Bungee (modified) Gear Thoughts

[Rick Harper]

G'day Wayne & Everyone ...

I would like to hear your, (and others), opinion on "fixing" our
Rebel

As you already know, I stuffed up big time - trying to win a spot
landing competition .... never again ! :o(

Anyway,... when I dumped the flap, (from FULL to negative - in 1/2 a
second) - just as I got hit by a big gust / rotor (strong quartering ON
headwind - along a strip lined with big trees) - and she lifted and
then FELL heavily, ... the thing that let go was the "drag link" - as I
call it ... the square tube piece that goes from between the floor
channels / carry throughs, down to the "X brace" - which is the joiner
between the strut down to the wheel on both legs & back up to the floor
on either side.

I made a set of legs - similar to your own design - copied from a Super
Cub plan set - obviously out of chrome moly. I also fitted a pair of
Carr McMaster Heavy duty compression springs - in place of the bungee
cords - (looks much neater, less air drag & work very well). The legs
are undamaged in ANY way - despite being punched up through the floor
when the other tyre dug in as the plane slid & turned !

Obviously I'm going to replace tha sqaure aluminium "drag link" tube
with chrome moly (which was the only piece of the original U/C set that
I used) , as I rebuild her .... but my question is:

WHAT would you do - (other than not let me fly it), to stop this
happening again ?

I have thought of some sort of heavy duty rubber "stop" - that might
compress as the coil spring bottoms out .... but then I wonder - am I
just expecting too much here .... ?

(I realise that at some point, a BAD enough landing is going to have
some repocussions - no matter what we do to beef things up - but I'm
just trying to think of ways to back up / remove this single point
failure from causing the same outcome in any future BAD landing)

BTW - I could not install the steel cable back up in the U/C - as is
called for with the aluminium bungee gear leags - as I had made the
"inner tube" of the sliding leg rather heavy walled - and there was no
room to fit a backup cable down the middle ....
Perhaps I could fit a cable - parrallel - down the back of the leg
assembly - outside the tubes ...( but it would look crappy I think)

Can you think of another way to make a "failsafe" / backup for this kind
of failure ???

AS always - yours, Bob's & other opinions are gratefully received !

Rick Harper
541R - under reconstruction :o(











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[Wayne G. O'Shea]

Weeeelllllll Rick...since you asked ! It's a first..never seen the upper
wishbone tube pulled out to date...you must have f'd up REALLY good (or bad)
!

The little cable inside the bungee tube per MAM's specs is useless. If the
bungees let go..the cable will snap...witnessed that first hand a few
times....like when we picked Bangle's off the taxi way at OSH in '95. If you
break the 4130 strut legs like you and I have built then that little cable
is really useless so no point in installing one inside the tubes anyhow.

What I have done as an "Alaskan" safety cable is to run a 3/16" cable from
the axle bolt (not the strut bolt) to the opposite struts top bolt This way
if the strut failed or ripped a bolt/strut out of the alum axle gusset the
cable would still hold since it's hooked to the axle bolt and the opposite
struts top bolt. Considering that you ripped the top tube out...this
obviously wouldn't help to any (if any) extent. I guess what you'd need is
the full x of cables like Atlee Dodges for the SuperCub....but if it gets
that bad on the Rebel I think it's going to get expensive anyhow!

Cheers,
Wayne

----- Original Message -----
From: "Rick Harper" <rjwh@optusnet.com.au>
To: <rebel-builders@dcsol.com>
Sent: Saturday, September 10, 2005 7:39 PM
Subject: Re: Bungee (modified) Gear Thoughts

G'day Wayne & Everyone ...

I would like to hear your, (and others), opinion on "fixing" our
Rebel

As you already know, I stuffed up big time - trying to win a spot
landing competition .... never again ! :o(

Anyway,... when I dumped the flap, (from FULL to negative - in 1/2 a
second) - just as I got hit by a big gust / rotor (strong quartering ON
headwind - along a strip lined with big trees) - and she lifted and
then FELL heavily, ... the thing that let go was the "drag link" - as I
call it ... the square tube piece that goes from between the floor
channels / carry throughs, down to the "X brace" - which is the joiner
between the strut down to the wheel on both legs & back up to the floor
on either side.

I made a set of legs - similar to your own design - copied from a Super
Cub plan set - obviously out of chrome moly. I also fitted a pair of
Carr McMaster Heavy duty compression springs - in place of the bungee
cords - (looks much neater, less air drag & work very well). The legs
are undamaged in ANY way - despite being punched up through the floor
when the other tyre dug in as the plane slid & turned !

