Radio Control: Helicopters
Paul Tradelius
4620 Barracuda Dr., Bradenton, FL 34208 E-mail: flytrade@earthlink.net
A few issues ago, I wrote about some of the simple and effective ways you can make your helicopter safer — to yourself and those around you. One of those ways had to do with carrying the helicopter and transmitter from the pits to the flightline.
My technique is to carry the transmitter in the left hand, with the left thumb holding down the throttle stick to make sure I don't have a runaway engine (should the wind blow my neck strap or shirt onto the throttle stick).
That comment got me an E-mail from Paul Eigisti (no hometown given), with an offer of one of his safe-flying practices. He wrote:
"In reference to item #7 in your June 1999 column: While your method is indeed good, and I've seen many pilots carry their equipment that way, I prefer another method. After I turn on the transmitter and receiver, and verify that the servos are functioning, I switch into throttle hold. Then I start the engine, and carry the helicopter to the flightline. Only when myself and the helicopter are in place, and I confirm that the throttle stick is in full down-position, do I turn off the throttle hold.
"Using this method, there is no chance of danger from the dreaded idle-up mode starts, or of bumping the throttle stick while carrying the helicopter to the flightline. Just my two-cents worth."
I like it. It solves the problem of something disrupting the throttle stick while the helicopter is being carried to the flightline. Even before that, though, it ensures that we don't start the engine in the idle-up mode. Not that this has ever happened to me, of course!
The only problem I can see is starting a cold engine. Some engines just need a little extra gas to get going until they are up to operating temperature and can maintain a good idle. However, the advantages of starting in the throttle-hold mode are certainly there, and I would recommend that you experiment with your engine to see if this technique would be suitable for you.
If your engine is hard to start in throttle hold, you may want to advance the throttle while checking the radio, but without the glow plug battery attached, and hold a finger over the muffler exhaust while turning the engine over with the electric starter. This will cause the engine to pressurize the fuel tank, and the open throttle will allow some fuel into the carburetor for easier starting. Bring the throttle back to idle, attach the glow plug battery, engage the throttle hold, and try to start the engine.
I received another interesting E-mail, asking my opinion about which helicopter kit is the fastest available. Unfortunately, I don't know who the requester is, because I only have his return E-mail address. But his interest in speed is something that comes up from time to time.
I'm not sure if there is one kit on the market that will fly faster than any other; what is important is that we understand what it takes to make a helicopter fly faster. It turns out that the principles for speed in a helicopter are about the same as those for other means of transportation:
- Light weight
- Low drag
- Plenty of available power
Weight
Imagine a helicopter is carrying a heavy load, so it takes all of the lift available just to keep it in a hover. With no excess lift, the helicopter can't climb or transition to forward flight.
Now suppose the extra weight is removed so the helicopter does have excess lift available. It can climb, accelerate into forward flight, or do a combination of both. Therefore, the lighter we can make the helicopter, the more excess lift will be available to make it go fast.
There was a time when many people thought a heavy helicopter actually flew faster than a lighter one; that was simply an illusion. When flying a heavy helicopter, you needed a strong engine and a lot of rotor blade just to get the helicopter to perform. That, combined with a slight dive to get the rock going downhill, gave the impression of a really fast machine.
Drag and Rotor Design
When we look at a standard pod-and-boom helicopter, there doesn't seem to be much we can do about its drag. The shape of the canopy, skids, and struts can be changed slightly to reduce resistance, which helps, but the real reduction in drag can come from the rotor system.
With the advent of highly maneuverable helicopters and 3D flying, rotor blade design has more or less settled on the fully symmetrical airfoil as a good compromise for all types of flying. Unfortunately, most things in aerodynamics are a compromise, and the full-symmetrical blade sacrifices some lift and increases drag when flying upright. If we wanted a helicopter to go fast, we wouldn't be interested in its inverted capabilities, and would want a rotor blade optimized for upright forward flight.
Reflex Airfoil
The best blade that comes to mind for speed is the old reflex airfoil. This is not a very popular rotor blade anymore, but it has a semi-symmetrical airfoil with a distinct upsweep to the trailing edge. I'm not sure of the exact aerodynamic principles behind the upswept portion, but it does seem to reduce overall blade drag while increasing lift.
Although I have never been particularly interested in increasing the speed of my helicopters, I have been impressed with the extra lift provided by such a blade when doing autorotations. I would therefore think that a reflex-airfoil blade would be a good starting point for extra speed, if you can still find them being produced.
Power
The last major factor in increasing speed is good, old-fashioned horsepower. The greater the power available, the faster we can turn the rotor blades and increase their pitch setting to propel the helicopter forward.
Conclusion
There is no single helicopter kit that is the fastest, because improvements can be made to increase the speed of any helicopter. However, I'm sure readers would be interested in hearing about your helicopters and what you have done to improve performance. I don't mean the triple-ball-bearing, gold-plated thingamajig, but what you have done to the engine, exhaust, rotor system, etc., that you really feel makes the helicopter perform better.
Let me know, and I can pass along the information in a later column. Photos would also be appreciated.
Transcribed from original scans by AI. Minor OCR errors may remain.
