RADIO CONTROL JETS
Jim Hiller, 6090 Downs Rd., Champion OH 44481
SUMMER IS BACK and jet flying is in full force here in the Midwest. I got a new turbine this winter—an ArtesJet Eagle—and with the good flying weather I have been flying it hard. My turbines get used.
ArtesJet Eagle
The ArtesJet Eagle is one of the newest turbines on the market and is an international effort: the turbine design is from Spain, it is manufactured in Mexico City, Mexico, and it is tuned and accessorized in California. Check out www.artesjet.com for complete information.
- Available versions:
- Stock Eagle: 27 lb thrust
- Super Eagle: 30 lb thrust
- Both engines are the same basic size and contain the same compressor as similarly rated turbines. They perform similarly in terms of throttle response and idle thrust.
- My Eagle is rated at 27 lb of thrust, and at 600 feet above sea level it produces slightly more than 27 lb of thrust on the test stand.
Intelligent Control System (I.C.S.)
The ArtesJet turbine comes equipped with a small, lightweight controller called the Intelligent Control System (I.C.S.). The I.C.S. functions much like an intelligent speed controller: it converts the throttle signal to control the fuel pump within preset limits and monitors the turbine for any parameters operating outside preset limits.
- It is a computer system that controls start-up and shut-down processes.
- A Hand Data Terminal (HDT) is supplied to monitor the engine’s performance and to program the turbine to match your radio.
Start-up and shut-down
The start-up and shut-down processes are similar to those of most turbines on the market today.
- Start-up: Initiated by cycling the throttle stick to full and back to idle. A small onboard starting-gas tank is used to light off on a glow plug. The fuel pump then pumps kerosene into the turbine to accelerate it to idle rpm. When the turbine stabilizes at idle, the I.C.S. returns throttle control to the radio system.
- Note: Unlike a JetCat’s starting process, the ArtesJet does not run up to 50,000 rpm and then throttle back to idle. You have to listen carefully or watch the HDT to determine when the turbine is at idle and you have throttle control.
- Shut-down: Immediate with reduction of the idle trim, followed by a cooling period using the onboard starter motor. The I.C.S. will continue the cooling cycle even if you turn off the transmitter (assuming you programmed your fail-safe correctly).
I like the supplied shutoff valves for the starting gas and the kerosene; they are robust brass units. The connection to the I.C.S. uses servo-type connectors, so regular servo extensions can be used if needed. The fuel pump is a nice-looking unit and so far has been trouble-free.
Fuel
The ArtesJet turbines use a 2.5% oil mixture in the fuel—roughly half of what my other turbines use. I keep my fuels separate to avoid mixing them up, but this cuts my fuel bill significantly since turbine oil is the most expensive part of the fuel cost.
My experience
Overall, I am quite happy with this new turbine. I have been flying it hard and heavy and have not had a flameout to date. It runs like a turbine should: starts reliably, throttles well, and stays within operating parameters so the I.C.S. does not shut it down.
There are a variety of suppliers building quality turbines now. Last weekend I looked at our small group of sport turbine modelers and saw an ArtesJet, a JetCat, a PST, and a SimJet turbine performing flawlessly. Turbines have come of age and there is a great selection available.
Flaps: why we use them
I heard a comment the other day about a jet model I was flying that did not have flaps; a gentleman questioned whether it was okay to fly a turbine model without them. The ensuing conversation showed a misunderstanding about flaps.
AMA does not require flaps on a turbine model because they are unnecessary in that sense. So why do we have them? Because they make landing your model easier. Flaps do two basic things for us:
- Increase lift, allowing lower landing speed.
- Increase drag, allowing steeper landing approaches.
- The first few degrees of flap travel—up to approximately 10°—add significant lift and not too much drag. This is useful when you want additional lift, such as during takeoff or when recovering from a slow, turning final approach.
- The remaining flap travel greatly increases drag while continuing to increase lift. The extra drag helps with spot landings and often allows the pilot to carry some throttle on final approach, using throttle to control the angle of approach and select the touchdown point more accurately.
Many jet models have clean designs, so the turbine’s idle thrust makes for a flat approach. The additional drag from flaps is a great aid in landing.
Flap quirks and aircraft-specific effects
Flaps have quirks. The first problem is pitch-trim changes. Flaps create lift behind the CG, which tends to push the nose down, but they also deflect air downward behind them, causing the airflow to strike the top side of the stabilizer and tend to push the tail down. Conflicting pitch-trim effects mean the balance between these determines the net pitch change for any airframe.
When flaps are extended at high angles, they create turbulence that can have strange effects on some airplanes. My experiences:
- Twin vertical-fin aircraft: The F-15 Eagle—particularly with loaded hardpoints—can start unwanted wing waggling when flaps are used. The same model with hardpoints loaded but without flaps extended lands straight and smooth.
- Swept-wing aircraft: On swept-wing models such as the old Starfire, F-86, F-100, or MiG-15/17/19, flaps help stabilize the landing approach and make these aircraft easier to set up for landing. These clean aircraft benefit from the additional drag of flaps, allowing the pilot to carry some throttle on approach.
- Delta and low-aspect-ratio wings: Delta-wing aircraft such as the F-16 or A-4 have low aspect ratios, so flaps don’t have as much effect. The F-16 uses flaperons located near the stabilizer. At travels up to approximately 15° they work well, but beyond that they can adversely affect pitch response. Low-aspect-ratio wings allow pilots to use angle of attack to control descent rate, as drag increases rapidly with angle of attack. By flying the approach at reduced speed, you can generate enough drag to carry power on final without heavy flap use.
Crow setup
I have begun using a crow setup to aid flying out of a local field with trees on the approach end of the runway. Crow lowers the flaps as normal and also raises the ailerons, effectively increasing drag for a much steeper approach. This technique has been used successfully by sailplane pilots.
- Effect: Increases drag so you get a much steeper approach.
- Pitch changes: My model does not require pitch-trim correction with regular flaps, but when I add the aileron-up crow, I get a large up-elevator pitch effect.
- Programming: I use a mix of 18% down-elevator with crow application. This provides a good, straight-pitch transition with flap/crow application and a steep approach, allowing me to fly from a relatively tight field by jet standards.
I hope some of this helps you with your model flying. I look forward to seeing you at the next jet meet.
Transcribed from original scans by AI. Minor OCR errors may remain.
