Today's Message Index:
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1. 06:28 AM - Re: Replacement Screws for Phillips (Glaeser, Dennis A)
2. 07:19 AM - Re: Re: Replacement Screws for Phillips (Hinde, Frank George (Corvallis))
Message 1
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| Subject: | RE: Replacement Screws for Phillips |
--> RV7-List message posted by: "Glaeser, Dennis A" <dennis.glaeser@eds.com>
I totally agree with Dick. I posted a similar analysis - based on shear
strength - on the RV list a while back. If the tanks fall off, you will
see torn aluminum, not failed fasteners!
I used to design aircraft structures, and already have the Microfastener
Torx screws on my wing tanks. I'm not flying yet, but also sleep
soundly with that decision.
Dennis Glaeser
7A - Fuselage
From: "Richard E. Tasker" <retasker@optonline.net>
Subject: Re: RV7-List: Replacement Screws for Phillips
While I agree that caution is always in order when you are more than
about 10 ft in the air, we can carry it to extremes sometimes. Let's
consider this discussion. On the RV9A (what I am building) there are 32
screws on the top and 32 screws on the bottom of the wing tanks. Each
#8 screw can withstand 1190 lbs of tensile force before it breaks - as
noted below and confirmed by my calculations. The wing tank holds 18
gallons of gas for a weight of 108 lbs. plus the weight of the tank of
(conservative SWAG) 50 lbs for a total weight of 158 lbs. There is some
leverage on the screws since the tank sticks out the front of the wing,
but not a whole lot since the brackets will act as the fulcrum and they
are several inches below the wing skins. Furthermore, true shear (which
this really isn't) results in a strength of 50-75% the value of the
tensile strength. So if we take the 32 screws times the tensile
strength of 1190 lbs time 0.5 (being conservative) we get a total yield
strength of 19,000 lbs. At ten Gs the 158 lbs of the tank will be 1580
lbs. This is still more than ten times below the ultimate yield
strength of the screws. Let's assume that we have a leverage factor of
2-3 times the actual weight - probably not true but let's be
conservative. Even this still gives a safety factor of four times - at
a stress level where the wings will probably be falling off. In
addition to all this, it is a well known fact that the dimpled joints
add considerably to the shear strength of a rivet or screw joint and we
have completely ignored this fact. We have also ignored the additional
screws on the end of the tank and the front wing support as well.
So... I plan to use the #8 MicroFastener torx screws on my wing tanks
and sleep very well at night.
Dick Tasker
Message 2
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| Subject: | RE: Replacement Screws for Phillips |
--> RV7-List message posted by: "Hinde, Frank George (Corvallis)" <frank.hinde@hp.com>
Cool...I hate the idea of painting over screws so this is a perfect
alternative, i.e paint first and put the SS screws in after
Thanks
Frank
Rv7a...bodywork and paint.
Do not archive
-----Original Message-----
From: owner-rv7-list-server@matronics.com
[mailto:owner-rv7-list-server@matronics.com] On Behalf Of Glaeser,
Dennis A
Sent: Tuesday, May 02, 2006 6:24 AM
Subject: RV7-List: RE: Replacement Screws for Phillips
--> RV7-List message posted by: "Glaeser, Dennis A"
--> <dennis.glaeser@eds.com>
I totally agree with Dick. I posted a similar analysis - based on shear
strength - on the RV list a while back. If the tanks fall off, you will
see torn aluminum, not failed fasteners!
I used to design aircraft structures, and already have the Microfastener
Torx screws on my wing tanks. I'm not flying yet, but also sleep
soundly with that decision.
Dennis Glaeser
7A - Fuselage
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