Part number needed- tail bracket

[BlakeinAlabama]

I am trying to confirm the part number for the item in the photo. It connects the vertical stab to the horz stab. Does anyone know the part number? I think I had the wrong one to start with. Thanks, Blake

[minton]

0331124 Fitting Rear Spar Lower C-170B

[BlakeinAlabama]

Out of curiosity, does anyone know if this part is on any other plane... 172, 180 etc?

[GAHorn]

0331124 Fitting Rear Spar Lower C-170B

Be certain to attach them using the correct NAS bolts.
NAS145-14 and -18 bolts (2 each)
(Blake... you must have missed the PM I sent you when you asked this question privately.)

[GAHorn]

Out of curiosity, does anyone know if this part is on any other plane... 172, 180 etc?

Blake... if you are looking for a salvage part.... why don't you contact wingnut (Del Lehmann) who responded to your question on this several MONTHS ago. He told you then he has several of them.

http://www.cessna170.org/forums/viewtop ... ket#p77405

[BlakeinAlabama]

I have contacted him, he send me his number last night. I wanted to make sure I had asked him for the right part number, as I had thought I was wrong, but I am on track now.

[minton]

NAS145-14 = MS20005-6
NAS145-18 = MS20005-9

I think I put enough zeros in there.

[n2582d]

Be certain to attach them using the correct NAS bolts.
NAS145-14 and -18 bolts (2 each)

And the correct washers which are not depicted in the IPC. Show this entry from Del to your A&P when he installs these parts.

[minton]

If the hole in the bracket is champhered (a Rounded Bevel) OR the area is to small to accept a washer, washer is sometimes not required as the ones the landing gear axel mounting holes.

My humble opinion

[Robert Eilers]

Every time I slip the airplane that bracket comes to mind - amazing that it holds the vertical stabilizer in place.

[GAHorn]

Every time I slip the airplane that bracket comes to mind - amazing that it holds the vertical stabilizer in place.

People should think twice before spinning these old airplanes.

[starkw1]

I discovered a cracked tail bracket on my ’48 170 during an annual about 12 yrs ago or so. My mechanic and I removed the bracket and being a metallurgist, I sectioned the bracket perpendicular to the crack to see how far it had propagated. It was scary to see that the crack had progressed about 2/3 of the way through one of vertical members, and about ¼ the way through the other. I then ordered a part from a well know salvage yard, but on careful examination, I discovered that it too was cracked. {Be wary of buying used brackets}. I ended up having a local machinist make me a pair of brackets from titanium 6 Al-4V which we installed, and they have been in service ever since.

There is a write up on this in the 170 News from 10+ years ago, though I no longer have the article.

[wingnut]

I discovered a cracked tail bracket on my ’48 170 during an annual about 12 yrs ago or so. My mechanic and I removed the bracket and being a metallurgist, I sectioned the bracket perpendicular to the crack to see how far it had propagated. It was scary to see that the crack had progressed about 2/3 of the way through one of vertical members, and about ¼ the way through the other. I then ordered a part from a well know salvage yard, but on careful examination, I discovered that it too was cracked. {Be wary of buying used brackets}. I ended up having a local machinist make me a pair of brackets from titanium 6 Al-4V which we installed, and they have been in service ever since.

There is a write up on this in the 170 News from 10+ years ago, though I no longer have the article.

Are you certain you are talking about the same part as the original poster? How did you get approval for titanium, and for what reason was titanium chosen? Also, when you refer to "one of the vertical members, and... the other", are you talking about the 2 vertical portions of one bracket, or 1 vertical portion of both brackets (each bracket has 2 vertical 'portions', and these brackets would require an ace machinist to make them) The original brackets are an extrusion; a very special one.

[n2582d]

Del (and other A&Ps) have you seen these brackets cracked before? I'm wondering if this is something I need to strip and dye check on my project.

[starkw1]

Del

Here is the article (text only) I mentioned before which was from Q1 1996 170 News. There are at least four '48 170's with cracked tail brackets: mine, the one I got from a salvage yard, one from another member who contacted me back in '96, and Blake from Alabama.

========================================
VERTICAL FIN BRACKET
Warren Starkebaum #4047 MN

There are two brackets that are used to attach aft
end of vertical fin on the 1948 C170 to the horizontal stabilizer.
I have had the opportunity to evaluate three such
brackets that have been cracked. lnitially, my mechanic
and I determined that one of the brackets on my airplane
was cracked. After unsuccessfully trying to obtain a new
part, a used bracket from a salvage yard was purchased,
and it too turned out to be cracked. After finally disassembling
the vertical fin on the 170, I discovered that not one,
but both attach brackets were cracked.
I have owned N2663V for the past eight years.
The aircraft was rebuilt by a local A&P school about 13
years ago, has about 1750 hours totaltime and has been
operated about 50-70 hours per year since I have owned
it.

Figure 1 is an illustration taken from the C170
series parts catalog. I shows the detail of the lower aft end
of the vertical fin and attach brackets. The bracket is attached
to the vertical fin with four rivets. The base of the
bracket is in turn attached to the horizontal stabilizerwith
a pair of cap screws on each side of the fin.

