RADIO CONTROL PYLON RACING
Duane Gall, 1267 S. Beeler Ct., Denver CO 80231; E-mail: [email protected]
SEE YA “LASER”!
The April 2004 column featured behind-the-scenes commentary from Dave Norman, who designed the Seeker Quickie 500 (Q-500) racer. He described how he went from the basic rules requirements (see www.modelaircraft.org/templates/ama/compreg.asp under “RC Pylon Racing”) to selecting key features based on observing other designs, drawing plans using a simple CAD program, and sending the CAD files to a laser-cutting shop to have the parts cut for easy assembly.
Laser-cutting is rapidly entering the mainstream. As prices drop and more modelers become proficient with CAD, it’s now possible to produce your own custom kit without going through the laborious task of transferring your drawings to the wood, cutting the parts, and sanding them to fit.
Of course you still have to glue them together; that’s almost a lost art these days. But again, high technology comes to the rescue.
A picture is worth a thousand words, and a CD can hold a thousand pictures. CDs now sell for approximately a buck each. As part of his preparation for selling kits, Dave has begun work on an assembly manual with many high-quality digital photos, which he plans to release on CD. It’s shaping up to be a great how-to for any model of this kind. An advance copy is available for viewing and download on Lewis Schwab’s Web site at www.lcsperformance.com/seeker/SeekerInstructions.html and at the North Central Pylon League’s Web site at www.ncplracing.org/.
The Seeker is not commercially available yet, and this mention is not intended to be an endorsement. I simply believe that this story offers a fascinating glimpse at what goes into a homegrown competitive effort—and, to the extent Dave is willing to share his insight and knowledge gained along the way, it can only help demystify and popularize this wonderful sport.
Wood?
The wood-versus-composite battle has been raging for roughly 10 years. In one corner we have Wood, wearing trunks that read “Cheaper but Not as Fast.” In the opposite corner we have Composite, wearing trunks that read “Experts Only! You Can’t Afford It!”
There are very few pure wood airplanes out there; most use space-age materials such as carbon fiber for reinforcement. And those who produce composite airplanes are rediscovering the value of wood, incorporating it into their all-molded structures because it’s better in many ways—not just cheaper.
One such manufacturer is Bruce DeChastel. His new Shotgun Q-500 and Polecat Quarter 40 (Q-40) are assembled with a great deal of time and care, using materials that include balsa. Because time is money, they aren’t cheap. They are composite and they are wood. Go to www.bigbruceracing.com/ to see these models. (The Shotgun has a conventional tail—not a V-tail. At one of our local races in May, John Williams set a course record of 1:12 with the Shotgun his first time out with it. Who says you need a V-tail to go fast?)
The moral of this story is that you can always make your way into the winners’ circle by investing time rather than money, if that is your choice. The availability of CAD and laser cutting only makes it that much easier.
Based on Dave Norman’s experiences as published here, I’ve begun work on a wood-fuselage Q-40. The complex curves will present a challenge, but the gains in stiffness and lightness should make the effort worthwhile. I’ll keep you posted.
STOL Survivor
Q-40 was conceived as a more scale-like sister event for Q-500 using an engine that is the same physical size (.40 cu. in.) and shares many of the same parts. Yet there hasn't been much "cross-pollination." Even in areas where Quickie is popular, local Q-40 races are rare. Why is this?
I don't think there's one simple answer, but rather a combination of factors working together:
- Airspeed. The awesome airspeed—180+ mph—is intimidating. Precision flying, lap after lap, close to the ground at a steady 180 mph takes some getting used to.
- Cost of the airplanes. To handle the flight loads at these speeds, Q-40 models must be well engineered and carefully built. This means purchasing a composite airframe for $350 or more or investing an equivalent amount of time in building an airworthy model.
- Propeller availability. Until recently, the need for a custom-made wooden propeller was a barrier. The high-rpm Q-40 engines aren't happy with an off-the-shelf wooden propeller, and a custom-whittled one would set you back $35 or more. A couple of bad landings could be expensive. That issue has gone away because the Contest Board has approved the APC 7.4 x 8.0 carbon-fiber propeller (part LP07480C): a $10 item that is more durable than wood and as fast as anything in competition.
- Field requirements. The number of flying fields that require Short Takeoff & Landing (STOL) techniques—where Quickies or other lightly loaded, slow-landing airplanes are better suited—affects participation. Not all clubs have a square mile of concrete on which to play.
- Lack of throttle. Q-40s typically have no throttle. The accepted method is to rig a servo so it pinches the fuel line, starving the engine. If the airplane is out of trim on a test flight, you face a choice between fumbling for trim while steering the model at top speed or shutting the engine off and immediately setting up a dead-stick landing with an out-of-trim airplane. Missing the runway by a few inches can suck a bushel of dirt into the engine through the open venturi.
For us hairy-chested racers, that's the definition of a relaxing afternoon. But can you blame a new person—or even an experienced Quickie pilot—for believing otherwise? I thought there had to be a better way.
Using a Quickie-style carburetor seemed a natural choice. Nelson and Jett make them. They interchange easily with the Q-40 venturi because the Quickie and Q-40 crankcases are the same. However, the stock carburetor will definitely slow you down; the engine will turn 200–500 rpm less compared with the venturi. Both have the same inner diameter, but the venturi's trumpet shape gives better airflow.
So the solution was to open up the Q-500 carburetor so that its inner shape matched the venturi's. As long as the barrel stayed open and the contours were smooth inside, the air wouldn't know the difference and it should run just as fast.
That raised the question I've heard so often: "Hey, can you do that?" Yep. The rule for Q-40, AMA event 422, specifies in section 16.1.2 (Powerplant), paragraph 3 (Intake): "a single carburetor or venturi with a maximum inner diameter of 9 mm (0.3543 inch). Carburetors or venturis may be modified and are not subject to availability rules." (I added the italics.)
Carburetor modification — procedure
It was easy from there. The basic steps I followed:
- Hold the throttle arm in the full-open (high throttle) position. Drill a 1/16-inch-diameter hole through the arm and partway into the carburetor body. Insert a 1/16-inch-diameter temporary pin to hold the barrel open.
- Working slowly and carefully on a drill-press stand (wearing safety glasses), flare the opening with a Vermont American 7/8-inch Beading Router Bit until the edge of the intake was very thin.
- Switch to a 1/2-inch tapered reamer and work by hand until the tapering cut was visible approximately halfway down the rotating part of the carburetor barrel.
- Repeat the tapering on the bottom end to give the air channel an hourglass shape.
- Blend the curves with a Dremel Moto-Tool felt cone and polishing compound.
- Gently run a 9 mm drill bit through the barrel to make sure it is exactly as large as the rules allow.
The engine I used was a Jett. The procedure is the same for a Nelson except that its plastic carburetor material cuts more easily than aluminum, so the first step can be accomplished using a handheld electric drill.
Results and notes
Does it work? Yes. I ran several tachometer tests and could not measure a difference between the modified carburetor and the venturi. In addition, I posted my best time ever (a 1:06) at the JPR/PowerMaster Gold Cup race earlier this year using the engine shown.
This setup will not actually idle. Landings are still dead-stick. But it does allow you to reduce power and cruise for a while until you decide it's time to set up an approach. You can also throttle back on the starting line to keep the engine cool—your engine may last longer because the shutdown is richer rather than lean—and if you're making the transition to Q-40 from something slower, you can fly the course at a reduced setting to start, and then open 'er up when you feel comfortable.
That's all for now. Stay safe and don't forget to read your rules!
MA
Transcribed from original scans by AI. Minor OCR errors may remain.
