[rebel-builders] rebel tailend wrinkles

[Jones, Michael]

hi garry

also in pics i dont think i see a doubler around rudder cable hole, all
openings should have a doubler who ever built it must have forgot, as for
tail cone thickness, my kit was 007 and it had .020 tail cone which i
upgraded to the elite tail cone !! a lot stronger now

mike#007

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com]On Behalf Of
Garry Wright
Sent: Tuesday, September 12, 2006 7:19 PM
To: rebel-builders@dcsol.com
Subject: Re: [rebel-builders] rebel tailend wrinkles


Thanks Jesse. I will do that. Much appreciated.

Garry

On Tue, 2006-09-12 at 15:34 -0700, Jesse Jenks wrote:

Garry,
I Just checked my manual and it is called FUS-89. It actually nests inside

the side skin and overlaps onto the inside of the FUS-30. The side skins

in

my manual are called FUS-22-1, but I think that's what you are calling
FUS-53. Anyway the FUS-89 would be easy to make yourself. They are about

16"

long in total. They have the edges bent up to make flanges. Just imagine

the

aft 16 inches of the side skin and that's what they look like, only a bit
narrower at the aft end. I think they are .025. You could really make them

as long as you want, but mine have about 5 inches on the side skin and

about

11 inches on the FUS-30. I don't have the holes cut for the elevator
pushrods yet, but the aft end of the fus 89 will be about at the front

edge

of the hole.
Jesse

From: Garry Wright <wrightdg@davincibb.net>
Reply-To: <rebel-builders@dcsol.com>
To: rebel-builders@dcsol.com
Subject: Re: [rebel-builders] rebel tailend wrinkles
Date: Tue, 12 Sep 2006 14:48:06 -0600

Jesse,

That was pretty sharp to notice that fus89 missing from the picture.
Thanks a bunch. It explains why the fus29's and fus53 failed I think.

Garry


On Tue, 2006-09-12 at 09:36 -0700, Jesse Jenks wrote:

Gary,
The other thing missing is the triangular reinforcement pieces on the

inside

of the fuselage sides. I think it's FUS-89. It goes between FUS-29 and

FuS-

30 on the inside.
Jesse

that

current

caused

by

ground

MAM

tail

that

is

a

about

same.

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[Ken]

Hmmm... if by torque, you are referring to the twist of the tailspring
due to side loading, then I can offer a bit of additional comment.

This is likely in the archives somewhere but from memory I found that
the single steel leaf spring that I tested would twist more than the
fibreglass spring.
A dual leaf spring twisted slightly less as long as there was either a
bolt or clamp at the aft end of the spring or if the tailwheel clamped
both spring leaves. Wayne's design did indeed have such a bolt. As the
spring twists during a side load, the weight on the tail applies more
torque as the twist increases -so I believe that a torsionally stiff
spring is desireable.

I did not have an aluminum "spring" to test but I'd guess that it would
twist even less.

Another consideration is that the force transmitted into the aircraft
tail cone from a given sideload also increases with the height of the
tail off the ground. A larger diameter tailwheel will increase the
torque on the spring from any given sideload. The small original MAM
tailwheel might actually be best here if that is your main concern...
That is one reason that I have so far stayed with the small stock
tailwheel and it may be part of the reason that MAM does not offer a
Scott 3200 type of tailwheel option. Similarly more curvature of the
tailspring will also increase that force so a low tail is a good thing
as long as the spring is stiff enough not to hit the rudder during a
firm landing.

The closer the tail spring is to a round cross section, the larger its
diameter, and the shorter it is, the more torsionallly stiff it will be.
The best tailwheel for the larger aircraft may not be best for the
Rebel. Again however I do not see any way that a tailwheel with a one
arm yoke makes any difference whatsoever.

Ken

Garry Wright wrote:

Wow. 0.02 fus30 is scary. I will certainly check it.

When I had the incident where the fibreglass tailspring delaminated, the
torque issue became forefront. It is quite signifcant but perhaps not
the central issue at work in this matter. The lack of a doubler on Fus30
and the total absence of fus89's seem to be the key factors. I do have
the larger diameter pneumatic wheel on order -got it on ebay today. I
think I will follow your lead and make the fus89 reinforcement
substantial - especially given that the left fus89 is to be repaired. I
really don't want to do this again. : ) Thanks for the comments Ken.

