Airframes Wide Body 4" in looking for 3 x 3 gear that fit wide body fuselage

[Skudrunner]

Other Than changing the Airworthiness to Experimental /Exhibition does any one know if there is a STC for Forward Gear for

a PA-18 Airframes 4 in Wide Body Fuselage ideally a 3 x 3 but I am open to suggestions?

Thank You

Mike

[Mr. Ed]

Same 3x3 that fits the standard width cub. Cabane is obviously wider to fit the wide body fuselage.

[Crash, Jr.]

Not only is the cabane vee wider but the shock struts are of a different length if you decide to run bungees. If not then just the cabane vee needs to be for a wide body. Not sure how the 3x3 works as far as the gear pulling both forwards and down on the cabane or if CubCrafters worked around that. Would be interested to hear how they run their shocks at an angle.

[Mr. Ed]

I was concerned about forward gear pulling in an arc (or sweep) relative to the cabane. I set up a jig with the gear to measure movement. No arc to the motion but you do have to angle the cabane forward so that all load paths are in a straight line. Make sure all angles you check are from the shock strut attach point on the gear leg to the cabane mounting point.

[skywagon8a]

I was concerned about forward gear pulling in an arc (or sweep) relative to the cabane. I set up a jig with the gear to measure movement. No arc to the motion but you do have to angle the cabane forward so that all load paths are in a straight line. Make sure all angles you check are from the shock strut attach point on the gear leg to the cabane mounting point.

Moving the cabane angle forward you will need a ball joint since the new pivot locations will not be moving parallel to the main gear bolts at the bottom longeron.

[mike mcs repair]

Moving the cabane angle forward you will need a ball joint since the new pivot locations will not be moving parallel to the main gear bolts at the bottom longeron.

You could do it in tubing fit up of cabane top


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[Skudrunner]

Moving the cabane angle forward you will need a ball joint since the new pivot locations will not be moving parallel to the main gear bolts at the bottom longeron.

Thank you
any idea where to get something like that a large
cabane with a ball joint

[mike mcs repair]

Thank you
any idea where to get something like that a large
cabane with a ball joint

Ball joint. Very bad idea there. Better to make cabane v have that angle built into upper joint when fit up for welding. I bet airframes can make you one, if they don’t already have one in stock.


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[stewartb]

So there must be a handful of guys reading this that have 3x3 gear. Did you change the cabane with the gear?

[skywagon8a]

Ball joint. Very bad idea there. Better to make cabane v have that angle built into upper joint when fit up for welding. I bet airframes can make you one, if they don’t already have one in stock.

All of the bolts in the landing gear must be parallel or there will be built in stresses. Where there are stresses, especially in high impact landing gears there will be failures.

[ak49flyer]

Yes cabane changes with the gear- I think CubCrafters has them. Top attachments are angled like Mike described to keep everything lined up.

[mike mcs repair]

All of the bolts in the landing gear must be parallel or there will be built in stresses. Where there are stresses, especially in high impact landing gears there will be failures.

And they still are, do a mock up.


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[Mr. Ed]

Agreed, top of cabane is modified so that the tube the bolt goes through is welded in to provide the angle the cabane needs. The bolt remains in its original orientation. Heim joint at the top is bad idea. If you get a wide body fuselage from a kit builder, get the cabane from them, providing them with the information on how far your gear will be extended forward. If you buy forward extended gear from TK, for example, they also sell a cabane made for that gear. I believe theirs is a 4” forward, so the cabane won’t be correct for a 3”.

[Gordon Misch]

The forward gear leg travel path and the cabane should be in the same plane. Merely angling the cabane will not accomplish that. The axis of rotation is by definition perpendicular to the plane of rotation. Changing the plane without changing the axis appropriately will cause binding. tipping the cabane forward puts it in a different plane than the plane of gear leg motion. How much binding is a separate question - maybe it's not enough to matter much, depending on bolt clearances???

