Newcomers
Bob Underwood Box 40, St. Peters MO 63376
I've just returned from AirVenture Oshkosh 1999, the Experimental Aircraft Association's (EAA) yearly event. I've seen enough airplanes to last quite a while. (The true aviation buff can probably never get enough.)
Each year when I attend the convention, I wonder about the citizens of Oshkosh. Their lives are certainly turned upside down for the week of the show as they fight traffic, listen to thousands of aircraft, and are unable to find a table at a favorite restaurant. But it's an interesting show, and you might want to see it sometime.
Look for the 2000 schedule for AMA's National Aeromodeling Championships. For most of July and a bit of August, you can become saturated with all of the elements of our hobby/sport. It's true that while many of the participants are not newcomers, you can pick up some very valuable ideas and learn more about AMA's proud 63-year history. It will also allow you the opportunity to visit AMA's wonderful museum and flying site. I know you'll find the visit stimulating and pleasant.
Let's spend some time considering the device used to power your model. Granted, if your model type is a hand-launched glider, rubber-powered, or a sailplane, we only need to suggest you take care of your arm and/or find a source of good rubber. But if you are inclined toward a glow, diesel, or gas engine, or an electric motor, other factors enter in. The first is obviously the matter of choice.
The greatest bulk of newcomers gravitate toward the glow-plug engine. You will find a wide range of glow-plug engines available. The choices include price, style, and brand. It's also true that you generally can locate product reviews of engines and kits more easily than anything else. These reviews can help you not only determine a best buy, but will acquaint you with terminology and standards to look for when purchasing an engine.
Your first consideration will probably be whether you want to go with a two-stroke or four-stroke engine. Typically, you will note that kits and Almost-Ready-to-Fly models (ARFs) will quote a range of engine sizes.
Generally, the four-stroke will list a somewhat larger-sized engine. This is a holdover from the very early days of the introduction of the four-stroke. At that time, there was a considerable power differential between the same-displacement two- and four-stroke engines.
Developments in recent years have resulted in the power gap becoming smaller. Generally, the four-stroke will swing a larger prop, albeit at a lower rpm. You are looking for pull, not speed, and that is what the four-stroke can provide.
The four-stroke also tends to be quieter than a two-stroke. They are more expensive, somewhat heavier, and require occasional maintenance in the form of valve adjustment. You will probably find many more two-strokes in trainers, especially because of the price. But don't rule them out; they perform quite well!
In most cases, you won't find gasoline engines in a newcomer's model, primarily because the gas types are found in the larger-displacement sizes—well beyond those used to power trainers. This is not to say that there aren't models available that could be used as trainers and utilize gas engines. They're just not commonly found.
There are advantages to gas engines. The fuel is quite inexpensive, and once gas engines are adjusted, they require very little attention. Pay attention, though, to the fact that the typical glow fuel tank and fuel lines are not compatible with gasoline. The same is true for some fuel filler valves. They are provided in gasoline or glow-fuel (alcohol) versions.
The same concerns hold true for the diesel engine. In reality, very few of these are found in the common trainer aircraft, for a variety of reasons.
First, the selection of engines available is quite small, especially in .40-size and larger. Second, converting a regular glow engine to diesel operation by changing the cylinder head is what creates most of the larger-sized diesel engines. Third, many individuals are reluctant to go in that direction because of the lack of help at the local field.
But don't dismiss the diesel! It uses very little fuel, and the fuel is quite inexpensive. The engine will provide considerably more power per cubic inch. It will also run much cooler than the standard glow engine.
If you are headed for non-messy and quiet, then you must consider an electric-motor-powered model. In recent years there have been fantastic leaps in the technology available. This is true both of the power availability and the duration of flight time. No one can dispute the ease with which the electric-powered model can be started: flip a switch, not a prop!
Illumination
- Displacement: The size of an engine, determined by the bore of the cylinder and the stroke of the piston. It is expressed in cubic inches (in this country such as .120, .60, .049, etc.).