Garry

On Tue, 2006-09-12 at 20:42 -0400, Ken wrote:

119R came with a 0.020 fus-30 so it is very possible that is what is on
68R. No typo there - twenty thou!

I don't understand the allegation that a single arm tailwheel applies
torque to the tail spring. I will go so far as to say it does not as I'm
fairly sure the center of your wheel is vertically located under the
center of the spring - same as it would be with any tail wheel. I do
believe that a single arm tailwheel yoke will be heavier than a dual arm
design for the same strength but that is the only structural compromise
that I see.

I believe that my dual leaf steel tailspring reduces most forces on the
tail structure by virtue of it being considerably more flexible than the
aluminum "spring". I prefer a single bolt through the spring design as
used in all road designs but it doesn't sound like that was a factor at
all here. I agree that a pneumatic wheel might also reduce peak stresses.

I believe that the lack of FUS-89 re-inforcements (see the bulletin) to
transfer loads into the Fus-29 is a factor here. Also the lack of
doubler around the rudder cable holes. FWIW I also elected to increase
the size of the triangular doubler that ties Fus29 to Fus 30 on the
sides of the fuselage.

Ken

Garry Wright wrote:

Hi Bob,

Yes. The doubled fus30 wasn't done. I think the notion was it would
never be used on wheels - until I fouled up the floats. The thing that
concerns me most is the damage to both fus 29's which goes beyond any
normal experience that people have reported. I haven't checked the
thickness of the original fus30 yet, suspect it was 0.25 not the current
0.32 due to the vintage of FOKM - 068R. The single arm tailwheel is
going back to ebay and will not be re-used by me. Thanks.

Garry

On Tue, 2006-09-12 at 12:02 -0400, Robert and Olga Johnson wrote:

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[Garry Wright]

Ken,

The tailspring on which I observed the twisting action was a fiberglass
unit which had delaminated. We attempted to get it to hold together with
hose clamps - the usual limp-home method applied many times by others
with the MAM tailwheel. In the case of the single arm tailwheel we were
distinctly unsuccessful in making this temporary field repair. We
couldn't even come close to being able to do it. It was at that time
that I recognized the magnitude of the twisting action from that
tailwheel design.

The conclusion I have come to about this incident is that the causes for
the failure are as follows in descending order:

1. Lack of doubler on fus30
2. Lack of inner reinforcement fus89
3. Tailwheel single arm twist
4. Small diameter wheel climbing a pavement step nearly 1/3 of its
diameter
5. Some degree of excess weight on tailwheel at time of event.

Clearly 1 and 2 are the key items.

Your point about the larger tailwheel applying more torque is correct.
In this particular case that would have been countered by the larger
wheels ability to climb the bump easier I suspect. On a paved runway,
that would not be in play and the sideload would indeed increase. The
increase in strength from adding the fus30 doubler and the fus89 should
be very significant indeed. Especially if the orig fus30 was 0.020.

Thanks for your observations.

Garry

On Wed, 2006-09-13 at 09:48 -0400, Ken wrote:

Hmmm... if by torque, you are referring to the twist of the tailspring
due to side loading, then I can offer a bit of additional comment.

This is likely in the archives somewhere but from memory I found that
the single steel leaf spring that I tested would twist more than the
fibreglass spring.
A dual leaf spring twisted slightly less as long as there was either a
bolt or clamp at the aft end of the spring or if the tailwheel clamped
both spring leaves. Wayne's design did indeed have such a bolt. As the
spring twists during a side load, the weight on the tail applies more
torque as the twist increases -so I believe that a torsionally stiff
spring is desireable.

I did not have an aluminum "spring" to test but I'd guess that it would
twist even less.

