Newcomers
Box 40, St. Peters MO 63376
An interesting thing happens when you visit the hobby shop (real or virtual) to buy your starting equipment.
What seems like a simple question escalates into a small mountain of "Oh, by the way!"s. These are the items suggested along the way so you can operate the model, including glow-plug wrenches, fuel, propellers, glow drivers, spare bits, and another this-and-that.
Your head is reeling, wondering whether you have everything you need and if it's the right "stuff."
Help is buried in the instructions for the major items you've purchased, but you probably haven't had an opportunity to read them yet!
One of the mysteries is the choice of propeller.
The choice for a trainer is not nearly as critical as it would be for a sophisticated pylon, pattern, or scale model. Maximum thrust or speed is not a primary goal; you simply need something that will haul the model skyward, allow it to cruise nicely, and let the engine run smoothly.
In recent years, significant progress has been made in producing efficient, quieter propellers. The materials that are used have moved from the almost-universal use of wood to composites of various types.
Tip shapes, airfoils, and different ideas about "loading" the engine are all a part of this revolution.
We've also moved from using the low end of the engine-size range to the upper end. The philosophy that you can always reduce the throttle setting rather than try to squeeze an extra 100 rpm has come into play.
Which propeller to use
During my newcomer years, the propeller recommendation chart that accompanied the engines was standard. You almost always saw a 10 x 6 on a .40 engine, an 11 x 7 on a .60 engine, and smaller sizes on the .15 and .19 engines.
The engines huffed and puffed through 10- to 12,000 rpm, unfettered by mufflers, but fitted with a butterfly-style exhaust stack cover that helped provide back pressure, so you could get a reliable (hopefully) idle.
Now we prop the engines for lower rpm, and bring the sound level down with mufflers, tuned pipes, and efficient propellers.
When you select a propeller, consider these factors:
- What does the engine manufacturer recommend? Use that as a starting point. Since you probably won't need to strive for maximum performance, there shouldn't be too much of a problem.
By reading the engine reviews published in some model magazines, you can obtain further information. While these reviews generally cover a wide range of sizes and pitches, propellers that fit in the engine's "comfort zone" will be suggested.
Engines are tuned or timed to work most efficiently in a particular rpm range. Two-stroke engines are often happier singing along at a higher rpm than four-strokes are. The latter is sometimes restricted to lower speeds because the valves tend to float at a higher rpm.
- Should I use wood or composites?
Wood or composites?
Good question, but difficult to answer! Wood doesn't tend to last as long. A ding on landing, a scrape here, a nick there, and it is history. But wood is inexpensive compared to most composites.
There is the possibility of inconsistency in the stiffness or hardness of a wooden propeller because of the nature of the wood itself. A broken knot, veins of softer wood, etc., contribute to create an unknown. The composite is generally more consistent.
In either case, frequently check the propeller for cracks or fatigue. Grasp the blades and twist or bend them to detect continuous strands running the length of the prop. Read any manufacturer instructions, and follow them carefully!
The trailing edge of the composite blade may be very sharp—dulling the edge is wise. You don't want a lawnmower-blade-type surface near your fingers. This is especially true with four-stroke engines, since you are hand-cranking them.
Always use a protective device to start an engine. This may range from an electric starter, to "chicken sticks," to a heavy glove. A large proportion of accidents occur because of a spinning propeller!
Although it doesn't take a rocket scientist to figure out that getting a part of your anatomy into something turning 10,000 rpm will hurt you, day in and day out someone does just that!
Safety steps
Here are some safety steps you can take:
- Paint the propeller tips a bright color, so you can see the arc.
- Never put your body in this propeller arc. It's common to see someone leaning over the model with his or her face inches away from the propeller!
- Adjust the needle valve from behind the propeller arc. Don't reach around! Engine manufacturers have recognized this, and most new engines have the needle valve angled away from the propeller, or allow you to place it in a remote position.
- Plan where you will place the starter box, cord, glow plug wires (if used), and transmitter to keep them out of the prop. Make this placement a ritual!
- Watch loose clothing, such as jackets, etc. If you use a transmitter lanyard or strap, make certain it is tucked away. It will naturally swing into the propeller if you're not careful.
- Have someone hold the model firmly! Work out signals ahead of time, so your holder will know your intent. Nothing is more disconcerting than to have your helper carry the model to the runway, and be surprised when you run up the engine to clear it out before takeoff.
- Throw away a damaged propeller. Break it, so others won't be tempted to retrieve it from the trash can. Don't try to glue it, splice it, etc.
I've heard individuals state, "Oh well, it's probably still balanced, since I ground off both tips [on takeoff]!" Don't believe it! You may not see the split that runs lengthwise in one or both blades.
- Give yourself plenty of runway-to-propeller-tip clearance. A minimum of one is advised. Even a model with tricycle landing gear will lose clearance on a hard landing!
- A spinner is often used to facilitate starting with an electric starter. You will find spinners with backplates and cones, metal backplates and plastic cones, and all plastic. Be certain that a firm means of attachment is used with whatever variety you use. More often than not, this is a machine screw through the cone into the nut that holds the propeller on. Keep it tight, and make certain that the cone is firmly seated in the backplate groove.
Also, allow adequate clearance between the cutouts in the cone and the propeller hub.
Transcribed from original scans by AI. Minor OCR errors may remain.
