Safety Comes First!
This month: Required reading for all CL fliers. Some good reminders about basic safety factors. Also, a note on gasoline in plastic fuel tanks.
John Preston
Introduction
As we promised in last month's safety column, the subject this time is safety in the control-line (CL) circle. Unfortunately, we have not been active in CL flying for many years, so all the material presented here comes from letters we've received from readers or articles that have appeared in club newsletters. We thank all the correspondents for the time they have taken to put their thoughts and experiences on paper.
A letter from Larry Miles of Mission, KS, is partly responsible for this column. Larry states:
"As the cost of oil continues to rise, cars keep getting smaller, the cost of modeling supplies rises and more people start looking for more inexpensive recreation, I believe that CL activity is going to take a sharp turn upward within the next few months. More and more people will start using school playgrounds, parking lots, neighborhood parks, etc., to fly their new planes. Many of the pilots will be beginners, unaware of the safety hazards unless they are forewarned.
"I believe that it would be worthwhile if you wrote a column of the basic do's and don'ts that would protect spectators, participants and aircraft. It might also be useful if you suggested to engine and kit manufacturers that they print a bulletin for inclusion within their engine package and/or kits similar to that column. Such an article would also serve as a good reminder to those who've flown for a number of years but for whom such basics have faded from our memories. I think we could all stand such a reminder."
We agree wholeheartedly with Larry that a list of do's and don'ts on CL (and, for that matter, also on RC and FF) operations would be a useful addition in promoting safe flying. However, as we previously stated, CL is not our strong point. On the other hand, if any readers would like to have a go at compiling such a list we would be glad to publish it for comments from our readers and see what we could do to publicize it. How about it? Any takers?
If we can find somebody to draft a "Safety Guidelines for CL Operation" document, perhaps they can make use of some of the following material that we have received.
Flying near power lines
First, another letter from Ken McClenahan, the electrical engineer who made some comments on our previous column concerning electrocution deaths of CL fliers due to contact with overhead power lines. Ken's letter has some suggestions concerning safe distances to keep in mind if you have to fly in the proximity of high-voltage power lines. We have been unable to come up with any positive recommendation even after looking at the National Electrical Safety Code (NESC), which is the bible to those involved with stringing power distribution lines, etc. Ken states:
"If you refer to the NESC, you should keep the following in mind:
- To the best of my knowledge, there have been no experiments on the subject of a human waving a 60- to 70-foot long conductor in the general direction of an energized overhead power line. One should always be extremely cautious when empirical evidence is lacking.
- Control-Line pilots are prone to wander around, especially in the downwind direction. Therefore it is advisable to use safe clearance values which are much more conservative than those listed in the NESC. Not being an expert on the subject, I didn't offer you any values for safe clearances, but I now think that I should offer my gut feelings on the subject, anyway, because you are unlikely to ever come up with a truly satisfactory answer (Amen, J.P.)."
Let the minimum safe distance be (K + n) feet, where n is the number of insulators in a string of suspension insulators on the overhead power line (no recommendation is made concerning pin, post or stick-type insulators, since there is no obvious way to relate these insulator types to the voltage on the line), and K is a constant with the following values:
- K = 30 when flying downwind from the line.
- K = 60 when flying crosswind from the line.
- K = 90 when flying upwind from the line.
- Add 60 ft. to K when flying a multiple-pilot event such as Combat.
The clearance should be considered to be the distance between the outer edge of the flying circle and the nearest point directly below the nearest phase conductor of the overhead power line.
Incidentally, the site used for Combat at the Nats last year had a clearance of about 30 feet both downwind and upwind. Needless to say, I thought it was an extremely hazardous location even though I flew anyway. Perhaps the AMA needs to have rules on the subject.
The last paragraph in Ken's letter may have been in response to a comment we made about CL at the 1979 Nats in our last letter to him. Perhaps, indeed, the AMA should have some rules on safe operation of CL and other types of models, too. We recently wrote to our district VP, Chuck Foreman, suggesting that the AMA should have a permanent safety committee. Chuck introduced this as a motion to an Executive Council meeting, and it was defeated until "more information from the submitter of the idea is presented." Unfortunately, the submitter doesn't seem to have had five minutes to himself recently to follow up on this. Perhaps when our busy summer schedule lets up we will get back to it. Any comments from readers on the formation of a safety committee will be welcomed. Send them to me.
