Newcomers

Newcomers

Bob Underwood

32 Hollandbush Ct., St. Charles MO 63304

IF YOU ARE at least a couple dozen years or so old, it’s probably happened to you. You’re cutting the grass or sweeping the driveway, and a little kid about the size of a fireplug comes along and asks, “What’re you doing?” The logic of your mundane pursuit has escaped the toddler’s notice — or so it seems.

My wife and I live in a cul-de-sac with close to 27 youngsters as neighbors — from babes in arms to teenagers — and we encounter the question frequently. I’m sometimes tempted to pause in the task of sweeping and intone, “Washing the dishes.” But that would damage precious minds.

When the youngster survives a few more years, the question changes. When given an answer or instruction, he or she follows with a single word: “Why?” The question is far more devastating to the adult because no matter what he or she is able to produce as an explanation, there is always the continued, endless “Why?”

Well, guess what? This is a “why” column! Don’t deduce that I have concluded that readers should be considered children — far from it! After writing this monthly missive for close to a decade, I’ve come to appreciate quite the opposite. But you must recognize that any newcomer, whether in life in general or modeling specifically, has to have “whys.”

• Why do most trainers have a steerable nose wheel? The use of a steerable nose wheel tends to create a more normal steering condition for the model until it reaches flying speed. With a “tail-dragger” (steerable tail wheel), the overall steering effect alters as the model transitions from taxi to takeoff speed. In many cases you need to give a touch of down-elevator to raise the tail in preparation to make the transition from surface control to flying control.

The model with a steerable nose wheel is already in a normal flying attitude when sitting on the ground. Most people find it easier with fewer things to consider and watch for.

• Why do the instructions call for my model to have the engine offset from the fuselage centerline? Not all models do! However, with some aircraft types and designs, a little offset to the right and/or down is indicated.

There are some forces associated with the laws of physics involved. For instance, as the propeller rotates in a specific direction, these forces impart movement away from a straight line. In order to compensate for this, sometimes the power plant is offset. In other cases, the design of the aircraft may address these problems.

Understand that anything done will be a compromise; not all flight conditions can be met at all times with one setup.

• Why do Electric models need cooling vents? You are so used to thinking “explosion” (rapid burning) when you think of a power device, you tend to forget that electric motors do produce heat.

The electric motors you most often come in contact with are not operating at the speeds and loads you expect in an Electric model. You also forget that the act of charging and discharging the battery-pack power supply produces heat. That heat becomes quite significant in the model because you expect the charging and discharging to be forced into a brief period of time.

• Why does a Control Line (CL) flier slip that thing around his or her wrist when he or she picks up the handle? The loop device slipped around the wrist is for safety. Its purpose is to restrain the model from flying away in the event that the flier should lose his or her grip on the CL handle.

There’s a hefty tug on the lines at times. It may seem like runaway CL models would not fly too far if the handle was dropped, but they have in many cases. Even though a modeler may have a good grip on the handle, factors such as greasy, oil-soaked hands can create a problem.

• Why does the club I’m joining require a rounded safety nut or spinner on engines? Although many modelers tend to associate such a requirement with the AMA Safety Code, it isn’t there! Safety nuts and spinners are required for certain competitive events and are certainly recommended for all engines with exposed threaded propeller shafts.

If you ask what prompted the use of such devices, the answer you receive is often associated with the model striking someone. Their use was actually prompted by a desire to keep individuals from being injured by the sharp, threaded shaft while hand-starting engines.

• Why do CL models have an offset rudder position? To control the model, there must be some tension on the lines as the airplane traverses the circular path. At higher speeds, centrifugal forces come into play. At lower speeds, you need help to continue to develop the tension.

More careful examination may reveal a variety of other compensating factors. These may include — in addition to a rudder offset — engine offset to the outside of the circle; a different-length wing panel on the inside as opposed to the outside of the circle, and line leadouts raked toward the rear at the wingtip. You may often find that the outer wingtip carries some weight as a compensating force as well.

• Why is fuel-tank placement important? You need to expect a consistent flow of fuel under many flying attitudes. Most engines do not employ a fuel pump; they rely on suction to draw the fuel to the engine.

As the attitude of the model changes and the fuel is consumed, you will find that the mixture will tend to “lean out” (less fuel, more air). If you place the tank too low in the compartment, it becomes much more difficult for the engine to draw the fuel toward the end of the flight. It’s important to keep the tank position so that the outlet line is slightly below the needle-valve position on the engine.

• Why is there an external fuel line running from the muffler to inside the fuselage on some models? It isn’t a “fuel” line; fuel doesn’t pass through it while the engine is running. This line is used to tap the pressure created by the muffler to pressurize the fuel tank. This allows a more consistent fuel flow throughout the flight. It acts the way a pump would.

• Why do the instructions tell me to isolate the fuel tank with foam? It isn’t to keep the fuel tank from breaking, nor is it the same thing you do with foam to isolate receiver and battery packs. Rather, the serious vibration levels in our models tend to cause hard-mounted tanks to produce foaming of the fuel.

In its most serious condition, the foaming allows air to pass through the fuel line to the engine. This changes the actual fuel/air mixture and creates a leaner situation. This is not a good thing!

• Why shouldn't I use the 1/2 oz. and 2 oz. glow fuel bottles as general storage? Glow fuel is a mixture of ingredients in specific proportions. Some of those ingredients evaporate quite freely — alcohol and nitromethane fit that pattern. Very old fuel may prove to produce inconsistent engine runs, hard starting, etc. Other chemical changes may occur, and moisture may be introduced.

AMA has indications that very old fuels stored in metal containers may produce flash fires or explosions when the cap is removed, so buy fresh fuel.

• What can I do if there is a broken pushrod? Who says you can't? If your friend had a problem doing it, it may have been because he wasn't careful! Use a tube, such as a plastic pushrod outer tube, a paper or cardboard tube, etc., and route it toward the tail. Keep it as far as possible from servos, and make certain that it is fully extended.

You may encounter greatly reduced range if you are using metal cable material or metal pushrods to the all control surfaces. In certain cases, covering materials or paints may include metal substances that inhibit signal transmission.

In any case, always carefully range-check the system with the engine off, then running, and use the manufacturer's recommendations.

Time's up. What are some of the "whys" you have come across? I'll be happy to pass them along to others.

Newcomers

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