Flap design rule of thumb for sailplanes

[Ricardo RW]

Hi there,

Is there a rule of thumb for a flap in a 2M sailplane?

I remember seen 30% of the chord but I'm not very sure about it. I couldn't even find where I read that tip.

I've searched the Lift Zone and RC Universe with negative results.

Could you please give me some advise?

Regards.

[Ollie]

It depends on which airfoil and the four functions (landing, thermal, lunching and penetrating into the wind).

For example see:
http://www.charlesriverrc.org/articles/drela-airfoilshop/markdrela-ag-ht-airfoils.htm
http://www.charlesriverrc.org/articles/aegea2m/markdrela_aegea2m.htm

[Ricardo RW]

Thank you Ollie,

I'll take a look to those links.

Regards.

[BMatthews]

That's way too much for flaps on most airfoils. Usually you're looking at around 18 to 20%.

[MarkusN]

The Quabeck (HQ...) wing sections, for instance, were designed for 22 % flap chord. With common model sailplane geometries flap deflections take care of the necessary trim changes themselves, i.e. there is little change in elevator trim necessary when you deflect the flaps.