Date: Wed, 13 Jan 1999 07:53:45 +0200 From: Rego Burger Subject: COZY: Static Loading? Does anybody have some experience with this subject to add or subtract from.... I have a problem with folks static loading wings and canards to extremes and then saying they're O.K. fitting them on aircraft and flying them. If you stretch material to it's limits it has been exposed to STRESS... this is not wise as I feel it now reduces it's servicability life-span. If an aircraft has DESIGN limits of +6g and -4g this does not mean your static load must be pushed to these limits prior to flight of those components. If the craft has these DESIGN limits it should only operate between +4,5g and -3g. So then, limit static loads to the OPERATIONAL levels... this will not over stress a usable component. Destructive testing will determine a break point, therefore the part will be out of action. I recall Burt pushing a L.E. canard to about +14g before it bust..... imagine someone static loading a canard to +10g and sticking it on to fly, he has possibly put 500000hrs of stress into the part in one day...ouch! R.B. RSA From: lschuler@cellular.uscc.com Date: Wed, 13 Jan 1999 09:40:16 -0600 Subject: Re: COZY: Static Loading? Rego wrote: >Does anybody have some experience with this subject to add or subtract >from.... >I have a problem with folks static loading wings and canards to >extremes and then saying they're O.K. fitting them on aircraft and >flying them. I'm not a structural engineer, but I do tend to agree; particularly if the parts are metal. Glass is different. My layman's understanding is that glass doesn't deform like metal; it just breaks when over stressed. If, in your 14G canard test, nothing (as in not a single strand of glass), is broken then the part is probably usable and it's life expectancy will continue as if new. 'Ultimate' loads in metals (I think) is the point at which permanent molecular deformation occurs causing the part to take a new set (shape etc). Glass failures are more catastrophic, where glass simply snaps. Metal failures are a bit more benign and the part just takes on a new shape (bend etc) unless the load continues over time. Thus the life-cycle or life expectancy relative to stresses in metal. Metal spars, for example, can be subjected to ultimate or near-ultimate loads and bend permanently, yet still remain attached to the fuselage (unless the load continues). Doing the same with a glass spar would ensure that it departs the fuselage at the instant of ultimate load application. The flight safety factor differences between these materials may be why 'ultimate' load is normally 1.5 times design load in metal planes and 2 times design load for glass. Kicker for loading a glass part is "knowing" if any of the glass strands broke or not; not easily determined. On the other hand, over-stressing is readily evident in metal; the part looks different (stays bent) when you take the sand bags off. Great item for discussion and further understanding of all (especially for us amateur 'experimenters'. Larry From: Epplin John A Subject: RE: COZY: Static Loading? Date: Wed, 13 Jan 1999 10:14:04 -0600 > -----Original Message----- > From: lschuler@cellular.uscc.com [SMTP:lschuler@cellular.uscc.com] > >Does anybody have some experience with this subject to add or subtract > >from.... > > >I have a problem with folks static loading wings and canards to > >extremes and then saying they're O.K. fitting them on aircraft and > >flying them. > > > Kicker for loading a glass part is "knowing" if any of the glass strands > broke or not; not easily determined. On the other hand, over-stressing is > > readily evident in metal; the part looks different (stays bent) when you > take the sand bags off. > > Great item for discussion and further understanding of all (especially for > > us amateur 'experimenters'. > > [Epplin John A] I usually don't get into these things, way over my flat head. But I have an idea here. First, load the structure to some point considerably less than the damage point and measure the deflection, could be simply measured with good instrumentation such as a machinists dial indicator or even with strain gages. Record these readings then load to the limits of the test, but not to catastrophic destruction. Unload and allow the system go relax, then apply the first load again and note the deflection. If you have broken any significant number of strands you should notice greater deflection. As I said, way over my knowledge and experience level, but how does this sound to you structural gurus? John epplin Mk4 #467, installing engine. From: cdenk@ix.netcom.com Date: Wed, 13 Jan 1999 17:10:09 -0600 (CST) Subject: RE: COZY: Static Loading? Static loading of structures is a routine way of proof testing, remembering that this is a test of only one loading condition. For Structural Steel, wood , and reinforced concrete the test load is 85% of the minimum failure load. For live loads typically the failure load is 1.7 times the maximum actual anticipated load. I have designed and supervised loads on precast concrete where the load was over 300 tons. Load bang when failure! From: cdenk@ix.netcom.com Date: Thu, 14 Jan 1999 17:23:37 -0600 (CST) Subject: Re: COZY: Static Loading? When loading a structure in bending, the extreme fibers get the most strain (stretch), and should be the first to break, and that would be visible. If a significant percentage of fibers broke, the deflections would not go back to the original shape. Is important to measure accurately. There have been more than a few full scale load tests on Ez's to satisfy foreign (to the USA) governments. I haven't heard of anything bad happening a a result.