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Attachment points - can someone explain safety issues?


Dave24
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Can anyone explain the safety issue thing with low or high attachment points?

I wasn't aware of safety problems and as a newbie would like to avoid getting caught up in any problems.

I tried to follow the recent link discussing it, but came away feeling lost since there wasn't a basic explanation of what the problems are.

Thx

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Thanks for the link.

I've read the articles but don't see any safety issues. I see the point that low hang points cause you to "wobble" under power more, but gives you a better ability to weight-shift. The opposite is true for high hang-points.

I also see the comment that you get used to either way and notice that many people/motors use low and many use high hang-points.

Is there something I'm missing, because I've heard about the "dangers" of low hang points, but don't actually see what the safety issue is.

Thanks for any advice on this.

Dave

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'Dangers' might be too strong a word, more potential design vulnerabilities?

If an arm breaks under load then you could be faced with an uncontrollable spiral due to the asymmetric loading. I believe this effect has been cited in one accident report. I know one very experienced instructor/constructor who prefers the high hang-point configuration for its inherent safety in this respect.

Perhaps others more experienced could comment on the theme?

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Fanman,

Thanks for highlighting that important distinction. Lazy writing - yes, as i understand it, It is indeed component failure that mostly raises concerns, not necessarily the actual arm itself which tend to be easier to engineer strength and reliability into.

To be more correct then; I point toward the whole assembly and the general design philosophy (swing arms in general) and their potential vulnerability.

A graphic illustration of your point just received by email. The letter below discusses the question being raised here rather well.

The letter, provided by the gentleman I referred to a short while ago, makes very interesting reading, particularly given the credentials of the author and his approach to the problem studied.

Investigation into the failure of a swinging arm mounting bolt on a Clemente Snap 145 Paramotor.

The lesson for me here is of the vital importance of a thorough pre-flight inspection.. every time.

  • Should we might consider 'self-lifeing' the critical components that are under repeated, regular strain?
    Replacing these components (correctly with manufacturer approved items) after a suitable interval (flying hours) or when they show any sign of wear might contribute to our safety by preempting a failure.

Sounds like one for our Engineering Members. Alan and Pete B might have some input for us.

As ever - all comments and views welcome.

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sounds like the man knows his stuff........:) as I am not going to have a fixed or high hang point again because I have been there ....before

And I dont like them...... :coptor:

You should be able to get them from any iron mongers possibly DIY store.

Parajet are the safest as far as I'm concerned in this area as the pin through the swing arm is supported on both ends.

Sorry about the poor picture

http://picasaweb.google.co.uk/lh/photo/MCY6x4eTTV5RqjaAH2EZng?authkey=Gv1sRgCJLFseGUvqOqIg&feat=directlink

http://lh3.ggpht.com/_sw1nEFvUHPI/SilQWc4Q2iI/AAAAAAAABfc/0voaOtB-v18/IMG00016-20090604-1235.jpg' alt='IMG00016-20090604-1235.jpg'>

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sounds like the man knows his stuff........:) as I am not going to have a fixed or high hang point again because I have been there ....before

And I dont like them...... :coptor:

You should be able to get them from any iron mongers possibly DIY store.

Parajet are the safest as far as I'm concerned in this area as the pin through the swing arm is supported on both ends.

Sorry about the poor picture

http://picasaweb.google.co.uk/lh/photo/MCY6x4eTTV5RqjaAH2EZng?authkey=Gv1sRgCJLFseGUvqOqIg&feat=directlink

http://lh3.ggpht.com/_sw1nEFvUHPI/SilQWc4Q2iI/AAAAAAAABfc/0voaOtB-v18/IMG00016-20090604-1235.jpg' alt='IMG00016-20090604-1235.jpg'>

And once the cage is in place it's not possible for the pin to come out.

Should I be looking at replacing the pin periodically along with shackels and fittings? I just upgraded to stainless carabiner.

Tom :acro:

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sounds like the man knows his stuff........:) as I am not going to have a fixed or high hang point again because I have been there ....before

And I dont like them...... :coptor:

You should be able to get them from any iron mongers possibly DIY store.

Parajet are the safest as far as I'm concerned in this area as the pin through the swing arm is supported on both ends.

Sorry about the poor picture

http://picasaweb.google.co.uk/lh/photo/MCY6x4eTTV5RqjaAH2EZng?authkey=Gv1sRgCJLFseGUvqOqIg&feat=directlink

http://lh3.ggpht.com/_sw1nEFvUHPI/SilQWc4Q2iI/AAAAAAAABfc/0voaOtB-v18/IMG00016-20090604-1235.jpg' alt='IMG00016-20090604-1235.jpg'>

And once the cage is in place it's not possible for the pin to come out.

Should I be looking at replacing the pin periodically along with shackels and fittings? I just upgraded to stainless carabiner.

Tom :acro:

What ever you feel comfortable with, If you feel that you are happy taking them out and inspecting them for wear (visable ) then do that if not then replace them every 12 months.

depends on how much value you put on your own peace of mind.

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