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Thread: Heavy Duty Landing Gear Specs

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    Aeronut's Avatar
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    Heavy Duty Landing Gear Specs

    I'm looking for the tubing dimension of the front and rear tubes of the "heavy duty" landing gear for the PA-18. Looking at manufacturers that sell this nominal type of landing gear, I haven't been able to find out the front and rear tube ODs for comparison.

    According to Piper drawing 10033, tube 82352-40 (which is 1.375" in diameter) is used as the front tube for the landing gear in the 10033-5/6 configuration. 82352-41/42, which has an OD of 1.25", is used for the rear tubes. These is the heaviest duty specs I could find. How do the aftermarket heavy duty landing gears vary from the Piper drawing?

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    Maybe cubcrafters will share their information or Alaska airframes or javron or Dakota Cobb

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    Atlee has size of tubes

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    Aeronut's Avatar
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    Thanks, Dirthog! I just checked and found the info here: https://fadodge.com/main-landing-gea...le-3-extended/. I haven‘t heard from the other manufacturers but have a hunch that 1.375“ is the heavy gear standard.
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    marcusofcotton's Avatar
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    Any idea of the wall thicknesses?
    Practicing open cockpit extremism

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    Aeronut's Avatar
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    Marcus, I"ll add that to this post if I hear anything from the manufacturers or other sources.
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    Olibuilt's Avatar
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    From TK-1 Racing website: FRONT AND GEAR TUBES ARE 1.50 X .058 WALL CHROMOLY TUBING.

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    Aeronut's Avatar
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    Thanks, Olibuilt. It‘s interesting for me to see that „heavy duty“ isn‘t a precisely defined term. Given the reputation of Atlee I‘m prone to believe that 1.375“ is an adequate beefed up landing gear size. But given the negative comments I‘d seen about the original PA-18 gear I wonder if folks aren‘t referencing the 1.25“ OD landing gear and not the 1.375“ of the Piper 10033-5/6 configuration.

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    The wall thickness is a very important dimension here.
    Regards, Charlie
    Super Coupe E-AB build in process
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    TK is unique since he uses 1-1/2” tubes front and rear. I believe Airframes and Atlee use 1-1/2 in front and 1-3/8 aft. I have no idea what Acme uses but with these EXP shops making 8,9, and even 10” extended gear? The tubes must be heavier duty.
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    TurboBeaver's Avatar
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    Well 40 years ago the term HD gear was what we all refered to after you took Standard gear to Atlee and he
    Beefed it up by adding saddle sleeves and gussets to the bottom cluster. Then for ski flying they would also sleeve the inside of the axle. Good luck
    E

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    Aeronut's Avatar
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    Great input! I‘ll look at the weight difference on that rear tube and make a call for myself on which I‘d prefer.

    Does anyone have a good method for notching the angle for the 1.5“ axle in the landing gear vee on a scratch build? I‘ll be doing the 3“ extended gear.

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    TurboBeaver's Avatar
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    When you crunch a gear leg the rear tube usually fails and kinks forward, sorta like a fuse so to speak. Beefing up that area too much may work against the engineering ......
    It's easy to make that tube larger, thicker walled, and add the bottom step to reinforce the triangle. But question is: Would you rather have the rear leg kinked, Or have the gear fittings, riped right off the fuselage, or caved in ??? When I guided with a Cub in Alaska, I never went hunting with out a Dodge " limp along" (reverseable) gear leg taped to the left wing strut........ It came in handy at times
    Good Luck.
    E
    Last edited by TurboBeaver; 09-08-2021 at 01:52 AM.
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    Failed rear tubes have pretty much gone away with bigger tires. I recall Atlee saying Bushwheels were unnecessary. And that was before 31s came out. Now just about all the guides I know use 35s as standard equipment. And oddly enough, guys with 35s and really long gear aren’t tearing out the attachments on the airframes. Big tires and good shocks on long gear work great.
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    TurboBeaver's Avatar
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    Here is a set of 35" tires off a modern day guides Cub. Just brought into town yesterday. Apparently 35" tires don't cure
    everything Olde boy....... I don't see a new gear leg fixing this one. Note airframe caved in on left side.Click image for larger version. 

