Safety Comes First
Box 4520, Milton FL 32572; E-mail: [email protected]
Control Line (CL) Question
I’ve always been intrigued by the speed of aircraft at CL events, and the airplane maneuvers that appear to defy physical laws.
CL airplanes move in circles so fast, you have to wonder what holds them together and keeps the lines attached. If you’ve never seen a CL airplane fly, consider spending a moment or two with local modelers to find out where they fly, and go watch—you’ll be amazed.
Although CL is fun to fly, modelers still have to be aware of the same safety concerns as their wireless counterparts, such as spinning props, engine and propeller noise, etc.
Dick Perry, the “CL Navy Carrier” columnist for Model Aviation, recently forwarded a question-and-answer E-mail to me that addressed the issue of CL safety.
How much pull should a line or model be able to withstand as it travels in tight circles? What is control line factor or pull?
Club Safety Officer William Crowley had a similar question:
“One of the members of our RC club decided to try some CL flying. As safety officer, the member asked me to check her aircraft over for airworthiness. I checked all the usual security of flying and control surfaces, hinging, and attachments, but I don’t know anything about the requirements for CL.
“I looked in our AMA Competition Regulations, but need help with how much pull the airplane should withstand. The airplane seems to be in the Carrier or Aerobatic group—it has flaps coupled with the elevator, it’s powered with a .35- to .40-size Fox engine (looks old) with a third-wire throttle setup.
“Looking in the regulations, page 50, the pull test should be 40 pounds. On page 28, the chart at the bottom shows figures such as 32G, with a pull test of two times the weight of the airplane in ounces.
“Two times the weight of a three-pound airplane—six pounds—is widely different than 40 pounds.
“What am I missing—can you clear this up for me? The modeler and I would sure appreciate your help—we want to fly safely!”
Dick’s Answer
“Thanks for the question, and especially for your interest in safety.
“The pull test for a Precision Aerobatics aircraft (page 50), with a .40 engine, assumes a relatively light model is flying at a speed appropriate for the event. The 32G (and higher) numbers listed at the beginning of the CL General rules section (page 28) are there to ease the math problem for someone with a scale, measuring weight in ounces.
“Using the 32G formula of twice the weight in ounces, the model you describe (three pounds = 48 ounces) would require a pull test of 96 pounds.
“The 32G pull tests are for Speed and Racing events in which models are quite different from the one you described.
“The model sounds like a Precision Aerobatics model, but it may be flown faster than what is usual for that event. My recommendation, to be sure you are on the safe side, would be to use a pull test of 20G (60 pounds), but the Carrier events in which I fly are generally considered performance events with higher speeds.
“I suspect a pull test of about 50 pounds would ensure safety in the conditions the model will be flying in. I would recommend three lines of a minimum diameter of .015 inches for the model. That assumes the three lines equally share the load during flight.
“The Brodak three-line bellcranks and handles share the load equally on all three lines. If the third line does not share the load, I recommend the elevation lines be a .018-inch diameter.
“If we run the math for a three-pound model, flying at 90 miles per hour (mph) on 60-foot lines, the flightload is just over 27 pounds. These conditions assume no acceleration induced by the pilot, crosswinds, turbulence, or other forces, which can cause occasional increases or decreases in the pull exerted by the model.
“The pull test is intended to provide a safety factor. In this case, using my recommendation would give a safety factor of two, which is about the minimum I’d use. If you find after flying the model, that the speeds are significantly lower than 90 mph, then a lighter pull test could be used for subsequent flying sessions.
“Be sure the area on the model that is held for the pull test is strong enough to carry the load without damage. The pull test should test the integrity of the model, as well as the control system.
“Good flying!”
Did you understand that? Heavier and faster models need stronger lines and structures to fly safely.
If you’d like to learn more about the hobby and/or get a more-detailed answer to a CL question, E-mail Dick Perry at [email protected].
Stability Unit (Futaba)
Although I haven't tried the Futaba unit myself, William says it keeps his airplanes so stable that he went out and bought another. He leaves them on full all the time; it makes the airplane extremely stable.
A nice feature of the Futaba unit is that it's proportional. Anything can be dialed in, from zero to 100%—whatever you want. Beginners start at 100%, and gradually cut down until they can fly with it off.
The unit senses the ground and the horizon, and adds appropriate servo inputs to keep the airplane level. The unit adds only three ounces to the airplane. Although I'm not aware of the price (TBA was expensive), it looks like I'll have to buy one and report on it in the next column.
Safety-Check Servos After Crashes
Flightline editor Jean Sellers provides the following safety tip:
- After a severe landing or crash, the servos need to be checked for damage to the gear trains.
- It is not necessary to open up the case; a real test is to rotate the servo output arm, without the servo being installed, and drive the gear train back through its reduction to the motor. This very severe test will show any weak or damaged gears by a ratcheting, or even a freewheeling action.
- If you decide to replace the gears, make absolutely certain that you find and remove all the broken teeth, as they are sometimes the same color as the silicone grease used to quiet the gear action. Check for teeth stuck into the wood gears, and look where the motor pinion is located for more hidden parts.
- When you install the output gear, be very careful that you orient it in the correct direction, to allow full circular travel looking at the position of the end-stop molding.
- Also check electrical connections for vibration damage and/or broken solder joints, usually found in servos with long wires attached to the motor.
Safety Check Antennas Regularly
These days, antennas come in all shapes and sizes, but they need a going-over once in a while to ensure continued operation.
- If you have a metal antenna, look it over regularly. Extend it to its maximum length and shake it up and down. If it collapses by sliding backward, replace it.
- Make sure you clean the antenna regularly. I use WD-40™ to lubricate and keep internal appendages clean.
- If you break the antenna, you can solder the pieces together with brass tubing while you wait for a replacement.
- Check antennas that screw into a threaded base by twisting them after extension. This ensures that they won't come loose while you are flying, and cause crashes. I know many modelers who lost airplanes because the antennas were not screwed down properly and/or fully extended.
- Receiver antennas also require maintenance. Keep the outside clean and oil free, and ensure it's routed at least two inches away from other wires in the aircraft.
- If the antenna gets shortened for some reason, send it in to get repaired, or call the manufacturer to inquire about the appropriate length. Most manufacturers will be happy to send additional wire that can be spliced onto the old and shrink-wrapped, or that can be used to replace the old. Depending on your level of electronic repair ability, splicing to the correct length is all you really need to do.
Until next month, keep the ailerons moving! MA
Transcribed from original scans by AI. Minor OCR errors may remain.
