamed of a retracting gear that is strong and reliable enough for competition. Secondly, I have been very interested in fiberglass for control line fuselages in team racers and speed models. They worked well, did not absorb fuel and weighed no more than a good balsa body. I wondered what the results would be in a large R/C model. The first step in these tests was to make one complete Astro Hog fuselage in balsa and another of fiberglass. All-up weight of the 'glass airframe was 10 ounces lighter! It was stronger in the problem areas and much lighter yet still sufficiently strong in the tail section, too.

This fully monocoque fuselage gave almost one inch more working area inside because it had no long motor mounts or awkward bulkheads and stringers. Light weight 3/32" balsa at the wing saddle and stabilizer gave all the rigidity necessary. Because we used a female mold the exterior finish was mirror smooth and we could incorporate extra details such as wing fillets and otherwise difficult compound curves. The pre-cut and sanded engine mounts were molded together with the skin so that it formed a very solid unit. By this time we were getting pretty excited and so started drawing lines for the Pylon Racer.

Construction of Gold Rush III with its fiberglass fuselage and retracting landing gear proved to be more time consuming than planned. We missed the Dallas Nationals in '60 by four days. But this was really an advantage since it meant time for a thorough check. There were a few nutty "bugs" too - like the landing gear escapement being mounted across the fuselage with butt glue joints only. On the second flight the gear came up just fine, but the flying gyrations loosened the glue and the gear stayed up! Belly landing, here we come. We were quite surprised ... she slid in smoothly. But you can bet that escapement mounting was changed and quick!

Storey sez retracting gear is suitable for control line use, too. Full size drawings for "Gold Rush" are on Hobby Helpers' new Group Plan #362A.

Although Pylon Racing is still a young event, several design requirements and compromises have become evident. I would class them basically as speed-vs-maneuverability, steady power plant, number of controls, easy ground handling, light weight and strong construction and for my own pleasure I like a touch of realism. Aim was to balance all these requirements in order to obtain a consistent performer. No two approaches are exactly the same which gives a variety of designs and styles on the line and in the air.

Starting at the top of the list, we have all seen some very fast models that could not take advantage of their speed because they could not fly straight and level and were grasshoppers in the turns. Conversely, there are planes and pilots that make perfect pylon patterns, but their speed is too low to get into the winner's circle. So it appears we should have a combination of each, and when compromise is necessary it would be best to shave a little off the top of each. If there had to be a choice, I would prefer sacrificing two or three miles per hour for finer, more accurate control. For example, the ailerons on my first pylon racer were adequate at high speed when all was well. But at less than full speed, or in those tough unusual positions I seem to get into, the control was too slow - much too slow. The ailerons on this new model are much larger and have less travel for smoother response at all speeds. These larger units could slow the airplane down a little - this is theoretical, but even if they did it would be well worth it.

This more accurate control means a higher average speed on the course as well as the "saving" factor described above. The faster your model flies, the more critical it becomes and the more practice it takes to fly a low tight pattern. Goofing a turn by going too far or too slow or over-controlling can mean precious seconds on your average speed. "S" curving down the straight-a-ways and jockeying for a good turn position also slows your time. An airplane that is quick, accurate and sure will save those seconds. Plain practice with your present model using various control travel ratios can be both pleasing and surprising. The ideas from just such experimenting are in the Gold Rush III. This was really fun trial and error.

The engine-and-fuel combination will probably lend more to consistency than any of the other factors, except for a pilot who may sometimes get a little extra nervous. Just as in C/L speed or team racing, a reliable engine is essential to achieve top performance. The powerplant must operate the same or as nearly the same as possible every time before we can practice racing, evaluate control response, check efficiency of fuel and propellers, or make any changes for improvement. I picked the McCoy 19 because it had the consistency I needed for such practice. Using a crankcase pressure fuel system, it developed the power to swing slightly larger props necessary for a large wing area model. An AMA .19 size model must have 766 sq. in. of wing area, more than many stunt jobs with .45s in the nose. For pressure use the Veco adapter with an .018" hole plus a one inch long piece of 1/32" ID tube in the fuel line to give non-surge running.

Fuels that are too hot or too cold, just as the "super hot" engines, can be a real problem. Those exotic home-brew fuels have probably caused more no-flights or incomplete flights than all other reasons combined. I have used Thimble Drome Sport fuel (blue can) for practically all my flying. It is a good medium range fuel for most weather conditions and will give the Mac about 12,000 rpm on a 9" x 7" or 8 3/4" x 7" prop. That means 85-plus mph on a two-way average for straight flight as timed by the FAST Club's FAI electric timers.

There are many ways to control a pylon racer. We have seen good planes with proportional, relay and relayless equipment. The question is really how many control surfaces must be moved to give accurate flight. Here again there is no single answer. Match your equipment with the controls you desire and are most comfortable with.

