RADIO CONTROL JETS
By Jim Hiller
6090 Downs Rd., Champion, OH 44481
Overview
This has been a great year for jet modeling. More modelers are getting into jets, and jet events are growing with many new faces attending. If you missed a jet meet this year, don't make that mistake next year — bring your jet and come join the gang!
SWB Mamba Turbine
This year the SWB Turbines Mamba has really come into its own. This is an 11-pound-thrust turbine built in the United States. Jeff Seymour produces this little turbine and is committed to providing modelers with a reliable, fuel-efficient engine.
- Jeff has run this turbine at higher outputs, but he has derated the Mamba to ensure reliability and durability. His intent is for your engine to last.
- SWB provides the Mamba as a complete package with setups for air start or full onboard autostart. The autostart setup is typical: an electric motor assists the turbine rotating assembly as it accelerates to idle RPM.
- The total weight of the Mamba and accessories is light for its size, and the ECU program benefits from SWB's aerospace turbine development experience.
- The Mamba rates among the best for low fuel consumption. This is a big benefit when flying a smaller turbine model because you can keep fully fueled takeoff weight lower with smaller fuel tanks. It can give new life to many classic ducted-fan models.
The SWB Mamba is competitively priced; get the latest information at www.swbturbines.com.
Onboard Electronics: Orbit M-SAVER and Chargers
A product I've started using this year is the onboard Orbit M-SAVER voltage meter. I've used onboard meters for years so I know the battery status before every flight.
- The Orbit M-SAVER readout is a single LED that flashes to indicate battery status. A single hole can be drilled, the LED inserted, and glued in place. This allows battery monitoring without removing the hatch.
- I set up models so I don't have to remove a hatch to turn on the radio switch or to air up brakes and retracts. Internal meters that can be mounted externally are a convenient solution.
- Orbit Electronics also makes a nice field charger. More information on these and other Orbit products is at http://orbitronic.de/. Orbit products are distributed by Golden West Models (www.goldenwestmodels.net).
Frequency Etiquette
As attendance at jet meets has grown, the issue of holding the frequency pin out for extended periods has become more important. Even with all available frequencies, modelers fly frequently at events. Be courteous and return the frequency pin promptly.
If you need your transmitter to perform maintenance on your model, use a direct servo control cord. Don't tie up the frequency pin. This message comes from fellow modelers, event contest directors, and transmitter impound staff.
How Turbine Engines Work
The turbine is unique among model powerplants because it uses continuous combustion. Unlike piston or Wankel engines that have a combustion cycle, the combustion flame in a turbine must be continuously maintained or it will flame out.
Combustion consists of three basic elements:
- Fuel (kerosene)
- Oxygen (from the air)
- Heat
If any of these elements is missing, the turbine will flame out. Thrust is controlled by varying only the fuel flow: increasing fuel raises heat, accelerating the turbine wheel, increasing compressor speed, drawing in more air, and producing more thrust.
Preventing Flameouts: Air Bubbles and Solutions
Understanding turbine combustion helps explain common failures and what to expect. The most basic failure is an air bubble reaching the fuel pump. When air enters the engine instead of kerosene, one element of combustion is missing and the flame goes out. The turbine may still spin, but the temperature starts to drop.
When the air bubble passes and kerosene returns to the engine, there may not be enough heat to immediately support combustion. Kerosene hitting hot metal parts can create smoke. When the temperature probe detects the cool-down, the ECU is normally programmed to shut down the fuel pump, halting fuel supply. This is the dreaded smoke out the tailpipe — a flameout that turns a jet-powered model into a heavy, fast glider.
Common solutions to prevent air-bubble-induced flameouts:
- Header tank (small fuel tank):
- Purpose: trap air bubbles so they don't reach the pump.
- Typical size: 2 to 8 ounces.
- Placement: plumbed between the main fuel tank and the fuel pump.
- Note: many fuel pickup lines are brass tubes that end in the middle of the tank. Some modelers use a flop tube, but this can be unnecessary or detrimental to header-tank effectiveness.
- Refueling: remove all air from the header tank when refueling. The vent-style line routed to the top of the header allows fueling by pumping fuel backward through the header to the main tanks.
- Ultimate Air Trap (UAT) by SWB Turbines (sold through Bob Violett Models, BVM):
- The UAT is a small tank with a bag pickup that breaks air bubbles into smaller ones that won't cause flameout. Proper setup and purging are required — read instructions and visit BVM’s site at www.bvmjets.com for tips.
- Modified paper-element automotive fuel filter:
- Described on the Georgia Jets website, this modification can perform a similar function. I’ve used this solution on a jet without a header tank with good results. See www.gajets.net for the article and other technical resources.
Solutions abound; choose one that fits your model and fly safely.
Automatic Shutdown Switch: When and How to Use It
An automatic shutdown switch (set up on its own channel on most turbine models) is underutilized but very helpful.
- Common assumption: the emergency shutdown switch is only for preventing post-crash fire when control is lost. That’s one use, but there are others.
- Throttle response on a turbine is slow, including returning to idle (often two to three seconds). If you shut off the fuel with the emergency shutdown, thrust stops immediately.
- Example: loss of directional control on takeoff (especially with crosswinds). If you pull throttle to idle, the aircraft may still blast off the runway under engine thrust. Using the shutdown switch kills thrust immediately and can greatly reduce damage to the aircraft and anything in its path.
Practice is essential. Mentally rehearse using the emergency shutdown switch each time you fly. Think through when and how to use it, then practice the motion on the transmitter. Train your reactions like athletes, race-car drivers, and pilots do — it works.
Final Thoughts
I hope this article has not scared anyone about turbine operations but has instead explained some unique issues of turbine-model flying. With the right equipment, setup, and practiced reactions, turbine flying is safe and rewarding.
Transcribed from original scans by AI. Minor OCR errors may remain.
