MH45 wing section info....

[miniphase]

What's the zero lift angle and pitching moment for
the MH45? I've found two sources- with differing figures

aero design website - cmo 0.007 and 0 lift of -0.27deg
b squared info - cmo 0.0058 and 0 lift 0.37deg

can anyone clarify?

thanks

[Ollie]

See:
http://www.mh-aerotools.de/airfoils/index.htm
"MH 45
Low moment coefficient airfoil for tailless model aircraft
See also MH 44, MH 60.

"Characteristics

Thickness: 9.85%
Comparatively high maximum lift coefficient.
Low moment coefficient of cm c/4 = +0.0145.
Can be used at Reynoldsnumbers of 100'000 and above.
Has been used successfully in F3B tailless model airplanes.
Similar to the MH 60, which might be better suited for Reynoldsnumbers above 100'000."

Use Martin Hepperle's data above.

The Cmo and Cl zero angle shifts with reynolds number. Read the polar diagrams for your purpose. Cmo is not constant with angle of attack and reynolds number! A-0 is not constant with reynolds number!

Too bad.

From Dr. Mark Drela:

"The culprit is the variation of the boundary layer thickness
and the movement of the separation bubble with Cl.
The boundary layer and bubble changes the effective camber shape
of the airfoil, which then causes the Cm to change. The effective
shape of the airfoil is plotted in Xfoil under the Cp vs x/c plot.

As you increase the Reynolds number the boundary layer and the
bubble get thinner, so the modifications to the camber line
get smaller. Hence the Cm variations get smaller as well.

- Mark


Center of pressure location is
x_cp = 0.25 - cm/cl

Aerodynamic center location is
x_ac = 0.25 - (dcm/dalpha)/(dcl/dalpha)"

[miniphase]

but don't the majority of our models operate within the same
reynolds range? and therefore if I need the cmo at the zero lift angle then there ought to be a constant set of figures, if not why
do the likes of the web sites I mentioned above bother quoting
any of the information?

[Ollie]

"--if not why
do the likes of the web sites I mentioned above bother quoting
any of the information?"

Perhaps the difference is the method used to not important for the purpose. What is you purpose?

I would not use B^2 data.

I would
http://www.aerodesign.de/english/profile/profile_s.htm
Based on X-Foil.
and
http://www.mh-aerotools.de/airfoils/index.htm
Based on X-Foil.
and
http://www.profili2.com/eng/default.htm
Based on X-Foil.

The are many kinds of error. Measuring error, estimate method error, editor error, etc. First I trust X-Foil best (low error). Second I trust wind tunnel measurements (low error for high reynolds number and high error for low reynolds number).

I am quessing that B^2's error is an editor error.

[miniphase]

I'm using the B squared spread sheet for calculating wing twist for swept flying wing slope models, as you have suggested it would seem that
the aerodesign figures are accurate when refering to the mh ploars, and perhaps the b sq info is an editorail error- but I'm the first to admit my understanding of polars is minimal!!!

just to add in no way do I want to discredit any of B squared documents of info etc, just trying to sort out this anomally

[Ollie]

You mean:
http://www.b2streamlines.com/Panknin.html
Do you mean Panknin twist speadsheet?

If you use Pankin twist speadsheet, one airfoil uniform from root to tip, then it doesn't change washout angle results. If you change the MH45 airfoil at one end and any other airfoil at the other end then, you change the washout angle results. Try it. You will like it.

[miniphase]

yup that's the one, it's worked well for my designs
so far, I've always used the aerodesign MH45 data, so i guess
my concerns were unfounded

thanks ollie