Pawnee landing gear

[wowway news]

Each side of the landing gear of the Pawnee is fastened with 3 bolts. Each
fore and aft outboard bolts connect through 2 sets of tabs welded to the
lower fuselage longeron. Our right hand gear is slightly loose at the
forward attach point . Either the holes in the 2 tabs are worn out-of-round
or the bolt is worn (or both). Do not know the actual condition as the bolt
has not been pulled yet (cold in the north country).
Have any other Pawnee operators seen this problem? If so, what was the
problem and what was your method to fix.

Duane Eisenbeiss
eisenbeiss at compuserve dot com

[R]

wowway news wrote:
If so, what was the
> problem and what was your method to fix.

The bushings in the landing gear attach points are probably worn.
Remove landing gear, inspect the bushings, and, the attach bolts, insert
new bushings, and, or, bolts, if found to be worn.

[uncl...@ix.netcom.com]

Open it up and inspect fully- no matter how cold. I have found the
mounting brackets broken. You really want to take a hard look at this.
We also change bolts at least once a year.
UH

[wowway news]

>Open it up and inspect fully- no matter how cold. I have found the
mounting brackets broken. You really want to take a hard look at this.
We also change bolts at least once a year.
UH<

We plan to remove the bolt for a complete inspection. Just have not done so
since the late Nov annual inspt. This is a work in progress. I was just
wondering if others had seen similar problem. The gear attach points have
been inspected as well as can be done without removing the gear.

When you say that you have found the mounting brackets broken do you mean
the actual tab or the weld attaching the tab to the longeron?

Thanks for the reply Hank.

Eisenbeiss

[son_of_flubber]

On Sunday, December 6, 2009 at 2:06:24 PM UTC-5, uncl...@ix.netcom.com wrote:

> We also change bolts at least once a year.
> UH

Is this just 'common sense' or is it recommended in a maintenance manual or AD?

I'm looking for information specifically about the failure of one of these bolts. I've scanned through the Piper PA-25 AD index and did not find an AD that mentions them. Are there known cases of these bolts failing and gear collapsing?

Maybe the information is out there and I just don't know how to find it. Sharing of your expertise is very much appreciated.

[Charlie M. (UH & 002 owner/pilot)]

It's called, "After having bolts break as well as tabs, it's easier to replace bolts & look things over frequently.... rather than wait until it breaks (usually middle of a busy day....)".

I've helped a few times, Hank has been through it a lot more times.

Depends on number of landings, how hard were they & how smooth the field.

I am not aware of a specific document stating the shorter changes/"look overs".

[uncl...@ix.netcom.com]

On Friday, August 21, 2015 at 9:12:52 PM UTC-4, son_of_flubber wrote:

It is a practical response to having had failures of the gear mounting brackets as well as bolts.
Ours is a 150 Pawnee converted to 180 so it has a somewhat lighter gear than the later 235. All the bolts on the 235 are one size larger.
Our field is rough and we do about 1000 landing a year with this airplane.
I am not aware of any AD nor any maintenance manual info on this.
UH

[Bill T]

We have a -235 model. The integrity of the gear is checked each annual, but not taken apart. I think in the 15 years we have had the Pawnee, the bolts, bushings were replace once. The shock cords, I think every five years. We operate on a paved runway, not rough gravel or sod.

BillT

[son_of_flubber]

PA-25-235 bolt failure pictures
https://imgur.com/a/MgE77

[howard banks]

Nice pictures but what we really need are clear closeups of the fracture surfaces and a clear description of the location of the origin of the fracture and the supporting structure, on the airframe and the undercarriage.
That might tell whether something more than just changing the bolts at some schedule prior to likely failure is sufficient.

[Bill T]

That bolt is the shock absorber attach point. I think most of the other questions have been directed to the other two bolts that did not fail in those pictures.
BillT

[son_of_flubber]

On Sunday, August 23, 2015 at 5:38:19 PM UTC-4, howard banks wrote:
> Nice pictures but what we really need are clear closeups of the fracture surfaces and a clear description of the location of the origin of the fracture and the supporting structure, on the airframe and the undercarriage.

