Safety Comes First
2812 Northampton St., N.W., Washington, DC 20015
This column addresses items of concern regarding safety aspects of model aviation activities. Content is the opinion of the author and does not necessarily represent the official position of the Academy of Model Aeronautics.
Sharing airspace with full-scale planes? Use caution! Helicopter preflight checklist. Learn how wind affects an RC plane's flight path for safety.
Fatal Attraction
Back in the September 1980 issue of Model Aviation, a columnist mentioned an incident on the West Coast involving a collision between an RC sailplane and a hang glider. Fortunately, the hang glider pilot suffered no serious injuries. The columnist commented that "simultaneous operation of RC sailplanes and hang gliders on essentially the same site appears to be a hazardous pursuit."
The October 1987 issue of the British model magazine Radio Control Models & Electronics (RCM&E) recently discussed another collision between a Slope Soarer and a hang glider in which the hang glider pilot suffered fatal injuries at Devil's Dyke, Sussex, England. No matter where you fly, if you share airspace with other aircraft—full-scale or models—there is an ever-present risk of collision.
The circumstances of the two incidents, some seven years apart, were similar enough to warrant a short discussion of the Devil's Dyke accident as a caution to those who fly RC sailplanes on slopes shared with hang gliders.
Apparently there had been previous cooperation problems at Devil's Dyke. An agreement had been worked out: hang gliders would confine their activities to the area to the left of the public house (pub), while RC fliers would use the area to the right.
On May 10, 1987, a model flier launched a Salto sailplane late in the afternoon. After flying about 10–15 minutes, he observed some hang gliders drifting into the airspace normally used by model fliers. Recognizing a potentially dangerous situation, the modeler elected to land his sailplane promptly. However, during the downwind leg of his approach a hang glider suddenly appeared in his field of vision. Despite attempted evasive action, a collision occurred.
A point close to the wing root of the sailplane struck and severed a 3 mm‑diameter flying wire on the hang glider's starboard wing. The hang glider's starboard wing promptly failed and was shortly followed by failure of the port wing. From an estimated altitude of about 80 ft., the hang glider pilot had insufficient time to deploy his parachute and sustained fatal injuries upon impact with the ground.
The model's weight of approximately four pounds, together with an estimated closing speed of 45–60 mph, generated forces the hang glider's flying wire could not withstand. At the inquest the verdict was "death by misadventure," meaning the deceased accepted the element of risk inherent in the activity; no charges were filed against the model sailplane pilot.
As anyone involved in a model-to-model midair collision will recall, concentration on flying one's own model often means that when a second aircraft appears in the field of vision, it is generally too late to take effective avoiding action.
Recommendation: if you fly on a slope where airspace may be shared with full-scale aircraft, have an observer present at all times whose sole job is to alert model pilots to encroachment by full‑scale aircraft. If your slope-soaring is a club activity and the slope is shared with a hang-gliding club, work out an amicable agreement between the clubs to minimize or eliminate the possibility of midair collisions.
Helicopter safety
In the October 1987 issue the Safety column carried an article sent by a reader that stated, "Because of the high degree of complexity and the greater number of moving parts, helicopters are probably more prone to mechanical failure than fixed‑wing models." A recent letter from Lt. Col. Paul Tradelius took issue with that statement.
Paul pointed out that, unlike many fixed‑wing models, mechanical parts of helicopters—such as control linkages—are often exposed and can therefore be inspected easily. Their added complexity doesn't necessarily make them more prone to mechanical failure if the flier performs a thorough preflight inspection.
I asked readers for a preflight checklist for helicopters; Paul responded and included such a checklist. Some parts of it may apply to fixed‑wing models as well.
Preflight checklist for model helicopters
- Always remember Murphy's Law: if something can go wrong, it will. Never assume that because a particular part has not given trouble in the past it will continue to work properly. INSPECT EVERYTHING.
- Never assume that something which isn't working correctly will be good enough for one more flight. Whatever is not working correctly will not fix itself, and things can only go from bad to worse.
- Get into a preflight routine and stick to it. Build a habitual pattern of checking everything in a certain sequence and way. Write a checklist if needed and add to it when you find other suspect areas.
- Some things to check on every helicopter:
- Give the overall helicopter a general examination. Look for cracks, loose parts, broken screws, warped or buckled components. Check welds and solder joints. Check engine or motor mount and firewall for cracks or loose bolts. Check main shaft for burrs, rough spots, or excessive play; verify hubs or drivers are secure.
- With the canopy removed, check that the radio installation is secure. Inspect the battery installation, switches and wiring for chafing, loose connectors, or pinched wires. Ensure wires are in place and properly tied down.
- Check servo installation and mounting; make sure servos are secure and that servo arms, clevises, and control horns are tight. Check linkages and pushrods for straightness and freedom of movement. Check pushrods from servos are secure to the servo arms and respective bellcranks; look for worn ball links and loose balls.
- Inspect the rotor head, flybar, and blade grips. Check rotor blades for nicks, delamination, cracks, or imbalance; make sure blade bolts and retainers are tight and that blades track properly.
