Spar Straps for Twins etc.???????

[Sheep Guts]

Ok here is a question for you Engineer Lame types and Casa Enginerring Types Regarding Spar Straps.

I want to know why these straps for PA-31s and C402 s and even King Airs is a requirement in Australia and nowhere else?

This costly requirement, has totally bewildered me?

Also to mention some people have told me this mod can actually weaken the Spar? Is this true?

What do the Aircraft manufacturors think?


The FAA and other world bodies that I talk too are also bewildered?

why? why? why?


Confused
Sheep

[bush mechanics]

Sheep,402cs have their spar straps caried out by memory around aprox 7000 hours,They also use aircraft cycles and then use a formula to work out spar life.Once strapped you can go to aprox 14000 hours.I did here that the yanks are looking at straping 402 as one C model lost a wing over the grand canyon.
Cheers.This AD was made up by our mates at CASA who always know more than the manafacturer.

[Sheep Guts]

Thanks BIK very enlightening.

I have been talking to our Mechanics here , and they say that a spar strap mod on a King Air, can make the Inspection for corrosion on the Spar next to impossible. This was then identified with Raytheon and they designed a different spar strap. Our company Aircraft here that do Airborne Fire Fighting get the Spar job done but our other Machines dont.
:)
Some the machines I fly here have 23,000 hrs :(

But they have allways been on a rigoress maintenance schedule set for the US ARMY and the Company I work still keeps this level of Maintenance up. Wing Bolt and Spar inspections are a regular occurence.

anyway thanks for the info
BIK

REGARDS
SHEEP

[High Altitude]

What about the 210? Some with 18000 hours...

[swh]

A problem with straps is that the tensile strength of the strap can be greater than the cap, eg stainless strap/Al cap put very high loads on the rivets, sometime larger size rivets are required to be used increasing the stress in the strap.

May need special adhesives or treatment to prevent dissimilar metal corrosion.

Also it is difficult for anyone apart from the manufacture to accurately know what the loads are in the spar at every station along the wing, placing a strap on the cap will change the load path through the wing.

Some manufactures have adopted spar web mods, rather than spare cap, this takes a bigger piece of metal to have the same effect as placing something on the cap as its a function (r^2) of the distance from the vertical distance from the spar.

[Charlie Foxtrot India]

Thanks BIK that was very interesting.

Not quite a twin but...next month I'm having the wing mod strap thingy done on my Tomahawk. With that and an engine overhaul my little PA38 will be good as new - even though it's the youngest in my fleet anyway:ugh:
Would like to hear from anyone who has had this mod done..


And to the Tomahawk detractors...23 years old and the tail STILL hasn't fallen off. Hmm, maybe it's not true about the tails after all!
:=

[bush mechanics]

HA,You can get or the info on c210 by getting the CAPs (continous airworthiness program)ManualAvailable from Tenix,Around 60 dollars.Alot of it is special inspections,(Edie current)But some of the inspections are stuff you can get done on a normall 100 hrly.IE controll yoke bearings.MAF actually when operating 402c in central australia maintained them on the CAPs well before the spar retirement was due
Cheers

[Torres]

Sheep. The Saunders Spar Strap on the King Air 200 is a US mod, not an Aussie only mod.