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Dave is right, most flying planes were just "built to plans" and
flew OK -- actually, most flew great, it was the landing . . . -- anyway,
most flew great based on the plans .
However, MY plans, "Construction of LS(1) 0417 Mod Canard" (page
1) clearly state: "Trial fit both spars at trailing edges . . . Some custom
fitting will likely be required @ B.L. '0-0'. Note, 3.5 deg + sweep aft of
spars at outboard tips." (emphasis added)
Note well: this is the sweep of the SPAR in the jigging templates,
not the sweep of the canard, but that is the sweep of 3.5 deg. occasionally
noted in this discussion.
Also: I am more aware of this than anyone as the ¿Proud? owner of
a canard built with the spar straight :-(
At 09:50 PM 10/5/2006 -0700, Dave Gall wrote:
Due to dihedral, the measurement of sweep is not as straightforward as it
may at first appear. The plans don't say anything about sweep, they only say
to put some reference marks on the jigging templates in a straight line. If
you do this, you then end up building the canard with the correct sweep.
What is the true sweep of the canard? NOBODY knows. Nobody CARES ('cept you
and me). What they do care about is that the canard was built "correctly."
If you look at the three-view of the airplane you will see that the trailing
edge of the canard is a straight line from tip to tip. THAT is the real
sweep of the canard, and I'd bet $100 that the designers themselves didn't
know what the true sweep of the quarter chord line of the canard is....
Now, two guys going out to the hangar to measure the sweep on Sam Hoskins'
plane (for example) will probably come back with two different measurements,
partly because one might forget to level the plane first and partly because
they might pick different places to take their measurements. For instance,
do you measure the sweep from the centerline or from the wing root, and do
you extrapolate the leading edge sweep into the fuselage cavity or just
assume a constant chord for that portion of the wing embedded in the
fuselage. These and other considerations make it VERY difficult to assign a
particular number to the sweep of such a flying surface and to be able to
definitively defend that number as THE correct number against all other
Better to just eschew such "hard numbers" as too hard to bother with. The
"hard numbers" you really want are those that will allow you to BUILD the
plane. The plans' scheme of level lines and reference marks allow that
without all the hullabaloo about imaginary engineering references. And if
you're worried about modeling the thing for X-Plane, keep in mind that the
great analog computer in the sky is a much better wind tunnel than any
computer will ever be.
David J. Gall
P.S. The answer to your question is to believe the plans. The guy with the
mill and thousands of hours in type isn't "wrong," just irrelevant. Like the
trig functions on your calculator are irrelevant to building one of these
On Behalf Of Jason MuscatHold on
Sent: Thursday, October 05, 2006 9:17 PM
Subject: RE: [Q-LIST] Re: Lay up sched?
Thanx Sam. I did read your site on the auto pilot and point
well taken. But with that, who do i believe with the wing
sweep then, the plans or the guy that has a mill + hours in
type that says something different? Take it easy guys, sorry
to offend you.
Sam Hoskins <<mailto:shoskins%40mchsi.com>email@example.com> wrote:
there, Jimbo. I have a feeling that Jason may be a multitalented<http://samhoskins.blogspot.com/2006_01_01_samhoskins_archive.html>http://samhoskins.blogspot.com/2006_01_01_samhoskins_archive.html
person. I think it may be great if someone were to create a
true representation of the plane. Sure, it is slowing down
his building time, but someone may benefit in the long run.
Having said that, I wonder if he read the story about my autopilot?