FIELD FOLLIES
by Frank Granelli
AT THE END of November's "From the Ground Up" installment, we left the fuel tank filled and in the right place to ensure trouble-free operation. The tank setup is good, you already know how to set the high- and low-speed needle valves, and the proper glow plug is in place. Now you just need to get the engine started to have a great flying day — the first of many.
Modern glow engines are so user-friendly that we only need to make the glow plug glow and then find some way to rotate the engine to get it started. With today's industry and modelers' imaginations being what they are, there are roughly five million tools to perform each operation. But we need someplace to house these millions of tools.
From 1970 to 1974 I housed all the field equipment I owned — a 2-ounce turkey baster with a fuel line attached, a 1.5-volt battery with alligator clips, a "chicken stick," and some tools — in a brown paper bag. The baster took five minutes to fuel a 16-ounce tank, the battery was always dead, the alligator leads were constantly shorting out against the engine's head fins, and the chicken stick kept breaking wooden propellers. If everything was actually working, the bag would rip open and spill everything onto the ground.
I do not recommend such limited equipment to anyone, but, in truth, it is all you actually need to get flying. Luckily there are better ways today.
Field Boxes and Batteries
It is a good idea to find a more permanent home than a paper bag for your field equipment. Many manufacturers offer field boxes. Expect a field box to be able to hold:
- All the tools you will need
- A gallon of fuel
- A fuel pump
- A glow starter
- A power panel
- A 12-volt battery
- An electric engine starter
Some field boxes, such as Great Planes' Master Caddy, are equipped to hold the aircraft during field assembly or repairs, but not for engine starts or runs. Although each field accessory (for example, a Thunder Tiger fuel pump) can be powered from its own battery, it is more convenient for most model pilots to use one 12-volt battery to run everything through a power panel.
Most field-box batteries are 12-volt "gel cells." Gel cells use common lead-acid technology in a form that does not spill or require venting. Motorcycle batteries are also often used, but they must be firmly fastened in an upright position and completely vented to the outside.
Popular capacities:
- 4 ampere-hours (Ah) — smaller field boxes
- 7 Ah — most popular and more than required for most flying days
- 9 Ah — a good choice if you sometimes forget to charge and expect high starting demands
A charger is required for these batteries.
If you plan to use high-power starts (for example, competition starts where only three minutes from start to airborne are allowed), consider a heavy-duty starter and the following battery arrangement I use for Pattern competition starts: a 4 Ah, 12-volt battery wired in series with a 4 Ah, 6-volt gel cell. This setup can deliver substantial starting power, but make sure your engine is not flooded — hydraulic lock from liquid fuel can be damaged by excessive starting torque.
Power Panels and Glow Igniters
Most electric fuel pumps and electric starters use 12 volts, but the average glow plug can be damaged by more than about 2 volts. If only one battery is used to power the field box, use a voltage-control system — most commonly a power panel.
Power panels:
- Supply the battery's full voltage to the starter and fuel-pump connections (usually via banana-plug connectors)
- Range from inexpensive/basic to sophisticated/expensive
- May include a charging jack for rechargeable single-cell glow igniters
Hobbico's Accu-Glo power panel automatically adjusts glow-plug power based on the plug's needs, helping slightly flooded engines (not hydraulically locked ones) start. It also indicates the field-box battery's power level and whether the glow plug is good.
A basic panel usually has a glow igniter charging jack but requires the pilot to manually adjust glow-plug power. A zero meter reading often means the plug connection is bad.
If you connect your starter directly to the battery without using a power panel, use appropriate starter and battery arrangements (see the Pattern-start system described above).
Independent glow-igniter systems:
- Rechargeable: 1.2-volt Ni-Cd battery (fixed or replaceable) — requires a charger
- Replaceable: 1.5-volt alkaline battery
Many independent igniters include a meter to indicate current to the glow plug. The meter is useful primarily to tell if the glow plug has completely failed (a zero reading). Look for igniters with a medium-length stem: short stems may not reach a glow plug inside a cowling, while long stems (~6 inches) tend to vibrate and loosen on uncowled engines. Medium-length igniters are the most versatile.
Fuel Pump and Fuel Handling
A typical field installation positions the electric pump on the outside of the field box to prevent it being knocked around while tools are removed and replaced. This location reduces the fuel-draw distance and the chances for fuel spillage.
