RC Helicopters
Eric Hawkinson, 319 Yellowstone Ave., Billings MT 59101; E-mail: eric@heliproz.com
IT'S ANOTHER great month to be enjoying the sport of Radio Control (RC) helicopters! Because it's now fully into flying season no matter where in the country you live, it's an even better month than some. As much as I enjoy the building, finishing, setup, and programming, it is the flying that really catches my fancy.
Because of my various jobs, I find myself flying many different RC helicopters. I do this because my jobs require that I have some level of familiarity with as many current kits and designs as possible. The nice part about this is that I have a good idea of what I like and don't like in a design or a distributor.
The downside—besides having a seriously overworked control card—is that no matter what you do with setups, each design has some different handling characteristics—sometimes better than what I'm used to, sometimes not, but each little difference in handling means there is some unlearning and relearning going on whenever I switch from one helicopter to another.
In some ways this could be helpful by making me a more flexible pilot. On the other hand, I suspect that pilots who fly only one or two helicopters consistently develop a finer level of control as they build time and familiarity.
Regardless of what helicopter I'm flying or what I intend to use it for, there is one maneuver that I want to do fairly early in the tryout process. It's the first advanced maneuver that I nag at students to master and the only advanced maneuver you will eventually have to do, whether you want to or not. The maneuver, as all experienced helicopter pilots have figured out, is the autorotation.
Autorotations are the helicopter equivalent of the "dead-stick" landing practiced by fixed-wing pilots. Like it or not, if you fly helicopters for any length of time, you will be forced to attempt an autorotation.
As good as modern RC helicopter engines are, there will come a time when one will let you down. You'll lose a pressure line, clunk line, or glow plug, or perhaps you'll just get so involved in flying that you will fly a bit beyond your fuel capacity. Whatever the cause, when you are in that situation your odds of making a successful controlled landing will be greatly improved if you have practiced autorotations in a nonemergency setting.
Before I get into setup and practice methods, I have included a table that may be of interest to you. It shows the difference in main blade tip speed at various head speeds between a Raptor 30 with 550mm main blades and a Vigor 60 with 700mm main blades.
Raptor 30 Vigor 60 RPM Tip Speed MPH Tip Speed MPH 1400 204 262 1500 219 281 1600 233 300 1700 248 319 1800 262 337
Disk Area Square Inches Square Inches 1886 3117
Note that the tip speed on the Raptor at a rather hefty 1,800 rpm is the same as the Vigor's tip speed at a bled-off 1,400 rpm! Since the speed of the air over the airfoil is a big factor in determining the amount of lift at any given angle of attack, this is a big difference. It is compounded by the fact that the energy stored in the blades is affected by the mass and the speed it is traveling.
Also note the difference in disk area between the Raptor 30, with its 49-inch blade span, and the Vigor's 63-inch span. This is much bigger than the difference in weight between the two helicopters, so the disk loading (similar to the wing loading on a fixed-wing aircraft) is lower on the larger machine.
The reason I included these comparisons is simply to point out that there is indeed an advantage to the larger machines in performing autorotations. The higher tip speed on the Vigor increases the lift generated and the stored energy, while the lower disk loading means a more-efficient conversion of that energy into lift.
Most people learn to fly on a 30-size helicopter because of the cost savings, which means you will most likely be learning autorotations on a 30-size machine. That's fine—fly what you have. Be aware that it's not just pilot skills that let the local hot dog shoot smooth autorotations with long hang time at the bottom with a 60- or 90-powered helicopter. The helicopter is helping him or her look good.
If you are happily into forward flight and past the nervous-novice stages, you should be working on autorotations. A good first step, though not absolutely necessary, is to get rid of whatever cheap and light wood blades you were training with, and replace them with a set of composite blades.
The price of good-quality fiberglass or carbon blades has been coming down in the past few years, and you will be surprised at the improved performance. These blades tend to be stiffer, heavier, and more efficient, and they help the machine store and release energy more predictably during an autorotation.
Transcribed from original scans by AI. Minor OCR errors may remain.
