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Replacement Screws for Phillips

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macrafic

Joined: 01 May 2006
Posts: 5

Posted: Mon May 01, 2006 7:43 am Post subject: Replacement Screws for Phillips

I agree with those who are looking for alternative screws to the AN-509 Phillip screws.  However, a bit of caution is in order, so that you know the difference between a structural and a non-structural application.  Van's plans do not point this out.  Here is the reply I got from MicroFasteners when I asked about their screws.  Microfasteners is the brand that has shown up quite a bit on various RV forums:



"Our stainless steel 100 degree flat head torx drive screws are all intended 

to replace the cross recessed screws of NASM24693 (which has superseded AN507) covering non-structural screws. Their tensile strength is 85,000 psi minimum, same as the requirement for structural screws of NASM24694 (which has superseded AN509,)  so the tensile strength for 8-32 screws is 1190 lbs, minimum. However their intended use is nonstructural and the grip length requirement of the structural screw spec is not met. 

 

We emphasize that these are not mil spec screws; first no testing has been done to verify that, apart from the different drive, they meet the 

requirements of either of the specs listed above, and second there is no mil spec covering these screws, to the best of our knowledge.



We don't have the AN509 spec, but the superseding NASM spec lists parts of three different compositions and hence strengths: low alloy steel at 125,000 psi, aluminum alloy at 62,000 psi and corrosion resistant (stainless) steel at 85,000 psi. Our parts are the latter. Please don't use them where the 125,000 psi parts are specified."

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retasker(at)optonline.net
Guest

Posted: Mon May 01, 2006 7:13 pm Post subject: 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

macrafic wrote:



 	  Quote: 	
		  



I agree with those who are looking for alternative screws to the AN-509 Phillip screws.  However, a bit of caution is in order, so that you know the difference between a structural and a non-structural application.  Van's plans do not point this out.  Here is the reply I got from MicroFasteners when I asked about their screws.  Microfasteners is the brand that has shown up quite a bit on various RV forums:



"Our stainless steel 100 degree flat head torx drive screws are all intended 

to replace the cross recessed screws of NASM24693 (which has superseded AN507) covering non-structural screws. Their tensile strength is 85,000 psi minimum, same as the requirement for structural screws of NASM24694 (which has superseded AN509,)  so the tensile strength for 8-32 screws is 1190 lbs, minimum. However their intended use is nonstructural and the grip length requirement of the structural screw spec is not met. 

 

We emphasize that these are not mil spec screws; first no testing has been done to verify that, apart from the different drive, they meet the 

requirements of either of the specs listed above, and second there is no mil spec covering these screws, to the best of our knowledge.



We don't have the AN509 spec, but the superseding NASM spec lists parts of three different compositions and hence strengths: low alloy steel at 125,000 psi, aluminum alloy at 62,000 psi and corrosion resistant (stainless) steel at 85,000 psi. Our parts are the latter. Please don't use them where the 125,000 psi parts are specified."





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=32048#32048





 

 

 





  




	


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michele.delsol(at)microsi
Guest

Posted: Mon May 01, 2006 9:48 pm Post subject: Replacement Screws for Phillips

Makes a lot of sense - there appears to be a huge amount of safety factor

built into the arrangement which attaches the tanks onto the spars. Consider

it another way. If Vans had put only the screws necessary to do the job with

a safety factor of 2, we would en up with a lot fewer screws - probably 3

out of every 4 would be eliminated. I figure that if I were to look at my

tanks and see only one screw every 4 inches or so, I'd not want to fly the

thing: Psychology 101.



Michele - RV8 fuselage

 



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dennis.glaeser(at)eds.com
Guest

Posted: Tue May 02, 2006 5:28 am Post subject: Replacement Screws for Phillips

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(at)optonline.net>

Subject: Re: 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

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frank.hinde(at)hp.com
Guest

Posted: Tue May 02, 2006 6:19 am Post subject: Replacement Screws for Phillips

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



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