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By: - 31st December 2016 at 01:31 Permalink - Edited 1st January 1970 at 01:00
Check for decay/rot, cracks, splits, glue failure & compression failures etc.
By: - 31st December 2016 at 08:15 Permalink - Edited 1st January 1970 at 01:00
so what do the one piece wood spar types do to ensure the fearless aviator comes back in one piece?
Wing frequency checks are a very good indicator of problems. I do these every annual. And putting flight pressure on wing in bend to check for play in attachments and cracks in the lower longeron from compression on arrivals. These do not require stripping the wing.
When stripping back the wing fabric the spar is very easy to inspect for damage. Think water ingress damage, insects, fungi, mechincal damage. Depending on the type of spar (box, I beam) glue deteriotation is by far the biggest factor. Both in the ply faces, and in their joint to longerons. There are inspection techniques depending on glue type used.
When properly looked after and inspected regularly, a wooden spar has a very very long life. I re-use the wood of old spars for new-built parts too.
By: - 31st December 2016 at 18:52 Permalink - Edited 1st January 1970 at 01:00
Wood stress members are completely different from metal components in that they do not have a stress life. They do not fatigue through stress cycling so, as related above; you just need to check they are in good nick with no untoward outside influences on their soundness.
Whilst on the subject of wood and an interesting but useless fact; the Mosquito wing was stressed to 85 tons. Now that's something for a few pieces of wood glued together!
Anon.
By: - 31st December 2016 at 19:07 Permalink - Edited 1st January 1970 at 01:00
When we built the new wings for the Slingsbt Kirby Kite prototype we proof loaded by putiing 320 Kg on them.
Dave
By: - 31st December 2016 at 23:11 Permalink - Edited 1st January 1970 at 01:00
Worth a butchers:
http://sportsmansvintagepress.com/product/aircraft-woodwork-rollen-drake/
By: - 1st January 2017 at 00:20 Permalink - Edited 1st January 1970 at 01:00
I recall the guys who looked after the BAe Mosquito panicking about spar life. The answer they were given was along the lines of 'what is the life of a tree?'. So, as ZRX says, it's down to inspection, and making sure the glue remains bonded. You can NDT glued structures to check for debonding, but it's quite tricky.
By: - 1st January 2017 at 03:29 Permalink - Edited 1st January 1970 at 01:00
Here ya go:
https://babel.hathitrust.org/cgi/pt?id=mdp.39015004477421;view=1up;seq=58
By: - 1st January 2017 at 08:26 Permalink - Edited 1st January 1970 at 01:00
You can NDT glued structures to check for debonding, but it's quite tricky.
I assume this is glued wooden structure. I would really appreciate if you could advise the methods and provide any references.
It's the condition of the glue particularly Kuarit types which is the concern.
I've seen a piece of work done by a university whereby a sample of an aged bonded structure was placed in a CAT scanners;- really good clear images but no good for a full sized component.
By: - 1st January 2017 at 09:31 Permalink - Edited 1st January 1970 at 01:00
Vega ECMAlong with clear knowledge of the subject, good eyes sight, sense of smell, torch and feeler gauges are the main prerequisites.
Thanks for the reply but that's really an external inspection technique as opposed to an NDT method which could look inside the bonded joint itself. Apologies for being picky.
By: - 1st January 2017 at 12:56 Permalink - Edited 1st January 1970 at 01:00
It's the condition of the glue particularly Kuarit types which is the concern.
Indeed. This spar failed an inspection last September. Kaurit joint between spar web and spar longerons had just given way. Now building a new spar for it. (Don't bother with the reddish glue in the left of the frame: that's Aerodux from a later repair).
By: - 1st January 2017 at 16:00 Permalink - Edited 1st January 1970 at 01:00
Wood inspection techniques are well established and have stood the test of time. Why do you think another method is required?Do you know just how much (unnecessary) cost would be imposed on owners by the type of testing you are suggesting.
Behind the spar web on Eric's photo are the top and bottom spar booms, which are consisting of spruce (or similar) sections glued together on scraf joints, not to mention the web/soldiers etc.... all totally inaccessible. From scrap spar which I've cut up the glue fairly regularly used is the same type (kaurit) which has failed in the photo.
