To Bob Patterson Re Main Gear failure

Bob Patterson · Post by **Bob Patterson** » Fri Feb 17, 2012 5:39 pm

I agree completely, Wayne ! The rear pickup IS a weak spot, but, as
you said, it is likely better to have the repair you did than much more
extensive damage. The major design objective with the Rebel was to have a
SAFE airplane ! Many parts are designed to fail progressively, crumpling to
absorb energy and save the pilot & passenger from harm. While they are
certainly as strong as certified aircraft requirements, the failure mode
is different !! I agree that the factory often gets blamed for pilots
failures - parts DO need to be inspected and replaced periodically on
all aircraft. (This is NOT meant to criticize anyone on this list -
as Wayne says, rumours have a way of GROWING ;-) !)

You mentioned the "bigger bandaid" - this came up at the meeting today
(we missed you !). Bill Tee (one of the Inspectors) mentioned an example:
De Havilland really made the gear on the Buffalo extra strong. It could
be dropped in from great heights without damage to the gear - unfortunately,
the main wing spar broke in several hard landings !! :-) Even the BIG
guys do these things !

Your comments about the "appearance of weakness" are right on ! Just
because it is a different material, in an unusual configuration, doesn't
mean it isn't strong. As I said today, Murphy Aircraft kits have MUCH
more extensive stress analysis and actual load testing and flight testing
than MANY other kits on the market - anybody seen ANY stress analysis
OR load testing for the original Wheeler Express ???!! (The one that
the tails fell off .... )

Anyone who has owned a certified aircraft for any length of time
KNOWS (from the pain in the wallet !) that ALL aircraft have weak areas,
requiring regular inspection, maintenance, and sometimes replacement.
I am VERY pleased with our Rebels in this regard - they have been MUCH
better than ANY of the certified aircraft we've owned and flown over
the last 40+ years - but they're not perfect. Nothing is !

But Rebels sure are fun to fly !! Thanks for your helpful comments
about how to do the repair - I'm SURE someone out there is going to be
referring back to that one day !!

....bobp

----------------------------orig.---------------------------------------
At 12:35 PM 1/9/00 -0500, you wrote:

Hello Bob, I think the big problem here is people do not differentiate
between what is wear and what is damage! Then when someone tells someone
about their oval pivot holes (like the Clairol advertisement) the story gets
bigger and bigger and then half way down the line the people blame the
factory for shabby parts! No I'm not defending MAM and No I'M not picking on
any builders! If we start beating each other up for our comments and
suggestions (which seems to be happening more and more), nothing is going to
be accomplished with this mail list. People will just get sick of it and
turn off their computers. Especially those that "have been there, done
that!" And I am pretty sure the majority of those on this list do not want
to loss the experience of those that have finished and flown their aircraft,
or some of the others like myself that are spending more time repairing the
damaged ones than building new ones. We know where they have failed and
usually why!!!! (generally stupidity on the part of the pilot)

As to pivot damage, those that are flying their Rebels, know that drop test
or not, the Murphy Aluminum strut braced gear is not the most robust! It may
survive a 3 G drop test (if Murphy tested this high), but only once as Grant
has warned, " you must inspect after any hard landing." (and 3 g's is hard,
trust me I've been along for the ride) Note that an aircraft that has a wing
loading of only 11 lbs per sq ft. only has to be dropped (and not fail) from
a height of approx. 13 inches to meet Certified standards.(onto a very
slippery, oiled surface) It may fail when dropped from a height of approx.
18.72 inches. Considering these numbers and considering the way I fly, the
gear has held up pretty good for me, as I quite often do tail wheel landing
on short rough strips and cut the power too soon. This causes the mains to
be slapped onto the ground from well above these height figures at very slow
speeds!

