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RC University: Engines & Motors



 


Learn the basics of RC Turbine Engines
Written by: Chad from Sin City Jets
 

Turbines 101

I can remember the first time I saw an RC turbine plane fly. It was about 8 years ago at the Sepulveda Basin in California, at an RC helicopter fun-fly. It was the noontime demo, and the pilot was flying a Comp-Arf Kangaroo. At the time, it was the absolute coolest thing I had ever seen. I could not believe how “real” it sounded. You could close your eyes and just imagine a full-scale F-16 flying above. I knew then that one-day, I would own an RC turbine fixed wing plane.

It would be another 5 years or so until I had the pleasure. The first thing I learned about turbines is, there’s a lot to learn about turbines. It wasn’t quite as simple as the “Fill & Go” style of glow or gas engines. There was a lot more to it, not to mention, to the layman, it was pretty intimidating.

To digress for a minute, most people that have been flying jets for a while, started with ducted-fan jets. These were jets flying with over-stressed, over-revved gas engines that were spinning ducted fans, instead of propellers, for that “scale” jet appearance. The people that pioneered the way with ducted-fan jets had to be some pretty good pilots, as the engines were not very reliable, the plane’s had high wing loadings, and the thrust to weight ratio was not in the pilot’s advantage.

Fortunately, real gas turbines would eventually make their way in to the RC market. While initially heavy, propane fueled, and not very powerful, today’s RC gas turbines are kerosene or Jet A powered and can generate anywhere from 3-52 pounds of thrust. Some production RC turbine aircraft even allow the option of installing two turbine engines, such as the big Mibo A-10.

So, getting started, the first thing a new jet pilot should do, is find a mentor already flying turbines in their area. There are a couple of resources for this, including both RC Universe (RCU) and the Academy of Model Aeronautics (AMA). Using the RCU jet forums, you can find quite a few like-minded people that love the thrill of flying RC turbines. The AMA also has a published list of turbine pilots in your area. Find someone you get along with and pick his or her brain.

After that, it’s time to pick out a good stable airframe. Resist the temptation to buy that 1/7th scale F-18 as your first turbine aircraft. While they look and sound cool, they do not make a good first turbine aircraft. Most scale fighter jets have the glide slope of a brick, and are not very forgiving. They also have relatively high stall speeds, making them extremely unstable at slow speeds. They also require a good command of using the throttle, not the elevator, to control one’s decent for landing. In the right hands, and after some practice, these planes can be a thrill to fly, but it’s good advice to start with something a little more forgiving. My first turbine aircraft was a Boomerang XL, and I would highly recommend it to anyone wishing to learn about turbines. Some other aircraft well suited for beginners are the Reaction 54, the Bandit Arf, and the Boomerang Elan. All of the above mentioned aircraft have retracts, flaps, and a speed range of 30mph to 150mph+, for a true learning experience in to the world of more complicated aircraft. They also have good slow-flight characteristics, allowing the new pilot to learn about proper approaches and turbine spool-up time. Turbine engines do not have the same throttle response as a nitro or gas engine, as such, even throttling up a turbine will be a new learning experience.

The next order of business is picking out your gas turbine engine. Just like any other product in the market place, there are varying degrees of quality when it comes to gas turbine engines. Suffice to say; that you will get what you pay for, just like most anything else. If you’re trying to enter on a budget, consider the RCU market place classified ads. There are always some great deals on used, quality turbines for sale, many of them are from people just like yourself that are moving up to the next level in RC turbines. Do your research, read seller’s feedback, and buy something that you can afford. Don’t over-extend yourself when it comes to your hobby. Expect to pay anywhere from $1500 for a good used turbine, to potentially $5,000 for a new, big-block turbine that you could launch a small child to the moon with.

Another thing to consider when purchasing a turbine is; what type of starting mechanism do I want. There are two main types currently in the market: propane- start and kerosene-start. Both have their advantages and disadvantages. Propane- start is the most common starting method. This method uses propane gas injected in to the turbine, and ignited by a standard glow plug to begin the starting process. The propane heats the turbine combustion chamber and gets the compressor spinning to a pre-determined RPM. Once ignited and running on propane, the engine will then automatically begin injecting kerosene in to the turbine. Once the start-up process is complete, the engine will continue to run on kerosene until you have exhausted your fuel tanks. While propane is the most common starting method, this is also the most complicated and potentially the most dangerous. As you (should) know, propane is very flammable. Plugging, unplugging, and filling on-board propane canisters can be dangerous. Caution should be used at all times with turbines anyway, but especially when dealing with propane gas.

