On Sun, 23 May 2004 11:51:27 -0700, jizhonghe wrote:


Kevin,

There must be some typo in your formular. I looked up my book (Design for
Fly) and is something like:

V=16.2*sqrt(WL/Cl)

Whoops, I accidentally left the sea level density out of that conversion
factor. Once I move the sea level density inside the conversion factor, I
get:

VS = 17.18*sqrt(WL/CLmax)

Thanks for pointing that out.

Are you sure your book says 16.2 and not 17.2? Otherwise I'm not sure
where the difference is.


The book also states that the Cl for a Fowler flap could be 2.8 compared
with 1.4 of no flap. So if I take your number of +1.0 for the LES(leading
edge slats), I think a Cl of 3.0 seems reasonable with some flap.

A Clmax of 3 is achievable with complex, multi-sloted flaps and slats.
But you likely won't achieve such a CL unless you have the means to do
lots of wind tunnel and/or development flight te$ting.

See:

http://adg.stanford.edu/aa241/highli...liftintro.html


Also remember my gross is reduced by almost 20% (not considering the
increase due to the additional slats because I don't how much more
weight) and the increase of the wing area by about 10%.

A basic C150 doesn't have very much useful load at the stock gross weight.
What useful load do you require for your mission? Exactly how do you
plan to reduce the empty weight, while increasing wing area and adding
slats and complex multi-slotted flaps?

For stock C150,
the wing loading is almost exactly 10 and V stall clean is 47kts. This
will give a Cl of only about 1.2. Oh well. Anyway if we use Cl=3 and
wing loading of 7 let's see what we get:

V=16.2*sqrt(7/3)= 24.7 kts

Wow. Geez! I'm sure at 30mph the formula might break (or Cl will change)
but anyway, I still think 40mph is not that unreachable.

Let me know when you've got some credible flight test results, showing
calibrated airspeeds at the stall of 40 mph at a useful gross weight.

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com