RAS is not the appropriate forum for the ongoing investigating of this failure. I understand that the limited information posted here is going to frustrate some people. I thought it was only fair to give a limited 'heads up'.

I'll say this. Nobody was injured. The failure occurred at 30-35 knots on launch. Towplane ground looped right. Glider went left. Glider pilot pulled the release promptly and never came close to colliding with the towplane. Glider pilot was holding a lanyard attached to the tow release handle.

[Papa3]

Towplanes of many different types probably suffer disproportionate gear failures due to the nature of the operation. I can come up with two L-19s and a 180HP Pawnee that had similar failures operating off of local gliderports. 20-30 takeoffs and landings in a day on busy days, many off of rougher than average grass strips.

Just sayin' - not that surprising.

P3

[Waveguru]

Could the bolts have been over torqued?

Boggs

[uncl...@ix.netcom.com]

On Monday, August 24, 2015 at 2:33:27 PM UTC-4, Waveguru wrote:
> Could the bolts have been over torqued?
>
> Boggs

Nope
Pawnees, as a group, have very stiff gears due to strong bungees, presumably needed when carrying loads of stuff.
This means that much of the time the only springing is the tires. That puts big sharp loads on the connections, particularly the hydrasorb/bungee assembly joint.
Photos show what appears to be a bracket for a safety cable. Good idea, but doesn't help if the bolts fail obviously. We're now changing bolts every 100 hr or so on our "little" Pawnee.
UH

[Waveguru]

But if it failed because of loads on the gear, wouldn't it fail at the end of the bolt instead of in the middle of the bolt like it shows in the picture?

Boggs

[uncl...@ix.netcom.com]

On Monday, August 24, 2015 at 9:31:37 PM UTC-4, Waveguru wrote:
> But if it failed because of loads on the gear, wouldn't it fail at the end of the bolt instead of in the middle of the bolt like it shows in the picture?
>
> Boggs

Nope. Hydrasorb end goes in a yoke on the gear leg that theoretically puts it in double shear. Wear everything a bit and it does try to bend the bolt.
UH

[son_of_flubber]

We have two PA-25-235s. We replaced all six bolts on the undamaged Pawnee before flying it.

The bolts on both planes were replaced the last time that the bungees were renewed. I don't have the details. I expect that we will replace the bolts more frequently going forward.

The FAA is in the loop.

[Craig Lowrie]

We have fitted cable restraining straps to our two Pawnees... They save
the plane and prop in most cases with this or a strut-end failure (of
which we have had a couple)..... Craig

[son_of_flubber]

On Tuesday, August 25, 2015 at 4:15:08 AM UTC-4, Craig Lowrie wrote:
> We have fitted cable restraining straps to our two Pawnees... They save
> the plane and prop in most cases with this or a strut-end failure (of
> which we have had a couple)..... Craig

From what I understand, there are at least two ways to rig the restraining cables that protect from a strut failure. One way is to anchor the cable to the bolt that broke. That is less than ideal when the bolt breaks.

[soaring4fun]

On Tuesday, August 25, 2015 at 4:15:08 AM UTC-4, Craig Lowrie wrote:

> We have fitted cable restraining straps to our two Pawnees... They save
> the plane and prop in most cases with this or a strut-end failure (of
> which we have had a couple)..... Craig
>
>

Craig, what strength cable did you use and where did you find the drawings or photo o exactly where to run the cable? From crop dusters? Any help is appreciated. My Pawnee bolts sheared (actually broke) and I know of another Pawnee that also had the very same happen. This was years ago. We change the bolts now...often. I have always wanted to put the cable around the top of the gear, but never researched it, so thanks for rattling the chain. Jayne

[di...@hotmail.com]

August 2017. Do you have the tech drawing or any reference which quotes the safety cable dimensions? We'd sure appreciate any info on just how long each cable should be. We have photos of cables installed on Pawnees, but need accurate length info. We operate two PA-25 Pawnee 235 as glider tugs. Dick Parker. Edmonton Soaring Club. Many thanks. < di...@hotmail.com >