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I am about to make up some tow lines for my new electric tow plane design, the Pulldog. This tow plane will be used to tow sailplanes up to around 18 lbs. I will be using yellow braided nylon #18 Mason's line for the main portion of the tow line. From everything I have found on the web, this line is 135 to 170 lb test. Before I make up several tow lines, I have a few comments/questions.
1) The whole subject of weak links puzzles me greatly. All the weak links I have seen used are in my opinion far too strong to serve as an actual weak link. I have yet to see a sailplane in trouble on tow break a weak link. It would seem the only benefit is the smaller diameter line size at the sailplane end which allows easier hook-up to the tow release.
2) Sometimes I have seen a weak link used on the tow plane end. I fail to understand why one would go to the trouble of using a tow line that is 150 to 250 (or more in some cases) lb test and then attach it with a line that is perhaps 70 lb test. With this set-up, to me, the tow line is only actually good for 70 lb. maximum. The only benefit I can see is protecting the tow plane in the event the tow line snags a fence, bush, or other ground based object on final approach. In this case the weak link might break and save the tow plane. But again, we really have only a 70 lb test tow line using a weak link at the tow plane.
3) At the sailplane end I can see the benefit of a weak link, assuming it is actually weak enough, to save a glider if the tow gets way out of shape and the glider and the tow plane can't release for some reason. But again, I've never actually seen a glider break a weak link on tow. Also, the weak link would need to be sized appropriately for each particular sailplane, and from what I have seen at aerotow events, the sailplane weak link tends to be a "one size fits all" approach.
4) Flags on the tow line. I have seen flags, ribbons, and streamers of various sizes used on tow lines. My observation has been that regardless of their original shape, they tend to get long and thin in the airflow, and thus not as visible as hoped. All of these various flags can be seen at lower altitudes, but I must admit I can't see them at release altitude, where it would be nice to know positively that the tow line has released from the sailplane. Also, in some cases, usually with smaller/lighter sailplanes, these flags tend to cause a fair amount of sag in the tow line in front of the sailplane, generating a nose-down moment on the sailplane. It is my belief these flags are not needed for drag on the tow line after release, and considering the lack of visibility at release altitudes, I find myself wondering if a flag actually serves any useful purpose.
So based upon all the above, I plan to make a tow line for my Pulldog that has the following features:
1) No weak links. On the tow plane end I plan to use a 10' length of the Mason's line, attached to the 90' main portion of the tow line with a swivel, and just put a loop in the front end that attaches to the release pin on the tow plane. This will allow me to change out the 10' section due to expected wear and tear. On the sailplane end I will have the usual swivel and snap assembly so the pilot can attach my tow line to his weak link. The sailplane pilot can use whatever weak link he feels is best for his sailplane.
2) I will have just one yellow ping pong ball on the towline, immediately ahead of the snap swivel assembly. The purpose of this is to make the end of the tow line easy to find on the ground.
So in summary, my tow line will be made entirely of yellow #18 Mason's Line, with a separate 10' section at the tow plane attached with a swivel, and merely a loop at the front to attach to the tow plane release pin. There will be another 90' of Mason's line going straight to the snap swivel assembly, with a yellow ping pong ball placed onto the line immediately ahead of the snap swivel assembly.
Comments, please. Am I all wet here?
HD
1) The whole subject of weak links puzzles me greatly. All the weak links I have seen used are in my opinion far too strong to serve as an actual weak link. I have yet to see a sailplane in trouble on tow break a weak link. It would seem the only benefit is the smaller diameter line size at the sailplane end which allows easier hook-up to the tow release.
2) Sometimes I have seen a weak link used on the tow plane end. I fail to understand why one would go to the trouble of using a tow line that is 150 to 250 (or more in some cases) lb test and then attach it with a line that is perhaps 70 lb test. With this set-up, to me, the tow line is only actually good for 70 lb. maximum. The only benefit I can see is protecting the tow plane in the event the tow line snags a fence, bush, or other ground based object on final approach. In this case the weak link might break and save the tow plane. But again, we really have only a 70 lb test tow line using a weak link at the tow plane.
3) At the sailplane end I can see the benefit of a weak link, assuming it is actually weak enough, to save a glider if the tow gets way out of shape and the glider and the tow plane can't release for some reason. But again, I've never actually seen a glider break a weak link on tow. Also, the weak link would need to be sized appropriately for each particular sailplane, and from what I have seen at aerotow events, the sailplane weak link tends to be a "one size fits all" approach.
4) Flags on the tow line. I have seen flags, ribbons, and streamers of various sizes used on tow lines. My observation has been that regardless of their original shape, they tend to get long and thin in the airflow, and thus not as visible as hoped. All of these various flags can be seen at lower altitudes, but I must admit I can't see them at release altitude, where it would be nice to know positively that the tow line has released from the sailplane. Also, in some cases, usually with smaller/lighter sailplanes, these flags tend to cause a fair amount of sag in the tow line in front of the sailplane, generating a nose-down moment on the sailplane. It is my belief these flags are not needed for drag on the tow line after release, and considering the lack of visibility at release altitudes, I find myself wondering if a flag actually serves any useful purpose.
So based upon all the above, I plan to make a tow line for my Pulldog that has the following features:
1) No weak links. On the tow plane end I plan to use a 10' length of the Mason's line, attached to the 90' main portion of the tow line with a swivel, and just put a loop in the front end that attaches to the release pin on the tow plane. This will allow me to change out the 10' section due to expected wear and tear. On the sailplane end I will have the usual swivel and snap assembly so the pilot can attach my tow line to his weak link. The sailplane pilot can use whatever weak link he feels is best for his sailplane.
2) I will have just one yellow ping pong ball on the towline, immediately ahead of the snap swivel assembly. The purpose of this is to make the end of the tow line easy to find on the ground.
So in summary, my tow line will be made entirely of yellow #18 Mason's Line, with a separate 10' section at the tow plane attached with a swivel, and merely a loop at the front to attach to the tow plane release pin. There will be another 90' of Mason's line going straight to the snap swivel assembly, with a yellow ping pong ball placed onto the line immediately ahead of the snap swivel assembly.
Comments, please. Am I all wet here?
HD
I have been flying with a 70lb. weak link on the towplane end of all my towropes since the 1990's and have never had one break.
AAA TT TN
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