Can microlights wings fail??

[bobthebuilder]

Come now guys ..... I think the bolt thing is getting a bit carried away. Respect where it is due please.....

To start with, trike wings that have been produced locally in a controlled production type environment such as that of Solo Wings (Micro Craft Africa as they are now known) were certainly not slapped together!
Come on guys, just take a look at a wing, yes .... even an older model, does it look poorly thought out and badly made? Come on, wipe away that dust and take a look .... Yip ... right on ... it Doesn't!
Load tests were performed under controlled conditions to meet specific requirements which are controlled by the CAA, which by the way, do inspect manufacturing facilities.

Jenya! Now there's a boy who has made us South Africans proud!
Okay .... I know..... strictly speaking he isn't reeaaalllly South African, but he has been here long enough. The man builds a world class product and, without the shadow of a doubt, knows his stuff!
After all, how many of us place our lives under the Dacron of his structures each weekend?

Manfred Springer is another fantastic example.

The term "Hardware Store Bolts" is rather loose, don't you think?
Whilst in some if not, most applications a freely available Grade 8.8 bolt will suffice, in others it will not. Professional outfits know what is acceptable.
Incidentally, AN Bolts are actually softer than Grade 8.8 and other commercially available fasteners.
I'm pretty sure that a professional aircraft manufacturer would not be sending their driver out to the local hardware store to randomly select some bolts that could potentially kill someone.

The problem lies not in the practices of the professional manufacturers, but in the misinformed owners who randomly change bolts because the originals were either lost, or replaced with "pretty" new ones.

[vernon11]

Well said Byron.
Vernon

[FAWGie]

Incidentally, AN Bolts are actually softer than Grade 8.8 and other commercially available fasteners.
I'm pretty sure that a professional aircraft manufacturer would not be sending their driver out to the local hardware store to randomly select some bolts that could potentially kill someone.

The problem lies not in the practices of the professional manufacturers, but in the misinformed owners who randomly change bolts because the originals were either lost, or replaced with "pretty" new ones.

AN Bolts are intended to be "softer" in the sense that they are not brittle, so will rather "bend" than "snap". Nobody is suggesting that the wings aren't built nicely, nor that the quality is lacking, but that does not whitewash the fact that a wing can be manufactured using non AN grade bolts and with CAA sanction.

I'm puzzled at your closing comment "The problem lies not in the practices of the professional manufacturers, but in the misinformed owners who randomly change bolts because the originals were either lost, or replaced with "pretty" new ones" - In my case, I bought a brand new aircraft from the manufacturer - it was one of the original bolts that failed and yes it was NOT an AN grade bolt. The manufacturers CEO at the time advised my AP that they used hardware store bolts and not AN grade bolts and that all their aircraft were manufactured in the same way.

I don't want to labour my point, except to ask that we please not wash off the point made that it is still advantageous and desirable to use AN grade bolts in all the strategic places. The costs of AN grade bolts are significant, but to my mind that is an aspect of safety that should not be compromised. If you want to be an ostridge and stick your head in the sand on this one, then be my guest, but if I owned a trike, I'd inspect the bolts and if found not to be AN Grade, then have them swopped out for AN grade.
I'm only posting these comments in the interest of safety and not targeting any manufacturer.....I had done just over 350 hours on my trike when my wing failed in flight and it could easily have cost me my life

[bobthebuilder]

I don't want to labour my point, except to ask that we please not wash off the point made that it is still advantageous and desirable to use AN grade bolts in all the strategic places. The costs of AN grade bolts are significant, but to my mind that is an aspect of safety that should not be compromised. If you want to be an ostridge and stick your head in the sand on this one, then be my guest, but if I owned a trike, I'd inspect the bolts and if found not to be AN Grade, then have them swopped out for AN grade.

I want to be an Ostridge, because I am by no means an expert, nor an aeronautical engineer, and would therefore rather place my life, and that of my PAX in the hands of people who are more experienced and qualified to make sound mechanical judgments.

