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02-20-2012, 09:51 AM
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Join Date: Nov 2005
Posts: 121
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Inspection panel screws
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
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02-20-2012, 10:50 AM
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Join Date: May 2006
Location: Houston
Posts: 2,012
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Quote:
Originally Posted by 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
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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.
Last edited by Low Pass : 02-20-2012 at 10:58 AM.
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02-20-2012, 03:23 PM
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Join Date: Jan 2008
Location: MERRITT ISLAND, FL
Posts: 360
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Screws in inspection plates
Quote:
Originally Posted by speyers
Does anyone know if inspection panels in the wing need structural screws?
-David
RV-8 Wings
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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
__________________
Don Stiver
RV8 "Little Pill" N6371S, Merritt Island, Fl.
BPE IO-390, Dual P-mag, MT 3-blade, AFP system
Steen Skybolt: Sold
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02-20-2012, 03:35 PM
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Join Date: Mar 2005
Location: Dallas area
Posts: 10,769
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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.
__________________
Mel Asberry, DAR since the last century.
EAA Flight Advisor/Tech Counselor, Friend of the RV-1
Recipient of Tony Bingelis Award and Wright Brothers Master Pilot Award
USAF Vet, High School E-LSA Project Mentor.
RV-6 Flying since 1993 (sold)
<rvmel(at)icloud.com>
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02-21-2012, 05:14 AM
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Join Date: Jan 2008
Location: MERRITT ISLAND, FL
Posts: 360
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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
__________________
Don Stiver
RV8 "Little Pill" N6371S, Merritt Island, Fl.
BPE IO-390, Dual P-mag, MT 3-blade, AFP system
Steen Skybolt: Sold
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02-21-2012, 10:56 AM
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Join Date: Nov 2006
Location: Azle, TX
Posts: 352
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[quote=Mel;631236]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.
__________________
Bill Grant, A&P
8KCAB, M20G
RV-4: Fuselage controls
Last edited by WSBuilder : 02-21-2012 at 11:11 AM.
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02-21-2012, 11:55 AM
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Join Date: May 2006
Location: Houston
Posts: 2,012
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[quote=WSBuilder;631561]
Quote:
Originally Posted by Mel
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.
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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.
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02-21-2012, 12:38 PM
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Join Date: Nov 2006
Location: Azle, TX
Posts: 352
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[quote=Low Pass;631582]
Quote:
Originally Posted by 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.
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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.
__________________
Bill Grant, A&P
8KCAB, M20G
RV-4: Fuselage controls
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02-21-2012, 01:26 PM
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Join Date: Dec 2009
Location: Boulder, CO
Posts: 4,435
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Quote:
Originally Posted by Low Pass
....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.
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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
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