Line integrity and end fittings
While electrocution may be a hazard to the flier of a CL model, being struck by the model or one of its component parts is more likely to be a hazard to the bystander or helper. Unlike RC or FF models, the path of a CL aircraft is fixed, and unless somebody strays into the circle, collision with a person should be a remote possibility. However, as most CL fliers know, lines can break, and engines have been known to come loose for one reason or another. We have received several letters on the subject of line integrity and one concerning breakage of engine mounts.
Larry Miles (again) has some suggestions to minimize the possibility of line breakage due to either fatigue or abrasion (or both) at the point where the line exits from the end fitting. Apparently, end fittings that use a copper or soft-brass sleeve, usually in conjunction with a brass thimble, may suffer from this problem. Figure 3 on page 16 of the current AMA rule book shows such an end fitting. The solution, to quote Larry: "A drop or two of epoxy at all points where the line would normally abrade against the end fitting has proven satisfactory. Solder might be better, though I was unable to get the solder to adhere to the cables."
We ran this suggestion past Ron McNally, chairman of the CL Contest Board. Ron's response was as follows: "The crimped tube ending for stranded control lines as illustrated in the AMA rule book, Fig. 3, p. 16, and as supplied on some ready-made lines, has a number of failure modes. The crimp itself probably always weakens the line to some extent. In my experience, when new lines fail during the pull test, they fail at the crimp. Neither factory crimping nor competitor crimping have a monopoly on this form of failure. Another failure mode occurs because the crimp creates a concentrated flexure point. A drop of epoxy may help, and in any case it shouldn't hurt much. I would not recommend solder, as this would only create another concentrated flexure point. The soldering heat may seriously weaken the lines, and the flux may, in time, also weaken the lines."
Ron concludes: "However, if you really want to do things right, you should use the method illustrated in the AMA rule book, CL General, Fig. 2, p. 16. This method, if done properly, creates an ending which is as strong as the lines themselves. It is not difficult to do properly; just don't create any kinks or sharp bends."
Another letter that pointed out the shortcomings of crimped ends on control lines was received from Jack Finkenhalt of Astoria, NY. Jack also had another safety tip to offer: "Flying Control Line (models) where high grass is involved presents a hazard to the flier. I have seen lines snag in grass at takeoff. The model, turning inward, left the ground and nearly struck the pilot."
Line clips and pull tests
Before leaving the subject of control-line integrity, a word about line clips. The best end fittings in the world will not help if the line clips let go. Mike Anderson, editor of the Sunbeam, newsletter of Ames Sundowners MAC, writes: "… double check your clips every time you walk past them. Check them on the way to the center of the circle and on the way back after a flight. Check them when you walk the lines for kinks and on the way back again...."
One last check to make is a pull test. Each plane and each set of lines should be pulled once a day. Just give a good pull on the handle while someone holds the plane. If you're going to pull the guts out of it, it might as well be on the ground.
We would like to draw attention to the pull-test chart which can be found in the current AMA rule book on page 15. If beginners feel that the forces specified in this chart appear to be excessive, we would ask you to watch the film footage on two multi-engine Scale CL models in the film Modeling's Grand Illusions. The angle at which the lines have to lean to restrain these models is a perfect example of the forces that can be generated in the lines.
Engine mounting for profile fuselages
To wind up the discussion of CL safety, we have some suggestions on engine mounting from Doug Dahlke of Oshkosh, WI. Doug sent us a sketch of a stunt model with profile fuselage which showed how the engine bearers were continued rearwards to terminate above and below the wing. Doug calls this approach "profile proof" and states, "This is the single most important thing you can do to a profile to improve engine run and safety together." Apparently, there are profile kits on the market in which the bearers terminate some distance ahead of the engine mounting, creating a weakness that could lead to the engine parting company from the fuselage.
Gasoline and plastic fuel tanks
One final note before signing off for this month. In our last safety column we stated that, despite some stories that are going around in modeling circles, gasoline does not dissolve either Sullivan or Kraft fuel tanks. During this last month, we have heard that Byron Originals has issued a bulletin advising against the use of gasoline in the Sullivan tank that has apparently been supplied with their kits. Despite their advice, we have no evidence to change our previous position.
John Preston 7012 Elvira Court Falls Church, VA 22042
Transcribed from original scans by AI. Minor OCR errors may remain.