Obviously I'm going to replace tha sqaure aluminium "drag link" tube
with chrome moly (which was the only piece of the original U/C set that
I used) , as I rebuild her .... but my question is:

WHAT would you do - (other than not let me fly it), to stop this
happening again ?

I have thought of some sort of heavy duty rubber "stop" - that might
compress as the coil spring bottoms out .... but then I wonder - am I
just expecting too much here .... ?

(I realise that at some point, a BAD enough landing is going to have
some repocussions - no matter what we do to beef things up - but I'm
just trying to think of ways to back up / remove this single point
failure from causing the same outcome in any future BAD landing)

BTW - I could not install the steel cable back up in the U/C - as is
called for with the aluminium bungee gear leags - as I had made the
"inner tube" of the sliding leg rather heavy walled - and there was no
room to fit a backup cable down the middle ....
Perhaps I could fit a cable - parrallel - down the back of the leg
assembly - outside the tubes ...( but it would look crappy I think)

Can you think of another way to make a "failsafe" / backup for this kind
of failure ???

AS always - yours, Bob's & other opinions are gratefully received !

Rick Harper
541R - under reconstruction :o(











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[Rick Harper]

Thanks Wayne ..

I'd recorded 600 landings in my log book - several in severely
adverse conditions (DOUBLE the published cross wind capability) ....
but this was the first time I ever dumped the flaps BEFORE she had
actually touched down ... it WON'T happen again ! :o(

Rick
541R
----- Original Message -----
From: Wayne G. O'Shea
To: rebel-builders@dcsol.com
Sent: Sunday, September 11, 2005 10:03 AM
Subject: Re: Bungee (modified) Gear Thoughts


Weeeelllllll Rick...since you asked ! It's a first..never seen the
upper
wishbone tube pulled out to date...you must have f'd up REALLY good
(or bad)
!

The little cable inside the bungee tube per MAM's specs is useless. If
the
bungees let go..the cable will snap...witnessed that first hand a few
times....like when we picked Bangle's off the taxi way at OSH in '95.
If you
break the 4130 strut legs like you and I have built then that little
cable
is really useless so no point in installing one inside the tubes
anyhow.

What I have done as an "Alaskan" safety cable is to run a 3/16" cable
from
the axle bolt (not the strut bolt) to the opposite struts top bolt
This way
if the strut failed or ripped a bolt/strut out of the alum axle gusset
the
cable would still hold since it's hooked to the axle bolt and the
opposite
struts top bolt. Considering that you ripped the top tube out...this
obviously wouldn't help to any (if any) extent. I guess what you'd
need is
the full x of cables like Atlee Dodges for the SuperCub....but if it
gets
that bad on the Rebel I think it's going to get expensive anyhow!

Cheers,
Wayne

----- Original Message -----
From: "Rick Harper" <rjwh@optusnet.com.au>
To: <rebel-builders@dcsol.com>
Sent: Saturday, September 10, 2005 7:39 PM
Subject: Re: Bungee (modified) Gear Thoughts

G'day Wayne & Everyone ...

I would like to hear your, (and others), opinion on "fixing" our
Rebel

As you already know, I stuffed up big time - trying to win a spot
landing competition .... never again ! :o(

Anyway,... when I dumped the flap, (from FULL to negative - in 1/2 a
second) - just as I got hit by a big gust / rotor (strong quartering

ON

headwind - along a strip lined with big trees) - and she lifted and
then FELL heavily, ... the thing that let go was the "drag link" -

as I

call it ... the square tube piece that goes from between the floor
channels / carry throughs, down to the "X brace" - which is the

joiner

between the strut down to the wheel on both legs & back up to the

floor

on either side.

I made a set of legs - similar to your own design - copied from a

Super

Cub plan set - obviously out of chrome moly. I also fitted a pair

of

Carr McMaster Heavy duty compression springs - in place of the

bungee

cords - (looks much neater, less air drag & work very well). The

legs

are undamaged in ANY way - despite being punched up through the

floor

when the other tyre dug in as the plane slid & turned !

Obviously I'm going to replace tha sqaure aluminium "drag link" tube
with chrome moly (which was the only piece of the original U/C set

that

I used) , as I rebuild her .... but my question is:

WHAT would you do - (other than not let me fly it), to stop this
happening again ?

I have thought of some sort of heavy duty rubber "stop" - that might
compress as the coil spring bottoms out .... but then I wonder - am

I

just expecting too much here .... ?

(I realise that at some point, a BAD enough landing is going to

have

some repocussions - no matter what we do to beef things up - but

I'm

just trying to think of ways to back up / remove this single point
failure from causing the same outcome in any future BAD landing)

BTW - I could not install the steel cable back up in the U/C - as is
called for with the aluminium bungee gear leags - as I had made the
"inner tube" of the sliding leg rather heavy walled - and there was

no

room to fit a backup cable down the middle ....
Perhaps I could fit a cable - parrallel - down the back of the leg
assembly - outside the tubes ...( but it would look crappy I think)

Can you think of another way to make a "failsafe" / backup for this

kind

of failure ???