Good practices for fuel-pump installation:
- Staple the pump's power leads away from the fuel container
- Use two layers of shrink tubing to protect pump wires where stapled
- Consider insulated staples as an additional precaution
- Place a small pan under the outlet to catch drips while refueling
- Carry a roll of paper towels in the box for cleanup
- Pull the banana plugs (pump and other accessories) at the end of the day to prevent accidental operation during packing or transit
Electrical shorts usually pose a bigger problem with metal fuel containers; be extra careful if you use gasoline or a metal bottle. If using gasoline or a metal glow-fuel container, position the fuel pump on the internal wall opposite the power panel. Electric pumps and metal containers are not a recommended combination in any case.
Note: fuel lines and pumps always contain some internal fuel. If a pump shorts internally and ignites, proximity to the bottle becomes a moot point because ignition could travel along the lines. Fortunately, glow fuel does not behave like gasoline in this regard.
Electric Starters and Accessories
There are many types and sizes of electric starters. Most pilots will require either:
- A 12-volt standard-duty starter (approx. $30), or
- A heavy-duty 12-/24-volt starter (approx. $70)
Both work well on trainer and "second model" engines. Buying a heavy-duty starter now may make sense if you expect to fly larger ARFs someday; the 12-/24-volt models give you 12, 18, or 24-volt options.
Starter cones:
- Numerous rubber-insert cone shapes are available and interchangeable among brands
- Cones are inexpensive and should be replaced every 3–4 years
- Cracks in white inserts indicate end of service life
Spinner considerations:
- All-plastic spinners: do not use in applications exceeding ~12,000 rpm
- Plastic cone with metal backplate: acceptable up to ~15,000 rpm but can be damaged by a misapplied starter
- All-metal spinners: resist starter damage, usable in all applications, balanced to reduce engine wear and increase rpm
Chicken Stick (Manual Starting)
A "chicken stick" is a padded rod used to rotate the propeller instead of using your fingers. With modern engines and advanced timing, a chicken stick is a wise precaution — it prevents hand damage from kickbacks. Every field box should include a chicken stick in case the electric starter system fails.
Meters, Chargers, Tachometers, and Tools
Digital voltmeters that test radio-system batteries are useful for sport flying and essential when a model's value is high. These instruments measure voltage while applying a simulated flight load on the receiver battery.
Safe recharge thresholds (conservative):
- 4.8-volt receiver packs: begin recharging at ~4.6 volts
- 6.0-volt receiver packs: begin recharging at ~5.8 volts
- 9.8-volt transmitter packs: begin recharging when less than ~9.6 volts
General rule: cease flying and begin recharging when the battery's voltage drops about 0.1–0.2 volts below its nominal capacity. Field chargers can extend your flying day while ensuring adequate radio-system battery capacity for safety.
A digital tachometer helps prevent lean runs, extends engine life, and prevents airframe damage that can result from off-runway landings caused by engine failure.
Essential tools (partial list):
- Ball-driver sets (English and Metric)
- A full set of screwdrivers
- Wrenches
- Extra spinner parts
- Propellers
- Spare glow-plug caddies
- Emergency adhesives
- Extra parts and hardware
There are many more items; check what other pilots keep in their flight boxes to learn practical additions.
Further Reading and Next Time
If you would like to see many of these extra items and how the Great Planes Master Caddy is built, visit the "Baggage Compartment" section of the Sport Aviator online magazine at www.sportaviator.com.
In this segment of the "From the Ground Up" series I have covered most of what newer model pilots need to know for successful engine management. Other parts of this series have addressed how to choose and install a radio system, how to construct a light electric-powered model, and what every new modeler needs to know about electric flight.
But even the best radio system and engine need something to hold them together and then get all of it into the air. That something — the airframe itself — will be the subject of the next part of this series. I will cover how to assemble an RTF trainer, and then how to assemble it so it lasts longer and flies better. ARF trainers will follow, along with many improvements to prolong an ARF's life and improve its flying qualities. See you then.
Frank Granelli 24 Old Middletown Rd. Rockaway, NJ 07866
Transcribed from original scans by AI. Minor OCR errors may remain.
