EV97 - Main spar structural failure

[turboplanner]

I agree. Very Responsible, very reassuring to customers, deserves to be supported.

 

Hope you swing a few your way out of this Peter.

 

 

[Garry Morgan]

Small no, it is a major factor, only tested to 3.2G and clam 4 G limit?? the fuse in now cracking on a few in Aust. Many of the imports don't use aircraft bolts, and I have seen cap screws beening used. An aircraft bolts apart from the quality, they only have thread for the washer and nut in safty, other bolts have long threads which bear on the structor , wernt we taught that was a no no as the thread can damage the parts they sit on? and cap screws are to hard for aircraft, and have seen many of these brake, I just refuse to use any thing but quality hard ware if I am flying in it. Many imported aircraft just are not built to our structural standards, but they look nice there is no question about that.???

 

 

[SilverWing]

Morgan Aeroworks - I'm not sure if this unprovoked rant is directed at the SportStar, or its successor, the Harmony. As it's appeared on this thread, I guess it must be. However, it's completely ill-informed, highly subjective and totally wrong in content. A few facts to spoil your day: the SportStar/Harmony has been physically tested to at least +6 -3 G and in fact considerably higher limits via computer modelling; I am completely unaware - and so is the factory - of any fuselage cracking in the aircraft; the SportStar/Harmony is constructed in a GA-licensed production facility and uses only aircraft quality materials, including all the nuts & bolts; the SportStar/Harmony has no cap screws, if these are present, they were added at a botched repair here in Australia. It is a ridiculous generalisation to say that 'Many imported aircraft just are not built to our structural standards' - just as it is to say that 'many Australian aircraft just are not built to international standards'. In fact, many imported aircraft are built to standards which are considerably higher than Australian standards, and vice versa. Get your hand off it and stop trying to spread such rubbish - it will not only damage yourself but also the whole market we are in.

 

 

[metalman]

I'd be careful with standards of construction comments, there's some pretty yucky photos out there

 

http://www.atsb.gov.au/publications/investigation_reports/2011/aair/ao-2011-126.aspx

 

 

[Bob Llewellyn]

Small no, it is a major factor, only tested to 3.2G and clam 4 G limit?? the fuse in now cracking on a few in Aust. Many of the imports don't use aircraft bolts, and I have seen cap screws beening used. An aircraft bolts apart from the quality, they only have thread for the washer and nut in safty, other bolts have long threads which bear on the structor , wernt we taught that was a no no as the thread can damage the parts they sit on? and cap screws are to hard for aircraft, and have seen many of these brake, I just refuse to use any thing but quality hard ware if I am flying in it. Many imported aircraft just are not built to our structural standards, but they look nice there is no question about that.???

Metallurgy... it's a fair simplification to say that there are two general approaches to fatigue resistance when it comes to selecting an alloy for a highly-stressed structural part; the more time-hallowed stems from the work of Griffith and Orowan, and is to use a material with a large elongation after reaching yield stress. The AN fasteners fall in this category, as demonstrated by their ability to bend 180 degrees around their own diameter. The idea is that the material will locally yield at the tip of a microcrack, and the crack will not propogate. It seems to work.

The other approach is to use an alloy / heat treament state with a very high strength, and so (if ferrous) a high fatigue limit; NAS aerospace bolts fall into this group, as do most cap screws. In all (ferrous / ferrous alloy) fasteners, the high strength comes from Martensite (a form of iron carbide), which also has a high intrinsic resistance to disintegration of the basic repeating structure in the atomic lattice. In other words, it is tough on a micro scale, as well as very strong on a macro scale. The high strength also gives the option of pre-tensioning such to avoid cyclic loads in the fastener, and so avoid any potential for fatigue.

 

It's simply a matter of engineering. The issue of thread bearing is more of shear transferance between the fastened parts; where a light-drive fit with only shank enclosed allows a continuous transition from the mode of frictive traction between the faying surfaces to the mode of bearing on the shank and shear in the bolt, substituting shank bearing area for threaded bearing area obviously requires the fastened parts to slip over each other before significant shear transferance into the bolt. After the first occurrence, the bolt mean stress is excessive, and a frictive assymetric preload exists. If such high load events recur, chafing and/or bolt fatigue failure are not far away.

 

Re "aircraft quality", I have also had the dubious pleasure of seeing a (released) box of 7/16" AN bolts, new, of which about half did not fall within the dimensional limits of the milspec... eccentric heads, oval shanks, varying shank diameters. As they were made to order, and cost about $16 per bolt, no-one was very happy about it.

 

 

[bexrbetter]

it will not only damage yourself but also the whole market we are in.

This is the main issue right here, it does no good for competitors to be on the attack in public, there are no winners in a sport already struggling to keep it's numbers.

 

If there are genuine safety concerns arising with a specific make and model, then there are eloquent ways and there are non-eloquent ways to bring them to light.

 

It's simply a matter of engineering.

Indeed.

 

 

[Garry Morgan]

An AD for sport star for fuse cracking if you havent seen it . and at least two in Australia?

 

 

[Garry Morgan]

I am sorry I was miss informed on the ADs on the sports star. but there cracks