I am in the process of building a Stuka with the 'exposed' ailerons and flaps. I believe there was also a German tri-motor, WW II vintage, that had the similar surfaces. I'm finishing up a Fiesler 'Storch' which has what I guess you'd call slotted ailerons and flaps. Some Storchs also had a secondary elevator surface mounted below and slightly forward of the elevator. Wondering why these surfaces appeared, and disappeared from the scene? It seems like these were pretty successful for their time-and maybe that's the answer! Interesting design features though. Any thoughts on the subject?

wsmalley,

Basically a way of creating a more powerful, more aerodynamically balanced, and easier to mass balance, control surface. Gives higher effect while reducing force needed to actuate. Similar to a stabilator horizontal tail, but of course at the cost of more drag. Also vulnerable to airframe icing, a concern for full scale. Will work fine on models. Don’t get the hinge line to far rearward. You want to retain at least some positive feedback. You still see these on some experimental aircraft. The surface attached to the elevator of the storch is a boost tab of sorts. You see smaller versions of this on modern stunt planes to reduce actuation forces. Hope that helps.

Multiflyer

The trimotor airplane you're reffering to was the Junkers JU-52.

Thanks for the explanation. That should equate to requiring smaller servos than might be expected for 'normal' control actuation. Guess they were the way to go in the 30's!

That type of control surface is from the time when aircraft were getting larger but hydraulic assist (power steering) wasn't yet used. What designers soon moved to is the conventional control surface with the hing line positioned more rearward. Basically the same result but streamlined. You can still find the other type of surface on some modern designs. For example, if I remember right, the experimental KitFlox ultralight used them?

Multiflyer

These were the first true STOLs. Needed very large control surfaces to give control at very low RE #

Been there and done that and they were very effective. See my McCessna attached. I static counterbalanced the ailerons with extended fishing sinkers adjustable on music wire supports.

Very nice.

It's tough to get good roll authority on large wing slower flying models. Those type control surface are a great alternative to just making larger normal control surfaces. Plus I really enjoy the extra craftsmanship. In this age of ARFs, you don't see as much home engineering anymore.

Multiflyer

More detail!

Looks like fun. I'd say a true sport flier if there ever was one.

Multiflyer