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Spar question

redhawk

Well Known Member
I am just curious...
Is a -3 with the wing spar mod of the same strength/integrity as a -3B spar?
 
Perhaps not, since they needed to redesign it after a failure. This is described in "27 Years of the RVator."

From memory, the problem with the original design was buckling of the spar laminations between fasteners. The original ship was glued and riveted, with the glue being used as an assembly aid. But it also provided some buckling stability for the laminations.

Dave
 
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RV-3 Spar

I am just curious...
Is a -3 with the wing spar mod of the same strength/integrity as a -3B spar?

If assembled per the plans, the original spar was fine, but after the loss of a couple 3's due to spar failure; it was determined that some builders failed miserably in the task of building the spar with some not even bothering to separate the many individual layers after drilling to remove the bis of metal shavings, etc. One "3" builder (now deceased) built three RV-3s and two had spar failures and killed the owner / pilots. With the spar being such a crucial component in the overall strength and safety of the a/c moved VAN to quickly begin to subcontract out spar construction, and provide it as a completed component in the kit.

Doug

RV-3A sold
RV-9A FWF / Mazda 13B FWF
 
The suspect failures were due to drilling the spar chord straps and not separating them and de-bur all holes.

So all the failures were all fatigue?

Later RV-3 spars (pre-built with higher quality) are structurally the same as the original?
(or did the beef them up)

Just curious because I do aircraft stress analysis, ultimate strength, fatigue for fun. Thanks
 
RV-3 Spar Mod

A bit of misinformation here.
Van was transparent with the static testing of the CN-Mods.
Main spar were static tested before they were released.
The new B spar came years later.
The CN Mod parts are still available form Vans.
Vans website has further info under the RV-3 specs.

MWG
 
My interest is primarily in the RV-3B, since that's what I'm building.

The new spar they are talking about is the one in the RV-3B.

There might well be more about this topic both in this source and elsewhere, and perhaps a diligent researcher can learn more. If so, I'd be interested in that.

Dave



From "27 Years of the RV8tor," page 382:

RV-3 Wing Update [12/96]
We have static tested another RV-3 wing which included spar modifications suggested by prior tests. This time, results were satisfactory. We have prepared modification kits which we are sending out to all RV-3 owners requesting it. Modification kits for Type II RV-3s have already been sent out. We are now in the process of designing a new spar for use on all future RV-3s, and for retro-fit on under construction RV-3s.

RV-3 Wing Test & Status [1998 1st]
by Van
Late last year we built a set of wings around an all new spar, patterned after the RV-8 spar. Static testing was successful. We loaded the wing to a simulated 9G load and it held, not just for the required 3 seconds, but for many minutes. Then a few more bags brought the house down. Though it would be nice to be able to say that it withstood loads well beyond expectation, it was just as satisfying to see it pass with results extremely close to our calculation.
We are now working or redrawing the wing plans and getting the new spar into production.
 
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