stall fences?
 

What the stall fences over a non swept back wing can prevent?(beech 1900) ? (if it's a stall fence or a layer fence)
pic here
i know why on a swept back wing but on a non one???

They are generally there to prevent a sudden and "unpredictable" loss of air flow over a surface. This will therefore normally reduce the stall speed and/or give more benign stalling charactistics. An aircraft with loads of them sticking out all over the place normally shows and aircraft designed with a (too small) budget which gets totally blown away away when the flight trials begin.

On the B-N Defender, the wing fences reduced wing drop at the stall from around 45° to around 10°, thus making the stall a lot more friendly, and ensuring that it actually met the certification standard.

I understand that the main effect it prevented was a substantial spanwise flow at high AoA.

G