Maybe after all that said, the Murphy gear has more of a visual appearance
of weakness than a structural one as most people are not used to seeing
landing gear made out of bolted together aluminum. I know that every
inspector or A.M.E. that has looked at my Rebels, first points at the bend
in the rear drag brace, going up to the attach fitting and says "this will
cause you problems and break here!" Even had a DABI want to snag it and make
me change it to go straight at the fitting like a welded cub fitting. The
funny thing is (if you find broken gear funny) that I have numerous broken
pieces(too many pieces in fact and none the fault of Murphy) of gear around
and not one of them has damage in the area of this curve in the drag brace.

The problem is, if the gear legs are built any stronger you start to
severely damage the fuselage due to the bigger bandaid problem. The bolt
pivot hole on the main gear leg will stay fairly round for years of normal
use. Make sure that the bolt does not turn in the fuselage fittings and that
the leg rotates on the bolt. If you allow the bolt to move in the fuselage
fittings and wear these out they are impossible (well almost) to replace,
but the upper stub of the leg is relatively painless to remove, purchase new
and replace. You can even put a sleeve in it, once, if the wear gets to high
or if you land semi hard and oval the hole! This is the "wear" people take
about I believe, from a hard landing. The pivot hole in the main leg will be
forced oval by the landing impact. This is better than the attach fittings
going oval or the main carrythough being damaged.

The weakest point of the gear attach from my stand point, seems to be the
rear attach fittings and bulkhead. this is usually the first fiece to get
ripped out of the floor. The new Rebel AULA I sold this summer was recently
taken on a short off runway excursion over a few small field rocks. the
impact against the last rock drove the rear gear fitting 1/2 inch back in
the floor. Not upward (like usually happens here and buckles the door sill),
but backwards, mangling the two bulkheads the fitting is attached to and
squashing and cracking the tapered corner wrap (fus 10) behind it. It also
bowed the rear gear brace significantly and oval'd the main leg
attatch/pivot hole.

The fix was to un-rivet the door sill skin and hold it back out of the way,
remove the damaged corner wrap and to cut a hole forward of the bulkheads in
the outer lower cabin floor for access to the bulkheads. I cut out the
damaged corners of the bulkheads and un-riveted them from the door sill
channel (they always seem to only mangle until they hit the half circle cut
out about 6 inches in) Then using 2 new square corner bulkheads, I
fabricated a new gear attach assembly and spliced it onto the old one. (With
an 8 inch overlap.) Made a new corner wrap, riveted in a patch panel
sandwiched between the original skin and the floor bulkhead and channels and
closed the doors sill skin and reinstalled the side skin panel and Fus 35
angle. Also replace the main gear leg stub to get a new pivot hole. Approx.
8 hours of work. This shows the rear attach area could definitely stand to
be stronger, BUT what would let go next that wasn't as easy to fix!!!!!

Sorry for the length, but once I start typing I just don't know when to shut
up!

Keep at it, the landing gear may not be the greatest, but the flying
characteristics are definetly worth it in the end!!!!!

Wayne G. O'Shea
www.irishfield.on.ca
-----Original Message-----
From: Bob Patterson <bob.patterson@canrem.com>
To: Murphy Rebel Builders List <murphy-rebel@dcsol.com>
Date: Saturday, January 08, 2000 11:14 PM
Subject: Re: To Bob Paterson Re Main Gear failure

Thanks ! That was only MY guess as to the possible cause - but, as you
say, it does sound reasonable .....

As to these gear bolts that are wearing - I have NO idea, as there have
been NO reports here of ANY gear bolt wear. Even Wayne, with constantly
moving gear legs, recently reported here that there is NO wear of his
gear bolts ! And he is certainly not alone in using die spring gear !

The assumption was that the bolts at the top of the main gear legs,
both front & back brace, would wear because of the swinging of the gear
as the loose bungees or springs allowed it to pivot outward. I believe
Gord Mohr sells a set of bushings to help prevent this wear, OR to install
IF wear appeared. So far, NOBODY in this area has seen any wear - there
certainly doesn't seem to be any on our Rebels...

The bungees are meant to be so tight that they do not move, except
to prevent damage to the fuselage, so there should normally be very
little movement at that joint. (The tires are meant to be the primary
shock absorbers.)

