byunghun54
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- Feb 3, 2009
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According to Piper drawings (for wooden spars and about same way for aluminum spars too), the
compression strut attach point at the front spar at the wing root is 1 29/32 hign
from the bottom of the front spar. For the rear attach point of the compression strut is 2
1/2 from the bottom of the rear spar. Rear spar is slightly raised (about 9/32") from the ref line to fit the design of the wing ribs due to concave bottom line of the ribs.
Therefore compression strut attach point at the rear spar is 2 25/32 high from the ref
line horisontally extended from the front spar bottom.
That means that the struts are raised 7/8" in elevation at the rear spar root mearsured from
the rib ref line which is vertical to both spars.
I examined all the compression fitting drawings and rib drawings so I am aware
that both spars and compression strut joined squarely and my description and
dementions are from the original factory drawings (some of them I myself scanned
from microfilm I obtained from Smithonian Museum) However anyone can discover this easily by carefully examining one of those PA-18 spar drawings.
I just wondered if anybody noticed such an unexpected location fo compression
strut during the (re)assembly of the original piper wings and thought about the
design philosophy of the wing.
Of course my initial thought was that Piper engineers intentionally put compression strut at staggering elevation on the spars to give a proper wing washout to creat the twisting moment at the root ( FYI at the wing tip the compression struts' elevation on front and rear spars are same if the 9/32 of concave feature of the wing is ignored).
However further examination of spar attatch points location at front and rear spar to the fuslage reveals that the above twisting moment created by compression strut is effectively nullified as these two spar butt to fuselage points are almost parellel to rib ref line instead of the compression struts' 7/8" offset ( 1.657 degrees off from the rib ref line) !!
Therefore, I may not ever found out the philosophy of the wing design but let me know if anybody had ever found this and given a deep thought about this.
compression strut attach point at the front spar at the wing root is 1 29/32 hign
from the bottom of the front spar. For the rear attach point of the compression strut is 2
1/2 from the bottom of the rear spar. Rear spar is slightly raised (about 9/32") from the ref line to fit the design of the wing ribs due to concave bottom line of the ribs.
Therefore compression strut attach point at the rear spar is 2 25/32 high from the ref
line horisontally extended from the front spar bottom.
That means that the struts are raised 7/8" in elevation at the rear spar root mearsured from
the rib ref line which is vertical to both spars.
I examined all the compression fitting drawings and rib drawings so I am aware
that both spars and compression strut joined squarely and my description and
dementions are from the original factory drawings (some of them I myself scanned
from microfilm I obtained from Smithonian Museum) However anyone can discover this easily by carefully examining one of those PA-18 spar drawings.
I just wondered if anybody noticed such an unexpected location fo compression
strut during the (re)assembly of the original piper wings and thought about the
design philosophy of the wing.
Of course my initial thought was that Piper engineers intentionally put compression strut at staggering elevation on the spars to give a proper wing washout to creat the twisting moment at the root ( FYI at the wing tip the compression struts' elevation on front and rear spars are same if the 9/32 of concave feature of the wing is ignored).
However further examination of spar attatch points location at front and rear spar to the fuslage reveals that the above twisting moment created by compression strut is effectively nullified as these two spar butt to fuselage points are almost parellel to rib ref line instead of the compression struts' 7/8" offset ( 1.657 degrees off from the rib ref line) !!
Therefore, I may not ever found out the philosophy of the wing design but let me know if anybody had ever found this and given a deep thought about this.