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    Last edited by TurboBeaver; 09-08-2021 at 02:02 AM.

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    That doesn’t look like the result of a gear failure. There are still lots of ways to wreck ‘em. I hear legacy gear plays a role. Tires won’t change that.
    Last edited by stewartb; 09-07-2021 at 08:06 PM.
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    Looks like the right hydrasorb/strut is broke, note the safety cable is holing up that side. The big 35 in tire is like skis lots of torque when you don't keep it straight. I have seen two sets of HD gear bent/broke at the middle of the front tube when 35's went sideways.
    DENNY

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    I see dented wings and baggy fabric, too.

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    Quote Originally Posted by stewartb View Post
    I see dented wings and baggy fabric, too.
    Where’s the propeller?

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    Gordon Misch's Avatar
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    Dropped in with trees on approach end? Damn, sorry!
    Gordon

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    TurboBeaver's Avatar
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    Here is another example of 35" tires and great shocks NOT being enough to make the difference....... Again major damage in boot cowl area. Big save here was when right gear separated from the shock, it came down on the POD! Which was strong enough to hold
    It up enough to NOT get the prop and crank! Bent spar in left wing???? Don't know........ It's a Darn shame, and I feel bad for both of these fellas. Anyone of us could have an accident, so I am not judging the pilots in anyway........
    But once again; how much does "overbuilding a gear leg" really buy you, As the fuselage is caving in??? It's obvious
    that 35's and Acme's still couldn't 'save the plane' again in this case.Click image for larger version. 

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    Last edited by TurboBeaver; 09-08-2021 at 01:38 AM.
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  22. #22
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    Generally a beefed up region transfers the load to a less beefed up region. It looks like it's all about finding that envelope of structural limitations and designing structural members to handle loads within normal to moderately high load cases (some hard landings). Great pics and information!
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    Yep. Takes some ham handed talent to damage the gear fittings with 35s and Acmes. It might have been easier on things if the rear gear leg folded but then I wouldn't have flown it out.
    Click image for larger version. 

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    On that SQ it looks like an Acme shock broke?

    To the gear tube and thickness thing? When is enough enough? Backcountry gear was eery light when I was putting my plane together. I never even considered using it. I went up the street and bought Airframes Super Duty gear.
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    Quote Originally Posted by stewartb View Post
    On that SQ it looks like an Acme shock broke?

    To the gear tube and thickness thing? When is enough enough? Backcountry gear was eery light when I was putting my plane together. I never even considered using it. I went up the street and bought Airframes Super Duty gear.
    Looks like aoss to me.


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    And no safety cables. Not that the shock failure caused the accident. The accident may have caused the shock failure. Either way a safety cable would have helped. Is there a gear failure in that pic? I don’t see one. Interesting that the right 35 had been changed to something smaller. Gotta be a story there.

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    Quote Originally Posted by TurboBeaver View Post
    When you crunch a gear leg the rear tube usually fails and kinks forward, sorta like a fuse so to speak. Beefing up that area too much may work against the engineering ......
    It's easy to make that tube larger, thicker walled, and add the bottom step to reinforce the triangle. But question is: Would you rather have the rear leg kinked, Or have the gear fittings, riped right off the fuselage, or caved in ??? When I guided with a Cub in Alaska, I never went hunting with out a Dodge " limp along" (reverseable) gear leg taped to the left wing strut........ It came in handy at times
    Good Luck.
    E
    So I'm pondering this as I fix a broken gear fitting and slight damage to the fuselage. I've got HD Javron gear with the middle step reinforcement. Maybe it is working against me?

