Thruster wing strut attachments - UK mandatory permit directive

[MadamBreakneck]

Those of you with UK design Thrusters (the Vision series, I believe) may be interested in this service bulleting from the Thruster factory. It affects all UK Thruster types using the aerofoil section struts. [added] Only those with aluminium alloy strut ends, steel ones are OK.

 

http://www.thruster.co.uk/documents/TAS_SB013.pdf

 

Joan

 

www.saxonMicro.co.uk

 

 

[pudestcon]

Those of you with UK design Thrusters (the Vision series, I believe) may be interested in this service bulleting from the Thruster factory. It affects all UK Thruster types using the aerofoil section struts. [added] Only those with aluminium alloy strut ends, steel ones are OK.http://www.thruster.co.uk/documents/TAS_SB013.pdf

 

Joan

 

www.saxonMicro.co.uk

The order does actually refer to T300 and TST Thrusters as well - both of which exist in Australia.

 

The photos show what looks to be a very similar part to that used in almost all Thrusters including the T500. I have just refurbished the struts on my T500 and this included removal of all 4 aluminimum plugs from the struts, inspection for corrosion (found a little surface "white rust"), treatment to remove the corrosion and apply boiled linseed oil to internal surfaces as per Tony Hayes literature, then etch prime and paint all exposed surfaces.

 

Check it out Thruster drivers as this is a major structural component helping keep you in the air.

 

Cheers,

 

Pud

 

 

[Thruster Bob]

Hmm ,

 

Looks like the same part on the T500.

 

I'll check it out next time.

 

Looks like the fault is due to material defect in the aluminium alloy bar used to make the parts. (some kind of inclusion. like a "cold shut" ).

 

"Cold Shut 2

 

(1) A discontinuity that appears on the surface of cast metal as a result of two streams of liquid meeting and failing to unite. (2) A portion of the surface of a forging that is separated, in part, from the main body of metal by oxide. "

 

I wouldn't think this kind of defect would exist in extruded material though?.

 

Thruster UK needs to trace back through their QC records to identify the batch and supplier of the alloy.

 

Then ensure all the parts made from this batch are recalled and destroyed.

 

The parts in the photo look like they are anodized, so I'm guessing that the acid used during the anodizing process leached into the edge of the defect, so in conjunction with atmospheric moisture this acid would slowly work its way through the length of the defect. Creating a small electrochemical cell between the oxide of the inclusion and the parent metal.

 

Hopefully all the Aussie thrusters won't suffer from this as their parts would be made from a completely different batch made a decade earlier in a completely different factory.

 

BTW (a long time ago) after I cleaned the surface white powder off my wing attachments, I polished them and sprayed them with clear lacquer.

 

The offer of a 15% discount on replacements is a bit cheeky , the parts would have been defective "as supplied" by the manufacturer, and "unfit for purpose" and should be replaced free of charge. Seems the UK laws on trade practices are softer than in Australia.

 

Cheers , Bob T

 

 

[pudestcon]

G'day Bob,

 

Yeh it does seem a bit cheeky by the manufacturer I'd agree.

 

I wonder who manufactures them in Australia now - the alum. plug I mean.

 

The plugs on my struts are not anodised and did not show any signs of the type of corrosion referred to in the order.

 

Here's a couple of photos of my 'work in progress' on the struts.

 

Pud

 

 

 

 

 

[Thruster Bob]

More on Strut Attachment & info on intergranular corrosion

 

Hi Pud.

 

I'm speculating the parts are made from 2024 alloy. (Based on your observations and mine of the powdery white corrosion)

 

It's usually known as "machining grade".

 

It has abysmal corrosion performance, even sitting on the metal rack in the shed it gets covered in a white frost.

 

Given the operating conditions, a 606x alloy would have been a much better choice for this part (or even marine grade 5052 alloy).

 

I think the original designers were led astray by the appeal of the higher UTS (60,000psi) of the 2024 vs ~40,000 & 30,000 psi for the other grades.

 

---------------

 

Ok My machinery handbook says 2024 is prone to intergranular corrosion, so I google it up

 

Intergranular corrosion - Wikipedia, the free encyclopedia

 

and in Paragraph 5 it says aluminium alloys with copper (=2024) are subject to exfoliation corrosion, resulting in leafing or lifting effect , which pretty much describes the photos in the AD.

 

A few more similar links:

 

Intergranular corrosion

 

Different Types of Corrosion: Intergranular Corrosion - Causes and Prevention

 

Different Types of Corrosion: Exfoliation or Layer Corrosion - Causes and Prevention

 

http://canteach.candu.org/library/20053207.pdf

 

Metal Improvement | Exfoliation Corrosion

 

(the above suggests cadmium plated fasteners may be implicated)

 

Exfoliation Corrosion - JAMWiki

 

and a tutorial on aluminium grades:

 

Argentum Solutions Inc. - Sterling Guidance on Corrosion and Materials Degradation

 

--------------------------------

 

Interestingly enough Austenitic stainless steel is subject intergranular corrosion after welding. This goes part of the way to explaining the failures on the other half of the wing attachment, where the TIG welded parts have the end of the weld (= stress raiser) near the high stress bend.

