RADIO CONTROL AEROBATICS
Ron Van Putte, 111 Sleepy Oaks Road, Ft. Walton Beach, FL 32548
Many of the letters I've been getting deal with two topics. The first involves what kind of model a beginning Pattern flier needs. Since the results of a reader survey on that subject were published last month, I won't be writing about it for a while.
The second topic concerns the kind of radio a beginning Pattern flier needs. A typical letter was from Jim Staggs of Albuquerque, New Mexico:
"I have been a sport RC pilot for ten years. I want to start flying Pattern with the goal of Nats-level competition. I am at the point in building a Curare where integration of the radio system must be considered.
"With all the hype out there concerning radio system features, I feel perplexed as to which features are useful (legal) to the Pattern flier. More specifically, would you chronicle for your readers those features you feel to be a genuine asset to the Pattern competitor and those you feel fall into other categories. Also, are there any features that cannot be used in competition?"
I've been preaching about this subject for years, but not recently. The theme I've tried to get across is that most of us do not really need the radio we are using. Let me explain by using an analogy.
There's hardly anyone who would claim to need a Lamborghini to drive to and from work. Yet many fliers feel they must have the latest high-technology radio equipment to fly in the Sportsman (Advanced or Masters) class. Why is that? I think ego and self-image have a lot to do with it.
Let's split out radio design features and examine their worth relative to the Pattern classes and a flier's ability. The questions to answer are: "What is needed to perform the maneuvers?" and "Based on the pilot's ability, can he or she take advantage of the radio system's features?"
The radio system features I'll discuss are:
- Number of channels
- AM / FM / PCM
- Servo reversing
- Dual rates
- Variable trace ratio
- Exponential
- Adjustable travel volume
- Control mixing
- Servos
Number of channels
If a model has retractable landing gear, all anybody really needs is a five-channel radio. So why do all the top-of-the-line radios have ten channels? Probably because it's more than five, six, seven, eight, and nine. Most ten-channel radio owners never use all of the channels, and couldn't figure out how to use them if they wanted to.
Let's get personal: "How many channels does your radio have, and how many do you use, Mr. Van Putte?" My answers are: eight and five. Why do I have an eight-channel radio? The simple answer is that it was a good buy, and I might want to install flaps, aileron differential, and inflight mixture control in my next model.
I have done all of those things on past models, but not all at the same time. Obviously, the key to answering the number-of-channels question is determining what you are likely to want to do during the lifetime of the radio.
The pilot's ability is not really a factor in the decision. The top-level pilots could whip up on all of us with four-channel (no retracts) systems.
AM / FM / PCM
AM/FM/PCM choice is mixed with other factors, like number of channels and other features, but the basic decision should be based on what works in your area. At my home field, I could fly anything; we don't have any interference from outside.
At some of the fields I fly from at contests, however, there is outside interference. Since you get greater rejection of outside interference as you go from AM to FM to PCM, I use a PCM radio. Assess your environment before making a choice.
Servo reversing
Servo reversing is not mandatory for any Pattern class level of pilot ability, but it certainly makes things a lot easier when installing your radio gear.
Back when servo reversing was not available, I had to go inside the servos to switch wires on the motor and feedback potentiometer. It was not easy or pleasant, nor 100% successful. Since almost all radios have servo reversing, it's something you usually don't have to worry about. Thank goodness!
Dual rates
Dual rates are not mandatory for the beginner classes (Novice and Sportsman). You use dual rates when you want to increase or reduce control authority of a particular function. The two most common ones are elevator and aileron. Most fliers flip to high-rate elevator for spins or snaps. Similarly, low-rate aileron is often used for slow rolls.
None of these maneuvers is in the Novice or Sportsman maneuver schedules, so neither dual-rate elevator nor aileron is necessary for those events. In fact, after using dual-rate aileron for slow rolls for more than ten years, I discovered that I didn't need it. (This obviously begs for an explanation, which I'll give later.)
Variable trace ratio and exponential
First, a description of variable trace ratio and exponential is needed. During normal radio operation, the servo will move the same amount for each incremental movement of the transmitter stick.
If variable trace ratio is selected, the radio will appear to operate the same way until a certain point in the transmitter stick's movement. At that point, the servo's movement will still be proportional to the incremental movement of the transmitter stick, but the amount of movement of the servo will be less. It's easy to visualize if you think of going up a ramp that changes angle about two-thirds of the way up. You can change the slope of the first ramp until the effect causes the system to feel "soft" about neutral. That is, it takes a lot more transmitter stick control input to disturb the model's flight path than before.
