Author: "Phil" <pjanderton@...> Time: Thu Feb 19, 2004 3:28 am PST Link
Builders -
Last night I cut the 7 lightening holes in VS 808PP spar doubler with
2" and 1 1/2" hole saws and a drill press. The holes are clean and
centred, but the final hole diameters are each about 1/16" larger
than specified by the drawings (2 1/16" and 1 9/16").
I asked Vans if there was a problem with this - they said they
couldn't guarantee it because it had not been tested by their
engineers, but they did not say "you must replace it". I guess this
is their standard answer to such questions - in their place I would
say the same.
I would appreciate any educated opinions. Is there any chance of this
being structurally unsound? My impression is that the design is very
strong (aerobatic, thick skins) and that having slightly larger
lightening holes would have little detrimental effect. Also the loads
on this component are concentrated on the hinge attachments, located
between the holes where this component is solid plate.
I would like to have some informed opinion to give my Technical
Counsellor when I mention this.
Thanks
Phil Anderton
Sydney, Aus
Author: "Michael" <michael@...> Time: Thu Feb 19, 2004 10:52 am PST Link
Phil,
My immediate guess would be "no problem" but to help with an
analytical answer, I would be happy to do a quick little FEA on the
spar. I would just use shell elements and put simple loading on the
model... perhaps tension only and then tension plus bending. Not
knowing the acual flight loads, this simple analysis can only be used
to compare the difference in stress levels obtained between using the
design hole versus the slightly larger hole. (which I suspect will be
slight)
I would need from you a description of the spar dimensions:
Spar Length.
Spar Metal Thickness.
Spar Web width.
Spar Flange width.
Lightening Hole Location.
Also let me know if the Spar is uniform or if it tapers.
I'm Building a 9A, so I imagine our plans don't exactly jibe.
Mike 90817
(Empennage nearly finished.)
You can send info directly to my email so as not to clutter this site
unnecessarily. I will be glad to post pictures of the results for
all to see if anything unexpected occurs.
--- In RV7and7A@yahoogroups.com, "Phil" <pjanderton@o...> wrote:
> Builders -
>
> Last night I cut the 7 lightening holes in VS 808PP spar doubler
with
> 2" and 1 1/2" hole saws and a drill press. The holes are clean and
> centred, but the final hole diameters are each about 1/16" larger
> than specified by the drawings (2 1/16" and 1 9/16").
>
> I asked Vans if there was a problem with this - they said they
> couldn't guarantee it because it had not been tested by their
> engineers, but they did not say "you must replace it". I guess this
> is their standard answer to such questions - in their place I would
> say the same.
>
> I would appreciate any educated opinions. Is there any chance of
this
> being structurally unsound? My impression is that the design is
very
> strong (aerobatic, thick skins) and that having slightly larger
> lightening holes would have little detrimental effect. Also the
loads
> on this component are concentrated on the hinge attachments,
located
> between the holes where this component is solid plate.
>
> I would like to have some informed opinion to give my Technical
> Counsellor when I mention this.
>
> Thanks
>
> Phil Anderton
> Sydney, Aus
Author: LR Frey <lrogerfrey@...> Time: Thu Feb 19, 2004 10:52 am PST Link
Phil, I can't be any more specific than Van's, but I would look at it this way....
Compare the area of the enlarged holes to the area of the doubler and then compare the area of the holes as specified to the doubler area. I'll bet the percentage of difference is small. (I,m 1700 miles from home and my drawings so I can't make this calculation right now).
Then, be comfortable with the distance of the hole to the edge of the doubler. 1/16 oversize will only be 1/32 closer to the edge at any given point!
Hope this helps rather than hinders...
Larry
Phil <pjanderton@o...> wrote:
Builders -
Last night I cut the 7 lightening holes in VS 808PP spar doubler with
2" and 1 1/2" hole saws and a drill press. The holes are clean and
centred, but the final hole diameters are each about 1/16" larger
than specified by the drawings (2 1/16" and 1 9/16").
I asked Vans if there was a problem with this - they said they
couldn't guarantee it because it had not been tested by their
engineers, but they did not say "you must replace it". I guess this
is their standard answer to such questions - in their place I would
say the same.
I would appreciate any educated opinions. Is there any chance of this
being structurally unsound? My impression is that the design is very
strong (aerobatic, thick skins) and that having slightly larger
lightening holes would have little detrimental effect. Also the loads
on this component are concentrated on the hinge attachments, located
between the holes where this component is solid plate.
