Light Aircraft Association

Morning all,

I've come up against a 'brickwall' at the moment in restoring my SIPA 903. For those of you who are familiar with the flap control mechanism on this aircraft I apologise now, but I will describe it only for those who don't. The flap control lever - rather like a Landrover handbrake in style - connects through a control link to a control horn which is 'c' pinned to an aluminium tube - that is fixed behind the trailing spar of the aircraft. The length of the bar is enough to reveal itself at each wing root (its about 6' long in total). The problem I have is that this tube is bent and beyond help. The O/D is 32mm which is a problem, and trying to source another has fallen at the first hurdle.

I've spoken to engineering and gone through my inspector only to find that the LAA suggest a bit of steel tube. Not the quite answer (due to weight issues/design etc) we were expecting, but what we need to know is the grade of material that the French used during the manufacture as it appears the tube is quite hard. Believe me we've had guesses by everyone, but on reflection, there are just too many to make a firm and safe decision.

Obviously getting the tube tested is the last port of call but after checking around my area (Hampshire), it appears that such a place that tests metal elludes me.

If anyone has any clue to my jabberings, please reply.

Kind regards,

Andrew

Perhaps an alternative is to calculate the flight loads on the tube/bar ( from your description I'm not sure which) from scratch and then replace it with a 1 1/4" OD 2024T3 or 6061T6 bar from Aircraft Spruce. If a tube, there are various choices of wall thickness to use to get the right strength/stiffness properties. As it is a flap, rather than a primary control or main spar under high stress or regular cyclic load, some compromise should be able to be reached with LAA ref a replacement.

http://www.aircraftspruce.com/menus/me/aluminum.html

Since it has bent in service you could taken the opportunity to increase the strength of the replacement anyway and this would build on the existing factor of safety.

Another way would be to calculate the bending moment, and shear strength properties of the existing item using basic engineering formulae for a series of assumed likely aviation aluminim alloy materials and then work out the requirement of the replacement on the worst case basis.

Or worst case, if you are 'happy' to risk destroying the existing part, you could set up a test rig to load the item to failure and then derive the material properties from the data obtained.

If you want further help let me know.

Regards
Steve

When Alcan pulled out of Banbury a few years ago, the labs split off as a separate company. They can be found at http://www.wmtr.co.uk/.
Beyond that, I have no specific knowledge of them.

Tensile testing should be easy if a suitable coupon can be cut from the old part, but that won't neccesarily reveal the grade. Spark analysis can be used to detect the chemical composition.

There's also Bodycote in Daventry - http://mt.bodycote.com/.

As for then sourcing a replacement of the right dimensions .......

G-SIPA,
Can you track down a metalurgical service in your area. Normally, all you need to supply them with is a small sample of filings of the material for them to conduct an analysis on it. Either that, or they will tell you where to get it done. This was a routine method of detecting material composition at my last place of work.

Bill

Do you know anyone in the RAF? At St Athan there is an NDT section who (for beer or charitable donations) might be persuaded to test a sample for you. A bit like a 'training session' for them? They did my weight-n-balance as a training job since it was a bit different from the usual VC10.

No warranty implied on their info or signatures, though.

Another possible line is your local university. Most engineering labs have a tensiometer, and the metalurgy labs usually have an analysis capability.

Good practice for an undergrad.

Give Engineering another call. They probably have a set of SIPA plans in the archive.

Thanks for the replies gents, I've finally handed the tube to my inspector....watch this space. With all due respect to engineering, they weren't much help - maybe next time?

Hi

Information about French specification material is difficult to find.

You might find some useful references here.

http://www.donfoster-racing.fr/materiaux_gb.htm

15CDV6 is a very good material,

I did give this information to JT some time ago but I guess it got lost in the wind.


Best of luck


Charlie.