However, at a certain point when more control authority is required, increased control pressure causes progressively more model response. The total amount of control authority remains the same as before.
With exponential selected, the servo will progressively respond more and more for each incremental movement of the transmitter stick. Again, visualize going up a ramp, only this time the ramp is continuously getting steeper. As for variable trace ratio, the total amount of control authority remains the same as before. Since the slope of the servo's response is very shallow about neutral, the control feel is similar to that of variable trace ratio.
What is the advantage of using variable trace ratio or exponential when flying Pattern? First, if either is used on aileron or elevator, the model will respond more smoothly about neutral—the model feels groovy. Even better, the judges will appreciate the model's smoothness since a major factor in judging criteria is smoothness and gracefulness.
Second, the same amount of control authority is still there; all you have to do is push the stick a little farther. While the really good fliers can control their stick inputs better than the rest of us, even they can benefit from using variable trace ratio or exponential.
I believe exponential is better than variable trace ratio because the control authority steadily increases as the transmitter stick is moved. There is a "knee" in the control response curve for variable trace ratio that sometimes causes problems.
For example, when performing outside loops I occasionally don't have quite enough down elevator fed in as the model approaches the bottom of a loop. When I feed in a bit more down elevator, I sometimes push the stick past the knee in the control response curve and get too much down elevator. This causes a kink in the loop—something the judges never miss—and I am appropriately penalized on my scoresheet.
I mentioned that I don't use dual-rate aileron for slow rolls anymore. I can get a tad of aileron input by using variable trace ratio with the initial slope dialed very shallow and holding the stick partly over. It works for me, and I don't have to fumble around trying to find the aileron dual-rate switch in the middle of a turnabout maneuver.
Why do I use variable trace ratio? My radio doesn't have exponential. (Maybe I can use this as a good excuse to convince my wife that I need a new radio.)
Adjustable travel volume
Adjustable travel volume provides the ability to adjust control throws at the transmitter. Although it is strictly a convenience feature and is not needed at any level of Pattern flying, I would not be without it. If you can afford a radio with adjustable travel volume, get it. Even though it won't make you a better Pattern flier, it makes life a lot simpler.
Control mixing
Aside from exponential or variable trace ratio, control mixing is probably the most-used extra feature of modern radios. It enables you to get a control response from one channel to a control input in another channel. The most common use is probably in rolling maneuvers.
Most models pitch when you apply rudder in knife-edge flight. If a flier can adjust the tendency out by changing wing or stabilizer relationships or varying the engine thrustline, he often does.
However, when all else fails (or he's just lazy), he can use control mixing. What you want is a tiny amount of elevator input opposite the model's pitching direction, so you mix rudder into elevator. This way, when the rudder is applied as the model approaches knife-edge flight, a bit of elevator can be applied in the appropriate direction.
The amount of elevator deflection is proportional to the rudder input. It takes some time to get just the right amount of mixing dialed in, but it's worth it.
Control mixing can make a real dog of a model perform much better. Does a Novice or Sportsman class flier need it? Probably not. Most situations where control mixing is a boon do not occur in the Novice or Sportsman maneuver schedules.
Servos
We all must have servos, but we do not all need the best that's on the market. I tell fliers to be realistic about their flying ability, and get the equipment that is consistent with their ability.
What does servo quality (and price) have to do with flying ability? If a pilot can use extra servo speed, torque, or precision, a high-priced servo would help him fly better. Most lower-level Pattern fliers simply do not fly well enough to take advantage of the superior characteristics of the higher-priced servos.
Here's a personal situation as an example: I am a good flier; I am not a great flier. I use Futaba 5101 servos on aileron. If I used Futaba 9101 servos instead of the 5101s, you could not detect an improvement in my flying, because I can't fly well enough to take advantage of their superior characteristics. Most Pattern fliers are just like me. Don't let ego and self-esteem control your wallet.
Legality and final thoughts
By the way, all of the features I mentioned are legal in Pattern competition. The only technology that is currently illegal is a feedback system that permits a pilot to fly preprogrammed maneuvers.
Choose your radio and components based on what you will actually use and what fits your flying environment and ability. Save your money for things that truly improve your flying, and don't buy high-tech because of ego.
Transcribed from original scans by AI. Minor OCR errors may remain.