[mike mcs repair]

The forward gear leg travel path and the cabane should be in the same plane. Merely angling the cabane will not accomplish that. The axis of rotation is by definition perpendicular to the plane of rotation. Changing the plane without changing the axis appropriately will cause binding. How much binding is a separate question.

you must ignore the strait up and down sides of the lower gear & shock strut, and same on lower cabane vee, and just make axis of bolt holes parallel and in alignment to gear bolts.... none of these joints are bolted tight from front to back, so it will all play well together without any binding....

[Skudrunner]

TK s aren't STC'd though and this is a certified PA-18 that's why my initial question was is it worth it to change the airworthiness to Experimental/Exposition category just for a Forward cant? Would buying a STC 3 x 3 and trying to do a 337 form on the cabane be a possibility - I'm open to all options

[ak49flyer]

“Up to installer to determine compatibility of multiple STC’s” or something like that. I’d have airframes or whoever build a copy of their 4-place cabane, but with the cant, and install it under the 3x3 STC.

[skywagon8a]

TK s aren't STC'd though and this is a certified PA-18 that's why my initial question was is it worth it to change the airworthiness to Experimental/Exposition category just for a Forward cant? Would buying a STC 3 x 3 and trying to do a 337 form on the cabane be a possibility - I'm open to all options

Aside from all of the above discussion, why do you want to move the gear forward? Is your CG where it is supposed to be? Throwing a tool bag in the baggage or installing a few pounds of ballast at the tail, corrects the CG.

[stewartb]

TK s aren't STC'd though and this is a certified PA-18 that's why my initial question was is it worth it to change the airworthiness to Experimental/Exposition category just for a Forward cant? Would buying a STC 3 x 3 and trying to do a 337 form on the cabane be a possibility - I'm open to all options

Cubcrafters has approved 3x3 gear. From a previous post it sounds like the cabane is adjusted. Why not ask Cubcrafters?

3" forward gear is about increasing the tail weight, usually on standard length airframes, to allow more aggressive braking. I know guys who have it and like it but my Cub's long tail is already plenty heavy so I stayed with standard gear. On the cabane angle thing? When switching to 6" TK-1 gear I had to replace my cabane. I assumed it was about suspension geometry but now I wonder if the strut angle needed correction at the cabane. Hmm.

[stewartb]

FYI. New cabane vee is angled..... It appears they don't make a cabane for wide body Cubs. That should be easy to overcome.

http://store.cubcrafters.com/3X3-STC...ft_p_1300.html

[DENNY]

Is there a bushing in the top holes of CC cabane V? Seems I remember hearing/reading about something like that. Hole looks kind of big in the picture.
DENNY

[RaisedByWolves]

Is there a bushing in the top holes of CC cabane V? Seems I remember hearing/reading about something like that. Hole looks kind of big in the picture.
DENNY

Yes at least on the ex gear, it’s a hard plastic.


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[Gordon Misch]

A related question - -

I'm replacing bungees on my -12 and on disassembly noticed some play at the lower shock strut attachment. I measured the hole in the strut and it is elongated, measuring about .012 to .014 oversize (the two struts are slightly different). That strikes me as a lot. The narrow dimension is also oversize, just not as much. That's what has me wondering.

I'm thinking to machine out the old bushing and weld in a new one, but want advice from here first. Should I leave well-enough alone, or do the repair?

Edit: By comparison, the hydrasorb holes are about .001 oversize.

Edit again: Piper dwg 12944 shows that hole reamed to .374 - .376. So I'm going ahead with re-bushing.

[mike mcs repair]

A related question - -

I'm replacing bungees on my -12 and on disassembly noticed some play at the lower shock strut attachment. I measured the hole in the strut and it is elongated, measuring about .012 to .014 oversize (the two struts are slightly different). That strikes me as a lot. The narrow dimension is also oversize, just not as much. That's what has me wondering.

I'm thinking to machine out the old bushing and weld in a new one, but want advice from here first. Should I leave well-enough alone, or do the repair?

Edit: By comparison, the hydrasorb holes are about .001 oversize.

Edit again: Piper dwg 12944 shows that hole reamed to .374 - .376. So I'm going ahead with re-bushing.

Can’t say on hole.

But always check shock struts for water & internal corrosion while you have it apart


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