Original Posted By: "DJ Vegh"
IF a rib is built rigidly enough and the fabric is stitched tightly, does the ribknow if it's being pushed up from the bottom or being sucked upfrom the top???Never mind. I guess you'd have to ask a rib. Just seems to me that the bottom strip is doing the load-carrying, hencethe push (or lift) would be felt on the bottom. The truss construction would distributethe load throughout the rib so the bottom strip wouldn't buckle. Hm-m-m-m-mgotta go find a rib to talk to. Maybe a prop, too.Larry________________________________________________________________________________
Pietenpol-List: Wedgies
RE: Pietenpol-List: Wedgies
Original Posted By: LAWRENCE WILLIAMS [mailto:lnawms(at)msn.com]
Answer: yes. It is standard stress analysis. You will _never_ get thefabric stretched tight enough to keep the entire rib in compression. It'sjust fabric, not steel bands. Without rib stitching, the uprights are goingto be in tension. With rib stitching, it is the lacing cord that keeps therib structure in compression and transfers the load to the bottom capstrip.Gene HubbardSan Diego-----Original Message-----
Answer: yes. It is standard stress analysis. You will _never_ get thefabric stretched tight enough to keep the entire rib in compression. It'sjust fabric, not steel bands. Without rib stitching, the uprights are goingto be in tension. With rib stitching, it is the lacing cord that keeps therib structure in compression and transfers the load to the bottom capstrip.Gene HubbardSan Diego-----Original Message-----
Re: Pietenpol-List: Wedgies
Original Posted By: Wizzard187(at)aol.com
>> IF a rib is built rigidly enough and the fabric is stitched tightly, does> therib know if it's being pushed up from the bottom or being sucked up> from the top???>> Never mind. I guess you'd have to ask a rib.>> Just seems to me that the bottom strip is doing the load-carrying, hence> the push (or lift) would be felt on the bottom. The truss construction wo> ulddistribute the load throughout the rib so the bottom strip wouldn't b> uckle.Hm-m-m-m-m gotta go find a rib to talk to. Maybe a prop, too.>> LarryLarry - good theory, if you are working with a solid. But fabric wings, oraluminum for that matter, are not solid - they flex. And if even aluminumflexes enough that it needs to be riveted to the wing, think how importantit is for fabric to be laced down!I know, we all fly high wing airplanes, and we can see how the air pushesthe bottom fabric. Wings don't fly well at negative angles of attack, sothere must be something to that "wind beneath my wings" bit. But, were youto fly in one of the fabric covered low wing airplanes (I have in mind oneof the P-21 or P-19 AAC trainers), you would be able to see how the suctionabove the wing tries to pull the fabric up - and would be convinced that A)ribs are under tension if B) the covering material is securely fastened.Also C) - you would be convinced of the value of rib lacing.Sorry if I'm preaching to the choir, and I don't want to flame anyone. ButI do firmly believe in what I've seen and done - and I believe fully inlacing the covering to the rib.________________________________________________________________________________
>> IF a rib is built rigidly enough and the fabric is stitched tightly, does> therib know if it's being pushed up from the bottom or being sucked up> from the top???>> Never mind. I guess you'd have to ask a rib.>> Just seems to me that the bottom strip is doing the load-carrying, hence> the push (or lift) would be felt on the bottom. The truss construction wo> ulddistribute the load throughout the rib so the bottom strip wouldn't b> uckle.Hm-m-m-m-m gotta go find a rib to talk to. Maybe a prop, too.>> LarryLarry - good theory, if you are working with a solid. But fabric wings, oraluminum for that matter, are not solid - they flex. And if even aluminumflexes enough that it needs to be riveted to the wing, think how importantit is for fabric to be laced down!I know, we all fly high wing airplanes, and we can see how the air pushesthe bottom fabric. Wings don't fly well at negative angles of attack, sothere must be something to that "wind beneath my wings" bit. But, were youto fly in one of the fabric covered low wing airplanes (I have in mind oneof the P-21 or P-19 AAC trainers), you would be able to see how the suctionabove the wing tries to pull the fabric up - and would be convinced that A)ribs are under tension if B) the covering material is securely fastened.Also C) - you would be convinced of the value of rib lacing.Sorry if I'm preaching to the choir, and I don't want to flame anyone. ButI do firmly believe in what I've seen and done - and I believe fully inlacing the covering to the rib.________________________________________________________________________________