40-2CD_&_TH7

[george fremin iii]

: If you invert the 40-2CD support brace, it MAY not provide adequate
: support. When on top, all you deal with is tension. When on bottom, you 
: have to consider buckling.  Does anyone know if it will work that way as 
: supplied by cushcraft? I'd be interested in a true engineering-type 
: analysis, not just some anecdotal stories of how well it works.


after i had reenforced the boom on one of W5KFT's 40-2cds
i have to say that i agree with the following.



----------------------------
Dave Leeson - writes:


Pull-apart of Struts

The struts don't add any wind survival to the boom, but they make it
look better by removing droop.  The struts are held together by hose clamps,
and the joints can be made stronger by pop-riveting.  Because I had greatly 
strengthened the boom and I used a short mast, I put the struts under
rather than over the boom.  This turned out to be a lesson in strength of
columns under compression, which is different from the same piece under 
tension; one has popped out and disappeared forever into the chapparal.

Dave Leeson, W6QHS


-- 

George Fremin III
Austin, Texas C.K.U.                        
WB5VZL
512/416-0140
geoiii at bga.com

>From k2mm at MasPar.COM (John Zapisek)  Sun May  8 07:04:21 1994
From: k2mm at MasPar.COM (John Zapisek) (John Zapisek)
Date: Sat, 7 May 94 23:04:21 PDT
Subject: 40m Buckling Brace
Message-ID: <9405080604.AA26604 at greylock.local>

Barry:

> If you invert the 40-2CD support brace, it MAY not provide adequate
> support.  When on top, all you deal with is tension.  When on bottom, you
> have to consider buckling.  Does anyone know if it will work that way as
> supplied by cushcraft?

Steve/N4TQO and I tried it at Al/AG6D's.  The supports did indeed buckle.
It happened at the ends of the support tubes which are flattened to make
the screw holes.  We ended up putting it up the way it was designed.

> I'd be interested in a true engineering-type analysis, not just some
> anecdotal stories of how well it works.

Too bad.  This anecdote is all you get.  --John/K2MM

>From barry at w2up.wells.com (Barry Kutner)  Sun May  8 13:09:38 1994
From: barry at w2up.wells.com (Barry Kutner) (Barry Kutner)
Date: Sun, 08 May 94 12:09:38 GMT
Subject: 40m Buckling Brace
Message-ID: <Ri8ZLc1w165w at w2up.wells.com>

k2mm at MasPar.COM (John Zapisek) writes:

> Barry:
> 
> > If you invert the 40-2CD support brace, it MAY not provide adequate
> > support.  When on top, all you deal with is tension.  When on bottom, you
> > have to consider buckling.  Does anyone know if it will work that way as
> > supplied by cushcraft?
> 
> Steve/N4TQO and I tried it at Al/AG6D's.  The supports did indeed buckle.
> It happened at the ends of the support tubes which are flattened to make
> the screw holes.  We ended up putting it up the way it was designed.
> 
> > I'd be interested in a true engineering-type analysis, not just some
> > anecdotal stories of how well it works.
> 
> Too bad.  This anecdote is all you get.  --John/K2MM

Your anecdote is all that is necessary. What I meant is I didn't want to 
hear "I/ve had it up 20 years and it's been fine." 
Barry


Barry N. Kutner, W2UP       Usenet/Internet: barry at w2up.wells.com
Newtown, PA                 Packet Radio: W2UP @ WB3JOE.#EPA.PA.USA.NA
                            Packet Cluster: W2UP >K2TW (FRC)
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