RADIO CONTROL JETS - 2005/05
Jim Hiller, 6090 Downs Rd., Champion OH 44481
Introduction
I have flown jets for a number of years and I now fly only turbines and electrics. I didn't even take out any of my piston-powered airplanes this year—only my daughter's Seniorita. This article outlines what it's like to fly jets and what you get when you buy a turbine.
The turbine and the ECU
Today's turbine engine is a complete package including the necessary accessories to start and run it. From a control standpoint, the heart is the electronic control unit (ECU). The ECU monitors the engine's temperature, rpm, and the throttle command position, and then controls the accessories necessary to run your turbine safely.
Typical ECU features:
- Programmable parameters (for example, maximum rpm to suit your installation and skill).
- Speed controller for the fuel pump and the starter.
- Glow-plug driver.
- Control of two solenoid valves for fuel and start-gas shutoffs.
- Fault reporting to tell you what went wrong during a failed start or shutdown.
Many turbines are supplied with a ground-support unit that plugs into the ECU so you can read engine status. With some turbines the unit is standard; with others it is optional. I strongly recommend purchasing the ground-support unit—it is invaluable for troubleshooting because it allows you to read fault codes.
Typical information available from the ECU/ground-support unit:
- Stored: total run time, number of starts, last flight data.
- Real-time: rpm, exhaust-gas temperature, fuel-pump voltage.
This data is great for maintaining your turbine.
Throttle and fuel metering
Throttling is controlled by the rate of fuel flow into the engine. A speed controller built into the ECU drives an electric fuel pump that controls the flow rate. The fuel line runs from the tank to the pump and from the pump to the turbine, with filters and shutoffs in between.
Important fuel-system items:
- Filters: essential to prevent contaminated fuel from clogging tiny nozzles. Nozzles can be very small (often made from hypodermic needles); a clogged nozzle typically must be returned to the manufacturer for repair.
- Fuel solenoid: a key electric shutoff valve controlled by the ECU; it ensures positive shutdown in case of a pump runaway or electrical failure.
- Manual fuel-shutoff valve: prevents kerosene from feeding the engine during nose-high attitudes (which could cause a hot start and visible burning during the next start).
Push-to-connect fittings
Push-to-connect fittings (often called Festo) are easy to use: push tubing in and small internal fingers grip it; to remove, push down on the colored plate and pull out the tube. Use the correct tubing (the supplied type) and replace the cut end before re-inserting to ensure a good seal.
Common practice and checks:
- Cut off tubing ends before re-connecting to ensure a fresh sealing surface.
- Check for air bubbles in the fuel tubing leading to the pump and for fuel leaks between the pump and turbine during the first run-up of each day.
Header tank
A header tank is strongly recommended if you perform aerobatics. Turbines are sensitive to air bubbles; when fuel is interrupted the combustion flame can go out and will not relight by itself. A telltale sign of a shutdown caused by an air bubble is a short (two-second) smoke trail as the fuel behind the bubble hits the hot combustion chamber and smokes.
Solution:
- Install a header tank between the fuel tank and the fuel pump. Commercial header tanks are available or you can make one inexpensively. There is no excuse not to use one if you fly aerobatics.
Startup and glow plugs
Manufacturers have developed reliable start sequences and informative start-sequence fault codes. Fly with the operator's manual and a ground-support unit to read faults—these resources will save you a lot of trouble. Keep the manual handy (I keep mine in my transmitter case).
A frequent start problem is old glow plugs. I typically get 40–50 starts from a glow plug before it becomes coated and unreliable. Symptoms differ by engine:
- Some turbines stop igniting the starting gas when the plug degrades.
- Others miss the first ignition but light on the second attempt.
If an engine that used to start reliably stops lighting, change the glow plug. Do not simply increase the plug voltage (that will burn the plug out and damage replacements). I have not seen an effective fault code specifically for degraded glow plugs, so check and replace them when starting problems emerge.
Flying with a turbine
Compared to propeller-driven models, turbines do not have instant throttle response, but they provide incredible power at speed. A propeller's effective airspeed is limited (approximately 120 mph from the propwash); the turbine exhaust can exceed 400 mph. At speeds beyond the prop's effective range, the propeller becomes a drag while the turbine continues to provide strong thrust—enabling very large jet loops limited only by eyesight and common sense.
Throttle management:
- You cannot fly at full throttle unless you want to fly extremely fast.
- Learn to use the throttle to control airspeed. Many Giant Scale 3-D pilots transition easily because they already use the throttle stick for speed control.
- Coordinate throttle and elevator: cruise at partial throttle, open throttle when pulling to climb or loop, reduce throttle in dives or during the backside of a loop, then return to cruise throttle in level flight.
Fuel sources and handling
Common fuel choices and notes:
- Jet-A from airports: readily available but be prepared to pump it into your fuel can (nozzle sizes differ). Bring a funnel or a large-mouth bottle. Avoid drawing from the truck bottom drain (where dirt collects) unless the truck is well maintained and the fuel is filtered.
- Hardware-store kerosene: usually low-odor and often very clean, but beware of algae growth in prepackaged kerosene that came in clear plastic bottles. Metal cans have not given me trouble.
- Gas-station kerosene: convenient and trouble-free in my experience; I use double filters on my fuel can and in the airplane and typically buy fuel no more than two weeks old.
Safety and quality checks:
- If Jet-A appears to have water in it, don't use it. Water can be invisible and will cause severe damage to your turbine. Filter and test fuel if necessary.
- Be aware of the gel point in cold temperatures—kerosene and Jet-A can thicken and stop flowing in cold weather.
A final fuel tip: always filter fuel you obtain from external sources before use to avoid clogging fuel nozzles with dirt.
Conclusion and recommendations
Turbine flying is advancing rapidly. Equipment is improving, ECUs are smarter, and turbines are becoming more user friendly. They require diligence and respect, but are rewarding and can become addictive.
Recommendations:
- Join a turbine club and spend time with experienced turbine pilots—they will show you the ropes and shorten your learning curve.
- Always follow the manufacturer's recommendations for installation, run-in, and maintenance. Proper setup and checks will keep you flying and reduce the risk of failure.
—Jim Hiller, 6090 Downs Rd., Champion OH 44481
Transcribed from original scans by AI. Minor OCR errors may remain.