Another consideration is that the force transmitted into the aircraft
tail cone from a given sideload also increases with the height of the
tail off the ground. A larger diameter tailwheel will increase the
torque on the spring from any given sideload. The small original MAM
tailwheel might actually be best here if that is your main concern...
That is one reason that I have so far stayed with the small stock
tailwheel and it may be part of the reason that MAM does not offer a
Scott 3200 type of tailwheel option. Similarly more curvature of the
tailspring will also increase that force so a low tail is a good thing
as long as the spring is stiff enough not to hit the rudder during a
firm landing.

The closer the tail spring is to a round cross section, the larger its
diameter, and the shorter it is, the more torsionallly stiff it will be.
The best tailwheel for the larger aircraft may not be best for the
Rebel. Again however I do not see any way that a tailwheel with a one
arm yoke makes any difference whatsoever.

Ken

Garry Wright wrote:

Wow. 0.02 fus30 is scary. I will certainly check it.

When I had the incident where the fibreglass tailspring delaminated, the
torque issue became forefront. It is quite signifcant but perhaps not
the central issue at work in this matter. The lack of a doubler on Fus30
and the total absence of fus89's seem to be the key factors. I do have
the larger diameter pneumatic wheel on order -got it on ebay today. I
think I will follow your lead and make the fus89 reinforcement
substantial - especially given that the left fus89 is to be repaired. I
really don't want to do this again. : ) Thanks for the comments Ken.

Garry

On Tue, 2006-09-12 at 20:42 -0400, Ken wrote:

119R came with a 0.020 fus-30 so it is very possible that is what is on
68R. No typo there - twenty thou!

I don't understand the allegation that a single arm tailwheel applies
torque to the tail spring. I will go so far as to say it does not as I'm
fairly sure the center of your wheel is vertically located under the
center of the spring - same as it would be with any tail wheel. I do
believe that a single arm tailwheel yoke will be heavier than a dual arm
design for the same strength but that is the only structural compromise
that I see.

I believe that my dual leaf steel tailspring reduces most forces on the
tail structure by virtue of it being considerably more flexible than the
aluminum "spring". I prefer a single bolt through the spring design as
used in all road designs but it doesn't sound like that was a factor at
all here. I agree that a pneumatic wheel might also reduce peak stresses.

I believe that the lack of FUS-89 re-inforcements (see the bulletin) to
transfer loads into the Fus-29 is a factor here. Also the lack of
doubler around the rudder cable holes. FWIW I also elected to increase
the size of the triangular doubler that ties Fus29 to Fus 30 on the
sides of the fuselage.

Ken

Garry Wright wrote:

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[Ken]

Hi Garry

FUS-89 comes from Bulletin 100594RB-3 issued in 1994.
MAM does not seem to list bulletins on the web site that have
subsequently been incorporated into the manual.

Here is the first paragraph:
" It has become evident over the few hundred hours of service that the
Rebel tail section can be damaged by repeated hard landings, rough field
use etc. More specifically the very aft cone section where the tail skid
attaches to the fuselage is subject to high stresses during landing and
ground manuevering, causing in extreme cases, cracking of the skin at
the rivets in the tailspring bulkhead (FUS-49) and more commonly some
oil canning and cracking in the bends of the wrap around skin (FUS-30),
aft of the tail skid attachment point."

It goes on to mention the obsolete laminated straps that were replaced
by the bulkhead and machined fittings for the forward tail spring bolt
and to also recommend the kickout tailwheel mod. All this became
standard sometime after 119R was shipped.

That bulletin introduced the doubler that is now known as part FUS-89.
The ones that I purchased were 14" long x 2" wide at the aft end. They
overlapped about 4" into the Fus-23-2 side skin forward of the bulkhead.
From memory they were wider (3 or 4") at the forward end to match the
width of the FUS-23-2 side skin and only twenty thou thick.

FWIW and to muddy the waters a bit ;) Near as I can tell, with the
current design or with the factory upgrades done, the doubling of the
rear of FUS-30 really addresses issues back at the rudder post rather
than up at the location of the FUS-89's. AFAIK doubling the aft end of
FUS-30 is a highly recomended Ontario mod that has never been endorsed
in writing by MAM. It is obviously a good idea though when you look at
what prompted it and those issues have also come up on aircraft that
were on floats.

