Cabin doors hinges backplates
 

Hi guys,
Trying to figure how to reinforce my cabin doors' hinges.
Don't like the idea of countersinking my outer shell and using AN509 nuts directly into the fiberglass.
Would prefer some king of a reinforcement bracket, so it will be aluminum/fiber/stell(hinge) sandwich.
While no problem doing that on the Cabin top, since there are pockets, the outer shell glued to the inner is so thin, that if i will add some kind of bracket it will sit on top of the door.

What are you guys doing?
is the per-plan countersinking lasts good enough? ideas?

Thanks!
Oren

Doors
 

I used SS 100 degree countersunk flush washers. Countersunk similar to the plans with the washers to spread the load...

Airward
 

I think construction is just as much an issue, when you have the doors on and off a zillion times. You want to be able to set the doors in the same alignment every time you put them on, and you are better off not fiddling around with separate nuts on the inside.

There is one after market product out there - here - but it comes at a way over the top price, and the top plates do protrude about 3mm.

You could easily make up the inside nutplates/reinforcement plates (epoxy'd in place inside the cabin top), and use temporary reinforcement (an external plate, or washers) on the outside of the door (only) during construction. Just use temporary AN3 bolts to attach/detach the doors, often just two bolts per hinge on the cabin top will do. Once you're done, choose what to do on the outside of the doors. Either follow the plans, keep your custom reinforcing plates, or countersink and use SS washers as Bob described.

A.

Countersinking is a very effective method of retention. Just because the flare on the screw is longer than the depth of the f/g layup doesn't mean it is not strong. I built per plans and find the hinges to be very firmly attached to the door. don't forget that you already have 1/4" steel plate acting as reinforcement for the f/g. Can't see why you need more.

We could all argue that the door skin could be thicker, but I haven't heard of anyone ripping the door off the hinges yet.

Larry

Hi Oren
 

Could you glass in a thin steel plate on the outside of the door without it being an obvious bulge?

Otherwise, maybe just go with the plans though i agree it ?feels? too flimsy.

Happened to me - when a National Guard C-130 did a full power reverse taxi on the ramp right in front of me. The pilot door departed the aircraft, snapping the hinges. I was happy the hinges themselves failed and not the screw heads pulling out of the cabin top or the door.

The cabin top and door were not damaged. Some replacement hinges and I flew the plane home.

My recommendation, for all screws in the door use #10 SS tinerman washers under the heads. Worked very well for me. Do not glass over the screw heads as then you will end up messing up your paint job if you ever needed to do associated maintenance.

Carl

Well, there's your answer. Hinges failed before the standard attachment to the f/g. Seems like good evidence that there is no real need to reinforce, as it is not the weak link.

Carl, good to hear the fix was simple. Wish I had thought to use tinnermans and leave unpainted. Mine are covered with bondo only, so easy to scoop out if the need arises.

Has anyone else noticed the flex in the cabin top/doors around the hinges? I've taken a close look at a couple of finished airplanes as the doors open and close, and there is a fair amount of movement in the fiberglass. Over the long term, that is a concern to me...

I have noticed some flex during opening/closing. Not really surprising given the size/weight of the door relative to the f/g thickness, not to mention the force of the damper on only one side. I am not overly concerned, as the f/g is not likely to deform while in the closed position, where it spends 99.9% of it's time. structure seems pretty rigid/stable in the closed position. I just can't see how a few hours of jostling over it's life can create real issues.

Just one man's thoughts.

Larry

Thank you guys!
I didn't think of the SS countersunk washers. Its a great idea ! will follow!!