[FAWGie]

I can accept your willingness to simply accept "what the experts" have to say in terms of "the manufacturers", but please don't forget that these individuals are mere mortals too and are driven by economic factors as well and that many of the microlights on the market today have relied on early designs as well as copying other products that entered the market. One must distinguish between quality of build, geometry in terms of aeronautical suitability and of course mechanical suitability.
Many adaptations of some of the best designs might have been well manufactured, but mechanical integrity might not be the same. A nice article on the history of the flex wing can be found in wiki here: http://en.wikipedia.org/wiki/Ultralight_trike

Please read this article: http://www.engineering.com/Library/Arti ... aster.aspx
Some of the best minds in the aeronautical and engineering fraternity have made some horrible mistakes which has cost many their lives. Aircraft design as we all know it is a set of compromises and cannot be fool proof nor mechanically perfect, but one should always try to minimise risk. In the case of my trike that I bought, the manufacturer justified his product post incident by stating that if AN grade bolts were to be used throughout, it would have made the product more expensive and that non type certified aircraft do not need to use certified aircraft parts. I've only mentioned my story (because it's real and happened to me personally) and over the past few years I've shared it with several owners who have discovered that their trikes were not made from AN grade bolts and they have had their AP's change them out. When I read the question asked by a concerned individual on this thread as to whether microlight wings can fail, I feel it my human duty to share that yes there are risks and that one can possibly further minimise those risks. Feel free to defend your own beliefs, but for me, I's rather spend the R2000 - R3000 and have peace of mind.

If you are still not convinced that structural wing failures can occur in microlight wings, then please read an AD put out by CAA in December 2004 - see here for the full AD: http://www.caa.co.za/resource%20center/ ... 062004.htm

I would like to highlight a section of the bulletin as follows:-

This Directive is a result of recent weight shift aircraft fatal accidents due to wing separation of various causes. This directive mediates the affects of structural failure leading to wing separation by instituting safety inspections and requiring installation of safety cables.

This AD was as a result of wing separation (Although not bolt related, but rather fatigue related) of well known brand trikes that lead to fatalities - brands that you express your total faith in them when you say "..... would therefore rather place my life, and that of my PAX in the hands of people who are more experienced and qualified to make sound mechanical judgments."

Again, I'm not having a go at any specific brand or manufacturer. In my case, I bought my trike new in December 1998 and sold it about a year after having my incident which was in 2005. On this forum, someone has kindly posted the Aquilla Wing Catalogue : https://www.google.co.za/url?sa=t&rct=j ... 7636,d.ZGU
dated 25/05/2005, which is post my trikes manufactured date and I'm please to see that the manufacturer changed the bolt in question (in my incident) to an AN grade bolt. See extract below:-

I'm pleased to see that from the parts list (Item 9 - part number 539-0) that trikes are now manufactured using an AN 34A Bolt (An aircraft grade bolt) and the second bolt that does not fasten the side flying cable uses a standard M8 x 90 bolt (Part 538-0)

There are many trikes of this brand manufactured prior to 2005 that might not have the AN grade bolt used in this strategic position. All I'm suggesting is that trike owners check what bolt is fitted and change it for an AN grade bolt and any others if it brings peace of mind.

In the context of the question asked by the person who started this thread, I feel justified in pushing the point that it might well be worthwhile in adding that extra element of safety, by ensuring that at least wing bolt failure is minimized through the use of AN grade bolts for the critical ones.

[bobthebuilder]

FAWGie, Steve is it?

Thanks for the fantastic and informative debate mate.
I have just finished reading the Wikipedia article. I didn't know anything about the history of trikes. I learned something today.

I had better go home, so will pick up on the rest of your post tomorrow morning.

Thanks again.

[bobthebuilder]

Just a quick one ....

This Directive is a result of recent weight shift aircraft fatal accidents due to wing separation of various causes. This directive mediates the affects of structural failure leading to wing separation by instituting safety inspections and requiring installation of safety cables.

I believe that we are the only country in the world that has this requirement.
Not to say that it is a bad one.

[bobthebuilder]

and another ....

The problem lies not in the practices of the professional manufacturers, but in the misinformed owners who randomly change bolts because the originals were either lost, or replaced with "pretty" new ones.

Anyone who adheres to the safety directives issued by the manufacturer, is no longer misinformed, but as you state, yes the manufacturer is not infallible.

One such local manufacturer lost his own son in an extremely tragic accident whilst testing one of their own aircraft.

It can happen!

[CVStrong]

Hi Guys,

Looking through this thread brought to mind what I was told while I was involved in building of a Helicycle a few years back...

