Author: Matt Russell
Edition: Model Aviation - 2009/02
Page Numbers: 139,140
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Radio Control Pylon Racing

Matt Russell <[email protected]>

Check out the Unlimited Scale Racing Association

Also included in this column:

  • Inside tips for the Sundowner Lite class

Racing is instinctive. No matter the contest—Tonka trucks, tuner cars, or Reno—racing is something almost anyone can relate to and enjoy.

What I’ve written about in this column so far covers many sanctioned AMA events popular across the country. However, other RC racing interests are strongly gaining in popularity. The Unlimited Scale Racing Association (USRA) is one with a colorful and passionate heritage. The 2006 racing season was one of the most popular, and MA’s coverage of the Rumble Over Rantoul received numerous positive letters and comments.

MA Editor Michael Ramsey wanted to share his experience at a recent Giant Scale racing event held at El Mirage, California, called the Frightfully Fast Bash. Here he is to tell you more.

From MA Editor Michael Ramsey

I was given the generous opportunity to not only travel and cover the 2008 USRA Nationals, held on Halloween weekend, but I was also invited to participate in the Sundowner class.

Every special interest has a basic competition level, and logically it must include readily available equipment that is versatile and affordable. The USRA decided that, for the time being, the entry-level class would focus on the success of the 80-inch-wingspan Hangar 9 Sundowner ARF.

In the upper classes of USRA competition, 1/3-scale models are flown. The IMAA-legal Sundowner is just a few percent larger than 1/4 scale. This model can start to look small on either end of the 1,800-foot, two-pole course, but its size is popular with everyday RC pilots.

This class of racing was officially introduced last year, with rules that stipulated the exact engine required. The effort was to make the Sundowner emulate the upper classes, so the Evolution 35cc gas engine was chosen.

I set up my model with the exact equipment Hangar 9 recommended. Different stabilizer support systems are available; one is hollow aluminum and the other is solid steel. I used the steel tubes. I’m a fan of four-stroke engines, so I chose the Saito 1.80. I would also be flying the model as a sport airplane, so this setup fit in well with most fields’ noise standards.

For those competitors with unlimited resources (also a racing necessity in the upper classes), at El Mirage the YS 1.70 proved to be the lightest and strongest powerplant of all the available engines on the market. It thrived on 45% nitromethane helicopter fuel and, with an APC 16x16 propeller, it could bite the air in bigger chunks. This setup required a pilot’s diligence in flight trimming.

As the Sundowner reaches top speed, its control sensitivity heightens tremendously; control-throw rates and exponential settings seriously helped the model—not only in pulling through the turns but also in managing entry and exit. After all, good speed is meaningless if the airplane can't be kept on the course.

On the heels of the YS setup were two-stroke engines—most notably the Moki 2.10 and the Mark 2.10. The Mark's popularity is high because its price and friendliness of use are long-standing traditions.

The Moki 1.80 is also a viable option. And because it has no propeller restrictions, it's possible that this engine, matched with a good pilot, could contend with the Moki 2.10- and YS 1.70-equipped Sundowners. Racing is so much fun that it's worth flying no matter what engine you use.

Four of the 23 Sundowner pilots at the Frightfully Fast Bash used the Saito 1.80. Early on, many of us were plagued with stock muffler-retention issues. Because the engine required the Saito 90° adapter to route the stock muffler, that adapter's threads ran parallel with the strongest axis of vibration.

After a series of Loctite experiments, tightening when it was hot, and tightening when it was cold, I finally resorted to reinforcing the snug jam nuts with J.B. Weld. Then the adapter broke and disappeared on the next flight. Sheesh!

This torturous exercise led to my now-proven love for the Slimline custom four-stroke muffler line, which is available for almost any four-banger on the market. Since I installed the Slimline, I have not complained once about an exhaust issue—and that's more of a relief than words can describe. The $90 investment is well worth every penny.

I was able to compensate for the heavier Slimline muffler by moving my four-cell, 1500 mAh battery pack from above the tank to just over the landing-gear plate.

A proper run-in of the Saito will assure that the engine's power improves with every run. Correct valve adjustment is also important. After nearly a gallon of running on 12.5% helicopter fuel, my Saito was still looking good on the inside—not polished like its ring should have been. Nonetheless, I stepped up the fuel to a 30% nitro helicopter blend.

An APC 15x12 proved to be a strong propeller for the Sundowner. However, leftover from my 1.20-engine RC aerobatics days was an APC 14.4x12 propeller that was nearly an ounce lighter and let the engine turn a bit faster.

Under the radar gun, my Sundowner was clocked in a downwind pass at 132 mph and did approximately 121 mph upwind. To say the smile on my face was big is an understatement.

Around the simulated course, the Sundowner could corner like it was on rails. I found that the recommended low-rate/exponential settings for the elevator were perfect for sport-flying and the high speeds the model was reaching on the course; there was no high-speed stalling whatsoever.

High-rate elevator was tested early and proved uncomfortable; therefore, I left it turned off. (That's an odd statement coming from a huge fan of 3-D rate controls.) Low-rate aileron was fine; however, I set it roughly 20% higher with 25% exponential so I could roll out quickly in an emergency.

During the official races, many of my fellow Saito 1.80 users and I faced issues—this time with our engines starving in the turns once the fuel tank depleted past a certain level. Most of us were stumped. What fuel and propeller choice we made had a lot to do with when the engine would quit.

Some were satisfied with running the needle slightly rich. It seemed that luck prevented this fix from solving my problem.

I was the only Saito user burning 30% and my tried-and-true 14.4x12 propeller. I was turning much higher rpm, which could mean that my fuel demands were possibly outside the capability of this sport engine's sensible and reliable design.

Some suggested that the tank was too low, and they were certainly right. With a sport propeller and sport fuel, the tank position was fine, and I never had issues while breaking in the airplane and engine. When I began asking for every bit of power from the engine, the tank placement became more critical.

Trouble with the Sundowner is that to get the tank higher, it needs to be moved back a good 3 inches. The Saito loves to have the tank as close to the carburetor as possible. Moving the tank back helped to a point, but the gravity-feed carburetor began to starve once more when the fuel level got low again.

The solution—and the lightest option—was installing a Perry N20 fuel pump from Conley Precision Engines. Like the Walbro-equipped gas engines used in the Unlimited-class models (which burn 80 ounces in six minutes), the Saito could finally keep running through the course because its fuel feed with the N20 was more constant. I actually didn't solve my engine problems until I got back home and rebuilt the fuel system.

Everyone was so helpful at the event in California. I can't thank everybody enough for making my first experience in Giant Scale racing a memorable one.

I'm looking forward to seeing everyone again this coming June in Ashtabula, Ohio, for a more successful attempt at what I've found to be a seriously fun and addictive part of aeromodeling.

MA

Sources

Transcribed from original scans by AI. Minor OCR errors may remain.