 

Perhaps the whole thruster wing attachment method might be a good example of "how not to design something" for an engineering class.

 

Cheers, BobT

 

 

[pudestcon]

Hi Pud.I'm speculating the parts are made from 2024 alloy. (Based on your observations and mine of the powdery white corrosion)

It's usually known as "machining grade".

 

It has abysmal corrosion performance, even sitting on the metal rack in the shed it gets covered in a white frost.

 

Given the operating conditions, a 606x alloy would have been a much better choice for this part (or even marine grade 5052 alloy).

 

I think the original designers were led astray by the appeal of the higher UTS (60,000psi) of the 2024 vs ~40,000 & 30,000 psi for the other grades.

 

---------------

 

Ok My machinery handbook says 2024 is prone to intergranular corrosion, so I google it up

 

Intergranular corrosion - Wikipedia, the free encyclopedia

 

and in Paragraph 5 it says aluminium alloys with copper (=2024) are subject to exfoliation corrosion, resulting in leafing or lifting effect , which pretty much describes the photos in the AD.

 

A few more similar links:

 

Intergranular corrosion

 

Different Types of Corrosion: Intergranular Corrosion - Causes and Prevention

 

Different Types of Corrosion: Exfoliation or Layer Corrosion - Causes and Prevention

 

http://canteach.candu.org/library/20053207.pdf

 

Metal Improvement | Exfoliation Corrosion

 

(the above suggests cadmium plated fasteners may be implicated)

 

Exfoliation Corrosion - JAMWiki

 

and a tutorial on aluminium grades:

 

Argentum Solutions Inc. - Sterling Guidance on Corrosion and Materials Degradation

 

--------------------------------

 

Interestingly enough Austenitic stainless steel is subject intergranular corrosion after welding. This goes part of the way to explaining the failures on the other half of the wing attachment, where the TIG welded parts have the end of the weld (= stress raiser) near the high stress bend.

 

Perhaps the whole thruster wing attachment method might be a good example of "how not to design something" for an engineering class.

 

Cheers, BobT

Jeez Bob!!

 

Are you a metallurgist?

 

The more I learn, the more I realise I don't know - but I've known that for a long time about all manner of things.

 

It's going to take me some time to read through the links you have provided. Thanks very much.

 

I'm satisfied that the treatment I have done to my struts will provide the integrity I'm looking for and daily and/or preflight inspections will keep me on top of it.

 

There is no doubt that maintenance on these rag and tube type aircraft is very high, but then, that is what we accept in our choice of flying machine.

 

Cheers,

 

Pud

 

 

[pudestcon]

Hmm , Looks like the same part on the T500.

I'll check it out next time.

G'day Bob,

 

Have you had a chance to check it out, and did you find anything?

 

Pud

 

 

[xair1159]

Pud,

 

A thought having viewed the photos of your artistic endevours:

 

I was involved in getting an a/c through UK "Section S" approval and one thing mentioned is paints and coatings.

 

Whatever you use, paint or powder coating etc. it must be brittle and not flexible or cracks in the base material could be masked until it is too late.

 

Nick

 

 

[Thruster Bob]

Hi Pud ,

 

Looked at them on the weekend,

 

My ends are good, there's a few spots of pitting corrosion (must be pinholes in the clear coating?)

 

Cheers, BobT

 

 

[pudestcon]

Pud,A thought having viewed the photos of your artistic endevours:

I was involved in getting an a/c through UK "Section S" approval and one thing mentioned is paints and coatings.

 

Whatever you use, paint or powder coating etc. it must be brittle and not flexible or cracks in the base material could be masked until it is too late.

 

Nick

G'day Nick,

 

My apologies for not replying sooner; I did read your post and thought I'd come back to it, and never did until now.

 

The paint I've used is just enamel gloss over an etch primer - both from a pressure pack spray can. I didn't think about flexibility of the paint. I reckon though, that the enamel paint, whilst having some flexibility, would not be as flexible as an acrylic paint. Luckily the connection points are very easy to get to for daily inspections so that's a plus.

 

What is your view on the paint I have used?

 

Pud

 

 

[Kyle Montanaro]

Hey guys,

 

Nice to read you first of all. I'm working on a T600n Sprint which was abandoned at the hangar. It has everything except for the wing struts which have been used to tie the aircraft to the ground. Problem was when the wind blew, the struts broke in half (where the solid black rod struts are bolted) . I've contacted Thruster UK but they don't make them anymore and I haven't found any second hand. Does anyone know of an approved repair scheme for them? I know it's not usual to do a repair scheme for a structural component like that but I think that's the only way if we want this baby to take to the Maltese Skies again....

