I was rereading again Hoerner's chapter on Leading Edge high lift devices.
My impression i that the only device that offers some value is the Krueger Flap.
His arguments are a decent increase in lift 0.5-0.6, positive pitching moment that could counteract the flaps negative pitch and could offer some performance increase at take off.
I also like that when the device is retracted it really has nearly no drag and the construction looks to me as the easiest of all these devices.
However he doesnt comment on the extension process.
What happens when you drive out such a LE flap?
Do you fall from the sky like a stone when you are midway thru the deployment process (negative camber-huge drag)?
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