- Glow Plug: The gadget in the cylinder head that acts like a continuously firing spark plug, igniting the fuel/air mixture. Hook a battery up to it and it glows red/orange. Start the engine, and the compression and firing of the engine keeps it lit (hopefully).
- Two-Stroke/Four-Stroke: The four-stroke has valves like an automobile engine. The two-stroke fires every revolution; the four-stroke doesn't.
- Diesel: No glow plug! No spark plug! Combustion is caused by the compression of the engine, which can be adjusted by a device in the cylinder head.
- Speed Controller: An electronic device used to control the amount of current to an electric motor. That's right — a throttle for an electric motor.
- Fuel Porting: The passageways used to get the fuel/air mixture from the venturi (air inlet) to the combustion chamber.
I must admit to a degree of ignorance regarding the comparison of the cost between the standard glow-engine setup and an electric one. Batteries and the requisite charger and speed controller are not cheap, but there is a trade-off in that you do not have to continually buy fuel. You may have to hunt around a bit in many clubs to find a "voltage guru" to help you.
One last thought: be careful. If you have not properly set the motor up, or have the throttle in the wrong place, the motor can start at high throttle as soon as you flip a switch. That can be quite a surprise if you aren't expecting it and you have a part of your anatomy in the wrong place!
Each of these types of power carries a bundle of choices and features. As you pore through the ads, you will run across many of the choices and features. Reference will be made to the bearings, types of fuel porting, metallurgy, and design. I can't begin to sort out all of the choices in this column. But I can provide you with some possible guidelines:
- You don't need the hottest feature-filled power plant available! Remember, you are building a trainer—not a Reno air racer. Consider price, dependability, and repair possibility. How easy is it to replace a broken needle-valve assembly? Does your local hobby shop stock parts?
- Lean toward the big end of the size recommendation. If the kit calls for a size range, head toward the high end. You can't squeeze out power that's not there! You can throttle back, though. Check carefully; frequently a larger-displacement size is available in an engine that is physically the same size as one that is of a smaller displacement. This is done by boring out the cylinder. A side benefit in some cases is that the larger-displacement engine is actually lighter! You'll find .53s that were .40s or .45s, .80s that were .60s, etc.
- Go for safety features, convenience, and quiet: Look for complete instructions, fuel recommendations, ease of mounting, muffler mounting (and whether it's included), and the position of the needle valve. While some engines still have the needle valve on the venturi at the front of the engine, others have needle valves that have been angled back to keep fingers away from the prop. Some, especially four-strokes, have the needle valve located at the rear of the engine. Still others have a remote needle valve that can be located anywhere up to several inches from the engine.
- Not all engine break-ins are the same! Check the instructions carefully. Not only will you find specific fuel recommendations (nitromethane content, lubricant type, etc.), but you will also find break-in methods. These vary according to the type of engine metallurgy and setup. Ignoring these instructions can reduce an engine to swap-shop bait very quickly.
- Cooling is important! While this is not a problem with most glow, diesel, or gas-engine trainers, it can be with electrics. Strange, huh? Sometimes we forget that not only do electric motors produce heat, but rapidly charging or discharging batteries produce heat, too. So do speed controllers. If you go electric, follow the equipment guidelines. The motor may be in the slipstream, but the batteries and controller probably are not.
- Match the prop to the engine or motor size and the model. Are you going to need a prop that will leave you less than one to 1-1/2 inches of ground clearance (and more may be needed from a grass runway)? You can go to a smaller diameter and more pitch, but you sacrifice pull for speed.
Consider your choices carefully. The final decision will be based on cost, ease of operation, sound level, upkeep, and a host of other factors. There is not one answer for what to use. Don't be intimidated by the local "expert" who claims that you are doomed to failure because your choice is not his or her choice. Check around. Get other opinions.
If the "expert" states you should only buy a "Super Turbo Nine" with twin bearings and an "AEX" piston/sleeve combination, visit another field to check it out; they're probably using turbos to drive the stakes for their shelters!
Transcribed from original scans by AI. Minor OCR errors may remain.
