The Murphy Builders Site

Posted: **Fri Feb 17, 2012 9:59 pm**

Hi Wayne,

Brian made the point that you "don't want caps and doublers ending at the
same point." I would imagine this is to prevent a "stress riser" from
occurring at that point.

My long cap ends 1.5 " below the top of the doublers. I am not an engineer
but my "feeling" is that it ends close enough to give support to the hinge
area without creating a stress riser.

You are correct that the new cap reaches only 2" above the original. When I
look at the overall upgrade, the doublers and the caps, it seems to me to be
a significant increase in strength over the original SR2500.

I would hope that if Brian had ANY CONCERN about the installation that he
would have advised me to redo it. I was at the #40 drilled stage. Redoing
would not have been a big deal. Simply ship some new raw stock.

I don't no why Brian didn't clarify MAM's original intention for this area.
??????

Well I'm all drilled up and feel confident the Fin will give rugged service.

I will ask Mike to remove my picture of the upper end of the spar caps.

It seemed strange to me too that there was no mention of riveting the spar
doublers. That's why I asked. I hate having to be a mind reader.

Well I moved on today. The aileron spade mod came in the mail and is
underway. Hopefully I will get a few days of smooth sailing to offset the
frustration of the past week.

Wayne, as usual thanks for all your input.

Regards,
Don Boardman
& Partner
Randy Bowers
SR130 Rome, NY

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Posted: **Fri Feb 17, 2012 9:59 pm**

Yes Don, that is definitely why you don't want them all to end in the same
place. You want a gradual transition, for the bending moment, and not a
quick strong to weak area that would/could cause the area to buckle/break
instead gradually spreading the load. Same reason that some of the wings
main spar doublers are "fork" ended instead of straight cuts and the other
doublers are staggered lengths to spread the load proportionally instead of
in one big step..

And you are right, if Brian had any concerns he WOULD have let you know!
Maybe the 3500 upgrade is over-killed in this area and because of that you
are good to go "as is"! Considering bolt sizes alone on the 3500 upgrades
this looks like the case for at least some areas, as even my 4300lb gross
UTVA's only have a 9/16 bolt in the wing lift strut to wing/fuselage
attachments and also the main wing attach bolts (and it is designed at
4.3g's x 150%).

As for lacking instructions, to side with MAM for a minute (again), it is a
lot easier to do the mods already knowing what you want to accomplish than
to take the time to photograph it at each stage and then write it up a
couple months after the fact while sitting at the factory (when the mods are
on a finished aircraft down the road at the airport). Remember they were in
a BIG rush to make S n F upon completion of the SR3500, reworked 2500, last
year. I'm sure Brian and crew will get the manual all cleaned up for future
builders if the current builders continue to be cautious, ask questions, and
provide some feedback (to MAM) along the way! I guess in some way that's why
for the last few years I have taken thousands of pictures through each
building stage and/or rebuild project. Someday, when I feel I have covered
most aspects of Murphy Metal construction and "field" repair, I will put
them out on CD for a photo style "pictures worth a thousand words" version
of the builders manuals.

:>)
Wayne G. O'Shea
www.irishfield.on.ca

----- Original Message -----
From: "Don Boardman" <dboardm3@twcny.rr.com>
To: <murphy-rebel@dcsol.com>
Sent: Friday, February 22, 2002 8:40 PM
Subject: SR Fin Spar Cap ... moving on

Hi Wayne,

Brian made the point that you "don't want caps and doublers ending at the
same point." I would imagine this is to prevent a "stress riser" from
occurring at that point.

My long cap ends 1.5 " below the top of the doublers. I am not an engineer
but my "feeling" is that it ends close enough to give support to the hinge
area without creating a stress riser.

You are correct that the new cap reaches only 2" above the original. When

I

look at the overall upgrade, the doublers and the caps, it seems to me to

be

a significant increase in strength over the original SR2500.

I would hope that if Brian had ANY CONCERN about the installation that he
would have advised me to redo it. I was at the #40 drilled stage. Redoing
would not have been a big deal. Simply ship some new raw stock.

I don't no why Brian didn't clarify MAM's original intention for this

area.

??????

Well I'm all drilled up and feel confident the Fin will give rugged

service.

I will ask Mike to remove my picture of the upper end of the spar caps.

It seemed strange to me too that there was no mention of riveting the spar
doublers. That's why I asked. I hate having to be a mind reader.

Well I moved on today. The aileron spade mod came in the mail and is
underway. Hopefully I will get a few days of smooth sailing to offset the
frustration of the past week.

Wayne, as usual thanks for all your input.

Regards,
Don Boardman
& Partner
Randy Bowers
SR130 Rome, NY

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