[speyers]

Does anyone know if inspection panels in the wing need structural screws? IE, on most Cessna's they are held in with PK or sheet metal screws, wondering if there is any structural reason the same could not be done on the wing inspection panels, fiberglass wing tips, and even cabin flooring?

-David
RV-8 Wings

 

[Low Pass]

Does anyone know if inspection panels in the wing need structural screws? IE, on most Cessna's they are held in with PK or sheet metal screws, wondering if there is any structural reason the same could not be done on the wing inspection panels, fiberglass wing tips, and even cabin flooring?

-David
RV-8 Wings

Wing inspection covers are structural (per Scott I believe it was at Van's). Wingtips are structural as far as I'm concerned as they are part of the wing (what happens if one falls off). Cabin flooring - depends on the part. But I personally wouldn't use sheet metal screws on any of these items (actually, can't think of one sheet metal screw anywhere in the plane). I substituted stainless flat head Torx to all the locations you mentioned 10-11 yrs ago with no ill effects.

Aside from the specific strength conparison between the two types of fasteners, I'd personally be concerned about the sheet metal screw not staying tight. Never seen a machine screw back out of a plate nut.

Just my 2 cents.

 

[APACHE 56]

Screws in inspection plates

Does anyone know if inspection panels in the wing need structural screws?
-David
RV-8 Wings

David,
The inspection panels on my wings are a combinations of#6 and #8 per plans and they are factory built. As I recall the smallest structural fastener is #10.
Don

 

[Mel]

Just because the "cover" is structural does not mean that the fasteners must be structural.

A good example is the rear baggage bulkhead. It is structural mostly in torsion. The fasteners are not necessarily structural.

 

[APACHE 56]

I stand corrected...

I incorrectly it appears thought inspection covers are just that inpection covers and are not structural. My belief was that if they were truly structural panels you would not be able to move or jack the aircraft without them being installed.

Don

 

[WSBuilder]

Just because the "cover" is structural does not mean that the fasteners must be structural.QUOTE]

This can't be true. If a panel/cover is required to carry structural load it must be translated to the surrounding structure via the fasteners unless there is a passive mechanical interconnect through the panel edges. I'd be surprised if the wing inspection covers provide more than aerodynamic load, in which case sheet metal screws are adequate. Most inspection covers/openings are round to mitigate stress concentration whearas RV's are rectagular with large corner radii which is slighty weaker. Floor panels are in shear; I'd bet Van's knows how much, and as such are made stronger by using structural screws. I see a lot of builders render floor covers non-structural by making them hinged, with no apparent ill effect, so they are probably not highly loaded.

 

[Low Pass]

Just because the "cover" is structural does not mean that the fasteners must be structural.QUOTE]

This can't be true. If a panel/cover is required to carry structural load it must be translated to the surrounding structure via the fasteners unless there is a passive mechanical interconnect through the panel edges. I'd be surprised if the wing inspection covers provide more than aerodynamic load, in which case sheet metal screws are adequate. Most inspection covers/openings are round to mitigate stress concentration whearas RV's are rectagular with large corner radii which is slighty weaker. Floor panels are in shear; I'd bet Van's knows how much, and as such are made stronger by using structural screws. I see a lot of builders render floor covers non-structural by making them hinged, with no apparent ill effect, so they are probably not highly loaded.

This is not a good assumption. I strongly recommend anyone not certain of the mods they're contemplating call the factory. I was told flatly that they're "structural". Good luck.

 

[WSBuilder]

This is not a good assumption. I strongly recommend anyone not certain of the mods they're contemplating call the factory. I was told flatly that they're "structural". Good luck.

As someone not daring to stray from the design I don't advocate as such. I always presume the factory is both conservative and right. Don't know why someone would stray on an issue like this. But I also know the tech help on the phone are clueless on this kind of detail and will always defer to build as designed. They are not consulting a finite element model of the wing when they answer you.
Having said that, on my -4 the wing access panel joggle, which accounts for much of the strength of a hole, is discontinuous and rectangular. That means it is carrying little strength. The hole is bisected by a rib so the skin is not carrying much load in that area.

 

[David Paule]

....on my -4 the wing access panel joggle, which accounts for much of the strength of a hole, is discontinuous and rectangular. That means it is carrying little strength. The hole is bisected by a rib so the skin is not carrying much load in that area.

This is a poor assumption. Shear is carried across these inspection panels and a bisecting rib wouldn't necessarily decrease the shear involved. The shear somehow needs to get from one side of the hole to the other.

Often - but not always - the frame around the hole is designed to carry the shear and any other membrane load, not the removable panel itself. You'd have to talk to Van's to find out, since it's not necessarily obvious by inspection.

Dave