Bungee replacement with alternative

[Neil Spooner]

Hi All,

Has anyone applied for a Mod' from the LAA re' the replacement bungees? If so it would be worth applying for a "Standard Mod" so others can use it without the aggravation of applying for a new mod' each time.

The photo shows a Nipper that has been modified, tho' I can't remember who it is!!

Neil

041.jpg (62.48 KiB) Viewed 17806 times

[Pat Blenkinsopp]

Great idea Neil.I would support that one, and have some of my own ideas on that.
It would save us all a lot of agro and expence. I need to replace mine soon
so might consider submitting the mod myself.
Will keep you posteed.
Kind regards,
Pat

[NeilD]

I'd apply for the bungee mod also.
Do we have any details on the bungee spec used in that photo?

It would actually be cheaper to buy the bungee, and pay the mod fee than get a new set of rings.

Neil

[Neil Spooner]

Hi All,

In order to pursue the mod', may I ask if anyone has a set of original bungees they could loan me to do a non destructive test. I believe the LAA will want to know what tension-per-displacement the originals are in comparison to the proposed ones, so a serviceable set (rather than remove mine) to do the test on would be great. I will buy a set of the proposed replacements and do the test if you like.

Neil

[NeilD]

Hi,

If we have a single original neiman ring, we can calculate the required bungee modulus. ( even if it is broken)
Strength will be greater in the bungee due to the strand form. If we duplicate the cross sectional area, that should satisfy requirements for the tensile strength. With specific calculation we may be able to reduce the csa, as the bungee form does not pack itself quite so well as the rings. We do need the modulus to give similar deformation under load.

Does anyone have the plans showing the rings? there may be a material property specified, ie hardness, Elongation at break, Ultimate tensile strength, and a modulus at 100% elongation.

[Neil Spooner]

Hi Neil,

Great to have an engineer on board! Alan Ayles may have the detail of the material. I have just remembered I have a spare set of nose rubbers, which are the same as one set of mains cut in half. I won't be able to do the comparison for another couple of weeks due to personal reasons. If anyone wants to "take up the batton" in the mean time feel free.

Neil

[microlightgary]

Is anyone running with this? I'm slowly working through Permit niggles on KI but I still need to replace the rings or fit bungees...
Personally, I think fitting bungees is a far superior solution, providing of course that they offer the same level of shock absorption on landing...

[Neil Spooner]

Hi,

I have a set of nose neeman rings (new) which are the main ones cut into half width, if you want to order a set of bungees, have them mailed to me, I can do a comparitive load test on the bungees to assess them. Once we have the data we could do a mod' request, I can then mail the bungees to you for fitting. (assuming all works out) Or I can send my 'rings to you to do the test.

My main neeman rings are almost new, so I have no need for bungees in the immediate future.

Neil

[NeilD]

Hi,
I should have some rings arriving for test soon - an original nose set, and my old mains.
We'll need to to check them for elongation vs load to do a comparison.
Depends if the LAA would prefer technical design data or just a demonstrative load/deflection and ultimate load test.

NeilD

[Neil Spooner]

Hi Neil

I will email Francis now and see if I can get a decision.

NeilS

[Neil Spooner]

Hi Neil,

I have had a reply from Francis, he says a load/deflection test is fine. I have a spare Nipper fuselage here with u/c fitted, so it would be very easy for me to do the test if you wish. Alternatively a jig could be made and used I am sure.

NeilS

[NeilD]

Hi Neil,

If you have a fuz set up , that would be ideal. no arguing with the data that way.

How do you plan to load it??

We may find that more bungee is required than will fit on the spools neatly though, as the packing density will not be as high.

[Neil Spooner]

Hi NeilD,

I will use the jig I used for my wing load test to bolt the fuselage to the workshop floor inverted; fit just one side of the Niemen Ring set to the u/c; with an electronic strain gauge measure load/distance. Then do the same test with just one LAS 1080HD bungee. That will give me a comparitive load test. Someone on the continent is already using these bungees, and I am told gets very similar ground handling characteristics. See the photo at the beginning of this post. This bungee is fitted incorrectly I feel, as the "crossover" needs to be underneath so that the "retraction" of the u/c isn't compromised with the a/c airborne (as it is on the forward bungee that you can't see) I can imagine this setup may be easier to fit, so you may not need the special tool I designed.

I will do the paperwork and photo log of the test for presentation to the LAA, which you can "top & tail" as you wish to present as a mod' request. If you ask for a repetative mod' to be considered it may be possible to reduce the effort for other Nipper owners to get the mod' approved at no cost......?

If you are happy to order and send me a pair of the 1080HD bungees available from LAS then I will do the test as soon as I am able. (My Niemen rings are in good condition, so I don't want these new ones on the shelf waiting to be used and going off!)

NeilS

[NeilD]

Hi,
I should be receiving an old rubber set on friday. I'll measure those up and look for the best match on LAS and get those in.

NeilD

[Neil Spooner]

......the 1080HD is what is fitted to the Nipper in the photo: http://www.lasaero.com/site/products/ar ... =B03A1AXE5
which apparently work the same as the original Nieman rings.