 

Best regards,

 

Kyle.

 

 

[pudestcon]

Hey guys,Nice to read you first of all. I'm working on a T600n Sprint which was abandoned at the hangar. It has everything except for the wing struts which have been used to tie the aircraft to the ground. Problem was when the wind blew, the struts broke in half (where the solid black rod struts are bolted) . I've contacted Thruster UK but they don't make them anymore and I haven't found any second hand. Does anyone know of an approved repair scheme for them? I know it's not usual to do a repair scheme for a structural component like that but I think that's the only way if we want this baby to take to the Maltese Skies again....

Best regards,

 

Kyle.

Have you got any photos you can post to the forum Kyle?

Pud

 

 

[Thruster Bob]

Hi Kyle,

 

I've been out of touch a bit.

 

I didn't think Malta had enough flat space to have airstrips?

 

Re struts, We don't have a factory as such anymore over here, I think Thruster Australia may be still be operating out of Evans Head?.

 

TOSG has pretty much faded away now, otherwise the guys at Watts Bridge would have helped you out.

 

Are the machined ends of the struts OK?

 

If so then you just need to replace the aluminium tube , it will probably be an inch size.

 

Any aircraft engineer could replace the tube. Although it needs to be anodised , so thats an extra cost.

 

Cheers, BobT

 

 

[Kyle Montanaro]

@Pud: I forgot to take my camera with me on my inspection, but I'll take some tomorrow. it's not pretty but it's simple.They're broken in a line perpendicular to the strut passing through the bolt-holes. Take a plastic straw, bend it and it'll crack from the weakest point. It's as simple as that. If you want, here's a picture of it when it was still the pride of the club: http://www.islandmicrolightclub.com/gallery/data/media/9/9H-UMC-landingrwy24-RBenettiR.jpg

 

@BobT: Haha of course we have runways, and they've been there since the 1930's. In WW2 the Brits used to call us "an unsinkable aircraft carrier" and at that time we had like 4 airstrips with 2 runways each operating hurricanes, spitfires, and later on vampires, nimrods and meteors. Unfortunately, when the government of that time wanted to have our "independance", we lost all that and all but one have been built upon :( The only one used as Malta International Airport is at Luqa and it's almost 5 miles long with another 3-mile runway at 90 degrees to it and that's all that's left for us. The local authorities aren't too microlight friendly neither, we have to endure the busy airspace everywhere we fly over here and we're not allowed to use the longer runway not even when the shorter one is (and quite frequently too) closed.

 

Anyways back to the Thruster: Well, yes all I need is the tube but these ones are Aerofoil section types. I don't think it's just about any kind of aluminum tube neither. I'm studying to become an EASA Category B1 Engineer and I know a repair scheme I can implement where I put a folded Aluminum plate over the bent part and just blind-rivet it at both ends and I could use aircraft-material and rivets (as used on Airbus and Boeing) and I can bet it will hold. But because of our Authorities, they won't really like that too much especially because I'm not a certified LAME yet. (Even if theoretically, a microlight does not require a certified LAME to work on it. )

 

 

[pudestcon]

One of the reasons I wanted to see photos was to see what section was used - round tube or airfoil, plus I'm always up for looking at airplane photos:smile: Nice looking aircraft but no tailwheel means it fails my test!!

 

I know the airfoil aluminium section is still available but I think you have to source it from the US. I'll see what I can find out. Another option would be to use a round tube section and have a light weight (plastic or fibreglass) section made up to cover the round tube.

 

There is no way I would entertain the idea of a repair in such an important structural member. I don't have any qualifications in aeronautical engineering but something tells me not to risk it.

 

Pud

 

 

[pudestcon]

Just did a google search for aircraft metals and came up with this in Australia.

 

http://www.airportmetals.com/stocklist.htm

 

Click on the pdf download icon below the text and download the "Aluninium Tube" document - it has airfoil section stock.

 

Pud

 

 

[Kyle Montanaro]

Awesome :) I'll give it a look. (but I'm on the other side of the planet).

 

Well... since I plan on having a career in aircraft maintenance, I don't see why I won't fix a Strut on a 2 seater 450kg microlight, when in a couple of years, I'll be signing off huge airliners with bigger problems...

 

But of course, I'll have a blueprint sent to Thruster, the local Authority, and I'll have it checked by someone who's already qualified for this stuff.

 

In any case, I can build a sample and test it to destruction.

 

Yes taildraggers are awesome... but they're pretty dangerous on concerete.. :/ and that's all we're allowed here :(