NLG Technical Analysis

[ferret]

Referenced is a pdf document that contains a technical analysis of the NLG. It references a Microsoft Excel spreadsheet that calculates and graphs the bending moments which is not directly downloadable. For those technical enough to use the spread sheet, PM me with your email address and I will send you the spread sheet.

http://www.brainiator.net/nlg_analysis_3_0.pdf

It has been a few years(15) since I have done this type of stress analysis, but it should be fairly accurate and notional. If not, I am sure someone will graceously point out my mistakes.

[terrye]

Very interesting analysis.
Couple of questions and comments:
1. You mention stress but I don't see where you have calculated the actual maximum stress in the round bar. Does the stress exceed the yield stress of the material (SAE 6150 heat treated to RC 42-44 from RV-6 plans. Su 193-203 ksi, Sy 177-186 ksi from Machinery's Handbook)?
2. Have you considered a column buckling failure mode in addition to the cantilever beam bending failure mode?
3. Impulse condition 2 tire spin up (P8). I do not believe that the braking coefficient is dependent upon tire pressure. I usually use 0.8 to 0.9 for a rubber tire on asphalt. Rough concrete may be a bit higher.
4. I believe the NLG (and MLG) are machined from bar then bent and heat treated, therefore not a forging. Welding SAE 6150 is not allowed according to ASM's Heat Treater's Guide. I think a new bar is a better solution.

[eurof2]

That is quite a thorough evaluation it looks like.

It caught my eye when you stated quote: "The cross section of the NLG decreases from EM to SJ." Where EM is the engine mount and SJ is down by the tire.

I thought I remembered somebody else talking about how the gear leg is actually largest at the top, (EM) and then tapers down to the smallest diameter somewhere in the middle (Near IP in your drawing) and then tapers back up to a larger diameter down at the bottom (SJ)

Did you base this analysis on the measurement of an actual gear leg or was it a drawing you received?


I am a little disheartened you seem to be pushing the blame off on to Vans to "emphasize the importance of maintaining proper
NLG tire inflation" and also "Van’s should provide a uniform design for a NLG side access panel that opens with a finger operated quarter turn fastener" I think they do a fine job of informing pilots what proper operating procedures are. If the pilots do not follow that for whatever reason (Too lazy to properly check tire pressure?) then they are accepting any risk that might come from ignoring that.

This is a high performance plane after all. High performance ALWAYS requires extra special care to work properly.