You are not alone in doing Chromolly gear - unfortunately, as you
suggested, the folks who did it here have suffered more than if they
had stayed with the factory setup. - But, that's what makes a horse
race, or - the Experimental Category !!! :-)
(absolutely No offence meant !) It really IS the builder's choice, and
all this forum can do is provide information on what others have done.

Hopefully, we will all end up with aircraft that please US,
and are safe, and that is all that matters !

.....bobp

---------------------------orig.-------------------------------------------
-
At 12:40 PM 1/2/00 +1100, you wrote:
Dear Bob (and everyone) ;

Thanks yet again Bob for your enlightening
reply regarding Earl Leamans
Main Strut failure !...(and all the other mod's you discussed).

It makes sense ......a hard / heavy landing ,..holes drilled in the main
leg for riveting skins on...
equals a main gear failure in my mind as well !
An up front answer rather than a protracted pile of justifications wins my
vote every time !
This kind of thing, plus Rich Bartmans previous gear failure (which came
from a HARD landing
due to an attempt to stretch the glide after a catastrophic engine failure
whilst on finals), plus
our plan to fly all the way around the Australian coast "one day" (and
being forced to land at
less than ideal sites...like "farmer Brown's paddock"), prompted me to
remake the landing
legs in chrome-moly steel.
I acquired the plans for a Super Cub from an aeronautical engineer friend
and merely adjusted
the distances for the pivot points...
Yes, the legs are a couple of pounds heavier...and, I KNOW that by making
one area
stronger, it shifts the "crumpling effect" in the event of a hard
"arrival"
, more, to the leg attach
points, but thats MY decision !.....
Don't you just l....o...v.....e democracy.....(and the Experimental
category).
Bob !...or anyone else......I have one more question regarding this "main
gear failure" thing.
Which BOLTS are the ones where all the wear is occurring in the landing
gear.
Rich Bartman describes them as hard to get to.....
Does this mean it's the ones in the floor space holding back the strut for
the tension arm of
the bungee (or in my case springs) gear ?....or somewhere else ?

Thank you linesmen, thank you ballboys........(ozzie joke....from tennis
matches)
Rick & Wendy Harper
16 Tor rd, Dee Why,
N.S.W. 2099
Australia
rjwh@ozemail.com.au
rjwh56@hotmail.com
Ph : 02 9971 7889
Mbl : 0416 041 007
Fax : 02 9938 1480
O'seas Ph : 612 9971 7889
O'seas Fax : 612 9938 1480

<!DOCTYPE HTML PUBLIC "-//W3C//DTD W3 HTML//EN">
<HTML>
<HEAD>

<META content=text/html;charset=iso-8859-1 http-equiv=Content-Type>
<META content='"MSHTML 4.72.3612.1706"' name=GENERATOR>
</HEAD>
<BODY bgColor=#ffffff>
<DIV><EM><FONT color=#000000 size=2>Dear Bob (and everyone)
;</FONT></EM></DIV>
<DIV><EM><FONT color=#000000
size=2>           &
n
bsp;       
</FONT></EM></DIV>
<DIV><EM><FONT color=#000000
size=2>           &
n
bsp;           &nbsp
;
       