- Check the swashplate and cyclic/collective linkages for free movement and correct operation. Verify control directions and proper travel on the transmitter and that endpoint adjustments are correct.
- Check tail assembly: tail boom, tail rotor hub and blades, tail drive (belt or shaft) for wear, proper tension and alignment. Inspect bearings, keepers and mounting for security. Check tightness of tail rotor drive setscrews; do not overtighten setscrews or they will become rounded. Turn the tail rotor gently by hand and feel for rough spots or binding.
- Inspect the horizontal and vertical fins.
- Turn the main rotor by hand in each direction and check for rough spots or binding.
- Inspect fuel system (or electrical power system) thoroughly. For glow/gas models check fuel lines for cracks and leaks, check tank for secure mounting and venting, and ensure fittings are tight. For electric models check battery condition and mounting, connectors and ESC wiring.
- Check engine or motor mounting, clutch or prop driver, muffler or exhaust connections, and that the glow plug or electronic ignition is functioning properly. Check clutch, starter shaft, main drive gear, and tail rotor drive gear move freely and mesh properly.
- Check that landing gear, tail boom, and braces are secure. Check tail rotor blades, blade holders, bellcranks, bellcrank arms, etc., for wear or damage. Lightly oil head and bearings where needed; oil lightly where appropriate on tail components.
- Do a final check of all fasteners and tighten as necessary, then perform a ground-range and control check before attempting flight. Turn around radio equipment and check both the radio and control movement for slop-free and smooth operation.
If any other helicopter modelers wish to comment or add to the above items on Paul's checklist, I'd be interested in hearing from them.
Wind
In the November 1987 Safety column I reprinted part of an article from a club newsletter explaining how to perform certain aerobatic maneuvers for Pattern contests. The part I reprinted concerned the Stall Turn and included the author's statement that when a Stall Turn is performed in a crosswind, the direction of the turn should always be into the wind rather than away from it.
About half a dozen readers responded. While most agreed that in a Stall Turn performed in a crosswind the turn should be into the wind, not all had the correct reasoning.
First, I'm talking about a steady‑state wind. Effects of wind shear, gusts, etc., are not part of this discussion.
Second, the pressure (or force) exerted on a model's tail by a crosswind exists primarily when the model is in contact with the ground. Once a model is airborne, there is no such thing as a crosswind relative to the model—once airborne the only wind it experiences is that due to its own motion through the airmass. In other words, the wind is always dead on the nose (except during a sideslip, when by definition the airplane has a sideways component of motion relative to the air). Thus, a "crosswind" for the model exists only to the extent that the airplane is moving sideways through the air.
If you follow competition aerobatics (model or full‑scale) where judges are seated on the ground, maneuvers must look correct relative to the ground to score well. Assume a crosswind blowing directly toward the flight line (90° to the flight line). If an airplane is to appear to the judges as a vertical climb, its axis will actually be angled into the wind. Similarly, after the turn portion of the maneuver is accomplished, the airplane must descend in a direction that appears vertical to the judges, again requiring the model's axis to be angled into the wind.
Because during both ascent and descent the aircraft's axis is angled toward the apparent wind, the airplane does not have to rotate a full 180° during the actual turn if the turn direction is into the wind. If a turn is attempted away from the wind, the axis must rotate through an angle greater than 180°, which takes longer and appears to the ground observer as a larger turn radius. Visually, this can make the maneuver resemble a Wingover rather than a Stall Turn, since the easiest recognizable difference between those maneuvers is the radius of the turn.
You may wonder why an article on aerobatics appears in a safety column. Consider this incident from a letter I received from Stasi Poulos of Dallas, TX:
"I was recently helping a newcomer to RC flying. He had soloed and become quite confident. He had lost almost all his fear about flying in the wind. One day I watched him take off into a 15 mph steady headwind. His ascent was beautiful until he turned downwind. He throttled back since the plane seemed to pick up so much speed on the downwind leg. The plane banked slightly, and he tried to correct with ailerons. In horror he hollered that his ailerons weren't working at all. Yet he still had throttle and elevator control. Convinced he had a mechanical or radio failure, he handed me the transmitter. I regained control, landed, and tried to explain what had happened.
"When the plane turned downwind, its airspeed did not change, but its speed over the ground did. My student felt the plane was passing him too fast. His solution was to throttle back. He failed to realize that while he reduced the speed at which the plane passed him, he had no real indication of the plane's airspeed. He had reduced the airspeed until the plane stalled. Ailerons change the lift of an aircraft's wings, and if there is no lift, they can swing all they want and you'll never know the difference. My student said, 'No way! The plane wasn't moving that slow.' What he really saw, however, was a stalled plane in a moving air mass."
Stasi's incident suggests how many radios may have been sent off for repair for failures that did not actually occur. An appreciation of the visual effect of wind on our models' flight characteristics has a direct bearing on how safely we fly.
Have a safe month, and watch out for those downwind turns!
Transcribed from original scans by AI. Minor OCR errors may remain.
