Tom & Cathy Friedland wrote:
>
> Hi Europaphiles
>
> I am about to set the wing angle of incidence for the wings on the
> fuselage. My XS manual calls for an angle of 2.5 degrees. I suspect
> this has been specified since the classic Europas with 80 hp. Is that
> correct? Now the XS's have longer lighter wings and usually more
> horsepower that results in faster cruise speeds. Faster cruise should
> result in more lift from the wing which will then cause more down lift
> from the stabilators and therefore more drag from both the wing and the
> stabs. ? So, does it not make sense to lower the wing angle (Alpha) to
> account what is expected to be a higher cruise speed and therefore make
> things more efficient?
>
> I am asking for comment from all of you smart guys out there for some
> theoretic discussions. What do you think? 2.1 degrees? 2.3degrees?
> Andy, I suspect that the factory will be hesitant to give an opinion....
> Ivan, Don, are you listening?
Before the smart guys jump in, I looked this up in one of them there
design books, like with all the the graphs and mind-bending formulae.
Author says you use a wind tunnel to set the angle for maximum L/D of
the fuselage (it contributes to lift) at design cruise. But even that
test will be approximate, without the wing attached. So, w/o a wind
tunnel and for sport plane class, just "assume two degrees" for fuse A
of A. For passenger transports, don't go too high, or it will be
tough to push the food carts uphill, he says.
The 2.5 deg. setting is not the fuse's A of A (but will determine it),
and is likely such a SWAG, too, without the booze cart restriction.
Could even be off. I didn't worry about optimizing it for more than
80HP cruise, reasoning that the relationship between wing A of A and
speed is nonlinear as speed increases, terminating at the point where
lift starts decreasing. Like where you need only tiny tweaks of a
trim wheel in fast cruise, the correct angle if known (nor a "914 XS
tweak") couldn't be obtained anyway by the method prescribed. Equal
both wings is most important.
Regards,
Fred F., A063
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