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Post by horicle on Jun 1, 2019 12:07:32 GMT 12
Remember the Canberra's. They only lasted 10 years in Kiwi skies. Before they were sold to India one was sent to the UK to investigate the practicality of a main spar replacement (or similar major surgery). The bits were taken off and it never flew again. I think I've got that right.
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Post by camtech on Jun 1, 2019 13:01:29 GMT 12
The story was that NZ6106 had a "main spar flaw".
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Post by davidd on Jun 1, 2019 16:12:05 GMT 12
To go back through several generations of aircraft, in fact to WW2, there were several types serving during the war years that had interesting stories to tell. The Airspeed Oxford was a wooden aircraft of course, but one of these disintegrated in a routine training flight in November 1942 (flying from Wigram) which killed the two trainees. Fortunately the incident was witnessed by at least one or two witnesses, who confirmed that the aircraft just started shedding bits of wing in level flight before eventually "plumetting to earth", completely out of control. It transpired that this was a case of faulty manufacture, with vital areas of the thin plywood upper skinning on one mainplane not being glued to the underlying structure, which eventually had to fail dramatically. There were, from memory, at least two other aircraft in service with serial numbers very close to the accident aircraft, and these were inspected closely, and also revealed very poor gluing practices used in their manufacture - however they were both repaired with a bit of judicious opening up the plywood skinning, a pot of the appropriate glue, and a brush. Later in the war the RNZAF took delivery of four PV-2 Harpoons, which were flight delivered from Hawaii. This type of aircraft was one of the relatively few cases known of an aircraft put into mass production with a very serious structural design flaw incorporated. Although the RNZAF was not directly caught up by this fault, it did suffer some consequences in that our own aircraft (which did not have this fault, as it had been "designed out" by the time they were built) were delivered about six months late. The design flaw resulted in the outer wings getting serious "stress wrinkles" on the upper skins, despite fact that they had not been carelessly overstressed, but because of some sort of faulty calculations at the design stage, a fact which was soon realized.
Of our postwar aircraft types, the Bristol Freighter, Hastings and Devons all suffered from wing designs which ultimately proved to have rather alarmingly short fatigue lives, which required fairly extensive and expensive major surgery to bring them up to an acceptable standard, with the Hastings having to trundle all the way to the UK to have this work done at Radlett, while the two smaller types were able to be dealt with in New Zealand by the RNZAF and civilian contractors. However this did not stop a civilian Bristol Freighter shedding a wing in NZ in 1957 near Harewood from a similar fault. Perhaps somebody else more qualified than I would like to take up these stories.
David D
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Post by xbaggy on Jun 1, 2019 18:11:08 GMT 12
I was an Airframe Fitter at 1RD from 1967 to 73. During that time I was involved in the Bristol Freighter wing resparing which involved opening up the wing skins along the wing spar, and removing the spar caps. New spar caps were drilled in a jig and the new caps fitted . This involved the skinny fellas crawling inside the wings with a rivet bucking dolly to install the rivets. At some stage the Devons had the bottom wing spar attachment fittings replaced with upgraded ones (maybe from alloy to steel but not sure of that). A crack was found in a modified one at Wigram, and the fleet was grounded with a one flight dispensation to fly to Woodbourne for inspection. Th a/c were jacked and treselled, and the bottom wing attachment bolts removed. (A real pain and time consuming job as the bolts had seized, and the area plastered in PRC sealant). The fittings were the then Eddy Current NDT crack tested. Lots of overtime was involved with lots of days "in leiu" taken. The Devons in storage in No5 hangar had not been modified, and when we took one out of storage, NZ1819 I think, I was involved in changing the spar fittings.
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Post by davidd on Jun 2, 2019 12:54:52 GMT 12
xbaggy, That must have been the second round of undertaking major work on the spars, etc, of Bristols and Devons, they were certainly done for the first time in the mid-1950s, and the Bristols were done well before the SAFE Bristol lost its outer mainplane near Harewood in 1957. Needless to say, they kept a very close eye on that generation of British aircraft for the rest of their lives (the aircraft that is!), and should not have been too surprised when the Strikemasters also showed weaknesses. However the Andovers seemed to avoid that type of trouble, or did they? No, I am fairly certain they did avoid it, although they had their own problems of course. David D
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Post by aircraftclocks on Jun 2, 2019 13:32:02 GMT 12
The reason for this in the Andover maybe found in the wing description, taken from the Andover 0000 course book:
The general configuration is that of a twin-engined, low wing monoplane with an upswept rear fuselage. Structurally, it is of fail-safe design, i.e., a fatigue crack or other local damage will not lead to sudden catastrophic failure or loss of control. It is of all metal construction in the general pattern of formers and stringers supporting aluminium alloy stressed skin. The wing is joined to the centre section to form continuous wing tip to wing tip spars; the fwt face of the rear spar web is the datum face from which all fore and aft fuselage stations are measured. The wings and tailplane have a dihedral of 7 deg, and 15 deg. respectively.
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Post by camtech on Jun 2, 2019 19:44:59 GMT 12
The reason for this in the Andover maybe be found in the wing description, taken from the Andover 0000 course book: The general configuration is that of a twin-engined, low wing monoplane with an upswept rear fuselage. Structurally, it is of fail-safe design, i.e., a fatigue crack or other local damage will not lead to sudden catastrophic failure or loss of control. It is of all metal construction in the general pattern of formers and stringers supporting aluminium alloy stressed skin. The wing is joined to the centre section to form continuous wing tip to wing tip spars; the fwt face of the rear spar web is the datum face from which all fore and aft fuselage stations are measured. The wings and tailplane have a dihedral of 7 deg, and 15 deg. respectively. Can certainly back that up re the Andover. Having read the fatigue meter after some severe turbulence coming out of Singapore, and finding a small crease on the wing surface, the manuals told us to check some minor details - no problems, so carry on back to NZ. Great respect for a fail-safe design! Trying to do a supply drop for SAS on Stewart Is, turbulence so bad, army dispatcher broke his arm, supply drop abandoned as too dangerous and back to Wigram.
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