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Oil Hatch bulging in flight

Berchmans

Well Known Member
I made the first flight of my RV-8 the other day and noted that the hinge side of the oil door bulges out slightly due to air pressure. I have used the hidden hinge and the standard vans latch fittings without the wing nut ears. Is there a good way to stiffen the door? I have thought about adding a small piece of channel to the underside of the door or possibly installing a couple more of the push and turn fasteners at the hinge corners.
 
Is there a good way to stiffen the door? I have thought about adding a small piece of channel to the underside of the door or possibly installing a couple more of the push and turn fasteners at the hinge corners.

Here's how I did mine. Seemed to keep the shape in line just fine.

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Here is how I did mine

Another approach is fiberglass over foam core. Not flying yet but seems very stiff.

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I replaced mine with .050 alum.. Never bulged or popped open since. It was time consuming getting the compound curve correct.
 
I have a hidden latch which is based on a simple piece of hinge (left over from seat rail) and operated by a pull/push piece of wire from the air inlet. It keeps it from going anywhere and a cleaner look (my opinion)
 
I carefully cut out the oil door recess and saved the piece of pink fiberglass. I bonded it with epoxy under the oil door and it is very stiff now.

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What Bruce said. It may be too late now, but for anyone still building, use the piece of fiberglass you cut out from the cowl and then fiberglass that to the underside of the door. Works great as a stiffener.

Chris
 
I think it is the hinge itself that is the problem

I made the first flight of my RV-8 the other day and noted that the hinge side of the oil door bulges out slightly due to air pressure.

From the OPs description, I don't think it is flexing in the door itself that is the problem.

I bent my own 'hidden hinge' recently and it turned out looking very similar to the manufactured item. However, I had made it out of 032 and that turned out to be too light. What was happening was that the large curved 'loop' section of the hinge (the section under his thumb in Bruce's picture above) had too much springiness in it. Even with the hinge firmly attached to both cowl and oil door, and the latch end held down, it took very little hand pressure to push the hinge end up from below.

Now the manufactured hinge is made of heavier material I'm sure, but there is a great deal of positive air pressure inside a flying upper cowl, despite even well sealed baffle. That kind of air pressure could very well overcome even heavier gauge hinges than mine. I believe that what Burke is seeing may well be flexing in the section of the hinge between it's attachment points on the cowl and oil door.

Maybe you guys with the Nonstop Aviation or McMaster hidden hinges could try pushing up with your fingers on the hinge end of your latched oil door while the cowl is off the aircraft and tell us what you see.
 
What Bruce said. It may be too late now, but for anyone still building, use the piece of fiberglass you cut out from the cowl and then fiberglass that to the underside of the door. Works great as a stiffener.
Chris

I knew I'd be pressurizing the cowl volume to some level much higher than stock as I shrank the exit, so I added eight plies of 9oz to the underside of the door when building. It's still not quite stiff enough. I'd suggest the foam core approach John used to get some section into the part. I'll probably retrofit.

This hidden hinge is the same style shown by John and Bruce. It's 0.065" 2024 and doesn't seem to flex under load. Use a little wet flox when you rivet it to the door.

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In Dan's photo he is pointint to the problem area. The bulging actually occures between where the hinge is riveted to the oil door and the cowling. I thought of adding some stiffening in this area or adding some of the spring loaded locking pins similar to Van's pins but with the wing nut feature. It's minor but one of those things you look at and it kind of bugs you
 
Mine bows up at the trailing edge corners too, but mine's on a 540 without a plenum. My oil door is therefore subject to under-cowl "plenum" pressures unlike the 360's typically. I like Andy's idea. I don't really feel like building a new door with a double latch, but a couple of fluted stiffners looks like a very workable idea.

Thanks!


Lee...
 
Thanks for all the responses. I now have lots of options on addressing issue. Still working on Phase 1 but as soon as I get the bird back home I will address and report on my fix.
 
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