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door hinge screw query

 
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rowlandcarson(at)gmail.co
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PostPosted: Mon Oct 31, 2016 5:36 am    Post subject: door hinge screw query Reply with quote

I’m in process of fitting the door hinges. I find that after I have counterbored the outer face of the door hinge tangs to hide the nuts, the ends of the screws at the thinner edges of the tangs are just proud of the surface. The nuts on those screws are only just in safety (2 threads visible). If I were to shorten the screws, I’d need to make the counterbore deeper to keep the nut in safety. But already, the thickness of tang remaining at the bottom of the counterbore seems (to me) surprisingly thin.

I wondered if I had countersunk the hinges too much, thus allowing the screws to protrude more, but I don’t think so. The MS24693-S272 screws are as flush as I can make them with the inner surface of the hinge leaf, and a trial fit of the MS525-10R10 screw in the opposing hole shows that, if anything, the CSK screw could be even more sunk in order to allow the hinge to close with the leaves parallel. However, I don’t feel happy about enlarging the hole in the hinge any more, nor about making the screw protrusion greater.
So, has anyone else had this issue and what did they do about the cosmetic aspect of the protruding screw?

If I grind off a little to bring it flush with the surface, it will no longer have 2 full threads visible beyond the nut to make it “in safety”. (But of course that will get potted in Redux/flox later and so be invisible to the inspector Smile )

If I leave it as is, there will be an ugly bump of filler.

Is there something clever I haven’t thought of?

in friendship

Rowland

| Rowland Carson ... that's Rowland with a 'w' ...
| <rowlandcarson(at)gmail.com> http://www.rowlandcarson.org.uk
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John Wighton



Joined: 18 May 2010
Posts: 241

PostPosted: Tue Nov 01, 2016 12:28 am    Post subject: Re: door hinge screw query Reply with quote

Rowland,

The manual 35_CBM - 35 FITTING DOORS from the Europa website, Fig 5 shows the intended design condition of the door hinge installation. The screws into the upper hinge leaf are shown countersunk with a knife-edge condition (poor practice #1), the figure is probably not to scale but there looks to be significant material for the counter-bore, a washer and the nut. It shows an almost flush screw (i.e. less than 1 complete thread as normally required) (poor practice #2). I note the lower hinge leaf has a protruding head fasteners with integral washer.(AN525-10R10) and a non counter-bored retaining nut (good practice #1).

The critical failure mode as drawn is a head-side pull through (due to tension and prying) of the upper screw. For high time aircraft this may be surpassed by a tensile failure initiated by a fatigue crack between the countersinks. Hence l think you could increase the depth of the counter-bore slightly to ensure one protruding screw thread and a flush OML (outer mould line). Minimise the countersinking.

Looking at my own aircraft l found both sides countersunk. This enables a slight over-parallel condition of the hinge leaves - to account for built tolerance (in other words there is no room for the head of the AN525-10R10). This has the slight benefit of ensuring both sides of the hinge flex a similar amount - thereby reducing the likelihood of a fatigue crack on the more flexible side (as drawn).

A redesign to today's interpretation of the regulations and compliance standards would require adherence to best practice design principles. This would most likely result in slightly thicker hinges, 130 deg countersinks with corresponding shallow head fasteners, a third fastener on each hinge (offset centreline to alleviate the prying action).

JW


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John Wighton
Europa XS trigear G-IPOD
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budyerly(at)msn.com
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PostPosted: Sat Nov 05, 2016 5:22 pm    Post subject: door hinge screw query Reply with quote

Rowland,
Attached is a .pdf on how I do doors in the shop.
Countersinking and alignment are explained. Hope this helps.
Regards,
Bud Yerly

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Custom_Flight_Door_Hinge_Installation.pdf
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John Wighton



Joined: 18 May 2010
Posts: 241

PostPosted: Sun Nov 06, 2016 11:35 pm    Post subject: Re: door hinge screw query Reply with quote

A gust caught the canopy as l was refuelling yesterday, l use a bungee with rubber hooks to secure the Mr Funnel, these are hooked around the open door moulding close to the hinge. The wind popped the oleo strut (weak ball-ends) causing it to slam. Not a problem normally but the rubber hooks jammed causing some big loads at the hinge.

The upper hinge leaf is bent but the heads of the fasteners did not pull through. Dismantling revealed the knife-edge countersink, which is so deep the hole is opened up to well beyond a 'fit' with the screws.

Repair is easy, but this incident does underline how marginal the hinges are even when built according to the manual.

Correction: Earlier l stated the lower screws on my aircraft were countersunk - they are not, being standard MS21042-3. Memory playing tricks.

JW


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Fred Klein



Joined: 26 Mar 2012
Posts: 503

PostPosted: Mon Nov 07, 2016 12:02 pm    Post subject: door hinge screw query Reply with quote

Quote:
On Nov 6, 2016, at 11:35 PM, John Wighton <john(at)wighton.net (john(at)wighton.net)> wrote:
The upper hinge leaf is bent but the heads of the fasteners did not pull through. Dismantling revealed the knife-edge countersink, which is so deep the hole is opened up to well beyond a 'fit' with the screws.Repair is easy, but this incident does underline how marginal the hinges are even when built according to the manual.

John�if memory serves, the hinge/door tang is designed as a failure point in order to ensure that the departure of an un-secured door does not inflict structural damage on the fuselage�F.
[quote][b] [quote][b]


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Fred Klein



Joined: 26 Mar 2012
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PostPosted: Mon Nov 07, 2016 2:02 pm    Post subject: door hinge screw query Reply with quote

…let’s try this again…
Quote:
On Nov 6, 2016, at 11:35 PM, John Wighton <john(at)wighton.net (john(at)wighton.net)> wrote:
The upper hinge leaf is bent but the heads of the fasteners did not pull through. Dismantling revealed the knife-edge countersink, which is so deep the hole is opened up to well beyond a 'fit' with the screws.Repair is easy, but this incident does underline how marginal the hinges are even when built according to the manual.

John…if memory serves, the hinge/door tang is designed as a failure point in order to ensure that the departure of an un-secured door does not inflict structural damage on the fuselage…F.

[quote][b] [quote][b]


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