Pawnee landing gear

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

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.

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

Could the bolts have been over torqued?

Boggs

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.