The other starting method is kerosene-start. This method simply uses the same kerosene (or Jet A) fuel that powers the turbine during flight, and a glow-plug element (similar to those found in diesel engines) to start the turbine. On start-up, electricity is applied to the glow plug, heating it up to a pre-determined level. Once fully heated, kerosene is then slowly pumped in to the starting chamber, where it is immediately heated and burned by the glow plug. While this method consumes quite a bit more electricity from your Engine Control Unit (ECU) battery, it is less complicated, and in some ways a more safe method of starting your turbine. The downside to kerosene-start turbines, is they are generally more expensive, and some of their glow plugs are not user-serviceable, meaning they have to be sent to a service center to be replaced. It is the author’s belief that all turbines will eventually be kerosene-start, due mostly to the simplicity of the start-up procedure.

So you’ve got your plane and you’ve got your engine, what next? Well, there’s the small detail about ground-support equipment. And the list can be as long or short as your credit card can handle. Some “must have” items include electric fuel cans (don’t even think about hand pumping), extra glow plugs (or kero plugs), a 12V power source (for either charging or powering ground equip), a plethora of tools (better to have a tool, than to need one), propane cans, a knee pad, a turbine cooling fan (saves wear and tear on your turbine starter motor), extra fuel cans, a fire extinguisher (AMA requirement), and anything else your mentor tells you. Be prepared (Seems like I’ve heard that before).

Another consideration should be your transmitter. That 4-channel 72mhz radio that came with you RTF trainer probably isn’t going to do the trick. The new 2.4ghz radios seem to be the wave of the future. Having only experience with JR radios, I can tell you they have some great 6, 7, 9 and even 12 channel radios. I have owned and used them all. Like anything else in turbines, sky’s the limit, however a good computerized radio with a decent set of mixes will last you for years to come. Most beginning turbine aircraft are going to use 5-7 channels, depending on how you have your control surfaces set-up. Some of the more complicated, scale-competition birds can use all 12 channels when adding speed brakes, bomb-drops, working canopies, etc.

Once you have your radio, plane, turbine, and support equipment, it’s time to earn your waiver. WAIVER?! No, it is not your God given right to fly turbine-powered aircraft anywhere you wish, at least not while being insured. The AMA has set up a turbine waiver system that allows all AMA members to earn a waiver that will allow them to fly turbine-powered aircraft at an AMA approved field. Details about this waiver system can be found on the AMA’s website, but include both a good knowledge of turbine equipment, starting procedures, flame-out procedures, landing procedures, and more complicated flight maneuvers. Remember, these aircraft are capable of speed exceeding 200 miles per hour. Striking any people or property with these aircraft could be detrimental to them, you, and the hobby as a whole. This leads me to the next topic, maintenance.

Take care of your equipment, and it will take care of you. I have been to numerous jet rallies and had a chance to view a lot of people’s aircraft. Some of them are immaculate, while others look as though they were in some kind of dust tornado. Interestingly enough, the pilots whose aircraft that look like they were in a dust tornado seemed to experience more problems (read as: crash more often). It may just be a coincidence, it may not, but the point is, if you are not continuously performing preventive maintenance, you may be doing crash repairs instead. Doing a good pre-flight and post-flight inspection of your aircraft may end up saving you thousands of dollars down the road.

This article was written to give you just a sample of what is involved in getting in to RC turbines. It should not be used as a complete guide. There are many different aspects to RC turbines and no written guide could ever replace the first-hand experience of a good, local mentor that can quickly address the “what if” questions. Ask a lot of questions, practice on a simulator, fly on a buddy box, (with a qualified, turbine waivered pilot) and most importantly, BE SAFE. Anyone reading this article is always welcome to contact me directly either through RCU (member name SinCityJets), my website (www.sincityjets.com), or email (chad@sincityjets.com)

Chad Russell

 
This article was furnished by Chad from Sin City Jets. If you are interested in the full text of this publication, please click here.
 



 



 
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