Kharon,
thanks for posting those links to the tiger moth manuals interesting reading!
Quote:
SvW # 70 –"Including the ends of the flying wires.
The inter-plane struts and their fittings must be the weakest points as most connect through a single bolt (from memory)".
There's a good start – I wondered what level of redundancy there is; i.e. how much of the 'bracing' can be lost before a wing 'breaks'. With apologies to the 'wizards' it looks as though there are 6 bracing wires; 2 flying, 2 landing and 2 inter-plane (cross bracing). The 'flying wires' attached to 6 'hard' points, the cross bracing to four within the inter-plane struts. That's 10 hard points in all, here the mathematics get difficult (for me) it's not possible to determine the ratio of load between the 'lift' bracing and 'landing' bracing, but the manuals indicate a higher percentage on the lift side during flight (which makes sense). So, the puzzle is, if a 'weak' point fitting had let go what is the gross effect?. To loose one of a possible four cross brace fitting is within the realms of probability, but would that cause the wing to break. The loss of one of a possible six flying wire fittings would be a more serious matter (mathematically speaking). I expect the ATSB will, in due course, provide the right answers, if at all possible. Previous reports into Tiger accidents have been very good, the 1998 one - ATSB 199800648 - in particular. They were careful then to examine all the possibilities.
You must assume that there is no redundancy with the flying wires. They weren't in the habit of adding an extra flying wire here or there for good luck even though it might appear like that in some of these older types.
this quote from section 1 page 1 of the tiger manual you linked to
"in normal flight flying loads are taken by two cables on each side forming a triangle between the upper ends of the interplane struts and fittings on the lower longerons at the front spar of the bottom plane. "
i.e the flying loads are taken by wires that connect the top of the interplane struts to the root of the bottom wing. So essentially they act in much the same way struts on a Cessna 172 do and they are most likely just as critical to the structural integrity of the wing as they are on a Cessna 172.
The Tiger Moth is a solid safe and time proven design. But it is a product of a very different era. "No worries she's built like brick sh*t house mate" is indicative of a potentially dangerous misconception many people have about these machines. it's not built like a brick sh*t house it's built like a light aircraft. It was the 82 aircraft design produced by DH in a 25 - 30 year period. They learnt structural design by trial and error, lots of static testing and a few dead test pilots. by 1935 they could produce safe and efficient structures that were comparable to the all metal cessnas that came along 15 years later (and are the backbone of GA to this day).
im skeptical of statements such as this
I found this interesting quote from an earlier report link, "The aircraft was stressed to withstand maximum loads of approximately 7.5g (acceleration due to earth gravity). Information from the manufacturer indicated that even with the reinforcing doubler delaminated and ineffective, the aircraft was designed to withstand manoeuvre loads of about 5g."
where did this come from?
The tiger is a safe aircraft but it shure as hell is no pitts special. Unless british aerospace produce an original stress report stating this or their own analysis which suggests this (which i doubt they have) you cannot accept this. Anyway British Aerospace no longer holds the type certificate for DH moth types. DH technical support does.