Radio Control Jets - 2010/12
Jim Hiller
Experimenting with EDF jet power
This summer I was introduced to large electric-ducted-fan (EDF)–powered aircraft, so I’ll give you a turbine-power flier’s take on big EDFs.
I fly with John Fulmer, and he has converted an old ducted-fan Super Eagle to a Byron fan with an XPS “soda can” motor powered by a 10-cell battery. This jet weighs almost 20 pounds, but it is performing impressively with the simple 10-cell setup. Another terrific model is “Billy D,” a grand old Byron F-16, which was beautifully built and painted and is powered by a Dynamax fan with an XPS soda-can motor.
All of that got me going, so I pulled out my old ducted-fan Usher F-100 that Dick Driftmeyer built and handed it over to Bill White, who is one of my club’s electric gurus. He installed a Dynamax fan, powered it with a Neu 1527/1.5Y motor, and put in a Castle Creations 140-amp speed controller. Battery power is supplied by a pair of five-cell 5000 mAh 30C XPS packs. The fan pulls 118 amps at full power, showing almost 3,900 watts — all in a model that weighs slightly more than 14 pounds with batteries.
Bill assured me that he installed a good setup. So off we went to fly the model, and it works! Performance on takeoff is good; there is plenty of power to climb clear of the trees and keep going. The motor/fan setup is nice for this jet. Flying the F-100 is fun. I especially like diving out of the sky to a low pass with no power, letting the airframe whistle by, and then getting on some power and flying away. It provides for a neat sound and experience.
But this electric thing isn’t all roses. Flight times are limited. We restrict ours to approximately 4 minutes, from start of takeoff to wheels on the ground. You have to spend the whole flight thinking about how to manage the available battery power. At full power the battery would be drained to 80% in less than 2 minutes. Flying the F-100 has been an education in battery management and understanding how to get the most from them.
We learned that time spent at full throttle is when the batteries heat up. One time we got them up to 140°F — the magical number that one should not exceed. That was on a flight during which we ran the system hard, including a full-throttle pass immediately before landing. We figure that the full draw with the packs already run down generated the heat. The batteries took 4,800 mAh to get back to a full charge.
During a typical well-behaved flight we used full throttle only on takeoff and performed the rest of the flight at 50%–75% power. The model attains fast cruising power, then uses momentum to return to altitude for the turns. With this technique we have flown for more than 4 minutes and landed with battery temperatures at 110°–120°F.
Experienced EDF modelers will tell me that we are battery-limited and that it is time to step up to the latest battery technology. The F-100 has room for more batteries and the power to handle a heavier battery setup, so I might budget for new batteries next season. In the meantime we are having fun cruising around with the old model — quietly. It has been a great model for Bill to use to step up to high-performance jet flying without the intimidation of a turbine. It’s almost as fast but not nearly as loud.
EDF power provides great experience in the latest expanding technology, but it lacks the sound and fury of jet aeromodeling. Performance of EDFs is getting to be great and our speed and vertical flight are good, yet we are still a year or two behind in battery technology; it only gets better. As I mentioned, flight times are limited, which leads to flights during which you spend a lot of time focusing on throttle management. It makes a big difference in flight times and battery temperature.
There are many ways to tackle EDFs, and now Bill White and I have one.
Jets Over Kentucky
This was my first year to attend Jets Over Kentucky at the Lebanon–Springfield Airport in Lebanon. What an event! A total of 116 registered pilots took 263 jets for one great week of flying, July 4–11. Yes, that's right — a full week. You can go early and fly often before the weekend crowds show up.
Lewis Patton did a great job with this event, and the community and airport personnel stepped up along with him to make everyone feel welcome. Lewis lived at the airport from 7 a.m. to 10 p.m. each day, working to keep things moving and solving problems as they came up. The facility was almost perfect for a jet event. There were plenty of paved areas for parking, start‑up, and campers, plus a large hangar for overnight model storage.
This event attracts some of the best jet modelers in the country and Canada too. This year's weather helped make it a great week of flying, camping, and hanging with fellow aeromodelers. The sponsors get behind this fly‑in — this year they even provided almost 18,000 square feet of tent area for the pilots. The pilot raffle featured some unbelievable items, ranging from top‑end radios to turbines and much more.
If you love jets, either as a pilot or a spectator, Jets Over Kentucky is a great event to attend!
Dealing with turbine starts and fires
Let's get back to turbines and how to deal with a failed start — not the simple one, but the one that includes flames. Many of us experience errant flames when things go wrong during start‑up, so let's prepare for it. At a jet meet this year I saw three fires. The pilots and crews handled two of those poorly, and one got scary.
Always have a fire extinguisher with you on the flightline. It's a simple thing to do.
That bad start will probably happen; we just don't know when. One situation in which this can happen is during a hot start caused by excess kerosene in the turbine. As the engine accelerates during start‑up, excess kerosene blows out the back end, where it combines with oxygen to create a flame. When that scenario happens, shut down the start sequence and give the flames a quick blast of the CO2 fire extinguisher. The fire usually goes out immediately, and without the turbine spewing out more kerosene there's no fuel to burn.
Don't get excited when you see flames. Deal with it. And whatever you do, don't fan the fire with a leaf blower — adding oxygen to the fire doesn't help.
The next situation is more complicated and tends to create the scary moments: excess starting gas in the fuselage (i.e., propane). I experienced that this summer on my BVM BobCat, which has an externally mounted turbine. The root cause of the excess propane was a leaking propane valve. As the start sequence initiated, the glow plug came on and lit the propane that had collected in the turbine. There was a bang, followed by a short shot of flames coming out of the turbine. I immediately shut down the start sequence. Because the extra propane had already burned off, the incident was over. Fixing the leaking propane valve was simple: I pulled it apart, cleaned out the dirt that caused the leak, and have had no more problems.
The next time I saw that happen was with an internally mounted turbine, which poses a new problem. Propane is heavier than air, so a propane leak can fill the fuselage, pooling in the bottom. When you initiate the start sequence, you may hear a pop from propane igniting in the turbine. Then the free propane settled in the lower part of the fuselage is lit. Again, handle this quickly and easily by shutting down the start sequence and administering a shot of the CO2 fire extinguisher. With no oxygen the fire goes out. If you get to it soon, no airframe components will have caught fire. Then you merely need to assess the damage and cure the problem.
Upcoming events
Having completed that lesson, it's time to pack and head to Litchfield, Illinois, for the IJMC (International Jet Model Committee) US Team Qualifier for the 2010 Jet World Masters, followed by Route 66 Jets. I love flying jets and having fun across the country.
Sources
- BVM Jets
(407) 327‑6333 www.bvmjets.com
- Xtreme Power Systems
2440 N. Kiowa Blvd. Lake Havasu City, AZ 86403 www.xtremepowersystems.net
- NeuMotors
(858) 674‑2250 www.neumotors.com
- Castle Creations
(913) 390‑6939 www.castlecreations.com
- Jets Over Kentucky
www.visitlebanonky.com/events/kyjets.htm
- Jet Pilots Organization
Jim Hiller 6090 Downs Rd. Champion, OH 44481
Transcribed from original scans by AI. Minor OCR errors may remain.
