strengthening for O320 and spring gear; floatreinforcement?

[Mike Davis]

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Subject: Re: strengthening for O320 and spring gear; floatreinforcement?
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Sorry I have no time today but will respond first of the week. But just for
thought, I agree. It is not the gear itself but the way it is attached.
Consider the Cessna gear box. A substantial structure. The Rebel structure
is
a "strap"? Sounds a little under done to me. One bolt head or bolt, yes
the
front one, and the whole leg retracts.
More later
Dave

Alister Yeoman wrote:

Hi Dave Bangle

Hope you dont mind me jumping in here, you have raised some interesting
points.

You have obviously been through the mill in regards to landing gear!

If I read your message correctly you regard the spring gear as the
potential problem rather than the attachment or load dissipation.

I have been concerned about the mounting system ( and load dissipation)

for

a while, as can been seen by the number of times I have metioned this

topic

in this forum, I now have reason to be even more concerned.

I have just removed my wings to do some 'mods' to the fuse as previously
discribed, and I found damage to the mounts that would have resulted in

the

loss of the right hand gear within a very short period of time.

The damage is to the forward stradle bolt mounting on the right side, the
main carrythrough member has cracked right thru' to the outside leaving

the

bolt loose to work and eventually pull thru'.

I remember thinking while mounting the gear that it seemed underdone in
this area, the rest of the carrythrough has been beefed up with plates on
top except the area that needs it most, and the edge clearances if you
follow the manual are not great.

The forces on this front bolt and surrounding mounting area are very great
under braking and rough ground etc.

I possibly could take a bit of the blame in that I did not retighten the
gear bolts until I had done about 20hrs, I believe it should be done
regularly over the first few hours of use ( hindsight of course!).

It is early days yet in regards to how I 'fix' this, but I think what I

may

do is run reasonably heavy piece of 4130 steel down the wing attach

bracket

across and down the forward carrythrough and also along inwards to meet up
with the top plates.(4130 may be a little easier to work----who cares

about

the weight if it holds!!)

I am considering welding another piece of 4130 around the stradle bolt

hole

as a doubler so that the bolt wont break out again with the limited edge
clearance available. I will be replacing the stradle bolt with 3/8" as in
the elite and increasing the diameter of the inboard bolt.

As you can see Dave, I am very sensitive about this area as you are, but I
see the potenial problems as more in the design of the mountings rather
than the gear inself which at this stage I consider to be more than
adequate.

Do you have any info that may make me want to reconsider my opinion?

What area's in the nose area do you consider need more strenght?

Cheers

Alister

----------

From: subersys <subersys@nidlink.com>
To: (Murphy Rebel) <murphy-rebel@dcsol.com>
Subject: Re: strengthening for O320 and spring gear; floatreinforcement?
Date: Friday, November 13, 1998 4:58 AM

Bob,
I dare to differ. I believe through 2 complete gear failures that the

spring

gear is probably a better system, stronger, safer, if used right out of

the

box. Having been the reason for the safety cable AD was the first

failure. And

a ground loop being the reason for the second. Had the gear stayed

together in

the ground loop incident I would not have spent the next 9 months

rebuilding.

Yet.........in getting and starting the mod for the spring gear the same

feeling

of nausea (and much greater in strength)overcame that actual

installation.

Everytime I have had that little voice induce nausea in my brain it was

for good

reason. That is why I sent the spring gear back and rebuilt the

original

gear

out of chromemoly. Yes it is heavier than the aluminum gear, but I

won't

be

rebuilding the airplane every other year. Twice is enough. In regards

to the

aluminum spring gear visualize this. Touch down on a rough mountain

strip and

encounter a gopher hole. I see bolt heads popping and the creation of a
retractable gear. Yes, the Murphy demos have not had a problem, but

keep

in

mind who has been flying the demos. Robin hasn't made a lot of bad

landings

lately. A drop test is fine and strainght down it will come through

every

time. Try a drop test while encountering that gopher hole at 30 mph.

Food for

thought.

I do agree that the bungee gear is better, but only after mods. I also
reinforced the fus between the front and rear attach point with 2"

square

tube.

No more wrinkling of skins in the door area.

I believe that any area of the airplane that is cause for concern needs

to be

looked at really hard, as I have had problems with every area that has

ever been

a concern. Don't consider that since Murphy designed it it must be

okay.

The

design testing is a result of years of use. More AD's will come and go

as

weaknesses are discovered. Better to look ahead and visualize the

trouble

before it happens.

The float fix. That became apparent right away after the groundloop.

The

rivets sheared full lenght of the door post, the windshield shattered,

the

engine almost left the firewall. I believe the nose area needs major

strength

mods. Just my own personal feelings. Created through experience.

Don't think I don't love the airplane. It is wonderful and I would

build

another in a heartbeat. What a joy to fly.

Dave Bangle

Bob Patterson wrote:

Alister,
I had another look at the "floatfix" bulletin, and it doesn't
mention the extra rivets - maybe just being updated now ??

All the more reason to check with Tech Support directly -

there

may be other recent additions as well.

I agree completely - if you're still building, ADD THE MODS !!
Even if you don't plan floats !

There is no question that the bungee gear is stronger, better
triangulated to spread the loads, and MUCH more effective in energy
dissipation (the friction of hundreds of strands of rubber, rubbing
over each other !). It is also 28 lb. lighter, and about $700 cheaper

!

BUT - the spring gear looks sexy, and "Cessna did it, so it
must be good" ..... Murphy bowed to customer demand.

You're right about the problems with Cessnas - ask anyone
who's owned one for a while about the inspections and problems with
the gear box structure . Again, these are things that the general
public DOESN'T hear about - they only hear the good bits. ALL aircraft
have problem areas (the fuel system on the Aeronca Sedan comes to
mind !! - horrible !!)

Please keep us posted on progress ....

Thanks ! .....bobp

--------------------------orig.--------------------------------------
At 07:56 PM 11/8/98 +1300, you wrote:

Thanks

addition

to

good

not on

to

reinforcement?

went

to

which

could

get

that

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