What OD 4130 will fit into 5/8 x .035

[Chuck in Indiana]

Are you saying I need further reduce the 0.06000 to 0.0555 to get a bit od free play in the fit.

No, it has to be under .555 to go into the 5/8 .035 tube. What I was saying is it's ok to use a 1/2".035 tube inside. The FAA regs say a maximum of 1/16" difference in diameters. .055" is a little less than 1/16 inch. (.0625) That will work and save you a bunch of machining on the larger tube you ordered.

[okdonn]

I think the confusion comes from subtracting the wall thickness (of one wall) from the outer diameter to find the inner diameter instead of accounting for two walls, thus needing to double the wall thickness and subtract that number from the outer diameter to find the inner diameter.
FWIW, I made this same mistake a couple of months ago ....
Chuck is correct IMHO.

[JonBlackmore Irish Eagle]

So got a foot of 5/8 x 0.095 about $20.00 incl post. Don't have a lathe so I made a mandrill to hold my tube and spin it on my drill press. Cleaned up some small pieces of 5/8 x .035 and used it as a gauge. So made to 88mm lengths so was able to turn it down to 9/16 x 0.5511.

Took a bit of time might be a bit over the top but I don't want to be sitting there wondering did I do it right.

[kennyrayandersen]

However many have talked about going to 0.028 on the 5/8 and 1/2 tube. Les Homan is making his third legal eagle this time he is going with .028. Perhaps John Bolding could chime in he has built more fuselages of this type than anyone. No one is going to want to tell you that it is OK unless he is a hired engineer.




The engineer that did the Double Eagle wing is a friend of mine, when he finished I asked him to do a back of the napkin workup on the Legal Eagle fuselage as I thought there might be some weight to be saved there.    Long story short he said $5K of engineering MIGHT save 5-6#.  Leonard went into rigor.    The XL fuselage as drawn weighs 33-34#, Les is reducing it by about a third. I wish him the best of luck.  I would put a chute on that one,  but that kinda defeats the purpose right.  That's why it's called Experimental.

As far as the splicing here's what I recommend to guys that forgot to buy 2 long tubes when they ordered their wood.  Figure out what lengths you need to put a BUTT splice BETWEEN the gear plates at Sta 3,  you are going to weld all around each tube to each plate so you really don't need either an inside or outside splice on the 5/8 longeron. Plus the vertical tube that comes off the longeron between the plates will saddle the longeron and be welded all around it as well.  The Cross tube does the same so we are talking a non-issue  John B

My day job is as a structural analyst. It would be quite easy to do an FEM of the fuselage, but just looking at it I believe I see some areas for improvement. The biggest load on the fuselage is a hard landing, no? That puts the lower (2) truss members in tension, while the upper (1) member is in compression. Tubes are much less capable in compression than tension. Therefore, it would seem the two lower members could be substantially lighter than the one upper one. That's one -- there are others. I don't have a set of plans yet, and haven't ordered any because I'm currently working in Korea, so hard to get them over here cheap. But at some point if I decide to build I will likely make a FE model of the fuselage (probably the wing as well). You guys can't afford me so I'd have to do it for free!

[JohnB]

Leonard and I have talked about inverting the rear fuselage for those (and other) reasons but it always end up being heavier.    With 200+ examples flying and no one has (to my knowledge) bent the rear fuselage in a landing yet Leonard is inclined to let well enough alone.
The gear seems the weak link (by design) in a hard landing,   I've rebuilt quite a few before the pilot got the hang of it.    I THINK if we went to a stronger gear we would start bending fuselages which are more difficult to fix.

[kennyrayandersen]

Leonard and I have talked about inverting the rear fuselage for those (and other) reasons but it always end up being heavier.    With 200+ examples flying and no one has (to my knowledge) bent the rear fuselage in a landing yet Leonard is inclined to let well enough alone.
The gear seems the weak link (by design) in a hard landing,  I've rebuilt quite a few before the pilot got the hang of it.    I THINK if we went to a stronger gear we would start bending fuselages which are more difficult to fix.

Optimization is not the easy part IMO; however, there are a couple of ways to approach it:
1) optimize exactly what you have -- that would require probably doing a FEM to generate loads for the individual structural members of the truss, and then 'right' sizing them.
or
2) looking at alternate configurations where the members are located in a [possibly] more optimal configuration - that would be followed by, or accompanied with it's own optimization.

Without actually doing the work, it would be difficult to tell which is lighter/better.