Piano Hinge Failure

[snopercod]

I had one of the "lugs" (I don't know the proper name), crack off on one of my gear door hinges. I understand that RVs use lots of these MS20001-P5 extruded aluminum hinges so I'm posting this for discussion:



You will notice that the throats in these old hinges have almost no radius at the corners - I estimate .005" max, and all edges are sharp. It's my belief that a fatigue crack started in the sharp corner where the actuator arm bolts on (the dirty area in the photo). The replacement hinge stock which just arrived from ACS has a nice radius in those corners - I estimate .020" - but the edges are still sharp. So I just ordered some Craytex wheels which I intend to use in my Dremel to break all those sharp edges to eliminate stress risers.

Comments or suggestions?

[Bill Rossmann]

The inboard gear doors take a beating when the engine is running bouncing back and forth on the ground. I had to replace the inboard hinges due to wear.
Bill

[snopercod]

Yup, the prop wash really beats up the inboard gear doors, especially on the R side. Have you considered stainless steel hinges? Also, I use the 321 SS welding rod for hinge pins; It fits better.

[rzbill]

The obvious solution John, is to get rid of the gear doors and keep the gear down and welded like a 'proper' airplane.....

But seriously when I built my 7A, all the hinge supplied by Vans was the rolled variety not the much stronger extruded style you are using. Not sure if this has been the case for all RVs. I just know what I received which matched the prints. I did put some extruded hinge in a couple of spots on my cowl that I wanted extra strength and more flange length.

No problems yet after 700 hrs but my hinges are not taking the beating that yours are.

Come to think of it... The hinge supplied for the cowl to fuselage joint was much heavier variety, still rolled though. Might be an option but you would have to replace both halves. If I see you at the hanger we can look up the part on my prints. I think it is non-aviation hinge but memory could be off.

Good luck, friend.

[snopercod]

Originally Posted by rzbill

If I see you at the hanger we can look up the part on my prints.

I'd like to see that. I fabricated a new set of hinges today (See, even us fiberglass guys can make aluminum parts if we have to ).

[ronschreck]

You might get more information on a Lancair forum as I assume these gear doors are on your Lancair 235 but I can tell you that gear doors on any airplane are among the most stressed components and therefore deserve the most critical and timely inspections and preventative maintenance. Not only are the doors subject to stress while airborne but they are often flapping in the breeze of the propwash during ground operation. Even the finest aviation components fail at some point. The trick is to repair or replace before they get to that point. You have discovered that point on this particular hinge and may choose to modify the hinge or replace with something else but then you will be waiting to see when and where the next failure point will be.

You are to be congratulated for doing a timely inspection which led you to find and address a failure point. It's a continuing process. Welcome to aviation!

[EXflyer]

Also note that there was quite a bit of tell tale showing in the form of black gook. The actuator attach point puts quite a bit of strain on the hinge at one point. Don't think there was a problem with it but with the actuator being attached there putting stress on that one hinge part also looks like the actuator load was not distributed evenly along its attach point. Just my take on what I would think about.

[snopercod]

What got me to thinking about those sharp interior corners on the piano hinge was the thread on Beechtalk regarding the Piper Arrow wing falling off down at Embry Riddle. The fracture in the wing attach fitting began at at a bolt hole with no chamfer. A member with an FEA program commented on how much sharp corners lower the allowable load.