Hence we could really do with a practical and low cost way of knowing that inaccessible kaurit is good, which is why I'm hoping Bruce might be able to give me some leads based on his experience.
I'm aware of a number of incidents where suspicion has focused on the condition of the kaurit but luckily these don't yet seem to have been in EASA backyard.....yet. Something only "stands the test of time" until the day arrives when it doesn't.
BTW I originally asked a question and didn't suggest any means of testing let alone an expensive one.
By: - 1st January 2017 at 17:58 Permalink - Edited 1st January 1970 at 01:00
OK, not long after RR299 crashed in 1996, BAe commissioned an inspection of Mosquito TA634 at the Mosquito Museum to determine if it might be viable for a return to flight. Accordingly, NDT technicians from Luton were engaged to carry out the work. They were able to determine that there were significant areas of glue separation on the airframe; particularly on the fuselage. There was an Aeroplane Monthly article published at the time, by Ian Thirsk. I cant be more precise than that - its a while ago - and before my kids arrived, so my memory is hazy! However, I did speak to the same people when I was looking to determine if TV959's original structure had a future, prior to it emigrating to NZ, and being discarded in favour (rightly) of new..
By: - 1st January 2017 at 18:13 Permalink - Edited 1st January 1970 at 01:00
Ex Brat
Please read more carefully;- there was no inference on part, indeed I clearly wrote it was unsuitable ("no good")
I've removed spar webs on two aeroplanes and scrapped one as a result of the accumulated findings. The decision to go in that deep with the degree material removal takes solely the inspection close to uneconomical to repair....... Even then you can't really inspect the boom bonds using eye, feeler gauges and nose......ever tried it yourself?
Really can't see the issue with asking a question about a possible less evasive alternative NDT from a comment from Bruce?
"X ray specs " -You clearly have no further serious input to answering the question posed.
By: - 1st January 2017 at 18:25 Permalink - Edited 1st January 1970 at 01:00
Having done a fair number of Kaurit glue surveys, the trend is that if there's no glue issues behing the spar, the spar is always fine, if structure is of the same age (watch for repairs). Opening up the d-nose usually is a good idea. When the d-nose ply is taken off the spar it is possible to put feelers into the glue joint of the web. I usually take the most exposed and highly loaded section. But..... an x-ray machine that fits a whole wing would be nice ?
I've cut a fair number of accident damaged spars but have not found any issues in the spar themselves apart from a very poor repair that should never have been signed off...
By: - 2nd January 2017 at 00:11 Permalink - Edited 1st January 1970 at 01:00
Bruce
Many thanks for this information, I'll see what I can find from back issues of Aeroplane Monthly.
I would really appreciate any further names who could shed a light on how this was done. Were any of the former Chester Mosquito support team involved as I might be able to get in touch with these guys?
The Kaurit glue problem has seen approx. 60 aircraft withdrawn from service in the U.K in the last 18-24 months.
I've been volunterally mentoring an engineering Uni student looking into potential NDT methods as a final year project. Any further help or information on this is very much appreciated.
Eric
I've done about half a dozen kaurit surveys todate and two fairly major reconstruction (one still in progress). My experience is that once you've found kaurit separation it's quite concerning establishing the full extent. In general my experience concur with your assessment. Many thanks for your posts..
By: - 2nd January 2017 at 06:38 Permalink - Edited 1st January 1970 at 01:00
Most welcome. If you are referring to the bga inspection programme for wooden Schleichers, I think poor maintenance and storage is a major factor. We seem to get less problems on the continent. Most issues I have seen so far are in the early Schleichers and license-built ones. The build quality on some is appallling in some cases. Have two rebuilds in the workshop at the moment, and there have been other too.
An extra NDT tool wood be nice. But costs are an issue as you say.
Posts: 251
By: Piston - 31st December 2016 at 00:46
I visited Shuttleworth for their engineering open day yesterday and asked how they judge the condition of the wing spars on their early aircraft, specifically the stripped Blackburn 1912 monoplane (which I think was the type undergoing maintenance in the maintenance hangar).
More modern types rely on FI, hours and/or NDT, so what do the one piece wood spar types do to ensure the fearless aviator comes back in one piece?