Radio Control Aerobatics - 2004/06

Radio Control Aerobatics

Eric Henderson 303 Shady Ln., Marlton NJ 08053 E-mail: [email protected]

This month I'll begin on a more technical note. Included are a series of excerpts from Dave Lockhart, who wrote an informative note about two-stroke and four-stroke engines. Dave is a top-level FAI pilot with at least 15 years of competitive experience. His observations present several less obvious angles that might not occur to casual pilots.

Excerpts from Dave Lockhart — Two-stroke vs. Four-stroke Engines

Dave wrote:

When looking at different engine designs, consider a couple of initial items:

• Initial price vs. secondary costs: The average two-stroke runs on lower nitro than the average four-stroke. Multiply that by the number of flights you make in a year.
• Vibration: The average four-stroke vibrates more than the average two-stroke. Estimate the effects on airplane longevity, servo gears, servo pots, etc., and include your time for maintenance.
• Maintenance cost of engine: Four-strokes have more parts and thus more potential parts cost and maintenance time. When I do the math, the two-stroke wins.
• Throttle linearity and consistency: Throttle linearity is often overrated; people have different ideas of what "linear" means (e.g., is 50% stick = 50% rpm?). Throttle consistency is what matters—if the throttle is consistent and predictable, it's easy to fly. If it doesn't feel linear, you can adjust the curve mechanically or in the radio.
• Influence of the exhaust system: The exhaust is primarily to quiet the engine and secondarily to avoid detracting from (or possibly increase) power.

How the exhaust affects a two-stroke differs greatly from a four-stroke because a four-stroke has dedicated intake and exhaust phases while a two-stroke shares them. In a four-stroke, the exhaust primarily scavenges exhaust gases and may slightly enhance torque in some rpm ranges depending on design. In a two-stroke, the exhaust can have a far greater influence: it can scavenge exhaust gases, increase the volume/density of the intake charge, and affect pressure (or vacuum) at the carburetor inlet. Thus the exhaust design can hugely affect torque curve, peak power, and throttle "linearity."

Two-strokes do not inherently suffer from lack of midrange torque or poor throttle response—poor setup can cause these issues in any engine. If your engine has a linear and consistent throttle and you aren't using a throttle curve, EFI, or an MC carburetor (or the O.S. equivalent), then you likely don't need them.

Many two-strokes are labeled as poorly carbureted because of rich/lean spots or hesitations, but most of the time the problem is a poorly designed or setup exhaust system (often designed for max power, not throttle response). Because the exhaust can influence pressure at the carburetor inlet, it can also affect mixture at the carburetor. If your two-stroke's carb has rich/lean spots, you can either return the exhaust to its original design or adjust the carburetor mixture at the affected throttle setting.

Fixing exhaust problems is the art of two-stroke tuning. If you copy the manufacturer's recommended setup (propeller, plug, fuel, pipe, tuned length, header), you usually won't have carburetor issues—the manufacturer has already done the tuning.

Why use EFI or an MC (Mixture Carb)? They allow the carburation to be matched to a greater variety of exhaust setups and can increase linearity and consistency compared to most stock setups. The O.S. EFI allows mixture setting at three points—idle, midrange, and high speed—and then regulates the mixture within a limited range. The MC (and O.S.-equivalent carburetor) allows adjustment almost anywhere (eight points is easy with a JR 10X). Both systems have advantages, including having no needle valves.

Thank you, Dave, for this gold mine of information.

Radio South — Company Profile

This month I take a close look at the products and services Radio South offers. You may have seen one of their bright-orange Ni-starter boxes on the flightline.

• History: Steve Helms formed Radio South in the summer of 1976 as a Pattern-oriented company. Tony Stillman began working for Radio South in 1978 and is the current owner.
• Inventory and products: Radio South carries many hard-to-find Pattern and IMAC specialty items and offers their own products, such as the Pro-Driver, MonoKote/UltraCote matching paints, and the Pro-Horns (ball-bearing).
• Experience and support: Tony Stillman attended his first Nats in 1976 and has CDed several Nats, Team Selections, and two World Championships. He has been the U.S. F3A team manager four times, including 2003 when the U.S. placed first as a team and third individually at the World Championships.
• Services: Radio South supports local Pattern events, the US Nats, and Team Selection competitions. They also offer radio repair for major brands (Futaba, JR, Airtronics, Hitec).
• Contact: www.radiosouthrc.com or (800) 962-7802.

New Model: Panacea

Radio South has introduced a new model called the Panacea, started about 18 months ago. It is similar to a Smaragd, using the same wing and tail airfoils. The fuselage can be built with either a pipe floor or a pipe tunnel.

Features include:

• Carbon-fiber (CF) landing gear and wheel pants (Dolly).
• CF wing and stabilizer tubes (PBG).
• Fiberglass/CF fuselage with removable engine cowl and canopy areas. (The canopy area is fiberglass; a clear-canopy version may be available in the future.)

Initial flight testing has been excellent. Todd Blose and Steve Kessler report excellent rolling and snap characteristics.

Common Questions and Advice

#### Why do fellow contestants keep pressing me to move up?

If the "fellow contestants" are in your class, it's most likely because you have become too good for that class. If they are in classes above you, the reason is less clear but often well-intentioned: once someone has taken the leap into higher competition and had success, they naturally want others to experience the same progress and joy. People tend to forget how hard the first step felt.

#### Leap of faith

For many, the initial move from sport flying to entering a fun-fly or Pattern contest is a major leap of faith. Once taken and experienced, subsequent steps seem easier. It takes courage to try higher-level classes like FAI; the class often feels two years ahead. FAI is the most demanding on equipment and requires top-of-the-line gear. The P-05 schedule, for example, has a vertical positive snap that needs strong power (or a very light model) to maintain height for the following midentry vertical 8.

FAI is for those who do not fear the leap of faith or the financial investment. Meanwhile, there are four AMA Aerobatics classes where airplanes a half-dozen years old can still be competitive.

#### Why compete when there is a dominant pilot in my class?

Humans have a competitive spirit that drives them to compete even when the odds seem slim. Chance elements—good air vs. bad air, better-maintained equipment—can change outcomes. You don't always need the latest gear to win; you often get more benefit from practice than from buying the newest equipment.

#### Why do pilots stop competing?

Based on an informal survey of pilots at various levels, reasons for quitting range from uncommon to common:

1. Some people are simply not cut out for competition. Competition can affect their enjoyment or behavior negatively, and they eventually quit, often for another sport.
2. Major life changes: new partner, new job, job loss, or children becoming involved in activities like T-ball, basketball, or soccer.
3. Cost: Competitors may feel they must spend too much to get acceptable scores, believing the latest equipment is required.
4. Time: Lack of flying practice time to handle new routines or perform well with existing ones leads to dissatisfaction.
5. Age and eyesight: An inevitable factor for many.
6. Judging: Many pilots who quit feel they aren't judged fairly. Reasons include judges not knowing the rules well enough to score geometry correctly, and entrenched prejudices or past feuds influencing judging.

Whatever the reason you decide to move on or hang it up, you need to try competing first. That first step is often the hardest. How is your competitive spirit doing?

MA

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