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Old Jul 01, 2009, 07:55 PM
working to the closest cm
jirvin_4505's Avatar
brisbane australia
Joined Nov 2002
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Question
Testing mono winch line - semi scientific

Probably question for the modeling science forum but I will ask it here first.

I have tried various lines on the winch and they obviously display different characteristics. I have used alternate line to the name brands and am not convinced that they are a substitute for the good stuff (fischer/speedline etc)

I remember from way back when I did industrial arts at school (early 70's) that you could test the elasticity of material by graphing its extension vs load. hazy here.. When the curve changed the material entered the non elastic region.

Quite a few years ago I attended a free flight seminar where the presenter described a similar method to test the quality of rubber in his Wakefield models. The energy potential in the rubber was the area under the elongation vs weight curve.

Could the energy retention (assumption -quality) in a winch line be tested in the same manner?

Any suggestions before I hang a bucket of weights on the end of a meter of 1.3mm mono and start graphing some data?

cheers Jeff
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Old Jul 01, 2009, 09:45 PM
VHO
glider misguider
Armidale NSW Australia
Joined Feb 2007
564 Posts
Jeff,

Yes... go for it.

Are you thinking of Hookes Law, or something like it? I guess you will work out how elastic the line is (before permanent elongation). You will a lot of weights and a ruler.

Good to see you back in the shed.

Hutton
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Old Jul 02, 2009, 02:52 AM
launch low, fly high
New Zealand, Hawke's Bay, Havelock North
Joined Dec 2004
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Jeff,

One minor thing (actually, two minor things).

On your test, would recommend measuring the hysteresis. That is, take data when increasing the load on the line, and also take data as you decrease the load on the line.

Also, I would recommend taking data with various rates of change of line tension. Unfortunately, it will be a bit difficult to get data at the same rate of change as the line will see in the acceleration part of the zoom phase. It is also unfortunate that this measure of elasticity at a high rate of change of strain is very important!

My experience shows some lines have much higher hysteresis at high strain rates, and other line types have low hysteresis at high strain rates.

BTW, expect to see some non-linearity in the stress-strain curve.
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Old Jul 02, 2009, 04:44 AM
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Jeff,
The other thing to remember is that the nylons properties are very sensistive to moisture content, so expect significantly different result for line that has been soaked in a bucket and line that has say been exposed to 40C 10% RH for a few days, as would be expect of your line at an Australian nationals.

Dave, who is always there to make thing more difficult.
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Old Jul 02, 2009, 08:01 AM
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USA, CT, Hamden
Joined Oct 2002
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I did some testing by hand a long time ago, the results were so messed up due to the nature of the material to relax. When I had an Instron tester available a few years later I still found it difficult to fixture and program for real world conditions. Results again didn't show me as much as I could learn from going out to the field and launching.

I guess I never really learned much at the field either but it's more fun to fly than to test.
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Old Jul 03, 2009, 08:20 PM
Registered User
clovis, ca
Joined Feb 2004
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I think figuring out a way to measure how well the line returns the energy is what we're looking for. Who cares how much energy line will store if it can only return or release the energy slowly?
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Old Jul 03, 2009, 08:45 PM
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jirvin_4505's Avatar
brisbane australia
Joined Nov 2002
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Yes i have been thinking along the same lines Need some type of dynamic test.

Thought of doing a bungy jump test on it and trying to find a way to log the results.

Thought of attaching a weight and dropping it then seeing how far back up the weight bounced. Logging the results would be interesting!

Wondered if a video would be fast enough, or a ram 2 altitude logger (on a long enough piece of mono) even wondered if the accelerometers in the Kids Wii could be put to use.

Any ideas?

cheers Jeff
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Old Jul 03, 2009, 09:16 PM
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Use the line as a catapult, how far can you toss a weight.
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Old Jul 03, 2009, 10:29 PM
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United States, CA, Midway City
Joined Dec 2003
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I've been trying to source some line and wondering how one would test the line to see how good (or bad) it is.

I was thinking if I have the test equipment this is how I would run the initial tests.

Take a diameter. Stretch until failure. Note percentage stretch and force. Repeat a few times to get an avg. Repeat with various line diameter.

Now take another piece same exact line. Stretch to 90-95% of avg failure force. Return to relaxation. What is line length now? How fast was rebound?

Do that 100x and see how the line reacts. The line I just got to test claims to be able to stretch 400-500 times without losing its elasticity and strength properties.

I'll volunteer some of this line for some R&D
Thanks.
TL
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Old Jul 04, 2009, 03:33 AM
I do this for fun!
Sunshine Coast, Australia
Joined Sep 2004
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fnnwizard raises a good point;

how much tension are we actually pulling during a launch, relative to line break point, and how do both these parameters change during the (sometimes quite long) service life of the line?

On the other hand, given that each real life launch is a unique event due to the wind profile, air density, piloting and even model setup changes, is any form of testing going to provide information to inform line selection choices better than simply getting hold of some line and giving it a go?

Don't get me wrong here please, I'm a believer in the value of testing. It's just that the more I think about this the less clear I am on the actual value of the results for this case.

For example, if the test results say Brand X gives its energy up faster when stretched to 95% of breaking strain, the questions that arise for me are:

1. how much will the next batch vary in performance?
2. what is the effect of age?
3. what is the effect of water content?
4. what is its performance at other stretch factors?
5. does Brand X durability impact on its usability (i.e. does it nick and cut easily)?

In sum, I wonder if there would need to be such a mass of testing to get really useful information as to render the process unworthwhile?

Ken.
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Old Jul 04, 2009, 02:59 PM
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There is somewhat a baseline of what line to use for conditions. Of course, a lot depends on the model. Am I safe to assume that becasue time on the line does not count against you, as long as line doesn't break, one would want highest stretch and fastest return to relax state? This would then equate to highest launch? I've yet to do a real F3B launch, but am anticipating.

All the variables involve makes it seem like winching F3B plane is an art, but if the expert can share their experiences it's got to be more scientific... I would think, but perhaps I am wrong.

Oh here's a chart to I found to help me get a ballpark of line to order.

F3B Mono Line Chart
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Old Jul 09, 2009, 05:32 AM
I do this for fun!
Sunshine Coast, Australia
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Thanks for that link fnnwizard!

Ken.
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Old Jul 09, 2009, 06:32 AM
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jirvin_4505's Avatar
brisbane australia
Joined Nov 2002
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I've been discussing this with David H and maybe I could get some comparative results by using the sligshot option.

Preliminary idea:-
Use a length of mono to project a weight horizontlly off the end of a table . Distance travelled may then indicate the dynamic nature of the mono.

The slingshot method would allow me to extend the line slowly and hold it for say 20 seconds at the expected extension.

So how much weight should I project to give a meaningfull result comparative to accelerating a model in a dive?

How much load on 1.3mm line would be feasible?

Need to find myself heavy duty spring scales (fish scales) to measure pull on the line.

cheers Jeff


The
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