Thanks yet again Bob for your enlightening reply regarding Earl
Leamans</FONT></EM></DIV>
<DIV><EM><FONT color=#000000 size=2>Main Strut failure !...(and all the
other
mod's you discussed).</FONT></EM></DIV>
<DIV><EM><FONT color=#000000 size=2></FONT></EM> </DIV>
<DIV><EM><FONT color=#000000 size=2>It makes sense ......a hard / heavy
landing
,..holes drilled in the main leg for riveting skins
on...</FONT></EM></DIV>
<DIV><EM><FONT color=#000000 size=2>equals a main gear failure in my mind
as
well !</FONT></EM></DIV>
<DIV><EM><FONT color=#000000 size=2>An up front answer rather than a
protracted
pile of justifications wins my vote every time !</FONT></EM></DIV>
<DIV><EM><FONT color=#000000 size=2></FONT></EM> </DIV>
<DIV><EM><FONT color=#000000 size=2>This kind of thing, plus Rich Bartmans
previous gear failure (which came from a HARD landing </FONT></EM></DIV>
<DIV><EM><FONT color=#000000 size=2>due to an </FONT></EM><EM><FONT
color=#000000 size=2>attempt to stretch the glide after a catastrophic
engine
failure whilst on finals), plus</FONT></EM></DIV>
<DIV><EM><FONT color=#000000 size=2>our plan to fly all the way around the
Australian coast "one day" (and being forced to land
at</FONT></EM></DIV>
<DIV><EM><FONT color=#000000 size=2>less than ideal sites...like
"farmer
Brown's paddock"), prompted me to remake the
landing</FONT></EM></DIV>
<DIV><EM><FONT color=#000000 size=2>legs in chrome-moly steel.
</FONT></EM></DIV>
<DIV><EM><FONT color=#000000 size=2>I acquired the plans for a Super Cub
from an
aeronautical engineer friend and merely adjusted</FONT></EM></DIV>
<DIV><EM><FONT color=#000000 size=2>the distances for the pivot
points...</FONT></EM></DIV>
<DIV><EM><FONT color=#000000 size=2>Yes, the legs are a couple of pounds
heavier...and, I KNOW that by making one area</FONT></EM></DIV>
<DIV><EM><FONT color=#000000 size=2>stronger, it shifts the
"crumpling
effect" in the event of a hard "arrival" , more, to the leg
attach </FONT></EM></DIV>
<DIV><EM><FONT color=#000000 size=2>points, but thats MY decision
!.....</FONT></EM></DIV>
<DIV><EM><FONT color=#000000 size=2></FONT></EM><EM><FONT size=2>Don't you
just   l....o...v.....e   democracy.....(and the
Experimental category).</FONT></EM></DIV>
<DIV><EM><FONT size=2></FONT></EM> </DIV>
<DIV><EM><FONT size=2>Bob !...or anyone else......I have one more question
regarding this "main gear failure" thing.</FONT></EM></DIV>
<DIV><EM><FONT size=2></FONT></EM><EM><FONT size=2>Which BOLTS are the
ones
where all the wear is occurring in the landing gear.</FONT></EM></DIV>
<DIV><EM><FONT size=2></FONT></EM><EM><FONT size=2>Rich Bartman describes
them
as hard to get to.....</FONT></EM></DIV>
<DIV><EM><FONT size=2></FONT></EM><EM><FONT size=2>Does this mean it's the
ones
in the floor space holding back the strut for the tension arm
of</FONT></EM></DIV>
<DIV><EM><FONT size=2></FONT></EM><EM><FONT size=2>the bungee (or in my
case
springs) gear ?....or somewhere else ?</FONT></EM></DIV>
<DIV><EM><FONT size=2></FONT></EM> </DIV>
<DIV><EM><FONT size=2>Thank you linesmen, thank you ballboys........(ozzie
joke....from tennis matches)</FONT></EM></DIV>
<DIV><EM><FONT size=2></FONT></EM> </DIV>
<DIV><EM><FONT color=#000000 size=2>Rick & Wendy Harper<BR>16 Tor rd,
Dee
Why, <BR>N.S.W. 2099<BR>Australia<BR><A
href="mailto:rjwh@ozemail.com.au">rjwh@ozemail.com.au</A><BR><A
href="mailto:rjwh56@hotmail.com">rjwh56@hotmail.com</A><BR>Ph : 02 9971
7889
<BR>Mbl : 0416 041 007<BR>Fax : 02 9938 1480<BR>O'seas Ph : 612 9971
7889<BR>O'seas Fax : 612 9938 1480</FONT></EM></DIV>
<DIV><EM><FONT color=#000000 size=2></FONT></EM> </DIV></BODY></HTML>

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