"A" model nose gear question

[WildThing]

Hi All,

I bought my 2003 RV-8A in FEB and am getting ready to do the (somewhat overdue) nose gear SB and install the new style fork. Here's the $64K question: Has anyone done or looked at just moving the top collar down 1" instead of cutting and re-threading the bottom of the gear leg? I called Van's and they said that they hadn't looked at it. My TLAR engineering degree (That Looks About Right) says that the extra hole is probably not an issue (?). The 1" of extra "down" leg on the gear tube below the bend would be subjected to more input from forward loads, but I'm having a hard time seeing that it would be failure prone. Any and all input appreciated - especially from actual load/stress analysis comparisons. Or some more TLAR engineering

THANKS!

[AlexPeterson]

Interesting idea - it would lower the tail a bit, might look a bit better sitting on the ramp. A little less margin for landing on the nose wheel, but nothing like the 6A I wouldn't think.

[rvbuilder2002]

The fit of the nose leg fairing will change... probably require a custom fairing.
The bending moment on the leg at the sharp fwd bend will increase (I would guess about 20%)
The tail will be 3.5 to 4 inches lower (my guess) when sitting on the ground.

[Ralph Inkster]

I'd suggest modifying the WD-631 swivel stop with a 1" longer tube extension, rather than drilling a second hole in the lower gear leg. Also I'd use the next thicker tube thickness for the mod as I've replaced two WD-631s on aircraft that had been damaged by unknowing rampies aggressively pushing back on the plane & you know what happens...

[WildThing]

Thanks guys. That's pretty much what I came up with. I expected to need to "extend" the gear leg fairing. It needs cosmetic work anyway.

Ralph - great idea! I hadn't considered a reinforcing tube/extension. I'll see if I can locate a piece of tube and weld it together as a modified WD-631.

[rvbuilder2002]

I didn't point it out in my other post, but it is entirely possible that the increase in bending moment this mod would cause to portions of the gear leg would 100% negate any benefit gained by doing the mod.
I.E. after all of the effort, you are no beter off than if you just left it as is,amd in a resale value consideration (assuming it might some day be one), you now have an airplane that has a one-off unproven mod done to it.

Have you investigated having the leg mod'ed as described in the S.B.?
I think the cost is quite reasonable (by aircraft dollars standards) and they turn them around relatively quickly.

[rvbuilder2002]

Originally Posted by Ralph Inkster

I'd suggest modifying the WD-631 swivel stop with a 1" longer tube extension, rather than drilling a second hole in the lower gear leg. Also I'd use the next thicker tube thickness for the mod as I've replaced two WD-631s on aircraft that had been damaged by unknowing rampies aggressively pushing back on the plane & you know what happens...

This type of damage is far more often caused when builders installed the WD-631 180 deg out of proper position. This is very common. The proper clocking of the part is with the stop tang facing Forward.

Improper clocking does two things. It reduces the pivot angle to less than what is needed when a pivot turn on one wheel is executed (puts a high load on the part every time a sharp turn is done), and it makes it very vulnerable in any nose wheel shimmy event (that is what usually destroys them).

[Jesse]

Originally Posted by WildThing

Thanks guys. That's pretty much what I came up with. I expected to need to "extend" the gear leg fairing. It needs cosmetic work anyway.

Ralph - great idea! I hadn't considered a reinforcing tube/extension. I'll see if I can locate a piece of tube and weld it together as a modified WD-631.

You are considering fitting a reinforcement and welding instead of just modifying the gear leg per the SB? We bought a die from McMaster for about $54 and did the mod ourselves, first adding the threads and the pin cutting of the extra with the die still on so it would clean the threads from cutting as it came off. Super easy job. I may be able to still put my hands on that die if someone wanted to borrow it.

[Ralph Inkster]

Originally Posted by rvbuilder2002

This type of damage is far more often caused when builders installed the WD-631 180 deg out of proper position. This is very common. The proper clocking of the part is with the stop tang facing Forward.

Improper clocking does two things. It reduces the pivot angle to less than what is needed when a pivot turn on one wheel is executed (puts a high load on the part every time a sharp turn is done), and it makes it very vulnerable in any nose wheel shimmy event (that is what usually destroys them).

I agree the preferable mod would be to do the SB method, just made the suggestion of modifying the WD631 to avoid the idea of drilling a second hole in the leg.

Also WD631 damage to the two aircraft mentioned was probably caused by repeated push backs without using a tow bar & letting the nose wheel forcefully jam sideways. in both cases the weldment orientation was correct. Damage in both cases were discovered during Annuals.

[AlexPeterson]

Originally Posted by Jesse

You are considering fitting a reinforcement and welding instead of just modifying the gear leg per the SB? We bought a die from McMaster for about $54 and did the mod ourselves, first adding the threads and the pin cutting of the extra with the die still on so it would clean the threads from cutting as it came off. Super easy job. I may be able to still put my hands on that die if someone wanted to borrow it.

Jesse, yours must be soft steel if it was super easy. Pete Howell and I did two of them, and they were a real bugger. Clearly in the "we'd never do that again" category. We had a tool room quality die set, and I've done plenty of machining, but wow, that was a real bugger. There is a thread (fun pun) on these forums about our trials.