What was explained to me regarding AN vs std metric bolts was that an AN bolt has a shorter threaded section, and more "shaft" to the bolt, thus if placed properly you do not get any shear forces in the thread area of the bolt...

If one places any form of shear force on the unthreaded part of a bolt, or at the threaded part, the shear for required for failure will be less on the threaded section...

Combining that, and that the quality control with AN bolts will be more intensive, it stands to reason that an AN bolt will have more predictable failure probabilities... hence higher safety...

Just a few points I thought pertinent to share...

Cheers
Craig

[FAWGie]

A nice article here about AN grade bolts: http://www.sportair.com/articles/Aircra ... 0Know.html

A short extract:

These questions will be answered in this series of articles on aircraft hardware. I hope to eliminate some confusion over what type of hardware to use and how to properly install it. To begin our discussion, it is absolutely imperative that you use nothing but aircraft grade hardware. Commercial grade hardware found in hardware or automotive stores is legal to use on an experimental airplane but should not be considered for even a moment. Why? Lets look at bolts as an example. Common steel bolts purchased from a hardware store are made of low carbon steel that has a low tensile strength usually in the neighborhood of 50,000 to 60,000 psi. They also bend easily and have little corrosion protection. In contrast, aircraft bolts are made from corrosion resistant steel and are heat treated to a strength in excess of 125,000 psi. The same comparison applies to most hardware items. So, use only aircraft quality hardware on your airplane.

[CVStrong]

So I did some more reading and looking, and here is a nice simple answer regarding the differences:

http://www.askbob.aero/node/575

Cheers

Craig

[shorebird]

Thanks for all of the great follow-up info, FAWGie. That's a terrifying story. But I would still consider that to be human error by the manufacturer, not a structural deficiency in trike wings. It can be safely stated that for the last decade at least, all trike wing manufacturers know that wing bolts need to be AN grade hardware. And any pilot should check their wing to ensure that the important bolts are exactly that.

But your experience still seems like an anomaly to me, since it is the direct result of human error. I am still curious about the original posted question: are there any instances of a PROPERLY BUILT trike wing failing, while flown within its operating limitations?

[shorebird]

I'm pretty sure that a professional aircraft manufacturer would not be sending their driver out to the local hardware store to randomly select some bolts that could potentially kill someone.

Well, according to FAWGie's story, that's exactly what Aquilla did. Although, it doesn't sound random, but rather a calculated move to save money. Obviously, they weren't deliberately trying to endanger anybody, but it certainly sounds like people were placed at increased risk. Some of this can be chalked up to the constant evolution of aviation knowledge regarding aircraft manufacturing. I'm sure the trike wings that are manufactured ten years from now will be safer than our wings today also. But when there is a known better choice available such as the AN bolt, it's pretty lame for a manufacturer to choose the lesser option, especially for something so obviously critical as wing hardware. Human error.

[bobthebuilder]

Think about this for a minute ..... (I don't know the answer by the way)

Lets talk about hang point bolt .... yes ... the Jesus bolt ... that's the one!
From a stress perspective, this bolt is in sheer. No arguments there.
All 450 kg's of your MAUW at 1G, or 1.8 Tons at 4G are trying to sheer this bolt.
What is more beneficial, a (I hate this term ...) "hardware store" grade 8.8 bolt, which is harder, and therefore more brittle, or a softer AN bolt?
Bear in mind that an AN bolt will not stand up quite as well from a wear perspective than a Grade 8.8

So ... which is better?
A softer AN bolt which is more prone to wear and is probably weaker in sheer (across the grip length), but malleable and prone to fatigue or ....
The harder Grade 8.8 Which is harder, more resistant to wear, but a bit more brittle?

I am not suggesting that we change our bolts, or that AN bolts are inferior, they most certainly are not if used in the correct application. I would however, like to understand the concept.
Can anyone explain this?

[bobthebuilder]

but rather a calculated move to save money.

I'm not so sure that AN bolts are much more expensive than (I hate this term ....) "hardware store" bolts.
An example ..... I paid R1.90 each for a quantity of 10 off AN3 bolts three months ago. This is a rough equivalent of an M5 bolt in terms of diameter only.
While an M5 bolt of a similar length would cost a few cents, I don't really see it costing thousands of Rands to to kit a wing out in AN attire. Maybe i'm wrong ....

Maybe we should find out for interests sake. Can someone provide a bolt list for a trike wing?