AS always - yours, Bob's & other opinions are gratefully received !

Rick Harper
541R - under reconstruction :o(











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[Ken]

Hi Rick
Which end of the cross tube pulled out? Can you describe it or post a
photo of the end of the tube?
Ken







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[Rick Harper]

G'day Ken ...

The end that's embedded IN the plane floor - between the two square
carry through tubes ... where there is a single 3/8" bolt (from memory)
... the other end , which is the "X Brace" - where the 4 tubes meet
about 10" below the floor - it held OK - with only two 1/4" bolts .....
obviously the 2 smaller bolts held more weight & spread the load better

BTW those front & rear "X brace" plates - (which are .125" 6061 from
memory) ... I put a .060" Chrome moly doubler plate either side ...
they didn't budge !

Rick
541R

PS Can't get any photos till I get out to the hangar - sometime later
next week
----- Original Message -----
From: Ken
To: rebel-builders@dcsol.com
Sent: Sunday, September 11, 2005 11:20 AM
Subject: Re: Bungee (modified) Gear Thoughts


Hi Rick
Which end of the cross tube pulled out? Can you describe it or post a
photo of the end of the tube?
Ken







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[Wayne G. O'Shea]

That damn "bigger Band-Aid syndrome" I always talk about....now I understand
Rick ! LOL

Wayne

----- Original Message -----
From: "Rick Harper" <rjwh@optusnet.com.au>
To: <rebel-builders@dcsol.com>
Sent: Saturday, September 10, 2005 10:38 PM
Subject: Re: Bungee (modified) Gear Thoughts

G'day Ken ...

The end that's embedded IN the plane floor - between the two square
carry through tubes ... where there is a single 3/8" bolt (from memory)
... the other end , which is the "X Brace" - where the 4 tubes meet
about 10" below the floor - it held OK - with only two 1/4" bolts .....
obviously the 2 smaller bolts held more weight & spread the load better

BTW those front & rear "X brace" plates - (which are .125" 6061 from
memory) ... I put a .060" Chrome moly doubler plate either side ...
they didn't budge !

Rick
541R

PS Can't get any photos till I get out to the hangar - sometime later
next week
----- Original Message -----
From: Ken
To: rebel-builders@dcsol.com
Sent: Sunday, September 11, 2005 11:20 AM
Subject: Re: Bungee (modified) Gear Thoughts


Hi Rick
Which end of the cross tube pulled out? Can you describe it or post a
photo of the end of the tube?
Ken







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[Ken]

Naw the steel plates just guaranteed that the two X plates didn't fail.
(Mine have AN3 bolts Rick) The top end is AN5 and I suspect that is the
weak end anyway in most cases from the point of view of ripping bolts
out of the square tube.

As it happens, I also laminated two steel plates at the X joint to
facilitate attaching the external safety cable. (I didn't like the
torque/bending moment that just fastening the safety cable to the
opposite bolt would apply.) The observation that MAM's safety cable is
pretty much useless is interesting because after some head scratching,
that is the same conclusion I came to back when I ran the numbers for
bungee and die spring strength a few years ago.

Rick, FWIW you could always double up those die springs like Wayne
tried. While they would still bottom out with the same applied force,
they would absorb twice the energy before doing so. In your case it
might make more sense to make the second spring stronger or use rubber
donuts (like you suggested) though. I think that was discussed once but
no one thought it was worth the effort. BTW don't worry about photos -
I think I've got the picture now.

Ken

Wayne G. O'Shea wrote:

That damn "bigger Band-Aid syndrome" I always talk about....now I understand
Rick ! LOL

Wayne

----- Original Message -----
From: "Rick Harper" <rjwh@optusnet.com.au>
To: <rebel-builders@dcsol.com>
Sent: Saturday, September 10, 2005 10:38 PM
Subject: Re: Bungee (modified) Gear Thoughts

G'day Ken ...

The end that's embedded IN the plane floor - between the two square
carry through tubes ... where there is a single 3/8" bolt (from memory)
... the other end , which is the "X Brace" - where the 4 tubes meet
about 10" below the floor - it held OK - with only two 1/4" bolts .....
obviously the 2 smaller bolts held more weight & spread the load better

BTW those front & rear "X brace" plates - (which are .125" 6061 from
memory) ... I put a .060" Chrome moly doubler plate either side ...
they didn't budge !

Rick
541R

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