So upgrades from day one include:
FUS-89 doublers
bulkhead and machined fittings at the tailspring forward bolt attachment
increasing the thickness of FUS-30 all the way to 32 thou now
the recent bulletin on the doubler bracket from FUS-31 to the tailpost
kickout tailwheel
and the doubling of the aft part of FUS-30 recommended by high time
Ontario builders and repairers such as Wayne, Bobp, etc.

Ken

Garry Wright wrote:

Can you confirm that it is a fus89 as Jesse suggested?

On Tue, 2006-09-12 at 18:13 +0000, Bob Patterson wrote:

Hi Garry !

Looks like you need to get a new manual. ;-) The piece Jesse is
talking about is like a scaled-down FUS-53 - a wide,tapered, bent-up
channel that nests inside the end of FUS-53, and extends it down into
the tail, about half way into FUS-30. It would be about 3 ft. long,
and made out of .025, I think.

It goes inside, and fastens to the skin. Hope that's enough
of a description -- see if you can get a new manual on CD from
the factory.

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[Garry Wright]

Hi Ken,

I suspect the 'in extreme cases' qualifier below could be dropped except
for ultralight versions of the Rebel. One thing to note is I think FOKM
was originally rated at 1450# gross and at that weight perhaps the
requirements are easier to meet. She does have the machined fitting for
the forward tailskid attach point.

I think your list of mods is complete and all will be done. Thanks

Garry

On Wed, 2006-09-13 at 10:54 -0400, Ken wrote:

Hi Garry

FUS-89 comes from Bulletin 100594RB-3 issued in 1994.
MAM does not seem to list bulletins on the web site that have
subsequently been incorporated into the manual.

Here is the first paragraph:
" It has become evident over the few hundred hours of service that the
Rebel tail section can be damaged by repeated hard landings, rough field
use etc. More specifically the very aft cone section where the tail skid
attaches to the fuselage is subject to high stresses during landing and
ground manuevering, causing in extreme cases, cracking of the skin at
the rivets in the tailspring bulkhead (FUS-49) and more commonly some
oil canning and cracking in the bends of the wrap around skin (FUS-30),
aft of the tail skid attachment point."

It goes on to mention the obsolete laminated straps that were replaced
by the bulkhead and machined fittings for the forward tail spring bolt
and to also recommend the kickout tailwheel mod. All this became
standard sometime after 119R was shipped.

That bulletin introduced the doubler that is now known as part FUS-89.
The ones that I purchased were 14" long x 2" wide at the aft end. They
overlapped about 4" into the Fus-23-2 side skin forward of the bulkhead.

From memory they were wider (3 or 4") at the forward end to match the

width of the FUS-23-2 side skin and only twenty thou thick.

FWIW and to muddy the waters a bit ;) Near as I can tell, with the
current design or with the factory upgrades done, the doubling of the
rear of FUS-30 really addresses issues back at the rudder post rather
than up at the location of the FUS-89's. AFAIK doubling the aft end of
FUS-30 is a highly recomended Ontario mod that has never been endorsed
in writing by MAM. It is obviously a good idea though when you look at
what prompted it and those issues have also come up on aircraft that
were on floats.

So upgrades from day one include:
FUS-89 doublers
bulkhead and machined fittings at the tailspring forward bolt attachment
increasing the thickness of FUS-30 all the way to 32 thou now
the recent bulletin on the doubler bracket from FUS-31 to the tailpost
kickout tailwheel
and the doubling of the aft part of FUS-30 recommended by high time
Ontario builders and repairers such as Wayne, Bobp, etc.

Ken

Garry Wright wrote:

Can you confirm that it is a fus89 as Jesse suggested?

On Tue, 2006-09-12 at 18:13 +0000, Bob Patterson wrote:

Hi Garry !

Looks like you need to get a new manual. ;-) The piece Jesse is
talking about is like a scaled-down FUS-53 - a wide,tapered, bent-up
channel that nests inside the end of FUS-53, and extends it down into
the tail, about half way into FUS-30. It would be about 3 ft. long,
and made out of .025, I think.

It goes inside, and fastens to the skin. Hope that's enough
of a description -- see if you can get a new manual on CD from
the factory.

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