Pawnee landing gear

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

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

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

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.

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


At 02:04 25 August 2015, son_of_flubber wrote:
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.

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.

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

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.