I would like to have some informed opinion to give my Technical
Counsellor when I mention this.
Thanks
Phil Anderton
Sydney, Aus
Van's Air Force - World Wide Wing
www.vansaircraft.net
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Author: "Mike Allardyce" <mallardyce@...> Time: Thu Feb 19, 2004 10:53 am PST Link
Phil, I doubt many folks will be willing to discuss structural
analysis with you. But, what the heck. In general terms, lightening
holes are used to decrease weight (duh). They also decrease the
component's moment of inertia. Stress in a component is inversely
proportional to moment of inertia. As the moment of inertia goes
down, stress goes up. The moment of inertia is dependent on cross
sectional area. The change in cross sectional area caused by 1/32"
per side is, in my opinion, insignificant. FWIW.
Mike (mechanical engineer, but 20 years out of school)
--- In RV7and7A@yahoogroups.com, "Phil" <pjanderton@o...> wrote:
> Builders -
>
> Last night I cut the 7 lightening holes in VS 808PP spar doubler
with
> 2" and 1 1/2" hole saws and a drill press. The holes are clean and
> centred, but the final hole diameters are each about 1/16" larger
> than specified by the drawings (2 1/16" and 1 9/16").
>
> I asked Vans if there was a problem with this - they said they
> couldn't guarantee it because it had not been tested by their
> engineers, but they did not say "you must replace it". I guess this
> is their standard answer to such questions - in their place I would
> say the same.
>
> I would appreciate any educated opinions. Is there any chance of
this
> being structurally unsound? My impression is that the design is
very
> strong (aerobatic, thick skins) and that having slightly larger
> lightening holes would have little detrimental effect. Also the
loads
> on this component are concentrated on the hinge attachments,
located
> between the holes where this component is solid plate.
>
> I would like to have some informed opinion to give my Technical
> Counsellor when I mention this.
>
> Thanks
>
> Phil Anderton
> Sydney, Aus
Author: "Roee Kalinsky" <kalinsky@...> Time: Fri Feb 20, 2004 11:44 am PST Link
Hi Phil,
Sorry to hear about your dilema. It happens. I can't say whether that
1/16" is significant or not, and neither can anyone else here. A lot of
builders disregard all kinds of minor mistakes, justified by pointing out
that there's margin built into the design. True, although you'd like to
retain that margin for the imperfections you don't know about, and for that
one time when you overstress the airframe inadvertently. Problem is that
without being able to do stress analysis on the design, you don't know how
much you're weakening it or how much you can afford to weaken it.
My feeling is that an occasional imperfect rivet in the middle of a long
row, maybe let it slide because there's a lot of redunduncy. But in this
instance it's a major structural member and I would probably replace it.
Small price to pay for peace of mind, but that's just my opinion. I'm an
engineer, but electrical not mechanical, so take it for what it's worth.
BTW, I just cut my VS-808PP last night. An adjustable fly cutter in the
drill press worked pretty well. I cut the holes just a hair undersized.
After I clean them up they should be pretty much dead on. If I had to do it
again, I would cut them even a little more undersized just to be sure. More
margin is better than less margin.
No worries dude, just a speed bump.
-Roee
-----Original Message-----
From: Phil [mailto:pjanderton@o...]
Sent: Wednesday, February 18, 2004 9:45 PM
To: RV7and7A@yahoogroups.com
Subject: [RV7Yahoo] VS 808PP lightening holes slightly over-size
Builders -
Last night I cut the 7 lightening holes in VS 808PP spar doubler with
2" and 1 1/2" hole saws and a drill press. The holes are clean and
centred, but the final hole diameters are each about 1/16" larger
than specified by the drawings (2 1/16" and 1 9/16").
I asked Vans if there was a problem with this - they said they
couldn't guarantee it because it had not been tested by their
engineers, but they did not say "you must replace it". I guess this
is their standard answer to such questions - in their place I would
say the same.
I would appreciate any educated opinions. Is there any chance of this
being structurally unsound? My impression is that the design is very
strong (aerobatic, thick skins) and that having slightly larger
lightening holes would have little detrimental effect. Also the loads
on this component are concentrated on the hinge attachments, located
between the holes where this component is solid plate.
I would like to have some informed opinion to give my Technical
Counsellor when I mention this.
Thanks
Phil Anderton
Sydney, Aus
Van's Air Force - World Wide Wing
www.vansaircraft.net
Yahoo! Groups Links