Landing gear

[zkelley2]

I was over at a prominent aircraft welding and parts store the other day and they had this in the bay.

20190801_155658.jpg

If I were staying on wheels I imagine I'd be doing something similar. I'm curious to see what the speed penalty is when they get it done.

[AZBearhawk272]

From a stress and structural integrity standpoint the
displayed execution may be weak. I understand the concept which is viable however the size of the
rod compression member in the spring / shock is suspect of being inadequate for the weights and
compressive loads on a 4 place. IMO/ FWIW

Kevin D
# 272

[Mark Goldberg]

The airplane in the picture is having some rather extensive mods done on it. All done by a shop that sees LOTS of PA18's. None of this approved by Bob or to my knowledge even consulting Bob. These changes might work out, or as Kevin (BH272) points out - maybe not. Mark

[tailwind]

I guess my question is why? Seems like the gear as Bob designed it is perfect just as it is.

[Mark Goldberg]

Remember this is in the land of PA18's up in Alaska. The PA18 is held up on a pedestal for being all the good that an airplane should be. And this owner took his plane for mods at a shop where they do extensive PA18 work. So naturally they are doing Cub like things to it thinking it will be an improvement. I guess we will see in time. Mark

[zkelley2]

It has failed when subject to considerable abuse, which we tend to do up here. The A model shocks really aren't adequate, hence the change and there's also been failures of the gear leg tubes in compression and at the shock strut attach point.

[zkelley2]

I share Mark's dislike of how much the cub is the be all end all. Cause it's not. But I'd be blown away if this wasn't modeled in CAD and not just randomly thrown together.
The gear you see on the PA18's anymore is not factory cub gear, because the factory cub gear has been found to be inadequate, so after many people having it fail, it was improved upon. The advantage the PA18 has in this area is they've had 60 or so year to do this and there's a lot of improvements over the original design.

[zkelley2]

From a stress and structural integrity standpoint the
displayed execution may be weak. I understand the concept which is viable however the size of the
rod compression member in the spring / shock is suspect of being inadequate for the weights and
compressive loads on a 4 place. IMO/ FWIW

Kevin D
# 272

I really doubt that considering their other engineering work over the years. They probably own more STC improvements on pipers than anyone.
Those are solid titanium rods, not tubing.

[tailwind]

It would be interesting to see how it performs. We probably will not see a follow up article of how it performs in the field.

[quadra]

I really doubt that considering their other engineering work over the years. They probably own more STC improvements on pipers than anyone.
Those are solid titanium rods, not tubing.

Can you please post a link to the original location of referenced images?
I can only zoom in on this one image but the construction clearly shows internally threaded tube with milled faces ( possibly above lock collars? ) and a central element that appears to use opposing threads on each end to allow for length adjustment... if that is the case the thread failure calculation or tube failure is lower than the assembly.. right?
Having said that, how is titanium appropriate for bush plane landing gear? even as a monolithic structure the only advantage of Ti is weight savings... awesome in a commercial carrier or a fighter that needs greater acceleration but if I am bouncing off a sandbar or frozen moose shit while trying to safely return to Earth I will rank toughness and elasticity WAY WAY above light weight... and good old steel owns the show in toughness. steel is far tougher and more elastic than Ti... If you want to add this material to your plane go have a great welder fab up your door frames or tail feathers out of Ti tube... as neither are expected to endure the loads that landing gear are designed for.. hell if you want to roll the dice, build your seat frames out of Ti, as it will only be a problem if you crash, right?
these are not gliders or solar global soaring projects they are STOL bush planes.
...rabble rabble rant,,,

[zkelley2]

Can you please post a link to the original location of referenced images?
I can only zoom in on this one image but the construction clearly shows internally threaded tube with milled faces ( possibly above lock collars? ) and a central element that appears to use opposing threads on each end to allow for length adjustment... if that is the case the thread failure calculation or tube failure is lower than the assembly.. right?
Having said that, how is titanium appropriate for bush plane landing gear? even as a monolithic structure the only advantage of Ti is weight savings... awesome in a commercial carrier or a fighter that needs greater acceleration but if I am bouncing off a sandbar or frozen moose shit while trying to safely return to Earth I will rank toughness and elasticity WAY WAY above light weight... and good old steel owns the show in toughness. steel is far tougher and more elastic than Ti... If you want to add this material to your plane go have a great welder fab up your door frames or tail feathers out of Ti tube... as neither are expected to endure the loads that landing gear are designed for.. hell if you want to roll the dice, build your seat frames out of Ti, as it will only be a problem if you crash, right?
these are not gliders or solar global soaring projects they are STOL bush planes.
...rabble rabble rant,,,

When I saw them the other day, I thought they were this new brand that was at our trade show in May, that was all titanium and lighter than the others. Upon closer inspection I think they are the AOSS system, which is only rated to 2300lbs. So... ya, not sure if they had them one off something for them for higher weights or what. AOSS isn't titanium, it's nickle plated steel.

The shop is Atlee Dodge.

[kestrel]

It has failed when subject to considerable abuse, which we tend to do up here. The A model shocks really aren't adequate, hence the change and there's also been failures of the gear leg tubes in compression and at the shock strut attach point.

What "events" are causing failures? How are the A model shocks not adequate? Sincere questions as I feel that I've worked my gear reasonably hard and not seen issues. However, I do have longer shocks/springs than normal and have not done anything like a ground-loop.

[Mark Goldberg]

I also take some exception to Zach's comments about the gear. But did not want to discuss it here on the forum. Mark

[zkelley2]

Sorry Mark, I don't have permission to post pictures of people's airplanes that are not mine. I'll give you a call later if you wish.

[alaskabearhawk]

https://bearhawkforums.com/forum/bearhawk-general-discussion-news/23769-engineering-change-for-bearhawk-4-place-and-patrol/page2

[zkelley2]

So turns out the airplane I'm talking about's gear failing is extremely likely that the failure has nothing at all to do with the design or strength of the landing gear, but previous damage and likely poor craftsmanship to begin with.