Gold Rush III uses an Orbit relay 6. It drives Duramites for elevator and a combined aileron-rudder, and an escapement for elevator trim in conjunction with the retracting gear. The relayless radios are much lighter but were unavailable way back when. Mounting is simply gobs of sponge and a couple of rubber bands shown in the profile view.

Combining aileron and rudder has become quite popular. Flight tests have shown it is much easier and more consistent to use aileron to roll an airplane on point smoothly and quickly to a 90 degree position for your pylon turn. Rudder itself will drop the nose while it banks the model and this can cause palpitations of the heart - this action results in those grasshopper antics that can be rough when two planes are in a turn at the same time. It costs nothing to link them (CAR), and when combined the rudder area and travel are both reduced. The results are smoother turns and better directional control on the straightaways.

You wouldn't really need rudder at all if the takeoff wasn't part of the timed run. I have found that if the wheels are hard rubber and placed between 15 and 17 degrees ahead of the actual CG, and your rudder travel is adequate, you should be able to steer the plane just like a race car regardless of the wind. This will also give you a lot of confidence when there are two or more planes at the starting line.

The escapement on the fifth channel operates both landing gear mechanism and the trim at the same time. There is a big change in the drag when that gear comes up and I feel this elevator trim is essential. It is a ground adjustable system and the fine threads on the IBM clevis unit allows very accurate settings for hands-off flying.

The retractable landing gear does add to the speed of the Gold J Rush, 4½ to 6 mph. The reduced drag helps keep a higher speed through the turn and acceleration after the turn, as well as take-off acceleration. Rubber bands do all the work of hauling it up and extending it for landing. We chose rubber bands because they are lighter than an electric motor, are very high in usable power and provide a quick operation. If you are like me, you are busy during take-off and don't want to let go of the controlling switches for too long a time, so the faster you can retract the gear, the safer it will be.

I must admit I always get a thrill when the gear snaps into the wheel wells and the plane goes by looking almost real. This system should work equally well on F/F and C/L models for that little extra performance or realism.

Our last two design items of light weight and strong construction should be grouped together. Selecting the balsa wood for the wing and tail carefully can mean a saving of four to eight ounces without sacrificing strength. Silk the wing and paper cover the tail for two or three more. All these little things do add up to higher performance and less crash damage. The average Pylon Racer weighs about four pounds, give or take a few ounces.

This brings us to making the fuselage and your question will be the same as mine. Does it have to be fiberglass? No, it doesn't. But I can promise you more strength and no additional weight, absolute settings for the wing and tail, clean and easy to maintain, no fuel problems and corresponding gain in weight, more room to work inside and ease of repair or very fast construction of another one. It's fun, go ahead and give it a try.

If I still haven't sold you on the merits of fiberglass, the plans do include ideas for a balsa fuselage. Cross section "C" shows a view through the engine mount area with the bulkhead, double sheet sides and Berkeley type 1/2 round planking for the compound curves. Very light and strong bulkheads can be made by sandwiching 1/4" balsa sheet between two pieces of 1/32" plywood and cutting to shape. Repeat this basic pattern on all cross sections except "I". Remember the engine mount will be 1/8" less on the outside or profile to fit into the smaller area.

If you are eager and ready to try fiberglass, look at cross sections "E" and "H". These represent the balsa pieces used in the pattern from which the mold is made. The fuselage will be in .two parts, a left and right side. The 1/4" x 2" sheet balsa will hold all the formers in true alignment. Those are 1/8" formers with 1/8" balsa sheet as noted on the profile plan and the 1/2 round planking for the curves. Each cross section should be repeated as "E" and "H". Set these formers on the 1/4" sheet and lay up your form (pattern). Sand it to the right size and don't be afraid to really put a finish on the pattern. A thick filler or primer material will give quick and good results. The better the finish on your pattern, the smoother your completed airplane, so give it a little extra.

Each half of the fuselage should be glued onto a rigid 3/4" or 7/8" piece of plywood that has also been well finished. The mold will be made of a water base material such as casting plaster or preferably Hydrocal, and we don't want any warps. Locate a dealer who handles casting materials and obtain that Hydrocal if at all possible. Get his ideas for a parting agent, too. He may have better ideas or newer products. If not, a good cooking grease like Crisco should be spread evenly over the pattern and the plywood. base.

If you use Hydrocal, mix as directed and apply a layer over the pattern and ply base. Use some canvass or binder and build up the thickness to no more than 1". Let the mix set up thoroughly before you remove your finished mold. If everything went well, the inside surface should be just perfect for the finished glass model. We will get into the lay-up techniques, coloring and completion of your fiberglass fuselage as well as the set up and check out of the landing gear in a subsequent article.

Gold Rush III Plans (sheet 1)

Gold Rush III Plans (sheet 2)

Posted November 28, 2013