    If the rear leg folding forward relieves some of the strain that is positive. What are the negative consequences?

    Does the gear toe out, break off, cause a loss of control. If I want the gear to break instead of the fuselage, what price do I pay in other damage? Let's assume a mountain strip with lots of hazards, not just a big flat gravel bar where I hit a rock, log or ditch that was too big. How many times did you replace that gear leg without some other consequence?

    Honest question.

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    Quote Originally Posted by DJ View Post
    So I'm pondering this as I fix a broken gear fitting and slight damage to the fuselage. I've got HD Javron gear with the middle step reinforcement. Maybe it is working against me?

    If the rear leg folding forward relieves some of the strain that is positive. What are the negative consequences?

    Does the gear toe out, break off, cause a loss of control. If I want the gear to break instead of the fuselage, what price do I pay in other damage? Let's assume a mountain strip with lots of hazards, not just a big flat gravel bar where I hit a rock, log or ditch that was too big. How many times did you replace that gear leg without some other consequence?

    Honest question.
    How many people choose in advance how, where and in what manner they are going to break their gear or some other component? I choose to go out of my way not to do any damage. Not always successful but do have a good track record.
    N1PA
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    If the rear leg folds backward that big 35 is going to keep pushing all the way back to the side of the fuselage. That will most likely bend break the front fitting and break bend whatever shock setup you have Safety cables will hold and drag everything along with the plane so you do have to look for parts. Once tire is next the fuselage the wingtip will now be finding hard/soft surface to dig into and pivot the plane to the side and forward. Depending on speed and amount of dig in once the prop folds back it may just come to rest or try to bounce to other wingtip. If soft enough you may get it over to include rudder damage. Seen that happen in a Champ with great results. Pilot hit something on landing on Bear hunting strip in the grass. Heard a big bang and went back into the air. Looked down and saw left tire was back more than when he left home. Flew to home airport, stoped engine and made sure prop was level on final (reports lots more drag than you would think!!) Landed on the tar and held off on right wheel as plane settled onto left wheel it folded back completely and wingtip slid on tar. No prop strike plane was flying two days later. The key was stoping prop and landing on hard surface so nothing digs in (think of all the gear up landing you see on tar, they just slide along. If the shock strut or shock fittings fail the gear will tuck under in flight on that side. Saw that one land on dirt and get both wings, prop, fuselage tail as it came back off the nose but two people on board where fine. I have see gear bend and not break, pilot was able to make it home but wingtip was very close to the ground. I would say bending or breaking tube tubes in the fuselage although harder to fix is usually something you can fly back out. Once the gear tabs not protected with safety cables or gear itself Breaks now you will have issues.
    DENNY
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  30. #30

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    As a point of interest, here’s what the attach structure looks like on my Cub. If you make stuff bigger and heavier you need to improve points of attachment as well.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  31. #31
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    That's exactly it. The overall structure of the plane (gear and fuselage) has to scale to match the load that's placed on it. A little lightweight PA-11 or J3 can run the stock gear and do some horrible things to it and never have a failure. Even a stock PA-18 on 31's when flown reasonably isn't overly abusive on the gear or fuselage structure so you have an equal loading between the gear and fuselage. The "Heavy Duty" gear came about when guides took stock cubs and started loading them heavily, running the biggest tires and doing pretty abusive things to the plane so then the stock gear failed. So then the gear gets bigger/thicker/heavier and so do the struts, and now you move the failure point to the fuselage. What follows is aftermarket frame builders beefing up gear fittings and sleeving the fuselage where the gear fittings are and you're back to a good place but the overall plane is much heavier and harder on gear and gear fittings. Energy dissipation is a factor of weight and speed so when you up either of those things you have to make up for it in structure.

    It's all very much dependent on the mission and how much you carry in the plane. The decisions on gear and various reinforcements follows those parameters. Obviously there are outliers to this as there are some folks that can break an anvil but this is a generalization.
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