During the annual inspection last year, my mechanic
discovered the left fin bracket to be cracked. He
became suspicious when he noticed a crack in the paint
on the bracket. Scraping away the paint, a small crack
was visible to the naked eye as shown in Figure 2A. Though
the bracket was clearly cracked, the tail was still rigid and
no movement of the vertical tail could be detected during
manual application of hand pressure to either side of the
top of the tail.
A large number of parts suppliers, including
Cessna, were contacted to locate new brackets (PN
00331'124). Not too surprisingly, I found no supplier who
could provide a new part. Similarly, I was unable to obtain
the specification for the part from Cessna or anyone else.
I did purchase a used bracket from a salvage yard,
but alas, it too was cracked in the same location on close
inspection under a stereomicroscope. At this point I consulted
my mechanic and the local GADO office to review
my options for fabricating replacement parts. FAR 21-39
21.306.b.2 indicates the aircraft owner may fabricate parts
for his own use. The local GADO personnel could not (or
would not) give a clear opinion whether or not it is legal for
the owner to subsequently sell the aircraft. ln any event, I
decided to go ahead and fabricate a new pair of attach
brackets.
The tail fin was removed from the aircraft and the
attach brackets removed from the fin. I am a metallurgical
engineer by training with access to a lab, so I used the
bracket from the salvage yard to determine the alloy type,
which turned out to be 2024 aluminum alloy. The hardness
of Rockwell 880 is consistent with this alloy in the T4
condition.
A careful low power miscroscopic examination was
carried out on both brackets from my airplane as well as
the one from the salvage yard. To my surprise, both of the
brackets from my airplane had cracks. As mentioned previously,
the salvage yard bracket was cracked also, although
the crack was not visible to the naked eye and
could only be observed under a microscope. I am certain
the crack would have been detected with a simple dye
penetrant test, though.
The crack in the left bracket is shown in Figs. A
and B. This crack had progressed approximately 1/3 of
the way through the section at the lowest rivet hole. Flexing
the bracket via finger pressure under a low power microscope,
one could easily see the crack opening and closing
slightly. Although not clearly visible in the photos, it
appeared that the crack initiated at a small dent on the
edge of the bracket as indicated by the arrow in Fig. 28.
The dent probably occurred during riveting the bracket to
the fin at an earlier time, perhaps when the aircraft was
rebuilt or repaired.
The crack in the right bracket is sown in Fig. 3.

Vertical Fin Attach Bracket
Figure 1

t2 TFIE 170 NEWS FIRST QUARTER 1996

LateralView of Bracket at Lower Rivet
Fig. 2A

End On View of Bracket
Fig. 2B

This crack was smaller than the one in the left bracket.
The crack initiated on one corner and propagated a relatively
shallow distance.
While I did not open the cracks in either bracket
to examine the fracture surfaces, I think it is certain these
were fatigue cracks that occurred due to excessive cyclic
loading on the tail. This could have occurred if the tail
wheel were prone to shimmy. ln the eight years I have
owned the airplane, this has never been a problem that I
was aware of, however. lt is possible that the cracks initiated
long before I purchased the airplane and propagated
slowly until telltale signs of cracked paint became visible.
It is likely that the small dent on the one bracket was a
contributing factor in the crack on that bracket. A small
ding in a critical location of a moderately loaded structural
part can be a problem!
The two brackets from my airplane and the one
from the salvage yard were used as the basis for cloning a
new part. These original parts were probably eXruded
sections, as evidenced by transverse surface scratches
visible under the microscope. The long member of the "T"
section is a little over 3 inches tall, making it difficult to
machine by conventional means. After discussing the design
and available fabrication techniques with my machinist,
we decided to fabricate the new brackets from Ti-6Al-
4V, a very common aerospace ( and medical implanil)
titanium alloy. This alloy is far superior to 2024 Al in terms
of yield strength, tensile strength, fatigue strength, or fracture
toughness. Additionally, it is easy to machine using
wire EDM (electric discharge machining), and we just happened
to have a wire EDM system in our shop. To fabricate
the brackets, we machined 3/4 inch thick blanks and
then drilled the rivet holes. The blanks were then stacked
(3 up) and the "T" section with the slot was wire EDM'd in
all three blanks together. The holes in the base of the
bracket were then machined, the parts alodined, and the
airplane reassembled and repainted.
My advice to the 1948 170 owners:
lnspect your fin attach brackets carefully. lf necessary,
get down on your hands and knees with a magnifying
glass and look carefully. lf there is cracked paint,
carefully remove it. lf you or your mechanic are at all suspicious
consider a dye penetrant test to confirm the presence
of cracks.
lf you do confirm the presence of even a small
crack in either bracket, do not fly the airplane.
lf new brackets are needed and you are considering
used parts, inspect the parts carefully under a microscope
or with dye penetrant before using, and preferably
buying, the parts. lf satisfactory parts cannot be located,
you may be forced to fabricate new parts as I did.

Crack in Right Vertical Fin Bracket
Figure 3
TTIE i70 NEWS FrRST QUARTER 1996 13.