Wing Spar Safety/Airworthiness Question

[Victor Bravo]

I removed the rest of the covering from my project airplane, and found something questionable. I would VERY much like to hear from the experienced folks here, whether they think this wing was built correctly or not.

The plans show the upper main spruce spar cap has a bevel, to match the airfoil contour. This allows the spar cap to be as tall as possible, and have as much "cross section" area as possible.

My airplane looks like it has a  non-beveled square spruce spar cap, with the .8mm plywood glued on top of it, then non-structural wooden shims above that to match the airfoil contour.

This means there is less wood in the structural spar cap, as well as the spar not being as "tall" (distance between the spar caps) as it is shown on the plans.

I am interested in the opinions of any engineers or highly experienced LE people as to whether this wing construction is safe or unsafe and by how much.

The wood construction using T-88 is a little sloppy but completely solid. All glue joints appear to be shake-proof, no creaking, cracking or peeling.

[Dan_]

Are the spar caps undersized, or are the ribs oversized..?

Even if the spar caps are too small, there is a way to save the wings perhaps.

[Dan_]

Since the nose ribs seem to fit the spar, I question the size of the ribs...

[Victor Bravo]

THANK YOU for the response Dan!

I will have to try and figure out whether he built the ribs oversize or the spar undersize. That will be this week's task

The plan set that I have shows that the spar is 6 7/8" tall at the rear edge, with a 10.5 degree taper on the forward edge. So I will go measure that ASAP.

My plans have four or five poorly Xeroxed pages of wing rib drawings with no dimensions, that have to be pasted together in order to have a full size rib drawing. I have no idea whatsoever if these Xeroxed pages have grown larger or smaller during the copying process, and there is no dimension on the height of the plywood leading edge rib or the forward edge of the main rib section.

To be honest, and with no disrespect intended to anyone, I've had free flight rubber powered model airplane plans that were better than this full sized aircraft plan.

[Victor Bravo]

This is what seems to be what I have on my wing. The rear of the nose rib is a little taller than the front of the spar, and the rear of the spar is well below the front of the rib capstrip.

The measurements will soon tell the tale, but in order for the spar to not match either nose rib or main rib... both the plywood nose rib AND the stick built main rib would both have had to be built oversize.... or the entire spar would have had to be built undersize.

[Victor Bravo]

Measured my wing this evening.

The upper spar and lower spar are both 3/4 x 3/4, with no chamfer or bevel. So there is very slightly more wood on mine than an exact plans built spar cap.

But the  spar "height" from the bottom of the lower cap to the top of the upper cap is 6.75 inches, instead of 6.875 inches as shown on the plans. Perhaps the extra sliver of upper spar cap compensates for the loss of 1/8 inch in height.

Because my "plans" are Xerox copies without several dimensions, I cannot measure the rib drawing on the paper and 100% trust that the printed paper is exact actual size. But the maximum height of the rib (max wing thickness) measures 8 1/16 on the airplane and 7 17/32 on the drawing. So the builder might or might not have made the ribs taller than they a re supposed to be.

The actual plywood nose rib at the root end of the wing measures 6 15/16 inches tall at the front of the spar, WITH the two layers of .8mm plywood included. This tells me the rib itself was cut to 6 7/8". But only the rear spar caps are supposed to be 6 7/8 tall, the spar cap bevel means that the nose rib should be a little smaller than that to match the contour. Again, there are no dimensions on the Xeroxed nose rib drawing so I have no idea what the height really is supposed to be. The Xeroxed drawing shows a nose rib height of 6 5/8 (the little drain hole at the bottom notwithstanding).

Can any one tell me if any of these numbers make sense, and whether my measurements reflect the actual design engineering dimensions? 

[Chuck in Indiana]

I'm late to the party here.. have been at the Pietenpol reunion..but I'd say that if you are happy with the glue joints and it is T88 just fly it. The wing has been tested to 4 Gs and even if it is compromised a little, you should be ok.
My lawyer says pay no attention to the above, so I am posting as a Tech counselor with EAAs insurance plan. 

[Victor Bravo]

Thanks Chuck, I'm very happy to hear anyone/everyone's opinions on this.

BTW, the plan set I have is serial number O-53, sold to a Bobby Laird in CA in March of 2007. I purchased this as part of Mr. Laird's estate sale along with two project aircraft (not LE's). Are these plans the same overall quality as the current plans, or has there been some major re-work/improvement/upgrade in the Legal Eagle plans in the last 17 years? I'm not any kind of engineer or a professional draftsman, but jeez.... comparing these plans to my old RCM-40, Goldberg Eagle, Andrews Aeromaster, and many other model airplane plans....

[Chuck in Indiana]

The current plans leave uh.. some room for interpretation. Just the same, if I were you I'd throw Leonard a few bucks for current ones.