The Murphy Builders Site

Have been talking to someone about the virtues of adding VG's to
a wing on a floatplane. As I understand it, VG's work by allowing
a higher angle of attack on the wing before the boundary layer
separates thereby lowering stall speed. But with a float plane,
the angle of attack of your wing on take-off is limited by your
float angle (throat angle) and the sweet spot (on the rear step,
but tails still clear of the water). So if you can't take
advantage of a higher angle of attack on take-off, how would VG's
help with float take-offs?

That made wonder about the Rebel STOL kit. How does it lower
stall speed? Does it also require a higher angle of attack?

Now if VGs or the STOL cuff created more lift (like more wing
area does) at the same angle of attack, then I can see how they
would help with float take-offs, but not sure if they do.

I can see why VG's help with tail dragger land planes, but not
sure about floatplanes.

Walter

-----Original Message-----
From: mike.davis@dcsol.com
[mailto:mike.davis@dcsol.com]On Behalf Of Bob
Patterson
Sent: Friday, December 16, 2005 8:26 PM
To: rebel-builders@dcsol.com
Subject: Rebel: STOL Cuff or VG's



Hi Walter !

I agree that you would have the problem of
dragging the heels
with the VGs at a higher angle of attack.

The McKenzie STOL kit does add wing area - it
extends about
3" forward of the leading edge, for the full span. Also, the
wing fences keep the airflow straight over the wing,
and minimize
the vortex at the aileron joint, for those who don't have a
fairing over that area (definitely "A Good Thing"tm -
the fairing)
The STOL kit likely adds lift too, since it increases
the camber
of the airfoil.

Looks like there can be a problem with high
angles, though -
look at the pics of Jack's Rebel:
http://www.murphyair.com/Product_Info/R ... iption.htm
.... the tails are clearly dragging !

This doesn't have to happen, but the STOL kit
definitely does
allow you to fly at higher angles, so a bit of discipline would
be needed (or, as you suggest, a wider opening for bigger float
angle !) ;-) :-)

I value the feedback from more experienced pilots, and
Carm Titus, who was already a very experienced float pilot,
added both the McKenzie STOL kit and the Fife Hoerner tips
to his amphib Rebel - and loved the improvement. Rumour has
it that he goes into 900 ft. long "lakes", using the GPS
so he can approach at 35 - 40 mph, since the ASI isn't
accurate that slow !! :-) Carm is probably the highest time
amphib Rebel pilot in the world, with over 1,000 hours on
the water - his home is on a lake !

Since Carm was so happy with the setup, several others
here have followed, and all are happy. I have both the McKenzie
STOL kit and the Hoerner tips on my Rebel, and can
climb happily
at 46 mph at 800 fpm at a ridiculous angle .... or 1,500 fpm
at 65 mph, at a more comfortable angle. There must be a lot
more lift there, for such a dramatic increase in the rate
of climb -- was about 1,100 - 1,200 fpm. Can't say what mine
will do on floats YET - maybe NEXT spring !!! (sigh ...)

With Pierre's Rebel, with 195 hp (!), and both
the STOL kit
and tips, PLUS NWA VGs, I've seen 2,100 fpm often, at
ridiculous
angles, and 60 mph !!

The tips will give you a quick, easy improvement. The STOL
kit takes a couple of days - not too hard, just large & awkward
- needs a couple of hands..... and more money. ;-) And the
bigger XP-360 engine, with the Prince prop, is really
exciting -
and you need even more money ! :-)

But you've already got a great performing Rebel -
"The best floatplane in the world !"tm !!!! ;-) :-)
Yours looks good, flies great, and cools well - just
enjoy it !! :-)

......bobp


-------------------------------orig.-------------------------
On Friday 16 December 2005 07:46 pm, Walter Klatt wrote:

Have been talking to someone about the virtues of

adding VG's to

a wing on a floatplane. As I understand it, VG's

work by allowing

a higher angle of attack on the wing before the

boundary layer

separates thereby lowering stall speed. But with a

float plane,

the angle of attack of your wing on take-off is

limited by your

float angle (throat angle) and the sweet spot (on

the rear step,

but tails still clear of the water). So if you can't take
advantage of a higher angle of attack on take-off,

how would VG's

help with float take-offs?

That made wonder about the Rebel STOL kit. How does it lower
stall speed? Does it also require a higher angle of attack?

Now if VGs or the STOL cuff created more lift (like more wing
area does) at the same angle of attack, then I can

see how they

would help with float take-offs, but not sure if they do.

I can see why VG's help with tail dragger land

planes, but not

sure about floatplanes.

Walter

-------------------------------------------------------
----------
List archives located at: https://www.dcsol.com/login
username "rebel" password "builder"
Subscription services located at:
https://www.dcsol.com/public/code/html-subscribe.htm
List administrator: mike.davis@dcsol.com
-------------------------------------------------------
----------

snip
But am still wondering if the VGs also provide more lift at a
given angle of attack.

Walter

snip
Looks like there can be a problem with high angles, though -
look at the pics of Jack's Rebel:
http://www.murphyair.com/Product_Info/R ... iption.htm
.... the tails are clearly dragging !